Abstract
Deep low permeability extra heavy oil reservoir has the characteristics of high formation pressure, high crude oil viscosity, and low permeability. Conventional steam injection thermal recovery has poor viscosity reduction performance and low productivity of a single well, which makes it difficult to develop this type of heavy oil reservoir. In this paper, core flooding experiment and microvisualization equipment were used to study the mechanism of improving the recovery of deep extra heavy oil by using water-soluble viscosity reducer; the realization of water-soluble viscosity reducer in numerical simulation was achieved by using nonlinear mixing rule; the reservoir numerical simulation model of water-soluble viscosity reducer displacement in test well group was established to optimize the development technical parameter of water-soluble viscosity reducer. The results show that compared with waterflooding, the oil displacement efficiency of water-soluble viscosity reducer is increased by 12.7%; water-soluble viscosity reducer can effectively reduce the viscosity of extra heavy oil, under the same temperature and permeability, the higher the concentration of viscosity reducer, the better the viscosity reduction effect, and the smaller the pressure gradient required at the same injection rate; the main mechanism of water-soluble viscosity reducer for enhancing oil recovery is to form oil in water emulsion, which can reduce the viscosity and interfacial tension of crude oil and reduce the residual oil saturation; in the pilot well group, the optimized injection concentration of water-soluble viscosity reducer is 3%, and the optimal injection amount of water-soluble viscosity reducer solution is 50 t/d; water-soluble viscosity reducer displacement was implemented in the pilot well group, the average daily oil of well group was increased from 1.8 t/d to 7.34 t/d, and the pilot well group has achieved good development performance.
Highlights
Deep low permeability extra heavy oil reservoirs refer to the oil reservoirs with buried depth more than 2200 m, reservoir permeability lower than 300 md, and crude oil viscosity greater than 10000 mPa·s at 50°C
Deep low permeability extra heavy oil reservoirs have the characteristics of deep burial depth, high formation pressure, low permeability, and poor crude oil fluidity, which leads to great difficulty in development and low productivity of a single well [1–10]
The effective development of deep low permeability extra heavy oil is mainly restricted by two factors: one is the high reservoir pressure caused by deep burial depth; the other is the difficulty of flow caused by low permeability and high viscosity of crude oil [11–18]
Summary
Deep low permeability extra heavy oil reservoirs refer to the oil reservoirs with buried depth more than 2200 m, reservoir permeability lower than 300 md, and crude oil viscosity greater than 10000 mPa·s at 50°C. Deep low permeability extra heavy oil reservoirs have the characteristics of deep burial depth, high formation pressure, low permeability, and poor crude oil fluidity, which leads to great difficulty in development and low productivity of a single well [1–10]. The effective development of deep low permeability extra heavy oil is mainly restricted by two factors: one is the high reservoir pressure caused by deep burial depth; the other is the difficulty of flow caused by low permeability and high viscosity of crude oil [11–18]. Because the enthalpy and specific volume of liquid-phase high-pressure hot water are far less than that of gas-phase saturated steam, its viscosity reduction radius is obviously weaker than that of steam, which leads to the difficulty of viscosity reduction by conventional steam thermal in deep low-permeability heavy oil reservoirs. This paper studies the mechanism and field application effect of viscosity reducer flooding in deep low permeability extra heavy oil reservoirs from three aspects of physical simulation, numerical simulation, and field application
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