Colloidal Dispersion Gels Improve Oil Recovery in a Heterogeneous Argentina Waterflood

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.

Design and analysis of different models of microfluidic devices evaluated in Enhanced Oil Recovery (EOR) assays

“…Water flooding reduced the residual oil saturation to 32.1% whereas CDG mixture with crosslinker decreased the residual oil saturation to 22.9%. The enhanced properties of CDG mixture with crosslinker are particularly useful in heterogeneous formation, where non-uniform pores results in an irregular flood front and incomplete volumetric sweep [10]. Experiments number 3 and 4 were performed with chip AB0 (Figures 5 and 6).…”

“…It was determined that CDG mixture with crosslinker agent decreased the residual oil saturation effectively compared to CDG mixture without crosslinker agent, implying significant potential oil recovery enhancement [10]. …”

“…The authors suggested that the enhanced properties of CDG over uncrosslinked polymer are particularly useful in heretogenous formations, where non-uniform rock results in an uneven flood front and incomplete volumetric sweep. In this type of rock, uncrosslinked polymer is not strong enough to overcome these adverse effects [10]. Besides, ALZATE [9] determined that CDG system increments viscosity compared to polymer when crosslinking agent is added.…”

“…A solution of separate gel "bundles" are formed in which a mixture of predominantly intramolecular and minimal intermolecular crosslinking reactions. By contrast, in "bulk gels" the crosslinking mechanisms form a continuous intermolecular network of polymer molecules [10]. CDG are used as a sweep improvement agent in EOR process for displacing the oil where the mobility ratio is unfavorable [10,11].…”

Enhanced Oil Recovery: An Update Review

“…Although these technologies are quite different from a technical standpoint, both are meant to improve volumetric sweep efficiency in mature waterfloods, especially in reservoirs with high permeability contrast and presence of thief zones. Documented CDG's projects include Daqing Field in China [96,102,103], El Tordillo [104] and Loma Alta Sur [105] fields in Argentina and in multiple U.S. oilfields [106,107]. Regarding BrightWater® [108], at the present time Milne Point in Alaska is the only field application discussed or documented in the public domain [109,110].…”