Investigation of Geophysical Anomalies Detected by an Airborne Survey of the Hatchel Area, Runnels County, Texas

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Bureau of Economic Geology (BEG) researchers and Railroad Commission of Texas (RC) staff investigated 41 sites in the 91-square-kilometer Hatchel area in Runnels County, Texas, that have airborne geophysical profiles similar to that expected of a potentially leaking well. Site investigations included (a) analysis of airborne measurements of ground conductivity and magnetic field strength, (b) interpretation of aerial photographs, (c) collection, analysis, and interpretation of ground-based geophysical measurements, (d) research of RRC well records, and (e) interpretation of the likely cause of the conductivity anomaly at each site.

In a previous study of the 1996 Hatchel airborne geophysical survey, BEG researchers identified 103 conductivity anomalies that might be caused by oilfield salinization. Each conductivity anomaly was classified as one of four types, depending on whether the anomaly was accompanied by a known well or a magnetic anomaly. The 1996 study suggested that airborne geophysical methods could be expected to discriminate oilfield sources of salinization from most natural and agricultural sources, but that follow-up, ground-based geophysical measurements were needed to discriminate among surface spills, evaporation pits, and potential leaking wells.

Site investigations and ground-based measurements allowed the development of an airborne geophysical signature that would be more likely to represent a leaking well than a conductivity anomaly alone. This profile consisted of a conductivity anomaly measured at both high (6,000 Hz) and intermediate (7,200 Hz) electromagnetic frequencies, coupled with a magnetic anomaly or a known well location. Because the original study examined representative examples of all types of conductivity anomalies, not all sites that matched a profile of a potentially leaking well were investigated. The current study examines all the profile-matching sites, combining ground-based measurements made in 1996 with those made in 1998 for this study.


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