Differences of Main Enrichment Factors of S1l11-1 Sublayer Shale Gas in Southern Sichuan Basin

In this study, shale cores from 20 wells in the S1l11-1 sublayer of Longmaxi Formation buried in shallow shale (<3500 m) and deep shale (>3500 m) in the southern Sichuan Basin, China were collected to compare their pore structures and gas-bearing properties using multiple experiments. Results showed that the deep layer has relatively lower brittle mineral content, which is disadvantageous in terms of the higher requirements it imposes on hydraulic fracturing. Results also showed that the most important factor controlling the differential enrichment of S1l11-1 shale gas in southern Sichuan Basin is porosity. Moreover, the porosity composition of shallow shale and deep shale has significant differences: the porosity of shallow shale is dominated by organic pores, while for deep shale, both organic and inorganic pores are important. The inorganic pores provide significant storage space for free gas in deep shale; their contribution warrants more attention. We also found that the difference in organic porosity of the shallow and deep shale samples resulted from large differences in pore development ability, while the highest inorganic porosity was concentrated near the optimal mineral composition when the content of quartz plus feldspar plus pyrite was about 70%. This study revealed the primary factor controlling the difference in gas content between shallow and deep shale and detailed the characteristics of microscopic pore structure, providing a basis for the exploration and development of deep shale gas in the Wufeng-Longmaxi Formation in the southern Sichuan Basin.

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Coupling between Source Rock and Reservoir of Shale Gas in Wufeng-Longmaxi Formation in Sichuan Basin, South China

Energies ◽

10.3390/en14092679 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2679

Author(s):

Yuying Zhang ◽

Shu Jiang ◽

Zhiliang He ◽

Yuchao Li ◽

Dianshi Xiao ◽

...

Keyword(s):

Source Rock ◽

Shale Gas ◽

Sichuan Basin ◽

Gas Content ◽

Potential Zone ◽

Hydrocarbon Generation ◽

Gas Generation ◽

Longmaxi Formation ◽

Siliceous Shale ◽

Organic Pores

In order to analyze the main factors controlling shale gas accumulation and to predict the potential zone for shale gas exploration, the heterogeneous characteristics of the source rock and reservoir of the Wufeng-Longmaxi Formation in Sichuan Basin were discussed in detail, based on the data of petrology, sedimentology, reservoir physical properties and gas content. On this basis, the effect of coupling between source rock and reservoir on shale gas generation and reservation has been analyzed. The Wufeng-Longmaxi Formation black shale in the Sichuan Basin has been divided into 5 types of lithofacies, i.e., carbonaceous siliceous shale, carbonaceous argillaceous shale, composite shale, silty shale, and argillaceous shale, and 4 types of sedimentary microfacies, i.e., carbonaceous siliceous deep shelf, carbonaceous argillaceous deep shelf, silty argillaceous shallow shelf, and argillaceous shallow shelf. The total organic carbon (TOC) content ranged from 0.5% to 6.0% (mean 2.54%), which gradually decreased vertically from the bottom to the top and was controlled by the oxygen content of the bottom water. Most of the organic matter was sapropel in a high-over thermal maturity. The shale reservoir of Wufeng-Longmaxi Formation was characterized by low porosity and low permeability. Pore types were mainly <10 nm organic pores, especially in the lower member of the Longmaxi Formation. The size of organic pores increased sharply in the upper member of the Longmaxi Formation. The volumes of methane adsorption were between 1.431 m3/t and 3.719 m3/t, and the total gas contents were between 0.44 m3/t and 5.19 m3/t, both of which gradually decreased from the bottom upwards. Shale with a high TOC content in the carbonaceous siliceous/argillaceous deep shelf is considered to have significant potential for hydrocarbon generation and storage capacity for gas preservation, providing favorable conditions of the source rock and reservoir for shale gas.

