Edmonton Geological Society
A Section of the Geological Association of Canada

 

Technical Talk: Hondo evaporites within the Grosmont heavy oil carbonate platform Alberta, Canada

  • 24 Nov 2010
  • 2:00 PM - 3:00 PM
  • ERCB/Alberta Geological Survey, 4th Floor - Twin Atria Building, 4999-98 Ave. Edmonton

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   Hondo evaporites within the Grosmont heavy oil carbonate platform Alberta, Canada

Mary Luz Borrero

Hans G. Machel

University of Alberta

 

The Upper Devonian Grossmont shelf complex is the world's largest heavy oil deposited hosted in carbonates with an estimated 400 bbls of initial volume in place. The Grosmont is located in east-central Alberta at deptsh ranging between 250m to approximately 1200m. At present the Grosmont is not under production; nevertheless, several in-situ recovery schemes are under consideration. This study involves log interpretation, core examination; facies description; strontium, sulphur, carbon, and oxygen isotope analysis.

 

 The Grosmont is subdivided into four shallowing-upward cycles. Most Hondo evaporites are now present in ponds of 1-2 townships in size as parts of the Upper Grosmont 3 and

Lower Grosmont , deposited in a series of small, shallow subaqueous brine ponds (salinas) or in an extensive lagoon. Evaporite minerals in the Hondo are present as gypsum and anhydrite, which are grouped into two categories: primary and secondary. The first group shows depositional features and five lithofacies where sulphate and fine-crystalline dolomite are intimately associated. Secondary sulfates were formed by precipitation from diagenetic solutions and are represented by anhydrite nodules and cement in molds or in fractures throughout the Grosmont, but especially in the upper part. Rare halite hopper molds show that evaporation reached or exceeded halite saturation at times, but halite is not preserved. In the eastern part of the area, the Hondo appears to have been dissolved and replaced by solution-collapse breccias and “bitumen supported intervals” which is a peculiar rock type that consists of bitumen-cemented, fine- to medium-crystalline dolomite crystals. On the other hand, in the western part of the study area the Hondo primary sulphate ponds may form effective reservoir seals on the scale of the sizes of these ponds. The role of the Hondo as a “seal” for hydrocarbon migration and entrapment is difficult to assess because it cannot be ascertained whether the evaporate minerals originally formed a regionally extensive deposit on the scale of the entire study area, and how much was removed by post-depositional dissolution.

Other diagenetic processes that were important in shaping the present reservoir characteristics were pervasive dolomitization and dolomite recrystallization, fracturing, and karstification.

 

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On Wed, November 24th at 2 p.m.
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