Secondary Porosity in Laumontite-Bearing Sandstones
Thermodynamic calculations indicate that, at diagenetic temperatures, laumontite is stable only in the presence of fluids of high pH and low . This is supported by experimental dissolution studies that suggest that laumontite is soluble in the presence of carboxylic acids. As both CO2 and carboxylic acids are produced prior to and during hydrocarbon generation, laumontite is unlikely to form in sandstones plumbed to source rocks during the maturation process. It is more likely that early formed laumontite cements will be destroyed and secondary porosity created by the processes associated with maturing kerogen. Thus potential reservoir rocks may be found in or below laumontite-bearing sandstones. Laumontite in hydrocarbon environments would most likely have formed late relative to hydrocarbon maturation. The sedimentary basins of California may demonstrate such a late-stage, hydrothermal origin for laumontite. The concept of laumontite as an economic basement for hydrocarbon exploration must be carefully evaluated on a case-by-case basis.
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Clastic diagenesis has evolved from a very descriptive science to a much more process-oriented study. This evolution has been driven by the realization that many hydrocarbon reservoirs have significant diagenetic compotents directly affecting porosity and permeability characteristics. The prediction in time and space of reservoir characteristics affected by diagenesis can greatly reduce the risk in the search for hydrocarbon accumulations, particularly in subtle targets lacking pronounced structural expression. This publication contains three sections designed to increase understanding in the processes controlling clastic diagenesis: Conepts and Principles; Aspects of Porosity Modification; and Applications of Clastic Diagenesis in Exploration and Production. The first two sections deal with processes controlling various aspects of clastic diagenesis, and the third section applies these principles and observations to specific examples. Altogether, the three sections contain 22 chapters.