- © The Mineralogical Society Of America
Zeolites have been reported in petroleum and natural gas reservoirs of a wide range of geological ages from many parts of the world. Such zeolite-bearing oil and gas reservoirs are not comparatively large in number and scale. However, where present in petroleum and natural gas reservoirs, zeolites can have profound effects on the quality of the reservoirs, affecting rock porosity and permeability. Zeolite-containing reservoir rocks vary widely lithologically, including not only porous, pelitic sedimentary rocks, but also volcanogenic rocks and even fractured intrusive and plutonic rocks.
Several different genetic types of zeolite occurrences have been distinguished and classified (e.g. Hay 1966, 1986, 1995; Iijima 1980, 1986), as Hay and Sheppard discussed and summarized in an earlier chapter (this volume). In addition, the organic origin theory for the formation of economic oil and gas resources seems to have been universally accepted, including the prominent kerogen decomposition theory summarized by Tissot and Welte (1978). Sedimentary basins filled by very thick sequences of sedimentary strata containing organic-rich source rocks and porous reservoir rocks are considered necessary for producing hydrocarbon resources. Such sedimentary basins develop primarily through rifting or in relation to arc formation at active plate boundaries, and they are often accompanied by heating and extensive volcanic activity. Most types of zeolite occurrence are consequently constrained to burial diagenesis, uplift-related late-stage diagenesis (Surdam and Boles 1979, Boles 1993), and hydrothermal alteration, as will be discussed in this chapter.
Zeolites in hydrocarbon reservoir rocks occur commonly as cements and grain replacements in the form of disseminated, microcrystalline aggregates and occasionally as macroscopic crystals in vugs and veins. It was in 1950s that Coombs and co-workers pioneered the petrologic study of rock-forming zeolites through their classic research on burial metamorphism of the Triassic geosynclinal deposits in South Syncline, New …