Mechanisms for the accumulation of deep gas in the southern Songliao Basin, China

Journal of Petroleum Science and Engineering 182 (2019) 106302

Contents lists available at ScienceDirect

Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol

Mechanisms for the accumulation of deep gas in the southern Songliao Basin, China

T

Yunliang Yu, Wenqing Niu*, Guang Yang, Mingxuan Niu, Shanshan Ma, Liya Tian College of Earth Sciences, Jilin University, Changchun 130061, China

A R T I C LE I N FO

A B S T R A C T

Keywords: CO2 CH4 Natural gas reservoir Volcanic rock Diffusion coefficient Songliao basin

The Lower Cretaceous Yingcheng Formation in the southern Songliao Basin contains inorganic CO2, hydrocarbon, and mixed-gas reservoirs and is overlain by Denglouku Formation sandstone hosting secondary hydrocarbon gas reservoirs. We measured the diffusion coefficients of CH4 and CO2 in volcanic rock samples collected from five wells in the Yingcheng Formation. Our results show that the diffusion coefficient of CH4 is greater than that of CO2. Following the accumulation of hydrocarbon gas in the Yingcheng Formation, the region was affected by movement along deep-seated faults, resulting in the upward migration of mantle-derived inorganic CO2 into hydrocarbon gas reservoirs in volcanic rocks of the Yingcheng Formation, displacing preexisting hydrocarbon gas. The hydrocarbon gas was transported upward into Denglouku Formation sandstone (which has favorable physical properties for gas storage) and was then enriched to form secondary gas reservoirs.

1. Introduction

magmatism, the presence of deep, large-scale faults, and late-stage fault re-activation (Sun et al., 2016). Large-scale basement faults and diapirs connected to form channels that facilitated the degassing and migration of mantle-derived CO2 (Yang et al., 2010). Previous exploration has shown that, under suitable conditions, volcanic rocks, in combination with a hydrocarbon source, cap, and trap (Zhao et al., 2008), can be excellent oil and gas reservoirs (Lv et al., 2003; Jia et al., 2007). Recently, volcanic rocks have become a favorable target for natural gas exploration (Feng, 2008). At present, high pure inorganic CO2 gas reservoirs, hydrocarbon gas reservoirs and mixed-gas reservoirs have been identified at depth within the Yingcheng Formation and are associated with deep-seated fault zones. In particular, high pure CO2 gas reservoirs have been found successively in the volcanic rock reservoirs of CS2 well, CS 4 well, CS 6 well and CS7 well, with inorganic CO2 content up to 98% (Lu et al., 2011). In the Denglouku Formation, we found high-purity hydrocarbon gas reservoirs, but through the evaluation of source rocks, it was found that the Denglouku Formation source rocks did not have hydrocarbon generation potential. CH4 carbon isotope analysis confirmed the homology of CH4 in the Yingcheng Formation and the Denglouku Formation, in order to interpret the mechanism of hydrocarbon gas diffused from the Yingcheng Formation to form the secondary gas reservoir in Denglouku Formation, the volcanic rock samples of the Yingcheng Formation from nine wells in the Changling fault depression,

As the earliest large-scale oil-bearing basin discovered in China, Songliao Basin has played a huge role in the development of China's petroleum industry (Fig. 1A), the Changling fault depression, the Dehui fault depression and the Wangfu fault depression in the southern Songliao Basin (Fig. 1B) are prolific hydrocarbon-bearing areas (Dong et al., 2015). The distribution of hydrocarbon gas reservoirs in the southern Songliao Basin is controlled by the distribution of source rocks and the development of faults. The formation of hydrocarbon reservoirs in the lower Cretaceous Yingcheng Formation was controlled predominantly by the distribution of source rocks in the Shahezi and Yingcheng formations (Dai, 2017; He et al., 2019; Cai et al., 2019). In the upper Denglouku Formation, hydrocarbon reservoirs were generated owing to the formation of traps that connected gas sources, as well as the presence of fractures that acted as migration channels for natural gas, resulting in the formation of secondary gas reservoirs. In the southern Songliao Basin, inorganic, mantle-derived CO2 gas reservoirs occur mainly within the Yingcheng Formation and sections III–IV of the Quantou Formation (K1q3−4). This phenomenon has resulted in a great deal of interest in the genesis of CO2 and the reservoir formation process in the Songliao Basin (Qu et al., 2016; Dai, 1996; Rui et al., 2018a, b). The tectonic setting determined the distribution of CO2 reservoirs in the region, and their formation was controlled by intermediate–mafic

*

Corresponding author. E-mail address: [email protected] (W. Niu).

https://doi.org/10.1016/j.petrol.2019.106302 Received 22 February 2019; Received in revised form 21 June 2019; Accepted 22 July 2019 Available online 23 July 2019 0920-4105/ © 2019 Elsevier B.V. All rights reserved.

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Fig. 1. Distribution map of fault depression in the study area.

There are 14 fault basins in the southern part of the Songliao Basin, of which the Changling fault depression is the largest area in the southern Songliao Basin. Due to the weak tectonic movement, good preservation conditions and large burial depth, the fault has most abundant natural gas resources in the southern Songliao Basin; The Dehui fault depression and the Wangfu fault depression are located in the fault zone of eastern part of the southern Songliao Basin. Although compared with Changling fault depression, the later tectonic movement is relatively strong, the amount of denudation is relatively large, and the buried depth is relatively shallow, but they are still abundant in oil and nature gas in the basin (Wang et al., 2018; Yang et al., 2017a; Li et al., 2011).

Dehui fault depression and Wangfu fault depression (Fig. 1C) in the southern Songliao Basin were collected for rock identification and reservoir physical property determination. The diffusion coefficients for CH4 and CO2 were measured in samples of Yingcheng Formation from five wells of the southern Songliao basin. We use gas isotope data and inferences on the coupling and timing of hydrocarbon gas and CO2 accumulation to show that early hydrocarbon gas was displaced by CO2 in the Yingcheng Formation reservoirs. Our data are used to constrain the mechanism for the formation of deep natural gas in the southern Songliao Basin, improve understanding of the distribution of the two gas types, and inform future exploration in the region. 2. Geological setting

3. Materials and methods

The Songliao Basin is a large Mesozoic and Cenozoic continental petroliferous sedimentary basin in eastern China (Fig. 1A), the basin has a double structure of fault-sag (Li et al., 2012; Sorokin et al., 2013; Zhao et al., 2016). According to the stress characteristics and genetic mechanism, the basin formation and evolution process can be divided into three stages, namely the early fault depression period (J3-K1), the middle and late depression period (K1-K2) and the later compressive fold period. (K2-Q) (Feng et al., 2010; Wang et al., 2015). During the fault depression of the Songliao Basin, the sedimentary strata (Fig. 2) from the old to the new were the Upper Jurassic Huoshiling Formation (J3hs), the Lower Cretaceous Shahezi Formation (K1sh), the Yingcheng Formation (K1yc), the Denglouku Formation (K1d), and the Quantou Formation I-II (K1q1−2); In the depression period, the sedimentary strata from the old to the new are the Lower Cretaceous Quantou Formation III-IV (K1q3−4), the Upper Cretaceous Qingshankou Formation (K2qn), the Yaojia Formation (K2y), and the Nenjiang Formation (K2n) (Wang et al., 2011; Cao et al., 2016, 2018). The Mesozoic volcanic rocks are widely developed in the Songliao Basin, which constitutes the main body of the strata during the fault period and is also the main reservoirs of the deep nature gas (Zou et al., 2006; Zhao et al., 2011; Meng et al., 2016).

