Experimental Study of Microgel Conformance-Control Treatment for a Polymer-Flooding Reservoir Containing Superpermeable Channels

Abstract

SummaryPolymer flooding has been widely used to improve oil recovery. However, its effectiveness would be diminished when channels (e.g., fractures, fracture-like channels, void-space conduits) are present in a reservoir. In this study, we designed a series of particular sandwich-like channel models and tested the effectiveness and applicable conditions of micrometer-sized preformed particle gels (PPGs, or microgels) in improving the polymer-flooding efficiency. We studied the selective penetration and placement of the microgel particles, and their abilities for fluid diversion and oil-recovery improvement. The results suggest that polymer flooding alone would be inefficient to achieve a satisfactory oil recovery as the heterogeneity of the reservoir becomes more serious (e.g., permeability contrast kc/km > 50). The polymer solution would vainly flow through the channels and leave the majority of oil in the matrices behind. Additional conformance-treatment efforts are required. We tried to inject microgels in an attempt to shut off the channels. After the microgel treatment, impressive improvement of the polymer-flooding performance was observed in some of our experiments. The water cut could be reduced significantly by as high as nearly 40%, and the sweep efficiency and overall oil recovery of the polymer flood were improved. The conditions under which the microgel-treatment strategy was effective were further explored. We observed that the microgels form an external impermeable cake at the very beginning of microgel injection and prevent the gel particles from entering the matrices. Instead, the microgel particles could selectively penetrate and shut off the superpermeable channels under proper conditions. Our results suggest that the 260-µm microgel particles tested in this study are effective to attack the excessive-water-production problem and improve the oil recovery when the channel has a high permeability (>50 darcies). The gels are unlikely to be effective for channels that are less than 30 darcies because of the penetration/transport difficulties. After the gels effectively penetrate and shut off the superpermeable channel, the subsequent polymer solution is diverted to the matrices (i.e., the unswept oil zones) to displace the bypassed oil. Overall, this study provides important insights to help achieve successful polymer-flooding applications in reservoirs with superpermeable channels.

Propagation of Swellable Microgels through Superpermeable Channels: Impact of Particle–Pore Matching Size Relationship

“…In Figure , the critical pressure gradients during gel injection are plotted against the particle/pore ratio. Some data points were extracted from our previous publications . The experimental data covers particle/pore ratio in the range from 0.67 to 1.77.…”

“…A typical channel model was prepared by creating a lengthwise fracture in an intact core. The fracture space was filled with silica sands to make a superpermeable and porous channel in the heterogeneous model . The basic parameters of the models are summarized in Table .…”

“…The permeabilities ranged from 55 to 221 darcies. The average pore size was estimated with the Carman–Kozeny equation …”

“…Recently, we evaluated the potential of microgels to improve effectiveness of polymer flood in heavy-oil reservoirs containing superpermeable channels . Unlike routine Newtonian fluids (e.g., water, oil), we observed that a minimum differential driving pressure was required for the gel particles to penetrate and transport in the superpermeable channels.…”

“…Micrometer-sized hydrogel particles were tested to solve the excessive water production problem. ,− The propagation behavior is important to determine the effectiveness of the gel treatment. ,− Meanwhile, however, the propagation is a complicated process due to the complex flow pathways in porous channels and the deformable nature of the particles. In field applications of gel treatments, the injection pressure is limited as the bottom hole pressure is usually constrained below the fracturing or parting pressure of the formation. ,− On the other hand, the gel materials should transport a certain distance away from the wellbore to achieve a satisfactory conformance control performance.…”