Geologic and Engineering Implications of Production History From Five Mesaverde Wells in Central Piceance Creek Basin, Northwest Colorado

Abstract

SummaryFive gas wells completed in low-permeability rocks of the Upper Cretaceous Williams Fork and Iles formations in the central part of the Piceance Creek basin, northwest Colorado, have been on continuous production for about 2 years. A general comparison is made between these wells and the Dept, of Energy 's Multiwell Experiment (DOE MWX) wells about 30 miles [48 km] to the southeast. The five wells were completed with gelled KC1 water/sand fractures in various intervals over a 3,000-ft [910m] section of largely fluvial and paludal rocks of the Williams Fork and Iles formations of the Mesaverde group. Flow has apparently stabilized at low flowing tubing pressures at a rate of 30 to 125 Mcf/D [0.84 to 3.5 × 103 m3/d] per well, with minor water and variable condensate volumes. On the basis of production information to date, attempts to select intervals with better-than-average effective permeabilities by state-of-the-art techniques were not successful. The study points out several important differences in the Mesaverde group between the area of the five wells and the MWX site. Formation temperatures are higher and levels of thermal maturity are lower in the area of the five wells than at the MWX site. High formation pressures were encountered in the lower part of the Williams Fork and Iles formations at the MWX site, while thus far, only near normal to slightly below normal pressures have been encountered in the Mesaverde group in the area of the five wells. Gas shows and gas production characteristics in the area of the five wells appear to be related in part to the availability of gas-generating source rocks. Gas shows are sparse in the upper 1,000 to 1,700 ft [305 to 520 m] of the Williams Fork formation, where good source rocks are uncommon. Gas shows generally occur in only the upper parts of sandstones in this interval, suggesting that discrete gas/water contacts (GWC 's) are present. Completion attempts in this interval are commonly hindered by higher-than-average volumes of formation water. In contrast, almost continuous gas shows occur throughout the remainder of the Williams Fork formation and underlying Iles formation, where good source rocks are abundant. Discrete GWC 's are rare in this interval. Completions in this part of the section are capable of sustaining continuous gas production. The differences in the Mesaverde group between the MWX site and the area of the five wells point out the need to expand the MWX data base to include other gasproducing areas in the Piceance Creek basin.