A Rock Fabric Approach to Reservoir Quality Characterization in Carbonates, Karachaganak Field, Northwest Kazakhstan
Kelly Bergman1, David Katz1, Ornella Borromeo2, Francesco Bigoni2, and Paul Wright3
1Energy Technology Company, Chevron Corporation, San Ramon, CA
2SPES - Sedimentology, Petrography and Stratigraphy Dept., Eni S.p.A. - Exploration & Production Division, San Donato Milanese, Italy
3BG Group, Thames Valley Park, United Kingdom
Karachaganak is a carbonate buildup located in the northeastern Pricaspian Basin composed of Tournasian to Early Visean cyclic shallow platform sediments and Late Visean to Serpukhovian microbial boundstone slope and cyclic shallow platform sediments. The ultimate goal of this project is to improve the predictability of reservoir favorable and destructive properties in an otherwise heterogeneous carbonate system. Reservoir quality is partially dependent on diagenetic alteration by dolomitization, anhydrite cementation, fracturing, and dissolution. This is an integrative study of reservoir quality depending upon a non-genetic rock fabric classification from thin section and core analysis, whole-core measurements, CT-scans, geochemistry, well and image logs, and multimineral analysis.
The cored intervals are dominated by two of eight rock fabrics, interparticle porosity and solution-enlarged interparticle porosity. Porosity and permeability fields behave predictably showing that diagenesis controls reservoir quality and a rock fabric classification is an effective approach to reservoir characterization. Interparticle porosity is the primary rock fabric in the lower part of the reservoir (Tournasian to Early Visean). The upper part of the reservoir (Late Visean-Serpukhovian) consists of numerous rock fabrics including solution-enlarged interparticle porosity, growth framework porosity, moldic porosity, vuggy porosity, intercrystalline porosity, microstylolite swarms, and microfractures. These rock fabrics are responsible for the greatest heterogeneity in reservoir quality and highlights the need to understand their origin and distribution.
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