Lithologic Reservoirs

Based on structural and tectonic geology, this paper discussed the distribution characteristics and their structural/tectonic controlling factors of the marine carbonate oil and gas accumulation around/on the intracratonic sags, paleo-uplifts and basin-mountain systems across the Sichuan superimposed basin. During the early stage of hydrocarbon accumulation formation, the intracratonic sags controlled the formation of high-quality source rocks, reservoir rocks and their assemblage, whilst the paleo-uplifts controlled the hydrocarbon migration and accumulation to form paleo oil reservoir and paleo gas reservoir. Subsequently, the basin?mountain systems changed the structural geology and adjusted the hydrocarbon accumulations to accommodate gas-fields across the basin. It is considered that the intracratonic sags are the essential factors for hydrocarbon accumulation in early stage, paleo-uplifts are the best places for hydrocarbon migration and accumulation, and the basin-mountain systems are the most important factor for hydrocarbon accumulation and adjustment in late stage. The coupling relationships accounted for hydrocarbon distri?bution in carbonates across the Sichuan basin. Therefore, it is suggested that the prospect areas of deep to super-deep reservoir in carbonates are in the middle and northern segments of the western Sichuan Basin, where could be dominant with large?scale primary and secondary gas reservoirs. There are four favorable factors as following: （1） wide-spread high-quality source rocks of Lower Cambrain black shale, （2） high-quality multi reservoir rocks, （3） good carrier or conducting network composed of faults and unconformities for hydrocarbon migration and accumulation, and （4） multi cap rocks composed of low?porosity and low-permeability carbonate, mudstone and gypsum-salt strata.

Shale gas-bearing property differences and their genesis between Wufeng-Longmaxi Formation and Qiongzhusi Formation in Sichuan Basin and surrounding areas

Zhou Wen， Xu Hao， Yu Qian， Xie Runcheng， Deng Kun

2016, Vol.28(5): 18–25 Abstract ( 532 ) PDF (692 KB) ( 760 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.002

Wufeng?Longmaxi Formation and Qiongzhusi Formation are explored and developed for shale gas simultaneously in Sichuan Basin and surrounding areas. Great successes have been achieved at Wufeng?Longmaxi Formation, but it is unsatisfactory in Qiongzhusi Formation. Based on the data of outcrop, production and former findings, the geologic features of marine shale were summarized in Sichuan Basin and surrounding areas, and the gas?bearing property differences and their genesis between Wufeng?Longmaxi Formation and Qiongzhusi Formation were analyzed. It is considered that the marine shale experienced the most significant characteristic of high thermal maturity and strong reformation in Sichuan Basin and surrounding areas, which differs greatly with marine shale in North America. The statistical data from a large number of production wells indicates that the shale gas output in Wufeng?Longmaxi Formation is better than that in Qiongzhusi Formation obviously. The shale in Qiongzhusi Formation is characterized by lower pressure coefficient, poorly developed organic pores and widely distributed asphalt at adjacent reservoir, which indicates that the unconformity surface at Tongwan stage destructed the shale gas?bearing property in Qiongzhusi Formation. It is considered that the hydrocarbon expelled along the Sinian top Tongwan unconformity surface since hydrocarbon generation and the residual shale gas is poor in Qiongzhusi Formation.

Carbonate diagenesis and its influence on reservoir: a case study from Yijianfang Formation in Shunnan area, central Tarim Basin

Meng Wanbin， Xiao Chunhui， Feng Mingshi， Fu Heng， Cao Zicheng， Sun Ru

2016, Vol.28(5): 26–33 Abstract ( 357 ) PDF (1257 KB) ( 444 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.003

