Relationship of near-surface magnetic anomalies to oil- and gas-producing areas

Observation of aeromagnetic patterns associated with the Cement oil field initiated a continuing program to investigate the association of shallow magnetic anomalies with the presence of oil and gas reservoirs. if local magnetic anomalies are detectable from an aircraft, the source of such anomalies will necessarily be present in the near-surface sedimentary strata as magnetic minerals sufficiently concentrated to allow airborne detection and identification by magnetic susceptibility measurement of drill cuttings. The results of analysis of cesium vapor magnetometer data are supported by exploration drill hole rock magnetic susceptibility data from four separated areas: (1) Caddo and Grady counties, Oklahoma; (2) Cheyenne County, Colorado; (3) San Juan County, Utah; and (4) southwestern Alabama. Results indicate a strong correlation of oil- and gas-producing areas with magnetic anomalies produced from the aeromagnetic data and with intervals of enriched magnetic rock strata in the shallow sedimentary environment. For the areas studied, 78-90% of oil and gas exploration drilling within the magnetic bright spot (MBS) anomalies is productive. Outside these anomalies, only 5-16% is productive. Analyses of minerals by X-ray diffraction and Mossbauer effect measurements have identified maghemite and greigite as the major iron-bearing minerals in the anomalous magnetic sedimentary intervals.