煤层气成藏的宏观动力能条件及其地质演化过程——以山西沁水盆地为例

Macroscopic dynamic energies for the formation of coalbed gas reservoirs and their geological evolution—A case study from Qinshui Basin in Shanxi Province

煤层气成藏维系于其能量平衡系统,宏观上受控于“四场互动”过程,核心是能量的有效传递及其地质选择过程。以沁水盆地为例,对构造动力能、热动力能、地下水动力能等宏观动力能的地质演化过程进行了深入探讨,阐明了不同宏观动力能对煤层气成藏的控制作用。结果表明:研究区构造动力能及其演化总体经历了4个阶段;热动力能及其演化和由其控制的煤化作用同样经历了4个阶段;地下水动力能及其演化包括3个阶段。其中,燕山中期的剧烈岩浆活动是宏观动力能条件演化的关键时期。以构造动力能为主线,将其他能量场贯穿起来,可知宏观动力能与煤层气成藏之间的耦合关系如下:盆地北部阳泉—寿阳区域,是煤层气成藏有利区域之一,但不利于煤层气高产;盆地南部晋城—阳城及沁水北部区域,不仅是煤层气成藏有利区域,而且利于煤层气高产;盆地中部沁源地区是煤层气成藏和高产的有利区域;盆地东部的屯留—襄垣区域是煤层气成藏有利区域之一,但不利于煤层气高产。

The formation of coalbed gas reservoirs depends on an energy homeostasis system controlled by the interactive processes of four fields on macroscopy. The core processes are the effective transfer of energy and the geological selective process.Taking Qinshui Basin as a case study, we have made a profound discussion on the geological evolution of macroscopic dynamic energies, such as the tectonic dynamic energy, thermodynamic energy and groundwater dynamic energy, and we have clarified controls of various macroscopic dynamic energies on coalbed gas reservoir formation. Our research results indicate that the evolution of tectonic dynamic energy, of thermodynamic energy, and of groundwater dynamic energy went through four phases, four phases and three phases, respectively. Among them, the intense magmation of the mid-Yanshan movement is the pivotal phase. Taking the tectonic dynamic energy as central and coupling it with all other energy fields, we could discern the coupling relations between macroscopic dynamic energies and the formation of coalbed gas reservoir in Qinshui Basin. The results show that the Yangquan-Shouyang area in the north past of the basin and the Tunliu-Xiangyuan area in the east are favorable for forming coalbed gas reservoirs, but not ones of highyield. In contrast,the Jincheng-Yangcheng-Qinshui area in the south basin area and the Qinyuan area in the middle of the basin are favorable for both the formation of coalbed gas reservoirs and highyields as well.