In order to understand the reservoir distribution and therefore to promote exploration, carbonate reservoir characteristics and diagenetic features of the Middle Ordovician Yijianfang Formation in Shunnan area and its influence on reservoir formation were studied based on the core and casting thin section observation and cathodo?luminescence spectroscope analysis coupled with core?measured porosity and permeability data. The results show that the carbonate reservoir of Yijanfang Formation in the study area is mainly composed of grain limestone, microcry?stalline limestone and algal bindstone. The main reservoir spaces are dissolved pores and fractures, which formed two types of reservoirs: fractured reservoir and fractured?cavity reservoir. The porosity of the reservoir ranges from 0.20% to 3.90% with an average value of 1.52%, and the permeability ranges from 0.003 mD to 5.84 mD with an average value of 0.62 mD. The reservoir is dominated by type Ⅲ with poor physical properties. The carbonate rocks underwent complex diagenesis including cementation, compaction/pressure dissolution, corrosion （karstification） and fracturing, of which cementation （including filling of dissolved pores by crystals） has strongly damaged the reservoir while corrosion （karstification） and fracturing were major mechanisms of reservoir formation in the Yijianfang carbonate rocks.

Genesis of dolomite of Changxing Formation in Tieshan-Shuangjiaba area, northeast Sichuan Basin

Zhang Yulu， Wen Huaguo， Zheng Rongcai， Zhou Gang， Zhang Bing， Cao Jixiang

2016, Vol.28(5): 34–43 Abstract ( 359 ) PDF (1011 KB) ( 343 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.004

As the main reservoir rock of Changxing Formation in the northeast Sichuan, the dolomite of reef flat facies has received more attention. Therefore, it is of great significance to comprehensively analyze its genesis in order to promote the natural gas exploration and development. The dolomite of Changxing Formation in Tieshan?Shuangjiaba area was analyzed from the aspects of structure, genesis and diagenesis. Based on the analysis of the dolomite order degree, cathodeluminescence, SEM, trace elements and stable isotopes, it is demonstrated that the dolomitization of dolomicrite of Changxing Formation took place in the relatively closed and strongly evaporated restricted sea basin behind the platform margin reef. The initial rocks of biogenic dolomite and crystalline dolomite are identified to be reef limestone and bioclastic limestone, which are originally deposited in the platform margin reef flat or intra platform reef flat. Geochemical characteristics of the dolomite inheriting properties of initial rocks significantly varied in different facies, which can be attributed to different sedimentary characteristics, namely the isolation and evaporation of the intra platform reef as well as the exposure and meteoric water leaching of the platform margin reef. Moreover, water?rock interaction in different types of dolomitization fluids was analyzed. Based on the analyses of the diagenetic environment of dolomite as well as dolomitization fluid properties and sources, combined with the hydrogeological model, the genesis of dolomite was studied. It is considered that the dolomicrite was formed by evaporating pump dolomitization during the penecontemporaneous period at near?surface with the dolomitization fluid of penecontem?poraneous high salinity evaporated seawater, while the biogenic dolomite and crystalline dolomite were formed by thermal convection dolomitization in the shallow to middle?buried diagenetic environments with the dolomitization fluid of synsedimentary high salinity evaporated seawater sealed in the stratum.

Characteristics and main controlling factors of dolomite reservoirs of Cambrian Loushanguan Group in the southeastern Sichuan Basin

Jiang Wenjian， Hou Mingcai， Xing Fengcun， Li Yong， Shi Xin， Wang Chao

2016, Vol.28(5): 44–51 Abstract ( 478 ) PDF (839 KB) ( 292 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.005

A large number of dolomite developed in Cambrian Loushanguan Group in the southeastern Sichuan Basin, with good oil and gas exploration prospect. However, the exploration degree in the study area is relatively low, and there are few studies on the characteristics of dolomite reservoir. Based on the outcrop observation, combined with cast thin section observation and physical property test of the samples from Jingzhu and Zhongba profile, the data of petrology, reservoir space and physical properties were applied to study the characteristics and main controlling factors of dolomite reservoirs. The result shows that the reservoir rocks are mainly crystalline dolomite and grain dolomite, the main reservoir spaces are intercrystalline pores and intercrystalline dissolved pores, intergranular pores, intergranular dissolved pores and nonselective dissolved pores. The porosity is well correlated to permeability, but pores varied greatly in different types of rock. The dolomite reservoir quality is affected by multiple factors, and the high energy environment controls reservoir distribution. The dolomitization and hydrothermal fluid dissolution improve the reservoir properties. The good quality reservoirs are mainly developed at the top of the upward shallowing cycles of the third?order sequence. This study results are basis for the next hydrocarbon exploration in the southeastern Sichuan Basin, and reference for the study on dolomite reservoir in other areas.