3.1. Samples In this contribution, the 9 volcanic rock samples of the Yingcheng Formation from nine wells in the Changling fault depression, Dehui fault depression and Wangfu fault depression in the southern Songliao Basin were collected for reservoir physical property and diffusion coefficients determination. 3.2. Rock property determination In this contribution, the reservoir physical property determination includes: density determination, porosity determination, permeability measurement, specific surface area determination, casting thin-sections identification, and pore-fissure characteristics image analysis of the casting thin-section. Porosity and permeability were measured by Model 9310 Automatic Mercury injection apparatus, and the specific surface area was measured by ASAP2020 specific surface area measuring instrument (low temperature nitrogen adsorption instrument). The working pressure of the 9310 Automatic Mercury injection apparatus is 2

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Fig. 2. Stratigraphic column in the southern of Songliao Basin (modified from Xi et al., 2015).

0.0035–206.843 MPa, the resolution is 0.1 mm3, and the pore volume and pore diameter that over 7.2 nm can be measured. The ASAP2020 specific surface area measuring instrument follows the SY6145-1995 standard, the detection method is a static nitrogen adsorption capacity method, and the measurement range of pore diameter is 1.7–300 nm. The casting thin-sections were identified by ZEISS polarizing microscope, and the pore-fissure characteristics of the casting thin-sections were analyzed by the digital instrument CIASS-2000 color image analysis system, which developed by the Institute of Image Information of Sichuan University. Firstly, the colored liquid glue is injected into the pore space of the rock under vacuum pressure, and then grind it into a rock flake after the liquid glue is solidified. Finally, the size, distribution and geometry of pores, the length and width of fissures, number and width of the throats were analyzed by CIAS-2000 color image analysis system, the pore-fissure structure characteristic data of the samples is obtained.

3.3. Diffusion coefficient determination To investigate the displacement and replacement of hydrocarbons by mantle-derived inorganic CO2, the diffusion coefficients for CH4 and CO2 were measured in samples from five wells at the Langfang Branch of the China Petroleum Exploration and Development Research Institute, Langfang City, Hebei Province, China. Diffusion coefficient determination process: A 2.5 cm × 2.5 cm column was drilled from the sample and dried in an oven at 80 °C. The sample was placed into an empty conical flask, held under vacuum for more than 6 h, and then placed in a holder. A pump was used to set the confining pressure to 15 MPa, and the core holder, two diffusion chambers, and the pipeline were evacuated. Two diffusion chamber intake valves were then opened, allowing CH4 and N2 gas to flow. The dry samples were measured at room temperature and pressure. The two diffusion chambers were set to a confining pressure of 5 MPa for CH4 and N2 gas sources. Methane and nitrogen concentrations were measured using a gas chromatograph at intervals of 0.5–2.0 h. At the end of this procedure,

3

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

we calculated the diffusion coefficients of CH4 and CO2. 4. Results 4.1. Source rock evaluation The Songliao Basin is a typical continental petroleum-bearing basin. The main source rocks for Lower Cretaceous reservoirs in the southern Songliao Basin are lacustrine mudstones and coal seams in the Huoshiling, Shahezi, and Yingcheng formations. The source rocks are widespread, stratigraphically thick, and contain abundant organic matter (Zhang, 2006). These source rocks are therefore classified as moderate to good-quality source rocks and are regarded as being capable of producing large volumes of natural gas (Zhang et al., 2006a,b). Most of the source rocks are highly mature, with others being classified as mature and over-mature (Ge et al., 2012). Source rock evaluation criteria that suitable for China's continental petroleum-bearing basins was proposed (Huang et al., 1984). In 1995, based on the results of Huang, China National Petroleum Corporation issued an industry standard for the evaluation of source rocks deposited in freshwater–brackish lacustrine settings. This standard was used to evaluate the abundance of organic matter in source rocks in the study area, with Table 1 reporting the results of the evaluation.

Fig. 3. The relationship between IH and Tmax.

4.1.1. Source rocks of the Denglouku Formation Drilling indicates that source rocks are rare within the Denglouku Formation and have a thickness of < 50 m. These rocks contain little organic matter (determined through measurements of organic carbon, chloroform asphalt “A”, and hydrocarbon generation potential) (Table 1). Excluding wells TS1 and LS14, the six Denglouku Formation samples yield TOC values of 0.04%–0.21% and S1 + S2 values of 0.09–0.22 mg/g, indicating that they represent poor source rocks. Li (2009) combined evaluation method of organic petrology and organic geochemistry to classify the kerogen types of the source rocks of the Changling fault depression. In the Denglouku Formation, the degradation potential of the four wells (YS101, YS102, YN1, and DB11) were all below 10, which was judged to be type III kerogen. The 3 of 4 samples from the YS1 well had a degradation potential of less than 10 and were type III kerogen. Comprehensive determination of organic matter abundance and organic matter type of hydrocarbon source rocks, the Denglouku Formation mudstones lack the potential for hydrocarbon generation, and therefore hydrocarbon reservoirs in the Denglouku

Formation are classified as secondary gas reservoirs.

4.1.2. Source rocks of the Yingcheng and Shahezi formations Three source-rock units occur in the Huoshiling, Shahezi, and Yingcheng formations, which underlie the Denglouku Formation. The primary source rocks are dark-gray limnetic mudstones and coalbearing deposits of the Shahezi Formation, which are widespread and stratigraphically thick (Xiao et al., 2009). These source rocks locally exceed 400 m in thickness and represent the most significant source rocks in the southern Songliao Basin. One source-rock sample from the Shahezi Formation yields a TOC value of 4.63% and a S1 + S2 value of 1.26 mg/g. Nine samples from the Yingcheng Formation yield TOC values of 0.97%–2.53% and S1 + S2 values of 0.29–4.87 mg/g (Table 1). IH and Tmax diagrams (Fig. 3) are available to distinguish the type of kerogen, the kerogen type of Yingcheng Formation is ⅡB—Ⅲ, which indicate the Yingcheng Formation is the well source rock for natural gas

Table 1 The abundance of organic material in samples from the Changling fault depression. TOC: Total organic carbon content; “A”: The content of chloroform asphalt “A”; “Cp”: The organic carbon that represents oil and gas in the rock is the total pyrolysis hydrocarbon in the rock × the percentage of carbon in the hydrocarbon; IH: Represents the amount of milligrams of pyrolysis hydrocarbon produced per gram of organic carbon pyrolysis; “D”: The percentage of available carbon that is degradable in source rocks is the total organic carbon; Tmax: The highest cracking temperature of the kerogen, which reflects the maturity of the kerogen. No

Well

1 2 3 4 5 6 7 8 9

F10 F12 CS2 CS12 CS5 CS8 TS1 TS5 TS6

10 11

TS8 LS1

12 13

LS14 XS1

Formation

K1d K1yc K1d K1yc K1yc K1yc K1d K1yc K1yc K1sh K1yc K1d K1yc K1d K1d K1yc

Sample number

8 2 2 2 2 2 1 1 3 3 1 1 3 1 2 3

TOC

“A”

Cp

Pg（S1+S2）

IH

D

Tmax

（%）

（%）

（%）

(mg.g−1)

(mg.g−1)

(%)

