基于修正后的物质平衡方程预测储气库库存量

Inventory forecast in underground gas storage based on modified material balance equation

针对应用传统物质平衡方程进行储气库库存量预测时误差较大的问题,开展储气库气水互驱模拟实验并分析渗流机理,建立考虑含气孔隙体积损失和储集层非均质性的物质平衡方程,并通过实例分析进行了验证。模拟实验结果表明:束缚水饱和度和残余气饱和度不应简单选取气藏开发数据,应开展气水多次互驱模拟实验来获取;水侵储集层改建储气库后用于储存气体的孔隙体积减小,且渗透率越低因水侵损失的孔隙体积越大。将原始含气储集层简化为水淹区、过渡带和纯气区,考虑各区域损失的原始含气孔隙体积及岩石、束缚水变形体积,定义物性分区参数描述储集层非均质性,对传统物质平衡方程进行修正。实例分析表明,储气库实际运行库存量与传统物质平衡方程预测结果差别较大,与修正后物质平衡方程预测结果基本一致。

In view of the gap between the gas storage inventory forecasted by the traditional material balance equation and the actual inventory, experiments of displacing gas by water and displacing water by gas were carried out, and the modified material balance equation considering pore volume loss due to water invasion and pay heterogeneity was deduced based on the percolation mechanism inferred from the experiments above, moreover the equation was verified by example analysis. The experimental results show that： the irreducible water saturation and residual gas saturation in underground gas storage （UGS） domain should be evaluated through water-gas seepage experiments because these parameters are different from the process of gas field development; the pore volume in the water flooded reservoir decreases after conversion for gas storage, and the pore volume loss increases rapidly when the reservoir permeability decreases. The net pay was divided into flooded zone, transitional zone and gas zone with the equations for pore volume loss cacanlating due to water flooded. Then one parameter describing reservoir heterogeneity was defined based on numerical simulation and eventually the traditional material balance equation was modified with the consideration of pore volume loss due to water invasion and reservoir heterogeneity. Example analysis result shows that the actual UGS inventory differs greatly from the inventory predicted by the traditional materal balance equation, but agrees with that calculated by the modified one.