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Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China
Petroleum xxx (2017) 1e8
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Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China Xuefei Yang a, b, *, Yaping Wang a, b, Xingzhi Wang a, b, Deming Zeng a, b, Longbo Xu a, b, Zisang Huang b a b
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 April 2017 Received in revised form 29 June 2017 Accepted 29 June 2017
With the extended petroleum exploration of the carbonate reservoir in the Longwangmiao Formation, Lower Cambrian in Sichuan basin, looking for a new favorable exploration area is the primary task in current exploration. This paper focusing on the dolomite reservoir in the Longwangmiao Formation in the Northern Sichuan basin, will evaluate the reservoir conditions, including reservoir lithology, reservoir spaces, physical properties and other basic characteristics. Combined with sedimentary environment study and diagenesis analysis, the genetic mechanism of Longwangmiao reservoir in study area will be discussed. It indicates that the reservoir rocks of Longwangmiao Formation in the study area are composed of dolarenite and crystalline dolomite, and the main reservoir spaces are intergranular dissolved pores, intragranular dissolved pores and intercrystalline dissolved pores. However, most of dissolved pores have been filled with bitumen, which lead to the reservoir properties very poor, both the porosity and permeability are worse than that of central Sichuan basin, so the reservoir in the Longwangmiao Formation in the Northern Sichuan basin is low-porosity and low-permeability reservoir. During the Early Cambrian Longwangmiao period, the study was near the old-land, and the energy of sea water was not enough to deposit many grain shoals, which cause the sediments are small with lots of quartz and muds. Moreover, because lacking of large scale karstification in the late diagenesis, there isn't much dissolved pores and vugs develop in the Longwangmiao Formation. Some Intergranular dissolved pores and intercrystalline dissolved pores formed by the early atmosphere water dissolved exist as some reservoir spaces, but most of them have been filled with bitumen, which was residual when the ancient oil reservoir transformed. Above factors cause the Longwangmiao Formation in the Northern Sichuan basin become not a very favorable reservoir in Sichuan basin. Copyright © 2017, Southwest Petroleum University. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Reservoir evaluation Dolomites Longwangmiao Formation Northern Sichuan basin
1. Introduction Carbonate reservoir in the Longwangmiao Formation of the Lower Cambrian is the most important petroleum target in deep
* Corresponding author. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China. E-mail address: [email protected] (X. Yang). Peer review under responsibility of Southwest Petroleum University.
Production and Hosting by Elsevier on behalf of KeAi
carbonate reservoir in the Sichuan basin. As the biggest single marine carbonate gas field in China, Anyue gas field in central Sichuan basin is famous for its thick dolomite reservoirs with high reservoir property and high content of gas [1,2]. Many scholars did lots of researches about the Longwangmiao reservoir in central Sichuan basin, and acquired many results of it. The characteristics of the grain shoals in Longwangmiao Formation [3e8], formation of dissolved pores and vugs [9e11], genesis mechanism of thick dolomite [12e14] and the reservoir characteristics and distribution of favorable reservoir have been researched deeply and been very clear [15e19]. These studies provide advantageous geological data and theoretical basis to the late petroleum exploration of the Longwangmiao Formation in the Sichuan basin.
http://dx.doi.org/10.1016/j.petlm.2017.06.003 2405-6561/Copyright © 2017, Southwest Petroleum University. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. 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 in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003
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With the extended exploration of the Longwangmiao Formation, Lower Cambrian in the Sichuan basin, reservoir characteristics and evaluation of the Longwangmiao Formation in the whole Sichuan basin and peripheral areas obtains more and more attentions. Some researchers did some work in the Southwest of Sichuan basin about the Longwangmiao reservoir, and reveal the characteristics and its main controlling factors of the Longwangmiao Formation [20]. Ren [21e23] studied the reservoir in the Eastern Sichuan basin, and compared the reservoir characteristics to the central basin, and reveal the reasons of the reservoir porosity becoming bad in Eastern basin. Above researches focus on the reservoir characteristics of the Longwangmiao Formation in the Southwest and Eastern Sichuan basin, and it has obtained lots of results. However, there is little research about the reservoir of Longwangmiao Formation in the Northern Sichuan basin. Only a few scholars did some work in the sedimentary face in the study area [24,25], but it is not clear about reservoir lithology, spaces, physical property and its genetic mechanism. This paper will focus on the Longwangmiao reservoir in the Northern Sichuan basin, evaluate its reservoir characteristics and discuss its formation. 2. Geological background The study area is in the Northern Sichuan basin, which is texturally located in North Sichuan Low-flat Belt and partially in Micangshan uplift. It includes Wangcang, Dazhou, Zhenba,
Chengkou and other areas (Fig. 1). During the early Cambrian Longwangmiao Period, Sichuan basin is located in a wide carbonate platform, and stably deposited a thick carbonate. Influenced by sea-level change, Longwangmiao Formation has two depositional cycles, which cause the sediments become coarse up forward [26]. The northern Sichuan basin located in the restricted platform, because it was nearby the old land during that time. The main rocks of the Longwangmiao Formation in the study area are grain dolomite and crystal dolomite with some terrigenous clastic. 3. Methods This paper selected the Longwangmiao Formation in Northern Sichuan basin as research target to describe its reservoir characteristics and discuss the reservoir genesis mechanism. More than 4 wells targeted to the Lower Cambrian Longwangmiao Formation had been drilled with cores in study area and 12 outcrops in Northern Sichuan basin have been observed (Fig. 1). To investigate the reservoir characteristic of Longwangmiao Formation, more than 120 samples of dolomites from wells cores and outcrops have been analyzed in thin section, routine physical property and SEM and cathodoluminescence emission analysis. The samples of thin section, were polished to 0.03 mm thick and been finished in the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University. Meanwhile, the porosity and permeability characteristics of Longwangmiao reservoir were obtained by the routine
Fig. 1. Tectonic location map of the Northern Sichuan basin and the generalized stratigraphy of the Longwangmiao Formation in the study area.
