Physical and chemical signals around oil and gas traps. [Advantages of magnetoelectric surveys over other geophysical and geochemical techniques]

Oil and gas reservoirs in the earth are non-equilibrium thermodynamic systems which are never at rest over geologic time. From the early time of precipitation of organic vegetable and animal decay products within the mud and ooze of sediments, migration of organic matter took place in a water-borne transportation process as a result of sedimentary compaction and other diagenetic processes. Entrapment of organic matter in transit is visualized to take place within upward-converging semi-permeable rock strata, the hydrocarbons being retained in one or more subhorizontal spaces therein. A hydrochemical plume is formed in the vertical escape path of the transporting waters. Those ascending waters can produce such effects as mineral alteration by leaching, changes in the redox properties of the rocks, temperature anomalies, residual traces of hydrocarbons, differential compaction, vertical electrotelluric currents, near surface electrical potential sinks, and magneto-electrotelluric effects. The latter will be shown to be of special interest as they are the basis of a versatile oil and gas exploration system bordering on direct oil-finding.