缝洞型低渗透碳酸盐岩油藏产量递减曲线分析

针对缝洞型低渗碳酸盐油藏,建立考虑启动压力梯度和动边界共同影响的三重介质低渗透油藏非线性非稳态渗流模型.鉴于数学模型的非线性和非齐次性,通过引入新定义的压力(量纲一)线性化压力扩散方程,应用Laplace变换和Duhamel原理结合Stehfest数值反演对模型进行求解,获得三重介质低渗油藏产量递减典型曲线,在产量递减双对数图上出现3个递减阶段和2个相对平缓稳定阶段;分析启动压力梯度、溶洞窜流系数、基质窜流系数、裂缝弹性储容比和溶洞弹性储容比与基质弹性储容比之比等敏感参数对产量(量纲一)的影响规律.计算分析表明,启动压力梯度越大,中后期产量递减曲线下降幅度越大.通过绘制的产量递减曲线图版,可以预测缝洞型低渗透碳酸盐岩油藏未来产量的变化.

Analysis of production decline curves in naturally vuggy and fractured carbonate reservoir with low permeability media

Aimed at naturally vuggy porosity and fractured reservoirs,a model of nonlinearity transient flow in triple porosity media with low permeability reservoir has been built under consideration of the comprehensive effects from threshold pressure gradient and moving boundary.According to the nonlinearity and nonhomogeneity of this mathematical model,by introducing a new defined pressure diffusion equation linearized by dimensionless pressure,Laplace transform and the principle of Duhamel in combination with Stehfest numerical inversion algorithm is used to solve the model.The production decline curves were plotted and results indicated that there were two decline periods and three steady periods in bilogarithmic graph of production decline curves.Finally,the sensitive parameters including threshold pressure gradient,vug interporosity flow coefficient,matrix interporosity flow coefficient,fracture storage ratio,the ratio of vug and matrix storage ratio on the dimensionless production decline were discussed.Calculation analyses indicated that the greater the threshold pressure gradient,the more drop of production decline curves at middle and later stage.Future production can be predicted by charts of production decline curves.