Natural and Experimentally-Simulated Stylolitic Porosity in Carbonate Rocks
Von Bergen, Donald
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https://hdl.handle.net/2142/72511
Description
Title
Natural and Experimentally-Simulated Stylolitic Porosity in Carbonate Rocks
Author(s)
Von Bergen, Donald
Issue Date
1988
Doctoral Committee Chair(s)
Carozzi, Albert V.
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Abstract
Stylolitic porosity in carbonate rocks was investigated in two parts: a natural example of stylolitic porosity and the experimental simulation of stylolitic porosity.
The natural occurrence of stylolitic porosity was studied by the detailed petrographic analysis of Lower Permian Wolfcamp limestones. Based on the observed, natural vertical succession of the microfacies and on the petrographic study of thin sections, an ideal, shallowing-upward sequence was derived, and from it a horizontal model was constructed. The latter consists of three microfacies in terms of depositional environments as follows: bioturbated calcisiltite (intermound); matrix-supported, phylloid algal calcarenite (mound flank); and a grain-supported, phylloid algal calcarenite (mound crest). The crest of this phylloid algal mound was deposited at or slightly above wave base. Two major diagenetic events were revealed. The first was exposure in a freshwater vadose environment and the second was deep burial. Existing reservoir porosity is primarily the result of late diagenetic dissolution and strongly stylolite-controlled. Dissolution along stylolite seams resulted in the formation of several pore types including well developed, suture-like, stylolitic pores, lamellar stylolitic pores, moldic and moldic-enlarged pores adjacent to stylolites, interparticle pores adjacent to stylolites, and vuggy, nonfabric selective pores which often crosscut the stylolites. In contrast, interstylolitic areas are consistently nonporous. Stylolitic porosity is best developed in sutured, high amplitude stylolites with no or little insoluble residue.
The second part of this research dealt with the artificial, laboratory-controlled, generation of stylolitic porosity in carbonate rocks under simulated deep burial conditions. Experimental dissolution preferentially occurred and developed along stylolites, including the opening of stylolite seams. Stylolite-controlled porosity types included partial and complete oomolds, Donezella algal molds, lamellar stylolitic pores, channel and vuggy nonfabric selective pores, and halos of microporosity which surrounded stylolite seams. Experimentally created pore systems are strikingly similar in terms of size and geometry to natural pore types.
Natural and experimental evidence illustrates that the presence of stylolites can be important in secondary porosity generation and enhance the reservoir quality of a carbonate rock. Sutured, porous stylolites behave as reservoirs and permit the circulation of undersaturated fluids creating halos of porosity adjacent to stylolite seams.
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