Radiometrics for the Petroleum Explorationist

ABSTRACT Ground radiometrics provide the petroleum explorationist with an economical means of gathering large volumes of data in a short time. Profiles generated by a radiometric survey delineate prospective acreage and permit judicious use of the exploration dollar. Observations and techniques presented in this paper represent the acquisition and interpretation of over 100,000 mi (160,000 km) of radiometric data. Radiometric and geochemical anomalies reflect surface and near-surface alteration by vertically migrating hydrocarbons. The observed decrease in natural radiation background over a petroleum reservoir is the result of several interactive factors: (1) the adsorptive capacity of hydrocarbons for radioactive particles, (2) the decrease of surface and near-surface porosity and permeability due to secondary mineralization, and (3) the increase of relatively low-radiation, secondary carbonates in the soil. High radiometric anomalies can be associated with faults, fracture systems, unconformable surfaces, or radioactive deposits that terminate in the near-surface. Radiometric survey design and acquisition require a thorough knowledge of instrumentation, calibration, window aperture, integration time, background level, temperature drift, survey accessibility and positioning, and targeted anomaly size and shape. The advent of data processing and the need for repeatable data necessitate proper annotation of surface changes and development of production analogs. Processing permits quantitative analysis and enhancement of radiometric data. Normalization and Rad-Stack processes correct profiles to an average-background level and enhance the signal-to-noise ratio by attenuating random events (e.g., cosmic radiation). The science of radiometrics is applicable in a fully integrated exploration program.