New methods for processing and interpreting marine magnetic anomalies: Application to structure, oil and gas exploration, Kuril forearc, Barents and Caspian seas

Abstract

New methods are presented for processing and interpretation of shallow marine differential magnetic data, including constructing maps of offshore total magnetic anomalies with an extremely high resolution of up to 1–2 nT, mapping weak anomalies of 5–10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks, estimating depths to upper and lower boundaries of anomalous magnetic sources, and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called “seismic gap” region in the central Kuril Arc vary from 10 to 100 km, with typical dimensions of 25–30 km. The area of the “seismic gap” is a zone of intense tectonic activity and recent volcanism. Deep sources causing magnetic anomalies in the area are similar to the “magnetic belt” near Hokkaido. In the southern and central parts of Barents Sea, tectonic blocks with widths of 30–100 km, and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km are calculated. Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea–Barents Sea paleorift indicate depths to the lower boundary of the layer of 12–30 km. Weak local magnetic anomalies of 2–5 nT in the northern and central Caspian Sea were identified using the new methods, and drilling confirms that the anomalies are related to concentrations of hydrocarbon. Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra. The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30–40 m and 150–200 m.

Keywords

• Geophysical survey
• Magnetic data processing
• Hydrocarbon prospecting
• Kuril Arc
• Barents Sea
• Caspian Sea