（°C）

0.43 2.01 0.44 0.97 1.25 1.37 2.62 1.24 1.14 4.63 1.48 0.27 1.14 1.13 0.21 2.53

– 0.1226 – 0.0452 0.3946 0.4471 – 0.0877 – – 0.2811 – 0.0512 0.0065 – –

– 0.13 0.02 0.06 0.34 0.41 – 0.09 – – 0.3 – 0.02 – – –

0.09 1.57 0.21 0.66 4.09 4.87 2.82 1.08 0.71 1.26 3.59 0.22 1.04 0.21 0.21 0.29

15.44 48

1.78 7

480

39 50 55.5

5.5 25.5 22.5

48

7

15～28 157

1.3～2.5 20

55

6.5

4

486 414.5 334.5 456 469 481.67 520 445 487 455.5 470.5 495

Organic type

III IIB III III III III IIB III

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Intragranular dissolution pores occur in some plagioclase grains. Quartz grains are granular and locally altered. Volcanic rocks from well CS105 are porphyritic dacites (Fig. 4e), which contain block structures. The phenocrysts (25%) comprise mainly plagioclase and quartz with minor biotite. Plagioclase phenocrysts are dominantly long, columnar, commonly corroded or fragmented, and locally sericitized. The matrix comprises felsic minerals and minor cryptocrystallites. Volcanic rocks from well DS9 are porphyritic andesites (Fig. 4f). Phenocrysts (15%) comprise mainly plagioclase and minor amphibole and quartz. Plagioclase grains are predominantly angular and are locally sericitized. Quartz grains are subangular–subrounded. Hornblende grains are long and columnar and locally display dark colors. The matrix (~85%) comprises partially oriented plagioclase grains and volcanic glass.

generation in the Changling fault depression. Since we can't get any data for IH and Tmax in Shahezi Formation and Denglouku Formation, the kerogen type of the two formations cannot be divided here. The experimental data (Table 1) show that the main source rocks of the Yingcheng Formation and the Shahezi Formation are very low in IH, which distributed between 15 and 157 mg/g, only one is greater than 120 mg/g, the kerogen type is Ⅲ type. The degradation potential (D) and pyrolysis hydrocarbon potential (Pg) data only have individual data points in the IIB type region, which can be concluded that the kerogen type of gas source rocks in the Yingcheng Formation and the Shahezi Formation are mainly type III and contain a small amount of type IIB. Samples from the Yingcheng and Shahezi formations yield vitrinite reflectance Ro values of 1.32%–1.93% and 1.53%–2.14%, respectively. Hydrocarbon generation in the source rocks began during the sedimentary period of K2qn-K2y. The source rocks are over-mature and supplied hydrocarbon gas to the Songliao Basin reservoirs during the fault-depression phase (Ge et al., 2012). In general, our data indicate that the Yingcheng and Shahezi formations contain abundant organic matter and have a high gas-generating capacity, which are good source rocks.

4.2.2. Physical properties The reservoir performance of volcanic rocks is controlled mainly by lithology/lithofacies, diagenesis, and tectonism. The development and type of primary pores are controlled by lithology/lithofacies. During diagenesis, primary pores and fractures may be preserved or destroyed, and secondary pores are generated. Fractures generated via tectonic stress connect pores, which is a key factor in the formation of effective volcanic reservoirs (Zhang et al., 2010). Volcanic gas reservoirs of the Lower Cretaceous Yingcheng Formation in the Songliao Basin are complex and heterogeneous. The measured physical properties of the nine samples from the Yingcheng Formation are reported in Table 2. Both the porosity and permeability of the 5 Yingcheng Formation volcanic rock samples that tested for diffusion coefficient are weakly positively correlated with specific surface area (Fig. 5). Porosity varies widely, from 2.3% to 29.3%, but the values are clustered within the range of 6.3%–13.6%. A wide range of permeability values was also measured, from 0.0035 to 9.25 mD (excluding well DS7, which yielded an anomalous permeability of 322 mD). Most samples (9 out of 12 determinations) yield permeabilities of < 0.1 mD. According to the volcanic reservoir description method (SY/T5830-1993), the analyzed samples represent typical high–medium-porosity, low–extra-low-permeability reservoirs. Pore-throat analysis has been widely applied in pore and permeability studies (Ma et al., 2017), and detailed classification criteria exist for pore throats in volcanic rocks. Of the nine investigated samples, samples in DS7, CS1-1, and CS3 contain pore throats (Fig. 6). There are 14 throats measured from the dacite samples of DS7 well, the number of throats is relatively large, with a wide throat radius (< 0.25–12.5 μm), and the throats with a width greater than 7.5 μm accounting for 50% of the total; The rhyolite samples of CS1-1 well measured 3 throats, the number of throats is small, all the throats radii are ≤7.5 μm, the width are narrow; Only 1 throat measured in the dacite samples of CS3 well, the throats radius is 0.25 μm, the number of throats is very small, and the width is extremely narrow. The reservoir pore space of volcanic rocks in the study area can be divided into primary pores, secondary pores and fissures. The microscopic pore-fissure characteristics in the casting thin-sections of the collected volcanic rock samples were analyzed, and the results show that the porosity and fissure development degrees of the samples with different lithology are significantly different. The micropores of the volcanic ash matrix in the tuff samples were developed, and the fissures in the volcanic lava samples were relatively developed, also intergranular micropores showed in the samples. The rhyolite sample of CS1-1 well (Fig. 7a) developed a large number of intercrystalline micropores, which were seriously altered by carbonation in the later stage; the rhyolitic crystal tuff sample of CS1-2 well (Fig. 7b) developed volcanic ash matrix micropores and intragranular dissolution pores (feldspar dissolved pores); the tuff sample of CS103 well (Fig. 7c) developed volcanic ash matrix micropores; the dacites samples of CS105 well (Fig. 7d) and DS7 well (Fig. 7 e), andesite sample of DS9 well (Fig. 7f) are volcanic lava, the rocks are dense, no intercrystalline micropores are found, but micro-cracks are developed. The microscopic pore

4.2. The characteristics of volcanic reservoirs in Yingcheng Formation The study area comprises mainly intermediate–acidic volcanic rocks that were erupted during the fault-depression phase (Du et al., 2012). These volcanic rocks represent a significant reservoir in the region. As a result of the faulting pattern, volcanic rocks are exposed over only a relatively small area, although a variety of lithologies occur. The primary pores in the volcanic reservoirs of the Yingcheng Formation are unfavorable for hydrocarbon storage. However, the development of various secondary dissolution pores and fractures during late-stage dissolution and tectonic activity greatly enhanced the reservoir performance of the volcanic rocks (Wang, 2009). We measured the physical parameters of volcanic rock samples from nine wells in the Yingcheng Formation to determine their reservoir performance. The samples were first identified by rock slice and then physical properties were measured, including rock porosity, permeability, and density. 4.2.1. Lithologic characteristics Four pyroclastic and five lava samples were obtained from the Yingcheng Formation. For the diffusion experiments closely combined with this paper, six volcanic samples were selected for lithologic characterization (Fig. 4). Volcanic rocks from well CS1 are rhyolitic debris–crystal welded tuffs (Fig. 4a) that comprise quartz and feldspar crystals (~70%), ash (~20%), and debris (~10%). Quartz crystals are xenomorphic, display granular textures, and are locally corroded. Alkali and plagioclase feldspar crystals are subangular and affected by kaolinization and sericitization, respectively. Debris is typically rhyolitic. The samples are cemented by fine-grained felsic material and ash, which display a pseudo-rhyolitic structure. Volcanic rocks from well CS103 comprise crystals (~5%) cemented by ash (~95%), display tuff textures, and contain block structures (Fig. 4b). Crystals comprise mainly angular–subangular quartz and feldspar with grain sizes of < 0.5 mm. Feldspar is predominantly alkali feldspar with minor plagioclase, and some feldspar grains are affected by sericitization and kaolinization. Volcanic rocks from well CS1-2 are rhyolitic crystal tuffs (Fig. 4c), which are composed of quartz and feldspar crystals (~25%) cemented by ash and very fine-grained quartz particles (~75%). Quartz crystals are xenomorphic and granular and are locally fragmented. Feldspar crystals are granular and highly altered. Rock debris is rare and is derived mainly from rhyolite. Volcanic rocks from well W21 are dacitic crystal tuffs (Fig. 4d) and comprise plagioclase and quartz crystals (~30%) cemented by ash (~70%). Plagioclase grains are typically angular, display prominent cleavage, and are commonly corroded, cracked, and affected by sericitization. 5

