An experimental study to control sand production in weakly consolidated sandstone formations: A chemical approach on formation strength

Sand production poses significant challenges in oil and gas production, affecting over 70 of oil wells, particularly with increasing water production. Evaluating sandstone formation strength as a function of water saturation under different reservoir conditions is therefore critical for mitigating this issue. This study investigates the influence of water saturation on the strength of weakly consolidated sandstone, focusing on silica dissolution. Additionally, it examines the effects of reservoir parameters such as time, temperature, and salinity on formation strength. Sodium phosphate was used as an inhibitor to mitigate silica dissolution. Unconfined Compressive Strength (UCS) tests were conducted to measure core strength, while UV-Vis spectrophotometry quantified silica dissolution. The results indicate that core strength decreases with increased water saturation, which accelerates silica dissolution. Notably, temperature and time exacerbate both strength reduction and silica dissolution. Distilled water had a more pronounced impact compared to seawater. At maximum water saturation (100), core strength dropped to 5.46 MPa, accompanied by 19.8 mg/l of silica dissolution. The most significant reduction in core strength (2.4 MPa) and the highest silica dissolution (32 mg/l) occurred at 90°C. Sodium phosphate effectively maintained core strength near its original value by limiting silica dissolution. Without sodium phosphate, core strength decreased from 9.56 MPa to 5.46 MPa, representing a reduction of over 67 compared to its original strength. In contrast, with 1 wt sodium phosphate, core strength only slightly declined from 9.56 MPa to 9.31 MPa. This study highlights the critical role of silica dissolution in sandstone weakening. Therefore, controlling silica dissolution with sodium phosphate is essential for maintaining formation strength and mitigating the risks associated with sand production. © 2025