ABSTRACT: East Calgary-Crossfield Elkton B Unit: Deposition and Diagenesis

EDWARDS, D. E., Krishelle Enterprises Ltd., Calgary, Alberta, Canada, and A. A. GORDON, PetroScan International Petrology Consultants, Calgary, Alberta, Canada

The East Calgary field has produced 1 tcf of natural gas since 1961 from the Mississippian Elkton Member of the Turner Valley Formation. Gas is trapped along the erosional subcrop edge of the porous Elkton Member, which was deposited in a shoaling environment on a restricted carbonate shelf.

Three primary depositional facies are represented in the Elkton: grainstone, wackestone, and mudstone. In addition, two diagenetic facies are present: tight limestone and breccia. The breccia facies forms both as a result of solution collapse (karsting) and from secondary crystal growth. The initial rock types have undergone five major stages of diagenesis:
1. Early cementation and compaction.
2. Dolomitization.
3. Karsting/porosity enhancement.
4. Late stage dolomitization.
5. Calcite cementation and de-dolomitization.

Porosity, permeability, and ultimate hydrocarbon recovery from the field are related to the depositional facies and diagenesis of the reservoir rock.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)