The effects of diagenesis on the petrophysical properties of tight gas sands

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:427025

Yin, P; Surdam, R C ^[1]

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1. Univ. of Wyoming, Laramie, WY (United States)

The Cretaceous Almond Formation sandstones in the Washakie Basin, Wyoming, were deposited in a marginal marine environment, and are generally rich in lithic fragments. These sandstones were modified extensively during post-depositional diagenesis, and have become tight below 8000 {+-} 1000 ft depth. Porosity and permeability in these tight sands is damaged by the deformation of lithic grains, precipitation of clays and quartz overgrowths, and late dolomite cementation. Remnant porosity generally takes the form of secondary dissolution pores. Dissolution of carbonate cement enhances both porosity and permeability in a few sands. Partial dissolution of feldspar and lithic fragments leads to the creation of micropores and precipitation of clay minerals, thereby enhancing porosity, but not permeability. Porosity and permeability vary significantly in the Upper Almond Formation sandstones. Below {approximately}8000 ft, porosity ranges from 0 to 15% and permeability ranges from less than 0.01 to 10 md. In this study, the sandstones with porosity greater than 8% are denoted porosity {open_quote}sweet{close_quote} sands, and sandstones with porosity greater than 8% and permeability greater than 0.1 md are denoted permeability {open_quote}sweet{close_quote} sands. These {open_quote}sweet{close_quote} zones are characterized by relatively coarse grain size, few lithic fragments, feldspar and carbonate dissolution, less quartz overgrowth and late dolomite cementation, and abundant intergranular slots. These {open_quote}sweet{close_quote} sands develop primarily in a high-energy depositional environments. In some cases, fracture porosity/permeability results in the enhancement of sweet zones in the Almond Formation sandstones.

• OSTI ID: 427025
• Report Number(s): CONF-960527--
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
GAS SATURATION
NATURAL GAS DEPOSITS
PERMEABILITY
POROSITY
SANDSTONES
SEDIMENTARY BASINS
WYOMING