Please cite this article in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003
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physical analysis of 67 samples. The test is finished in the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology. Combined with the sedimentary research of the Longwangmiao Formation, we field observations of Nanjiang and Qiaoting outcrops, we have investigated 8 wells to find out the typical sedimentary signs and research the sedimentary facies of Longwangmiao Formation, especially the depositional environment of the reservoir. To research the main diagenesis of Longwangmiao Formation, about 200 slices of thin sections and cathodoluminescence emission analysis have been studied in order to find out each typical diagenesis sign. Based on above research studies, the relationship between Longwangmiao reservoir and deposition, diagenesis, and tectonism have been discussed. 4. Results 4.1. Petrology The lithology in the Longwangmiao Formation in study area includes limestone, dolomite and some sandstone. The reservoir rocks are dolarenite and crystalline dolomite. 4.1.1. Dolarenite Dolarenite is the main reservoir rock in the study area. It is middle-thin bedded or lenticular, gray to brown, with some pores develop which can be seen directly in the rock, porosity is
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about 3e5% (Fig. 2a). Under the microscope, separation and grinding degree of dolarenite is relatively poor, and contain some arenite quartz. This kind of reservoir rock has some intergranular dissolved pores and intragranular dissolved pores (Fig. 2b), which are the important reservoir spaces. 4.1.2. Crystalline dolomite Crystalline dolomite reservoir is mainly developed in the powder- finely crystalline dolomites in the Longwangmiao Formation in the study area. Dolomite crystals are euhedralsubhedral, with few arenite quartz and muds (Fig. 2c). Intercrystalline pores and dissolved pores are very common in the reservoir, with a porosity of 2e3%. However, lots of intercrystalline pores are filled with bitumen nowadays (Fig. 2d). 4.2. Reservoir spaces The main reservoir spaces in the Longwangmiao Formation are intergranular dissolved pores, intragranular dissolved pores and intercrystalline (dissolved) pores, and some fractures also develop in the study area, but little primary pores exist in the Longwangmiao Formation. 4.2.1. Intergranular dissolved pores Intergranular dissolved pores are mainly developed in the dolarenite and some oolitic dolomite. On the macro, these pores occur as “pinhole” (Fig. 2a), while under the microscope, dissolved phenomena is very obvious. Almost all the sparry rim
Fig. 2. Petrology of reservoir in the Longwangmiao Formation, Lower Cambrian in the Northern Sichuan basin. (a) Grain dolomite, pores develop well as “Pinhole”, Longwangmiao Formation, Zhujiaba. (b) Dolarenite with some dissolved pores, Longwangmiao Formation, Bashan. (c) Finely crystalline dolomite with some intercrystalline pores, Longwangmiao Formation, Well Mashan1, 7309 m. (d) Powder crystalline dolomite with intercrystalline pores, Longwangmiao Formation, Bashan.
Please cite this article in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003
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cementations formed in the first phase during the diagenesis process are residual (Fig. 3a). 4.2.2. Intragranular dissolved pores Some granular dolomite has some intragranular dissolved pores in the Longwangmiao Formation. Grain internal completely dissolved and formed mold hole (Fig. 3b). This kind of
pores occurred not very frequent in the study area. Its genesis may be related to the early atmospheric fresh water leaching effect, it mainly develops in the top of grain shoal, eg, the dolarenite in the top of layer 28. Affected by the recrystallization, granular dolomite transformed to the crystalline dolomite with particle residual structure (Fig. 3c). The intercrystalline pores in the particle
Fig. 3. Reservoir spaces of the Longwangmiao Formation, Lower Cambrian in the study area. (a) Intergranular dissolved pores are filled with bitumen, dolarenite, Longwangmiao Formation, Well Mashen1, 7309 m. (b) Intragranular dissolved pores, Dolarenite, Longwangmiao Formation, Bashan. (c) Intercrystalline pores in the residual oolitic dolomite, most pores have been filled with bitumen, Longwangmiao Formation, Qiaoting. (d) Intercrystalline dissolved pores with irregular boundary because of dissolution, most pores have been filled with bitumen, finely crystalline dolomite, Longwangmiao Formation, Qiaoting (e) A group of fractures develop in the powder crystalline dolomite, Longwangmiao Formation, Shatan. (f) Enlarged picture of (e), the fracture is half filled with some dolostones, Longwangmiao Formation, Shatan.
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develop well, and are very common in the Longwangmiao Formation in study area, but most of these pores are filled with bitumen. 4.2.3. Intercrystalline dissolved pores In addition to the above intercrystalline pores form in the grain dolomite with residual particle structure, more intercrystalline pores are develop in the finely crystalline dolomite in the Longwangmiao Formation. Pores are irregular because of dissolved (Fig. 3d). This kind of pores occurred very frequently, but most of them are now filled with bitumen. 4.2.4. Fractures Fracture develops in the Longwangmiao Formation in study area. From the field observation, several groups of fractures develop very well in the Longwangmiao Formation in study area. Most of them occurred as a group (Fig. 3e), most of them are filled with dolomite or quartz, only a few fractures are half filled with dolomite or non-filled (Fig. 3f).
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Table 1 Porosity of dolomites in the Longwangmiao Formation in different outcrops of the Northern Sichuan basin. Outcrop
Samples amount
Minimum (%)
Maximum (%)
Average (%)
Zhengyuan Shuimo Yangba Bashan Shixihe Shatan
21 5 29 2 1 12
0.40% 1.05% 0.43% 0.96% / 0.23%
6.01% 4.53% 4.91% 8.94% / 2.79%
1.95% 2.54% 1.73% 4.95% 1.08% 0.95%
many dissolved pores develop in 28 layer of Bashan (Figs. 2b and 3b). The reservoir in Bashan might be the most favorable place in the Northern Sichuan basin. Besides, Shuimo located in the Northwest of study area, the reservoir of Longwangmiao Formation also has a relatively high value, with an average of 2.54%. Zhengyuan and Yangba also have some favorable reservoir with a high porosity which can reach 6.01% and 4.91%. However, most samples in these two area have a small porosity, which lead a relatively low average porosity.
