过采空区抽采下组煤煤层气技术及工程应用初探--以晋城寺河井田为例

Technology of across-goaf drainage of coalbed methane from a lower coal seam group and its primary application: Taking Sihe mine field as an example

晋城矿区寺河井田3号煤层经多年的煤矿开采,形成了大面积的采空区,大面积的卸压提高了下组煤(9号、15号)的渗透率,但由于采空区阻隔和煤层气地面预抽技术的局限,致使下组煤煤层气尚未得到有效抽采。为保证煤矿的安全生产和产能的释放,结合采空区特征,采用过采空区钻完井及压裂工艺新技术,分析施工参数及后期产能情况,评价过采空区抽采下组煤煤层气技术的应用效果。结果表明:地面钻井开发过采空区下组煤煤层气资源时,应首先进行井位优选及井身结构优化,以保证钻井的成功率;采用氮气置换套管钻井工艺及低压易漏注浆加固等穿采空区钻完井技术,不仅可以有效降低采空区煤层气自燃甚至爆炸风险,而且保证了穿采空区段固井质量;优化采空区下组煤层压裂施工参数并设计不同井位的煤层气井压裂工艺,有效扩展裂缝长度,同时也避免了“压穿”等压裂事故发生;精细化排采管控措施可以有效扩大泄流半径,提高单井产能。现场一百余口过采空区煤层气井排采实践表明,单井最高产气量达到8832 m^(3)/d,日均产气量达到2694 m^(3),验证了过采空区抽采下组煤煤层气技术可行,可推广应用。

After many years of coal mining,a large area of goaf had been formed in the No.3 coal seam of Sihe mine field in Jincheng mining area,the pressure relief in a large area increased the permeability of the lower coal seams(seams No.9 and No.15),however,due to the limitation of goaf barrier and surface pre-extraction technology of coalbed methane,the coalbed methane of the lower coal seam group had not been effectively extracted,in order to ensure the safe production of the coal mine and the release of production capacity,based on the characteristics of goaf,a new technology of drilling,completion and fracturing in goaf was developed,focusing on the analysis of construction parameters and production capacity in the later stage,and the application effect of coalbed methane extraction technology cross the goaf in the lower coal seam group was evaluated.The results show that when the surface drilling is used to develop coalbed methane resources in the goaf,well location optimization and wellbore structure optimization should be carried out first,which can effectively ensure the success rate of drilling.The nitrogen replacement casing drilling technology and low pressure leakage grouting reinforcement technology can not only effectively reduce the risk of spontaneous combustion and even explosion of coalbed methane in the goaf,but also ensure the cementing quality of goaf section.The fracturing parameters of coal seam under goaf were optimized and the fracturing technology of coalbed methane wells with different well locations was designed to effectively extend the fracture length and avoid fracturing accidents such as fracturing through.Fine drainage control measures can effectively expand the drainage radius and improve the single well productivity.The drainage practices of more than 100 CBM wells across goaf show that the maximum gas production of a single well reached 8832 m^(3)/d,and the daily average gas production was up to 2694 m^(3),which verifies the feasibility of the across-goal CBM extraction technology of the lower coal seam group and can be popularized and applied.