煤层气储层压裂负效应作用机理

Mechanisms of hydro-fracturing negative effect to coalbed methane seams

储层压裂是煤层气工程中提高采收率的主要措施之一,但同时受压裂液侵入和煤粉的影响会对储层造成伤害,从而抑制了煤岩储层渗透率的有效提高。基于孔隙压力变化对煤岩应力状态改变的力学分析,研究分析了压裂过程中压裂液对裂隙面附近煤岩的作用机理;通过煤岩应力状态变化的研究,确定了煤层气压裂过程引起裂隙面附近煤岩发生不同破坏特征的破坏模式;并根据压裂对煤层气工程产生的负效应,进一步给出了煤层气排采过程中的降压速率上限值确定方法。研究分析表明,压裂对煤层气储层改造具有明显的两面性,对煤层气的长期高效排采具有很大的局限性,必须严格控制压裂施工工艺及排采降压规律,才能达到有效提高排采效率的目的。

The hydro-fracture in coalbed methane seams is a significant measure for enhancing the productivity of coalbed methane production. During the fracturing process,the seams will be strongly impacted by fracture fluid invasion and coal fines,which would significantly suppress the permeability. Based on mechanical analysis to the change in stress state of coals due to pore pressure,the mechanisms of hydro-fracturing upon the coals adjacent to both sides of fracture was investigated in this paper. Moreover,the failure modes of coals with the different failure features were determined,depending on the analysis on the changes in stress state. Furthermore,based on the negative effect of hydrofracture on the productivity,the determination method of upper limit depressurization rate was provided. Therefore,it can be concluded that the hydro-fracture has dual characteristics to enhance the efficiency,and also has some limitations to the long-term depletion of coalbed methane. The technologies must be continuously optimized in the future,and then the efficiency enhancement can be smoothly achieved.