煤层气开采初期井底压力的合理控制范围研究

 合理的井底压力与煤岩力学特性及井周应力分布密切相关，而井周应力分布与井周是否产生提高绝对渗透率的贯通裂隙均有相互依赖的关系。首先，根据韩城煤岩的室内试验结果，分析煤岩不同应力状态与绝对渗透率的关系和变化规律；然后，基于弹塑性理论，通过考虑储层井周存在裂隙区时的弹塑性应力分析，建立井周应力与井底压力之间关系的数学模型，探讨确定保持或稳定提高绝对渗透性的合理井底压力范围，并将其应用于韩城煤层气井的排采数据分析。通过研究发现，在既定煤层气工程条件下，控制合理的井底压力可使煤储层绝对渗透率随煤层气的开采而逐渐增大，进而提高产能。

STUDY OF REASONABLE CONTROLLING RANGE OF BOTTOM-HOLE PRESSURE IN INITIAL STAGE FOR COAL BED METHANE PRODUCTION

Reasonable bottom-hole pressure is closely related to the mechanical properties of coal rock and the stress distribution around the well，and there is an interdependent relationship between the stress distribution around the well and the pass-through cracks which can increase the absolute permeability. Firstly，based on the experimental results of coal rock in Hancheng，the varying law of the absolute permeability with the different stress states around the well is analyzed in this paper. And then，according to the elastic-plastic theory and through the elastic-plastic analysis to the rock around the well of fissures，the mathematical models on the relationships between the stress around the well and the bottom hole pressure are established. Finally，the reasonable range of the bottom hole pressure is obtained to maintain or improve the absolute permeability，and to be applied in the practical analysis of coal bed methane(CBM) engineering in Hancheng. Thus，under a given condition of CBM engineering，it can be found that the absolute permeability will do higher growing and the methane production will be further improved，if the bottom-hole pressure can be controlled reasonably.