Gel under Dynamic Stress in Porous Media: New Insights using Computed Tomography

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Abstract
Crosslinked polymer gels are widely utilized to reduce water production from oil and gas producing wells. Zitha et al. (2002) developed a theory accounting for the basic mechanisms of gel extrusion by water through matrix porous media, i.e., compression, yield and flow. Their model predicted pressure drop and saturation changes over the gel-treated porous media during gel yield and extrusion by brine. The pressure drops were successfully compared to yield and displacement of an organically crosslinked gel formed insitu by water from Berea sandstone cores. This paper reports for the first time the measurements of saturation changes during such yield, and displacement experiments using X-ray Computed Tomography (CT) scanning. The experiments were performed using Bentheimer sandstone cores treated with gels containing 3 wt% polyacrylamide polymer (PAM) and 2 wt% polyethyleneimine crosslinker (PEI) shut-in at 55°C (131°F) for 22 hours under high pressure drops up to 89 bars (1,291 psi). Total organic carbon analyses indicated that no polymer retention or adsorption took place during gelant placement into Bentheimer sandstone cores. CT images indicated that the displacing brine saturations were independent of position, although, saturations increased with time. In addition, the breakthrough pressure occurred at a relatively later time compared to the critical pressure. New insights into the existing saturation models are given, which will provide a better understanding of the pressure and saturation changes with time.

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