For the sake of environment protection, shallow formation waters were studied for the preparation of guar gum fracturing fluids in gas fields, west Sichuan. The fracturing fluid prepared with formation water had viscosity of 100 mPa·s after shearing 60 min(170 s-1) at 45 ℃, rate of permeability impairment of only 23.86%, surface tension of 27.82 mN/m, rate of swelling reduction of 87.5%, residue content of 518 mg/L. The formation water fracturing fluids were successfully used in SF382 and SF384, which respectively improved natural gas production of 1.14×104 m3/d and 1.68 ×104 m3/d. This technology enabled the reuse of formation sewage water in gas fields.

The high water cut oil wells were unable to product normally because of the existance of fracture and natural microfracture in the low permeability fractured reservoir. In order to avoid the injected water going across to the old seam of oil wells in the process of water flooding and enhancing the sweep efficiency and oil recovery, the superfine cement plugging technology was put forward. Based on the optimization of water cement ratio of superfine cement, the concentration of corrosion inhibitor, reducing agent and defoaming agent in the plugging system was optimized, and the mechanical deformation capacity was also evaluated. The results showed that the optimum water cement ratio of superfine cement was 0.7 and the optimum cement slurry was the mixture of 800 head superfine cement, 0.4% corrosion inhibitor, 0.5% reducing agent and 0.5% defoaming agent. Because of the double efficacy of plasticizing and toughening, the slurry system had good mechanical deformation capacity and the flexural strength reached 48.9 MPa. This can completely met the plugging strength requirements in the field. This system has good application prospect in the old seam plugging of oil well in the fractured reservoir.