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Fig. 4. Photomicrographs of Yingcheng Formation volcanic rocks., a. CS1 (3574.00 m); b. CS103 (3726.57 m); c. CS1-2 (3671.15 m); d. W21 (1399.00 m); e. CS105 (3926.57 m); f. DS9 (2010.60 m).

structure of volcanic reservoir samples is highly heterogeneous as a whole, and the development of primary and secondary pore-fractures are important affection factors for the reservoir performance of volcanic rocks. Comprehensively compare the information of porosity, permeability, throat with casting thin-sections, shows that there is no significant correlation between porosity and permeability due to the high heterogeneity of volcanic rocks. 4.3. The formation of hydrocarbon and CO2 gas reservoirs CO2 gas reservoirs in the study area are concentrated in Yingcheng Formation volcanic rocks and comprise either pure CO2 or a mixture of CO2 and natural gas. The overlying Denglouku reservoirs contain only methane gas. We have shown that the Denglouku Formation lacks the potential for hydrocarbon generation that the gas was derived mainly from the underlying Yingcheng Formation. In this section, we show that

Fig. 5. Relationships among specific surface area, porosity, and permeability.

Table 2 Physical properties of the Yingcheng Formation volcanic rocks. Well

Well depth

Lithology

m CS1

3574.00

CS103 CS105 CS1-1

3726.57 3926.57 3727.90 3688.60 3749–3919 3671.15 3717.82–3831 3883–3690 3020.11 1399.00 2435.50 2010.60

CS1-2

CS3 W21 DS7 DS9

Rhyolitic debris-crystal welded tuff Tuff Dacite Rhyolite Breccia Rhyolite Rhyolitic crystal tuff Rhyolite Rhyolite Dacite Dacitic crystal tuff Dacite Andesite

Permeability

Porosity

Rock density

Specific surface area

CH4 Diffusion coefficient

CO2 Diffusion coefficient

mD

%

g/cm3

m2/g

cm2/s

cm2/s

0.011

5.4

2.48

0.9183

7.66E-06

7.20E-06

9.25 0.0077 1.22 0.086 1.89 0.0086 0.06 0.037 0.0035 0.02 322 0.071

29.3 2.3 13.6 8.0 7.34 6.4 7.34 6.3 4.7 12.6 3.3 3.3

1.92 2.64 2.29

1.20449 0.72726 1.48609

7.78E-06

5.66E-06

Date source

▲ 2.49

1.47609

5.48E-06

4.97E-06 ▲

2.53 2.33 2.53 2.53

1.44722 4.69497 0.79501 1.91823

▲ = Data from (Xu, 2010). 6

1.51E-06

1.34E-06

4.81E-07

4.15E-07

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

mixed source (Dai et al., 1994). The presence of mantle-derived helium is indicated by 3He/4He values of > 1.4 × 10−6 (Dai, 1996; Wang et al., 2004) and by helium isotopic ratio R/Ra values of > 1 (Xu, 1997). We collect the δ13C and He isotopic compositions of 14 hydrocarbon gas and CO2 samples from the Changling fault depression (Table 3). The samples yielded δ13CCO2 values of −15.30% to −4.91% with most between −7.50% and −6.30%. Helium associated with CO2 yielded 3 He/4He values of 2.65 × 10−6 to 2.94 × 10−6 and R/Ra values of 1.90–2.08. A previous study of 15 volcanic samples from the southern fault depression of the Songliao Basin yielded 3He/4He values (measured in volcanic inclusions) of 1.30 × 10−6 to 7.33 × 10−6 (with most between 1.92 × 10−6 and 5.21 × 10−6) and R/Ra values of 0.93–5.24 (Tao et al., 2012). The above data record a mixture between mantlederived helium and natural gas and indicate that the high-purity CO2 in the southern Songliao Basin was derived mainly from an inorganic source in the mantle. Gas compositions for samples from the Yingcheng and Denglouku formations in the southern Songliao Basin are listed in Table 4. Samples from the Yingcheng Formation contain high-purity CO2 or a mixture of CO2 and hydrocarbon gas. Wells CS1-3 and DS5 intersect high-purity CO2 gas reservoirs, containing 97.09%–99.29% and 98.50% CO2, respectively. Wells CS1-2, CS103, CS1, and CS1-1 are mixed-gas reservoirs containing CO2 and CH4 concentrations of 12.48%–68.33% and 20.05%–69.44%, respectively. In contrast, the overlying Denglouku Formation contains only hydrocarbon gas. Samples from wells CS1-3, CS103, CS1, H5, and N102 contain 80.70%–93.99% CH4 (the sample from well H5 yielded a CH4 content of 80.70%, whereas the other samples all yielded concentrations of > 90%). Despite the occurrence of these high-quality hydrocarbon reservoirs, according to the source rock evaluation above the Denglouku Formation mudstones do not have the capacity for hydrocarbon generation. CH4 gas reservoirs in the Denglouku Formation are therefore interpreted as secondary gas reservoirs. The carbon isotopic compositions of natural gas from the Yingcheng and Denglouku formations are characterized by rich heavy carbon isotope and a negative carbon isotopic sequence (a decrease in δ13C with increasing carbon number; Table 3) in methane. Methane from the Yingcheng and Denglouku formations yielded δ13C values of −26.07‰ to −15.70‰ and −20.80‰ to −17.63‰, respectively. This similarity in the composition of methane carbon indicates that hydrocarbon gas in

Fig. 6. The frequency of pore-throat types in the analyzed samples.

the CO2 is inorganic, we also determine the diffusion coefficients of CH4 and CO2, combined with existing CH4 carbon isotopic compositions to explore the coupling mechanism of reservoir-forming between the two gases. 4.3.1. Inorganic CO2 genesis and CH4 distribution CO2 may be generated through both organic and inorganic processes (Dai et al., 1995; Zhu et al., 2014; Liu et al., 2018). Previous studies indicate that CO2 gas from Songliao Basin reservoirs comprises less than 99.0% magmatic CO2 (Dai et al., 1995; Chen et al., 1996; Lu et al., 2009; Qu et al., 2016). Elemental and isotopic compositions can be used to determine the geochemical characteristics and genetic types of natural gas. Furthermore, carbon isotopic compositions can be used to identify the source of CO2 (Dai et al., 1995). A δ13CCO2 value of greater than −8‰ and a CO2 concentration of greater than 60% generally indicate an inorganic source. In contrast, a δ13CCO2 value of less than −10‰ and a CO2 concentration of less than 20% are typical of an organic source. δ13CCO2 values of −8‰ to −10‰ typically reflect a

