The mechanism of hydraulic fracturing-assisted oil displacement technique applied to enhance oil recovery by high-pressure reduced adsorption
The hydraulic fracturing assisted oil displacement(HFAD)technique,which is based on large-scale hydraulic fracturing,has been applied to the old oilfields with extra high water cut,achieving a remarkable effect of enhanced oil recovery(EOR).To fur-ther clarify the impact of HFAD technique on the oil displacement efficiency of HFAD agents,the paper investigates the adsorption loss of HFAD agents on the porous media surface under high pressure.Firstly,by carrying out dynamic adsorption experiments un-der ordinary pressure and high pressure conditions,changes in the dynamic adsorption capacity of HFAD agents on the core surface during HFAD process were compared and analyzed.In combination with conventional mercury injection experiment and scanning electron microscope(SEM)test,the mechanism of reduced absorption under high pressure was clarified.Then the impact of high-pressure reduced adsorption on enhanced oil recovery by HFAD technique was confirmed by the physical simulation experiment of re-verse hydraulic fracturing-assisted oil displacement.Research shows that the dynamic adsorption capacity of HFAD agents on the core surface is decreased with the increase of the displacement pressure difference.When the displacement pressure differences are 0.5 MPa,1.0 MPa and 1.5 MPa,the dynamic saturated adsorption capacity of HFAD agents on the core surface is decreased by 40.67％,62.17％and 72.38％,respectively,as compared with that under the displacement pressure difference of 0.1 MPa.At a high pressure,the core pore structure is changed,i.e.,the average pore radius and seepage velocity are increased,fluid seepage re-sistance is decreased,and the dynamic saturated adsorption capacity of HFAD agents on core surface is reduced.Additionally,the oil displacement efficiency of HFAD agents can be improved by reduced absorption under high pressure,which is 1.96 times higher than that under ordinary pressure.In conclusion,high displacement pressure in the HFAD process can effectively reduce the dynamic ad-sorption capacity of HFAD agents in reservoirs,thus improving the oil displacement efficiency.The research results are of important guiding significance for further EOR in the field application stage of HFAD technique.
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维普
