Preparation and performance of an environmental-friendly degradable semi-interpenetrating network temporary plugging agent for acidification

Since 1896, acid stimulation technology has been widely using in world's reservoirs. Temporary plugging agent (TPA) was one of the key materials for achieving uniform acidification of long wellbore in heterogeneous reservoirs. To solve the problems of uncontrollable crosslinking time, incomplete degradation, and weak acid resistance of existing polymer TPA, this study developed a novel TPA named SAXG using environmental-friendly materials. The formula of SAXG was optimized, and its performances were tested through a series of SEM, FT-IR, temporary plugging, core displacement, etc. Some interesting insights have been gained. First, SAXG, a type of hydrogel, was formed through calcium ion cross-linking and intermolecular forces. The optimal formula of SAXG was 0.7 wt% sodium alginate + 0.3 wt% sodium gluconate through orthogonal experiments, with deformation and gelation time as the objectives. Secondly, the gelation time of SAXG was controllable, from 14 min to 456 min. SAXG can be completely degraded in the ground or reservoir, and factors such as temperature and acid only affect its degradation rate. Finally, the core permeability after temporary plugging acidification increased by 2.79 times compared to that after traditional acidification. The breakthrough pressure of SAXG was 9.1 MPa, and the permeability recovery rate after SAXG degradation was as high as 98.6%.