致密砂岩岩心水驱前缘形貌演化规律研究

Morphology evolution of water flooding front in tight sandstone cores

摘要:

致密砂岩油藏水驱开发效果与水驱前缘形貌密切相关，因此，水驱前缘形貌准确预测是评价致密砂岩油藏水驱开发效果的关键。目前大多数储层水驱前缘演化模型均假设储层为均质储层、未考虑储层微观结构，不能有效预测致密砂岩油藏水驱前缘形貌演化规律。结合水驱前缘形貌演化实验及分形理论，明确了致密砂岩油藏水驱油过程中水驱前缘平均位移及分形维数演化规律。在此基础上，结合朗之万方程、随机理论及贝克莱-列维尔特理论（Buckley-Leverett理论，简称BL理论），建立了致密砂岩油藏水驱前缘演化模型。研究表明：理论计算与实验结果具有很好的一致性，验证了理论模型的正确性。致密砂岩油藏水驱前缘边界位置受到宏观平均位移（BL理论控制）及水驱前缘形貌分形维数（水相黏度及岩石非均质孔隙结构控制）共同作用影响。研究结果揭示了致密砂岩岩心水驱油产生复杂驱替边界的物理力学机理。

Abstract:

The development effect of water flooding in tight sandstone reservoirs is closely related to the morphology of water flooding front， so accurate prediction of the water flooding front topography is the key to evaluating the water flooding development effect of tight sandstone reservoirs. Most current water flooding front evolution models assume that the reservoirs are homogeneous and do not consider the microstructures of the reservoirs， so they cannot effectively predict the evolution law of the water flooding front in tight sandstone reservoirs. In this work， by combining the water flooding front morphology evolution tests， and the fractal theory， the evolution of the average displacement and the fractal dimension of water flooding front in tight sandstone reservoirs are studied. On this basis， by combining the Langevin equation， the stochastic theory， and the Buckley-Leverett theory， a theoretical model for predicting the water flooding front evolution in tight sandstone reservoirs is established. The results show that the theoretical calculation is in good agreement with the experimental results， which verifies the correctness of the theoretical model. The boundary position of water flooding front in tight sandstone reservoirs is influenced by the macroscopic average displacement （controlled by the Buckley-Leverett theory） and the fractal dimension of water flooding front topography （controlled by water phase viscosity and rock heterogeneous pore structures）. The results reveal the physical and mechanical mechanism of complex displacement boundaries caused by water flooding in tight sandstone reservoirs.