Iles Formation Research Articles

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

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.

Appropriate Stratigraphic Nomenclature for Coal Reservoirs in Piceance Basin, Colorado: ABSTRACT

Coal-bearing intervals occurring within the Upper Cretaceous Mesaverde Group in the Piceance basin have been described by various authors. The most current and widely accepted work has the Sego, Corcoran, Cozzette, and Rollins Sandstone Members comprising the Iles Formation. The overlying Williams Fork Formation is divided into the basal Bowie Shale Member and Paonia Shale Member, with the upper remaining section undifferentiated. Coal seams associated with the Iles Formation belong to the Black Diamond coal group. The Fairfield coal group and the South Canon coal group are part of the Bowie Shale Member. These two coal groups, continuous throughout the basin, are also called the Sommerset in the Sommerset coal field and the coal measures in the Grand Mesa coal field. Although priority of nomenclature dictates otherwise, established usage of the Cameo coals for coal seams in the Bowie Shale Member should be continued as the most appropriate nomenclature. The basal coal seam of the proposed coal group is laterally continuous throughout the Piceance basin. A second coal seam 40-120 ft (12-37 m) above the basal coal also has large areal extent. Both coal seams, as existing and potential future pay zones, are of significant economic importance and should, in ascending order, be classified as the coal A and D seams. The coal seams in the Paonia Shale Member, extremely variable in thickness, continuity, and quality, have been established as the Coal Ridge coal group. End_of_Article - Last_Page 846------------

Mancos-Mesaverde (Upper Cretaceous) Intertonguing Relations Southeast Piceance Basin, Colorado

In the southeastern Piceance basin, Delta, Garfield, Mesa, and Pitkin Counties, Colorado, gas has been discovered in sandstones of the Mesaverde Formation (Upper Cretaceous) that interfinger with the Mancos Shale. Electric log correlation from within the basin to the outcrop along the Book Cliffs, Colorado, shows that the producing sands belong to the Corcoran and Cozzette Members of the Mesaverde. These two members and the Rollins Sandstone can be traced in wells across the basin from the outcrop in the type area, near Grand Junction, to the outcrop along the southern Grand Hogback, thus demonstrating their continuity across the basin. By the use of eight measured surface sections, correlations of these members northward along the Grand Hogback has shown that the Corcoran and Cozzette are correlative with the non-marine part of the Iles Formation, near Meeker, and that the Rollins Sandstone is the lithogenetic equivalent of the Trout Creek Sandstone of northwestern Colorado. Fossils from below the Corcoran Member and from above the Cozzette Member date these two units as Campanian and place them stratigraphically between the base of the Baculities scotti faunal zone and the top of the Exiteloceras jenneyi faunal zone. Shoreline trends of the Corcoran and Cozzette Members are generally east-northeast in the southeastern Piceance basin. This east-northeast trend is divergent from a broad north-south trend in the Western Interior as a whole. Shoreline movements during the deposition of these members were transgressive toward the northwest or landward direction and regressive toward the southeast or seaward direction. These northwest-southeast shoreline movements probably did not proceed beyond the limits of the present structural Piceance basin. In the southernmost part of the Piceance basin, where most Corcoran-Cozzette gas discoveries have been made, these sandstones were deposited in an offshore marine environment of low to moderate wave and current action and are therefore silty and have low poros ty and permeability. The total thickness of the Cozzette Member ranges from 0 to 220 feet and isopach trends of the Cozzette conform generally to the east-northeast shoreline trend of this unit. The total Corcoran Member ranges from 0 to about 180 feet in thickness, but it can not everywhere be separated from the upper sandstones of the Sego Member; the combined maximum thickness of the Corcoran and upper Sego reaches 300 feet.

Mesaverde Group in Adjoining Areas of Utah, Colorado, and Wyoming: ABSTRACT

The mixed marine and nonmarine Mesaverde group (Late Cretaceous) overlies and intertongues with the marine Mancos shale or its equivalents and underlies and intertongues with the marine Lewis shale or underlies continental rocks of latest Cretaceous or Paleocene age. The area studied is approximately 200 miles square on both sides of the Wyoming and Utah-Colorado state Formations and members in 7 smaller geographic subdivisions are described and related in terms of Lee's (1915) genetic units to a standard four-fold section in the Rock Springs uplift consisting from oldest to youngest of the Blair, Rock Springs, Ericson, and Almond formations. Data from 14 measured surface sections and more than 120 wells were used to make isopach maps of individual formations, members and tongues. These maps show that basins and relative arches of Late Cretaceous time correspond fairly well with those of Tertiary time and that the maximum thickness of a genetic unit is at the zone of transition from continental to marine sedimentation. Numerous minor transgressions and regressions of the sea are imposed on a general eastward regression during Mesaverde time followed by a major transgression during Lewis time and a complete withdrawal of the sea after Lewis time. There are numerous cyclothems consisting of gray marine shale, tan marine siltstone and sandstone, gray and white beach sandstone, coal, brown carbonaceous shale, and gray to brown carbonaceous siltstone. Both transgressive and regressive deposits are present. Two probable controls of intertonguing are recognized: (1) intermittent delivery of sand and mud by streams along a subsiding delta front and reworking by marine currents; (2) several rather rapid changes of sealevel or landlevel, either tectonic or eustatic. Most of the sediments were derived from areas west of the Wasatch line. Toward the close of Mesaverde deposition, local uplifts in the site of the present Uinta Mountains and possibly the Wind River Mountain provided a source for sediments. Short-ranging fossils are scarce in the Mesaverde group in this area. The marine shale tongues generally contain long-ranging arenaceous foraminifera and the marine sandstones contain Ostrea sp., Inoceramus sp., Halymenites major and worm tubes; the faunas are useful as indicators of paleoenvironments, but are not useful for stratigraphic correlations. No new formation names are proposed. Several unnamed sequences should be mapped and traced laterally before they are named. The Lazeart sandstone is raised from member to formational rank. The Rimrock sandstone and the Asphalt Ridge sandstone of Walton (1944) are considered members of the Iles formation. End_of_Article - Last_Page 954------------