Novel Temperature-Responsive\nOrganic Polymer Gel for\nEfficient Abandonment of Aged Porous Chalk Formations Characterized\nby X‑ray Computed Tomography

The transition of the oil and gas industry toward renewable\nenergy\ndemands effective plugging and abandonment (P&A) of aging reservoirs.\nThe first step of the P&A process involves depressurizing the\nannulus and production tubing by clogging the flow path from the bottom\nof the well. Under challenging conditions, the P&A process faces\nsignificant difficulties due to downhole issues like mineral scale\ndeposition. This study introduces an innovative thermoresponsive polymer\ngel designed to temporarily seal low-permeability chalk reservoirs\nby direct injection into the reservoir formation. The gel, synthesized\nfrom polyacrylamide through free radical polymerization and modified\nvia partial amination, forms a stable three-dimensional network when\ncombined with an organic cross-linker. This stability is achieved\nin response to the low-temperature ranges (60–80 °C) characteristic\nof these wells. This development not only facilitates temporary P&A\nbut also presents a viable alternative to cement for P&A, potentially\npreserving wells for future CO<sub>2</sub> storage. It could also\nbe used to seal off a reservoir after CO<sub>2</sub> injection, to\navoid potential future CO<sub>2</sub> leak. The study’s novelty\nlies in its focus on plugging low-permeability environments (around\none millidarcy), a comparatively underexplored area. The gel’s\nperformance was evaluated under various pH, temperature, and salinity\nconditions, and in both fractured and nonfractured chalk core samples\nusing a core flooding system and 3D imaging with microcomputed tomography\nfor real-time monitoring. Our findings reveal significant insights\ninto the gel’s behavior, distribution, and the broader implications\nfor its application in challenging geological settings.