Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin

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Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin Xiaoguang Li Exploration and Development Research Institute, PetroChina Liaohe Oilfield Company, Liaoning, 124010, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 June 2019 Received in revised form 15 November 2019 Accepted 22 November 2019 Available online xxx

The Huanxiling oilfield is located in the southern part of the western slope of the western sag in Liaohe depression. The west side of this oilfield is connected with two sets of high-quality source rocks of Member 3 and Member 4 of Shahejie Formation in Qingshui sub-sag. The oilfield has fan delta, turbidite fan and other types of reservoirs, it also has cap rock of thick mudstone in Member 3 and Member 4 of Shahejie Formation. Under background of the warped basement, the warped fault-block draped compound trap zone are developed, which includes nine types of trap. From perspective of hydrocarbon accumulation, the slope of this area has always been the target area for hydrocarbon migration and accumulation. Inclusion analysis shows that there are multiple stages of hydrocarbon charging in this area, and the main reservoir forming period is the sedimentary period of Member 3 of Shahejie Formation and the sedimentary period of Dongying Formation. High-quality source-reservoir-cap conditions ensure large-scale hydrocarbon accumulation in this area. Based on the theory of compound hydrocarbon accumulation, many types of oil and gas reservoirs, including light oil reservoir and heavy oil reservoir, have been found in this area, with total reserves of 500 million tons. In view of the oilfield characterized by large reservoir burial span, multiple oil-bearing strata, strong heterogeneity and various types of oils, multi-batch seismic data processing & interpretation technology and thin reservoir inversion technology based on geological model are established in the preliminary exploration period, steam-flooding physical simulation technology of heavy oil, oil-reservoir fine description technology of thermal recovery heavy oil, steam huff and puff technology of ordinary heavy oil and steam-flooding technology of mid-deep buried heavy oil are developed in the development period, and technologies such as separate-layer injection, selective injection, sand control and lifting of heavy oil are matched and improved. These technology series provides technical guarantee for efficient exploration and development of Huanxiling oilfield. © 2020 Chinese Petroleum Society. Publishing Services by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Heavy oil exploration and development Reservoir-forming conditions Steam huff and puff Steam flooding Huanxiling oilfield Liaohe depression Bohai Bay Basin

1. Introduction The Huanxiling oilfield is located in the southern part of the western slope of the western sag of Liaohe depression (Fig. 1). It develops seven sets of oil-bearing strata (Archean, Mesozoic, Member 4, Member 3 and Member 2þMember 1 of Shahejie Formation, Dongying Formation and Guantao Formation) vertically and is one of the most oil-rich fields in Liaohe depression or even Bohai Bay Basin. The Huanxiling oilfield is a large-scale monoblock heavy oil block developed earlier in China, and the steam huff and

puff of ordinary heavy oil in this oilfield achieves good recovery result, the first industrial demonstration area of steam flooding of mid-deep buried heavy oil in China has been established in this oilfield. In this paper, favorable geological and reservoir-forming conditions and exploration & development technologies for largescale monoblock heavy oil reservoirs in Huanxiling oilfield are discussed, and it can provide technical reference for efficient exploration and development of large-scale onshore monoblock heavy oil reservoirs.

E-mail address: [email protected]. https://doi.org/10.1016/j.ptlrs.2020.01.004 2096-2495/© 2020 Chinese Petroleum Society. Publishing Services by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004

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Fig. 1. Location of Huanxiling oilfield showing that the Huanxiling oilfield is located in the southern part of the western slope of the western sag of Liaohe depression.

2. Exploration & development overview of the Huanxiling oilfield 2.1. Exploration history The main idea to guide exploration of the Huanxiling oilfield has undergone four major changes (ECPGLO, 1993; Liao et al., 1996; Ma and Niu, 1997; Tian et al., 2002). In the first period, guided by the idea that the local higher point oil controlled oil distribution, the Huanxiling structural belt was discovered through seismic data acquisition in 1973. At the end of March 1975, the Well Du4 was tested in Member 4 of Shahejie Formation (Dujiatai oil layer), and a high-yield oil flow of more than 100 tons a day was obtained, thus, the Huanxiling oilfield was discovered. In the second period, based on secondary structural belt, the oilfield was fully analyzed and its’ exploration was carried out. At this period, it was recognized that the secondary structural belt in the sag controlled the oil-bearing area, height of the reservoir and oil-gas-water combinational relationship. Each secondary structural belt was taken as a basic unit of oil and gas exploration for comprehensive evaluation and overall deployment. In this period, two monoblock heavy oil zones (Well Block Jin25 and Well Block Qi40), were discovered. In the third period, the concept of “compound oil and gas accumulation zone” was introduced, and the oil and gas exploration idea of compound oil and gas accumulation zone in the slope of the western sag was formed, which effectively guides oil and gas exploration, and exploration effect was significant, the oil-rich blocks including the Well Block Jin607, Well Block Jin612 and Well Block Huan103, were found consecutively. In the fourth period, under the guidance of the theory of oil enrichment in the whole oil-rich sag, fine exploration scopes not only constrain the secondary structural belts, but also extend to the whole sag. Major breakthroughs are made in the exploration of lithologic reservoirs in the slope to su-bsag transitional belt and sub-sag belt. It is recognized that the lithologic reservoirs in the subsag area is an

important target for finding new reserves. Change in the exploration idea in different period brings about major discoveries, and Well Jin307 and Well Jin310 drilled in the area achieve industrial oil and gas flows. After many years of exploration, the overall reserve in this oilfield is up to 500 million tons. 2.2. Development history The development process of heavy oil reservoirs in thw Huanxiling oilfield can be divided into four periods. The first period is from 1984 to 1985, and is the preparation and test period of thermal recovery technology. High efficiency heat insulation pipe, thermal recovery packer and other technologies were developed; the feasibility of steam huff and puff development in midedeep buried and mid-thick interbedded reservoirs was verified by field test, and an annual oil production was up to 430  103 t. The second period is from 1986 to 1990, and is the scale implementation period of steam huff and puff. Steam huff and puff development technologies were continuously matched, researches on key technologies such as subdivision layer development and infilling adjustment, and main blocks of heavy oil reservoirs were fully developed by steam huff and puff, and production of the oilfield was continuously increased. The third period is from 1990 to 2004, and is the period of improving steam huff and puff technology and exploring EOR technology. Well infilling adjustment and combined huff and puff technology were studied and tested, process technologies such as reservoir pretreatment, separate layer steam injection, sidetracking overhaul and sand control were further improved and matched, and development well spacing was reduced to 83 m and 70 m, the annual oil production exceeded 3  106 t, and the test of steam flooding after huff and puff was carried out in this period. The fourth period is from 2005 to present, and is the stage of conversion mode to enhance oil recovery. The steam flooding development technology is gradually matured and matched, is applied in mid-deep buried heavy oil reservoir in Well Block Qi40 in

Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004

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industrial scale; the annual oil production of the steam flooding is up to 0.5  106 t. Up to now, the Huanxiling oilfield has been maintained at an annual oil production of 1.1  106 t, a recovery rate of 0.72%, and recovery percent of reserves of 29.7%.

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the eastern side of the sag subside substantially and forming typical dustpan-like sag. Large-scale rapid extension and rifting led to form deep or semi-deep lake in the sag with thick dark mudstone and widespread turbidity sediments. At this stage, the main oilgenerating sub-sags in the sag were formed.

