The prediction of structural fractures in coal seams of the Kuba coalfield, China: an application for coalbed methane (CBM) recovery development

Zhou Zhang,Min Zhoua,Di Gao,Yun-Xing Cao,Bao-An Xian

doi:10.4154/gc.2019.26

Abstract

The structural fracture system in a coal reservoir enables coalbed methane (CBM) percolation and migration. It plays an important role in CBM exploration and exploitation (recovery) development. Nearly vertical strata with Mesozoic bituminous coal seams in the central part of the Kuba coalfield of the Xinjiang Province in China were studied using large-scale mapping of the structural fractures on the surface, and a using a technique for comparing and analyzing sections of the underground coal mine. This investigation verified that similar structural fractures are developed in the underground coal seams as those on the surface, , and surrounding rocks represent the same tectonic layer. Meanwhile, a corresponding relationship between the characteristics of the development of fractures - including the growth directions and degree of development of fractures in coal seams and the surrounding rocks - was established. Based on this, the research presents a new method for predicting a pattern of fractures in coal seams and the coal structure, respectively. Finally, the study area was divided into zones with dense, moderate and un-developed fractures. The method should be applicable in various coal-and-gas engineering fields, for example the prediction of fractured zones in coal seams, the prediction of coal structure, and for projecting the well arrangement in the exploration and development of economic recovery of CBM.

Highlights

The fracture system of a coal reservoir provides an important space for coalbed methane (CBM) adsorption, diffusion, and migration (LAUBACH et al, 1998; PASHIN & GROSHONG, 1998; DAWSON & ES TERLE, 2010; MOSTAGHIMI et al, 2017)
Vertical strata with Mesozoic bituminous coal seams in the central part of the Kuba coalfield of the Xinjiang Province in China were studied using large-scale mapping of the structural fractures on the surface, and a using a technique for comparing and analyzing sections of the underground coal mine. This investigation verified that similar structural fractures are develo ped in the underground coal seams as those on the surface, and surrounding rocks represent the same tectonic layer
The method should be applicable in various coal-and-gas engineering fields, for example the prediction of fractured zones in coal seams, the prediction of coal structure, and for projecting the well arrangement in the exploration and development of economic recovery of CBM

Summary

Introduction

The fracture system of a coal reservoir provides an important space for CBM adsorption, diffusion, and migration (LAUBACH et al, 1998; PASHIN & GROSHONG, 1998; DAWSON & ES TERLE, 2010; MOSTAGHIMI et al, 2017). It is important to be able to define the studied coal’s fracture system as reliably as possible. This is not always possible and can be demonstrated by the following two aspects: Firstly, there are practical difficulties in studying the subject as coal seams generally occur deep underground, where the fractures cannot be observed and measured directly. Due to a high degree of heterogeneity in coal seams, the observational and geophysical data of a few samples cannot re flect the development characteristics of the fracture system in the coal seams of the whole development zone. In the whole fracture system, the structural frac ture is the main channel of coalbed methane migration and the main contributor of its permeability

Methods

Results

Conclusion