A major problem facing all scientists working in the field of source rock evaluation is choice of an analytic mix which yields necessary and sufficient data that are dependable, economical, and not unnecessarily redundant. Chevron handles this problem by combining microscopic observations with measurements of the total organic carbon (TOC) and the hydrogen-carbon (H/C) ratio of the organic matter (OM). This combination of analyses yields two independent estimates of organic quantity, quality (type), and maturation, the three organic parameters which are necessary for a proper source-rock evaluation.

Despite the strong subjective element, we consider microscopic organic analysis (MOA) indispensable to an accurate evaluation of organic quality and maturation. In addition, MOA is useful in detecting analytic errors in geochemical measurements, uphole cave, contamination from organic well additives, and the presence of reworked OM. MOA is, however, quite subjective and requires continuous calibration against geochemical numbers to minimize errors in judgment.

Geochemical analyses of kerogens are objective, precise, accurate, lend themselves readily to comparison between different laboratories, and are appealing both to geologists using source-rock data and to management. However, most of them are bulk measurements and cannot resolve the kerogen into its components as can microscopic analysis. In addition, many geochemical measurements do not discriminate between effects due to maturation and effects due to different organic types.

Used together, MOA and geochemistry strongly complement each other and minimize the possibilities of incorrect interpretation of the generative potential and generative history of the OM.

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