Cross-linked polyacrylamide gel as loss circulation materials for combating lost circulation in high temperature well drilling operation

Cross-linked polymer gel has been broadly used to plug severe lost circulation and to improve the strength of the near-wellbore in natural fracture or carbonate cave strata. Gelation time and gel strength are the key factors for gel plugging. In this study, a cross-linked polymer gel with controlled gelation time and high gel strength was fabricated at high temperature, named HTCMG. It was prepared from an acrylamide monomer, crosslinking agent and initiator by free radical polymerization. To extend gelation time at high temperature, colophony was used here to encapsulate the initiator. This complex was characterized under the Fourier transform infrared spectroscopy (FT-IR), by thermogravimetric analysis (TGA) and under the scanning electronic microscopy (SEM). The effects of pH, temperature, monomer concentration and salt concentration on gelation time were assessed. To examine the viscoelastic property and tensile strength of HTCM, HAKKE Mars 40 and uniaxial compression apparatus were employed, respectively. The plugging property of HTCMG was tested by the core displacement test and high-temperature and high-pressure (HTHP) fracture plugging test. According to the results, HTCMG can form gel in temperature range of 80-150 degrees C, and the gelation time can be practically adjustable. The results of the core displacement test revealed that the bearing capacity of HTCMG can reach a peak of 9.8 MPa at 150 degrees C, and it can effectively plug 3 mm-width slot. HTCMG is characterized by a lower plugging time, a higher successful plugging ratio and lower economic cost than normal loss circulation materials, suggesting that HTCM is useful for addressing the lost circulation of high-temperature well, and it is of huge significance to engineering application.