3. Geological reservoir-forming conditions 3.1. Tectonic and sedimentary evolution of the western sag According to characteristic of regional tectonic movement and stratum development, the Cenozoic in the western sag experiences three evolution stages: crustal arch, rifting and depression. The rifting stage can be further divided into three stages: initial rifting, deep rifting and continuous rifting-attenuation (Fig. 2). The sedimentary evolution characteristic of the rifting stage controls oil and gas enrichment in the western sag (Xie et al., 2010). 3.1.1. Initial rifting stage This stage corresponds to the sedimentary period of Member 4 of Shahejie Formation. At this time, fault activity in the northern part of the western sag was strong and that in the southern part of the western sag was weak. Therefore, Member 4 of Shahejie Formation is mainly distributed in the western part of the sag in the west of the Xingxi fault. The sedimentary environment of this stage was semi-deep to shallow lake, and mainly developed fan delta sedimentary system and lacustrine mudstone deposits. 3.1.2. Deep rifting stage In the sedimentary period of Member 3 of Shahejie Formation, the western sag entered the deep rifting period with rapid expansion and large-scale subsidence. Niuxintuo, Taian, Lengjiabao and Dawa faults in the sag were joined together to form the main fault system. The main fault was pulled apart and subsided, making

3.1.3. Continuous rifting-attenuation stage This stage corresponds to the sedimentary period from Member 1 and Member of Shahejie Formation to Dongying Formation. At the end of the sedimentary period of Member 3 of Shahejie Formation, three sags in Liaohe depression experienced different degrees of uplift and denudation. In the Early Oligocene, the regional extension rifting was intensified again, and the basement subsided differentially. From the sedimentary period of Member 2 of Shahejie Formation to the sedimentary period of Member 1 of Shahejie Formation, the water body gradually expanded, the sag was dominated by shallow lake sedimentary environment, and developed fan delta system and lacustrine mudstone. During the sedimentary period of Dongying Formation, the sag expanded again and the basement subsided differentially, the southern part of the sag subsided faster than the northern part of the sag. Affected by strike-slip stress field, the main fault in the sag produced right-lateral displacement, and the positive and negative structures in the sag developed into the current form. 3.2. Oil source conditions During the sedimentary evolution process of the western sag, several sets of source rocks of Member 4, Member 3 and Member 1 of Shahejie Formation were developed in the shallow to deep lacustrine environment in the western sag. The Member 4 and Member 3 of Shahejie Formation are the main oil-generating layers with superior geological and geochemical conditions (Zhu, 2002; Li

Fig. 2. Depositional-tectonic evolution of the western sag in the Liaohe depression. E3d1 indicates Member 1 of Dongying Formation; E3d2 indicates Member 2 of Dongying Formation; E3d3 indicates Member 3 of Dongying Formation; E3s1 indicates Member 1 of Shahejie Formation; E3s2 indicates Member 2 of Shahejie Formation; E3s3 indicates Member 3 of Shahejie Formation; E3s4 indicates Member 4 of Shahejie Formation; E3f1 indicates Upper Member of Fangshenpao Formation; E3f2 indicates Lower Member of Fangshenpao Formation.

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et al., 2008; Liu et al., 2010). Through comparison of several biomarkers of crude oil with those source rocks, it can be found that the strong-reduction saline semi-deep lacustrine crude oil mainly distributed in the northern part and western slope of the western sag is similar to the strong-reduction saline semi-deep lacustrine source rocks in Member 4 of Shahejie Formation, both have high ratio of Pr/Ph, slope distribution form of C27, C28 and C29 regular steranes, and are rich in C28 regular sterane and have high Ga/C30hopane value, etc. Weak reduction to weak oxidation freshwater semi-deep to deep lacustrine crude oil is widely distributed in the western sag; through oil-source correlation, it can be confirmed that this kind of crude oil originates from source rocks in Member 3 of Shahejie Formation characterized by ratio of Pr/Ph from 1.0 to 2.0, moderate or low Ga/C30-hopane value, low Ol/C30-hopane value, low ratio of long-chain tricyclic terpane/hopane, high ratio of rearranged sterane/regular sterane and 4-methylsterane. 3.2.1. Source bed with large thickness and wide distribution area During the sedimentary period of Member 4 of Shahejie Formation, shallow lacustrine facies thick-beded source rocks were widely distributed in the western sag. Thickness of source rocks in the Yuanyanggou sub-sag in the southern part of the sag is from 50 to 100 m. During the sedimentary period of Member 3 of Shahejie Fromation, the western sag was wholly in a deep to semi-deep lake sedimentary environment, where hugely thick oil-generating layers were developed. Thickness of source rocks in the middle part of Member 3 of Shahejie Formation are generally from 200 to 400 m, and more than 600 m in the center of the sag. Thickness of mudstone in the lower part of Member 3 of Shahejie Formation is generally from 50 to 300 m and maximally more than 400 m, showing substantial material basis for oil generation (Fig. 3). 3.2.2. Source rocks with high abundance and good type of organic matter Source rocks in the southern part of the western sag have good conditions. The source rocks in Member 4 of Shahejie Fromation have mainly Type I and Type II1 kerogens (Fig. 3) and an average TOC of 2.83% (Table 1). The source rocks in Member 3 of Shahejie Formation have Type II and Type III kerogens (Fig. 3) and an average TOC of 1.99% (Table 1). According to the geochemical indexes of all mudstones, the source rocks in Member 4 and Member 3 of Shahejie Formation basically belong to good source rocks. Number in the brackets represents amount of samples. 3.2.3. Source rocks with good thermal evolution environment According to geothermal results of Liaohe depression, the western sag has an average geothermal flow value of 66 mw/m2, indicating an “hot basin” with mediumerelatively high geothermal flow value and corresponding geothermal gradient. According to measured geothermal data, in the Yuanyanggou subsag and Qingshui subsag supplying hydrocarbon for Huanxiling area, the formation at the depth of 2000 m has a geothermal temperature of 65e85  C, indicating it is already in the low-temperature thermal evolution stage; while the formation at the depth of 3000 m has a geothermal temperature of 95e120  C, indicating it is in the low to mid-high temperature thermal evolution stage. According to relationship between Ro and burial depth in Liaohe depression, if Ro of 1.30% is taken as the lower limit of the main oil-generating belt, the corresponding depth in the southern part of the western sag is about 5000 m. There is a wide main oil belt vertically, generally, formation with buried depth of 2000e5000 m all belongs to this belt, and the lower limit depth of the subsag area can be even up to 6000 m. This is favorable for organic matter to be fully transformed into oil and gas, therefore, abundant oil and gas resources can be generated and provide a solid foundation for formation of

Huanxiling oilfield. From Ro contour map in the southern part of the sag, it can be seen that Member 3 and Member 4 of Shahejie Formation have maximum Ro of 1.80%, indicating high evolution degree of source rocks (Fig. 3). 3.3. Reservoir conditions There are many reservoir rock types in the Huanxiling area, such as metamorphic rock, clastic rock and magmatic rock, but the main reservoir rock type is clastic rock in Paleogene Shahejie Formation. The basement rock of the sag is mainly Archaeozoic granitic gneiss and mixed granite. Under the action of internal and external geological forces, such as long-term tectonic movement, weathering & denudation and leaching, the reservoir space is mainly fractures with some dissolution pores, which is favorable for oil and gas accumulation. The Mesozoic clastic rock and igneous rock and Fangshenpao Formation igneous rock also have storage capacity. From distribution of discovered reserves, the Paleogene sandstone reservoir is the main reservoir in the Huanxiling area. The clastic reservoirs in the Huanxiling area have following basic characteristics. 3.3.1. Relatively large-scale sedimentary system with great thickness of sand body Due to small and narrow lake basin of Liaohe rift, frequent tectonic activity, the palaeogeographic environment is complex; influenced by multiple provenances and short-distance transportation, the lake basin is obviously characterized by rapid filling and deposition, leading to form relatively small-scale different types of sedimentary systems in each sag. The southern part of the western sag is a relatively open lacustrine basin; therefore, relatively large-scale fan delta sedimentary system or fan deltasublacustrine fan sedimentary system are developed in this area, its distribution area generally range from tens of square kilometers to 100 km2, and some can be more than 300 km2. For example, the distribution areas of Qijia and Xibaqian fan delta systems in Member 1þMember 2 on the western slope in the western sag can reach 332 km2 and 336 km2 respectively. On the other hand, persistence and phase of block faulting activities lead to form dual characteristics of inheritance and dislocation migration of each sedimentary system. In a system, there are many sand layers vertically, so cumulative thickness of sand layers is large. For example, sandstone-dominated sedimentary systems developed in different sedimentary periods in the Huanxiling oilfield: some fan delta-sublacustrine fan systems (Shuguang, Qijia, Huanxiling and Xibaqian) were developed in sedimentary period of Member 4 of Shahejie Formation; some fan delta systems (Qijia and Huanxiling) were developed in Member 1þMember 2 of Shahejie Formation. These sedimentary systems formed in different sedimentary periods are dislocated and overlapped, so there are many sand layers with large total thickness. During the subsidence period of Member 3 of Shahejie Formation, cumulative thickness of sand layers in fan delta-sublacustrine fan system in the Huanxiling area is 550 m, and the sand layers are dislocated, overlapped and widely distributed, and the sublacustrine fan can extend to the sedimentary center, thus, different sand bodies are multiply and continuously distributed. 3.3.2. Many types of sedimentary systems Due to change of water body caused by tectonic activities, many types of sedimentary systems are developed in the Huanxiling area in the southern part of the western sag, such as fluvial system, alluvial fan system, fan delta system, delta system, sublacustrine fan system, etc. The sedimentary systems in different sedimentary periods are quite different (Fig. 4). Shahejie Formation, as the main

