--> Abstract: Reliable Quantitative Forecasting of Basin Hydrocarbon Richness--Novel Geophysical Approach, by Thane H. McCulloh; #90977 (1975).
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Abstract: Reliable Quantitative Forecasting of Basin Hydrocarbon Richness--Novel Geophysical Approach

Thane H. McCulloh

The hydrocarbon richness of thoroughly explored large sedimentary basins correlates surprisingly closely with a simple numerical index derived by specially developed objective procedures from descriptive quantitative measurements of differential regional gravity, basin sedimentary rock volume, and differential regional topographic relief. The correlation establishes a novel basis for reliably predicting quantitatively the total discoverable hydrocarbons-in-place in undrilled virgin basins or under-explored basins of large size. Regional gravity surveys of reconnaissance quality plus estimates of basin sedimentary rock fill derived from basin configuration models based on conventional Previous HitreflectionNext Hit-seismic data and standard aeromagnetic and/or Previous HitrefractionNext Hit-seismic basement-dept determinations suffice to employ the correlation. An important qualification is that the gravity data must not have been used in arriving at the estimate of basin shape and volume.

"Hydrocarbon richness" is defined as the total volume of all found hydrocarbons-in-place (in an intensively explored basin) divided by the total volume of all sedimentary rock composing the basin fill. It is expressed in volume of oil equivalent-in-place/unit volume of rock. Gas and NGL are included with original oil-in-place and expressed as bbl of oil equivalent after conversion on an energy-equivalence basis.

The "numerical index" is defined as the singular weighted average basin-related Bouguer gravity anomaly divided by the total volume of all sedimentary rock in the basin. It is expressed in milligals/unit volume of rock. Special filtering, integrating, and weighting techniques were developed and employed to separate the basin-related gravity anomaly from its surrounding regional background and objectively, but simply, to quantify the singular difference between the two. In many instances adjustment is required for differential gravimetric effects coupled with regional differences in elevation between the basinal area and surrounding ground, and a simple procedure has been developed to estimate objectively such differential effects.

Shallow basins (less than 5,000 to 10,000 ft of maximum fill) and basins of small area (less than 1,000 to 2,000 sq mi of surface area) are governed by different Previous HitlawsTop than large basins. Hydrocarbon richness (or "leanness") for such basins does not correlate closely with the numerical index derived from large and deep basins, and care must be taken to avoid mistaken predictions developed for them. Presumably the same may prove true for very young basins of large size that are not in isostatic balance because of crust-mantle dynamics, possibly including excessively high heat flow. Exceptions to the correlation spotlight problems for future research just as the existence of such a correlation spotlights other problems.

AAPG Search and Discovery Article #90977©1975-1976 Distinguished Lectures