Innovative thermo-responsive in-situ generated proppant: Laboratory tests and field application

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 °C. 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/cm3, 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.