Abstract
The bottlenecks of hydraulic fracturing in oil and gas reservoirs are related to placing proppants into narrow fractures and their long-distance transportation through the fracture.To break through the technical bottleneck,a thermo-responsive in-situ generated proppant(IGP)is proposed in this study.The IGP,which is a phase-transition fluid(PF)before the phase transition,is mixed with non-phase-transition fluid(NPF)in a certain proportion,thus obtaining a phase-transition fracturing fluid system(PFFS).The latter is injected into the reservoir in liquid form,and PF undergoes a phase transition under the stimulation of the reservoir temperature to generate IGP to prop fractures.NPF occupies some fracture spaces,which serve as high-conductivity flow channels for oil and gas after the NPF flow back.IGP could be formed in any fracture with different widths and realize long-distance transportation.A series of tests were performed,yielding the PFFS viscosity of about 56 mPa s at 20 ℃.The higher the temperature,the lower the viscosity before the phase transition,providing sufficient injectability to enter and prop artificial fractures of any width.The IGP apparent density was about 1.04 g/cm~3,and the roundness and sphericity of its particles were about 0.9.The phase transition time was reduced by adding more phase-transition adjusting agents(PTAA)and increasing the temperature.The drag reduction rate reached 69% at the PTAA content of 0.15%,strongly reducing the required pump's injection pressure.Under the same conditions,IGP had higher conductivity than quartz sand and ceramsite.Field application results proved that the stimulation effect is better than that of a conventional fracturing treatment,and the proposed fracturing material and procedure required less powerful and complicated equipment,simplified the treatment procedures,and reduced treatment time and cost.Therefore,it is a potential advanced material in future stimulation of oil and gas reservoirs.
NSTL