On Improving Water-Based Drilling Mud Swelling Control Using Modified Poly(Vinyl Alcohol)s.

One of the most challenging issues when drilling under high-temperature, high-pressure (HT/HP) conditions is wellbore instability caused by clay swelling and fluid loss of the drilling mud. One of the most difficult issues when drilling under high-temperature, high-pressure (HT/HP) conditions is wellbore instability caused by clay swelling and fluid loss in drilling mud. Two modified PVOHs, nonionic and cationic polymers made from sodium bentonite clay and deionized water at concentrations of 0.08, 0.28, and 0.49 wt.%, were introduced to WBM percent. A series of specific gravity and mud rheology experiments at 25, 55, and 85 °C indicated that both values drop monotonically with increasing temperature, regardless of PVOH addition or concentration. A temperature increase of 30 °C decreases the mud viscosity of WBM (without PVOH) by 18% from its starting value, on average. Only 0.1% of cationic and nonionic polymer reduces viscosity by 10% and 0%, respectively. Experimenting with mud samples for 5 h revealed that adding nonionic polymers enhances mud filtration by up to 34.7%, 1.25 times more than that achieved from cationic polymers under the same filtration circumstances. Increasing the filtration temperature moderately affects mud cake generation due to increased mud swelling index and preferential adsorption by nonionic polymer. The latter observation was corroborated by determining the polymer content of the filtrates. Therefore, it was shown that nonionic polymers adsorbed more (118.9 mg/g) than cationic polymers (84.51 mg/g). Increased filtration temperature moderately affects mud cake generation due to increased mud swelling index and preferential adsorption by nonionic polymer. The latter observation was corroborated by testing the filtrates for the polymer content. As a result, it was discovered that nonionic polymer adsorbed more (118.9 mg/g) than cationic polymer (84.51 mg/g). Thermogravimetry analysis (TGA) finally tested the thermal stability of polymers.