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Comparison of capillary pressure curves with scanning electron microscope photographs of resin pore casts indicates that the mercury invasion of oolitic limestones is controlled by the pore throat size rather than the pore size.The Cotswold Hills stretch for nearly 60 miles, part of an outcrop of Jurassic rocks that runs NE from the Dorset coast to the North Sea off Yorkshire. The porosity values ranged from 2.5 to 35.9%, the permeabilities from 0.011 millidarcies to 6 darcies, and mercury-injection capillary pressure measurements showed a range of behavior from mercury invasion mostly at low pressures to mostly at high pressures, and some specimens had invasion over a range of pressures. Fourteen porosity types were identified: primary intraparticle within ooids, lithic clasts and bioclasts (both constructional and destructional by boring), primary interparticle, both normal and shelter, secondary eogenetic in ooids, secondary mesogenetic due to fabric-selective dissolution of ooids, lithics, bioclasts and cement, secondary mesogenetic partly fabric-selective, secondary mesogenetic not-fabric-selective, and secondary telogenetic resulting from neomorphism.
Twenty-three samples of oolitic limestone ranging in age from Devonian to Pleistocene were studied petrographically and petrophysically. It was also found that an excessive pore pressure difference across the specimen, especially near the end of a test, tended to cause channeling due to mechanical breakage, which destroyed much of the dissolution texture. These pressures, which exceed values found in nature by one or more orders of magnitude, were used to increase the degree of undersaturation to compensate for the time factor. Two values of the partial pressure of carbon dioxide were used (9.35 and 17.27 atm) and both produced similar results. Variation of the specimen orientation, using horizontal and vertical samples, produced no change in the result. It is concluded that oomoldic porosity can result from textural variation between components and does not necessarily imply that the ooids had an unstable mineralogy. The result was selective dissolution of the ooid cortical layers, with the sparite cement preserved undissolved. Eleven laboratory experiments were performed in which samples of a tightly cemented Mississippian oolitic calcarenite were submitted to simulated burial conditions, and undersaturated carbonic acid solution was forced to pass through them. If the interparticle space is tightly cemented, any fluids passing through the rock must pass from grain to grain through the microporosity. These equant micropores are locally constricted to plates or tubes only 0.1 (mu)m in their short dimension (s), which are "throats" between the larger equant micropores. In oolitic limestones the individual grains are microporous, and the microporosity consists of irregular equant pores 1-3 (mu)m in size which are located between the rhombic to anhedral carbonate crystals which make up the ooid cortex. Dissertation or Thesis Dissertation Keyword(s) Geology Abstract Title Porosity in Oolitic Limestones Author(s) Rich, David William Department/Program Geology Discipline Geology Degree Granting Institution University of Illinois at Urbana-Champaign Degree Ph.D. 
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