Multiphase And Multi-component Phase Equilibrium Experiment And Calculation Research For Oil Reservoir

At present,enhanced oil recovery（EOR）such as gas injection and flooding have been widely used in petroleum industry,resulting in a large number of multiphase and multicomponent phase equilibrium problems.Similarly,in the process of oil and gas production and transportation,there is also plenty of multiphase and multi-component phase equilibrium problems such as wax deposition,hydrate formation,and asphaltene precipitation.Therefore,the study of multiphase and multi-component equilibria is essential.From literature research,this paper studied the multiphase and multicomponent equilibria from two aspects of experiment and algorithm.A visible swelling test producer was proposed,and real oil tests were completed.At the same time,the multiphase and multi-component Rachford-Rice equation was deduced.Focusing on the analysis of existing intervals,two robust and effective algorithms were developed,and the corresponding computer simulators were developed.What is more,an automatic-generating analysis test software was designed and developed.The original algorithm and the two new algorithms were tested for tens of millions of times,which proved the stability and rapidity of the algorithm proposed in this paper.This article has achieved the following results:（1）The common water-gas-oil swelling test is hard to observe.For this reason,a visible swelling test was proposed.Using ethane,CO₂,Niobrara oil（from the U.S.）and distilled water,a total of four groups of twenty-five sets of swelling tests were completed.The microscopic flow of the fluid was observed,and the blank of the ethane three-phase swelling test was filled.（2）A new multiphase multi-component Rachford-Rice equation which is monotonically successively decreasing in its corresponding variable space was constructed.Based on this feature,a robust successive-substitution method was designed.Using Matlab language,the algorithm was programmed into a simulator and was tested by three mechanism examples,three real production examples,and a four-phase example.It was proved that the method is robust and could solve all multi-phase multicomponent equilibrium problems.（3）Although the successive-substitution method is stable,the calculation speed is slow.Newton-Raphson method is widely used in the industry and is famous for its fast calculation speed.However,Newton-Raphson algorithm depends on the initial guess and often converge to the wrong root.For this reason,we designed a Hybrid Newton–Successive Substitution Method.It combines the high speed of the Newton-Raphson and the stable of the successive-substitution.Matlab language was used to compile the algorithm into a simulator,and software for randomly generating test cases was carried out.The research tested ten million calculations with the Newton-Raphson,successive-substitution,and the Hybrid Newton–Successive Substitution Method.The results showed the Hybrid Newton–Successive Substitution Method can solve all the multiphase and multi-component equilibrium problems effectively and robust.（4）The common oil-gas-water flash calculation ignores the dissolution of hydrocarbon in the water phase and the effect of brine.For this reason,a complete oil-gas-water three-phase flash calculation was proposed in this research.In the meanwhile,the Hybrid Newton–Successive Substitution Method was verified using the experiment result,while the method was accurate and useful.