Abstract:

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

Key words: evolution of karst aquifer, karst basin, evolution of flow field, palaeo-karst, numerical simulation