Fine Characterisation of Remaining Oil Using Time-Varying Numerical Simulation: Experimental Study, Characterisation in Model, and Application in QHD Oilfield

Abstract

For water-flooding oilfields, both indoor experiments and mine field practices have confirmed that long-term water flooding can change physical properties, wettability, and fluid parameters. The comprehensive performance of these changes is that the relative permeability curve of oil and water changes dynamically. Usually, numerical simulation does not consider the change of reservoir properties, which will cause the mismatch of history matching. This error is especially obvious in the high water-cut period. It further affected the understanding of remaining oil and the prediction of subsequent production. Therefore, time-varying numerical simulation is required for fine numerical simulation in high water cut period to improve the accuracy and reliability of model prediction. In order to solve the above problems, a set of fine reservoir numerical simulation process integrating core experiment, logging, dynamic and geological knowledge was established. The specific workflow is as follows: The data of core particle size analysis, X-ray diffraction and cast thin section were used to study the change law of reservoir physical properties and wettability after water flooding, which confirmed that the reservoir was re-stimulated under long-term water flooding. The relative permeability curves before and after water flooding were compared using natural cores. After water flooding, the relative permeability curves shifted to the right and the residual oil saturation decreased. It is confirmed that the relative permeability curves will change with water flooding. Carried out 500∼2000PV water flooding laboratory experiment, determined the oil displacement efficiency under high multiple flooding, calculated the residual oil saturation changes with the displacement multiple and physical properties. Using pore cross-sectional area flux to continuously characterize the temporal changes of properties during the simulation process. In this way, the accurate conversion of the attribute change law from the laboratory core to the actual model is realized, and the deviation caused by the change of the mesh size is avoided. In the simulation process, the changing laws of the attributes are defined separately according to the partitions, and the iterative modification of the attributes is realized in each time step. When time-varying numerical simulation is applied to the QHD oilfield, the matching degree of history matching has been improved. Time-varying simulation is an important means to improve the history matching effect of high water-cut water drive oilfields, and can help oilfields understand the true remaining oil distribution. This method has been extended to Bohai SZ, BZ and other oil fields.