Shale reservoir characteristics and influencing factors of the Lower Silurian Longmaxi Formation in the eastern Sichuan Basin

Li Ke， Wang Xingzhi， Zhang Xingyi， Yao Jichao， Wu Qingmin

2016, Vol.28(5): 52–58 Abstract ( 405 ) PDF (858 KB) ( 497 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.006

The shale gas exploration of the Lower Silurian Longmaxi Formation in the eastern Sichuan Basin has achieved a major breakthrough, so the research of reservoir quality, especially the influencing factors of favorable reservoir deve?lopment, is significant for the next exploration of marine shale in Sichuan Basin. Based on core observation and rock slice identification, combined with scanning electronic microscope X?ray diffraction, this paper studied the reservoir characteristics of the Lower Silurian Longmaxi Formation in the eastern Sichuan Basin, and determined the main con?trolling factors for the formation of favorable reservoir. The minerals in the study area are mainly composed of quartz and clay minerals, with little calcite, dolomite and pyrite. Kerogen type is mainly sapropel（Ⅰ）, and humic?sapropel（Ⅱ1） comes second. The mass fraction of TOC is 0.10%?8.67%, and the average value is 1.49%. The Ro is 1.63%?2.81%, and the average value is 2.18%. Geochemical characteristics show a rich organic matter and high maturity. Reservoir space can be divided into two categories: pores and cracks, in which intergranular pores, organic pores and structural fractures are dominant. The shale reservoir development in the study area is affected by the sedimentary environment, shale brittleness, organic matter abundance and maturity.

Lithofacies classification and its relationship with reservoir of the Lower Paleozoic Wufeng-Longmaxi Formation in the eastern Sichuan Basin

Zhu Yiqing， Wang Xingzhi， Feng Mingyou， Li Ke

2016, Vol.28(5): 59–66 Abstract ( 434 ) PDF (861 KB) ( 751 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.007

With the establishment of the “Chongqing Fuling” national demonstration zone of shale gas, organic?rich shale of the Lower Paleozoic Wufeng?Longmaxi Formation has become a key research objective in the eastern Sichuan Basin, and a larger number of relevant research results have been obtained. However, there has been a great divergence in the scheme of the shale lithofacies classification. The quartz content, quartz genesis and shale lamina type were applied to divide the shale lithofacies based on field geological profile, core observation and shale structure component. According to the gas content, total organic carbon content and quartz content of the Well WQ2 in the eastern Sichuan Basin, the relationships between shale lithofacies and reservoir properties were evaluated. The shale lithofacies was divided into seven types: silicon?poor laminar shale facies, silicon laminar shale facies, silicon?rich laminar shale facies, silicon?poor non?laminar shale facies, silicon non?laminar shale facies, silicon?rich non?laminar shale facies and biological siliceous shale facies. It is considered that the silicon non?layer shale facies is favorable for shale gas accumulation in the eastern Sichuan Basin.

Controlling factors for shale gas enrichment of the Lower Jurassic Dongyuemiao member in the northern Sichuan Basin

Gao Jian， Lin Liangbiao， Ren Tianlong， Huang Qichen， Yu Yu

2016, Vol.28(5): 67–75 Abstract ( 426 ) PDF (733 KB) ( 438 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.008

