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

Abstract

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 of the Nisku depositional sequence occurred as below wave-base ramp buildups overlying basinal to fore-slope facies. A ubiquitous deepening event followed bioherm development, with deposition of relatively deep subtidal facies grading 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 evaporate facies with minor subaqueous siliciclastic influx. Differences in facies comprising this shelf-interior setting and the shelf-margin setting are evident. However, the major depositional cycles can be correlated between these two settings, indicating a basin-wide, eustatic control on Nisku deposition. At Joffre Field, favorable reservoir properties are confined to the reef boundstone facies and the shallow subtidal packstone/grainstone facies. Reservoir heterogeneity is complicated by depositional and diagenetic factors. Early pervasive dolomitization and late anhydrite plugging contribute to reservoir heterogeneity in the field. Variations in unit thicknesses and interrupted lateral continuity contribute significantly toward difficulties in reservoir development of the field.more » Core data based isopach maps and cross-sections indicate three main bioherms 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.« less