考虑动态滤失系数的垂直井压裂缝延伸机理研究

Study on Vertical Well Fracturing Fissure Extensional Mechanism Considering Dynamic Leak-off Coefficient

为了深入探讨应力场、裂隙场、渗透场三场耦合条件下的压裂缝延伸规律。首先基于有效应力原理,考虑煤储层应力敏感性,建立了动态渗透率计算模型;其次,考虑相应的滤失系数动态变化对裂缝扩展的影响,基于PKN模型建立了改进的压裂缝延伸模型,并进行实际单井的应用及分析;最后,运用ABAQUS软件模拟滤失系数动态条件下应力演化规律与压裂缝延伸过程,并将理论值与数值模拟值进行对比分析。结果表明,压裂缝延伸过程中储层渗透率变化最大,增大了约22.25倍;滤失系数次之,增大了约7.03倍;孔隙度变化最小,增大了约2.02倍,而裂缝延伸距离随压裂时间的增长而增长,但前期增长较快,后期基本趋于稳定,当压裂时间为60min,压裂缝延伸距离为141.23m,与数值模拟结果(132.8m)较为吻合,从而验证了模型的正确性,研究成果可为实际施工控制提供理论依据。

To further discuss fracturing fissure extensional pattern under the coupled stress,fissure and permeation three fields,firstly established dynamic permeability computational model based on effective stress principle,considering coal reservoir stress sensitiveness.Then established modified fracturing fissure extension model based on PKN model considering corresponding impact from leak-off coefficient dynamic variation on fissure extension;and carried out actual single well application and analysis.Finally,used ABAQUS software simulated stress evolution pattern and fracturing fissure extension process under leak-off coefficient dynamic condition,and comparatively analyzed theoretical values and numerical simulated values.The results have shown that during the fracturing fissure extension process,the variation of reservoir permeability is the largest,it has increased about 22.25 times;leak-off coefficient the second,increased about 7.03 times;porosity the least,increased about 2.02 times.While the fissure extension distance has increased along with the time,but quicker in earlier stage,later stage basically toward stable.When fracturing time is 60min,fracturing fissure extension distance will be 141.23m,rather consistent with numerical simulated result 132.8m,thus has verified correctness of the model.Studied results can provide theoretical basis for practical construction control.