Leak-off During Placement of Cr(III)-Partially Hydrolyzed Polyacrylamide Gelling Solution in Fractured Porous Media

Abstract

During waterflooding of a fractured formation, water may channel through the fracture or interconnected network of fractures, leaving a large portion of oil bearing rock unswept. One remedial practice is injection of a gelling solution into the fracture. Such placement of a gelling mixture (referred as gelant) is associated with leak-off from the face of the fracture into the adjoining matrix. As the gelant gets more crosslinked, the gelant encounters more resistance in flowing into the porous matrix. This article addresses the build-up of flow resistance as the Cr(III)-partially hydrolyzed polyacrylamide gelant, at various stages of crosslinking flows into the matrix. Flow experiments were conducted at constant injection pressure in unfractured Berea rocks that represent a matrix adjoining a fracture. Before entering the core, gelants underwent post-mixing delays, shorter than their gel time. On continued displacement, flow resistance developed that reduced the flow rate further. More delay, after mixing of gelant hastened, the build-up of resistance to flow and the resistance was contained nearer to the inlet face. Effect of flow over fracture face on the build-up of flow resistance in the matrix was also evaluated by conducting displacement of gelant in two fractured slabs. In one case, a part of the injected fluid came out of the fracture outlet with the rest leaking off into matrix. In the other case, all the fluid that entered into the fracture leaked off into the matrix. Build-up of flow resistances in the matrix for the two cases was compared. A simple conceptual model is presented that could explain the flow of gelant and build-up of resistance in porous rock at constant injection pressure.

Effects of Fracture and Matrix on Propagation Behavior and Water Shut-off Performance of a Polymer Gel

“…As shown in Figures and , with the reduction of the matrix permeability from 100 to 10 mD, the injected pore volume of the gelant decreased from 0.51 to 0.44 PV and the injected fracture volume was reduced from 1.76 to 1.18 FV as the pressure gradient reached a stable value, i.e., when the fracture widths of cores are similar, to achieve a stable injection pressure, a relatively small volume of the gelant is required to be injected into a fractured core with relatively low matrix permeability. It is because that the degree of the gelant diffusion or penetration from fracture into matrix decreased with the reduction of the matrix permeability, and it results in a reduction of the cumulative lost volume of the gelant . The effect of the matrix permeability on the loss degree of the gelant was discussed in the section .…”

“…It is because that the degree of the gelant diffusion or penetration from fracture into matrix decreased with the reduction of the matrix permeability, and it results in a reduction of the cumulative lost volume of the gelant. 20 The effect of the matrix permeability on the loss degree of the gelant was discussed in the section 3.1.4.…”

“…19 Seright held that the leak-off or loss of the gelant was harmful to the gel formation in fracture, and a main objective for the application of the "preformed gel" in his experiments was to eliminate the gelant loss. 17 On the contrary, Ganguly et al 20 proved that a proper loss degree of gelant from fracture into matrix contributed to the water shut-off performance. Except for Seright and Ganguly, few scholars have been investigated the loss behavior of the water shut-off agent during its injection in fracture.…”

Influence of Hydrolyzed Polyacrylamide (HPAM) Molecular Weight on the Cross-Linking Reaction of the HPAM/Cr3+ System and Transportation of the HPAM/Cr3+ System in Microfractures

“…However, the flow characteristics of the HPAM/Cr 3+ system in a fracture channeling path are different from those in porous medium channeling path; thus, the research results of the transportation of the HPAM/Cr 3+ system in the conventional reservoir cannot be applied to a fractured tight reservoir. However, there are only a few studies on the transportation of the HPAM/Cr 3+ system in natural microfractures, and almost all of those are focused on the loss of the gelling solution from the fracture face into the adjoining matrix. − Thus, it is necessary to study the influence of the M w of the HPAM on the transportation of the HPAM/Cr 3+ system in microfractures to improve the application effect of the HPAM/Cr 3+ system in a fractured tight reservoir.…”

Plugging mechanisms of polymer gel used for hydraulic fracture water shutoff

“…Junjian et al studied the filtrate behavior and water shutoff performance of a certain gel in fractured media (11). Ganguly et al reported that the gel plugging agent could cement the fracture surface during the gelling of the plugging agent, thus enhancing its fracture plugging performance (12). So far, the effect of the leak off degree of the plugging agent components on its gelling effect and plugging performance has not been characterized quantitatively.…”