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A Quantitative Evaluation of Shale Gas Content in Different Occurrence States of the Longmaxi Formation: A New Insight from Well JY‐A in the Fuling Shale Gas Field, Sichuan Basin

Acta Geologica Sinica - English Edition ◽

10.1111/1755-6724.13816 ◽

2019 ◽

Vol 93 (2) ◽

pp. 400-419 ◽

Cited By ~ 5

Author(s):

Ling TANG ◽

Yan SONG ◽

Qianwen LI ◽

Xiongqi PANG ◽

Zhenxue JIANG ◽

...

Keyword(s):

Quantitative Evaluation ◽

Shale Gas ◽

Sichuan Basin ◽

Gas Content ◽

Gas Field ◽

Longmaxi Formation

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Factors Controlling Shale Reservoirs and Development Potential Evaluation: A Case Study

Geofluids ◽

10.1155/2021/6661119 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Chao Luo ◽

Hun Lin ◽

Yujiao Peng ◽

Hai Qu ◽

Xiaojie Huang ◽

...

Keyword(s):

Shale Gas ◽

Mineral Content ◽

Gas Content ◽

Longmaxi Formation ◽

Development Potential ◽

Reservoir Characteristics ◽

Lower Silurian ◽

Single Well ◽

Shale Reservoir ◽

Shale Reservoirs

The shale of the Lower Silurian Longmaxi Formation is an important gas-producing layer for shale gas development in southern China. This set of shale reservoir characteristics and shale gas development potential provide an important foundation for shale gas development. This study takes wellblock XN111 in the Sichuan Basin, China, as an example and uses X-ray diffraction (XRD), scanning electron microscopy (SEM), isothermal adsorption, and other techniques to analyze the shale reservoir characteristics of the Lower Silurian Longmaxi Formation. The results show that the Lower Silurian Longmaxi Formation was deposited in a deep-water shelf environment. During this period, carbonaceous shale and siliceous shale characterized by a high brittle mineral content ( quartz > 40 wt . % , carbonate mineral > 10 wt . % ) and a low clay mineral content (<30 wt.%, mainly illite) were widely deposited throughout the region. The total organic carbon (TOC) content reaches up to 6.07 wt.%, with an average of 2.66 wt.%. The vitrinite reflectance is 1.6–2.28%, with an average of 2.05%. The methane adsorption capacity is 0.84–4.69 m3/t, with an average of 2.92 m3/t. Pores and fractures are developed in the shale reservoirs. The main reservoir space is composed of connected mesopores with an average porosity of 4.78%. The characteristics and development potential of the shale reservoirs in the Lower Silurian Longmaxi Formation are controlled by the following factors: (1) the widespread deep-water shelf deposition in wellblock XN111 was a favorable environment for the development of high-quality shale reservoirs with a cumulative thickness of up to 50 m; (2) the high TOC content enabled the shale reservoir to have a high free gas content and a high adsorptive gas storage capacity; and (3) the shale’s high maturity or over maturity is conducive to the development of pores and fractures in the organic matter, which effectively improves the storage capacity of the shale reservoirs. The reservoir characteristic index was constructed using the high-quality shale’s thickness, gas content, TOC, fracture density, and clay content. Using production data from shale gas wells in adjacent blocks, a mathematical relationship was established between the Estimated Ultimate Recovery (EUR) of a single well and the Reservoir Characteristics Index (Rci). The EUR of a single well in wellblock XN111 was estimated.

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Classification and Evaluation on Shale Gas Reservoir for Wufeng-Longmaxi Formation in Chuannan Area, Sichuan Basin

Lithosphere ◽

10.2113/2021/3364731 ◽

2021 ◽

Vol 2021 (Special 1) ◽

Author(s):

Jianlin Guo ◽

Chengye Jia ◽

Dongbo He ◽

Fankun Meng

Keyword(s):

