About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 9. (September)

First Page: 1417

Last Page: 1417

Title: Effects of Diagenesis on Reservoir Properties in Lobo Sandstones, Webb County, Texas: ABSTRACT

Author(s): Steven C. Alexander, Thomas T. Tieh, Robert R. Berg

Article Type: Meeting abstract

Abstract:

Cored intervals of the late Paleocene Lobo sandstones of Webb County, Texas, were studied between depths of 9,066.5 and 9,900.5 ft (2,763.5-3,018 m). Diagenesis has extensively modified these sandstones, both compositionally and texturally. Porosities and permeabilities within the sandstones range from 6 to 28% and 0.01 to 10.0 md, respectively. Porosity and permeability are dependent on depositional facies and diagenetic history.

Density and sonic logs, coupled with petrographic analysis, were used to delineate the burial history of the sandstones. Primary porosities as high as 40% were reduced to 25-30% through a combination of compaction, bioturbation, and quartz cementation during the first 3,000 ft (914 m) of burial. Calcite cement, up to 26%, infilled essentially all remaining pore spaces and decreased porosity to irreducible levels between 3,000 and 6,500 ft (914 and 1,981 m). During deep burial, secondary porosity was created by the dissolution of calcite cement and framework grains. This last stage of sandstone diagenesis appears to be in response to the generation of abnormally high fluid pressures in surrounding shale sections.

End_of_Article - Last_Page 1417------------

Copyright 1997 American Association of Petroleum Geologists