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Fig. 3. Distribution of source rock in Shahejie Formation in the southern part of the western sag showing that source rocks have great material potential for oil generation. (a) Distribution of source rocks in the middle part of Member 3 of Shahejie Formation; (b) distribution of source rocks in the lower part of Member 3 of Shahejie Formation; (c) distribution of Dujiatai source rocks in Member 4 of Shahejie Formation.

Table 1 Geochemical indexes of dark mudstones in the western sag showing that the source rocks in Member 4 and Member 3 of Shahejie Formation basically belong to good source rocks. Strata Dongying Fm. Member 1 of Shahejie Member 2 of Shahejie Member 3 of Shahejie Member 4 of Shahejie

S(%) Fm. Fm. Fm. Fm.

0.17 0.54 0.48 0.59 0.42

(198) (216) (141) (388) (158)

TOC (%)

“A” (%)

1.07 1.85 1.38 1.99 2.83

0.0219 0.1103 0.1125 0.1375 0.2167

(198) (216) (141) (388) (158)

(43) (74) (35) (85) (38)

Total hydrocarbon (ppm)

Hydrocarbon/C (%)

“A”/C (%)

Alkanes/Aromatics

60 (43) 358 (74) 472 (35) 543 (85) 1142 (38)

0.71 1.68 2.37 2.59 3.92

2.81 5.25 5.89 6.13 7.65

1.42 1.29 1.46 1.62 1.72

(42) (74) (34) (84) (37)

(42) (74) (34) (84) (37)

(43) (74) (35) (85) (38)

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Fig. 4. Sedimentary facies of main oil-bearing strata in the Huanxiling area. (a) Sedimentary facies of Huanxiling-Xibaqian fan body in Member 2 of Shahejie Formation; (b) sedimentary facies of Huanxiling-Xibaqian fan body in Upper sub-member of Member 3 of Shahejie Formation; (c) sedimentary facies of Huanxiling-Xibaqian fan body in Middle sub-member of Member 3 of Shahejie Formation; (d) sedimentary facies of Huanxiling-Xibaqian fan body in Lower sub-member of Member 3 of Shahejie Formation; (e) sedimentary facies of Huanxiling-Xibaqian fan body in Dujiatai oil layer of Member 4 of Shahejie Formation.

reservoir formation in this area, has different sedimentary characteristics from bottom to top. (1) Member 4 of Shahejie Formation. It deposits in the initial period of lake basin development, some delta fans (such as Qijia, Huanxiling and Xibaqian) are well developed. Controlled by palaeogeomorphology, the strata deposition in this period had a characteristic of filling and leveling up, and the fan bodies are distributed continuously. The lower part was the channel and the higher part was the shoal (Fig. 4).

(2) Lower sub-member of Member 3 of Shahejie Formation. It deposits in the initial period of lake basin development, the lake basin begins to expand, and the provenance supply is under compensation and is dominated by pointeprovenance supply. Controlled by two provenances (Xibaqian and Huanxiling), the fan bodies are distributed in two directions, SW direction (Huan132 fan body in the northwest) and SE direction (Jin607 fan body in the south). The Xibaqian fan can be divided into two branches which extend southward and southeast respectively, the sand body is large in scale and underwater distributary channel sand bodies are developed.

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(3)

(4)

(5)

(6)

The Huanxiling fan in the north extends southward. Fronts of these two fans intersect at the southeastern part of the area, forming continuous front sand bodies with a larger scale (Fig. 4). Middle sub-member of Member 3 of Shahejie Formation. It deposits in the deep rifting period. Elevation difference between provenance area and sedimentary area is increased and the lake basin is deepened, a large amount of coarse debris is transported to the deep-water lake basin through high-density flow during flood period, thus, different-scale turbidite bodies are deposited. The Huanxiling area is dominated by fan middle subfacies of turbidite fan at bottom of the lake, at this time, the Huanxiling and Xibaqian fan bodies are mainly developed in this area. Among which, the Huanxiling fan body is distributed in SE direction and its scale is large, sand bodies occur in the form of NW belt and deep-water mudstone deposits among sand bodies (Fig. 4). Upper sub-member of Member 3 of Shahejie Formation. It deposits in the post deep-rifting convergence period, and is dominated by fan delta-sublacustrine fan facies deposits. Due to tectonic uplift and denudation, the upper step strata in Xibaqian and Huanxiling areas are denuded, the sand bodies in the remaining strata mainly is fan delta front sand bodies from Xibaqian provenance; the sand bodies are small in scale and become into turbidite sand bodies of sublacustrine fan toward the lake basin (Fig. 4). Member 2 of Shahejie Formation. It deposits in the rifting convergence period, when the debris supply is abundant and the lake basin is shallow, so it is production of short-distance transportation near provenance. Three large fan delta deposits (Qijia, Huanxiling and Xibaqian fan deltas) are developed in the oilfield under the control of Huanxiling and Xibaqian provenances (Fig. 4). Member 1 of Shahejie Formation. The underwater distributary channel sand bodies in fan delta front inherit distribution characteristic of Member 2 of Shahejie Formation. In this sedimentary period of Member 1 of Shahejie Formation, the Huanxiling provenance is more developed than in the sedimentary period of Member 2 of Shahejie Formation, and its distribution range become more widely. For estuary dam and sheet sand bodies, the single layer is thinner and its distribution range is smaller, but on the plane, many sets of sand bodies can be overlapped and continuously distributed, and vertically, sandstone and mudstone have good differentiation. Channel sand bodies are well developed with good connectivity, and mostly occur in the form of medium and thin interbeds (Fig. 4).

With the increase of burial depth, the clastic reservoirs turn worse in physical properties gradually. The reservoirs of Es1 and Es2 members are best in physical properties, with an average porosity of 22.7% and an average permeability of 447.3 mD, the Es3 member is next, and the Es4 member is worse. At the same burial depth, the newer the stratum, the better the physical properties are, and vice versa. 3.3.3. Good physical properties of sedimentary bodies Lithology of Paleogene clastic reservoirs mainly includes medium sandstone, coarse sandstone, pebbly sandstone and glutenite. The main type of reservoir space is pore, which can be further divided into primary pore, secondary pore and mixed pore. Intergranular pore caused by primary sedimentation and intergranular dissolution pore formed by secondary dissolution are developed, mixed super-large pore and secondary moldic pore also can be seen (Fig. 5). Dissolution is the most important constructive diagenesis

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in the study area. There are three main causes of secondary dissolution pore in this area, namely, leaching of atmospheric fresh water, decarboxylation of organic matter and hydrocarbon cracking (Meng and Sun, 2007). The Paleogene in Liaohe depression is mostly in the early to middle diagenesis stage. Even at depth of 4000 m, its primary porosity can be up to 15%. In addition, there are secondary pore development zones in different depths. Although primary pore and secondary pore are further reduced at depth of more than 4000 mp, secondary pore still exists. The reservoirs at depth of 5000 m in the western sag can still have a total porosity of 10%. In general, the Paleogene sandstone reservoirs in Liaohe depression have high porosity and permeability at depth less than 3000 m, especially in favorable facies belts of each sedimentary system. For example, the underwater channel sand bodies in Xinglongtai fan delta system have a porosity of 20%e30% and a permeability of 2000e6000 mD (even more than 10000 mD); the flood plain has a porosity of 15%e30% and permeability of 500e3000 mD. The mid-fan channels of Lianhua sublacustrine fan in the Gaosheng area have a porosity of 20%e33% and permeability of 2000e3000 mD.

