Advances in Earth Science ›› 2018, Vol. 33 ›› Issue (2): 213-224. doi: 10.11867/j.issn.1001-8166.2018.02.0213

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Three-dimensional Quantitative Fracture Analysis of Tight Gas Sandstones Using Industrial Computed Tomography: A Case of Bashijiqike Member in Tarim Basin

Yichi Zhang( ), Xinfang Ma *( ), Shicheng Zhang, Shan Han, Sijie Qin, Chi Zhang   

  1. China University of Petroleum, Beijing 102249, China
  • Received:2017-07-27 Revised:2017-12-04 Online:2018-02-20 Published:2018-02-20
  • Contact: Xinfang Ma;
  • About author:

    First authors:Zhang Yichi(1991-),male,Yizheng City, Jiangsu Province,Master student. Research areas include oil and natural gas engineering.

  • Supported by:
    Project supported by the National Natural Science Foundation of China “The research of Horizontal Well fracturing in tight oil reservoirs”(No.51574255)

Yichi Zhang, Xinfang Ma, Shicheng Zhang, Shan Han, Sijie Qin, Chi Zhang. Three-dimensional Quantitative Fracture Analysis of Tight Gas Sandstones Using Industrial Computed Tomography: A Case of Bashijiqike Member in Tarim Basin[J]. Advances in Earth Science, 2018, 33(2): 213-224.

Fractures are the main fluid-flow pathways in tight-oil sandstones, and they have significant influence on tight-oil distribution, exploration, and development. Cores and image logs are commonly unavailable because of their high costs. Therefore, employing conventional logs for fracture detection is imperative for tight-oil sandstones. Fractures, such as intragranular fractures, grain-edge fractures, and transgranular fractures, are abundant in the tight sandstones. Fractures improve storage and permeability and impact distribution of natural gas. Tight gas sandstone samples are imaged at high resolution industrial X-ray computed tomography (ICT) systems to provide a three-dimensional quantitative characterization of the fracture geometries. ICT has the advantage of performing three-dimensional fracture imaging in a nondestructive way. Fracture networks were quantitatively analyzed using a combination of 2-D slice analysis and 3-D visualization and counting. The core samples were firstly scanned to produce grayscale slices, and the corresponding fracture area, length, aperture and fracture porosity as well as fracture density were measured. Then, the 2-D slices were stacked to create a complete 3-D image using volume-rendering software. The open fractures (vug) were colored cyan whereas the calcite-filled fractures (high density objects) were colored magenta. The surface area and volume of both open fractures and high density fractures were calculated by 3-D counting. Then, the fracture porosity and fracture aperture were estimated by 3-D counting. The fracture porosity and aperture from ICT analysis performed at atmospheric pressure were higher than those calculated from image logs at reservoir conditions. At last, the fracture connectivity was determined through the comparison of fracture parameters with permeability. Distribution of fracture density and fracture aperture determined the permeability and producibility of tight gas sandstones. Altogether, combined X-ray tomography, image processing help visualize and quantify the complexity and heterogeneity of naturally fractured geological samples in views of applications to integrated reservoir petrophysical and geomechanical characterization.

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