Relation of thorium‐normalized surface and aerial radiometric data to subsurface petroleum accumulations

Abstract

A new exploration method has been developed using surface and aerial gamma‐ray spectral measurements in prospecting for petroleum in stratigraphic and structural traps. Formerly troublesome lithologic and environmental variables are suppressed by correcting potassium and uranium readings using a new process of thorium normalization. Normalized potassium shows characteristic low concentrations above petroleum deposits. Normalized uranium shows higher values than normalized potassium over petroleum and generally lower values elsewhere. We attribute these anomalies to effects of microbial consumption of microseeping light hydrocarbons. Studies of National Uranium Resource Evaluation (NURE) Program aerial, gamma‐ray, spectral data covering portions of six states have shown characteristic normalized potassium and uranium anomalies above 72.7 percent of 706 oil and gas fields. Additionally, an average of 27 similar untested anomalies were found for each 1000 square mi (2600 square km) covered. Similar aerial gamma‐ray spectral data are available over large portions of potential petroleum areas of the U.S. including Alaska and Australia. Preliminary tests in two basins in Australia showed positive correlation between radiometrically favorable areas and known oil and gas regions. Ground‐based, gamma‐ray, spectral measurements found the same types of potassium and uranium anomalies over all twelve fields evaluated. Since 1988, our research of surface radiometric data coupled with soil gas hydrocarbon and soil magnetic susceptibility surveys has resulted in discovery of four oil and gas fields in Concho County, Texas.

Spectrometric gamma radiation of shale cores applied to sweet spot discrimination in Eastern Pomerania, Poland

“…One of most successful models was developed by Saunders et al (1993). A basic assumption is that whatever changes the apparent concentration of thorium also affects the concentration of uranium and potassium in similar, predictable ways.…”

“…Based on detailed studies of radiometric measurements in oilfields, Saunders et al (1993) developed a relationship between 238 U, 40 K and 232 Th data in order to help identify HA. 40 K concentrations appear to be significantly lower over oil and gas fields, and 238 U was found to be slightly concentrated in profiles over Alabama Ferry, Leona, O.S.R., and Lonesome Dove Fields, Texas (Saunders et al 1993;Prost 2014).…”

“…The characteristics and fluctuations of the DRAD (the mathematical expression of hydrocarbons anomalies, defined by Saunders et al 1993) values in non-oil and gas producing areas can be estimated by Fig. 3 Set of calibration cylinder standards (8, 10 cm diameters) used to calibrate the gamma logger.…”

“…A basic assumption is that whatever changes the apparent concentration of thorium also affects the concentration of uranium and potassium in similar, predictable ways. If hydrocarbons are not present, 238 U, 40 K and 232 Th should be in natural and constant proportions (Saunders et al 1993).…”

“…The first thorium normalization method for hydrocarbon exploration was introduced by Saunders et al (1993) and concerned only surface and aerial measurements. The methodology was also applied in active exploration oil fields in 6 American states, 2 Australian basins and the Wadi Araba Desert in Egypt (El-Sadek 2002;Al-Alfy et al 2013).…”