Abstract Water well profile control is the main way to control water channeling in low-permeability fractured reservoirs, and preformed particle gels (PPGs) are commonly used. A preformed particle gel was prepared and the synthesis conditions were optimized. The temperature and salt resistant performance, plugging performance were investigated and the field application was tested. The results showed PPGs exhibited good temperature and salt resistant performance. PPGs with larger particle size showed greater plugging strength but shorter valid period. Field tests suggested that multiple rounds of profile control should be employed using PPGs with different particle sizes to achieve deep profile control.
In order to explore the process of acid- and CO 2 -induced degradation of wellbore cement and the development of pre-existing leakage channels in wellbore cement under sulfate-rich geological CO 2 storage conditions, wellbore cement samples were immersed in SO 4 2- -bearing brine solution for 7 days, and the samples after reacting with the low and circumneutral pH solutions were scanned by a micro-CT scanner. HCl+Na 2 SO 4 solution was used to simulate the low-pH condition in deep formation waters and the possible existence of high sulfate ion content in deep formation waters. The acidification and carbonation results were compared, and the results given different pH values and different curing conditions were compared as well. The results show that the degradation of cement was related to the pH value of the reaction solution. There was a significant dissolution in the exterior of the cement sample after exposure to the low-pH solution, but the dissolution surrounding a penetrating borehole at the center of the sample (mimicking a leakage pathway within the wellbore cement in geological CO 2 storage environment) was limited. Comparison between acidification and carbonation results in this study shows formation of a thick carbonate layer due to cement carbonation, and this layer was not observed in the acidification result. As for different curing conditions of cement samples, no significant difference in cement alteration depth was observed for the acidification case. For the carbonation case, precipitations in the borehole occurred in the cement sample cured at ambient pressure, while the cement sample cured at high pressure did not produce any precipitation in the borehole. This study provides valuable information on how low pH-induced corrosion and HCO 3 - -induced cement carbonation contribute to structure evolution of wellbore cement in SO 4 2- -bearing brine under geological CO 2 storage environment.
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