射孔参数对薄煤层群压裂起裂的影响研究

Influences of perforation parameters on the fracture initiation in thin coal bed groups

薄煤层气藏较高的应力敏感性和互层性导致其改造效果受射孔参数影响尤为突出。将渗流-应力-损伤耦合模型应用于薄煤层群射孔参数优化研究中,结合现场测井与施工资料,模拟了各射孔参数下薄煤层压裂裂缝的起裂与拓展,基于储层损伤体积定量评价射孔参数对改造效果的影响;分析了影响煤层产能的因素和间接压裂的增产机理,并开展了薄煤层顶底板间接压裂的数值模拟。模拟结果表明:射孔数对损伤体积的影响最大,射孔深度和相位角次之,射孔间距影响最小;与常规压裂相比,顶底板射孔的间接压裂需要更长的泵注时间和压力。本研究建立的有限元数值模型可用于分析近井筒裂缝起裂问题,对现场射孔和压裂优化设计具有指导意义。

The stimulation effect of thin-coalbed gas reservoir is particularly influenced by perforation parameters due to its higher stress sensitivity and interbeded characteristics.In this paper,the seepage-stress-damage coupling model was used to optimize the perforation parameters of thin coal bed group,and combined with field logging and construction data,the initiation and propagation of hydraulic fractures in thin coal beds was simulated under different perforation parameters.Then,based on the reservoir damage volume,the influences of perforation parameters on the stimulation effect were quantitatively evaluated.Finally,the factors influencing coal bed productivity and the stimulation mechanisms of indirect fracturing were analyzed,and the indirect fracturing of the roof and floor of thin coal bed was numerically simulated.The simulation results show that the number of perforations has the greatest influence on the damage volume,perforation depth and phase angle take the second place,and perforation spacing has the least influence.Compared with the conventional fracturing,the indirect fracturing of roof and floor perforation needs longer pumping time and higher pumping pressure.The finite element numerical model established in this study can be used to analyze the fracture initiation near the wellbore and is of instructive significance to the optimization design of field perforation and fracturing.