Study on quantitative evaluation methods for water-flooded layers via dynamic reconstruction of the original formation resistivity

The accurate identification and quantitative interpretation of water-flooded layers are important in hydrocarbon reservoir development, which provides essential guidance for optimizing development plans and enhancing oil recovery. For mature oilfields characterized by high water cut and high current recovery levels, the identification of water-flooded layers and the extent of water flooding in each well has become a critical challenge that must be addressed to increase the development efficiency. This study presents a novel quantitative interpretation method for determining water-flooded layers, as demonstrated by an analysis of the dense conglomerate reservoir in the Baikouquan Formation of the Triassic system in the Xinjiang Oilfield. The methodology is based on the restoration of the original formation resistivity after water flooding, with the oil saturation reduction rate constituting a pivotal parameter. First, a well profile is established by selecting representative well groups that include both wells from the early reservoir development phase that were not water-flooded and wells currently in development that have been water-flooded. On the basis of the detailed stratigraphic correlation, the formation resistivity of the nonflooded strata equals the original resistivity of the water-flooded strata. Subsequently, by integrating physical property parameters from the same stratigraphic level with the difference in resistivity between the deep and intermediate zones, a model is developed to recover the original resistivity of the water-flooded layers. Second, by applying Archie’s formula to calculate oil saturation values before and after flooding, the oil saturation reduction rate can be obtained, thereby eliminating the effects of conglomerate lithology and heterogeneity. In conjunction with core dripping experiments, the water-flooded layers of the Baikouquan Formation conglomerate reservoir were classified into five grades. The criteria for identifying the corresponding oil saturation reduction ranges across these five grades were established, thereby enabling quantitative evaluation of the water-flooded layers. This method has been demonstrated to yield favorable outcomes in the interpretation of the actual reservoir water-flooded layers. The method is effective for interpreting actual water-flooded reservoir layers. Field validation on Wells Y and M indicates that the calculated results achieve 90% consistency with production profiles. This method provides a novel approach to the precise evaluation of water-flooded layers and can offer technical support for the design and optimization of development schemes for reservoirs exhibiting significant heterogeneity.