Four-Dimensional Geological Modeling of Stress-Sensitive Reservoirs of Abnormally High-Pressure Carbonates

Abstract

\n The abnormally high-pressure carbonate dual-medium reservoir of the Kenkiyak Pre-salt oilfield in the littoral Caspian Basin has strong stress sensitivity. With the development of the oil field, the formation pressure drops and the fractures gradually close, resulting in a decrease of the effective permeability of the dual-media reservoir over time. So it is necessary to establish three-dimensional geological models of the dual-medium reservoirs at different times, which is the 4-D geological model.\n Firstly, the reservoir matrix and fracture permeability model under the original conditions is established by using the dual-medium three-dimensional geological modeling method; Secondly, the formation pressure model for a given period is established by taking the measured well-point formation pressure in a certain period as hard data and combining with the formation pressure change trend in different zones; Thirdly, the carbonate reservoir types are identified by borehole imaging and conventional logging, and the geological model of the reservoir types in the original state is established. Finally, using the relationship between confining pressure and permeability reduction rate of different types of reservoirs obtained by core stress sensitivity experiments, and based on the original matrix and fracture permeability models, the matrix and fracture permeability models of different types of reservoirs at a given period are obtained.\n Using the method proposed in this paper, the original matrix and fracture permeability model can be corrected to the matrix and fracture permeability model after the formation pressure drops at a certain period, and the 3D geological model of carbonate reservoir in any given periods can be obtained. Newly drilled wells at present confirmed that the geological model established by this method is reasonable and reliable. Taking the data of new wells completed during this period as hard data and the above three-dimensional geological model as soft data, an updated dual-medium model is established, which is more in line with geological reality. Based on the updated geological model, the deployment of oilfield adjustment schemes and well location optimization studies are carried out. The match between the new drilling data and the prediction results reached more than 90%.\n The method solves the problem of updating the 3D geological model caused by the permeability change of the stress-sensitive reservoir, ensures that the geological model truly reflects the underground geological characteristics, and can be widely applied to the 3D geological modeling of stress-sensitive reservoirs.