The Lower Jurassic shale is good for gas accumulation in northern Sichuan Basin, and its exploration has succeeded in recent years. Compared to Daanzhai member of Ziliujing Formation, the research of Dongyuemiao member of Ziliujing Formation is limited, so the potential of shale gas resources need to be further studied. The data of organic geochemistry, X diffraction and scanning electron microscopy, combined with conventional helium test and isothermal adsorption, were applied to study the geologic characteristics of organic?rich shale of Dongyuemiao member. The results show that the kerogen type is mainly Ⅲ type, the abundance of organic matter is high and its thermal evolution is in the middle mature stage. The shale composition is mainly quartz and clay minerals which are mainly composed of illite/smectite, illite, kaolinite and chlorite. The shale reservoir is composed of inorganic pores and fractures. The porosity and permeability of shale are 3.1% and 0.751 mD in average respectively, but the permeability of most of the samples is less than 0.1 mD. The porosity is correlated positively with permeability. The adsorption ability of shale is relatively strong, which is favorable for shale gas enrichment, meanwhile, it is difficult for desorption of shale gas. It is considered that Dongyuemiao member is relatively good for shale gas accumulation, and the sedimentary facies, lithology assemblage, fracture, and isolation layer are key factors for the shale gas enrichment.

Evaluation of shale gas reservoirs based on gray fuzzy theory: a case study from Longmaxi Formation in Nanchuan area, Chongqing

Fang Huihuang， Wang Jilin， Gong Yunpeng， Zhang Yating

2016, Vol.28(5): 76–81 Abstract ( 405 ) PDF (443 KB) ( 395 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.009

Shale reservoirs are characterized by much influencing factors, complicated relationship between porosity and permeability, as well as strong heterogeneity, so it is difficult to evaluate. In order to determine the weight of eva?luation parameters for shale gas reservoirs, Longmaxi shale in Nanchuan area of Chongqing was taken as an example, and the gray correlation analysis method and fuzzy comprehensive evaluation method were applied to evaluate the shale reservoir quality. The result shows that the total organic carbon content （TOC）, vitrinite reflectance （Ro）, effective thickness, porosity, brittle mineral content and permeability are the main factors affecting the shale reservoir quality, and the weights are 0.257 9, 0.133 1, 0.119 1, 0.149 6, 0.139 2 and 0.201 1, respectively. The comprehensive evalua?tion factor of shale reservoir is 0.41?0.93 through the fuzzy mathematics calculation of each parameter. On this basis, the distribution of shale gas reservoirs of Longmaxi Formation in Nanchuan area was predicted.

Lithofacies paleogeographic characteristics in the Late Triassic in the North China area

Lin Yuxiang， Zhu Chuanzhen， Zhao Chengjin， Wu Yuchen

2016, Vol.28(5): 82–90 Abstract ( 410 ) PDF (929 KB) ( 571 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.010

There are few studies on the Late Triassic lithofacies paleogeography in North China, which leads to little understanding of sedimentary pattern and evolution law. Under the guidance of sequence stratigraphy theory, combined with the formation development characteristics, the Upper Triassic in North China area was divided into two isochronous stratigraphic units, Carnian and Norian?Rhaetian, and the lithofacies paleogeographic maps were compiled respectively. During the Late Triassic, the topography of the North China area is lower in the west than that in the east, the stratum is thicker in the west than that in the east, and its sedimentary type is dominated by nonmarine deposits. The main sedimentary area in the North China area is mainly located in the Ordos Basin and the southern North China. The Ordos Basin is an open inland depression based on fluvial?lacustrine clastic sedi?ments, whose lithofacies is coarse in the north and fine in the south, and stratigraphic thickness is thin in the north and thick in the south, so the sedimentary center is near the south, and oil and gas resources of the Upper Triassic are mainly distributed in the central and western areas of the basin. The main sedimentary types in the southern North China are fan delta facies, fluvial facies and shore?shallow lacustrine facies, and the sedimentary center and sub?sidence center continuously migrated to the northwest. Sedimentary formation is mainly developed in Jiyuan depression and scattered in other areas. Due to the poor reservoir properties, the oil and gas resources of upper Triassic are scarce. The study on lithofacies paleogeographic characteristics of Late Triassic in the North China area reveals the laws of basin evolution, sedimentary system, source rock, reservoir distribution and their mutual relationships in that period. It is considered that the Late Triassic in the North China area mainly exists three types of source?reservoir?cap rock assemblages, including self?source and self?reservoir，up?source and down?reservoir, and down?source and up?reservoir. It is pointed out that Yanding delta, Huanxian delta, Tianshuipu delta and Huanxian?Ganquan area of Ordos Basin and Jiyuan area are favorable for hydrocarbon exploration.

