WAG Optimization Algorithms Based on the Reaction of Producing Wells

Abstract

Abstract Selection of optimal technological parameters of water-alternating-gas injection (WAG) in the oil reservoir is an important task. Technological parameters of WAG include volume ratio of injected water and injected gas, and total volume of water and gas (in reservoir conditions), injected in one cycle. The paper contains results of studing of efficiency of WAG with various technological parameters. Technological parameters of WAG had constant values and values varying in time depending on the reaction of producing wells for several algorithms. Injected water and gas are distributed unevenly in the reservoir due to difference in their viscosities and also because of the heterogeneity of reservoir permeability. Distribution of saturations and relative permeabilities of fluids in the reservoir are being changed during WAG. It may require changes in the technological parameters of WAG during injection. Compositional hydrodynamic simulation was used for the studies. The simulation took into account hysteresis of relative permeabilities and their change depending on the surface tension between oil and gas. The model for the simulation had the properties of the achimov deposits in Western Siberia. Fluidal model was adapted to a series of tests of samples of reservoir fluid. End points of relative permeabilities and the dependence of oil relative permeability in three-phase flowing was being selected during playback the results obtained with the replacement of oil by water, gas and WAG in core samples. Multivariate calculations were performed for uniform and nonuniform distribution of permeability (by area and by thickness) in the oil reservoir. It was considered waterflooding, gas injection, water alternating gas injection and simultaneous water-gas injection. The simulation results showed that the oil recovery for a heterogeneous reservoir may differ significantly depending on technological parameters of WAG. The wrong choice of technological parameters of WAG can lead to substantial loss of oil recovery. It was developed algorithms for adjust technological parameters of WAG based on water-oil ratio and gas-oil ratio of producing wells of the impact area. Implementation of WAG by using these algorithms can achieve a maximum or close to a maximum oil recovery compared with water flooding, gas injection and WAG (simultaneous or separate injection of water and gas with constant in time of technological parameters). These algorithms can be used for implementation of WAG when distribution of permeability by area and by thickness is uncertain.