Evaluation of the exploration prospect and risk of marine gas shale, southern China: A case study of Wufeng-Longmaxi shales in the Jiaoshiba area and Niutitang shales in the Cen’gong area

2021 ◽  
Author(s):  
Qiyang Gou ◽  
Shang Xu ◽  
Fang Hao ◽  
Yangbo Lu ◽  
Zhiguo Shu ◽  
...  
Keyword(s):  
Shale Gas ◽  
Southern China ◽  
Hydrocarbon Generation ◽  
Material Base ◽  
Pore Connectivity ◽  
Significant Difference ◽  
Dip Angle ◽  
Angle Fractures ◽  
Hydrothermal Activities

The Wufeng-Longmaxi shales and the Niutitang shales are the most important organic-rich marine shales in southern China. To fully understand the significant difference in drilling results between the two sets of shales, the accumulation conditions of shale gas were systematically compared. The Niutitang shales have a superior material base of hydrocarbon generation for higher total organic carbon than the Wufeng-Longmaxi shales. Due to the influence of hydrothermal activities and carbonization of organic matter, however, the porosity, pore volume, pore size, and pore connectivity of Niutitang shales is obviously lower than that of Wufeng-Longmaxi shales. The natural fractures of Wufeng-Longmaxi shales are dominated by horizontal bedding fractures, and most of them are filled by calcite. By contrast, the high dip-angle fractures are more developed in the Niutitang shales. Especially, these fractures remain open in stages during the process of serious uplift and denudation movements. Thus, the seal conditions of the Niutitang shales are poor, which is further not conducive to the enrichment of shale gas. Our work also suggests that the exploration and development of highly over matured marine shales in southern China should follow the principle of “high to find low, and strong to find weak.”

scholarly journals Coevolutionary Dynamics of Organic-Inorganic Interactions, Hydrocarbon Generation, and Shale Gas Reservoir Preservation: A Case Study from the Upper Ordovician Wufeng and Lower Silurian Longmaxi Formations, Fuling Shale Gas Field, Eastern Sichuan Basin

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Zhijun Jin ◽  
Haikuan Nie ◽  
Quanyou Liu ◽  
Jianhua Zhao ◽  
Ruyue Wang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Sichuan Basin ◽  
Hydrocarbon Generation ◽  
Upper Ordovician ◽  
Gas Field ◽  
Pressure System ◽  
Lower Silurian ◽  
Eastern Sichuan Basin ◽  
Eastern Sichuan

Shale gas deposits are self-sourced, self-accumulating, and self-preserving in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation of the Fuling Shale Gas Field in the eastern Sichuan Basin. They were both seemingly mixed by secondary oil cracking and kerogen cracking gases during the high maturation window. The reservoir space primarily consists of mineral pores and organic matter (OM) pores, and the shale gas was mainly trapped by a high-pressure system. In this study, the Fuling O3w-S1l Shale Gas Field in the eastern Sichuan Basin was used as a case study to discuss the coevolutionary process and organic-inorganic interactions of hydrocarbon generation, accumulation, and preservation. The results indicate that the processes and mechanisms of organic-inorganic interactions and coevolution of hydrocarbon generation and reservoir preservation are quite different among the shale graptolite zones (GZ) with respect to hydrocarbon generation, types and characteristics of shale gas reservoirs, seal characteristics, and their spatiotemporal relations. In the WF2-LM4 GZ, the favorable OM, biogenic authigenic quartz and organic-inorganic interactions are highly coupled, leading to the high level of coevolution demonstrated within the field, as well as to the favorable conditions for shale gas accumulation. Conversely, the overlying LM5-LM8 GZ seemingly exhibits early densification and late charge and has a reverse mode of reservoir development (i.e., low degree of coevolution). These two coevolutionary processes were conducive to the development of a high degree of spatiotemporal matching between the reservoir (i.e., WF2-LM4 GZ) and the seal (i.e., LM5-LM8 GZ). This is due to underlying differences in their coevolutionary histories. The synthetic work presented here on the coevolutionary processes and mechanisms of formation for organic-inorganic interactions and hydrocarbon generation and reservoir preservation reveals insights into the driving mechanisms of shale gas enrichment, providing a basis for effectively predicting favorable enrichment intervals for shale gas worldwide.

scholarly journals The Genetic Mechanism and Evolution Process of Overpressure in the Upper Ordovician–Lower Silurian Black Shale Formation in the Southern Sichuan Basin

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 238
Author(s):  
Xiaoqi Wang ◽  
Yanming Zhu
Keyword(s):  
Shale Gas ◽  
Southern China ◽  
Pressure Coefficient ◽  
Fluid Pressure ◽  
Initial Pressure ◽  
Gas Production ◽  
Controlling Factors ◽  
Formation Mechanisms ◽  
Hydrocarbon Generation ◽  
Upper Ordovician

The overpressure phenomenon is a widespread occurrence in unconventional shale gas reservoirs. Multiple overpressure shale gas fields were discovered in southern China, and there is no doubt that the gas production per well increases with increasing pressure coefficient (the ratio of the reservoir fluid pressure to the corresponding normal hydrostatic pressure). Thus, successful evaluation and production strategies of organic-rich shale deposits require an understanding of the evolution of the pressure coefficient and its controlling factors in these deposits. In this paper, drilling engineering data of a typical well were collected, and clay mineral tests and overburden diffusion coefficient experiments were conducted. Based on multiphysics simulations, this paper analyzes the overpressure characteristics and formation mechanisms of overpressure in the Longmaxi Formation shale, as well as its geological evolution and controlling factors. The results show that the large amount of shale gas is the cause of overpressure formation rather than disequilibrium compaction. The simulation results show that pressure coefficients of the typical well range from 0.84 to 1.49. The current pressure coefficient increases with increasing pressure coefficient after the last hydrocarbon generation. A large initial pressure coefficient (>1.9), short lifting time (<100 Ma) and small lifting amplitude (<4000 m) are favorable for the preservation of shale gas.

Sign in / Sign up

Export Citation Format

Share Document