Relationship between magnetic anomalies and hydrocarbon microseepage above the Jingbian gas field, Ordos basin, China

Abstract

In this study, soil magnetic measurements (susceptibility and hysteretic parameters) and soil hydrocarbon analyses were conducted on samples from three profiles (profiles I and II run across, and profile III runs parallel to the trend of the Jingbian gas field in the Ordos basin, central China) to determine the relationship between the magnetic anomalies (e.g., volume-specific magnetic susceptibility k) and the hydrocarbon seepage environments. The results document a strong correlation between magnetic susceptibility and soil-gas hydrocarbon concentration. Furthermore, the spatial distribution of k and hydrocarbon anomalies correlate with those of the gas field. In addition, magnetic minerals in the soils with higher susceptibility are predominantly magnetite, with little or no substitution of titanium compared to that of samples with lower susceptibility (<7 × 10-5 SI [International Unit of susceptibility]). These results provide strong evidences for the formation of highly magnetic minerals in close association with hydrocarbon seepage. Recognition of such seepage-induced magnetic anomalies can be used to facilitate the exploration for oil and gas in China and elsewhere. © 2004. The American Association of Petroleum Geologists. All rights reserved.