Characteristics and Quantitative Prediction of Fractures of Tight Reservoir in Chang 7 Member in Longdong Area

doi:10.7657/XJPG20210205

Abstract

Abstract:

In the tight reservoirs of the Chang 7 member in the Upper Triassic Yanchang formation in the Longdong area of the Ordos basin, fracture development is the primary factor affecting oil and gas distribution and well productivity. According to outcrop profiles, cores, casting thin slices and imaging logging data, the distribution of the fractures in the Chang 7 reservoir were characterized quantitatively, the controlling factors on the fracture development were clarified, and finally combining with rock mechanics and numerical simulations, the fracture distribution was quantitatively predicted. The study results show that in the Chang 7 reservoir in the study area, (a) large-angle structural fractures are developed, which are effective and poorly filled with mineral cements; (b) the average linear density of macroscopic fractures is 0.31 fracture/m, the average areal density and average porosity of microscopic fractures are 0.25-0.50 μm/μm² and 0.32%, respectively, such fractures can increase reservoir spaces, connect the intergranular and intragranular pores, and enhance pore connectivity; (c) 4 groups of fractures were found, striking northeast-southwest, northwest-southeast, near east-west and near north-south respectively, and of which the fractures in northeast-south direction are the most developed; (d) the fractures are mainly developed inside the rock layer with powerful deformability and terminate at the lithological interface or bedding surface, 5 cm to 20 cm high, and up to 110 cm at the most; and (e) the higher the content of brittle minerals in the rock, the finer the particles, the denser the rock, and the thinner the formation, the higher the degree of fracture development. The distribution law of the fractures in the Chang 7 member in the Longdong area quantitatively predicted through finite element numerical simulation is consistent with the results from the actual measurement.

Key words: Ordos basin, Longdong area, Yanchang formation, Chang 7 member, tight sandstone, structural fracture, quantitative prediction

CLC Number:

TE122.21

SU Xiaocen, GONG Lei, GAO Shuai, ZHOU Xinping, WANG Zhaosheng, LIU Bo. Characteristics and Quantitative Prediction of Fractures of Tight Reservoir in Chang 7 Member in Longdong Area[J]. Xinjiang Petroleum Geology, 2021, 42(2): 161-167.

Figures/Tables 8

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Table 1

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