4.3. Physical properties To study the petrophysical properties of the dolomite reservoir in the Longwangmiao Formation in the study area, about 67 pieces of samples were tested in porosity and permeability, it shows that the porosity is mainly focused in the area of 2e3%, about 57.1% samples are in this area, and the average values of porosity is 3.19% (Fig. 4), which is lower than that of reservoir in central Sichuan basin with a value of 5.49% in grain dolomite [17]. The permeability has a same phenomenon with a relatively low value, almost 64.5% samples located in the area of 10 5e10 3, and the average permeability of all the dolomite in study area is only 0.05 md. It indicates that physical properties of Longwangmiao reservoir in the Northern Sichuan basin are with low porosity and low permeability, which is worse than that in Central basin. Combined with the research of petrology and reservoir spaces, it can also reveal the poor reservoir property of the Longwangmiao Formation in Northern Sichuan basin is related to lots of residual muds and sands, because muds and sands would prevent the recrystallization and other favorable diagenesis. During the Longwangmiao period in Early Cambrian, the study area was nearby the old-land, many clastic and muds deposited consequently, which lead the Longwangmiao dolomite in study area is not as pure as the dolomite in central basin. In different areas of Northern Sichuan basin, the reservoir porosity of the Longwangmiao Formation is also very different. From Table 1, it can be seen that the porosity has a wide range from different places, the samples from the Bashan have the highest porosity value, the maximum porosity can reach 8.94%, and the average is 4.95%. Combine with outcrop observation,
5. Discussion From the above results, it shows that the reservoir property of the Longwangmiao Formation in the Northern Sichuan basin is not as good as reservoir property of Longwangmiao Formation in the central Sichuan basin. It will be discussed in this paper that the reason why reservoir in study area is not very favorable and the formation different between Longwangmiao reservoir in the northern Sichuan basin and central Sichuan basin. 5.1. Located in unfavorable sedimentary facies During the Longwangmiao Period in early Cambrian, the whole Sichuan basin was located in a wide carbonate platform, and the sea water deepen from the west to the east [27]. The study area was located in a restricted platform which was nearby the old land, and the sea water in the study area was not very deep, while some area can deposit small grain shoals [8,28,29]. In the area of Shatan- Zhujiaba- Fucheng- Bashan, the energy of sea water was heavy enough to deposit some grain shoals. From the thickness map of grain dolomite, it can be seen that the grain dolomite in these area can reach 25 m (Fig. 5a). However, the energy became weak east towards, in the area of well mashen1, the thickness of grain dolomite decreases to 15 m, and few grain shoals deposited. Although the western of the study area was located in an environment with relative high energy of sea water, the sediments rock is not very good for reservoir formation, because lots of quartz and muds deposited. There was an old land
Fig. 4. Petrophysical properties of dolomite in the Longwangmiao Formation, Lower Cambrian in study area.
Please cite this article in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003
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Fig. 5. Thickness map of grain dolomite and the sedimentary facies map in the Longwangmiao Formation in the Northern Sichuan basin (a. Thickness map of grain dolomite; b. Sedimentary facies map) (Modified from Ref. [8]).
Please cite this article in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003
X. Yang et al. / Petroleum xxx (2017) 1e8
locating in the west of the Sichuan basin, and affected by the old land, many clasts can deposit in the study area, especially in the western of research area. From the map of sedimentary facies (Fig. 5b), it indicates that in the western area, the depositional environment was mixed tidal. Combined with the energy of sea water and the old land, it can be seen that in the eastern of study area, the sea water was deep and the energy was not heavy enough to deposit grain carbonate, it is not a favorable facies to the carbonate reservoir; while in the western of study area, the grain shoals deposited with lots of quartz and muds, which will prevent the advantage diagenesis, it is also not very favorable facies. 5.2. Lack of large-scale dissolution The reservoir spaces in the Longwangmiao Formation mainly are intergranular dissolved pores and intercrystalline dissolved pores, and it is lack of large scale dissolved pores and vugs related to the karstification. Combined with the regional tectonic history of the Sichuan basin, during the Caledonian, the central Sichuan basin uplifted and formed a large paleo-uplift named LeshanLongnvsi uplift, and most area have suffered from a long time karstification [2,18]. During the Caledonian karstification, Anyue area in the central Sichuan basin was located in the slope of the karst environment, which cause lots of dissolved pores, vugs and fractures developed. Those large amount of pores are the main reservoir spaces of the Longwangmiao Formation in the Central Sichuan basin. Compared with central Sichuan, Northern Sichuan basin was far from the Leshan-Longnvsi paleo-uplift, and there is no other karstification during the diagenetic process. However, the dissolved pores occurred in the Longwangmiao Formation are all formed in the Syngenetic period, and the sediments dissolved by the atmosphere fresh water very early. 