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EDWARDS, KIMBERLY K., Colorado State University, Fort Collins, CO; WILLIAM R. ALMON, WILLIAM C. DAWSON, and DOUGLAS K. McCARTY, Texaco EPTD, Houston, TX; and FRANK G. ETHRIDGE, Colorado State University, Fort Collins, CO

Abstract: Seal Capacity in Lower and Upper Cretaceous Shales, Denver Basin, Colorado

Sealing capacity plays a crucial role in the petroleum system. Consequently, understanding the characteristics of seals has become a worthwhile investment for the petroleum industry. The Skull Creek and Graneros marine shales in the Denver basin have been selected because of the availability of data. The characteristics of these marine shales have been correlated with seal capacity in the context of sequence stratigraphy. Seal capacity was primarily analyzed with the following data: capillary pressure, pore throat geometry, texture, organic content, mineralogy, depositional environment and sequence position.

Preliminary results for the Skull Creek in the Fort Collins are show the best seal to be in the upper parts of the transgressive deposits. This facies represents a deep neritic environment and includes the condensed section and the upper parts of the facie stratigraphically below it. This laminated grayish-black shale has silt lens with preferred grain orientation in thin section. Capillary pressure data show a well-sorted fine-grained clay (0.007 micron) with low porosity and permeability. X-ray diffraction analyses show this facies to have the highest amount of total clay, consisting of I/S, illite, kaolinite, and chlorite. The amount of total organic carbon is low and probably of terrestrial origin. This contrasts with the younger Graneros, which has higher amounts of TOC and is a potential source rock. The Graneros also represents transgressive deposits but with less sediment input, thus making it a more clay-rich fissile black shale. Capillary pressure data shows this to be a finer-grained (0.005 micron), better-sorted clay.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana