Experimental study and field verification of fracturing technique using a thermo-responsive diverting agent

Abstract Fracturing is an essential measure to increase well productivity, especially in low-permeability reservoirs. When the reservoir has the characteristics of large stress difference, less natural fracture and poor brittleness, it is difficult for fracturing to form complex fracture and the effective stimulation reservoir volume (ESRV) is low, which leads to low well productivity. Therefore, temporary plugging and diverting stimulation technology (TPDST) has been developing to increase ERSV and the complexity of fractures. Diverting agents are crucial in TPDST. However, existing diverting agents with the characteristics of poor injection property (e.g. difficult to pass through screens completion), reservoir damage, poor controllability of plugging strength, or limited application temperature are not satisfactory. Hence, this study aimed to develop a novel diverting agent with the property of solution (sol) - gel - sol transition behavior at different temperatures. Through a series of laboratory experiments, the key performances of the thermo-responsive diverting agent (TRDA) were tested and evaluated. The findings demonstrated that the viscosity of TRDA was about 8 mPa·s at room temperature, and it had good injection property. The plugging strength was controllable, and the damage to core permeability was almost zero. Both the phase transition times from sol to gel and from gel to sol decreased with the increase in temperature. Moreover, the TRDA also had good compatibility with the reservoir fluid, fracturing fluid, and acid fluid. Besides, the TRDA was successfully used in hydraulic fracturing and acid fracturing. The field test results showed that the maximum injection pressure increment was about 20 MPa, and the micro-seismic monitoring demonstrated that new fractures were formed. The production and injection data confirmed that the stimulation effect was remarkable. Thus, the TRDA was shown to have great application potential.