The extreme heterogeneity of carbonate in the form of fracture corridors and super-permeability thief zones challenges the efficient sweep of oil in both secondary and tertiary recovery operations. In such reservoirs, conformance control is crucial to ensure injected water and any enhanced oil recovery (EOR) chemicals optimally contact the remaining oil with minimal throughput. Gel-based conformance control has been successfully applied on both sandstone and carbonate reservoirs. In-depth conformance control in high temperature reservoirs is still a challenge, due to severe gel syneresis and the associated significant reduction in gelation time.

In this work, a laboratory study was conducted on a polymer/chromium gel system for a high-temperature carbonate reservoir to evaluate the gelant formulation potential for diversion and recovery improvement. We perform four oil displacement experiments on carbonate core samples to demonstrate oil recovery improvement by gel treatment. In these tests, the gel solution was injected into specially prepared heterogeneous carbonate composite core samples, in which different configurations of high permeability channels were created. Gel treatment was conducted after waterflooding and was followed by chase waterflooding while monitoring oil production. Oil recovery improvement by gel treatment was 18% of original oil in core (OOIC) in the composite core with high permeability channels extending midway through the composite while the improvement was 38% OOIC in the composite core with channels extending all the way through the composite. This indicates that the high permeability channels were effectively blocked and bypassed oil was successfully mobilized after gel treatment.

This laboratory study provides more insight into the mechanisms of oil-recovery improvement by gel treatment. Moreover, it clearly demonstrates the oil-recovery potential of in-depth gel systems in heterogeneous reservoir applications at high temperatures.

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