Stoakes Consulting Group Ltd

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Stratigraphy and Depositional Facies of the Gilwood Sandstone – High Prairie Region, West Central Alberta

Overview

The emphasis of this study is a comprehensive stratigraphic and sedimentological examination of Gilwood Member Sandstones on the south east margin of the Peace River Arch. An assessment is made of the potential for further hydrocarbon discoveries, and each exploration play-type is mapped and ranked according to its proven reserves and future exploration potential.

The Gilwood Member within this study area is composed of subarkosic conglomeratic sandstones to finer-grained siltstones and shales. These lithotypes are repeated in a number of fining-upward cycles recognized throughout the study area. Analysis of the vertical succession of lithotypes and their lateral variation suggests that the Gilwood sandstones were deposited in a braided stream/alluvial plain depositional regime. These Gilwood braided stream deposits exhibit excellent porosity and permeability. Early cementation by ferroan calcite preserved the original uncompacted nature of the sediment. Later solution removal created a secondary enlarged pore system, which is responsible for the good reservoir quality associated with the Gilwood Member. Later cementation by anhydrite charged fluids is thought to be local from the overlying Fort Vermilion evaporitic section. The Shadow and McLeans Creek fields lie beyond the depositional limit of the Fort Vermilion and appear to have escaped this diagenetic episode. Reservoirs in the High Prairie field appear to have been adversely affected by anhydrite cementation.

The study area is located in west central Alberta from Townships 71 to 79 between Ranges 9W5 and 24W5 and encompasses the fields at High Prairie, Gilwood, Shadow, McLeans Creek, Little Horse and Gift. At the time of the study 678 wells penetrated the Watt Mountain Formation or deeper within the study area. Cored intervals from 201 wells (over 2,500 metres) were examined at the AEUB Core Research Centre.

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Product – Five Volume Report

  • fully illustrated text (65 pages, plus clour and B&W figures) documenting stratigraphy, depositional setting, play types, exploration potential, core descriptions, and database;
  • 4 regional and 10 field stratigraphic cross sections;
  • 13 maps (isopach, structure, & sandstone thickness) at 1:50,000 and 1:150,000 scales;
  • 15 stratigraphic picks from Top Beaverhill Lake to Top PreCambrian;
  • 678 well database available in hardcopy and digital formats;
  • core descriptions from 201 wells described with internally consistent correlations;
  • petrographic analyses of 26 thin sections.

Gilwood Study Update – Completed 1997

  • Update Area: Township 71 to 79 between Ranges 15W5 and 25W5.
  • 5 New Maps