Control of Fault Related Folds on Fracture Development in Kuqa Depression, Tarim Basin

Abstract

In the multi-stage evolution process, the fault-related folds in the Kuqa depression are derived or associated with a large number of structural fractures, and the spatial distribution is very complicated. It is of great significance for gas field development to know the distribution law and main control factors of fractures. Taking Dabei, Keshen, Dina2 and Kela2 gas fields as examples, the fracture development characteristics of different fold types are analyzed by using core, imaging logging and seismic data, and the control effect of fold style evolution on fracture development is revealed by using finite element simulation method. Fracture development has obvious correlation with reservoir quality and fold style. The density of fractures in Dabei and Keshen gas fields with low porosity are much higher than that in Dina and Kela gas fields with relatively high porosity. Dabei and Keshen anticlines, are dominated by shear network fractures and exist less tension fractures due to their low amplitude (relatively large interlimb angle), while the tension fracture proportion increases within Dina and Kela anticlines due to their high amplitude (relatively small interlimb angle). The high-value areas of tension fracture is mainly located near the cores of anticlines and the faults, while that of shear fracture is obviously correlation with faults. Further study shows that open folds with interlimb in range of 120º–70º have significant influence and controlling on effectiveness of fractures, but they are not apparent in the gentle folds with interlimb angle in range of 180º–120º. The fracture development heterogeneity of the imbricated double thrust structure with very different scale fracture is stronger than that of the back thrust structure with relatively small scale difference fracture. Finite element simulation showing the development and distribution of structural fractures are obviously controlled by fold uplifting amplitude, distance from fault plane and fault sliding displacement, especially when the fold uplifting amplitude is in the range of 410–450 m, the fracture density value is the largest. This study has effective guidance for development plan of newly discovered gas fields and comprehensive management of developed gas fields of the piedmont thrust belt in Kuqa depression.KeywordsKuqa depressionFault related foldFractureFinite element simulation