Fracture Characteristics and Quantitative Prediction of Sand-Mudstone Interbedded Tight Reservoir

Abstract

The rocks of Bashjiqike Formation in Kuqa depression are thick-very thick-bedded sandstones interbedded with siltstone and thin-bedded mudstone. The structural fractures are well developed in the formation, which were caused by multi-stage tectonic movements. Fracture development are not only controlled by regional stress field, faults, and folds, but also significantly affected by mudstone interlayer and lithologic interface. Based on core observation, CT scanning and imaging logging interpretation, the fracture development characteristics of sand-mudstone interbedded rock combinations are analyzed. The fractures developed in thin interbedded distributary channel sandstones have high linear density, dominated by dense netlike fractures. The fracture density in the middle of the thick-bedded sandstones is low, and in the upper and lower ends is high. A series of compressive tensile stress conversion fractures are developed near the sand mudstone interface. The fractures are first generated in the sandstone and gradually expand to the mudstone by penetrating or semi penetrating mudstone or terminating at sand-mud interface. Based on the study of single well fracture characteristics and rock mechanics experiment, a 3 D geomechanical model of interbedded reservoirs of KS 2 block in Kuqa depression is established. Through the applicability analysis of classical rock strength theory, the failure criterion of composite rock is defined. Using the platform of ANSYS elastic-plastic finite element module, the paleotectonic stress field simulation and spatial fracture distribution prediction are carried out. According to the simulation results, the fractures in the thin-interbedded reservoirs and near the interface of sand and mudstone have the highest density, followed by those in thick sandstone, and the fracture density of thick mudstone is the lowest; fractures with large aperture are most developed in the high part of the structure; meanwhile, fracture aperture tends to decrease with the increase of depth. This study addresses a new idea for fracture prediction of interbedded reservoirs, and the prediction results can provide a geological basis for development and deployment of KS 2 gas reservoir.

Copyright 2022, IFEDC Organizing Committee.

This paper was prepared for presentation at the 2022 International Field Exploration and Devel-opment Conference in **’an, China, 16–18 November 2022.

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