Genetic Mechanism of Intragranular Fractures in Low-Permeability Sandy Conglomerate Reservoir and Their Significance in Petroleum Exploration: A Case Study from Triassic Baikouquan Formation in Mahu Sag, Junggar Basin

Abstract

Abstract: The sandy conglomerate reservoirs of Baikouquan formation of Mahu sag in northwestern margin of Junggar basin are low-porosity and low-permeability reservoirs, where the intragranular fractures act as the important flow paths. Less researches have been made in terms of genetic mechanism and development of intragranular fractures at home and abroad. This paper systematically analyzes the identifying characteristics, genetic mechanism, development process and distribution of intragranular fractures in low-porosity and low-permeability sandy conglomerate reservoirs, according to the macroscopic and microscopic characteristics of intragranular fractures development, combining with drilling and seismic data, by means of relationship characterization of the palaeotectonic stress value-the intragranular fractures, and intragranular fracture physical modeling experiment. It is considered that the intragranular fractures in Baikouquan formation are structural-diagenetic fractures genetically, the generation of the fractures is related to the properties of compression, shearing and torsion, internal defect of grains, tectonic stress and stress effect; the main influence of intragranular fractures on the reservoir is to improve reservoir permeability, and the effective configuration of intragranular fractures in coarse grains-intergranular matrix pores among sand grains-microfissures is the key factor to generate high-quality and high-efficiency reservoirs of Baikouquan formation; the intragranular fractures are mainly distributed in Middle-Lower Triassic Baikouquan formation vertically and mostly in Wuerhe-Xiazijie faulted belt in plane. The development degrees of intragranular fractures in Karamay-Baikouquan and Wuerhe-Xiazijie faulted belts are different due to the changes of stress effect mode and rigid grain content. Constrained by thrust fault distribution, the development degree of intragranular fractures is weakening from the faulted zone to slope area, but tends to increase at strike-slip faults.

Key words: Junggar basin, Mahu sag, Triassic, Baikouquan formation, sandy conglomerate, intragranular fracture, thrust fault, strike-slip fault

XU Yang, MENG Xiangchao, LIU Zhanguo, SHAN Xiang. Genetic Mechanism of Intragranular Fractures in Low-Permeability Sandy Conglomerate Reservoir and Their Significance in Petroleum Exploration: A Case Study from Triassic Baikouquan Formation in Mahu Sag, Junggar Basin[J]. Xinjiang Petroleum Geology, 2016, 37(zk(English) ): 40-48.

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