Use of a Polymer Gel for Killing a High-Temperature and High-Pressure Gas Well

Abstract

Summary In the processes of oil and gas drilling, gas easily invades wellbores and adversely influences the safety in high-pressure gas reservoir drilling activities. In this study, a polymer gel was prepared for well killing in high-pressure gas reservoirs. The gelation performance of the gel under different conditions was experimentally examined. The gel can maintain high shear resistance, high-temperature resistance, and high-temperature long-term stability at 160°C and is thus suitable for the long-term isolation of high-temperature formations. The gel is sensitive to high concentrations of salt ions and must be prepared in the field using saline solutions with Na+ and Ca2+ concentrations lower than 20 000 and 500 mg/L, respectively. The gel can be easily oxidized and disintegrated by acidic solutions. The gel disintegration rate may reach 100% when subjected to ammonium persulfate and hydrochloric acid aqueous solutions at 160°C. Moreover, the polymer gel performance in application scenarios was examined. The gel density can be increased using barite and magnetite. The water loss percentage of the gel is less than 10% at 160°C, rendering its use suitable for well killing in openhole intervals, especially in water-sensitive formations such as mudstone and shale. The permeability recovery of the gas reservoir core is more than 90% when gasflooding is performed with oxidative degradation of the gel. The gel exhibits excellent well kill capacity, with a maximum value of 8.8 MPa/100 m after aging at 160°C for 3 days. Successful field test was conducted in the Tarim Basin, Xinjiang, China, which indicates that the gel can be used for well killing in high-temperature and high-pressure gas reservoirs.