玛湖油田致密砾岩油藏CO2前置压裂提产机理OA

Aiming at the problem of low recovery of conventional hydraulic fracturing due to development of com-plex pore structures and high proportion of small pores in tight conglomerate reservoir with"three lows"(low pres-sure coefficient,low oil saturation and low formation saturation pressure difference)characteristics in Mahu Oil-field,the mechanism of CO2 pre-pad fracturing to enhance oil recovery in tight conglomerate is studied systematical-ly in 3 aspects of improving microscopic pore throats producing,enhancing oil mobility and strengthening fractures network stimulation through high-pressure and high-speed core injection,high-temperature and high-pressure me-dia interaction and pseudo-triaxial fracturing simulation experiments.The results show that high-pressure injection of CO2 significantly changes the microscopic pore throat structure,increasing total porosity of core by 7.7%when displacement pressure difference is increased by 6 MPa,and lower limit of pore throat producing is reduced from 0.1 μm to 0.03 μm.High-pressure injection changes wettability of rock to neutral,and significantly reduces interfa-cial tension and adhesion work of oil,effectively improving CO2 molecular adsorption and oil displacement efficien-cy.CO2 has obvious effects on increasing energy and reducing oil viscosity,and has strong solubility to acid-soluble minerals and weakly cemented substances in conglomerate,effectively increasing oil displacement energy of forma-tion,improving reservoir properties and enhancing oil fluidity.CO2 pre-pad can significantly increase complexity of hydraulic fractures network and increase drainage area.The research reveals comprehensive production enhance-ment mechanism of CO2 pre-pad fracturing in tight conglomerate reservoirs,and provides key theoretical foundation for optimization of fracturing process parameters and large-scale promotion of this type of reservoir.