Sedimentary characteristics and favorable reservoir distribution of the upper submember of the third member and the lower submember of the first member of Shahejie Formation in Lixian Slope

Chen Ji， Xu Fengqiang， Liu Chao， Cui Junfeng， Pan Wenli， Xie Lianying

2016, Vol.28(5): 91–98 Abstract ( 407 ) PDF (824 KB) ( 379 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.011

In recent years, fine exploration target of lithologic?stratigraphic reservoirs has been proposed for Lixian Slope, which needs to divide and re?understand the sedimentary facies more clearly. Through core and logging data, the sedimentary characteristics of the upper submember of the third member and the lower submember of the first member of Shahejie Formation were studied, and the distribution of favorable reservoir was determined. Braided channel facies and braided river flood plain facies are developed in the upper submember of the third member of Shahejie Formation, while braided river delta front subaqueous distributary channel and shallow?shore lake beach bar are developed in the lower submember of the first memeber of Shahejie Formation. Based on the distribution characteristic of favorable reservoirs, the sand bodies with reservoir properties from good to poor are as following: braided river delta front subaqueous distributary channel, braided river channel, shallow?shore lake beach bar, braided river delta front mouth bar. During the sedimentary period of the upper submember of the third member of Shahejie Formation, braided channel next to flood plain argillaceous source rocks are developed in Tongkou area and Xinqiao?Jiuchen area, and these areas are favorable for lithologic?stratigraphic reservoirs exploration. During the sedimentary period of the lower submember of the first member of Shahejie Formation, braided river delta front subaqueous distributary channel and shallow?shore lake beach bar are developed in Jiucheng?Xiliu areas, and these areas are favorable for looking for exploration potential area .

Restoration of formation compaction and inversion of deposition rate in Dianqianbei exploration area

Zhang Tingshan， Zhang Zhicheng， Wu Kunyu

2016, Vol.28(5): 99–106 Abstract ( 337 ) PDF (570 KB) ( 444 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.012

The Dianqianbei exploration area is a potential shale gas development zone, located in the southern margin of the Sichuan Basin. In order to identify the restoration of formation compaction and inversion of deposition rate, this paper established the Upper Ordovician to Quaternary model of layered acoustic and porosity with depth by using optimization models combined with the traditional methods, then carried out layered back ripping based on the principle of rock skeleton unchanged, acquired the original formation sedimentary thickness and segmented deposition rate, and discussed the relationship between the deposition rate and the abundance of organic matter of shale formation. The results show that the deposition rate is lower and tow?wave like in Dianqianbei area. It increased rapidly to its peak and dropped in early period, then climbed up slowly and downed to valley in later period. The deposition rates of Silurian Longmaxi Formation and Loureping Formation are 77.97 m/Ma and 113.47 m/Ma respectively. The shelf environment with slow deposition rate is beneficial to enhance the organic matter abundance of shale. The results are references for researching stratigraphic burial evolution and shale gas exploration and development.

Using log data to calculate the organic matter abundance in shale：a case study from Longmaxi Formation in Changning area, southern Sichuan Basin

Hu Xi， Wang Xingzhi， Li Yizhen，et al

2016, Vol.28(5): 107–112 Abstract ( 374 ) PDF (440 KB) ( 521 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.013

Sufficient organic matter is the material base of hydrocarbon generation. Hence, the potential of hydrocarbon generation highly depends on the organic matter abundance. To obtain accurate organic matter abundance in shale is important for the exploration and development of shale gas. Taking the shale in the lower section of Longmaxi Formation in Changning area in southern Sichuan as an object, and considering TOC content as the evaluating parameter of the organic matter abundance, this paper worked out three calculation formulas for getting TOC content according to the correlation between different well logging data and testing TOC content, then verified the calculation results and analyzed the error. The result shows that the formulas of Δ lg R-DEN method and DEN?U multiple regression method are with larger correlation coefficients and the calculation results coincide well with the TOC content of sample analysis. In single well, at the bottom of the lower section of Longmaxi Formation, the TOC content is higher than that in the upper part and it obviously decreased from bottom to top. The result of DEN?U multiple regression method shows the minimum error and strong adaptability, it can be widely applied in Changning area.

