Development and evaluation of an environmentally friendly water-block-prevention agent for drilling and completion operations in tight sandstone gas reservoirs

Abstract

Water-block damage during drilling and completion can reduce gas flow in tight sandstone reservoirs because water-based fluids are easily retained in narrow pore throats. In this work, a non-fluorinated environmentally friendly water-block-prevention agent hexadecyldimethyltertiary amine quaternized silicone oil (FSS) was synthesized from hexadecyldimethyltertiary amine, epoxy-terminated polyether silicone oil, and acetic acid via a quaternization addition reaction. The molecular structure of FSS was characterized by Fourier-transform infrared spectroscopy, and its surface activity, wettability, and water-block-prevention performance were evaluated and compared with a fluorocarbon anionic water-block-prevention agent, PFAc. The results show that FT-IR analysis confirmed the successful synthesis of FSS; at a concentration of 0.2 wt%, FSS substantially reduces the surface tension of water to 24.93 mN/m, showing a strong surface-tension reduction ability. At test temperatures ranging from 20 to 140 °C, the surface tension of 0.3 wt% FSS remained within 23.0 to 26.5 mN/m, indicating good thermal tolerance. After soaking sandstone core chips in a 0.5 wt% FSS solution, the water contact angle on the sandstone surface increases from 28° to 86.7°, indicating that FSS can shift the wettability of sandstone core surfaces from strongly water-wet toward neutral-wet. Following core permeability recovery evaluation with 0.3 wt% FSS, core permeability recovery rate reached 83.67%, indicating a relatively high water-block-prevention performance under the tested conditions. Overall, the comprehensive performance of FSS is comparable to that of fluorinated water-block-prevention agents PFAc, while offering improved environmental compatibility and broader application potential.