Study Of Numerical Simulation With Water Flooding Heavy Oil Reservoir Based On Nonlinear Seepage

In recent years, people’s demand for oil and natural gas is increasing as the rapid development of China’s economic and the improvement of people’s living standards, but the development of China’s conventional crude oil has been in the middle and late periods currently, crude oil production declines gradually and cannot meet people’s demand. In September 2013, China has become the world’s largest oil consumer; Daily oil imports reached 6.3 million tons that exceeded the United States of 6.24 million tons. United States Energy Information Administration (EIA) predicted that the situation would last, and the gap of daily average oil import between the two countries will expand further. In order to alleviate this situation and reduce our dependence on foreign oil, efforts to exploration and development of unconventional oil and gas reservoirs has become more and more important. Heavy oil has enormous reserves and has great practical significance for improving China’s energy structure and intensifying the pressures of supply and demand for oil. Heavy oil is different from the conventional crude oil because that it is rich in resin and asphaltene, wax and other macromolecule polymer which leads to high viscosity, poor liquidity, and difference from the rheological property of Newtonian fluid, its seepage characteristics like non-Newtonian flow, the production of heavy oil is more difficult than conventional crude oil due to these factors.Numerical reservoir simulation technology is an effective auxiliary tool for the development of reservoir, which can provide technology support for developing heavy oil reservoir better. It uses numerical method to solve the mathematical model which describes the movement of oil, gas and water in order to know the movement pattern of oil-gas-water in reservoirs, it is also a powerful tool for the development plan of new oil and gas field, the development program adjustment of old oil and gas field, and the method selection and plan design of enhancing oil recovery that can help to enhance oil recovery and economic benefit, but currently the common commercialization numerical reservoir simulation software mostly based on Darcy seepage law, the results got by using these software to simulate the heavy oil reservoir with nonlinear seepage will appeared larger of deviation inevitably, forecast of production indicators will be also far away from the actual production. There is an urgent need for suitable numerical reservoir simulation software to simulate heavy oil reservoir accurately in order to improve forecasting accuracy and develop heavy oil reservoirs better.This paper researches on heavy oil rheology behavior and nonlinear seepage law through experiment, establishes flash vaporization black oil model on the base of black oil model, analyzes the difference between nonlinear seepage equation and Darcy seepage equation, introduces the concept of apparent viscosity, makes heavy oil nonlinear module embed into flash vaporization black oil model through flow amendment coefficient, develops heavy oil reservoir nonlinear seepage numerical simulation software, the software considers the influence of heavy oil nonlinear seepage, makes up the shortage that the common commercialization numerical reservoir simulation software does not reflect the heavy oil nonlinear seepage, and passes the reliability test, better results are obtained by using the software to simulate the actual reservoir.The main works of this paper are as following:(1) Heavy oil flow rheology behavior experiment:the relationship between heavy oil shear stress and shear rate is no longer simple linear relationship in QHD32-6 oilfield and SZ36-1 oilfield, it manifests obvious nonlinear relationship and has non-Newton fluid of rheological characteristics; temperature has larger influence on heavy oil rheological curve, there is the same shear rate, the higher temperature, the lower corresponding shear stress; When the shear rate is 40/s, the shear stress of QHD32-6 oilfield heavy oil at 25℃ is more than 4 times as at 70℃; for SZ36-1 oilfield, when the shear rate is 40/s, the shear stress of SZ36-1 oilfield heavy oil at 25℃ is about 3 times as at 70℃; there is the same temperature and same shear rate, the shear rate of QHD32-6 oilfield heavy oil is above SZ36-1; The change of Heavy oil viscosity performances differently within different shear rate range, the decrease rate of heavy oil viscosity is large with the increasing of shear rate in the situation of lower shear rate, but the decrease rate of heavy oil viscosity is less with the increasing of shear rate in the situation of higher shear rate; temperature is an important influence factors on heavy oil viscosity, there is the same shear rate, the corresponding heavy oil viscosity is difference largely at the different temperature conditions.(2) Heavy oil nonlinear seepage law:Heavy oil threshold pressure gradient is reducing as the increasing of permeability at the same viscosity situation; Heavy oil threshold pressure gradient is increasing as the increasing of viscosity at the same permeability situation; The relationship between heavy oil threshold pressure gradient and mobility meets power relationship, heavy oil threshold pressure gradient is reducing as the increasing of mobility; Permeability and viscosity are the two main influence factors for heavy oil threshold pressure gradient, mobility reflects the two factors integrated and can be used to represent threshold pressure gradient.(3) Flash vaporization black oil model:establishing flash vaporization black oil model referred to the design and realization of black oil model, including:① Establishing mathematical models, including the assumptions of mathematical modeling, movement equations, differential equations, auxiliary equations and boundary conditions;② Establishing numerical models, including numerical methods, differential equations, oil and gas component balance equations;③ Getting and dealing with parameter, including the value of permeability and well production;④ The solution process of flash vaporization black oil model is given lastly.(4) Heavy oil nonlinear module:analyzing the difference between nonlinear seepage equation and Darcy seepage equation, introducing the concept of apparent viscosity, making heavy oil nonlinear module embed into flash vaporization black oil model through flow amendment coefficient, heavy oil nonlinear seepage can be achieved in the model.(5) Heavy oil reservoir nonlinear seepage numerical simulation software: developing heavy oil reservoir nonlinear seepage numerical simulation software, testing its reliability including zero balance test, symmetry test and that the calculated results were compared with the mature commercial simulation software, test results show that heavy oil reservoir nonlinear seepage numerical simulation software can be suitable for reservoir simulation calculations.(6) The application of heavy oil reservoir nonlinear seepage numerical simulation software:using software on actual heavy oil reservoir simulation, simulation results showed that the higher threshold pressure gradient, the less daily oil production, the faster production water rate rising, the lower crude oil recovery percent; For improving heavy oil reservoir development effect, using thermal recovery for the development of heavy oil reservoir, improving formation temperature, reducing oil viscosity, increasing mobility, decreasing threshold pressure gradient, reducing the impact of threshold pressure gradient on production farthest.