Quantitative study of the effect of cavern width on reflection amplitude of migration section

Li Fanyi， Di Bangrang， Wei Jianxin， et al

2016, Vol.28(5): 113–116 Abstract ( 390 ) PDF (294 KB) ( 481 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.014

In recent years, a phenomenon that reflection amplitude of migration section increases with the cavern width was proposed in researches about the seismic response of carbonate cavern reservoir. Based on the concept of spatial wavelet, the relationship between reflection amplitude of migration section and the width of geological body was discussed by analyzing the horizontal trace amplitude function of horizontal geologic body derived from the focal beam theory, and the results from the theoretical study were verified through numerical and physical seismic forward modeling experiments. The result shows that when the geologic body width is less than the critical width of amplitude, the reflection amplitude of migration section increases with the width of geologic body, and when the geologic body width is larger than the critical width of amplitude, the influence of geologic body width on reflection amplitude of migration section is weakly. The critical width of amplitude is proportional to the seismic wavelength, and is inversely proportional to the sine of the maximum emergence angle. In practical, the critical width of amplitude can be obtained by seismic forward modeling. This research is favorable for the quantitative study of seismic amplitude of small geologic bodies.

Application of modified unbiased grey model to the prediction of oil and gas field production

Huang Quanhua， Fu Yunhui， Lu Yun， Chen Chong， Liu Tong

2016, Vol.28(5): 117–122 Abstract ( 285 ) PDF (376 KB) ( 447 )

doi: https://doi.org/1673-8926（2016）05-0117-06

There is no inherent deviation in unbiased grey model which can improve the prediction accuracy to a certain extent. However, if use unbiased grey model directly in the actual application, the predicted results can not meet the requirements of prediction accuracy. The power function method and metabolism method were applied to improve the unbiased grey model, and a modified unbiased grey model was proposed. Based on the data of annual oil production of oilfield, unbiased grey model, power function?unbiased grey model and modified unbiased grey model were established respectively, and then the predicted results by these models were compare with actual oil production. The results show that the modified unbiased grey model has higher prediction accuracy than the other two models. The average relative error is only 5.53%, the small error probability is greater than 0.95, and the mean square deviation ratio is 0.34. The results predicted by the modified unbiased grey model have high fitting degree with actual oil production, so this model can be used to predict oil and gas field production.

Another discussion on slippage effect

Li Chuanliang， Zhu Suyang， Liu Donghua， Nie Kuang， Deng Peng

2016, Vol.28(5): 123–129 Abstract ( 1141 ) PDF (465 KB) ( 632 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2016.05.016

Gas permeability of rock is higher than liquid permeability with high dependence of pressure, which is considered to be caused by slippage effect or Klinkenberg effect. Slippage effect means that gas flows through pores without any friction with the wall of pores, which is a wrong view to permeability measurement. The high pressure dependence of gas permeability is the result of misuse of gas viscosity. Gas viscosity changes dramatically with pressure under low pressure condition, but a certain gas viscosity is chosen to determine the gas permeability in laboratory. Slippage effect makes the measurement of gas viscosity impossible. Irregular thermal motions of gas molecules lead to collide into walls of pores at random, which prevents the gas molecules slip from walls of pores. The gas permeability of rocks is higher than liquid permeability, which is the result of comparison of fluid molecule size with the pores of rock. There is no free molecular motion in discrete form underground at all. A pore with only a few methane molecules in it is not worth being exploited, and is not worth being studied. Slippage effect does not make any sense for production practice. It is suggested not to take the slippage correction for gas permeability measurement.