Using 1,2 dimethylimidazole to improve gel thermalstability for wellbore plugging in ultra-high temperature fractured reservoirs

Abstract

Working fluid loss as well as formation damage is usually encountered as a big challenge during well completion and workover for fossil-fuel production. Polymer gel is widely used for wellbore plugging to isolate the working fluid and the reservoir for controlling fluid loss and protecting the reservoir. However, with the increasing number of ultra-high temperature well (>180 °C) operations, the thermal stability of the gel plug is increasingly required. In this paper, 1,2 dimethylimidazole (C₅H₈N₂) is first used to prepare a gel plug. The effects of C₅H₈N₂ on gel gelation at dynamic heating mode, viscosity, elasticity, thermal stability and temporary plugging performances are evaluated at 190 °C. It is found that the addition of C₅H₈N₂ does not affect the gelation, while a slightly viscosity-reducing effect is exhibited. At 190 °C, the gel without C₅H₈N₂ broke down within 4 hours and lost its temporary plugging performance, while the gel with 20% imidazole remained unbroken after 60 hours. For the fractured core (5 cm in length) plugging experiments, the addition of 15% C₅H₈N₂ significantly increased the breakthrough pressure of gels from 0.2 MPa to 1.9 MPa compared to pure gels (without C₅H₈N₂). The enhancement mechanism of C₅H₈N₂ is investigated. Recommendations for the application of gels with C₅H₈N₂ are given in the paper. This paper provides an avenue for the development of gel plug to deal with wellbore temporary plugging jobs in ultra-high temperature fractured reservoirs.

GRAPHICAL ABSTRACT

Keywords:

• 1,2 dimethylimidazole
• gel
• wellbore plugging
• ultra-high temperature
• natural gas well
• fractured reservoirs
• dynamic heating

Additional information

Funding

This work is supported by Distinguished Young Scholars Fund in Sichuan (Award No. 2019JDJQ0036), Fok Ying-Tong Education Foundation, China (Grant No. 171043), Regional Innovation Cooperation Project of Sichuan Province (Grant No. 2020YFQ0036) and Youth Science and Technology Innovation Team Fund of Southwest Petroleum University, China (Award No. 2018CXTD08).