Abstract
Multi-phase tectonic movements and complex geological structures limit the exploration and hotspot prediction of coalbed methane (CBM) in structurally complex areas. This scientific problem is still not fully understood, particularly in the Bumu region, Southwest China. The present paper analyses the occurrence characteristics and distribution of CBM based on the comprehensive analysis of CBM data. In combination with the analysis of the regional tectonics setting, geological structure features and tectonic evolution. The control action of multi-phase tectonic movements on CBM occurrence are further discussed. Results show that the Indosinian local deformation, Yanshanian intense deformation, and Himalayan secondary derived deformation formed the current tectonic framework of Enhong synclinorium. The intense tectonic compression and dextral shear action in the Yanshanian and Himalayan movements caused the complex geological structures in Bumu region, composed of the Enhong syncline, associated reverse faults and late derived normal fault. The CBM distribution is complex, which has the central and western NNE-trending high gas content zones along the syncline hinge zone and the reverse faults. The geological structure controls on CBM enrichment are definite and important. Based on geological structure features and responses of gas content, methane concentration, and gas content gradient, the gas controlling patterns of geological structure are determined and can be classified into five types: the reverse fault sealing, syncline sealing, monoclinal enrichment, normal fault dispersion, and buried floor fault dispersion types. The structural compression above the neutral surface plays an important role in the syncline sealing process, which is indicated by an increase in gas content gradient. The EW-trending tectonic intense compression and dextral shear action in the Himalayan movement avoided the negative inversion of NNE-trending Yanshanian compressive structure and its destruction of CBM reservoir. However, the chronic uplift and derived normal fault during Himalayan period caused the constant dissipation of CBM.
Highlights
Coalbed methane (CBM) resources are abundant in China, where early-stage large-scale CBM development is undertaken actively [1]
The results of this study provide new insights and improved understanding of the influence of fold neutral surface and fault sealing on CBM, which may have significant implications for CBM exploitation in structurally complex areas
(5) Buried floor fault dispersion type: No 9 coal seam located near the buried f1, f3, and f4 reverse faults is characterized by the low gas content, methane concentration, and gas content gradient, which is generally lower than 10 m3 /t, 60%, and about 1.8 m3 /t/100 m, respectively (Table 2)
Summary
Coalbed methane (CBM) resources are abundant in China, where early-stage large-scale CBM development is undertaken actively [1]. The coal-bearing basins in China experienced multi-phase tectonic movements in geologic history and developed complex geological structures [3]. Syncline structure is a favorable area in terms of CBM reservoir formation, mainly due to the increase in coal seam buried depth and gas content [7,21]. The Enhong synclinorium is located in the eastern Yunnan region, Southwest China, with abundant coal resources (Figure 1) [26]. Bumu region as the research area because of the rich geological and CBM data available, which is located in the central part of the Enhong synclinorium. The results of this study provide new insights and improved understanding of the influence of fold neutral surface and fault sealing on CBM, which may have significant implications for CBM exploitation in structurally complex areas. Fault, 8-Red river fault, 9-Mi’le-Shizong fault, 10-Nanpanjiang fault, 11-Youjiang fault
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