Simulation Study On Gas-Liquid-Solid-Three-Phase Flow Of CO₂ Foam Fracturing In Wellbore

With the development of science and technology,the demand of people for oil and gas resources is increasing,and conventional oil and gas resources can no longer meet the demands for energy in today's society,the unconventional oil and gas resources are getting more attention,but it is impossible to produce oil and gas without reservoir reform.Hydraulic fracturing is an effective simulation method,but the fracturing fluid will have a physical and chemical interaction with the formation,which will cause varying degrees of damage to the reservoir,thus reducing the production of the reservoir after fracturing.In order to resolve the question by hydraulic fracturing,CO₂ foam fracturing technology is proposed and gradually applied to unconventional oil and gas resources exploitation.CO₂ foam fracturing fluid has the advantages of high viscosity,easy flowback,and water conservation,which can effectively improve production.At present,the research of temperature and pressure of CO₂ foam fracturing fluid in the wellbore and the friction only consider the gas-liquid two phases,ignoring the influence of solid phase on the fluid properties,which has a large error to the results.This paper establishes the CO₂ foam fracturing fluid gas-liquid-solid three-phase flow model to calculate the temperature and pressure and friction in the wellbore.Based on the research content of this paper,the following results are as follows:(1)The model of CO₂ foam fracturing fluid was established.The accuracy of the model is verified by comparing with the measured temperature and pressure data of fracturing wells.The average temperature error and average pressure error of CO₂ fracturing is 5.51%,and the is1.6%,respectively,The average temperature error of gas-liquid-solid three phases CO₂ foam fracturing is 2.7%.(2)CO₂ foam fracturing pressure decreases with the increase of injection mass flow rate.When the mass flow rate increases by 10 kg/s,the bottom hole pressure of gas-liquid-solid three-phase flow decreases by about 5 MPa and the temperature decreases by 0.5?.The bottom hole pressure of gas-liquid two-phase flow decreases by about 8 MPa and the temperature decreases by 0.4?;The temperature of CO₂ foam fracturing fluid in the wellbore increases with the increase of injected foam quality.Under the same conditions,the temperature increase of gas-liquid-solid three phases is higher than that of gas-liquid two phases when the foam quality is increased;Considering the influence of proppant,the hydrostatic column pressure of CO₂ foam fracturing fluid in the wellbore gas-liquid-solid three phases is higher than that of gas-liquid two phases,and the pressure increases with the increase of proppant volume concentration.Proppant has a significant impact on the pressure of CO₂ foam fracturing fluid,while the change of proppant volume concentration has no obvious effect on the temperature of CO₂ foam fracturing fluid.(3)During the fracturing process,fracturing fluid enters the formation through the perforation,and the proppant erodes the perforation,resulting perforation become smooth,reduced frictional,and increased perforation diameter.With the increase of fracturing fluid injection time,the perforation diameter gradually increases,and the perforation expands rapidly in the initial stage of injection.With the increase of time,the expansion speed gradually slows down.As the diameter of the perforation erosion increases and becomes smooth,the friction decreases gradually;With the increase of injection flow rate,the effect of fracturing fluid on perforation erosion will be increased.With the increase of injection time,the effect of different injection flow rates on perforation erosion will be more obvious;The increase of the initial diameter of the hole will lead to the decrease of friction,and the smaller the initial diameter of the hole,the faster the expansion rate of the hole diameter.