3.4. Cap rock conditions The large-scale oilfields in Liaohe depression are mainly distributed in the Paleogene Shahejie Formation and basement buried hill (Fig. 6). The Huanxiling oilfield is dominated by Shahejie Formation reservoir which contributes 89.8% of the total reserves, of which, Member 1þMember 2, Member 3þMember 4 of Shahejie Formation account for 31.8% and 58% of the total reserves, respectively. Distribution of regional cap rocks controls distribution of large oilfields. There are three sets of regional cap rocks (Member 4, Member 3 and Member 1 of Shahejie Formation) and multiple local cap rocks in the western sag. Development and distribution of regional and local cap rocks obviously control distribution and enrichment of oil and gas in different intervals. The Xinglongtai, ShuguangHuanxiling and Gaosheng oilfields discovered in the western sag are all distributed under the regional cap rocks. From Damintun sag in adjacent area, the regional cap rocks also control distribution of large oilfields.

3.5. Trap conditions and hydrocarbon migration 3.5.1. Fault transportation system There are three-stage large-scale fault systems in the area. The first stage faults extend from the basement to Member 4 of Shahejie Formation and occur as the westward-dipping normal faults formed by warping of basement, it control the basement structure form. The second stage faults extend from Member 3 of Shahejie Formation and terminate in Dongying Formation, and some faults break to the basement; it are faults generated in the process of basin rifting and occur as the eastward-dipping normal faults, and some have synsedimentary characteristic; it control sedimentary thickness of Member 3 and Member 1þMember 2 of Shahejie Formation (Fig. 7). The third stage faults, mainly develop in the sedimentary period of Dongying Formation, are largely near EWtrending faults formed by strike-slip activity in this period; some faults cut Member 3 of Shahejie Formation, but most of faults are mainly distributed in Member 1þMember 2 of Shahejie Formation. These three-stage fault systems crisscross and overlap with each other to form fault transportation system in this area (Guo et al., 1998).

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Fig. 5. Microscopic characteristic of typical clastic reservoirs in the Huanxiling oilfield showing that intergranular pore and intergranular dissolution pore are developed. (a) Intergranular dissolution pore; (b) intergranular pore.

Fig. 6. Distribution of large oilfields in the Liaohe depression showing that the large-scale oilfields in Liaohe depression are mainly distributed in the Paleogene Shahejie Formation and basement buried hill. The size of red circles represents the scale of oilfields. Es3U indicates Upper sub-member of Member 3 of Shahejie Formation; Es3M indicates Middle submember of Member 3 of Shahejie Formation; EsL3 indicates Lower sub-member of Member 3 of Shahejie Formation. The relative size of red circles represents the relative scale of oil reservoirs.

Fig. 7. Reservoir profile through Well D202 to Well D143 showing that these three-stage fault systems form fault transportation system. Ed indicates Dongying Formation; Ng indicates Guantao Formation.

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3.5.2. Characteristic and type of traps The tectonic movement in the Huanxiling area in the southern part of the western sag is characterized by extension, and differential subsidence and continuous deep burial of the basement lead to extensive development of syngenetic faults. Three nearly EWtrending main faults cut this area into three buried hill belts (namely, Xibaqian buried hill belt, Huanxiling buried hill belt and Qijia buried hill belt). The structural form of Member 4 of Shahejie Formation is mainly controlled by underlying palaeogeomorphology and three groups of faults. These three groups of faults are NE-trending faults, NE-trending to nearly EW-trending faults and NW-trending faults. The NE-trending faults are the main faults in this area, which control tectonic framework and stratigraphic sedimentation to form a series of NE-trending structural belts (Fig. 8). The NW-trending fault and NE-trending to nearly EW-trending secondary faults cut faulted nose-shaped structural belt into several fault blocks and fault nose traps. The structural shape of Member 3 of Shahejie Formation is a monocline on the whole, which is characterized by high in the NW and low in the SE, steep in the east and gentle in the west, deep in the east and shallow in the west. Under the background of the southeastwarddipping slope, the nearly EW-trending southward-dipping normal faults cut the slope into a series of EW-trending and southeastward-dipping fault terraces. The fault terraces are cut by secondary NE-trending eastward-dipping faults into a series of fault nose structures (Fig. 8). In local area, affected by palaeogeomorphology, the drape structures are formed. The structural shape of Member 1þMember 2 of Shahejie Formation is complex;

9

under the background of the southeastward-dipping slope, the NEtrending southward-dipping main faults cut the area into a series of NE-trending southeastward-dipping fault terraces, and the NWtrending secondary faults divide the NE-trending fault terraces into fault blocks and fault noses (Fig. 8). Formation of traps is controlled by both fault block movement state and fault activity of basement. Basic form of the traps includes fault anticline, fault nose, fault block (fault terrace), horst and graben, etc. Multi-stage and inheritance of fault activities link basement with cap rocks and deformation structures at different levels in cap rocks. Activity state of basement fault block controls distribution of sedimentation and favorable facies belt, and then various non-structural traps are formed. This makes it possible for traps of different levels in the sag to be connected and combined according to a certain genesis to form composite trap zones. The composite trap zone here not only refers to combination of multi-types of traps on the plane, but also emphasizes vertical combination of traps. The warped fault block draped composite traps are mainly developed in the Huanxiling area, including nine types of trap: buried hill trap, stratigraphic onlap trap, draped anticlinal trap, lithologic pinchout trap, fault block trap, rolling anticlinal trap, nose-shaped structural trap, unconformity barrier trap and heavy oil self-sealing trap (Fig. 9). Under the background of the warped basement, there are hundreds of traps of different sizes and shapes in the Huanxiling area which provide a large number of accumulation places for oil and gas. 3.5.3. Hydrocarbon accumulation phases Homogenization temperature of inclusion of reservoirs in

Fig. 8. Structural plane distribution of bottom of Member 2 of Shahejie Formation in the Huanxiling oilfield.

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Fig. 9. Schematic diagram of trap types in the Huanxiling area showing that nine types of trap are developed in the Huanxiling area. (1) Buried hill trap; (2) stratigraphic overlap trap; (3) draped anticlinal trap; (4) lithological pinch-out trap; (5) fault block trap; (6) rolling anticline trap; (7) nose-shaped structural trap; (8) unconformity blocked trap; (9) heavy oil self-sealing trap.

Formation in this area, which is from 28 Ma to 39 Ma, and the peak time of hydrocarbon accumulation corresponds to the sedimentary period of Dongying Formation. The late sedimentary period of Dongying Formation is not only the migration and accumulation period of the shallow-middle buried oil and gas, but also the adjustment and re-accumulation period of oil and gas in deep reservoirs. In the Huanxiling area, the hydrocarbon accumulation is characterized by multi-stage slow accumulation, which mainly depends on its unique geological conditions. The Huanxiling oilfield is located in the southern part of the western slope of the western sag, which is the long-term hydrocarbon migration direction area; oil and gas generated in oilgenerating sags migrate to the slope along large faults and highpermeability sandstone layers, when there are favorable traps, the oil and gas will be accumulated in these traps. The oil and gas initial migration period in the Huanxiling area is earlier than that in the deep rifting zone and steep slope zone. Due to long distance migration of oil and gas, therefore, oil and gas migration lasts for a long time and the hydrocarbon accumulation has multiple stages, this is reflected by wide span range of the homogenization temperature (Fig. 10). Fig. 10. Distribution of homogenization temperatures of inclusions of reservoirs in Well Huan603 in the Huanxiling area showing that homogenization temperature of inclusion of reservoirs in Member 4 of Shahejie Formation mainly ranges from 100 to 110  C.

