Novel Temperature-Responsive Organic Polymer Gel for Efficient Abandonment of Aged Porous Chalk Formations Characterized by X-ray Computed Tomography

The transition of the oil and gas industry toward renewable energy demands effective plugging and abandonment (P&A) of aging reservoirs. The first step of the P&A process involves depressurizing the annulus and production tubing by clogging the flow path from the bottom of the well. Under challenging conditions, the P&A process faces significant difficulties due to downhole issues like mineral scale deposition. This study introduces an innovative thermoresponsive polymer gel designed to temporarily seal low-permeability chalk reservoirs by direct injection into the reservoir formation. The gel, synthesized from polyacrylamide through free radical polymerization and modified via partial amination, forms a stable three-dimensional network when combined with an organic cross-linker. This stability is achieved in response to the low-temperature ranges (60-80 °C) characteristic of these wells. This development not only facilitates temporary P&A but also presents a viable alternative to cement for P&A, potentially preserving wells for future CO₂ storage. It could also be used to seal off a reservoir after CO₂ injection, to avoid potential future CO₂ leak. The study’s novelty lies in its focus on plugging low-permeability environments (around one millidarcy), a comparatively underexplored area. The gel’s performance was evaluated under various pH, temperature, and salinity conditions, and in both fractured and nonfractured chalk core samples using a core flooding system and 3D imaging with microcomputed tomography for real-time monitoring. Our findings reveal significant insights into the gel’s behavior, distribution, and the broader implications for its application in challenging geological settings.