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.