 C,

Member 4 of Shahejie Formation mainly ranges from 100 to 110 secondly from 90 to 100  C and from 80 to 90  C (Fig. 10). According to burial history and geothermal history recovery results, the inclusion formation time with the homogenization temperature of 90e100  C and 100e110  C are the late sedimentary period and the end of sedimentary period of Dongying Formation respectively, and the inclusion formation time with the homogenization temperature of 80e90  C is the sedimentary period of Member 3 of Shahejie Formation (Fig. 11). This indicate hydrocarbon accumulation time generally is from the end of sedimentary period of Member 3 of Shahejie Formation to the end of sedimentary period of Dongying

3.6. Oil and gas reservoir characteristics 3.6.1. Reservoir types The Huanxiling oilfield is controlled by structure on the whole and by sand body development locally. Most of reservoirs are lithologic structural reservoirs (Feng et al., 2009; Li et al., 2010). Well Block Qi40 is a typical block of Lianhua oil reservoir, where the oil reservoir is buried at depth of 625e1050 m, the oil-bearing interval is 74.4 m thick on average, and the effective thickness of single layer are 5e10 m. Vertically, the oil reservoir can be divided into two oil layer groups and 10 sub-layers (Fig. 12). Distribution of the oil reservoir is mainly controlled by structure and sedimentary facies belts. The oil reservoir is a lithologic-structural heavy oil reservoir sealed by faults. Connectivity of the oil reservoir is controlled by provenance, sedimentary facies belt and

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Fig. 11. Stratigraphic burial history of Well Huan603 in the Huanxiling area showing that the inclusion formation time with the homogenization temperature of 90e100  C and 100e110  C are the late sedimentary period and the end of sedimentary period of Dongying Formation respectively, and the inclusion formation time with the homogenization temperature of 80e90  C is the sedimentary period of Member 3 of Shahejie Formation.

hydrodynamic strength; the underwater distributary channel sand bodies along provenance direction have good connectivity, and the connectivity coefficient is 0.88; while the sand bodies (underwater distributary channel sand body, sand body between underwater distributary channel or delta front thin sand body) crossing the water flow direction have poor connectivity with an average connectivity coefficient of 0.71. Well Block Jin45 is a typical block of Yulou oil reservoir, where the oil reservoir is buried at depth of 922.6e1055 m, the oil-bearing interval is 76.3 m thick on average, thickness of the oil reservoir are from 7.0 to 40.0 m with an average of 20.9 m. The oil reservoir can vertically be divided into two oil groups (Yu I oil group and Yu II oil group) with two independent oil-water systems, and further can be

subdivided into 12 sub-layers. The Yulou reservoir in Well Block Jin45 is lithologic structural reservoir in genesis; distribution of the oil reservoir is mainly controlled by secondary faults in high position, and locally controlled by sand body distribution; the oil reservoir also can belong to the layered edge-bottom water oil reservoir in driving type (Chen et al., 2014) (Fig. 13). Thickness of the single oil layer is small and generally ranges from 3 to 8 m, there are many oil layers which are distributed dispersedly. The oil reservoir has average permeability variation coefficient of 0.8, average permeability penetration coefficient of 2.5 and average permeability gradient of 10.8, indicating strong heterogeneity. Therefore, breakthrough along a single layer likely occurs during heavy oil thermal recovery, which affects development effect.

Fig. 12. Reservoir profile of the Lianhua oil reservoir in Well Block Qi40 in the Huanxiling oilfield showing that the oil reservoir can be divided into two oil layer groups.

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Fig. 13. Reservoir profile of Yulou oil reservoir through Well Jin45-018-243 to Jin45-17-30c in Well Block Jin91 in the Huanxiling oilfield showing that distribution of the oil reservoir is mainly controlled by secondary faults in high position, and locally controlled by sand body distribution.

3.6.2. Oil type dominated by ordinary heavy oil and extra heavy oil In the heavy oil in the study area, some light fraction are lost, and steroid and terpenoid cyclic compounds are also affected to a large extent, but 25-norhopane and non-hydrocarbon compounds dominated by oxygenated compounds occur (Wang et al., 2001; Li et al., 2008). These prove that the heavy oil in this area experience strong biodegradation and water washing (Wang et al., 2001). Identification of bacterial microorganisms and associated natural gas shows that anaerobic biodegradation is the main cause of heavy oil in the Huanxiling oilfield (Li et al., 2008). Influence of groundwater on crude oil is mainly manifested in that active water body is the carrier of bacteria and nutrients needed for survival of microorganisms such as inorganic salts (Connan, 1984). Most of the heavy oil in the study area contacts with surface water, the water comes in the form of bottom water, edge water or even surrounding water, indicating the groundwater is very active (Li et al., 2008). Closer to the oil-water interface, the lower the content of saturated hydrocarbons and hydrocarbon compounds and the stronger the biodegradation will be (Huang et al., 2004). It can be seen that in the long-distance migration and preservation process of oil migration to the west slope, caused by combined effects of biodegradation, formation water washing, oxidation, high formation temperature and poor sealing ability of regional cap rocks, and loss of large amount of light components in crude oil and concentration and accumulation of heavy component lead to form heavy oil reservoirs (Li et al., 2008; Cai and Ju, 2010). The heavy oil is dominated by ordinary heavy oil and extra heavy oil, with a viscosity range of 200e35000 mPa s (50  C surface degassing) (Table 2).

4. Key technologies for exploration and development 4.1. Technologies for seismic data processing and reservoir prediction 4.1.1. Multi-batch seismic data merging processing and interpretation technology The twice 3D data acquisition was completed in the Huanxiling

oilfield around 2000. Influenced by many factors in seismic data acquisition and processing with different years, seismic results of different blocks have differences in phase, frequency and energy, etc, which makes it impossible to carry out overall interpretation. In order to meet need of overall research, overall understanding and overall evaluation of favorable oil accumulation belts in this area, a processing of large area contiguous seismic data is carried out. During the data processing, the seismic data consistent processing technologies are developed (Riekett and Lumley, 1998; Cheng et al., 2004). (1) Wavelet consistency processing technologies such as phase adjustment of geophone, frequency matching of geophone and vibroseis matching processing, are used to eliminate differences of excitation and reception of wavelet data collected in different years and well blocks. (2) Comprehensive interval transit time correction technologies such as instrument delay correction, relocation of detection point, datum static correction and residual static correction are used to eliminate interval transit time among different locations and beam lines of data collected in different years and well blocks. (3) Amplitude, phase and frequency consistency processing technologies such as surface consistent amplitude compensation, surface consistent deconvolution, surface absorption compensation and spatial residual amplitude compensation, are adopted to eliminate differences in energy, frequency and phase of data collected in different years and well blocks. (4) Technologies of fold number adjustment and data regularization are used to eliminate difference in fold number and offset distribution of data collected in different well blocks and different years. Through application of the above processing technologies, consistency of seismic data and quality of seismic processing results are improved significantly, data collected in different years and well blocks are spliced together seamlessly, as a result, overall structural pattern is clearer and quality of seismic imaging is improved

Table 2 Analysis result of crude oil samples from major blocks of Huanxiling oilfield. Oil layer

Guantao Yulou Xinglongtai Lianhua

roa/g$cm3

moa/mPa$s

Freezing point

Wax content

Surface 20  C

Surface 50  C



%

%

1.0035 0.999 0.963e0.976 0.9498e0.969

35400 13955 1302e5500 169.04e2640

18 17 19e10 0e18

3.69 1.75 3.48e5.20 1.22e7.12

44.5 40.8 20e29.1 8.22e33.49

C

Asphaltene

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Fig. 14. Comparison of seismic data of the Huanxiling area showing that overall structural pattern is clearer and quality of seismic imaging is improved obviously through application of processing technologies. (a) Old seismic data; (b) prestack time migration data.