Shale Gas ◽

Sichuan Basin ◽

Gas Content ◽

Brittleness Index ◽

Type I ◽

Gas Reservoir ◽

Longmaxi Formation ◽

Positive Correlation ◽

Gas Saturation ◽

Shale Gas Reservoir

Abstract Based on the comprehensive statistic and analysis on some representative geological and physical data, the classification criteria on net pay for shale gas reservoir of the Wufeng-Longmaxi formation in Shunan area, Sichuan Basin, are proposed, which include porosity (φ), gas saturation (Sg), density of rock (DEN), brittleness index (BI), and gas content (Vt). When the porosity, gas saturation, brittleness index, and gas content are larger than 3%, 30%, 40%, and 1 m3/t, respectively, and the density of rock is lower than 2.7 g/cm3, then this formation can be seen as the net pay. The application of two key parameters, gas content and brittleness index, could reflect the reservoir resource basis and fracability, respectively. The gas content has a positive correlation with porosity and total organic volume, and the brittleness index has a positive correlation with siliceous and carbonate content. According to the range of these two parameters, the net pay can be classified into three types. For type I, the gas content and brittleness index are larger than 4 m3/t and 50%, respectively. For type II, either the gas content or the brittleness index is lower than 4 m3/t and 50%. For type III, the gas content should be larger than 1 m3/t and lower than 4 m3/t, and the brittleness index is between 40% and 50%. The field application case indicates that the Wufeng formation and low member of the Longmaxi formation have good quality and mainly consist of type I and II formations. In addition, it is found that there is a positive correlation between the penetration ratio for type I formation and the testing production and estimate ultimate recovery (EUR). While this ratio is larger than 50%, the testing production rate and EUR will be over 15×104 m3/d and 8000×104 m3 with a probability of 92%, which meet the requirement of exploitation with reasonable economic benefits.

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Characteristics of Organic Matter Particles and Organic Pores of Shale Gas Reservoirs: A Case Study of Longmaxi-Wufeng Shale, Eastern Sichuan Basin

Minerals ◽

10.3390/min10020137 ◽

2020 ◽

Vol 10 (2) ◽

pp. 137

Author(s):

Guochang Wang ◽

Shengxiang Long ◽

Yongmin Peng ◽

Yiwen Ju

Keyword(s):

Organic Matter ◽

Shale Gas ◽

Sichuan Basin ◽

Pore System ◽

Gas Reservoirs ◽

Sem Images ◽

Eastern Sichuan Basin ◽

Eastern Sichuan ◽

Organic Porosity ◽

Organic Pores

Heterogeneity of organic matter (OM), including size, type, and organic pores within OM, is being recognized along with increasing study using SEM images. Especially, the contribution of organic pores to the entire pore system should be better understood to aid in the evaluation of shale reservoirs. This research observed and quantitatively analyzed over 500 SEM images of 19 core samples from Longmaxi-Wufeng Shale in the eastern Sichuan Basin to summarize the features of OM particles and OM-hosted pores and their evolution during burial. The features of organic pores as well as the embedded minerals within OM particles enables to recognize four different type of OM particles. The organic pore features of each type of OM particles were quantitatively described using parameters such as pore size distribution (PSD), pore geometry, and organic porosity. The PSD of weakly or undeformed porous pyrobitumen indicates that the large organic pores (usually 200 nm to 1 um) is less common than small pores but the major contributor to organic porosity. The organic porosity of OM particles covers a large range of 1–35%, indicating a high heterogeneity among OM particles. Based on analysis of 81 OM particles, the average of organic porosity of the five samples were calculated and ranges from 3% to 12%. In addition, samples from well JY1 have higher organic porosity than JY8. These results helped to reveal how significant the organic pores are for shale gas reservoirs. In addition to presenting many examples of OM particles, this research should significantly improve the understanding of type and evolution of OM particles and contribution of OM-hosted pores to the entire pore system of high to over mature shale.

