Thermosetting resin is gaining more acceptances in Plug and Abandonment due to its excellent mechanical properties after set and ability for placement in locations cement cannot reach. A thorough understanding of its curing behavior such as gel time is essential to ensure safe placement and a good seal. This paper investigates the pressure-sensitive gelation behavior of polymer resin under in-situ conditions, and the pressure effect on the gel time of thermosetting resin was evaluated.
An innovative assessment methodology named CAPT (Consistency under Applied Pressure Test) was created to assess the curing process of thermoset resins in a pressurized consistometer. A series of resin samples were tested at temperatures ranging from ambient to 120°C with applied pressures up to 10,000 psi. The consistency was initially used to indicate the gel structure development of the resin while it was gelling. Based on the consistency data, the relationship between applied pressure and gel time of resins was studied and a new approach of modeling the curing process with the influence factor of pressure was proposed.
The primary observation was the confirmation that the gelation process of thermosetting resin under applied pressure was faster than that under atmospheric pressure. However, the gel time had big variations. The pressure sensitivity mainly depended on the initiators and it was only partly dependent on the temperature. There was a threshold value for the pressure effect on the gel time. Below the threshold, the gel time only decreased by around 5%. Above the threshold, the pressure effect was much larger where the gel time decreased by 20% - 30%. This could be mainly attributed to the thermodynamic effect caused by pressure accelerating the polymerization process, resulting in a shorter gel time. Meanwhile, these results help explain why the curing behavior of thermosetting resin placed underground where high pressure is encountered often differs from the laboratory-predicted performance. Besides indicating the relative strength development, consistency analysis could also be used to assess the pressure effect on the gelation process of a resin sample in down-hole operations with applied pressures. Thus, CAPT would be more suitable than a conventional reactivity test to propose a new approach of modeling the gel time of thermosetting resin systems with the influence factor of pressure.
CAPT is a novel method to accurately evaluate the curing process of thermosetting resin and indicate its relative strength development. This helps engineers reach a good balance between designing proper operations and preserving mechanical properties in the plug and abandonment process.