obviously, signal-to-noise ratio of seismic data of mid-deep buried layers is enhanced by about 50%, and main frequency of seismic data is obviously increased and is up to 25e30 Hz which is 5 Hz higher than previous data main frequency (Fig. 14). Interpretation work of continuous data is carried out study paleogeomorphology of the study area, which provides a foundation for search of subsequent targets. 4.1.2. Thin reservoir inversion technology based on geological model Model-based the seismic inversion is based on the geological model which is constantly modified and updated by using the optimal iterative perturbation algorithm to make forward synthetic seismic data of the model best match actual seismic data, and the final model data is the inversion results. Under thin reservoir geological condition, due to limitation of seismic frequency bandwidth, accuracy and resolution of direct inversion method based on ordinary seismic resolution can’t meet requirement of oilfield development. Based on the model-based seismic inversion, limited bandwidth of seismic data can be supplemented by high frequency and complete low frequency information of well logging data to get high resolution formation wave

impedance data, which are favorable conditions for fine description of thin reservoirs. This method is characterized by seismic-logging joint inversion, low-frequency and high-frequency information are from logging data, and structural characteristics and mid-frequency information are from seismic data. Multi-solution is the inherent characteristic of the model-based seismic inversion. The key to reduce problem of multi-solution is to establish the initialization model correctly (Fig. 15). The accuracy of based-model inversion results depends not only on geological characteristic, number of drilled wells, well location distribution, resolution and signal-to-noise ratio of seismic data of the target area, but also on precision of processing. The main technical links in processing include: reservoir geophysical characteristics analysis, logging curve standardization, seismic wavelet extraction, and establishment of initial wave impedance model, etc. The model-based inversion technology can combine seismic data with well logging, break through limitation of traditional seismic resolution, and theoretically obtain same resolution as well logging data. It is the key technology of fine description in oilfield development stage. The multi-solution is the inherent characteristic of the modelbased seismic inversion method, which mainly depends on

Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004

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Fig. 15. Initial geological model of thin reservoir inversion technology based on geological model. s1z represents the middle part of the Member 1 of Shahejie Formation; s12 represents Member 1 and Member 2 of Shahejie Formation; s332 represents 2nd oil formation of Lianhua Oil layers of the Member 3 of Shahejie Formation; s3r represents Rehetai oil layers of Member 3 of Shahejie Formation; s3d represents Dalinghe oil layers of Member 3 of Shahejie Formation; s3L represents Lianhua oil layers of Member 3 of Shahejie Formation; s4d represents Dujiatai oil layers of Member 4 of Shahejie Formation.

degree of coincidence between initial model and actual geological condition. Under the same geological condition, the more wells drilled, the more reliable the results will be, and vice versa. Seismic data plays two main roles in the process of the modelbased inversion: one is to provide formation and fault information to guide interpolation and extrapolation of logging data to establish the initial model; the other one is to constrain the geological model in the effective seismic frequency band to converge in the correct direction. Therefore, improving resolution and interpretation accuracy of seismic data in the model-based inversion is an important way to reduce multi-solution (Fig. 16 and Fig. 17). 4.2. Lab experimental technology for heavy oil thermal recovery 4.2.1. Loose and unconsolidated core processing and analysis technology Heavy oil reservoirs in the Huanxiling oilfield are poorly consolidated, and the core is loose. So it is difficult to prepare test samples using conventional methods. Through repeated tests, freezing preservation and processing technology and equipment for unconsolidated core are improved, and contamination of drilling fluid can be analyzed during coring process. After taken out of the well, the core is cleaned, packaged, cryopreserved, frozen and encapsulated. During the sampling process, samples are cooled at temperature below 170  C, and taken by dustless drilling, and removed oil by solvent extraction. Sample analysis and testing equipment is equipped to meet a series of testing and analysis requirements, such as porosity, permeability, rock electricity, capillary pressure curve, reservoir sensitivity evaluation, oil-steam (hot water) relative permeability, and oil displacement efficiency, etc. At present, absolute error of porosity repeatability testing of unconsolidated core is only ±1.0% (Fig. 18). 4.2.2. Physical modeling technology for steam flooding proportion After steam huff and puff exploitation under depressurization,

the heavy oil reservoirs would become even more heterogeneous, making steam flooding more complex in mechanism and more difficult to control. On the basis of solving the elastic energy modeling, the model parameters of uniform application conditions of steam stimulation and steam flooding are derived to realize the linkage simulation of multi-thermal recovery in the whole process. On this basis, 2D and 3D proportional physical models similar to the prototype are established, and the maximum working temperature is 350  C and the maximum working pressure is 15 MPa, thus, the physical models can be used to carry out physical modeling of multi-well types multi-well groups, stratigraphic rhythm and planar heterogeneity of the reservoir. Through indoor physical modeling, contributions of crude oil viscosity reduction, steam distillation, thermal expansion, steam flooding and water flooding to oil recovery enhancement are quantitatively evaluated, and expansion and development characteristics of steam flooding chamber in heterogeneous reservoirs are figured out, effects of reservoir plane, vertical heterogeneity and formation dip on steam flooding result are also studied, as shown in Fig. 19. These studies provide basic parameters for understanding mechanism and optimizing parameters of steam flooding in mid-deep buried heavy oil reservoirs.

4.3. Fine description technology for heavy oil reservoir 4.3.1. Classification and evaluation technology of mid-deep buried heavy oil geological body Classification and evaluation of heavy oil geological body is to deepen understanding of reservoir characteristics and development characteristics based on reservoir development mode, which plays an important role in guiding reservoir engineering design. From single well evaluation, the classification and evaluation technology for mid-deep buried heavy oil geologic body is developed, which mainly includes three steps: determination of regional single well evaluation criterion and parameter weight, cross-well connectivity evaluation and well-group comprehensive

Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004

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Fig. 16. Planar distribution of average wave impedance of Yulou oil reservoir.

classification evaluation. Taking Well Block Qi40 as a typical example, reservoir thickness, permeability, interlayer and variation coefficient are selected as main evaluation parameters to establish evaluation criteria for graded geological bodies in different regions (Table 3). The connectivity weight is introduced to optimize characterization parameters of cross-well connectivity, and the cross-well injection-production corresponding relationship is comprehensively analyzed; weights of classification parameters are determined by grey relational analysis method, and geological body condition of steam injection wells and production wells are comprehensively considered, thus, evaluation of regional wellgroup geological body is completed. On this basis, individualized design for Well Block Qi40 well group is completed, and the first development plan for domestic mid-deep buried heavy oil reservoir is compiled. 4.3.2. Cross-well seismic continuity evaluation and seepage barrier description technology In order to solve the problem that there are great differences between conversion well groups and single well production effect in the middle-late stage of heavy-oil reservoir development, the cross-well seismic continuity evaluation and seepage barrier description technology is developed. In this technology, through cluster analysis of reservoir seismic waveform continuity and combined with ant-tracking, area of seismic waveform variation is located, and the cross-well seismic continuity evaluation model is established; according to contact relationship of reservoir sand bodies, the seepage barrier can be divided into five types, to analyze

injection-production corresponding relationship. On this basis, cause of seepage barrier formation is analyzed, and type and spatial development rule of seepage barriers are determinated, which can provide a basis for adjustment of steam flooding development (Table 4). 4.4. Steam huff and puff development technology for mid-deep buried heavy oil reservoirs Most heavy oil reservoirs in the Huanxiling oilfield are characterized by thin interbedded reservoirs and deep burial depth, high heat loss of steam huff and puff and low reserve utilization. For above problems, through many years of research and practice, key technologies such as engineering design, compound huff and puff, infilling adjustment for mid-deep heavy oil steam huff and puff are established, matching technologies such as zonal and selective steam injection, sand control and desilting are developed, and high efficiency steam huff and puff development of mid-deep heavy oil reservoirs is realized. 4.4.1. Reservoir engineering optimization design technology for steam huff and puff In view of characteristics of long oil-bearing intervals and multiple oil-bearing layers of the heavy oil reservoirs, the development layers are divided according to factors such as reservoir thickness, intra-layer heterogeneity, interlayer distribution, edge and bottom water development and productivity, so as to reduce interlayer contradictions and ensure development independence. In the design process of well pattern and spacing, considered

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Fig. 17. Plane distribution of average wave impedance of Xinglongtai oil reservoir.

development economy, adjustment flexibility and subsequent replacement, the square well pattern with basic well spacing of 200e167 m is designed. For large reservoir burial depth, development of interlayer and large heat loss in steam injection development, some key parameters such as steam injection intensity, steam dryness and cycle increment are optimized (Zhao, 2003). In typical huff and puff block of Well Block Jin45 in the Huanxiling oilfield, the reservoir is divided into four development layers vertically, and the well spacing of the square well pattern is infilled from 167 m to 83 m. In this way, 20 years at the recovery rate of more than 1.2% is realized, the periodic recovery degree is 38%, and an estimated recovery factor is 42%.

