Schlumberger

Carbonate Advisor Petrophysics and Productivity Analysis

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Quantitative producibility and textural analysis for carbonate reservoirs

Unlike sandstones, with their well-characterized correlations of porosity, permeability, and other reservoir properties, the heterogeneous pore systems of carbonate rocks defy routine petrophysical analysis. Carbonates are deposited primarily through biological activity. The resulting rock composition of fossil fragments and other grains of widely varying morphology produces highly complex pore shapes and sizes. Carbonate mineral species are also comparatively unstable and are subjected to multiple stages of dissolution, precipitation, and recrystallization, adding further complexity to the porosity and permeability of the rocks. Any comparatively simple relationships that might have existed between depositional attributes, porosity, and permeability are obscured by these multiple physical, biological, and chemical influences, operating at different scales, during and continuing after deposition.

Accounting for reservoir heterogeneity

The principal challenge for the accurate evaluation of carbonate formations is accounting for reservoir heterogeneity on a multiplicity of scales—of the grains, the pores, and the textures. The solution is Schlumberger Carbonate Advisor petrophysics and productivity analysis. This novel approach meets the carbonate challenge by integrating a comprehensive suite of petrophysical logging measurements for the quantitative determination of reservoir producibility in carbonate formations.

Integrating measurements for complete formation evaluation

Schlumberger Carbonate Advisor analysis integrates measurements from the ECS elemental capture spectroscopy sondeMR Scanner expert magnetic resonance service, and other logs to deliver a single, complete formation evaluation of carbonate reservoirs. The interpretation methodology consists of sequential steps with multiple inputs to evaluate specific related reservoir properties: lithology and porosity, pore type and permeability, and relative permeability and saturations. The result is not the sparse data points conventionally obtained from laboratory core analysis and delivered long after the well has been drilled, but a continuous log of Schlumberger Carbonate Advisor analysis detailing the quantitative producibility of the nonfractured carbonate reservoir.

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Finding Anhydrite Not Seen in Conventional Evaluation

Lithology evaluation (right) of a carbonate formation correctly identified dispersed nodular anhydrite in comparison with the conventional ELANPlus evaluation made with triple-combo logs.
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Resolving Dolomite Content in Barite-Weighted OBM

Capture Technology for Complex Carbonates
Schlumberger Carbonate Advisor analysis used the accurate yield measurements of magnesium from the ECS elemental capture spectroscopy sonde, which is unaffected by barite and oil-base mud (OBM), to quantify the dolomite (CaMg(CaCO3)) content of the reservoir rock—a key indicator of reservoir rock quality. Read the article