5.3. Filling of bitumen cause lead pores dramatically reduced According to the history of hydrocarbon evolution and accumulation, it indicates that the shale in the Qiongzhusi Formation, Lower Cambrian in the Northern Sichuan basin was the main hydrocarbon source rocks, which began produce petroleum from the Early Silurian [30,31]. During the Late Permian to Early Triassic, it was in the peak of oil generation, and most of oil poured into the rock space of the Cambrian. In this time, the original ancient oil reservoir formed. In the Late Triassic, the oil began transferred, and the original oil reservoir turned into a gas reservoir, during this period, bitumen formed as consequence. These bitumens were residual in the pores, which lead lots of pores blocking [32]. Approximately 80% pores in the Longwangmiao Formation are filled with bitumen in the study area, and there are few effective pores for favorable reservoir nowadays. 6. Conclusion (1) Reservoir rock in the Longwangmiao Formation, Lower Cambrian in the Northern Sichuan basin is composed of dolarenite and crystalline dolomite, and the main reservoir spaces are intergranular dissolved pores, intragranular dissolved pore and intercrystalline pores, with low porosity and low permeability. (2) In the western of the study area, some grain shoal can be deposited in this area due to the relative high sea water energy, but many quartzes clastic and muds can also be deposited because nearby the old land. Eastern towards, the water became deep, which lead that less grain shoals
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deposited in the Eastern of the study area. Thus, the Northern Sichuan basin didn't locate in a favorable sedimentary facies during the Early Cambrian. (3) On the aspect of diagenesis, there was no significant karstification happened in the Longwangmiao Formation in study area, because the study area was far away from the Leshan-Longnvsi paleo-uplift during the Caledonian tectonic movement. Affected by the early atmosphere water dissolved in the Syngenetic period, only a small amount of dissolved pores formed. (4) In the study area, an ancient original oil reservoir had been existed, when the ancient original oil turned into gas, bitumen formed as consequence. These bitumens were residual in the pores, which lead lots of pores blocking nowadays. References [1] J.H. Du, C.N. Zou, C.C. Xu, H.Q. He, P. Shen, Y.M. Yang, Y.L. Lei, G.Q. Wei, Z.C. Wang, Y. Yang, Theoretical and technical innovations in strategic discovery of huge gas fields in Longwangmiao Formation of central Sichuan paleo-uplift, Sichuan Basin, Pet. Explor. Dev. 41 (3) (2014) 1e10 (in Chinese with English abstract). [2] C.C. Xu, P. Shen, Y.M. Yang, B. Luo, J.Z. Huang, X.F. Jiang, J.R. Xie, Y.J. Cen, Accumulation conditions and enrichment patterns of natural gas in th lower Cambrian Longwangmiao Fm reservoirs of the Leshan-Longnüsi Paleohigh, Sichuan Basin, Nat. Gas. Ind. 34 (3) (2014) 1e7 (in Chinese with English abstract). [3] M.D. Jin, X.C. Tan, L. Li, et al., Characteristics and distribution of grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area, Sichuan Basin, JOPC 17 (3) (2015) 347e358 (in Chinese with English abstract). [4] X.F. Yang, X.Z. Wang, H. Tang, et al., Research sedimentary microfacies of the Longwangmiao Formation in moxi area, central Sichuan Basin, Acta Sedimentol. Sin. 33 (5) (2015) 972e982. [5] T. Ma, X.C. Tan, L. Li, et al., Sedimentary characteristics and distribution of grain shoals in the lower cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas, J. Palaeogeogr. 17 (2) (2015) 213e228. [6] J.M. Du, B.M. Zhang, Z.C. Wang, et al., Sedimentary model and reservoir genesis of dual grain banks at the Lower Cambrian Longwangmiao Fm carbonate ramp in the Sichuan Basin, Nat. Gas. Ind. 36 (6) (2016) 1e9. [7] J.M. Song, S.G. Liu, Y.H. Zhao, et al., Characteristics and sedimentary geological significant of Lower-Middle Cambrian tempestites in central Sichuan basin, Acta Pet. Sin. 37 (1) (2016) 13e25. [8] Yao Genshun, Zhou Jingao, Zou Weihong, et al., Characteristics and distribution rule of Lower Cambrian Longwangmiao grain beach in Sichuan Basin, Mar. Orig. Pet. Geol. 22 (3) (2013) 1e7. [9] S.G. Gao, Z.M. Hu, W.G. An, et al., Distribution characteristics of dolomite reservoir pores and caves of Longwangmiao Formaiton gas reservoirs in the Sichuan basin, Nat. Gas. Ind. 34 (3) (2014) 103e109. [10] M.D. Jin, W. Zeng, X.C. Tan, et al., Characteristics and controlling factors of beach-controlled karst reservoirs in Longwangmiao Formation, Moxi-Gaoshiti area, Sichuan Basin, NW China, Pet. Explor. Dev. 41 (6) (2014) 650e660. [11] X.F. Yang, et al., The Early Hercynian paleo-karstification in the block 12 of Tahe oilfield, northern Tarim Basin, China, Carbonates Evaporites (2016), http://dx.doi.org/10.1007/s13146-013-0167-0. [12] X.F. Yang, X.Z. Wang, Y.M. Yang, et al., Diagenesis of the dolomite reservoir in Lower Cambrian Longwangmiao Formation Formation in central Sichuan basin, Geol. Sci. Technol. Inf. 34 (1) (2015) 35e41. [13] Tian Yanhong, Liu Shugen, Zhao Yihua, Song Jinmin, Song Linke, Sun Wei, et al., Diagenesis of Lower Cambrian Longwangmiao Formation reservoirs in central area of Sichuan Basin, China, J. Chengdu Univ. Technol. Sci. Technol. Ed. 41 (6) (2014) 671e683. [14] X.F. Yang, et al., Dolomitization by Penesaline sea water in Early Cambrian Longwangmiao Formation, Central Sichuan basin, China, J. Earth Sci. 28 (2) (2017) 305e314. [15] J.G. Zhou, C.C. Xu, G.S. Yao, G. Yang, J.Y. Zhang, Y. Hao, F. Wang, L.Y. Pan, M.F. Gu, W.Z. Li, Genesis and evolution of lower Cambrian Longwangmiao Formation reservoir, Sichuan Basin, SW China, Pet. Explor. Dev. 42 (2) (2015) 158e166 (in Chinese with English abstract). [16] Liu Shugen, Song Jinmin, Zhao Yihua, Zhong Yong, Song Linke, Tian Yanhong, et al., Controlling factors of formation and distribution of Lower Cambrian Longwangmiao Formation high quality reservoirs in Sichuan Basin, China, J. Chengdu Univ. Technol. Sci. Technol. Ed. 41 (6) (2014) 657e670. [17] X.F. Yang, et al., Reservoir characteristics and main controlling factors of the Longwangmiao Formation in the Moxi area, central Sichuan Basin, China, Arab. J. Geosci. 9 (3) (2016). [18] Y.L. Li, F.R. Wu, D.J. Liu, et al., Distribution rule and exploration prospect of the Longwangmiao Fm reservoirs in the Leshan-Longnüsi Paleouplift, Sichuan Basin, Nat. Gas. Ind. 34 (3) (2014) 61e66 (in Chinese with English abstract).
