Enhanced hydrophobically modified polyacrylamide gel for lost circulation treatment in high temperature drilling

Abstract

Cross-linked polymer gels have attracted a strong interest for lost circulation treatment in drilling operation. However, the application of gels in high temperature loss zone was still limited due to the problems of short gelation time, weak strength, poor thermal stability, etc. In this paper, a novel cross-linked modified polyacrylamide gel (HMP-Gel), which consisted of a hydrophobically modified polyacrylamide (HMP) and crosslinker polyethyleneimine (PEI), was designed and developed. The novel HMP was synthesized to form and strengthen the gel structure due to the crosslinkable amide groups and associable hydrophobic moieties, and PEI was used to extend gelation time at high temperature. In detail, the HMP of acrylamide (AM), octadecyl acrylate (OA), and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) was prepared using micellar copolymerization under the best conditions. The molecular structure of HMP was characterized using FT-IR, gel permeation chromatography and environmental scanning electron microscope (ESEM). In gelation process, effects of PEI concentration, HMP concentration, temperature and salinity on gel performance (plugging efficiency and gelation time) were systematically investigated. Plugging performance of HMP-Gel was studied using both the HTHP carbonate bed filtration loss test and HTHP crack plugging test. Rheological property of HMP-Gel was studied to access the elastic properties and gel strength. Results of various factors on gel performance indicated that HMP-Gel showed the good plugging efficiency for carbonate bed and controllable gelation time in the temperature range of 100–150 °C. Results from plugging tests indicated that the HMP-Gel had better sealing ability than HPAM-gel for both the high permeable carbonate bed and 1-3 mm cracks loss zone. And the breaking pressure of HMP-Gel could reach 1000 psi and 600 psi for carbonate bed and 3 mm slot, respectively. Additionally, HMP-Gel also showed high elasticity, gel strength, and excellent thermal stability at 140 °C. Finally, the micro-morphology of gel was further analyzed through ESEM. A new strategy of using hydrophobically modified polyacrylamide to strengthen the gel structure was proposed, and extensive laboratory tests suggested that HMP-Gel could be considered as an efficient plugging material and showed great potential in applications for lost circulation in high-temperature well.