--> --> The basin that keeps on giving: The successes and challenges of horizontal drilling in the Uinta Basin, Utah

AAPG Rocky Mountain Section Meeting

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The basin that keeps on giving: The successes and challenges of horizontal drilling in the Uinta Basin, Utah

Abstract

The Uinta Basin in northeastern Utah has been a major source of oil and gas since the 1950s, with over 16,000 wells targeting oil from the Eocene Green River Formation (GRF) and natural gas from both the Paleocene/Eocene Wasatch Formation and Upper Cretaceous Mesaverde Group. Since 2010, operators have drilled nearly 300 horizontal wells, both ~5000 ft laterals (XL) and ~10,000 ft laterals (SXL), targeting tight oil reservoirs in the GRF and underlying Flagstaff/Wasatch Formation. Many of these wells have been very successful, on par with other major U.S. shale plays, but several challenges exist including limited sweet spot extent, variable reservoir pressure, and rapid changes in lacustrine facies, as well as other logistical challenges (waxy crude, transportation, limited market, etc.). The most successful horizontal target is the Uteland Butte member of the lower GRF. To date, 86 XL and 51 SXL horizontal wells have been drilled with a cumulative production of 22 million barrels of oil equivalent (BOE). The SXL wells average ~1400 BOE per day initial production (IP - first full month) with the best performing well producing ~2500 BOE per day IP. The XL wells average ~400 BOE per day IP but range from <100 BOE up to 1600 BOE per day, depending on reservoir pressure. Gas to oil ratios (GORs) for Uteland Butte wells (first year of production) average 1.3 mcf/bbl. The underlying “Wasatch” interval is the second most successful target but could soon become the first. The “Wasatch,” as defined by operators, consists of interbedded lacustrine carbonates (Flagstaff?) and fluvial/deltaic sandstone. Currently 62 horizontal wells target the Wasatch, mostly in the upper carbonate benches (Wasatch 5 and 4), with cumulative production of 11 million BOE. The 38 SXL wells average ~1300 BOE per day IP, while the 23 XL wells average ~700 BOE per day IP but range from <100 BOE to ~2000 BOE, again depending on location and pressure. GORs for Wasatch wells average 0.9 mcf/bbl. Several additional horizontal targets (Castle Peak, Black Shale, Douglas Creek) show potential in the GRF and will be discussed in terms of current and future production. The expansion and continued success of unconventional development in the Uinta Basin indicates that a comprehensive resource assessment is needed to address overall potential in these new targets.