Laboratory study and field verification of a thermo-responsive water shutoff agent

For the low-pressure and low-permeability oil reservoirs, water injection development and hydraulic fracturing stimulation are essential. The ideal water flooding mode is piston-like displacement. However, due to the heterogeneity of reservoirs, most of the injected water flow to oil wells along the dominant channel (i.e., high permeability area, natural fractures, or artificial fractures), which causes the decrease of oil displacement efficiency, the premature water breakthrough of oil wells, and high water content. Hence, over a span of decades, a compelling body of work has focused on the development of water shutoff agents. According to its working mechanism, water shutoff agents were divided into selective and non-selective water shutoff agents. However, the water shutoff agents mentioned above have been tested in more than 350 wells of Changqing oilfield, and the success rate was unsatisfactory. Therefore, this study aimed to develop a thermo-responsive water shutoff agent (TRWSA) with high plugging strength and compact structure. Through a series of laboratory experiments, the key performances of TRWSA for field application were tested and evaluated. First, the initial viscosity of TRWSA was 34.5 mPa s, which could easily pass through any completion tool (e.g., screen pipe and gravel pack) and enter any size fracture. Second, the TRWSA was non-water soluble and its phase-transition characteristics were not affected by guar gum fracturing fluid. Third, the phase transformation position of TRWSA could be determined by adjusting the SA-DST dosage and the wellbore-reservoir temperature. Fourth, its plugging strength was greater than 19.1 MPa and the volume retention rate was up to 99.13%. In addition, the field application results showed that oil production increased from 0.08 m3/d to 5.37 m3/d, and water content decreased from 98.6% to 9.8%. The TRWSA was satisfactory and had a great application prospect.