Fig. 7. Casting thin-section images of rock samples. a. CS1-1, (3671.15): b. CS1-2, (3671.15 m): c. CS103, (3726.57 m). d. CS105, (3926.57 m): e. DS7, (2435.50m): f. DS9, (2010.60 m). 7

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Table 3 Geochemical characteristics of gas in the southern Songliao Basin. Well

▲

CS1

CS1-2▲

Depth m

Formation

3753 3350–3594 3697–3704 3838 3697–3704

▲

CS2 CS103▲ CS1-1▲ CS6▲ CS2▲ YS1■

3498–3511 3880 3739

K1yc K1yc

K1yc K1 d K1yc K1yc K1 d K1 d

3466 3495

K1yc

Natural gas component carbon isotope（δ13C/‰） CH4

C2H6

C3H8

−22.42 −26.07 −16.54 −18.30 −23.40 −15.70 −19.78 −22.40 −22.20 −23.48 −17.63 −20.40 −20.80 −23.02

−23.42 −26.86 −24.34 −25.00 −26.55

Isotope series

(3He/4He)/10−6

R/Ra

2.88 ± 0.08

2.06

2.65 ± 0.07

1.90

2.94 ± 0.08 2.91 ± 0.08

2.10 2.08

CO2 −4.91 −6.98 −6.64 −11.60 −8.65 −6.40 −10.60 −11.90 −7.50 −6.37 −6.62 −14.30 −15.30 −6.85

−26.45

−28.16 −27.00 −26.90 −29.88 −24.60

−30.74 −27.00 −30.32 −24.20

−24.70 −25.90

−26.55

C1 > C2 C1 > C2 C1 > C2 C1 > C2 C1 > C2 < C3

negative negative negative

C1 > C2 > C3 C1 > C2 C1 > C2 C1 > C2 > C3 C1 > C2 < C3

negative negative negative negative

C1 > C2 C1 > C2 > C3

negative negative

mixed

Notes: ▲ = Data from the Sinopec Jilin Oilfield Branch; ■ = Data from Cao (2010). Table 4 The compositions of natural gas from the Yingcheng and Denglouku formations of the southern Songliao Basin. Well

CS1-3

Formation

K1d K1yc

CS1-2

K1yc

CS103

K1d K1yc

CS1

K1d K1yc K1yc K1d K1d K1yc

CS1-1 H5▲ N102▲ DS5■

Depth

CH4

C2H6

m

Volume percentage（%）

3471–3552 3528–3534 3786 3787 3889 3697 3838 3511–3498 3732.5 3733.5 3820.5 – 3594–3753 3880 1852.8–1941.2 1638–1665.4 3102–3142.8

91.71 92.58 2.41 1.98 0.43 69.44 20.05 92.03 61.87 62.1 24.54 – 66.78 22.89 80.7 93.99 1.52

– 1.7 – – – – – 2.17 – – – – – – 17.79 1.9 0.11

C3H8

– 0.19 – – – – – 0.28 – – – – – – – – –

N2

CO2

– 5.11 – – – – – 4.82 4.8 4.64 62.62 – – – 1.2 3.84 1.1

0.19 0.39 97.09 97.56 99.29 21.95 68.33 0.61 31.65 31.63 12.48 0.54 22.31 58.23 0.3 0.12 98.5

Fig. 8. The diffusion coefficients of CH4 and CO2 in the studied volcanic rock samples.

Note: ▲ = Data from Zhao et al. (2006); ■ = Data from Fu (2010).

5. Discussion

the two formations shares a common origin.

5.1. Influence of reservoir physical properties on the diffusivity of natural gas

4.3.2. Diffusion coefficient of CH4 and CO2 To investigate the displacement and replacement of hydrocarbons by mantle-derived inorganic CO2, we measured the diffusion coefficients of CH4 and CO2 gas in rock samples collected from five wells in the Yingcheng Formation (Table 2, Fig. 8). Our results show that the diffusivity of CH4 is greater than that of CO2 gas in the same rock samples, but in different types of volcanic rock samples, the diffusivity of the two gases of is also different. Volcanic lava samples from well CS105 yielded the highest measured diffusion coefficients on account of the presence of abundant fractures (Fig. 7d). Volcaniclastic samples from wells CS1 and CS1-2 yielded relatively high diffusion coefficients, while those of pyroclastic rocks in Wells W21 are smaller than those in Wells CS1 and CS1-2, but they are still one order of magnitude higher than those in Wells DS9, mainly because of a large proportion of ash, loosely packed structures, and relatively good pore connectivity. A lava sample from well DS9 yielded the lowest diffusion coefficients (an order of magnitude lower than the other analyzed samples) owing to the lava has few primary pores and the matrix has no obvious alteration, indicating that the rock is dense and the permeability is poor (Fig. 7f).

The tuff samples yield significantly better physical properties than those of the lava samples, which is attributed to the structural characteristics of the former. The tuffs display typical tuffaceous textures and comprise crystals and a high proportion of ash, and they also contain intergranular pores and loosely packed structures, resulting in high porosity and permeability. The lava samples such as rhyolite, dacite, and andesite contain pores, devitrified micropores, and matrix micropores; however, these pores are small and poorly connected, and therefore the lava reservoir properties are inferior to those of tuffs. The sample from well CS103, located in the fault zone of the central uplift, was collected from a depth of 3726.57 m. Although this sample contains up to 95% ash (Fig. 4b), the depth of burial resulted in enhanced compaction and diagenesis, which makes the rock denser. Casting thin-section images (Fig. 7c) indicate that late-stage alteration was extensive and involved mainly carbonate. Pores are relatively well developed and connected. The sample yields a substantially lower density compared with other measured samples and has higher permeability and porosity. From the throat test results of 9 rock samples, it can be seen that the

8

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

permeabilities, and specific surface areas, but substantially lower CH4 and CO2 diffusion coefficients, compared with samples from wells CS1 and CS1-2. This indicates that in addition to differences in pore size, distribution, and connectivity, the two sets of samples are variably affected by the properties of interior pore surfaces. The sample from well W21 comprises ~30% plagioclase as well as quartz crystals. The plagioclase crystals contain intragranular dissolved pores and are commonly corroded, fragmented, and sericitized. The formation of secondary pores and argillization alteration would have increased the CO2 and CH4 adsorption capacity of the internal pore surfaces of crystals and consolidated ash. For samples with abundant primary porosity and high adsorptivity, gas throughputs are further reduced, resulting in significantly lower diffusion coefficients. Our results show that the diffusivity of CH4 is greater than that of CO2 gas in the same rock samples. Therefore, the analyzed rocks have higher adsorption capacities and lower diffusion capacities for CO2 relative to CH4. CO2 is thus more readily adsorbed onto pore surfaces than CH4. Therefore, when CO2 enters a reservoir saturated with CH4, methane molecules are desorbed from pore surfaces and replaced by CO2.

