Research and Application of in Situ Gel Reinforced Foam System: Experimental and Field Study in Ordos Basin

The large volume of injected water flowed along the high permeability zone, which led to serious problems in the middle and late stages of flood development in ultra-low permeability fractured reservoirs. In this paper, we developed a novel gel-foam plug by using silica gel as a liquid phase dispersing medium for foam, evaluated and optimized the foaming and gelation performance of the gel-reinforced foam system. The gas-to-liquid ratio, injection volume, injection concentration, injection speed, and injection mode of the plugging agent were optimized by core-flooding experiments, and oilfield tests were conducted in oil fields. The plugging agent was formulated as follows: 5% sodium silicate +0.15% activator +0.2% delayed activator +0.6% foaming agent. The strength of the gel-reinforced foam system was 21702 mPa·s and the gelation time was 40 h, with the foaming volume of 869 mL and a foaming half-life of 960 s. The laboratory test results showed that the optimal gas-liquid ratio was 3:1, injection volume was 0.2 PV, injection concentration was 900 mg/L, injection speed was 0.04 PV/a, and injection method was four-slug injection in ultra-low permeability fractured reservoir. The water cut was reduced by 12.69%, the valid period was more than 8 months, and the cumulative oil increase volume was 173.98 t. The novel gel-foam developed in this paper was a new option for water treatment in this type of reservoir.