煤矿井下长钻孔分段水力压裂技术研究进展及发展趋势

Research progress and development trend of staged hydraulic fracturing technology in long-borehole underground coal mine

“十三五”以来,围绕“我国煤矿井下煤层区域增透瓦斯高效抽采和坚硬顶板岩层弱化区域治理”两大难题,将定向长钻孔与分段压裂技术结合,通过技术攻关与装备研发及工程试验,在煤矿井下定向长钻孔分段水力压裂技术和装备研发及工程示范应用等方面均取得了明显进展。主要表现在如下4个方面:(1)开发了适合于煤矿井下煤岩层裸眼定向长钻孔不动管柱和动管柱两种分段水力压裂工艺技术与工具,不动管柱分段压裂工程应用钻孔长度突破了500 m,单孔压裂实现了5段;动管柱分段压裂钻孔长度工程应用突破了800 m,单孔压裂实现了17段。(2)研发了煤矿井下低压端加砂压裂泵组和高压端加砂压裂装置,低压端加砂泵组压力达到了70 MPa,排量达到90 m^(3)/h,携砂比达到20%;高压端加砂压裂装备耐压能力达到55 MPa,一次连续加砂压裂的砂量达到750 kg;低压端和高压端加砂装备均在现场进行了工程应用,应用结果表明装备均具有较好携砂压裂能力。(3)建立了碎软煤层围岩分段压裂和硬煤顺层钻孔分段压裂区域增透瓦斯高效抽采技术模式,前者在山西阳泉矿区和陕西韩城矿区应用钻孔瓦斯抽采纯量均值分别达到了2811 m^(3)/d和1559 m^(3)/d,后者在陕西彬长矿区应用钻孔瓦斯抽采纯量达到了2491 m^(3)/d。(4)探索出了坚硬顶板强矿压煤矿井下定向长钻孔分段水力压裂主动超前区域弱化治理的新模式,工程应用钻孔长度突破了800 m,坚硬顶板分段水力压裂治理后,顶板来压步距、动载系数和最高压力值较未压裂区分别下降了18.9%~70.6%,5.8%~7.9%,13.7%~19.4%,有效治理了工作面坚硬顶板引起的强矿压灾害。随着煤矿井下分段水力压裂技术改进和煤矿智能开采发展的实际需要,提出了煤矿井下大排量高压力智能压裂泵组、井下长钻孔裸眼分段压裂智能工具等装备和煤矿井−地联合分段水力压裂技术研发方向,以更好地推动煤矿井下水力压裂技术与装备发展,为煤矿安全高效绿色智能开采提供技术和装备支撑。

Since the“13th Five-Year Plan”,significant progress has been made in the directional long-borehole staged hydraulic fracturing technology,equipment development and engineering demonstration application of underground coal mine through the technical research,equipment development and engineering test with directional long-borehole and staged hydraulic fracturing technology in combination,focusing on the two major issues of regional permeability enhancement,efficient gas drainage and rock weakening treatment of hard roof for coal seams in underground coal mine in China.It is mainly manifested in the following four aspects:(1)Two staged hydraulic fracturing technologies and tools with/without rig movement have been developed.Specifically,the borehole hydraulically fractured in stages without rig movement has exceeded 500 m in engineering application,with up to 5 stages of single-hole fracturing achieved.Besides,the borehole hydraulically fractured in stages with rig movement has exceeded 800 m in engineering application,with up to 17 stages of single-hole fracturing achieved.(2)The sand fracturing pump set for the low-pressure end and the sand fracturing device for the high-pressure end of underground coal mine were developed.Definitely,the sand fracturing pump set for the low-pressure end has the pressure up to 70 MPa,the displacement up to 90 m^(3)/h and the sand carrying ratio up to 20%.The sand fracturing device for the high-pressure end has the bearing pressure up to 55 MPa and the sand volume for one-time continuous sand fracturing reaching 750 kg.Besides,the sanding equipment for the low-pressure end and the high-pressure end have been applied in the field engineering,of which the results show that the equipment has good sand carrying and fracturing performance.(3)An efficient gas drainage technology model with regional permeability enhancement was established for the staged fracturing in the surrounding rock of broken-soft coal seam and in the borehole along the hard coal seam.The former was applied in Yangquan mining area in Shanxi and Hancheng mining area in Shaanxi,with the net volume of gas drained from the borehole reaching 2811 m^(3)/d and 1559 m^(3)/d respectively,while the latter was applied in Binchang mining area in Shaanxi,with the net volume of gas drained from the borehole up to 2491 m^(3)/d.(4)A new mode of regional weakening treatment for the active leading area of staged hydraulic fracturing of directional long-borehole in the underground coal mine with hard roof and strong underground pressure has been explored.Specifically,the directional long-borehole hydraulically fractured in stages has exceeded 800 m in engineering application.After the staged hydraulic fracturing treatment of hard roof,the pressure step,dynamic load coefficient and maximum pressure value of roof have been reduced by 18.9%‒70.6%,5.8%‒7.9%and 13.7%‒19.4%respectively compared with those in the unfractured area,effectively controlling the strong ground pressure hazard caused by the hard roof of the working face.With the improvement of staged hydraulic fracturing technology in underground coal mine and the actual requirements of the development of intelligent coal mining,the research and development requirements have been put forward for the equipment such as the large-displacement and high-pressure intelligent fracturing pump set in underground coal mine,the intelligent tools for staged hydraulic fracturing in underground long-borehole and the integrated coal mine-ground staged hydraulic fracturing technology,so as to better promote the development of hydraulic fracturing technology and equipment for underground coal mine,and thus provide technical and equipment support for the safe,efficient,green and intelligent mining in coal mine.