Geological Factors and Reservoir Properties Affecting the Gas Content of Coal Seams in the Gujiao Area, Northwest Qinshui Basin, China

Zhuo Zou,Jiapeng Li,Dameng Liu,Yingjin Wang,Yidong Cai

doi:10.3390/en11051044

Abstract

Coalbed methane (CBM) well drilling and logging data together with geological data were adopted to provide insights into controlling mechanism of gas content in major coal seams and establish gas accumulation models in the Gujiao area, Northwest Qinshui Basin, China. Gas content of targeted coals is various in the Gujiao area with their burial depth ranging from 295 to 859 m. Highly variable gas content of coals should be derived from the differences among tectonism, magmatism, hydrodynamism, and sedimentation. Gas content preserved in the Gujiao area is divided into two parts by the geological structure. Gas tends to accumulate in the groundwater stagnant zone with a total dissolved solids (TDS) value of 1300–1700 ppm due to water pressure in the Gujiao area. Reservoir properties including moisture content, minerals, and pore structure also significantly result in gas content variability. Subsequently, the gray correlation statistic method was adopted to determine the most important factors controlling gas content. Coal metamorphism and geological structure had marked control on gas content for the targeted coals. Finally, the favorable CBM exploitation areas were comprehensively evaluated in the Gujiao area. The results showed that the most favorable CBM exploitation areas were in the mid-south part of the Gujiao area (Block I).

Highlights

Coalbed methane (CBM) as an unconventional natural gas is a key energy resource, and its recovery can reduce both greenhouse gas emission and mining explosions [1,2]
The generation, migration, and accumulation of CBM in coal seams are affected by multiple factors including coal rank, geological structure, burial depth, hydrological condition, coal properties, and reservoir characteristics [4,5,6,7,8]
Roi is the degree of correlation between the gas content and the i‐th influencing factor, and n is the number of samples

Summary

Introduction

Coalbed methane (CBM) as an unconventional natural gas is a key energy resource, and its recovery can reduce both greenhouse gas emission and mining explosions [1,2]. With the increase in gas demand, CBM has been paid more attention, so an evaluation of gas resources and gas controlling factors has been required [3]. Gas content in coal seams is critical for gas resource assessment during CBM exploration and exploitation. The generation, migration, and accumulation of CBM in coal seams are affected by multiple factors including coal rank, geological structure, burial depth, hydrological condition, coal properties, and reservoir characteristics [4,5,6,7,8]. Geological factors, hydrological factors, and reservoir properties affecting gas content in coals have been normally interlinked [9,10]. Gas content may increase first and decrease sharply when coal rank reaches anthracites, as found

Methods

Results

Conclusion