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Fracture Patterns and Petrophysical Properties in the Kuqa Depression, Tarim Basin, and Their Relationship With Regional Folding


The Kuqa Depression of the Tarim Basin hosts a prolific hydrocarbon system. The main reservoirs are characterized by tight sandstone with low-porosity and low-permeability, buried at more than 5000 m depth. In the Bashijiqike Formation, hydrocarbon production mainly comes from secondary porosity created by dissolution and fracturing. The Bashijiqike formation have undergone multiple phases of deformation associated with burial, uplift, folding, thrusting and rapid subsidence. With the aim of evaluating the reservoir quality, we studied fracture patterns and petrophysical properties of the Bashijiqike formation with data collected from Dabei and Kelasu anticlines. We document four fracture systems whose distribution is related to regional stress field, thrusting and local folding. In the Kelasu Anticline, the North-South system is parallel to the maximum horizontal principle stress, showing higher intensity closed to the ridge. Calcite veins filled in the fractures show a characteristic of bending, indicating they form earlier than folding or during folding. The East-West system is parallel to the fold axis, showing a trending of decreasing fracture intensity from limbs to hinge end to crest. Fractures observed on the cores show existence of E-W shearing. Crosscutting relationships suggest that the shearing fractures formed earlier than the tension fractures that due to the local outer arc extension. The Northeast-Southwest and Northwest-Southeast systems are symmetrical with respect to the fold. In the Dabei Anticline, the Northwest-Southeast system parallels to the maximum horizontal principle stress, showing higher fracture intensity than other systems. The Northeast-Southwest system parallels to the fold axis, showing lower fracture intensity at crest with local increments at the limbs. In addition, we analyzed petrophysical properties include porosity and permeability of the Bashijiqike formation in relation to their structural position within folds. The higher porosity and permeability are recorded in the hinges and forelimbs of the both anticlines. It is indicated the best reservoir quality is associated with dissolution and fracturing. The results show how fracture distribution and petrophysical properties depends on structural position and fold evolution. Our work illustrates the folding serve as controls on the fracture patterns and petrophysical properties, providing favorable reservoir targets for prospecting in the compressional basin.