Use of a Polymer Gel for Killing a High-Temperature and High-Pressure Gas Well
Yingrui Bai, Chengtong Liu, Jinsheng Sun, Kaihe Lv
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.