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Abstract
An extensive, on-going investigation into the effectiveness of a micro-emulsion (ME) as a stimulation fluid additive is being conducted. Results from a population of 114 wells and 498 stimulation stages of hydraulic fracture stimulation provide the basis for this report. As part of the basis for the performance analysis, twenty four of the wells are producing from the Lance interval in the northeastern Pinedale Anticline area of the Green River Basin, Wyoming. The remaining 90 wells produce from the northern Denver-Julesburg Basin Codell and Niobrara formations. In both data sets about half of the wells had 1.5 gallons of ME per thousand used throughout the fracture stimulations, but at no other time during in-well operations. The stimulation fluid systems in the remaining wells contained no similar interfacial tension / surfactant system. Based on the performance matched reservoir properties and degree of effective stimulation, these comparisons and other performance metrics were used to assess the potential benefit arising from using ME. The determination of potential benefit was assessed using classical statistical methods to ensure that the interpretation was as unbiased as possible. From that analysis, there is distinct and clear benefit to be gained from using the micro-emulsion to facilitate placing the fracture stimulations, to increase effective fracture length and especially to increase hydrocarbon recovery from the wells in which the micro-emulsion system is used.

Review of Prior Work
The Codell-Niobrara reservoirs in the DJ Basin have been studied extensively (Refs. 1 – 4). Characterization of the reservoir system is well documented. Almost 80 percent of the wells in this study are in the “oily” portion of the Codell-Niobrara reservoir system. Likewise, the Lance formation in the Green River Basin has received considerable attention (5 – 8, 10). In particular, an analysis of the impact of micro-emulsions on well performance has previously been reported for the Green River Basin, Lance Formation (Ref. 5), in which ME is shown to facilitate placing the fracture stimulations, to increase effective fracture length, to minimize damage arising from operational shut-ins and to increase gas recovery of wells in which ME is used. The results of that investigation are relied upon in this study, as well.

Similar studies have been conducted in the Canyon Sands of West Texas by Pursley, Benton, Nordlander, etal. (6). They concluded that the wells in which a micro-emulsion (ME) was used a) had better reservoir conductivity, b) longer effective fracture lengths, c) better resistance to damage resulting from shut-in events and d) better long-term performance than those without it. Reports have been made regarding the impact of ME on formation damage mitigation (7). Other studies have particularly investigated the impact of zone isolation (8, 9) and proppant type effectiveness (10). Neither of these employed rigorous normalization procedures to ensure proper assessment of the impact of reservoir quality, etc. The latter authors did note that the use of semi-log “decline curve analysis” was ineffective.