Abstract: Sequence Stratigraphic Concepts Applied to Integrated Oil and Gas Field Development, Denver Basin

R. J. Weimer, S. A. Sonnenberg, W. M. Berryman, T. L. Davis

Sequence stratigraphic concepts have been used to analyze the petroleum geology of a 9-township producing area (T1,3S; R64,66W) on the east flank, but near the center, of the Denver basin. Key surfaces and associated facies, identified from 24 cores and over 600 logs, established a detailed sequential time relationship of strata and a clearer delineation of the petroleum traps.

By using two types of erosional surfaces caused by relative sea level changes, the J Sandstone (100 to 150 ft thick) was subdivided into the J1, J2 and J3 members, and the D Sandstone (4 to 60 ft thick) into the D₁ and D₂ members. Sandstone trends for each member, associated pools and production data, and structure were then mapped by integrating geology, geophysics and petroleum engineering data bases.

The reservoirs and pools in each of the members have unique geographic distributions based on the environments of deposition, preservation under unconformities, and diagenesis. From oldest to youngest, the J₃ is a highstand regressive sandstone capped by a lowstand surface of erosion. The J₂ is a fluvial-estuarine sandstone deposited in an incised valley fill and capped by a transgressive surface of erosion. The J₁ has a lower marine shale, and an upper sandstone deposited in channels of a birdfoot delta and related marine bar complex. The D₂ is a shoal water birdfoot delta with production from distributary channels and channel mouth bars. The D₁ is a fluvial channel sandstone within an incised valley fill.

Several new interpretations for basin center petroleum occurrences have resulted from this study:

1. A 50 ft organic-rich marine shale, with high gamma ray readings, is an overlooked source rock in the lower Graneros Shale overlying the D Sandstone. Measured TOC values are from 2 to 3 percent.

2. Seals in traps for individual pools are related to faults, diagenesis, facies changes to shale, and clay plugs in meander belt channel complexes.

3. Wrench faulting enhances production in some pools, and provides seals in others.

4. Although segmented into individual pools, a continuous oil and gas column is present across the study area with no observed water legs in any field. This leads to a high success ratio in drilling statistics.

5. The petroleum potential of low resistivity low contrast pays in the J₂ fluvial sandstones has been overlooked because incorrect log interpretations regard them as non-productive and water wet.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994