沁水盆地15号煤层顶板分段压裂水平井适应性及产气效果预测

Coal No.15 Roof Staged Fracturing Horizontal Well Adaptability and Gas Production Effect Prediction in Qinshui Basin

沁水盆地北部松塔区块煤层气资源条件较好,但现有直井产量低、抽采效率并不理想。为探索新的地面煤层气开发方式,从地应力和岩石力学性质两个影响压裂的关键参数出发开展了15号煤层顶板分段压裂水平井在松塔区块的适用性研究。利用数值模拟方法对顶板压裂裂缝延展规律及煤层气井产能进行了效果预测。研究结果表明,组合弹簧模型计算方法得到的煤层及顶板三向应力数据可靠,顶板及煤层垂向应力最大,易形成垂直裂缝,且顶板最小水平主应力大于煤层最小水平主应力,预示压裂形成的垂直裂缝更易穿过顶板延伸至煤层,形成有效沟通裂缝;顶板杨氏模量是煤层的4.16~5.50倍,且泊松比低,脆性大,压裂形成裂缝较煤层压裂裂缝更长、更稳定。模拟顶板压裂裂缝半长为158.6m,较直接煤层压裂裂缝半长提高40.1%。产能预测结果显示,水平井单井10年累计产量为1.68×10^(7) m^(3),10年平均采收率为45.43%,与直井相比,单井产量大,采收率高。综合研究认为煤层顶板分段压裂水平井技术在松塔区块具有较好的适用性和产气潜力。

CBM resource condition in the Songta block,northern Qinshui Basin is rather good.However,existing straight wells have shortcomings of low yield,drainage efficiency unsatisfactory.To explore new surface CBM exploitation mode,the paper has carried out adaptability study for Songta block coal No.15 roof staged fracturing horizontal well evolved from ground stress and rock mechanical property two key aspects impacting fracturing emphatically.Using numerical simulation has carried out effect prediction on roof fracturing fissure extension regularity and CBM well capacity.The studied results have shown that the spring group model computation acquired triaxial stress data of coal seam and roof are reliable.Computed results have shown that the vertical stress on coal seam and its roof is the maximum,easy to form vertical fissures,and minimum horizontal primary stress of roof is larger than that of coal seam,indicated fracturing formed vertical fissures are easier to pass through roof extend to coal seam and formed effective link-up fissures.Roof Young’s modulus is 4.16~5.50 times of coal seam,again with low Poisson’s ratio,larger brittleness,longer and stabler fracturing formed fissure length.Simulated roof fracturing fissure half length is 158.6m,larger than immediate coal seam fracturing fissure half length 40.1%.Capacity predicted results have shown that horizontal single well decade cumulative yield is 1.68×10^(7) m^(3),decade average recovery ratio 45.43%,compared with straight well,per-well yield larger,recovery ratio higher.Comprehensively considered that the coal roof staged fracturing horizontal well technology has better adaptability and gas production potential in Songta block.