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Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China Xuefei Yang a, b, *, Yaping Wang a, b, Xingzhi Wang a, b, Deming Zeng a, b, Longbo Xu a, b, Zisang Huang b a b
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 April 2017 Received in revised form 29 June 2017 Accepted 29 June 2017
With the extended petroleum exploration of the carbonate reservoir in the Longwangmiao Formation, Lower Cambrian in Sichuan basin, looking for a new favorable exploration area is the primary task in current exploration. This paper focusing on the dolomite reservoir in the Longwangmiao Formation in the Northern Sichuan basin, will evaluate the reservoir conditions, including reservoir lithology, reservoir spaces, physical properties and other basic characteristics. Combined with sedimentary environment study and diagenesis analysis, the genetic mechanism of Longwangmiao reservoir in study area will be discussed. It indicates that the reservoir rocks of Longwangmiao Formation in the study area are composed of dolarenite and crystalline dolomite, and the main reservoir spaces are intergranular dissolved pores, intragranular dissolved pores and intercrystalline dissolved pores. However, most of dissolved pores have been filled with bitumen, which lead to the reservoir properties very poor, both the porosity and permeability are worse than that of central Sichuan basin, so the reservoir in the Longwangmiao Formation in the Northern Sichuan basin is low-porosity and low-permeability reservoir. During the Early Cambrian Longwangmiao period, the study was near the old-land, and the energy of sea water was not enough to deposit many grain shoals, which cause the sediments are small with lots of quartz and muds. Moreover, because lacking of large scale karstification in the late diagenesis, there isn't much dissolved pores and vugs develop in the Longwangmiao Formation. Some Intergranular dissolved pores and intercrystalline dissolved pores formed by the early atmosphere water dissolved exist as some reservoir spaces, but most of them have been filled with bitumen, which was residual when the ancient oil reservoir transformed. Above factors cause the Longwangmiao Formation in the Northern Sichuan basin become not a very favorable reservoir in Sichuan basin. Copyright © 2017, Southwest Petroleum University. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Reservoir evaluation Dolomites Longwangmiao Formation Northern Sichuan basin
1. Introduction Carbonate reservoir in the Longwangmiao Formation of the Lower Cambrian is the most important petroleum target in deep
* Corresponding author. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China. E-mail address: [email protected] (X. Yang). Peer review under responsibility of Southwest Petroleum University.
Production and Hosting by Elsevier on behalf of KeAi
carbonate reservoir in the Sichuan basin. As the biggest single marine carbonate gas field in China, Anyue gas field in central Sichuan basin is famous for its thick dolomite reservoirs with high reservoir property and high content of gas [1,2]. Many scholars did lots of researches about the Longwangmiao reservoir in central Sichuan basin, and acquired many results of it. The characteristics of the grain shoals in Longwangmiao Formation [3e8], formation of dissolved pores and vugs [9e11], genesis mechanism of thick dolomite [12e14] and the reservoir characteristics and distribution of favorable reservoir have been researched deeply and been very clear [15e19]. These studies provide advantageous geological data and theoretical basis to the late petroleum exploration of the Longwangmiao Formation in the Sichuan basin.
http://dx.doi.org/10.1016/j.petlm.2017.06.003 2405-6561/Copyright © 2017, Southwest Petroleum University. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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With the extended exploration of the Longwangmiao Formation, Lower Cambrian in the Sichuan basin, reservoir characteristics and evaluation of the Longwangmiao Formation in the whole Sichuan basin and peripheral areas obtains more and more attentions. Some researchers did some work in the Southwest of Sichuan basin about the Longwangmiao reservoir, and reveal the characteristics and its main controlling factors of the Longwangmiao Formation [20]. Ren [21e23] studied the reservoir in the Eastern Sichuan basin, and compared the reservoir characteristics to the central basin, and reveal the reasons of the reservoir porosity becoming bad in Eastern basin. Above researches focus on the reservoir characteristics of the Longwangmiao Formation in the Southwest and Eastern Sichuan basin, and it has obtained lots of results. However, there is little research about the reservoir of Longwangmiao Formation in the Northern Sichuan basin. Only a few scholars did some work in the sedimentary face in the study area [24,25], but it is not clear about reservoir lithology, spaces, physical property and its genetic mechanism. This paper will focus on the Longwangmiao reservoir in the Northern Sichuan basin, evaluate its reservoir characteristics and discuss its formation. 2. Geological background The study area is in the Northern Sichuan basin, which is texturally located in North Sichuan Low-flat Belt and partially in Micangshan uplift. It includes Wangcang, Dazhou, Zhenba,
Chengkou and other areas (Fig. 1). During the early Cambrian Longwangmiao Period, Sichuan basin is located in a wide carbonate platform, and stably deposited a thick carbonate. Influenced by sea-level change, Longwangmiao Formation has two depositional cycles, which cause the sediments become coarse up forward [26]. The northern Sichuan basin located in the restricted platform, because it was nearby the old land during that time. The main rocks of the Longwangmiao Formation in the study area are grain dolomite and crystal dolomite with some terrigenous clastic. 3. Methods This paper selected the Longwangmiao Formation in Northern Sichuan basin as research target to describe its reservoir characteristics and discuss the reservoir genesis mechanism. More than 4 wells targeted to the Lower Cambrian Longwangmiao Formation had been drilled with cores in study area and 12 outcrops in Northern Sichuan basin have been observed (Fig. 1). To investigate the reservoir characteristic of Longwangmiao Formation, more than 120 samples of dolomites from wells cores and outcrops have been analyzed in thin section, routine physical property and SEM and cathodoluminescence emission analysis. The samples of thin section, were polished to 0.03 mm thick and been finished in the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University. Meanwhile, the porosity and permeability characteristics of Longwangmiao reservoir were obtained by the routine
Fig. 1. Tectonic location map of the Northern Sichuan basin and the generalized stratigraphy of the Longwangmiao Formation in the study area.
