Subsidence above irregular-shaped reservoirs

The exploitation of liquids and gases from certain depths can cause land subsidence, which poses a threat to the safety of surface pipelines and buildings. Accurate subsidence prediction is an important part of environmental impact assessment involving oil and gas reservoir development. Currently, the analytical method research on land subsidence due to oil and gas reservoir development only focuses on regular reservoir shapes and uniform pressure drop, the numerical research has the problem of low calculation accuracy in far-field large grid. There exists limited guiding significance for actual reservoir development. In this study, we extended the classical Geertsma's method by considering the mechanical effects due to uneven pore pressure drop and changes in fluid density in the reservoir. Accordingly, we established a complete description of the equivalent body force and equivalent surface force. Further, we obtained the solution based on Mindlin's basic solution and the convolution method. The proposed method exhibited better generality than others, and can ensure the same solution accuracy in the far and near fields. We conducted case studies to demonstrate that this method can be used to directly evaluate actual oil reservoirs of any shape and pressure distribution. It can also be used to accurately analyze the maximum subsidence position. The calculation results showed that the decrease of reservoir pressure will cause land subsidence, and the decrease in fluid density leads to a certain uplift effect on the formation, resulting in forming subsidence, micro-uplift and stable areas on the land. Moreover, the position of the maximum subsidence point changes with the change in pressure distribution. The proposed method demonstrated guiding significance for actual reservoir development.