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Use of Computer-Generated Maps of Oil and Gas Development and Exploration Intensity for Delineating Producing Trends, Denver Basin, Colorado, Nebraska, and Wyoming

Debra K. Higley, R. F. Mast, D. L. Gautier

Exploration intensity maps were used in conjunction with existing or generated maps of depositional environment, structure, thermal maturity, core porosity, and production data to delineate trends and assess oil and gas resources for the Denver basin as part of the U.S. Geological Survey's Federal Lands Assessment Program. Maps illustrating oil and gas production, shows, and dry holes were constructed for the Denver basin using the Petroleum Information WHCS data base, with mapping and statistical software developed by the U.S. Geological Survey. Data from more than 36,000 drill holes in the Denver basin were entered into a program that divides the basin into ½ mi2 grid cells and analyzes show and production data for drill holes within each grid cell.

The primary producing formation is the Lower Cretaceous J sandstone of the Dakota Group, which has produced most of the more than 800 million bbl of oil recovered from the Denver basin. Illustrated on the intensity map are several northeast-trending zones of production, which cut across Arapahoe, Adams, and southwestern Washington Counties, Colorado, subparallel to structure contours. Most of this production is from stratigraphic traps within delta plain sandstones, and the trends may represent distributary channel systems in this portion of the basin. Thermal maturation maps show that a large number of fields occur outside the area in which J sandstone source rocks have attained the maturation level equivalent to the lower boundary of oil generation (a vitrinite reflectance--Ro --of 0.60%). This indicates that lateral hydrocarbon migration occurred and that the northeast trends represent migration pathways. Production from the J sandstone is absent in most of the southern and eastern parts of the basin, probably due to the absence of effective traps and/or by greater hydrocarbon migration distances. The Wattenberg field in Adams and Weld Counties, Colorado produces gas from delta-front sandstones. This field is located on a relative high between the two structurally deepest parts of the basin near Denver and Cheyenne. Vitrinite reflectance data indicates that source rocks were heated sufficiently to generate gas (lower window, 1.35 Ro).

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.