The Formby oilfield was discovered at the outbreak of World War II on the site of active surface oil seepage in the West Lancashire sub-basin, onshore UK. The field produced a modest quantity of oil from shallow, predominantly Triassic-age, reservoirs, at depths of between 12m and 80m. The field was abandonment in 1965. In the search for adjacent analogue accumulations,Aurora Petroleum has conducted a resistivity tomography survey to provide information away from historical well control. Longer line lengths and wider electrode spacing than typically used in civil engineering applications has enabled an increase in the theoretical depth of investigation to around 95m. An initial control line, acquired across the Formby field, demonstrated the utility of the method in detecting structural features, changes in stratigraphy, and hydrocarbon charge. Afurther 14 lines acquired to the south and east of the original field have highlighted one strongly analogous prospect, also associated with active surface seepage. If this structure is proven by drilling, resistivity tomography will assume a leading role in the delineation of the limits of the accumulation and in the search for further nearby oil- charged shallow structures.
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