--> Abstract: Petrologic-Petrophysical Relationships, West Sak and Ugnu (Brookian), Northern Alaska, by T. C. Mowatt, D. O. Ogbe, V. A. Kamath, and G. D. Sharma; #91004 (1991)

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Petrologic-Petrophysical Relationships, West Sak and Ugnu (Brookian), Northern Alaska

MOWATT, THOMAS C., U.S. Bureau of Land Management, Anchorage, AK, and D. O. OGBE, V. A. KAMATH, and G. D. SHARMA, University of Alaska, Fairbanks, AK

Petrographic-mineralogic analyses have been combined with petrophysical information derived from wireline logs, as part of an investigation of geological and engineering characteristics of the West Sak and Ugnu (Brookian) stratigraphic intervals in several wells in the central portion of the Alaskan Northslope.

The strata are semi- to unconsolidated clastics--sand, silt, clay in size--"cemented" by viscous (API gravity 8 degrees to 22 degrees) hydrocarbon material. This presents serious problems in terms of sample integrity during borehole recovery and subsequent storage, transportation, and sample preparation. Pressure changes from subsurface to surface conditions pose particular difficulties.

Textural relationships in thin section are often problematic with respect to original relationships in the undisturbed subsurface. In-situ analyses--e.g., wireline logs--represent the potentially most useful means of elucidating petrophysical-engineering properties of concern to drilling, completion, and production. Petrographic-mineralogic analysis of sample materials, as feasible, is essential for rigorous application of such in-situ techniques.

The present work confirms the heterogeneous nature of the West Sak and Ugnu intervals, with frequent, often substantial proportions of silt-clay size materials associated intimately within, and/or interbedded with, coarser grained reservoir intervals. Major intervals with moderate-good reservoir properties are recognized, as well as significant intervals ranging from relatively poor reservoir quality to good seal quality materials.

Hydrocarbon production will undoubtedly require enhanced recovery techniques, hence thorough, detailed reservoir/nonreservoir characterization will be imperative to achieve viable efficiency.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)