考虑基质收缩效应的煤层气藏产能评价

Productivity Evaluation of Coalbed Methane Reservoir with Matrix Shrinkage Effect

针对基质收缩效应严重影响煤层气藏产能评价和预测的问题,运用稳态扩散和达西渗流规律建立煤层气藏压裂直井基质扩散方程和裂缝系统渗流方程,引入新的拟时间函数来解决物质平衡方程中存在变量的问题,在保证精度的情况下提高了计算速度,得到了煤层气藏有限导流垂直裂缝井不稳定渗流压力及产量的解析解。结合时间叠加原理,实现了实际生产数据与理论数据的拟合。将研究结果应用于评价及预测实际煤层气藏产能,结果表明:基质收缩效应对产能评价和预测的影响主要发生在生产的后期,并且会使得渗流区域渗透率增加,提高了地层能量的利用率。适于基质收缩型煤层气藏压裂直井的产能评价方法,对煤层气藏开发和产能评价具有重要意义。

Aiming at the problem that matrix shrinkage effect seriously affects the productivity evaluation and prediction of coalbed methane reservoir, the steady state diffusion and Darcy flow law were used to establish the matrix diffusion equation and fracture system flow equation of fractured vertical well in coalbed methane reservoir, and a new pseudotime function was introduced to solve the problem of variables in the material balance equation, which improved the calculation speed under the condition of ensuring accuracy, and the analytic solutions of unsteady seepage pressure and output of finite conductivity vertical fracture well in coalbed methane reservoir were obtained. Combined with the time superposition principle, the fitting of real production data and theoretical data was realized. The study results were applied to evaluate and predict the productivity of actual coalbed methane reservoir, showing that the influence of matrix shrinkage effect on productivity evaluation and prediction mainly occurs in the late stage of production, and the matrix shrinkage effect increases the permeability of seepage zone and thus improves the utilization ratio of formation energy. The productivity evaluation method suitable for fractured vertical well in matrix shrinkage type coalbed methane reservoir is of great significance to the development and productivity evaluation of coalbed methane reservoirs.