Stratigraphic and Diagenetic Controls on the Distribution of Reservoir Properties in the Devonian Nisku Formation at Joffre Field, Alberta

Abdul Al-Bastaki, John D. Humphrey, and Clyde H. Moore

The Frasnian Nisku Formation facies succession in Joffre Field represents an overall major shallowing-upward cycle. Superimposed on this are three megacycles (fourth-order cycles). Several parasequences (fifth-order cycles) are also present. initiation o the Nisku depositionaI sequence occuered as below wave-base ramp buildups overlying basinaI to fore-slope facies. A ubiquitous deepening event followed bioherm development, with deposition of relatively deep subtidal facies grding up into shallow subtidal facies. This second shoaling event culminated in progradation of peritidal lithologies over shallow subtidal grainstones and packstones. Final flooding of the peritidal facies, coupled with basinward restriction, resulted in the deposition of a subtidal evaporite facies with minor subaqueous si1iciclastic influx. Differences in facies comprising this shelf-interior setting and the shelf-margin setting (Anderson and Machel, 1988) are evident. However, the major depositional cycles can be correlated between these two settings, indicating a basin-wide, eustatic control on Nisku deposition.

At Jofire Field, favorable reservoir properties are confined to the reef boundstone facies and the shallow subtidal packstone/gainstone facies. Reservoir heterogeneity is complicated by depositional and diagenetic factors. Early pervasive dolomitization late anhydrite plugging contribute to reservoir heterogeneity in the field. Variation unit thicknesses and interrupted lateral continuity contribute significantly toward difficulties in reservoir development of the field.

Core data based isopach maps and cross-sections indicate three main biohemis that correlate well with the distribution of porosity in the lower megacycle. Topography on these bioherms controlled the thickness and distribution of facies of the middle megacycle. For example, grainstone shoals of the middle megacycle were properly located over bioherms. Excellent correlation is observed between the distribution of porosity and permeability, location of the bioherms and the grainstone shoals, and distribution of areas with the highest cumulative production in the field.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California