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Fault and Fracture Pattern Controls Hydrocarbon Accumulation: An Integrated Structural, Geomechanical and Microscopic Study in the Northern Slope of the Tazhong Uplift in Tarim Basin, NW China


Fault and fracture pattern controls hydrocarbon accumulation: An integrated structural, geomechanical and microscopic study in the northern slope of the Tazhong uplift in Tarim basin, NW China

FeiNing, Jinbiao Yun, zhongpei Zhang

Exploration & Production Research Institute, SINOPEC

Abstract: Recently, a newly drilled well around strike-slip faults in the northern slope of Tazhong uplift reached a production of more than 150 cubic meters per day. It has been proved a huge potential in oil and gas exploration near the strike-slip fault in such area. Beside fault and fracture pattern which influence reservoir quality, production contribution also comes from the capacity of cap sealing which is also one of the key factors in hydrocarbon production.

In order to understand the characteristic of fault and fracture pattern, capacity of cap sealing, and their relationship on hydrocarbon accumulation. After fine interpretation on geometry of strike-slip fault and fracture network, 5 groups of carbonate rock samples in the Northern Slope of Tazhong uplift were selected, they are all from Yingshan Formation which is in upper part of Lower Ordovician and at the same depth in the different wells, geomechanical analysis is employed to test the cap rock’s critical confining pressure of brittle to ductile transition, microscopic method such as X ray diffraction and rock CT scan methods were used to understand the characteristic and micro structures of fracture networks in brittle and ductile state respectively and the sealing capacity affected by such difference was analyzed..

The results are listed as follows: 1) the strike-slip fault is characterized by segmentation and extensional part have more abundant fracture network; 2) the critical confining pressure of carbonate rocks of Yingshan Formation from brittle to ductile is calculated as 74.16Mpa which goes to the depth of 6249m; 3) the content of calcite and quartz in carbonate rocks affects the depth of brittle to ductile transition; 4) wave impedance value of rock in ductile deformation is bigger than that in brittle deformation; 5) rock CT scan shows that micro pores of sample contract when they are in ductile deformation.

In addition to physical property of the cap rock itself, micro fractures generated by structural events is an important factor that control fault and fracture pattern and affect the effectiveness of cap rocks. We analyzed the experiment results integrated with comprehensive static micro sealing capacity examination of carbonate cap rocks and conclude that reservoir-cap assemblage developed below brittle-ductile transition depth is an optimal target for hydrocarbon exploration.

2019 AAPG Annual Convention & Exhibition

19-22 May 2019 San Antonio, Texas