New Superfine Cement Plugging System and It’s Laboratory Plugging Performance for High Permeability Sandstone Reservoir After Polymer Flooding

Multiple circular extract techniques has been adopted in Daqing oil field for long time, resulting in many problems including high dispersion of remaining oil in sandstone reservoir, extensive development of preponderant seepage channels, ineffective circulation, and failing to enhance recovery efficiency. According to the structural characteristics of the high permeability sandstone reservoir after multiple circular polymer flooding, a new superfine cement plugging system was developed with superfine cement and auxiliary agents. The injection capacity, the injection mode, the injection parameter and the simulation of the plugging performance were studied. As a result, the initial setting time (60–120 h) and the final setting time (120–240 h) of the plugging system could be controlled. The injection viscosity was less than 50 mPa·s. The suspension of the system was stable, and the sedimentation rate decreased with increasing of time. In the first 12 h, the sedimentation rate dropped from 9.9 cm/h to 1 cm/h, and after 25 h, the system sedimentation rate was less than 0.5 cm/h. The compressive strength was higher than 20 MPa after solidification. With the injection rate of 1 mL·min−1, and the slug combination of 0.2 PV polymer and 0.9 PV plugging system, the injection pressure of a 30 cm long core (Water permeability measurement 500–5000 mD) was less than 0.8 MPa, the plugging rate was greater than 90% (Maximum 95.96%). This research shows that the new superfine cement plugging system can realize the permanent plugging of the preferential seepage channels of the sandstone reservoir after the polymer flooding, reconstructing the reservoirs and remodeling the oil reservoirs, which provides technical support for exploiting the top of thick oil reservoirs and the residual oil in the medium-low permeable oil reservoirs efficiently, further enhancing the oil recovery rate.