Colloidal Dispersion Gels Improve Oil Recovery in a Heterogeneous Argentina Waterflood

Abstract

Abstract The Loma Alta Sur Field is a mature waterflood in the Neuquén Basin of Argentina. The productive formation (Grupo Neuquen) consists of numerous fluvial, multi-layer sandstone packages. Extensive diagnostics, including tracers, injection profiles, review of historical production and reservoir fluid analysis corroborated the combined effect of reservoir heterogeneity and an adverse mobility ratio. High concentration polymer gels, sometimes called "bulk gels", can be effective in reducing water channeling in naturally fractured formations or in reservoirs with multi-darcy permeability anomalies. However, the Loma Alta Sur Field produces from a multi-layer unfractured matrix rock reservoir and is not a candidate for traditional bulk gel treatments. Uncrosslinked polymer is an alternative for improving an adverse mobility ratio, but is most effective in relatively homogeneous reservoirs in order to minimize polymer breakthrough in offset producing wells. The primary objective of the the operator in this pilot was to improve volumetric sweep efficiency. CDG's were selected for the Loma Alta Field for several reasons:CDG's offer significantly higher adsorption and residual resistance factors than uncrosslinked polymerCDG's can be injected in matrix rock andfresh water was not required for gel formation at low polymer concentrations. Extensive diagnostics were applied before and after the CDG injection, including tracers, injection profiles and analysis of historical production data. Post treatment analysis of the CDG treatments indicate positive oil and water trends in the pilot area. Introduction The Loma Alta Sur field is located in the province of Mendoza in the Neuquén Basin of Argentina (Figure 1). The productive reservoir is the Grupo Neuquen Formation, which is characterized as heterogeneous multi-layer sandstone. In an effort to control the vertical distribution of injected water, injection wells are completed with downhole selective injection mandrels. However, the combined effects of heterogeneity within the individual layers and the extremely adverse mobility ratio motivated the operator to evaluate techniques for in-depth volumetric sweep improvement. Polymer is a traditional alternative for viscosifying water and lowering the mobility ratio. However, relatively homogeneous reservoirs are preferred in order to avoid polymer breakthrough in offset producing wells. The objective of the operator was to apply a staged chemical injection program that would reduce water channeling in the highest permeability layers and, as a secondary benefit, improve the oil-water mobility ratio.