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physical analysis of 67 samples. The test is finished in the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology. Combined with the sedimentary research of the Longwangmiao Formation, we field observations of Nanjiang and Qiaoting outcrops, we have investigated 8 wells to find out the typical sedimentary signs and research the sedimentary facies of Longwangmiao Formation, especially the depositional environment of the reservoir. To research the main diagenesis of Longwangmiao Formation, about 200 slices of thin sections and cathodoluminescence emission analysis have been studied in order to find out each typical diagenesis sign. Based on above research studies, the relationship between Longwangmiao reservoir and deposition, diagenesis, and tectonism have been discussed. 4. Results 4.1. Petrology The lithology in the Longwangmiao Formation in study area includes limestone, dolomite and some sandstone. The reservoir rocks are dolarenite and crystalline dolomite. 4.1.1. Dolarenite Dolarenite is the main reservoir rock in the study area. It is middle-thin bedded or lenticular, gray to brown, with some pores develop which can be seen directly in the rock, porosity is
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about 3e5% (Fig. 2a). Under the microscope, separation and grinding degree of dolarenite is relatively poor, and contain some arenite quartz. This kind of reservoir rock has some intergranular dissolved pores and intragranular dissolved pores (Fig. 2b), which are the important reservoir spaces. 4.1.2. Crystalline dolomite Crystalline dolomite reservoir is mainly developed in the powder- finely crystalline dolomites in the Longwangmiao Formation in the study area. Dolomite crystals are euhedralsubhedral, with few arenite quartz and muds (Fig. 2c). Intercrystalline pores and dissolved pores are very common in the reservoir, with a porosity of 2e3%. However, lots of intercrystalline pores are filled with bitumen nowadays (Fig. 2d). 4.2. Reservoir spaces The main reservoir spaces in the Longwangmiao Formation are intergranular dissolved pores, intragranular dissolved pores and intercrystalline (dissolved) pores, and some fractures also develop in the study area, but little primary pores exist in the Longwangmiao Formation. 4.2.1. Intergranular dissolved pores Intergranular dissolved pores are mainly developed in the dolarenite and some oolitic dolomite. On the macro, these pores occur as “pinhole” (Fig. 2a), while under the microscope, dissolved phenomena is very obvious. Almost all the sparry rim
Fig. 2. Petrology of reservoir in the Longwangmiao Formation, Lower Cambrian in the Northern Sichuan basin. (a) Grain dolomite, pores develop well as “Pinhole”, Longwangmiao Formation, Zhujiaba. (b) Dolarenite with some dissolved pores, Longwangmiao Formation, Bashan. (c) Finely crystalline dolomite with some intercrystalline pores, Longwangmiao Formation, Well Mashan1, 7309 m. (d) Powder crystalline dolomite with intercrystalline pores, Longwangmiao Formation, Bashan.
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cementations formed in the first phase during the diagenesis process are residual (Fig. 3a). 4.2.2. Intragranular dissolved pores Some granular dolomite has some intragranular dissolved pores in the Longwangmiao Formation. Grain internal completely dissolved and formed mold hole (Fig. 3b). This kind of
pores occurred not very frequent in the study area. Its genesis may be related to the early atmospheric fresh water leaching effect, it mainly develops in the top of grain shoal, eg, the dolarenite in the top of layer 28. Affected by the recrystallization, granular dolomite transformed to the crystalline dolomite with particle residual structure (Fig. 3c). The intercrystalline pores in the particle
Fig. 3. Reservoir spaces of the Longwangmiao Formation, Lower Cambrian in the study area. (a) Intergranular dissolved pores are filled with bitumen, dolarenite, Longwangmiao Formation, Well Mashen1, 7309 m. (b) Intragranular dissolved pores, Dolarenite, Longwangmiao Formation, Bashan. (c) Intercrystalline pores in the residual oolitic dolomite, most pores have been filled with bitumen, Longwangmiao Formation, Qiaoting. (d) Intercrystalline dissolved pores with irregular boundary because of dissolution, most pores have been filled with bitumen, finely crystalline dolomite, Longwangmiao Formation, Qiaoting (e) A group of fractures develop in the powder crystalline dolomite, Longwangmiao Formation, Shatan. (f) Enlarged picture of (e), the fracture is half filled with some dolostones, Longwangmiao Formation, Shatan.
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develop well, and are very common in the Longwangmiao Formation in study area, but most of these pores are filled with bitumen. 4.2.3. Intercrystalline dissolved pores In addition to the above intercrystalline pores form in the grain dolomite with residual particle structure, more intercrystalline pores are develop in the finely crystalline dolomite in the Longwangmiao Formation. Pores are irregular because of dissolved (Fig. 3d). This kind of pores occurred very frequently, but most of them are now filled with bitumen. 4.2.4. Fractures Fracture develops in the Longwangmiao Formation in study area. From the field observation, several groups of fractures develop very well in the Longwangmiao Formation in study area. Most of them occurred as a group (Fig. 3e), most of them are filled with dolomite or quartz, only a few fractures are half filled with dolomite or non-filled (Fig. 3f).
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Table 1 Porosity of dolomites in the Longwangmiao Formation in different outcrops of the Northern Sichuan basin. Outcrop
Samples amount
Minimum (%)
Maximum (%)
Average (%)
Zhengyuan Shuimo Yangba Bashan Shixihe Shatan
21 5 29 2 1 12
0.40% 1.05% 0.43% 0.96% / 0.23%
6.01% 4.53% 4.91% 8.94% / 2.79%
1.95% 2.54% 1.73% 4.95% 1.08% 0.95%
many dissolved pores develop in 28 layer of Bashan (Figs. 2b and 3b). The reservoir in Bashan might be the most favorable place in the Northern Sichuan basin. Besides, Shuimo located in the Northwest of study area, the reservoir of Longwangmiao Formation also has a relatively high value, with an average of 2.54%. Zhengyuan and Yangba also have some favorable reservoir with a high porosity which can reach 6.01% and 4.91%. However, most samples in these two area have a small porosity, which lead a relatively low average porosity.
