Cavitation-Jet Well-Cleaning and Permeability Enhancement Technology Based on the Synergistic Effect of Dual Cavitation: Principle, Tool, and Field Application

Summary Wellbore scaling and formation blockage critically constrain production capacity in sandstone reservoir-aged wells. Cavitation-jet technology is an economically efficient solution to increase the production of aged wells. However, subject to the power limitations of surface high-pressure pump systems, the erosion performance of cavitation jet has proved difficult to improve further, emerging as a primary bottleneck in advancing the technology’s application efficacy. To address this, we conducted this study to elucidate the self-excited cavitation modulation mechanism and flow field characteristics of an angular Helmholtz cavitation-jet nozzle (AHCJN) based on dual-cavitation synergy while also validating the feasibility of applying AHCJN for sandstone reservoir permeability enhancement. Finally, we designed a cavitation-jet well-cleaning and permeability enhancement tool and carried out flow field analysis and field application. Our research shows that the essence of the modulation mechanism of the self-excited cavitation jet by the AHCJN is the coupling effect of the fluid resonance principle and boundary layer instability. Under operational conditions of 30 MPa injection pressure, 0.1 MPa confining pressure, and 10 times the standoff distance, the AHCJN generates pulsed cavitation jet with peak pressure of 30.22 MPa, pulse amplitude of 9.82 MPa, and frequency of 2.5 kHz. The dual-cavitation jet effectively breaks sandstone, enhancing permeability by 12.59 times and 8.56 times at 12 times and 20 times standoff distances from the jet-drilled hole area, respectively. The numerical simulation under actual operating conditions reveals that the impact peak pressure of the cavitation-jet well-cleaning and permeability enhancement tool can reach 34.166 MPa, and a circular cavitation area is distributed around the jet impact area, with a total cavitation area of 288.91 mm², which can achieve full coverage operation around the well. After the stimulation in Well W of the Yanchang Oilfield, the liquid production increased by 93.71%, while the oil production increased by 70.42%. Well W has maintained stable production for 6 months consecutively to date, with an input/output ratio of 1:3.35. Our research results are expected to provide a theoretical basis and field reference for the cavitation-jet well-cleaning and permeability enhancement technology to achieve the production increase of aged wells in sandstone reservoirs.