Geochemical Hydrodynamics of Oil and Gas Accumulation

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Earth processes which accompany the compaction of sediments containing inorganic and organic salts and hydrocarbons were simulated in a laboratory compaction cell. The conditions for movement of organic matter from the environment of clays and shales to aquifers were demonstrated experimentally and the theoretical implications are discussed. Flow of compaction fluids into shales (acting as membranes) results in an increase in Salt concentration and salting out of organic ions and hydrocarbons. A working hypothesis of oil origin and migration is built around these essential geologic phenomena. Other environmental effects are produced by fluid flow and the accumulation of mineral and organic matter in the vicinity of oil pools and in the overlying sediments. Since the constituents of petroleum and the fluids which transported them are reduced systems, they tend to develop a reducing environment in the neighborhood of oil accumulations. The state of oxidation or reduction in the sediments affects the mineral assemblage present and therefore may provide a clue to the presence of nearby oil accumulations. Various sub-surface logging methods can detect these anomilies. Introduction Statement of the Problem Although the origin of hydrocarbons and petroleum are usually treated as one subject, a distinction should be made between them. The origin of hydrocarbons refers to the manner of their formation and the source material from which they were derived. The extracts of soils and sedimentary rocks contains hydrocarbon yet these are not considered petroleum since they do not have the same distribution of organic class material found in petroleum. Evidently the origin of petroleum involves the selective removal and migration of dispersed hydrocarbons in sediments and their ultimate accumulation in geologic structures. It is, therefore, necessary to search for a process which can explain the observed distribution of hydrocarbons found in petroleum. In addition, the removal of a dispersed hydrocarbon phase from clays and shales is known to present grave difficulties. Capillary differences between shales and coarse grained sediments have been used to explain the release of hydrocarbons. However, capillary pressure differences cannot explain their release unless a continuous hydrocarbon phase exists between the pores within the shale.