Research and application of microfoam selective water plugging agent in shallow low-temperature reservoirs

Abstract There exists a large interlayer pressure difference in the oil wells of the Fuyu oilfield, and the high-pressure layer has a relatively high liquid production. The low-pressure layer is characterized by a relatively low liquid production, and water shut-off is urgently needed. Selective plugging technology is designed to temporarily block the oil layer before plugging the water layer, which is suitable for low-temperature shallow reservoirs. The foaming comprehensive exponent is considered to optimize the formula of the temporary plugging agent, consisting of 200 mL clean water, 0.25% sodium hexadecyl sulfonate, 0.8% sodium carboxymethyl cellulose, and 0.8% soluble starch. In addition, the formula of the multicomponent gel plugging agent is designed via extremum difference analysis, and the formula is 5% acrylamide (AM), 5% acrylic acid (AA), 0.8% PVA, 0.3% N,N-methylenebisacrylamide, 0.1% ammonium persulfate, and 0.2% sodium hydroxide. The selective plugging performance and permeability recovery characteristics of the system are evaluated. The experimental results show that the microfoam temporary blocking agent is more suitable for a core permeability ranging from 100–200 × 10−3 μm2, and the plugging agent can quickly gel at low temperatures. Field tests in a typical well show that the breakthrough pressure gradient of the temporary plugging layer reaches 3.5 MPa/m, thereby effectively protecting the low-pressure layer, and the fluid production of the high-pressure layer is reduced from 13.7 m3/d to 0.6 m3/d, thus realizing the purpose of plugging the high-pressure layer.