Pore-Level Examination of Gel Destruction During Oil Flow

Pore-scale X-ray computed microtomography (XMT) images were obtained at a variety of oil (hexadecane) throughput values after Gel placement in cores [involving a pore-filling Cr(III)-acetate-hydrolyzed polyacrylamide (HPAM) gel]. For each pore in our image volume, we followed oil and water saturations as a function of oil throughput. These studies were performed both in water-wet Berea sandstone and in hydrophobic porous polyethylene cores. In hydrophobic porous polyethylene, oil saturations increased and gel was destroyed (presumably dehydrated) quite quickly in the smallest pores. Also, oil saturations increased and gel was destroyed quickly in the largest pores. In contrast, oil saturations rose much more gradually for the most common or intermediate-size pores (around 10(-4) mm(3)). The minimum in oil saturation vs. pore size may result from a balance between gel dehydration by oil film growth vs. gel extrusion. In contrast, in water-wet Berea sandstone, increases in oil saturation occurred evenly over all pore sizes (10(-6) to 0.02 mm(3)) for all oil throughput values. Consistent with imbibition and drainage studies performed before gel placement, oil apparently had equal access to Berea pores of all sizes and, thus, uniformly dehydrated gel in pores of all sizes. Gel extrusion did not appear to be significant in the Berea pores.