Abstract
Oil or gas production causes reservoir depletion. It occasionally induces reservoir compaction and subsidence and horizontal earth surface movement. Oil and Gas are found in 3D shape structures such as anticline, or inclined fault traps. In addition, the ground surface, where we observe the earth surface movements above such 3D reservoirs, may not be flat. The earth surface movements are affected by topography of ground surface above reservoirs and 3D reservoir shape. However, the 3D-analysis of subsidence problem has not been researched sufficiently for the complexity of 3D structural modeling. This paper analyzes 3D reservoir and earth surface geometry effect on subsidence and horizontal earth movement during reservoir compaction, using a 3D boundary element model(BEM). BEM is suitable for the 3D subsidence model, because the complex topography of ground surface and 3D reservoir meshes can be easily constructed. The conclusion shows that(1)if the reservoir depth is large, or small but reservoir shape isn't very complex, the results produced by conventional models(flat and horizontal reservoir with a flat ground surface)give similar results for subsidence and horizontal movement if some adjustment is made for reservoir area, depth, and thickness. Therefore, for the analysis of subsidence and horizontal movement, we can use the conventional models made for geological adjustments. However, for the inversion problem(ex. Inversion analysis of reservoir compaction using surface movements as input data), the 3D position of reservoir plane must be input from other information such as seismic analysis;(2)if the reservoir depth is small, the exact 3D reservoir shape and non-flat ground surface topography with mountains or valleys should be modeled to simulate the subsidence and horizontal movement during reservoir compaction, because the subsidence and horizontal movement are uniquely affected by each 3D reservoir shape and mountain or valley size and location.
