Feasibility of 4D Gravity in Reservoir Monitoring

Gravity monitoring of hydrocarbon reservoirs has been already successfully applied in a few cases. However, it may easily fail in many other cases, depending on different parameters of rocks and fluids, as well as different geometry of the reservoir formation. A feasibility study is needed before any decision taking. It is normally performed with a full and detailed modeling of the gravity signal caused by the density change related to reservoir re-saturation by different fluid during hydrocarbon extraction, including enhanced oil recovery, as well as gas/steam injection. The correct estimate of rocks and fluids effective densities is crucial, considering other rock properties like porosity and permeability. As well, reservoir geometry plays a significant role, especially depth, thickness and horizontal extent of the re-saturated zone. A simple technique was developed to estimate the feasibility of the 4D Gravity application to reservoir monitoring, based on graphs and tables. However, if such technique indicates a reasonable chance to record 4D signal, then a full and complex feasibility study is still recommended to provide details of possible fluids contact displacements in 3D space.