The method of calculation of 3D-distributions of current recoverable oil reserves of water-flooded fields and the sweep efficiency of these reserves by displacement is developed. The objects of research are deposits at late stages of development and with hard-to-recover reserves. These reserves are characterized by low rates of production and non-achievement of project oil recovery. There is a technological possibility of additional recovery of such reserves. However, the effectiveness of these technologies depends on knowledge of the structure of residual oil reserves. The problem of adequate localization of mobile reserves cannot be solved within the framework of "linear" models, in which the residual oil saturation is determined by the static distribution in the volume of the object of development and does not depend on the development systems. Experience in the development of a huge number of fields shows that the technological oil recovery factor significantly depends on the density of the well grid and the rate of selection.
The main idea of the proposed approach is the transition from the traditional concept of 3D-digital hydrodynamic modeling to the generalized concept based on idea that localization of reserves depends on the intensity of drainage, which is characterized by the corresponding capillary number. This will allow to create a digital model of localization of current oil reserves and will provide a unique opportunity to calculate the current sweep efficiency of displacement and to build maps of this parameter. The authors have implemented a method of dynamic calculation of phase permeability, developed algorithms and created software that makes it possible to use traditional linear simulators such as Eclipse to simulate nonlinear filtration processes. The authors have generalized the notion of current sweep efficiency and highlighted lessons learned and the current displacement coefficients. The article gives examples of calculations and maps of localization of reserves and coverage of oil reserves by displacement.
The transition to this new concept makes it possible to count non-draining region of oil, oil reserves them and to identify poorly drained sites areas and to develop maps. This will improve the success from drilling infilled wells and sidetracks by 10-15% (70%) and recovery factor 5-7%. For digital models of nonlinear filtration, the concept of the current sweep efficiency of displacement can be significantly expanded: it becomes possible to perform a direct calculation of the accumulated, the current sweep efficiency and their dynamics, to form new sweep efficiency maps for displacement of current oil reserves and maps of oil reserves not covered by displacement process.
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