4.4.2. Combined steam huff and puff technology In order to solve key problems of low cycle production, low oil-

steam ratio and oil well string in the mid-deep interbedded heavy oil reservoir during the middle-late stage of steam huff and puff production, the combined huff and puff technology is developed and breaks the previous single huff and puff mode of single well (Wang, 2006; Wan and Luo, 1998; Zhang, 1999). Through well pattern combination, well type combination and medium combination, the steam heat utilization rate and huff and puff effect are improved. The combined huff and puff technology mainly includes multi-well huff and puff, binary steam chemical huff and puff, ternary composite huff and puff, and intermittent huff and puff, etc. Field practice shows that the combined huff and puff technology is an effective method to improve development effect of heavy oil reservoirs in the middle-late stage of steam huff and puff. It can improve vertical steam absorption condition, prolong huff and puff production by 2e4 cycles and increase recovery factor by 2e3%.

Fig. 18. Loose heavy-oil core (a) and finished sample by freezing treatment (b).

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Fig. 19. Effects of reservoir heterogeneity and dip angle on steam flooding. (a) Vertical heterogeneous simulated temperature field diagram; (b) simulated temperature field diagram with formation dip of 15 ; (c) plane heterogeneity simulated temperature filed diagram. K represents permeability.

Table 3 Classification standard of geological bodies in Well Block Qi40. Zone classification

Main zone Edge water development zone Interlayer development zone

Reservoir thickness/m

Permeability/mD

Type A

Type B

Type C

Type A

Type B

>25 >30 >50

15e25 20e30 30e50

<15 <20 <30

>2 >2 >1.5

1.5e2 1.5e2 1.0e1.5

Interlayer frequency/ layer number per 100 m

Proportion of single layers with thickness of more than 5 m

Coefficient of variation

Type C

Type A

Type B

Type C

Type A

Type B

Type C

Type A

Type B

Type C

<1.5 <1.5 <1.0

<15 <10 <18

15e20 10e15 18e25

>20 >15 >25

>0.5 >0.5 >0.4

0.2e0.5 0.2e0.5 0.2e0.4

<0.2 <0.2 <0.2

<0.5 <0.5 <0.4

0.5e0.7 0.5e0.7 0.4e0.6

>0.7 >0.7 >0.6

Table 4 Distribution patterns and main identification markers of seepage barriers for steam flooding development in Wellb Block Qi40. Genetic Analysis of classification main controlling factors

Barrier type

Identification mark

Key description

Adjustment idea

Tectonic genesis Sedimentary genesis

Large stratigraphic dip type Sand body disconnected type

Stratigraphic dip greater than 15 , aggravating steam overlap Mainly superimposed seismic waveform, anttracking value greater than 0.7, affecting the injection-production correspondence. Permeability lower than 500 mD, ant-tracking value of 0.3e0.7, affecting steam sweep

Dip description

Row well-pattern inter welladjustment group replacement Multi-well-point fluid production well pattern Well point Deployment of faciesreplacement controlled well pattern

Stratigraphic dip Sand body connectivity Sedimentary micro-facies

Differential reservoir quality type controlled by facies Interlayer Interlayer Stratigraphic coefficient less than 0.3, differential heterogeneity heterogeneity type higher than 4, uneven vertical reserve utilization, breakthrough along monolayer Intralayer Thick sedimentary Inverse rhythm in the bottom, hot-water heterogeneity rhythmic type displacement in the lower part of thick layers over 5 m thick, low degree of reserve utilization

Evaluation of interwell seismic continuity Study of sedimentary microfacies

Targeted deployment measures

Recombination of Interlayer (Intralayer) steam injection layers replacement Steam flooding with Description of intralayer straight- horizontal heterogeneity, description of well combination single sand body tracking Description of interlayer heterogeneity

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Fig. 20. Annual oil production curve of steam flooding of Well Block Qi40.

4.4.3. Infilling adjustment Considering heterogeneity of heavy oil reservoir and production mechanism of steam huff and puff, a multilayer dynamic boundary and meshless reservoir model is established through analysis of sealed coring and dynamic testing data of inspection wells, to solve oil supply boundary change caused by multiple adjustment of well pattern. With this model, changing process of “three fields” around huff and puff wells can be clearly described to realize quantitative study of saturation and quantity of residual oil. Based on heating radius of steam huff and puff in different reservoirs and oil products, the well spacing is further infilled from the basic well pattern, the interwell reserve utilization degree and reservoir recovery are

improved; through dynamic infilling, the well spacing of steam huff and puff is gradually infilled from 83 to 70 m, as a result, the stable production time of development would be prolonged by 2e3 times and the recovery factor of huff and puff would increase by 15e20%. 4.4.4. Steam huff and puff matching t technology In order to solve serious vertical heterogeneity, vertical uneven steam absorption and low reserve utilization degree of interbedded reservoirs, stratified steam injection technologies, such as pitch selective steam injection, stratified quantitative steam injection, separate steam injection and stratified recovery with sealing in the lower layer and recovery in the upper layer, stratified steam

Fig. 21. Structural schematic diagram of layered steam injection tubing string. (a) Eccentric fishing type; (b) concentric tubular type.

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Fig. 22. Annual heavy oil production curve of Huanxiling oilfield.

distribution, separate layer steam injection allocation, and separate steam injection and stratified recovery of large drift diameter with sealing in the lower layer and recovery in the upper layer are developed and applied, and a perfect separate steam injection technology is formed. Through scale application in heavy oil blocks in the Huanxiling oilfield, these technologies enhance vertical utilization degree of reservoirs from 50% to 70%. For severe sand production and low rate of well opening in heavy oil block of the Huanxiling oilfield, according to characteristic of sand production in different periods, a series of sand control technologies for thermal recovery, such as wire-wound screen tube of gravel packing sand control, metal fiber screen tube sand control needle, peach shell resin artificial well wall sand control, high temperature sand-fixing agent sand control, composite perforation sand control and fracturing sand control, are developed and applied. The fracturing sand control technology can effectively solve oil well permeability reduction caused by conventional sand control methods, it becomes the main sand control method at present, which can extend pump inspection cycle by 2e3 times. 4.5. Steameflooding development technology for mid-deep buried heavy oil reservoir The steam flooding technology is the main replacement method after heavy oil steam huff and puff, and is applied in shallow reservoirs on large scale. For low recovery rate of heavy oil steam huff and puff in the Huanxiling oilfield, after more than 20 years of research, joint development mechanism of steam flooding and denudation in mid-deep buried heavy oil (buried depth 1000 m) is deepened, and four development stages of steam flooding thermal connection, steam flooding, steam breakthrough and denudation adjustment are established, ten key technologies for steam flooding reservoir, such as engineering optimization design, tracking control, separate steam injection and high-temperature lifting, etc. The steam flooding recovery of mid-deep buried heavy oil is about 60%, which is over 25% higher than that of steam huff and puff. 4.5.1. Engineering optimization design technology for mid-deep steam-flooding reservoir According to characteristic of the Huanxiling heavy oil reservoir, steam flooding screening criterion is established based on key parameters such as reservoir burial depth, reservoir thickness, reservoir physical properties, oil saturation and reservoir pressure, etc. By means of indoor physical modeling and numerical

