Experimental And Numerical Modelling Study On PVT Properties Of Foamy Oil

Numerous scholars studied the anomalous production performances,in terms of high oil reservoir factor and low production gas oil ratio,on primary production in solution-gas-drive heavy oil reservoirs,and found that the most significant reason for these phenomena is foamy oil flow.Based on the literature review,various pressure depletion tests were conducted in this study according to the dynamic mechanism in foamy oil production.The relations between the volumes changing of the foamy oil with the decline time under different pressure depletion styles and rates（For the constant pressure rate depletion,the depletion rates were 0.5 kPa/min,1.0 kPa/min,2.0 kPa/min and 4.0 kPa/min.For the constant volume rate depletion,the depletion rates were 0.5 cm³/hr,1.0 cm³/hr,2.0 cm³/hr and 4.0 cm³/hr）were researched,especially,bubble nucleation,bubble growth and bubble coalescence processes were studied in-depth.A new numerical model,foamy oil reaction rate model,was developed,and the test results were simulated by using this new model,as well,sensitive analyses were conducted on the main parameters,including reaction factors（k₁,k₂）and the times(t_pbp,t_cgp),at which the pseudo bubble point pressure and the critical gas saturation pressure occurred.Compared with the previous researches,different test approach was applied in this study.In the previous ones,the foamy oil stability was mostly focused on,and no effects on the pressure depletion rates were studied.The relationship between foamy oil volume and pressure depletion rates indicated that,the nucleated bubbles start to immigrate to the top of the system during the pressure depletion process,due to the gravity difference,leading to shorter distance from the bubbles to the gas-liquid interface occurred in the pressure depletion tests.So that,the gas evolved from the system quickly when the pressure declined to the critical saturation pressure,rather than slowly occurred in the sudden pressure decline process,which studied by former researchers.For different pressure depletion styles,the pseudo bubble point pressure decreases with the increases of pressure depletion rate.That is to say,with pressure depletion rate increases,the pressure at which the bubbles start to nucleate decreases.The compressibility of the heavy oil-methane system increases with pressure decreases,but the compressibility of the foamy oil decreases when the pressure is lower than the critical gas saturation pressure.For different pressure depletion rates,at the end of the depletion process,the rate of the free gas evolves from the system decreases with the pressure depletion rate increases.The reaction rate model in which the reaction factor was considered,was developed,based on the previous modeling studies（equilibrium models and non-equilibrium dynamic models）.For the first time,this new model mentioned that,during the foamy oil flow process,the continuous reaction rates among the solution gas,dispersed gas and free gas relate to the pressure depletion rates.This new model can be used to explain the effect factors better than the previous ones:k₁ and k₂control the gas phase changes from solution gas to dispersed gas and dispersed gas to free gas,respectively.Via numerical modelling study,we found that,with pressure depletion rate increases,the reaction factors k₁ and k₂ increase,that is to say,the transformation rates among the three types of gases have a proportional relationship with pressure depletion rates.Sensitive analysis results show that,the main factors in the reaction rate model are k₁ and k₂,they affect the gas types and gas mole concentrations.Although the effects of t_pbpbp and t_cgpgp are not remarkable,they can be used as the modification parameters to shorter the errors of the tests in the simulation process.