Matrix-related pore networks in mudrocks are composed of nanometer- to micrometer-size pores. In shale-gas systems, these pores, along with natural fractures, form the flow-path (permeability) network that allows flow of gas from the mudrock to induced fractures during production. A pore classification consisting of three major matrix-related pore types is presented that can be used to quantify matrix-related pores and relate them to pore networks. Two pore types are associated with the mineral matrix; the third pore type is associated with organic matter (OM). Fracture pores are not controlled by individual matrix particles and are not part of this classification. Pores associated with mineral particles can be subdivided into interparticle (interP) pores that are found between particles and crystals and intraparticle (intraP) pores that are located within particles. Organic-matter pores are intraP pores located within OM. Interparticle mineral pores have a higher probability of being part of an effective pore network than intraP mineral pores because they are more likely to be interconnected. Although they are intraP, OM pores are also likely to be part of an interconnected network because of the interconnectivity of OM particles. In unlithifed near-surface muds, pores consist of interP and intraP pores, and as the muds are buried, they compact and lithify. During the compaction process, a large number of interP and intraP pores are destroyed, especially in ductile grain-rich muds. Compaction can decrease the pore volume up to 88% by several kilometers of burial. At the onset of hydrocarbon thermal maturation, OM pores are created in kerogen. At depth, dissolution of chemically unstable particles can create additional moldic intraP pores.

Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores

Dolomite: occurrence, evolution and economically important associations

Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: Standard partial molal properties of organic species

Products and distinguishing criteria of bacterial and thermochemical sulfate reduction

Preface 1. Introduction to rock physics 2. Rock physics interpretation of texture, lithology and compaction 3. Statistical rock physics: combining rock physics, information theory, and statistics to reduce uncertainty 4. Common techniques for quantitative seismic interpretation 5. Case studies: lithology and pore-fluid prediction from seismic data 6. Workflows and guide lines 7. Hands-on References Index.

Quantitative Seismic Interpretation: Applying Rock Physics Tools to Reduce Interpretation Risk

The maturation of organic material in hydrocarbon source rocks and inorganic diagenetic reactions in reservoir sandstones are a natural consequence when a prism of sedimentary rocks is buried. We can predict the distribution of porosity and permeability enhancement in potential hydrocarbon reservoirs by integrating the reaction processes characterizing the progressive diagenesis of a reservoir/source rock system. A variety of observations suggests that the organic solvents needed to increase aluminosilicate and carbonate solubilities in sandstones can be generated either by thermal or oxidative cracking of carbonylic or phenolic groups from kerogen in adjacent source rocks. For example, nuclear magnetic resonance (NMR) spectra of kerogen show that peripheral carbonylic and phenolic groups are released from the kerogen molecule before liquid hydrocarbons are generated. Experimental data indicate these water-soluble organic species can significantly affect the stability of both carbonates and aluminosilicates. Water-soluble organic acid anions (carboxylic) have been observed in oil-field waters in concentrations up to 10,000 ppm, and they commonly dominate the alkalinity in the fluid phase from 80° to 120°C. We can model the integration of organic and inorganic diagenetic reactions by constructing a series of potential reaction pathways with increasing temperature for a system that includes aluminosilicates, carbonates, organic chelate species (carboxylic and phenolic), and CO2. The important chemical divides in these diagenetic flow diagrams are dependent on temperature, the nature of the pH buffer (carbonate species or organic acid anion species), and the relationship between organic acid anions and PCO2 (P = partial pressure). Forward predictive capabilities result when this general diagenetic model is placed in a time-temperature framework. The detailed organic and inorganic geochemistry and the general thermal scenario used in the time-temperature ana ysis must be basin specific. Casting the diagenetic history of a sandstone into this type of process-oriented model helps us move from a descriptive mode to a predictive mode of analysis. Two types of information result: (1) general optimum conditions for porosity and permeability enhancement in sandstones are delineated and (2) specifically, the degree and potential for porosity and permeability enhancement are determined. Predictive models have been developed for several tectonic settings, including rift or pull-apart basins and intermontane or Laramide basins. From these reconstructions, we can forward-predict the porosity-enhancing potential of a diagenetic system based on an understanding of the reaction process in a time-temperature framework.

Organic-Inorganic Interactions and Sandstone Diagenesis

The Chemistry of Secondary Porosity

Simulation of industrial-scale CO2 storage: Multi-scale heterogeneity and its impacts on storage capacity, injectivity and leakage

The authigenic minerals, principally zeolites, in the Pleistocene to Holocene consolidated and unconsolidated sediments of the Magadi basin in the Eastern Rift Valley of Kenya have been investigated. Samples were available from outcrops as well as drill cores. The following reactions can be documented: (1) trachytic glass + H 2 O → erionite, (2) trachytic glass + Na-rich brine → Na-Al-Si gel, (3) erionite 4- Na + → analcime + K + + SiO 2 + H 2 O, (4) Na-Al-Si gel → analcime + H 2 O, (5) calcite + F-rich brine → fluorite + CO 3 −− , (6) calcite + Na-rich brine → gaylussite, and (7) magadiite → quartz + Na + + H 2 O. Erionite is the most common zeolite present, but minor amounts of chabazite, clinoptilolite, mordenite, and phillipsite were also recognized. Erionite can form directly from trachytic glass by the addition of H 2 O only. It is characteristic of the Magadi basin because of the low content of alkaline earths in the volcanic glasses and in the solutions interacting with them. Analcime is common in outcrops of the High Magadi and Oloronga Beds. It forms from erionite by a reaction probably initiated by a lowering of the silica activity, which results from the transformation of magadiite to chert. Analcime in the drill-core samples grew at the expense of a Na-Al-Si gel. This gel forms at the lake shore and is washed into the lake during flooding conditions. Fluorite is common in the core samples and can be explained by reaction of the fluoride-rich brines with calcium in the sediments, principally detrital calcite. Authigenic albite and potassium feldspar were not recognized, probably for reasons of reaction kinetics. The presence of authigenic minerals can be accounted for by considering the chemical compositions of the starting materials, mainly volcanic glasses, and the brines they come in contact with. Lake Magadi represents a unique opportunity for studies of diagenesis because authigenic minerals are forming there at the present time and because the evolution of its waters is well known.

Mineral reactions in the sedimentary deposits of the Lake Magadi region, Kenya

A new model is proposed for the depositional environment of the Green River Formation of Wyoming, which is based on a combination of lake and playa environments. We propose that oil shales and trona beds accumulated in shallow lakes which were fringed by large playa flats. In these playa flats alkaline brines evolved through evaporation and precipitation of calcium carbonate and protodolomite in the capillary zone near the ground-water table. Dolomitic mudstones, marlstones, and calcareous and siliciclastic sandstones were the products of occasional floods on the playa; chief evidence consists of the assemblage of sedimentary structures found in these rocks, indicating frequent exposure to air, strong shallow-water currents, transport, and resedimentation. The playa-lake model leads to a more consistent picture of the hydrology, brine evolution, mineral formation, and sedimentation in the Green River basins than the previously accepted stratified lake concept.

Ronald C. Surdam

Papers

Organic-Inorganic Interactions and Sandstone Diagenesis

The Chemistry of Secondary Porosity

Simulation of industrial-scale CO2 storage: Multi-scale heterogeneity and its impacts on storage capacity, injectivity and leakage

Mineral reactions in the sedimentary deposits of the Lake Magadi region, Kenya

Depositional Environment of the Green River Formation of Wyoming: A Preliminary Report