ABSTRACT: Defining "Sweet Spots" in Sedimentary Basins through Practical Application of Reservoir Quality Technology
PAXTON, STANLEY T. , Oklahoma State University, Stillwater, Oklahoma
Analysis of the distribution of porosity and permeability in some of the world’s premier hydrocarbon provinces reveals that clastic reservoir quality (RQ) varies predictably with an established set of independent geologic variables. These variables, or "controls," can be arranged in a scale-dependent hierarchical order. Beginning at the nucleus of the hierarchy, the controls include facies/stratigraphy, provenance, fluid types, pressure, faults/fractures, and temperature. The hierarchy is considered a checklist of important factors that can be employed by geoscientists and reservoir engineers to evaluate RQ potential in exploration settings.
The recognition and relative importance of these RQ controls was established through an integrated approach to RQ assessment, with emphasis on testing and ranking of key variables based on geologically constrained porosity/permeability populations. Each of these controls is quantifiable and mappable within the context of regional geology. Analyses commonly reveal that once porosity/permeability populations are partitioned according to the regional geology via simple statistics, rock property variations appear to be as expected in terms of fundamental geologic principles.
Practical application of these learnings to locating the occurrence and distribution of RQ "sweet spots" in a basin or trend is best achieved with a series of maps that represent each of the RQ controls. These individual maps are composited to construct a "sweet spot" map for each of the prospective stratigraphic intervals. To test the predictive capabilities of these maps, qualitative comparisons can be drawn between the "sweet spot" maps and (1) the mapped distributions of core analysis porosity/permeability and (2) producing fields. We commonly find that the optimum RQ in an area can be attributed to coincidence of favorable conditions for several of the RQ controls rather than dominance by a single control.
To date, we find a high degree of correspondence between the sweet spot maps and (1) reservoir porosity/permeability, (2) the distribution of producing fields, and (3) the regional geologic framework. This correspondence suggests that our identification of RQ controls is nominally correct.
The presentation will also include discussion of the (1) characteristics of successful case studies, (2) implications for prediction of RQ in deepwater reservoirs, and (3) recommendations for future technical work.
Note: This material is based in large part on methods developed and work performed while the author was affiliated with ExxonMobil Upstream Research Company, Houston, TX.
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