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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
DOI: 10.1306/02072219057
Mechanism and continuity of gypsum smears in the East Qiulitage anticline, Kuqa foreland basin, China
Tong Wu,1 Xiaofei Fu,2 Haixue Wang,3 Mingxu Lu,4 Lingdong Meng,5 and Lei Gong6
1Key Laboratory of China National Petroleum Corporation (CNPC) Fault
Controlling Reservoir and Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development, Ministry of Education, Northeast Petroleum University, Daqing, Heilongjiang, China; [email protected]
2Key Laboratory of CNPC Fault
Controlling Reservoir and Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development, Ministry of Education, Northeast Petroleum University, Daqing, Heilongjiang, China; [email protected]
3Key Laboratory of CNPC Fault
Controlling Reservoir, Northeast Petroleum University, Daqing, Heilongjiang, China; [email protected]
4Daqing Oilfield Company, Daqing, Heilongjiang, China; [email protected]
5Key Laboratory of Oil & Gas Reservoir and Underground Gas Storage Integrity Evaluation of Heilongjiang Province and Key Laboratory of Mechanisms of Oil & Gas Accumulation and Source Evaluation of Heilongjiang Province, Daqing, Heilongjiang, China; [email protected]
6College of Geosciences, Northeast Petroleum University, Daqing, Heilongjiang, China; [email protected]
Abstract
Smears are formed when faults cross-cut layered sequences. They have been observed within mudstone, shale, siltstone, carbonate, coal, and others. Gypsum smears were observed on a section of the East Qiulitage anticline in the Kuqa foreland basin when describing segmented reverse faults. Samples including gypsum and mudstone were collected to study why gypsum developed smears instead of mudstone. Based on mechanical tests, we investigated the formation mechanism of gypsum smears. The uniaxial compressive strength tested using a Schmidt hammer and the peak strength and cohesion tested using a triaxial test system at different confining pressures suggest that mudstone is stronger than gypsum; as the confining pressure increases, the strength contrast increases, and gypsum is more ductile than mudstone. Finally, we propose that the competence contrast between layers is the most fundamental factor controlling the formation of smears in the process of fault
deformation. Once a smear is formed, the
fault
throw and source bed thickness control its continuity. The gypsum smear factor derived from the shale smear factor is used to evaluate the continuity of sheared gypsum smears, which are continuous where the gypsum smear factor is 3.5–4 or less. Faults seal when smears are continuous; determining the mechanism and continuity of smears is important in cross-
fault
fluid flow problems, especially in oil and gas transport situations.
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