Petrology and reservoir properties of Point Lookout sandstone, Southern Ute Indian Reservation, La Plata county, Colorado

Conference · Fri Sep 01 04:00:00 EDT 1989 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5567532

Keighin, C W ^[1]

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1. Geological Survey, Denver, CO (USA)

Natural gas is produced from regressive marine Point Lookout Sandstone of Late Cretaceous age underlying much of the Southern Ute Indian Reservation. The sandstones comprising the Point Lookout are quartz rich, fine to very fine grained, and they contain moderately variable quantities of potassium feldspar and lithic fragments. Locally, the sandstone is tightly cemented by carbonate cement; clays are not important as cementing agents, although they significantly reduce permeability of some samples. Though dissolution of grains and lithic fragments created some secondary porosity, most pores appear to be primary. Petrophysical and petrographic (thin section and SEM) analyses indicate that pores in the Point Lookout Sandstone are very small; many occur as intergranular micropores between crystals of authigenic clay. Measured ambient porosity varies between 4 and 20%; reduction of porosity by increasing confining stress is variable but is typically small. Ambient permeability ranges between 0.03 and 82 md. Permeability in some samples is very sensitive to increasing confining stress, especially in samples in which initial permeability is low. In these cases under confining stress approximating reservoir conditions, in-situ permeability may be less than 5% the ambient permeability. Even though the gross appearance of the samples from two core holes penetrating the Point Lookout Sandstone is similar, measurements indicate that reservoir properties vary significantly within the sandstone.

• OSTI ID: 5567532
• Report Number(s): CONF-8910195--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 73:9
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CLAYS
COLORADO
DIAGENESIS
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
PERMEABILITY
PETROGRAPHY
POROSITY
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
USA