throats measured in samples of CS1-1 and CS3 contain rare narrow pore throats that do not affect permeability; The rock samples of the DS7 well measured a relatively large number of throats, and the throat radius was relatively large, and the casting thin-section (Fig. 7e) shows a 25-μm-wide crack, which penetrated the field of view. This crack results in an anomalously high measured permeability of 322 mD, which is 4–5 orders of magnitude greater than those of other analyzed samples, despite a low porosity of 3.3%. No throat was found in the other 6 samples. In summary, pore throats in the Yingcheng Formation reservoirs are rare and unevenly distributed, which may restrict fluid flow in the reservoirs. In addition to the physical properties of the volcanic rocks, porosity, permeability, and reservoir performance are affected by the presence of fractures. Volcanic reservoirs typically occur adjacent to deep fractures, with the formation of cracks in reservoirs and faults providing conduits that facilitate the migration of deep natural gas into the reservoir. Therefore, volcanic rocks are generally considered as being favorable reservoirs for the accumulation of natural gas, play a controlling role in the accumulation of natural gas. 5.2. Diffusion coefficients analysis of CH4 and CO2

5.3. Mechanism for the accumulation of natural gas 5.2.1. Factors affecting the diffusion coefficient of natural gas The diffusion of natural gas through rock is controlled primarily by the abundance of pores and their degree of interconnectivity. A high pore connectivity reduces diffusion resistance, resulting in a high diffusion coefficient. However, diffusion coefficients are also affected by the total pore space (which affects gas-adsorption capacity), the presence of secondary dissolution pores, the presence of internal clay minerals, and the generation of secondary fractures during deformation. Volcaniclastic and lava reservoirs contain pore-space types distinct from those of typical sandstone reservoirs, comprising primary crystal pores, gas pores, dissolution pores, and micro-cracks. Lava reservoirs contain predominantly secondary pores such as gas pores, dissolution pores, and micro-cracks. The connectivity between pores and microcracks is uncertain, and they are randomly distributed in the reservoirs. This porosity heterogeneity and the presence of micro-cracks have significant effects on gas diffusivities. Assuming a similar porosity, samples containing micro-cracks will yield higher diffusion coefficients than those containing only primary crystal pores (Yan, 2011). The interior surfaces of pores in volcanic rocks are different from those in sedimentary rocks, which typically comprise quartz, which does not adsorb gas. Therefore, the diffusion of gas through pores in sedimentary rocks is not affected by internal surface area. In contrast, the internal surfaces of volcanic rock pores comprise mainly ash, feldspar, and dissolution pores. Dissolution results in the argillization of crystals, and ash and clay have high gas-adsorption capacities, and therefore the internal surface area of volcanic pores can have a significant effect on gas diffusion. According to the conventional physical-chemical properties, the molecular weight and molecular radius of CO2 are larger than CH4 (Yang et al., 2017a), and CO2 should also have a displacement effect on CH4 in space.

The gas production peak of source rocks in the southern Songliao Basin (hosted in the Huoshiling, Shahezi, and Yingcheng formations) were deposited chiefly during the sedimentary period of early–middle stage of Denglouku formation (middle stage of lower Cretaceous) and the early stage of the Nenjiang formation (middle stage of upper Cretaceous, Lu et al., 2010), hydrocarbon gas generated during this period continuously migrated into volcanic rocks of the upper Yingcheng Formation and became enriched to form hydrocarbon reservoirs. The primary period of hydrocarbon accumulation in the Yingcheng Formation reservoirs occurred at 82 Ma (upper Yaojia formation; Yang et al., 2010; Yang et al., 2011), whereas the accumulation of hydrocarbons in the upper Denglouku Formation occurred slightly later at 79 Ma (lower Nenjiang formation; Yang et al., 2017a). During the deposition of the Qingshankou Formation, source rocks in the Huoshiling, Shahezi, and Yingcheng formations underwent oil cracking to gas and dry gas (Jin et al., 2014). The source rocks were buried to depths of > 2400 m, whereas the overlying Denglouku Formation was buried to 1800–2000m (this unit is presently located at a depth of ~3500 m, which is in the late A to B substage of middle diagenetic stage). The reservoir hosted in Denglouku formation has undergone only weak diagenesis and has favorable physical characteristics (Yin et al., 2019) for the storage of hydrocarbons. A submarine volcanic eruption occurred during the deposition of the upper Qingshankou Formation, close to wells Qian124–Qian109, southwest Qian'an County, to the north of the Changling gas field. The erupted basalt has a maximum thickness of ~80 m and is distributed over an area of ~10.5 km2 (Han et al., 1988). This eruption was coeval with a basaltic eruption of the Datun volcano near Changchun (Zhang et al., 2006a,b), indicating that volcanic eruptions were common in the region at this period. The submarine volcanic eruption resulted in the re-activation of preexisting deep faults (as imaged in the Songshen section; Yang et al., 2001). After being enriched in the lower crust, mantle-derived inorganic CO2 migrated along these faults into the Yingcheng Formation volcanic hydrocarbon gas reservoirs (Yang et al., 2010). Upwelling CO2 then displaced the CH4, which migrated upward into Denglouku Formation sandstones, where it was enriched to form a secondary gas reservoir. This model explains the occurrence of highpurity CO2 and mixed CO2–hydrocarbon gas in the Yingcheng Formation and exclusively hydrocarbon gas in the Denglouku Formation reservoirs. It can be seen from the analysis above that the porosity, permeability, fissure, and internal surface properties of the pores have a

5.2.2. Relationship between gas diffusion rate and petrophysical properties Our results show that specific surface area is positively correlated with porosity and permeability (Table 2 and Fig. 5). Permeability and specific surface area are negatively correlated with the diffusion coefficients, whereas porosity is only weakly negatively correlated with the diffusion coefficients (Fig. 9). We propose that samples with high porosities, and consequently larger internal surface areas, have high gasadsorption capacities, which limits the diffusion of gas, resulting in low diffusion coefficients. However, our conclusions are based on a small number of samples, and more analyses are required to provide a statistically sound interpretation. Volcaniclastic samples from well W21 yielded higher porosities, 9

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al.

Fig. 9. Relationships among the porosity, permeability, specific surface area, and diffusion coefficients of volcanic rocks.

3. The upwelling of inorganic CO2 along active deep faults was the primary controlling factor on the formation of the gas reservoirs hosted in Yingcheng and Denglouku Formations. Future hydrocarbon exploration for natural gas in the area should be focused around deep faults within the Yingcheng and Denglouku Formations.

controlling effect on the diffusibility of the gas. The surrounding rocks at the top and bottom of the volcanic rocks of Yingcheng Formation are all normal sedimentary rocks, and the volcanic rocks also contain sedimentary rock interlayers (Cai et al., 2010). A large number of pores, volcanic debris pores and fissures can be formed in volcanic rocks due to magma blasting, condensation and later tectonic activities, which provide fluid communication between volcanic rocks and upper-lower sedimentary rocks. The primary pores, secondary dissolution pores and fissure spaces became upwelling channel for late mantle-derived CO2. CH4 from the Yingcheng and Denglouku Formations yielded similar carbon isotopic compositions. As the Denglouku Formation does not have hydrocarbon generation potential, we infer that CH4 was derived from the underlying Yingcheng Formation. Our results show that in similar rocks, the diffusivity of CH4 is greater than that of CO2. Furthermore, high temperatures in the basin resulted in the excitation of natural gas molecules, enhancing their diffusivity, supporting our hypothesis that CH4 in the Denglouku Formation represents hydrocarbon gas displaced by mantle-derived inorganic CO2 in the lower Yingcheng Formation. The upwelling of inorganic CO2 during the activation period of deep faulting was the main controlling factor for the existing combination of gas reservoirs in Yingcheng and Denglouku Formation. Future exploration for natural gas in the Songliao Basin should therefore be focused around deep faults within the Yingcheng and Denglouku Formations.

