scholarly journals Accumulation Mechanism of Marine Shale Gas Reservoir in Anticlines: A Case Study of the Southern Sichuan Basin and Xiuwu Basin in the Yangtze Region

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Kun Zhang ◽  
Yan Song ◽  
Shu Jiang ◽  
Zhenxue Jiang ◽  
Chengzao Jia ◽  
...  
Keyword(s):  
Shale Gas ◽  
Sichuan Basin ◽  
Large Scale ◽  
Horizontal Stress ◽  
Burial Depth ◽  
Depth Range ◽  
Upper Ordovician ◽  
Lower Silurian ◽  
Marine Shale ◽  
Accumulation Mechanism

The study of tectonics is one of the important aspects of shale gas preservation. It is vital for understanding how to determine the enrichment regularity of marine shale gas in anticlines. This paper focuses on typical shale blocks in the southern Sichuan Basin and shale in the Upper Ordovician and the Lower Silurian. In this study, triaxial unloading tests, permeability tests perpendicular and parallel to the stratification plane, FIB-HIM tests, and inclusion analyses are carried out with real drilling data. The enrichment regularity of marine shale gas in anticlines is studied by considering 2 aspects: the angle of the limbs and the burial depth. For anticlines with adjacent synclines, the migration regularity of shale gas is considered by 3 aspects: the dynamics, channels, and processes of migration. This study reveals that a limb angle greater than 120° reflects relatively good conditions for shale gas preservation, while limb angles lesser than 70° indicate relatively poor conditions. This study also suggests that during the process of uplift, large-scale concentrated fractures will form at a certain depth range and horizontal stress field, resulting in the large loss of shale gas. The regression equation of the fractured depth (H) and the horizontal stress (S) is presented as H=15.404S−754.41 (with a correlation coefficient R2=0.6834). The stratification plane and the organic pores form the migration channel of natural gas that is horizontal to the stratification plane in shale. Under the condition of both anticlines and contiguous synclines, shale gas escapes through fractures resulting from extrusion along the anticline and the uplift effect. In addition, driven by differences in the formation pressure coefficients, shale gas is capable of migrating in a short-distance stair-type style from synclines to the adjacent anticlines. Thus, if the drilling costs allow, the well locations should be placed in the more deeply buried synclines.

Caledonian detachment deformation and deposition in the Fuling gas field of the southeastern Sichuan Basin in China: Implications for the Lower Silurian Longmaxi Shale gas exploration and production

2018 ◽  
Vol 6 (4) ◽  
pp. SN119-SN132
Author(s):  
Dengliang Gao ◽  
Taizhong Duan ◽  
Zhiguo Wang ◽  
Xiaofei Shang
Keyword(s):  
Pore Pressure ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Large Scale ◽  
Time Structure ◽  
Small Scale ◽  
Upper Ordovician ◽  
Gas Field ◽  
Lower Silurian ◽  
Southeastern Sichuan Basin

The Fuling gas field in the southeastern Sichuan Basin is the first and the largest shale gas play in China that has been producing primarily from the organic-rich shale in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation. Newly processed 3D seismic data along with well-completion data in the gas field reveal important structural, depositional, and reservoir details in the Lower Paleozoic sedimentary section. Lateral (along-stratal) variations in time structure and bed curvature demonstrate the diversity in faults that can be classified based on their orientation (regional and cross-regional), scale (small, intermediate, and large), and mode (contractional, extensional, and wrench). Vertical (cross-stratal) variations in time structure and bed curvature demonstrate that the deformational intensity increases from the Lower Cambrian to the Upper Ordovician, then decreases from the Upper Ordovician to the Silurian. Seismic isochron and facies analyses indicate that the structural deformation influenced the syntectonic deposition of turbidite sand in a channel complex above the reservoir. The pore pressure, porosity, and gas productivity of the reservoir are the highest in the central portion of the field, where small-scale faults dominate, but drop significantly at the edges of the field, where large-scale lineaments dominate. The relationships suggest that faults and fractures could either reduce or enhance pore pressure, porosity, and gas productivity, depending on their scale. Large-scale faults have the most negative impact on gas enrichment and pressure build-up, leading to reduced pressure, porosity, and productivity; whereas, small-scale ones have the least negative or even positive impact on gas enrichment and pressure build-up, leading to increased pressure, porosity, and productivity. These observations and interpretations offer new insight into the dynamic interplay among tectonic deformation, syn-tectonic sedimentation, and reservoir integrity during the Caledonian (Late Ordovician to Silurian) in the southeastern Sichuan Basin (China).

scholarly journals Basic characteristics and accumulation mechanism of Sinian−Cambrian giant highly mature and oil-cracking gas reservoirs in the Sichuan Basin, SW China

2017 ◽  
Vol 36 (4) ◽  
pp. 568-590 ◽  
Author(s):  
Bing Luo ◽  
Yu Yang ◽  
Gang Zhou ◽  
Wenjun Luo ◽  
Shujiao Shan ◽  
...  
Keyword(s):  
Natural Gas ◽  
Lower Cambrian ◽  
Sichuan Basin ◽  
Large Scale ◽  
Oil And Gas ◽  
Source Rocks ◽  
Burial Depth ◽  
Sw China ◽  
Accumulation Mechanism ◽  
Oil Cracking

Old Mesoproterozoic−Cambrian successions have been regarded as an important frontier field for global oil and gas exploration in the 21st century. This has been confirmed by a recent natural gas exploration breakthrough in the Sinian and Cambrian strata, central Sichuan Uplift, Sichuan Basin of SW China. However, the accumulation mechanism and enrichment rule of these gases have not been well characterized. This was addressed in this work, with aims to provide important guidance for the further exploration while enriching the general studies of the oil and gas geology in the old Mesoproterozoic–Cambrian strata. Results show that the gas field in the study area is featured by old target layers (Sinian–Lower Cambrian), large burial depth (>4500 m), multiple gas-bearing intervals (the second and fourth members of the Sinian Dengying Formation and the Lower Cambrian Longwangmiao Formation), various gas reservoir types (structural type and structural–lithologic type), large scale (giant), and superimposing and ubiquitous distribution. The giant reserves could be attributed to the extensive intercalation of pervasive high quality source rocks and large-scale karst reservoirs, which enables a three-dimensional hydrocarbon migration and accumulation pattern. The origin of natural gas is oil cracking, and the three critical stages of accumulation include the formation of oil reservoirs in Triassic, the cracking of oil in Cretaceous, and the adjustment and reaccumulations in the Paleogene. The main controlling factor of oil and gas enrichment is the inherited development of large-scale stable paleo-uplift, and the high points in the eastern paleo-uplift are the favorable area for ​natural gas exploration.

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