Open File Report 1986-03

Open File Report 1986-03

OFR 1986-03

Jurassic Rock Creek Member in the Subsurface of the Edson Area (West-Central Alberta)

Author(s) Losert, J. Date 1986-01-01

This study is focused on the Rock Creek Member, a widespread Middle Jurassic clastic unit in west-central Alberta, and is a part of the Regional Subsurface Geology Program jointly sponsored by the Alberta Energy and Natural Resources (AENR) and the Alberta Research Council (ARC).

Interest in the Rock Creek Member dates from the late 1970's when sandstones of this unit were recognized as important reservoir rocks extending over an area of more than 20 000 km� in the west-central Plains and adjacent Foothills. However, despite hundreds of wells drilled through the Rock Creek, its hydrocarbon reservoirs were frequently by-passed and the unit itself was often misidentified. In addition, local names, (for example, Niton, Granada) have been used to denote sandstones of the Rock Creek unit and added to the confusion about its stratigraphic position and age.

Besides insufficient paleontological dating of strata at the Jurassic-Lower Cretaceous boundary, many of the questions relating to Rock Creek stratigraphy stem from the complex inter-relationship with overlying, and also often hydrocarbon-bearing, Lower Cretaceous sediments including Lower Mannville Ellerslie ("Basal Quartz") Member and Cadomin Formation. This is especially true for areas where intervening "Upper Fernie" and Lower Cretaceous shales are missing and where Ellerslie or Cadomin sandstones rest directly on Rock Creek sandstones. In such areas hydrocarbon reservoirs in Rock Creek and Ellerslie (or Cadomin) sandstones may be in communication; this often leads to exploration and production problems and also creates difficulties related to definition of individual hydrocarbon reservoirs and productive zones for legal purposes, such as lease continuation and deeper rights reversion.

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