Fracturing Technologies with Profile Control and Water Shutoff for Medium and High Water-Cut Wells in Ultra-Low Permeability Reservoirs of Changqing Oilfield

Due to the influence of the high-permeability zone, the water cut will increase and reservoir stimulation results are poor when conventional refracturing is implemented in the ultra-low permeability reservoirs of Changqing Oilfield at the medium and high water-cut development stage. Focusing on the long-term injection-production development practices of typical reservoirs and infill well production data, this paper uses 3D geological modeling to analyze the stimulation mechanism of fracturing with profile control and water shutoff in medium and high water-cut oil wells. The influences of fracturing parameters on the effect of repeated stimulation were studied, and a refracturing concept hinging on “profile control and water shutoff in the pad adding stage to control water cut and dynamic multistage temporary plugging fracturing to improve single-well production” was advanced. PEG-1 gel was developed through laboratory experiments and when the mass fraction of its main agent achieved 5%-10%, gel strength would be maintained at a high level. With an optimal injection flow rate of 1.5 m³/min and an injection volume of 300-600 m³, the high-permeability zones at the fracture depth of 40-80 m could be effectively plugged. In this way, the dynamic multistage temporary plugging fracturing technology was optimized. As a result, the net pressure in the fractures was increased to above 5.0 MPa, fractures extended from the low-stress zone to the high-stress zone, and the production of the oil remaining laterally was thereby produced. Field test results showed that average daily oil production improvement per well was 1.07 t/d and water cut was reduced by 9 percentage points after the measure was implemented, which indicated that the goal of increasing oil production while controlling the water was accomplished by refracturing the medium and high water-cut wells. The proposed fracturing technology with profile control and water shutoff provides a new technical concept for the repeated stimulation of medium and high water-cut wells in ultra-low permeability reservoirs of Changqing Oilfield.