4.3. Physical properties To study the petrophysical properties of the dolomite reservoir in the Longwangmiao Formation in the study area, about 67 pieces of samples were tested in porosity and permeability, it shows that the porosity is mainly focused in the area of 2e3%, about 57.1% samples are in this area, and the average values of porosity is 3.19% (Fig. 4), which is lower than that of reservoir in central Sichuan basin with a value of 5.49% in grain dolomite [17]. The permeability has a same phenomenon with a relatively low value, almost 64.5% samples located in the area of 10 5e10 3, and the average permeability of all the dolomite in study area is only 0.05 md. It indicates that physical properties of Longwangmiao reservoir in the Northern Sichuan basin are with low porosity and low permeability, which is worse than that in Central basin. Combined with the research of petrology and reservoir spaces, it can also reveal the poor reservoir property of the Longwangmiao Formation in Northern Sichuan basin is related to lots of residual muds and sands, because muds and sands would prevent the recrystallization and other favorable diagenesis. During the Longwangmiao period in Early Cambrian, the study area was nearby the old-land, many clastic and muds deposited consequently, which lead the Longwangmiao dolomite in study area is not as pure as the dolomite in central basin. In different areas of Northern Sichuan basin, the reservoir porosity of the Longwangmiao Formation is also very different. From Table 1, it can be seen that the porosity has a wide range from different places, the samples from the Bashan have the highest porosity value, the maximum porosity can reach 8.94%, and the average is 4.95%. Combine with outcrop observation,
5. Discussion From the above results, it shows that the reservoir property of the Longwangmiao Formation in the Northern Sichuan basin is not as good as reservoir property of Longwangmiao Formation in the central Sichuan basin. It will be discussed in this paper that the reason why reservoir in study area is not very favorable and the formation different between Longwangmiao reservoir in the northern Sichuan basin and central Sichuan basin. 5.1. Located in unfavorable sedimentary facies During the Longwangmiao Period in early Cambrian, the whole Sichuan basin was located in a wide carbonate platform, and the sea water deepen from the west to the east [27]. The study area was located in a restricted platform which was nearby the old land, and the sea water in the study area was not very deep, while some area can deposit small grain shoals [8,28,29]. In the area of Shatan- Zhujiaba- Fucheng- Bashan, the energy of sea water was heavy enough to deposit some grain shoals. From the thickness map of grain dolomite, it can be seen that the grain dolomite in these area can reach 25 m (Fig. 5a). However, the energy became weak east towards, in the area of well mashen1, the thickness of grain dolomite decreases to 15 m, and few grain shoals deposited. Although the western of the study area was located in an environment with relative high energy of sea water, the sediments rock is not very good for reservoir formation, because lots of quartz and muds deposited. There was an old land
Fig. 4. Petrophysical properties of dolomite in the Longwangmiao Formation, Lower Cambrian in study area.
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Fig. 5. Thickness map of grain dolomite and the sedimentary facies map in the Longwangmiao Formation in the Northern Sichuan basin (a. Thickness map of grain dolomite; b. Sedimentary facies map) (Modified from Ref. [8]).
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locating in the west of the Sichuan basin, and affected by the old land, many clasts can deposit in the study area, especially in the western of research area. From the map of sedimentary facies (Fig. 5b), it indicates that in the western area, the depositional environment was mixed tidal. Combined with the energy of sea water and the old land, it can be seen that in the eastern of study area, the sea water was deep and the energy was not heavy enough to deposit grain carbonate, it is not a favorable facies to the carbonate reservoir; while in the western of study area, the grain shoals deposited with lots of quartz and muds, which will prevent the advantage diagenesis, it is also not very favorable facies. 5.2. Lack of large-scale dissolution The reservoir spaces in the Longwangmiao Formation mainly are intergranular dissolved pores and intercrystalline dissolved pores, and it is lack of large scale dissolved pores and vugs related to the karstification. Combined with the regional tectonic history of the Sichuan basin, during the Caledonian, the central Sichuan basin uplifted and formed a large paleo-uplift named LeshanLongnvsi uplift, and most area have suffered from a long time karstification [2,18]. During the Caledonian karstification, Anyue area in the central Sichuan basin was located in the slope of the karst environment, which cause lots of dissolved pores, vugs and fractures developed. Those large amount of pores are the main reservoir spaces of the Longwangmiao Formation in the Central Sichuan basin. Compared with central Sichuan, Northern Sichuan basin was far from the Leshan-Longnvsi paleo-uplift, and there is no other karstification during the diagenetic process. However, the dissolved pores occurred in the Longwangmiao Formation are all formed in the Syngenetic period, and the sediments dissolved by the atmosphere fresh water very early. 5.3. Filling of bitumen cause lead pores dramatically reduced According to the history of hydrocarbon evolution and accumulation, it indicates that the shale in the Qiongzhusi Formation, Lower Cambrian in the Northern Sichuan basin was the main hydrocarbon source rocks, which began produce petroleum from the Early Silurian [30,31]. During the Late Permian to Early Triassic, it was in the peak of oil generation, and most of oil poured into the rock space of the Cambrian. In this time, the original ancient oil reservoir formed. In the Late Triassic, the oil began transferred, and the original oil reservoir turned into a gas reservoir, during this period, bitumen formed as consequence. These bitumens were residual in the pores, which lead lots of pores blocking [32]. Approximately 80% pores in the Longwangmiao Formation are filled with bitumen in the study area, and there are few effective pores for favorable reservoir nowadays. 