Mapping Petroleum Migration Pathways Using Magnetics

We report the formation of magnetic minerals in petroleum reservoirs. Eleven wells from Wessex Basin in Dorset, southern England, were sampled from the British Geological Core Store, across the main reservoir unit; Bridport Sandstone and the overlying Inferior Oolite, which forms the caprock. Sampling was carried out based on physical evidence of oil stain and a high magnetic susceptibility reading. The samples were chemically extracted to determine which were naturally stained with hydrocarbon and which were not. Magnetic analysis was carried out on all the samples: this including hysteresis analysis at low temperatures (5-15K) and room temperature, and low-temperature thermogmagentic analysis. The results indicated a marked increase both in abundance and strength of magnetic materials in samples found to be stained by hydrocarbon.