Development and Testing of a Foam-Gel Technology to Improve Conformance of the Rangely CO2 Flood

Abstract

Thirty-six thousand four hundred barrels of CO 2 gelled foam were successfully placed via an injector well into the Rangely Weber Sand Unit in Colorado. The treatment objectives were ͑1͒ to improve volumetric conformance in this CO 2 flood by reducing excessive CO 2 breakthrough through fractures, and ͑2͒ to increase oil recovery from the associated producers. Local reservoir characteristics indicate the need for a large-volume treatment to achieve these goals. The required treatment volume is beyond the economic limits of standard gel systems. Foam gel technology is one way to economically achieve in-depth conformance improvement at Rangely by replacing 60 to 80% of the liquid phase by the less expensive CO 2 phase. A gelled foam system was specifically designed for application to Rangely conformance problems. The field-tested surfactant/gel system was designed according to the following criteria: ͑1͒ to produce strong and robust gelled foams under the harsh pH conditions of a CO 2 flood, ͑2͒ to provide enough gelation delay to achieve the injection of a large foam volume with manageable injectivity reduction, and ͑3͒ to considerably reduce the unit cost of the treatment fluid relative to standard non-foamed gel systems. This paper describes the methodology used to design and test the optimum gelled foam system for Rangely. Laboratory results are presented to support the chemicals system selection, including gelation kinetics experiments, surfactant selection, and corefloods with supercritical CO 2 at field conditions. The candidate well selection process is described, including injection profile surveys, offset well response, and bypassed reserves calculation. Data taken during the injection phase of the program, including injectivity history and on-site quality control monitoring of the chemical system behavior, are given. Finally a preliminary assessment of the impact of the treatment on CO 2 cycling rates and incremental oil production is presented.

Selectively Shutting Off Gas in Naturally Fractured Carbonate Reservoirs

“…Polymer gels have become popular for conformance treatments (Thach et al 1996;Friedmann et al 1999;Sydansk and Southwell 2000) because they can be injected with low viscosities to easily penetrate targeted formations. The desired penetration depth can be managed to some extent with adjustable gel strength setting times, additional reduced (compared to suspended solid particles based fluids) gel strengths, and availability of gel-breaking solutions, which often eliminate the need to use drilling tools for removing the excess remaining in the hole.…”

Water shutoff and conformance improvement: an introduction

“…Key field applications of the Cr(III)-acetate-HPAM gel involved injecting large gel volumes, notably by Marathon in the Oregon Basin field in Wyoming (Sydansk 1990;Sydansk and Moore 1990;Sydansk and Southwell 2000), by Amoco in the Wertz field in Wyoming (Seright 1995a), and by Chevron in the Rangely field in Colorado (Friedmann et al 1999;Hild and Wackowski 1999;Hughes et al 1999). Injected gel volumes ranged from 5000 to 37,000 In water zone: 0.2 ft x 5,000 = 1,000 ft.…”

“…Foam-gel treatments were also applied at Rangely (Friedmann et al 1999;Hughes et al 1999). The major motivation for using foam gels instead of gels was a hope that the chemical costs associated with the large gel volumes could be reduced by up to 80% (because much of the liquid gel volume was replaced with gas).…”

Study on a Novel Gelled Foam for Conformance Control in High Temperature and High Salinity Reservoirs

“…K. Asghari [38], Wang X. [39] and F. Friedmann et al [40] proved that the gel-foam is effective at blocking high permeability zones, improving oil recovery by water flooding in the low permeability zones. T.L.…”