Over 13,000 active oil and gas wells and more than 740 million bbl of oil have been produced from conventional vertical wells in Utah's Uinta Basin (Fig. 1). Located within the basin, the Monument Butte area is among the top 100 oil fields in the United States. Operators with a strong presence in the Monument Butte area are also pursuing ideal target zone(s) for horizontal wells by evaluating various sections of the reservoirs and utilizing the availability of technological advances made in recent years in horizontal drilling. Determining the reservoir water source zones to curb water disposal costs and ascertaining the productivity of different segments of a well to evaluate its profitability are more important than ever considering the current economic situation.

This paper will highlight the completion diagnostic results obtained from using oil-soluble and water-soluble tracers during the completion of eight conventional vertical wells in the Monument Butte area. The eight wells selected for this study are located in Sections I, II and III in Uintah County; the wells were drilled through and completed for comingled production in the Green River and Wasatch formations. Through the deployment of hydrocarbon tracers and fluid tracers, oil contribution and water production were evaluated across all zones. Between 3 and 12 hydraulic fracturing treatments were pumped into each vertical well. The fracturing treatments were designed similarly and each stage was meant to stimulate a unique target zone or formation. Moreover, for each well, each stage design had a unique set of oil-soluble and water-soluble tracers. Oil-soluble tracers were used to quantify the hydrocarbon contribution for each segment from samples taken during the course of 30 and as long as 410 days. In addition, the water-soluble tracers were used to clearly determine the water source intervals, allowing the abandonment of deeper wet zones, thus realizing a significant cost savings from not drilling and completing the bottom 800 to 1,000 ft of each future well.

Finally, the unique sets of oil and water tracers were also used to evaluate the short-term and long-term productivity of each pay zone, with the intention of identifying the best formation(s) to target in horizontally drilled wells.

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