Abstract:

A possible mitigation strategy for leaks from CO2 reservoirs is the introduction of a physical barrier in the form of injected sealant material. An organically crosslinked polymer (OCP) system was investigated as a potential sealant material for leaks from CO2 reservoirs. The OCP system has been extensively used in the oil industry to address conformance issues related to fracture shutoff, gravel pack isolation, waterconing, casing leak repair, and high permeability streaks. The initial viscosity properties of the sealant were tested first for later use in modeling and core flood experiments. Viscosity measurements demonstrate that gel times for this polymer system could be altered by changing the concentration of the crosslinker or by changing the gel setting temperature. Maximum gel times of 8.5 hours could be achieved with a crosslinker concentration of 1.0%. Sandstone core flood experiments were performed to determine changes in permeability when the polymer gel was placed within artificial fractures. Core flood tests were carried out at reservoir conditions of 50° C and 7 MPa. Permeability tests revealed a reduction of 100% in fracture permeability after sealant emplacement for two rock core samples (Core 1 and 2). Further reductions in overall core permeability were measured after CO2 exposure. CT scans of these sealed rock cores were carried out last in order to visually assess the location of the sealant within the fracture. These scans revealed that the aperture and distribution of the sealant in the fracture varied along the length of the cores. The fracture in Core 1 had an absence of sealant material within the middle of the core. Core 2 had a more uniform distribution of sealant material along its fracture length. The results from the experimental tests were used to create a basic injection scheme that modeled sealant injection via a horizontal well to a target fracture plane. The high initial viscosity was shown to create large differential pressures during injection. Formation penetration was limited by this sealant property and the short gel time. Despite these limitations, under ideal conditions, a physical barrier with an approximate radius of 5 m could be created using this polymer sealant system. These tests performed on the OCP system affirmed its potential as a candidate for controlling leaks from CO2 reservoirs. Field scale trials of this sealant should be performed to gain insight beyond that of these modeling and laboratory tests.

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Copyright 2014, Thomas Henry Aird: Please note that the reports and theses are copyright to their original authors. Authors have given written permission for their work to be made available here. Readers who download reports from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the author, Thomas Henry Aird.