Oil and gas reservoirs in the earth are nonequilibrium dynamic 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 occurred in a water borne transportation process as a result of sedimentary compaction and other diagenetic processes. Entrapment of organic matter in transit is visualized as occurring within upward-converging semipermeable 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 are of special interest, as they are the basis of a versatile oil and gas exploration system bordering on direct oil finding.
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In the business of petroleum exploration, the topic of migration has enjoyed a great bounty of ideas and opinions while, at the same time, suffering a famine of facts. This publication tontains papers on geologic constraints on migration mechanisms, oil migration limitations, the importance of water-mineral-organic matter interactions, and the nature of shales.