Acknowledgments The authors would like to acknowledge the funding by the project (Project No.41472101) sponsored by the Natural Science Foundation of China and supported by the Langfang Branch of the China Petroleum Exploration and Development Research Institute. References Cai, D.M., Sun, L.D., Qi, J.S., et al., 2010. Characteristics and evolution of volcanic reservoirs in Xujiaweizi fault depression. Acta Pet. Sin. 31 (3), 400–406. Cai, L.X., Xiao, G.L., Lu, S.F., et al., 2019. Spatial-temporal coupling between high-quality source rocks and reservoirs for tight sandstone oil and gas accumulations in the Songliao Basin, China. Int. J. Min. Sci. Technol. 29, 387–397. Cao, J., 2010. Reservoir Characteristics and Natural Gas Genesis of Volcanic Gas Reservoirs in the Yingcheng Formation of Songnan Gas Field. pp. 41–43. Cao, H.S., Kaufman, A., Shan, J.X., 2016. Sulfur isotope constraints on marine transgression in the lacustrine Upper Cretaceous Songliao Basin, northeastern China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 451, 152–163. Cao, Y., Gao, S.L., Qiao, X.Y., 2018. Natural gas genesis and accumulation of volcanic rocks in the Yingcheng Formation, Changling fault depression, southern Songliao Basin. J. Xi’an Shi you Univ. (Nat. Sci. Ed.) 33 (4), 27–35. Chen, F.J., Zhao, H.L., Chen, Z.N., 1996. Structural feature of Mesozoic-Cenozoic extensional basins and Earth dynamics background in Eastern China. Earth Sci. 21, 357–365 (in Chinese with English abstract). Dai, J.X., 1996. Geochemistry and accumulation of carbon dioxide gases in China. AAPG Bull. 80, 1615–1626. Dai, J.X., 2017. Giant Coal-Derived Gas Fields and Their Gas Sources in China, Chapter 6Large Coal-Derived Gas Fields and Their Gas Sources in the Songliao Basin. pp. 371–445. Dai, J.X., S, Y., Dai, C.S., et al., 1994. Inorganic genetic carbon dioxide gas accumulations and their characteristics in East part of China. China Offshore Oil Gas Geol. 8 (4), 215–222. Dai, C.S., Song, Y., Sun, Y., 1995. Genesis and distribution of carbon dioxide gas reservoirs in east China. Sci. China, Ser. B 25, 764–771. Dong, T., He, S., Yin, S.Y., et al., 2015. Geochemical characterization of source rocks and crude oils in the upper cretaceous Qingshankou Formation, changling sag, southern Songliao Basin. Mar. Pet. Geol. 64, 173–188. Du, J.H., Zhao, Z.H., Jiao, G.H., 2012. Control factors and distribution prediction of highquality reservoirs of Mesozoic volcanic rocks in Songliao Basin. China Pet. Explor. 4, 1–8. Feng, Z.Q., 2008. Volcanic rocks as prolific gas reservoir: a case study from the Qingshen

6. Conclusions 1. The presence of primary and secondary pores can greatly increase the capacity for rocks to adsorb CH4 and CO2. The formation of secondary dissolution pores and argillization enhance the adsorption of CH4 and CO2, limiting gas throughputs, and greatly reducing CH4 and CO2 diffusivities. 2. The diffusivity of CH4 is greater than that of CO2 in similar rock types, and CO2 was therefore able to displace CH4 in the studied volcanic reservoirs. CH4 and CO2 isotopic data and the timing of gas accumulation and fracturing indicate that late faulting resulted in the migration of mantle-derived inorganic CO2 into the Yingcheng Formation volcanic hydrocarbon gas reservoir, displacing previously accumulated hydrocarbon gas. The displaced gas then migrated upward into Denglouku Formation sandstone, where it was enriched to form secondary gas reservoirs. 10

Journal of Petroleum Science and Engineering 182 (2019) 106302

Y. Yu, et al. gas field in the Songliao Basin, NE China. Mar. Pet. Geol. 25, 416–432. Feng, Z.Q., Jia, C.Z., Xie, X.N., et al., 2010. Tectonostratigraphic units and stratigraphic sequences of the nonmarine Songliao basin, northeast China. Basin Res. 22 (1), 79–95. Fu, X.F., et al., 2010. Distribution law of mantle-origin CO2 gas reservoirs and its controlling factors in Songliao basin. J. Jilin Univ. (Earth Sci. Ed.) 40, 253–263. Ge, Y., H, Z.L., S, L.Z., et al., 2012. Controlling factors on high quality reservoir of tight sandstone of Denglouku Formation in Changling Fault Sag, southern part of Songliao Basin. J. Cent. South Univ. (Sci. Technol.) 43 (7), 2691–2700. Han, G.L., Zhao, H.T., Bian, J., 1988. Relationship between the injected basalt in Qingshankou Formation and oil/gas in Zhongyang Depression. Songliao basin. Exp. Pet. Geol. 10 (3), 248–255. He, F.F., Zhu, R., Jin, A.M., et al., 2019. Hydrocarbon preservation and formation water geochemistry in abnormal pressure system in the Bawu area of Lishu depression, Songliao Basin, China. J. Pet. Sci. Technol. 37, 1176–1183. Huang, D.F., Li, J.C., Z, D.J., et al., 1984. Terrestrial Organic Evolution and Hydrocarbon Generation Mechanism. pp. 84–95. Jia, C.Z., Zhao, W.Z., Zou, C., et al., 2007. Geological theory and exploration technology of lithologic strata oil and gas reservoirs. Pet. Explor. Dev. 34 (3), 257–272. Jin, X.H., Yan, X.B., Sun, D.S., et al., 2014. Fluid inclusion characteristics and hydrocarbon accumulation process of deep reservoirs in Changling rift, Songliao Basin. Oil Gas Geol. 35 (5), 609–613. Li, Y., 2009. Comprehensive Study on Source Rocks of Shiwu and Changling Fault Depressions in the Southern Songliao Basin. pp. 21–29. Li, H.G., Xue, H.T., Huang, W.B., et al., 2011. Prospect of deep source rock exploration in Dehui fault depression. Sci. Technol. Eng. 11 (27), 6578–6582. Li, S.Q., Chen, F.K., Siebel, W., et al., 2012. Late Mesozoic tectonic evolution of the Songliao basin, NE China: evidence from detrital zircon ages and Sr-Nd isotopes. Gondwana Res. 22 (3–4), 943–955. Liu, X.B., Fu, X.F., Liu, D.M., et al., 2018. Distribution of mantle-derived CO2 gas reservoir and its relationship with basement faults in Songliao Basin, China. J. Nat. Gas Sci. Eng. 56, 593–607. Lu, X.S., Yan, S., Liu, S., Ma, S.F., Wei, L.C., 2009. Distribution and migration– accumulation mechanism of mantle –derived CO2 in Songliao basin. Acta Pet. Sin. 30, 661–666. Lu, S.F., Sun, H., Wang, W.M., et al., 2010. Key factors controlling the accumulation of volcanic gas reservoirs in the deep part of Songliao Basin. J. Daqing Pet. Inst. 34 (5), 42–47. Lu, X.S., Wei, L.C., Song, Y., et al., 2011. Analysis of reservoir forming mechanism of high CO2 gas reservoirs in Changling fault depression, southern Songliao Basin. Nat. Gas Geosci. 22 (4), 657–663. Lv, B.Q., Zhang, Y.J., Wang, H.Y., et al., 2003. Current status and prospects of Mesozoic and Cenozoic volcanic oil and gas reservoirs in eastern China. Offshore Oil 23 (4), 522–529. Ma, S.W., Luo, J.L., Chen, C.Y., et al., 2017. Classification and evaluation of microscopic pore structure of volcanic reservoirs: taking Carboniferous volcanic rocks in the Xiquan area in the eastern Junggar Basin as an example. Pet. Exp. Geol. 39 (5), 647–654. Meng, Q., Zhang, S., Sun, G., et al., 2016. A seismic geomorphology study of the fluvial and lacustrine-delta facies of the Cretaceous Quantou-Nenjiang Formations in Songliao Basin, China. Mar. Pet. Geol. 78, 836–847. Qu, X.Y., Chen, X., Yu, M., Liu, Li, 2016. Mineral dating of mantle–derived CO2 Charging and its application in the southern Songliao Basin, China. Appl. Geochem. 68, 19–28. Rui, Z.H., Cui, K., et al., 2018b. A comprehensive investigation on performance of oil and gas development in Nigeria: technical and nontechnical analyses. Energy 158, 666–680. Rui, Z.H., Wang, X., et al., 2018a. A realistic and integrated model for evaluating oil sands development with steam assisted gravity drainage technology in Canada. Appl. Energy 213, 76–91. Sorokin, A.P., Malyshev, Y.F., Kaplun, V.B., et al., 2013. Evolution and deep structure of the Zeya-Bureya and songliao sedimentary basins (east Asia). Russ. J. Pac. Geol. 7 (2), 77–91. Sun, J., Gamboa, E., Schechter, D., et al., 2016. An integrated workflow for characterization and simulation of complex fracture networks utilizing microseismic and horizontal core data. J. Nat. Gas Sci. Eng. 34, 1347–1360.

