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Study On CO2 Foam Fracturing Fluid System For Enhancing The Recovery Of Oil And Gas Reservoirss

Posted on:2021-01-29Degree:MasterType:Thesis
Country:ChinaCandidate:X H ZhangFull Text:PDF
GTID:2381330602483886Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
With the rapid development of industrialization,conventional oil/gas reservoirss are drying up,and the efficient development of unconventional oil/gas reservoirss,such as low permeability reservoirss,is crucial to alleviate the contradiction between energy supply and demand.Fracturing is one of the most effective stimulation methods for low permeability unconventional oil/gas reservoirss.The application of carbon dioxide(CO2)foam as fracturing system to enhance crude oil recovery and shale gas recovery is a combination of enhancing oil/gas recovery with greenhouse gas economic utilization and carbon sequestration,and has become a research hotspot in the oil/gas field in recent years.Since CO2 bubbles are difficult to exist stably in the aqueous phase,and the stabilizing effect of conventional surfactants on CO2 foam is generally poor,it is a great challenge to prepare CO2 foam with ideal stability,especially CO2 foam with adaptability to low permeability oil/gas reservoirss Therefore,the research on the generation and stabilization mechanism of CO2 bubbles,the development of CO2 foam stabilizers with excellent performance,and the establishment of a method for generating stable small-sized CO2 bubbles are not only of great theoretical significance,but also of high application value for promoting the application of CO2 foam fracturing system.In this paper,hydrophobically modified water-soluble polyelectrolyte(HMPE)was used as polymeric surfactant to stabilize the CO2 bubbles.The gas flow method and pressurization-decompression method were used to produce millimeter-sized and micron-sized CO2 bubbles respectively.The CO2 foam system had excellent static stability,dynamic stability and rheological properties,revealing the influencing factors and mechanism of the generation and stability of CO2 bubbles in different size ranges.Furthermore,the interaction between CO2 foam and solid particles was explored,and it was found that the CO2 foam system had a superior-bearing capacity for proppants and the advantage of low friction resistance.This shows that the CO2 foam system has important prospects as a foam fracturing fluid to improve oil and gas recovery.The main contents of this paper were listed as below:(1)The stability of CO2 foam prepared by HMPE solution was studied,and the stabilization mechanism was discussed.Firstly,the bulk phase properties of HMPE solution were investigated.The critical association concentration(CAC)of the solution was 0.14 wt%,and the viscosity of the solution decreased with increasing shear rate,showing the pseudoplastic behavior.The millimeter-sized CO2 bubbles produced by gas flow method had good static stability,the dynamic apparent viscosity also remained high value under the dynamic shear for a long time.The study of interfacial rheology showed that the elastic modulus(G’)of CO2 foam is larger than the viscous modulus(G"),showing the elastic characteristics.HMPE molecules adsorbed on the interface to form a dense foam film,which improved the stability of CO2 foam.Moreover,HMPE can enhance the apparent viscosity of CO2 foam,improving the liquid carrying capacity and slow down the liquid drainage of the liquid film.The pressurization-decompression method was used to produce micron-sized CO2 bubbles.The diameter of the microbubbles was about 30~50 μm.The electrical interface enabled the bubbles to self-lubricated and reduced the friction resistance of foam fluid.The results showed that the number of CO2 microbubbles increased significantly with the increase of equilibrium pressure.The attenuation of microbubbles was mainly caused by the diffusion of CO2 gas through liquid film.This work provideed theoretical guidance for the development and application of CO2 foam with good stability.(2)Investigate the sand-carrying performance of CO2 foam system prepared by HMPE solution.Firstly,the interaction and mechanism between CO2 microbubbles and ceramsite were explored,and it was found that CO2 microbubbles could be firmly attached to the surface of ceramsite.The sand-carrying performance of CO2 foam fracturing fluid system was evaluated by static settlement experiment.The static settling velocity of CO2 foam was 1.6 × 10-6 m/s at loading 35%ceramsite,which was much lower than the reported value in the literature and fully meeted the requirements of the maximum allowable settling velocity of proppants in practical application.Combining the experimental results of various aspects,the sand-carrying mechanism was revealed.This work provideed theoretical basis and technical support for the construction design of foam fracturing system in the exploitation of oil/gas reservoirss.(3)The performance of CO2 foam prepared by the composite system of SiO2 nanoparticles/surfactant CTAB and HMPE was studied.The bulk phase properties of the composite system solution and the static stability,viscosity and viscoelasticity of the CO2 foam were investigated.The results showed that SiO2 nanoparticles and HMPE molecules adsorbed on the CO2/liquid interface,which made the CO2 foam has good stability.SiO2 nanoparticles blocked the cross-linking between adjacent CO2 bubbles,reduced the dynamic apparent viscosity of C02 foam,and reduced the friction resistance of the foam fracturing fluid system.The CO2 foam prepared by CTAB/HMPE composite system had a good stability.Most interestingly,the stability of CO2 foam formed by the system was higher than that of N2 foam.The mechanism was revealed by the combination of molecular simulation and experiment,it was found that the interaction energy between the polar base of CTAB and CO2 was larger.The research work revealed a new way for the further optimization of CO2 foam system.In summary,the hydrophobically modified water-soluble polyelectrolyte HMPE was used to stabilize the CO2 foam in this paper and the formation and stabilization mechanism were explored.The method of preparing CO2 bubbles with different sizes was established.The CO2 foam system had excellent sand-carrying performance and can reduce friction resistance,which had an important prospect as a foam fracturing fluid to improve the recovery of low-permeability oil/gas reservoirss.This work not only provideed theoretical guidance and experimental basis for the efficient development of low-permeability shale oil/gas reservoirs,but also broadened the application range of hydrophobically modified water-soluble polyelectrolytes,which had both theoretical significance and application value.
Keywords/Search Tags:CO2 foam, Polymeric surfactant, Fracturing fluid, Microbubbles, Low-permeability oil/gas reservoirs
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