Oil & Gas Geology ›› 2016, Vol. 37 ›› Issue (1): 117-124.doi: 10.11743/ogg20160116

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Stress sensitivity anisotropy and its microscopic mechanism of tight oil and gas reservoirs: A case from the Chang-6 reservoir in Ansai oilfield of Ordos Basin

Zhang Zhiqiang, Shi Yongmin, Li He   

  1. School of Earth and Space Science, Peking University, Beijing 100871, China
  • Received:2015-06-03 Revised:2016-01-04 Online:2016-02-08 Published:2016-03-02

Abstract: Study on stress sensitivity anisotropy of continental tight reservoirs in China plays an important role in evaluation of reservoir damage during the exploitation of low permeability oilfield.In view of the practical problems,the X,Y and Z columns from three inter-perpendicular orientation of three typical samples from Chang-6 reservoir in Ansai oilfield of Ordos Basin are used to test permeability by changing confining pressure under the in-situ condition and study the relationship between permeability and effective stress.In addition,microscopic mechanism and anisotropy of stress sensitivity in tight oil and gas reservoirs are analyzed through integrating various data including casting thin sections,scanning electron microscopy and XRD,etc.The results demonstrate that stress sensitivities of different rock samples are different and stress sensitivities of the same rock sample are also quite different in different directions.The ranking of stress sensitivity index from strong to weak is fine-grained lithic feldspathic sandstone,feldspar lithic quartz siltstone and medium to fine-grained lithic feldspathic sandstone,and the ranking of anisotropy coefficient from strong to weak is feldspar lithic quartz siltstone,medium to fine-grained lithic feldspathic sandstone and fine-grained lithic feldspathic sandstone.Microscopic experiments indicate that mineral composition,the arrangement and pore structure characteristics of different types of reservoir are key factors to cause reservoir stress sensitivity anisotropy.Therefore,stress sensitivity anisotropies are quite different in different types of tight reservoirs,and the microscopic heterogeneity characteristics of reservoirs are the major factors influencing stress sensitivity and anisotropy.This understanding is of great significance to highly-efficient exploitation of the continental heterogeneous tight reservoirs in Ordos Basin.

Key words: stress sensitivity, permeability anisotropy, microscopic heterogeneity, oilfield development, tight Oil & Gas reservoir, Ordos Basin

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