低渗透油藏不稳定渗流规律的研究

用无因次分析法对低渗透岩心的实验数据进行了分析 ,得出新的渗流规律。具体表述为 :低于亚临界雷诺数 (Rem=8.5× 10 -5)为非达西渗流 ,其运动方程为v =c(dp/dl) 3 ;高于亚临界雷诺数为达西渗流。从微观角度出发 ,应用边界层理论进一步证实了这一渗流规律。运用新的运动方程 ,建立了低渗透油藏不稳定渗流的数学模型。根据拉氏变换和Stehfest数值反演 ,求得了有限半径井的实空间近似解 ,并应用数值分析方法验证了近似解析方法的可行性。对低渗透油藏的压力动态特征以及边界对压力动态影响的分析结果表明 ,低渗透油层试井曲线的压力动态特征为 :短时曲线与达西渗流模型相似 ,而长时曲线则受到非达西渗流的影响。对于恒压边界油藏 ,压力趋于稳定的时间比达西渗流要迟一些 ;在无限大地层中 ,其导数曲线是一簇平行的倾斜线。对于同一区域低渗透油层试井曲线 ,其导数曲线出现“阶跃”的时间较迟的井区 ,流动系数比较好 ;反之则较差

Non-steady flow in low-permeability reservoir

The experimental data of fluid flow in porous core with low permeability were analyzed with simulation theory and plotted as a log log typical curve. It was found that the curve was in non linearity under the critical dimensionless number, which was determined on the properties of porous media, fluid and drive force. At the same time, the physical and mechanical analysis based on the micro boundary theory demonstrated the same conclusion as the experiment. Based on the new nonlinear flow theory, three typical transient flow models for low permeability reservoirs were built. Approximate analytical solutions in Laplace space were obtained. The solutions can be inverted from Laplace space into the real time domain with the Stehfest numerical algorithm. The pressure transient behavior of model was achieved. The analysis on transient pressure and pressure derivative behaviors of fluid flow in the low permeability reservoir shows that the approximate method agrees to the numerical method. The short term curve of well testing for the low permeability reservoir was the same that of Darcy flow model, and the long term curve was influenced by the non Darcy flow.