溶蚀作用下古岩溶盆地系统中介质场演化模拟

Simulation of the Media Field Evolution in Palaeo-karst Basin System under the Dissolution

为了研究古岩溶盆地在溶蚀作用下碳酸盐岩油气储层介质场的演化规律,基于地下水渗流理论和碳酸盐溶蚀动力理论,用数值模型模拟了均质盆地和非均质盆地2种岩溶盆地含水系统发育过程。岩溶盆地含水系统演化过程中总伴随着裂隙差异溶蚀,不管均质盆地还是非均质盆地,都越来越非均质化,强溶蚀带集中在潜水位及优势裂隙附近,在侵蚀基准面和构造裂隙及层理等大裂隙处会形成高孔隙率、渗透率的良好储层。受介质场非均质化反作用,岩溶高地区潜水位随系统演化不断下降,潜水面处的强烈溶蚀随水位不断下切而使高地区改造成竖直裂隙发育的厚储层;坡地区水平径流活跃,易于形成水平裂隙发育的储层;平原区水位相对稳定,溶蚀作用主要发生大裂隙和侵蚀基准面处,但在大裂隙网内经溶蚀可形成局部高孔隙率储层。对比两子模型发现,在岩溶盆地含水系统中,主导渗流场都要经历由局部流场向二级流场、二级流场向全局流场的转变,前者发生在坡地区内部,后者发生在坡地区与平原区之间;流畅的渗流场转换更有利于介质场发育,受大裂隙网导水作用,非均质盆地比均质盆地更快捷、更顺利地实现主导流场升级,溶蚀作用更强烈,3 ka后非均质盆地比均质盆地的孔隙率增幅大34%。

In order to study the evolution of media field of oil-gas reservoirs in the palaeo-karst basin under the carbonate dissolution,based on groundwater flow theory and carbonate dissolution kinetics,two numerical mo-dels including a homogeneous basin and a heterogeneous basin were built to simulate the karst aquifer system development process.With fracture dissolution differences in the basin evolution progress,whether the homogeneous or heterogeneous basin,karst aquifer systems were increasingly non-homogenized,while the erosions were focused on the fissures in the water table and near constructive bedding and other large cracks,which would form a good penetration and high-porosity reservoir.As the heterogeneity in the media field,groundwater level in the mountain areas was falling,and thick vertical fractured reservoirs were formed with strong incision on the water level.In the plain area,dissolution mainly occured around large cracks and the base level,where local corrosional fracture networks could be formed as high porosity reservoirs.Comparing the two sub-models,the dominant flow field must be changed from the local to the secondary,and the secondary to the overall flow field,which the former occurred in the mountainous area,while the latter occured between the mountain and plain areas.The more smoothly the flow field converted,the more conducively the media field development.By the greater role of hydraulic conductivity in fracture network,the heterogeneous basin achieved the flow field faster and more smoothly than that of homogeneous basin,and dissolution was stronger;the porosity of the heterogeneous basin is 34% larger than that of homogeneous basin after 3,000 years.