沁南西—马必东区块煤层气高效建产区优选技术

Optimization technology of efficient CBM productivity areas in Qinnanxi-Mabidong Block,Qinshui Basin,Shanxi,China

沁水盆地南部是我国目前规模最大的煤层气生产基地,浅部开发工程布置的逐渐完成,必然要将眼光转向深部,开采难度增大。为此,准确圈定高效建产区尤为重要,沁南西—马必东区块正是如此。面对这一新的技术挑战,分析深部煤储层特点,结合沁水盆地南部前期煤层气井生产实践,首先划分出资源基础、产气条件、储层可改造性3个优选层次,进而从含气性、渗透性、疏导性、可采性四个方面提出了高效建产区优选标准和流程,形成了"三层四性"高效建产区优选技术。研究认为,建产区开发潜力体现为关键地质条件指标的组合,包括高于经济极限的煤储层含气量,单位长度微裂隙总宽度≥50μm,可疏导指数≥30 nm,地应力状态处于垂直应力≥最大水平主应力≥最小水平主应力或最大水平主应力≥垂直应力≥最小水平主应力状态,以原生—碎裂结构煤为主,局部构造相对简单,可动用面积≥30%等。基于这一标准,在沁南西—马必东区块优选出3个高效建产区,部署了5口试采井,获得单井日产气量2 000 m^3以上的实施效果,验证了优选技术方法的可靠性,为沁水盆地深部煤层气区块高效建产区优选提供了技术示范。

The southern part of the Qinshui basin is currently the largest CBM production base in China.With the gradual depletion of the shallow CBM resources,it will inevitably need to turn its attention to the deep CBM and the difficulty of mining will increase.Thus,it is particularly important to accurately locate the efficient CBM productivity areas as it is the case in the Qinnanxi-Mabidong block. Faced with this new technical challenge,the characteristics of deep coal reservoirs were analyzed.In combination with the production practice of coalbed methane wells in the early stage of the southern Qinshui basin,the three priority levels of resource base,gas production conditions and reservoir reformability were first divided,and then in terms of four properties such as gas-bearing properties,permeability,methaneleading ability and recoverability,the preferred standard and processes of the efficient CBM productivity areas are proposed,which forms the＂three-levels four-qualities＂efficient CBM productivity areas optimization technology.The study indicates that the development potential of the productivity area is embodied as a combination of key geological con-ditions,including that coal reservoir gas content above the economic limit,microfracture width per unit length is greater than or equal to 50 μm,methane-leading index is greater than or equal to 30 nm,geo-stress is in the state of vertical stress≥the maximum horizontal principal stress≥the minimum horizontal principal stress or the maximum horizontal principal stress≥the vertical stress≥the minimum horizontal principal stress,the coal structure is dominated by intact coal-cataclastic coal and the local structure is relatively simple with the movable area is greater than or equal to 30%.Based on these criteria,three efficient production areas were selected in the Qinnanxi-Mabidong block. Five test production wells were deployed and more than 2 000 m3 of gas production per well was verified.Therefore,the reliability of the preferred technical method was verified and the success of Qinnanxi-Mabidong has provided a successful demonstration of technology for the selection of efficient deep CBM productivity areas in the Qinshui Basin.