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Sedimentary facies of marine shale gas formations in Southern China: The Lower Silurian Longmaxi Formation in the southern Sichuan Basin

Journal of Earth Science ◽

10.1007/s12583-015-0592-1 ◽

2016 ◽

Vol 27 (5) ◽

pp. 807-822 ◽

Cited By ~ 18

Author(s):

Yizhen Li ◽

Xingzhi Wang ◽

Bin Wu ◽

Guoqin Li ◽

Dule Wang

Keyword(s):

Shale Gas ◽

Sichuan Basin ◽

Southern China ◽

Sedimentary Facies ◽

Longmaxi Formation ◽

Lower Silurian ◽

Marine Shale

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The Effect of Diagenetic Evolution on Shale Gas Exploration and Development of the Longmaxi Formation Shale, Sichuan Basin, China

Frontiers in Earth Science ◽

10.3389/feart.2021.661581 ◽

2021 ◽

Vol 9 ◽

Author(s):

Jia Wang ◽

Xianfeng Tan ◽

Jingchun Tian ◽

Long Luo ◽

Xuanbo Gao ◽

...

Keyword(s):

Shale Gas ◽

Sichuan Basin ◽

Pore Space ◽

Ion Beam ◽

Central Basin ◽

Burial History ◽

Longmaxi Formation ◽

Diagenetic Evolution ◽

Basin Margin ◽

Exploration And Development

Diagenetic evolution is an important controlling factor of shale gas reservoirs. In this study, based on field outcrop and drilling core data, analytical techniques including X-ray diffraction (XRD), field emission scanning electron microscope combined with a focused ion beam (FIB-FESEM), and energy-dispersive spectroscopy (EDS) analyses were performed to determine the diagenetic evolution of the Longmaxi Formation shale and reveal the effect of diagenetic evolution on the shale gas exploration and development in the Sichuan Basin, Southwest China. The eodiagenesis phase was subdivided into two evolution stages, and the mesodiagenesis phase was subdivided into three evolution stages in the basin margin and center. Absorbed capacity and artificial fracturing effect of the Longmaxi Formation shale gas were related to mineral composition, which was influenced by sedimentary characteristics and diagenetic evolution. The diagenetic system in the basin margin was more open than that in the basin center due to a different burial history. The more open diagenetic system, with more micro-fractures and soluble constitute (e.g., feldspar), was in favor for the formation and preservation of secondary dissolved pores and organic pores in the basin margin. The relatively closed diagenetic system with stronger compaction resulted in deformation of pore space in the central basin.

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Dissolution pore types of the Wufeng Formation and the Longmaxi Formation in the Sichuan Basin, south China: Implications for shale gas enrichment

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2018.11.042 ◽

2019 ◽

Vol 101 ◽

pp. 243-251 ◽

Cited By ~ 20

Author(s):

Haikuan Nie ◽

Chuanxiang Sun ◽

Guangxiang Liu ◽

Wei Du ◽

Zhiliang He

Keyword(s):

South China ◽

Shale Gas ◽

Sichuan Basin ◽

Longmaxi Formation ◽

The Sichuan Basin ◽

Pore Types

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Logging Evaluation Method and its Application for Measuring the Total Organic Carbon Content in Shale

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.962-965.51 ◽

2014 ◽

Vol 962-965 ◽

pp. 51-54

Author(s):

Zhi Feng Wang ◽

Yuan Fu Zhang ◽

Hai Bo Zhang ◽

Qing Zhai Meng

Keyword(s):

Organic Carbon ◽

Total Organic Carbon ◽

Shale Gas ◽

Sichuan Basin ◽

Evaluation Method ◽

Organic Carbon Content ◽

Geochemical Analysis ◽

Data Logging ◽

Longmaxi Formation ◽

Sedimentary Structures

The acquisition of the total organic carbon (TOC) content mainly relies on the geochemical analysis and logging data. Due to geochemical analysis is restricted by coring and experimental analysis, so it is difficult to get the continuous TOC data. Logging evaluation method for measuring TOC is very important for shale gas exploration. This paper presents a logging evaluation method that the shale is segmented according to sedimentary structures. Sedimentary structures were recognized by core, thin section and scanning electron microscope. Taking Wufeng-Longmaxi Formation, Silurian, Muai Syncline Belt, south of Sichuan Basin as research object, the shale is divided into three kinds: massive mudstone, unobvious laminated mudstone, and laminated mudstone. TOC within each mudstone are calculated using GR, resistivity and AC logging data, and an ideal result is achieved. This method is more efficient, faster and the vertical resolution is higher than △logR method.

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