Development and Plugging Mechanism of High Strength Epoxy Resin-Based Plugging Agent Used in Offshore Oil and Gas Wells with Sustained Annular Pressure

The problem of annular pressure buildup is especially prominent in offshore high temperature and high pressure oil and gas wells, which is prone to causing leakage, corrosion and failure of wellbore structure, thereby seriously endangering operational safety and wellbore integrity. To address the limitations of conventional cement and resin type plugging materials in flowability, curing controllability and mechanical properties, a novel high-strength epoxy-based plugging agent for operation under non-drilling string conditions was developed. This plugging agent is formulated by blending 35%-55% epoxy resin, 5% hyperbranched resin, 20%-30% diluent and 10%-40% medium-temperature curing agent. This plugging agent was evaluated in laboratory experiments on its rheology, mechanical properties, thermal stability and sealing performance. The experimental results show that this plugging agent has a good rheology at temperatures between 25 ℃ and 65 ℃ (with viscosity ranging from 35 to 185 mPa·s), a curing time that can be controlled between 0.11 h and 25 h, a compressive strength ranging from 31 to 63 MPa, and a bonding strength greater than 11 MPa/8 cm at temperatures between 20 ℃ and 100 ℃. It possesses excellent thermal stability (with decomposition temperature up to 380 ℃), and achieves zero permeability under 20 MPa gas pressure. With high strength, high temperature resistance and excellent sealing capacity, this plugging agent can be used in complex offshore environment and can provide technical support for annular pressure control in offshore wells.