6. Conclusion (1) Reservoir rock in the Longwangmiao Formation, Lower Cambrian in the Northern Sichuan basin is composed of dolarenite and crystalline dolomite, and the main reservoir spaces are intergranular dissolved pores, intragranular dissolved pore and intercrystalline pores, with low porosity and low permeability. (2) In the western of the study area, some grain shoal can be deposited in this area due to the relative high sea water energy, but many quartzes clastic and muds can also be deposited because nearby the old land. Eastern towards, the water became deep, which lead that less grain shoals
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deposited in the Eastern of the study area. Thus, the Northern Sichuan basin didn't locate in a favorable sedimentary facies during the Early Cambrian. (3) On the aspect of diagenesis, there was no significant karstification happened in the Longwangmiao Formation in study area, because the study area was far away from the Leshan-Longnvsi paleo-uplift during the Caledonian tectonic movement. Affected by the early atmosphere water dissolved in the Syngenetic period, only a small amount of dissolved pores formed. (4) In the study area, an ancient original oil reservoir had been existed, when the ancient original oil turned into gas, bitumen formed as consequence. These bitumens were residual in the pores, which lead lots of pores blocking nowadays. References [1] J.H. Du, C.N. Zou, C.C. Xu, H.Q. He, P. Shen, Y.M. Yang, Y.L. Lei, G.Q. Wei, Z.C. Wang, Y. Yang, Theoretical and technical innovations in strategic discovery of huge gas fields in Longwangmiao Formation of central Sichuan paleo-uplift, Sichuan Basin, Pet. Explor. Dev. 41 (3) (2014) 1e10 (in Chinese with English abstract). [2] C.C. Xu, P. Shen, Y.M. Yang, B. Luo, J.Z. Huang, X.F. Jiang, J.R. Xie, Y.J. Cen, Accumulation conditions and enrichment patterns of natural gas in th lower Cambrian Longwangmiao Fm reservoirs of the Leshan-Longnüsi Paleohigh, Sichuan Basin, Nat. Gas. Ind. 34 (3) (2014) 1e7 (in Chinese with English abstract). [3] M.D. Jin, X.C. Tan, L. Li, et al., Characteristics and distribution of grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area, Sichuan Basin, JOPC 17 (3) (2015) 347e358 (in Chinese with English abstract). [4] X.F. Yang, X.Z. Wang, H. Tang, et al., Research sedimentary microfacies of the Longwangmiao Formation in moxi area, central Sichuan Basin, Acta Sedimentol. Sin. 33 (5) (2015) 972e982. [5] T. Ma, X.C. Tan, L. Li, et al., Sedimentary characteristics and distribution of grain shoals in the lower cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas, J. Palaeogeogr. 17 (2) (2015) 213e228. [6] J.M. Du, B.M. Zhang, Z.C. Wang, et al., Sedimentary model and reservoir genesis of dual grain banks at the Lower Cambrian Longwangmiao Fm carbonate ramp in the Sichuan Basin, Nat. Gas. Ind. 36 (6) (2016) 1e9. [7] J.M. Song, S.G. Liu, Y.H. Zhao, et al., Characteristics and sedimentary geological significant of Lower-Middle Cambrian tempestites in central Sichuan basin, Acta Pet. Sin. 37 (1) (2016) 13e25. [8] Yao Genshun, Zhou Jingao, Zou Weihong, et al., Characteristics and distribution rule of Lower Cambrian Longwangmiao grain beach in Sichuan Basin, Mar. Orig. Pet. Geol. 22 (3) (2013) 1e7. [9] S.G. Gao, Z.M. Hu, W.G. An, et al., Distribution characteristics of dolomite reservoir pores and caves of Longwangmiao Formaiton gas reservoirs in the Sichuan basin, Nat. Gas. Ind. 34 (3) (2014) 103e109. [10] M.D. Jin, W. Zeng, X.C. Tan, et al., Characteristics and controlling factors of beach-controlled karst reservoirs in Longwangmiao Formation, Moxi-Gaoshiti area, Sichuan Basin, NW China, Pet. Explor. Dev. 41 (6) (2014) 650e660. [11] X.F. Yang, et al., The Early Hercynian paleo-karstification in the block 12 of Tahe oilfield, northern Tarim Basin, China, Carbonates Evaporites (2016), http://dx.doi.org/10.1007/s13146-013-0167-0. [12] X.F. Yang, X.Z. Wang, Y.M. Yang, et al., Diagenesis of the dolomite reservoir in Lower Cambrian Longwangmiao Formation Formation in central Sichuan basin, Geol. Sci. Technol. Inf. 34 (1) (2015) 35e41. [13] Tian Yanhong, Liu Shugen, Zhao Yihua, Song Jinmin, Song Linke, Sun Wei, et al., Diagenesis of Lower Cambrian Longwangmiao Formation reservoirs in central area of Sichuan Basin, China, J. Chengdu Univ. Technol. Sci. Technol. Ed. 41 (6) (2014) 671e683. [14] X.F. Yang, et al., Dolomitization by Penesaline sea water in Early Cambrian Longwangmiao Formation, Central Sichuan basin, China, J. Earth Sci. 28 (2) (2017) 305e314. [15] J.G. Zhou, C.C. Xu, G.S. Yao, G. Yang, J.Y. Zhang, Y. Hao, F. Wang, L.Y. Pan, M.F. Gu, W.Z. Li, Genesis and evolution of lower Cambrian Longwangmiao Formation reservoir, Sichuan Basin, SW China, Pet. Explor. Dev. 42 (2) (2015) 158e166 (in Chinese with English abstract). [16] Liu Shugen, Song Jinmin, Zhao Yihua, Zhong Yong, Song Linke, Tian Yanhong, et al., Controlling factors of formation and distribution of Lower Cambrian Longwangmiao Formation high quality reservoirs in Sichuan Basin, China, J. Chengdu Univ. Technol. Sci. Technol. Ed. 41 (6) (2014) 657e670. [17] X.F. Yang, et al., Reservoir characteristics and main controlling factors of the Longwangmiao Formation in the Moxi area, central Sichuan Basin, China, Arab. J. Geosci. 9 (3) (2016). [18] Y.L. Li, F.R. Wu, D.J. Liu, et al., Distribution rule and exploration prospect of the Longwangmiao Fm reservoirs in the Leshan-Longnüsi Paleouplift, Sichuan Basin, Nat. Gas. Ind. 34 (3) (2014) 61e66 (in Chinese with English abstract).
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Please cite this article in press as: X. Yang, et al., Evaluation of dolomite reservoirs in the Longwangmiao Formation, Lower Cambrian in Northern Sichuan basin, China, Petroleum (2017), http://dx.doi.org/10.1016/j.petlm.2017.06.003