摘要
水力压裂是煤层增透和煤层气增产的关键技术。压裂过程中的渗流诱导应力对煤层分段压裂效果具有重要影响。建立分段压裂渗流诱导应力的理论模型,采用有限差分法进行煤层分段水力压裂数值模拟,探究压裂过程中应力场演化规律及渗流诱导应力的作用机制。设计正交试验,以水平主应力差作为指标进行方差分析,探究初始水平主应力差、泵注排量、分段间距对渗流诱导应力的影响程度和作用机制,并提出压裂优化方案。研究结果表明:注水初期会产生较大的渗流诱导应力,导致有效应力峰值下降,使后续起裂位置起裂压力增大,增加起裂难度;压裂过程中与压裂后的渗流诱导应力影响机制不同,压裂过程中泵注流量的影响滞后于分段间距滞后于原始水平主应力差,压裂后3个因素影响程度排序为:分段间距>泵注流量>原始水平主应力差。根据原始地应力差异,提出压裂优化措施:当原始主应力差较大时,可以适当降低分段间距,并增大泵注流量;当原始主应力差较小时,可以适当增大分段间距,并减小泵注流量,据此在保证无卸压盲区的同时可以达到较大的压裂范围。以上分析可以为压裂施工参数优化设计提供参考。
Hydraulic fracturing is a key technology to permeability enhancement and production stimulation of coalbed methane. The seepage induced stress in the process of fracturing has an important influence on the effect of sectional hydraulic fracturing. In this paper, a theoretical model of seepage induced stress of sectional fracturing was established, and the finite difference method was used to carry out numerical simulation of simulation hydraulic fracturing of coal seam. The evolution law of stress field and the action mechanism of seepage induced stress in the process of simulation hydraulic fracturing were also explored. Besides, an orthogonal experiment was designed, which was carried out by variance analysis with the horizontal principal stress difference as an index to explore the influence degree and action mechanism of initial horizontal principal stress difference, pumping displacement and segment interval on seepage induced stress. And the fracturing optimization scheme was proposed. The results have shown that large seepage induced stress generates at the initial stage of water injection, which decreases the effective stress peak, increases initiation pressure of subsequent initiation position and difficulty of crack initiation. The influence mechanism of seepage induced stress is different between during and after fracturing. The order of influence degree among three factors after fracturing is: segment interval > pump flow rate > initial horizontal principal stress difference. According to the original in-situ stress difference, the fracturing optimization scheme is proposed. When initial principal stress difference is large, the segment interval can be appropriately reduced and increase the pump flow rate;while interval principal stress difference is small, the segment interval can be appropriately increased and reduce the pump flow rate to achieve a large fracturing range without pressure relief blind area. The above analysis can provide reference for optimization design of fracturing operation param
作者
胡千庭
刘继川
李全贵
张跃兵
胡良平
宋明洋
石佳林
邓羿泽
HU Qianting;LIU Jichuan;LI Quangui;ZHANG Yuebing;HU Liangping;SONG Mingyang;SHI Jialin;DENG Yize(State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing 400044,China;School of Resources and Safety Engineering,Chongqing University,Chongqing 400044,China)
出处
《采矿与安全工程学报》
EI
CSCD
北大核心
2022年第4期761-769,共9页
Journal of Mining & Safety Engineering
基金
国家自然科学基金项目(52074049)。
关键词
分段水力压裂
诱导应力
有限元
数值模拟
sectional hydraulic fracturing
induced stress
finite element
numerical simulation
