Adsorption and desorption of coalbed methane are generally at a dynamic equilibrium state under the undisturbed coal reservoir. However, as the reservoir pressure drops to a certain value during the extraction of coalbed methane, the equilibrium state is destroyed and thus more coalbed methane desorbs and escapes from coal to wellbore. Here the corresponding bottom-hole fluid pressure is called initial gas production pressure (IGPP) in the development practice of coalbed methane wells. This paper, which has taken Changzhi-Anze block in the central-southern part of Qinshui basin as the study object, addresses the distribution characteristic and control factors of IGPP of coalbed methane wells and then explores the key factors affecting IGPP using grey correlation analysis theory. The results indicate that IGPP varies from 1.09 MPa to 6.57 MPa, showing a distribution law with high in the middle and low in the west and east of the study area, which presents a similar distribution characteristic with burial depth, thickness, coal rank, gas content, original reservoir pressure, and in-situ stress. Further, through grey correlation analysis, it concludes that the correlation degrees of control factors affecting IGPP of coalbed methane wells in the descending order are decline rate of working fluid level, water yield before gas production, reservoir pressure, coal thickness, coal rank, minimum horizontal principal stress, burial depth, and gas content. Among these factors, engineering factors, including decline rate of working fluid level and water yield before gas production, present a key controlling effect, because they can determine the smooth migration pathway directly during initial water production. And another key factor, original reservoir pressure also builds strong and positive correlation with IGPP under the interaction of other geology and reservoir factors, revealing the capability of gas desorption and the transmission of pressure drops.

中文翻译：

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沁水盆地中南部长治-安泽区块煤层气井初始产气压力多因素控制

煤层气在未受扰动的煤层下吸附和解吸一般处于动态平衡状态。然而，在煤层气提取过程中，随着储层压力下降到一定值，平衡状态被破坏，更多的煤层气从煤层中解吸逸出到井筒中。这里相应的井底流体压力在煤层气井开发实践中称为初始产气压力（IGPP）。本文以沁水盆地中南部长治-安泽区块为研究对象，针对煤层气井IGPP分布特征及控制因素，运用灰色关联分析理论探讨影响IGPP的关键因素。 . 结果表明，IGPP 从 1.09 MPa 变化到 6.57 MPa，研究区呈中高、西、东低的分布规律，其埋深、厚度、煤阶、含气量、原始储层压力、地应力等具有相似的分布特征。进一步通过灰色关联分析得出，影响煤层气井IGPP的控制因素的关联程度从高到低依次为工作液位下降率、产气前产水量、储层压力、煤层厚度、煤阶、最小值水平主应力、埋藏深度和含气量。其中，工液位下降速度和产气前产水率等工程因素起关键控制作用，因为它们可以在初始产水过程中直接确定平滑的迁移路径。而另一个关键因素，原始储层压力在其他地质和储层因素的相互作用下也与IGPP建立了很强的正相关，揭示了气体解吸和压降传递的能力。