Tao, S.Z., Dai, J.X., Zou, C., et al., 2012. The rare gas isotopes of volcanic rock enclosure and the genesis of natural gas accumulation are traced in the Songliao Basin. J. Rock 28 (3), 927–938. Wang, L.W., 2009. Discussion on the special characteristics of deep gas enrichment conditions in Songliao Basin. China Pet. Explor. 14 (4), 6–12. Wang, L.S., Guo, Z.Q., Ma, Z.H., et al., 2004. Geochemistry characters of inorganic natural gas. J. Jilin Univ. Earth Sci. Ed. 34 (4), 542–545. Wang, J.Q., Yang, G., Xue, L.F., et al., 2011. Tectonic evolution of the Changling fault basin and its relationship to oil and gas accumulation. Min. Sci. Technol. 21, 427–432. Wang, P.J., Zhao, R.L., Meng, Q.A., et al., 2015. Cretaceous Songliao Basin: dynamic environment from volcanic rift to intracontinental depression. Geosci. Front. 22 (03), 99–117. Wang, Y., Deng, S.W., Fan, J., et al., 2018. Natural gas geological conditions in key fault depressions in the southern Songliao Basin,Resource potential and exploration direction. Nat. Gas Geosci. 29 (10), 1455–1464. Xi, K.L., Cao, Y.C., Jens, J., et al., 2015. Quartz cement and its origin in tight sandstone reservoirs of the Cretaceous Quantou formation in the southern Songliao basin, China. Mar. Pet. Geol. 66, 748–767. Xiao, Y.J., Xu, Y.D., Wang, D.X., 2009. Formation conditions and reservoir-forming patterns of volcanic rocks, eastern changling depression. Nat. Gas Geosci. 20 (4), 538–543. Xu, Y.C., 1997. Helium isotope distribution and tectonic setting in natural gas. Geosci. Front. 4 (3–4), 185–189. Xu, H.J., 2010. Identification and Evaluation of Volcanic Reservoirs in the Southern Fault Depression of the Songliao Basin. pp. 30–31. Yan, J., 2011. Volcanic Gas Reservoir Supply and Exhaust Mechanism. pp. 47–48. Yang, G., Xue, L.F., Liu, Z.B., et al., 2001. Deep seismic section interpretation and deep geological study in the Songliao Basin. Oil Gas Geol. 22 (4), 326–336. Yang, G., Zhao, Z.Y., Zhang, W., 2010. Distribution and accumulation of inorganic CO2 in southern Songliao Basin. J. Jilin Univ. (Earth Sci. Ed.) 40 (4), 933–938. Yang, G., Zhao, Z.Y., Shao, M.L., 2011. Changling Fault Depression CO2 gas reservoir and hydrocarbon reservoir accumulation characteristics. Pet. Explor. Dev. 38 (1), 52–58. Yang, G., Fan, Y.Y., Liu, C.L., 2017a. Gas accumulation mechanism in Denglouku formation of Changling fault depression, southern Songliao Basin, China. Glob. Geol. 20 (4), 170–175. Yin, C.H., Sun, L.D., Liu, C., et al., 2019. Reservoir characteristics and controlling factors of Denglouku formation in Shuangcheng area, Songliao Basin. Pet. Geol. Oilfield Dev. Daqing 38 (2), 1–6. Zhang, Y.M., 2006. Deep hydrocarbon accumulation conditions in the northern part of the Shiwu fault depression in the southern Songliao Basin. J. Oil Gas Technol. (J. Jianghan Petroleum Inst.) 28 (3), 53–56. Zhang, H.H., Xu, Y.G., Ge, W.C., et al., 2006a. Geochemistry of late Mesozoic-Cenozoic basalts in Yitong-Datun area, Jilin province and its implication. Acta Ptrologica Sin. 22 (6), 1579–1596. Zhang, Y.M., Li, M., Li, R.L., 2006b. Laws of natural gas accumulation in the deep strata of the southern Songliao Basin. Oil Gas Geol. 27 (6), 841–848. Zhang, Q.C., Hu, S.Y., Wang, L.W., 2010. Formation and distribution of CO2 volcanic gas reservoirs in the Songliao Basin. Acta Petrol. Sin. 26 (1), 109–120. Zhao, L.B., Huang, Z.L., Ma, Y.J., et al., 2006. Geochemical characteristics and genesis of deep natural gas in the Dehui fault depression in the southern Songliao Basin. Nat. Gas Geosci. 17 (2), 177–182. Zhao, W.Z., Zou, C.N., Feng, Z.Q., et al., 2008. Geological characteristics and evaluation techniques of deep volcanic rock gas reservoirs in the Songliao Basin. Pet. Explor. Dev. 35 (2), 129–141. Zhao, W.Z., Zou, C.N., Chi, Y.L., et al., 2011. Sequence stratigraphy, seismic sedimentology, and lithostratigraphic plays: upper Cretaceous, Sifangtuozi area, southwest Songliao Basin, China. Am. Assoc. Petrol. Geol. Bull. 95 (2), 241–265. Zhao, Z.H., Xu, J., Jiang, X.H., et al., 2016. Deep geological structure and tight conglomerate gas exploration in songliao basin. Pet. Explor. Dev. 43 (1), 12–23. Zhu, G.Y., Wang, Z.J., Dai, J.X., Su, J., 2014. Natural gas constituent and carbon isotopic composition in petroliferous basins, China. J. Asian Earth Sci. 80 (5), 1–17. Zou, C.N., Tao, S.Z., Gu, Z.D., 2006. Formation conditions and distribution rules of large lithologic oil-gas fields with low abundance in China. Acta Geol. Sin. 80 (11), 1739–1751.

11