simulation, development layers, well pattern combination and injection-production parameters are optimized, and complex optimization design well patterns, such as double-square type well pattern and straight-horizontal well combination stereoscopic development pattern, are developed innovatively. The optimization design technology of non-hydrocarbon gas assisted steam flooding is tackled, so as to provide the most economical and effective operation parameters for field test (Hong, 1994; Liu, 1997; Gong et al., 2007). The engineering optimization design technology of mid-deep heavy oil steam flooding reservoir makes the development depth limit of steam flooding increase from 800 m to 1400 m. The technology is used in industrial scale in Well Block Qi40, a typical steam flooding block in the Huanxiling oilfield, which makes the oil recovery rate increase from 1.3% to 2.0%; the oilfield is expected to produce at stable production of more than 0.5  106t for more than 8 years; it is estimated that the recovery rate can reach 60% which is increased by 27.7% (Fig. 20). 4.5.2. Quantitative description technology of residual oil distribution for steam-flooding mid-deep heavy oil reservoir Affected by many factors, such as reservoir geological condition and operation conditions distribution of residual oil is complex, and mature residual oil research methods are few and have obvious limitation (Yu, 1997; Xu et al., 2005). In view of above problems, methods of residual oil distribution by steam flooding are developed, and “five research methods” and “five residual oil models” are proposed. The residual oil distribution is studied by using permeability ratio, fluid production profile analysis method, saturated steam division method, three-parameter method, regional partition method and fine numerical simulation method, etc. It is found that the reservoir physical property, steam override and degree of well pattern perfection are the main factors to affect the residual oil distribution. Five types of residual oil distribution modes are proposed, which are developed at the bottom of thickbedded layer, lower part of interlayer development well section, plane non-sedimentary channel direction, dipping position of inclination well group and incomplete well pattern area. These five types of residual oil distribution modes indicate the direction of adjustment potential, which lay a foundation for the deployment of steam flooding adjustment and deployment. 4.5.3. Tracking and adjustment technology for mid-deep steam flooding In the process of steam flooding of mid-deep buried heavy oil

Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004

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reservoir, the reservoir is increased in the heterogeneity due to due to influence of the depressurization in the early steam huff and puff, and is very difficult to adjust. With the expansion of steam chamber as a core, the adjustment concept of “production deciding injection” is established, and the adjusting technical ideas of “targeted huff and puff in the thermal connectivity stage to promote connectivity, individualized parameter adjustment in the displacement stage to ensure equilibrium, selective injection and production control in the breakthrough stage to adjust direction, and integrated well location deployment in the denudation stage to slow down decline” are proposed. A number of adjustment technologies are studied, including steam soak effect, multi-well fluid production, micro-fracturing, non-hydrocarbon gas assistance, intermittent steam flooding and hot water flooding, etc. And the implementing technical boundary and adjustment index parameter of design is optimized, so as to promote the uniform expansion of steam chamber and increase reserve utilization. Through adjustment in well groups and individual wells, the Well Block Qi40 has the vertical utilization degree of the steam flooding increasing from 72% to 80% and the stable production time increasing from 3 years to 8 years, showing remarkable effect. 4.5.4. Layered steam-injection technology for mid-deep steam flooding In order to improve the vertical sweep efficiency of steam flooding and reduce the steam override and breakthrough along a single layer, and layered steam injection pipe strings of eccentric fishing type and concentric tubular type are designed (Fig. 21). These strings enable layered steam distribution in two-three layers, can work at the temperature of up to 360  C and pressure of up to 17 MPa, and meet the requirement of steam flooding in mid-deep buried heavy oil reservoirs with depth of less than 1600 m. Moreover, these strings have the advantage of simple fishing operation and intelligent ground layered control. Through the application of layered steam injection technology, the vertical utilization degree of steam flooding in Well Block Qi40 is up to 75% and the qualification rate of layered injection can reach 100%. 4.5.5. High-temperature lifting technology for mid-deep steam flooding Because of high injection temperature of mid-deep steam flooding, problems such as high-temperature stuck pump, sandproduction pump stuck, serious corrosion of pump and valve leakage are likely to occur in the production process of steamflooding wells. For this reason, the high temperature lifting technology of high-temperature ceramic pump and high-temperature floating ring pump is developed. By using the ceramic plunger and floating ring with the characteristics of high-temperature resistance, corrosion resistance, high toughness and strong sand carrying capacity, the steam flooding oil pump reaches the temperature resistance of more than 180  C. At present, T44m and T57m all-ceramic pumps have been successfully applied to realize normal lifting at the reservoir temperature of 200  C and pressure of 2e3 MPa, and single well drainage capacity of 50e70 t/d, which meets the design requirement of the steam flooding. Through research and application of 15 key supporting technologies at thermal recovery reservoir, steam huff and puff and steam flooding, the Huanxiling oilfield is developed efficiently, the annual stable heavy oil production of more than 2 million tons for 20 years is realized (Fig. 22) with the recovery factor of 35%. The annual production of the steam flooding reaches 0.50  106 t, and the steam flooding increases oil by 3.65  106 t compared with the steam huff and puff, which provides a strong support for the longterm development of Huanxiling oilfield.

5. Conclusions (1) The Huanxiling oilfield in the western sag of Liaohe Oilfield has abundant oil resources, and it is a typical warped faultblock draped compound trap zone in China. Abundant oil supply, high-porosity and high-permeability reservoirs of Paleogene, good cap rock conditions, and multi-fault composite hydrocarbon transportation system are the basis of the formation of the large oilfields in this area. Since the beginning of exploration, technologies of multi-batch and large-area seismic data merging processing are developed, major breakthroughs in oil and gas reservoir exploration are made in this area, thus, this area is an important target area for hydrocarbon exploration at present and even in the future. (2) During long-distance migration of oil and gas, due to biodegradation, formation water washing and oxidation, a large amount of light components in crude oil are lost, and heavy components are concentrated and accumulated to form heavy oil reservoirs in this area. The heavy oil here is largely common heavy oil and extra heavy oil. (3) In combination with the geological characteristics of heavy oil reservoirs in the Huanxiling oilfield, the steam huff and puff development technology for mid-deep heavy oil reservoirs is developed and perfected, and special technologies such as infill adjustment and combined huff and puff suitable for the characteristics of the regional reservoirs are established, which enable the stable production period of huff and puff to prolong significantly and the recovery factor of huff and puff to reach 32%. (4) Through the research of conversion from steam huff and puff to steam flooding technology, the first demonstration area of steam flooding in mid-deep reservoir is established in China, and a series of steam flooding technologies suitable for the characteristics of mid-deep reservoirs is developed, making the reservoir recovery factor raise to 60%, which provides a technical reference for the development of heavy oil reservoirs in China. Acknowledgements The work was supported by the National Science and Technology Major Project of China (No. 2011ZX05006-005) Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.ptlrs.2020.01.004. References Cai, G.G., Ju, J.C., 2010. An approach to heavy oil accumulation mechanism and indepth exploration in western Liaohe depression. Special Oil Gas Reservoirs 17 (4), 35e38 (in Chinese). Chen, H.Q., Zhao, Y.C., Gao, X.J., Xie, W., Mu, J.D., 2014. High-resolution sequence stratigraphy and its application in the fine-scale stratigraphic correlation of the Yulou reservoir in the west depression of the Liaohe Basin. J. Stratigr. 38 (3), 317e323 (in Chinese). Cheng, J.X., Zhu, L.H., Yang, C.C., 2004. Putting 3D seismic data together based on wavelet transform. Oil Geophys. Prospect. 39 (4), 406e408 (in Chinese). Connan, J., 1984. Biodegradation of crude oils in reservoirs. In: Brooks, J., Welte, D.H. (Eds.), Advances in Petroleum Geochemistry. Academic Press, London, pp. 299e335. Editorial Committee of Petroleum Geology of Liaohe Oilfield (ECPGLO), 1993. Petroleum Geology of China (Volume 3): Liaohe Oilfield. Petroleum Industry Press, Beijing (in Chinese). Feng, Y.L., Lu, W.H., Meng, X.Y., 2009. Eogene sequence stratigraphy and stratigraphic and lithologic reservoirs prediction in Liaohe west depression. Acta Sedimentol. Sin. 27 (1), 57e63 (in Chinese).

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Please cite this article as: Li, X., Accumulation conditions and key exploration & development technologies of heavy oil in Huanxiling oilfield in Liaohe depression, Bohai Bay Basin, Petroleum Research, https://doi.org/10.1016/j.ptlrs.2020.01.004