碎软煤层夹矸间接压裂开发煤层气技术研究

Study on Indirect Fracturing Technology for CBM Development in the Parting of Broken Soft Coal Seams

目前间接压裂技术已成为低渗碎软煤层高效开发技术。文章以大宁—吉县区块5号煤层为研究对象,提出利用夹矸间接压裂技术提高煤层气开发效果,通过开展煤层夹矸可压性评价、水力压裂数值模拟、现场试验等研究,建立了低渗碎软煤层夹矸水平井分段压裂的工艺流程,揭示了该技术下水力裂缝的扩展规律。研究结果表明:与煤分层相比,夹矸的脆性和可浸泡性较好,可压性更高;在夹矸中进行压裂能够沟通上下部煤层,大幅降低施工压力与裂缝延伸压力,减少煤粉产出,裂缝延伸好,增产效果显著。射孔点距夹矸顶面0.5 m时,对夹矸上下煤层改造效果最优;夹矸煤层最小主应力差异系数为1.1时,水力裂缝在夹矸段少量扩展后,迅速向夹矸与煤层间的弱面延伸,进而撕裂夹矸上下部煤层,建立渗流通道。研究成果为低渗碎软煤层气开发提供了新的技术思路,同时可为射孔段优选以及压裂设计提供参考。

Indirect fracturing technology has become an efficient development technology for low-permeability and broken soft coal seams.In this work,the No.5 coal seam in the Daning-Jixian block was taken as the research object,and indirect fracturing technology in the parting of coal seam was proposed to improve the Coalbed Methane(CBM)development effect.Through the fracability evaluation of the parting of coal seam,hydraulic fracturing numerical simulation,field tests and other studies,the technological process of horizontal well staged fracturing in the parting of low-permeability and broken soft coal seams was presented,and the fracture propagation law under this technology was revealed.The results show that compared with coal seams,the parting has better brittleness and immersion and higher fracability.Hydraulic fracturing in the parting can communicate with the upper and lower coal seams,greatly reduce construction pressure and fracture extension pressure,and decrease the output of pulverized coal,resulting in desirable crack extension and remarkable enhancing production effect.When the perforation position is 0.5 m away from the top surface of the parting,the fracturing effect of the upper and lower coal seams of the parting is the best.When the minimum horizontal principal stress difference coefficient between the parting and coal seam is equal to 1.1,the hydraulic fractures spread rapidly along the weak surface between the coal seam and parting after a small amount of expansion in the parting layer,and then the upper and lower coal seams of the parting are torn apart and the seepage channels are formed.The research results provide a new technical approach for CBM development in low-permeability and broken soft coal seams and provide a reference for perforation location optimization and fracturing design.