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Variation of permeability with porosity in sandstone diagenesis interpreted with a fractal pore space model (2000)

H. Pape ; C. Clauser ; J. Iffland

In: Pageoph, Bonn, 4, vol. 157, no. 4, pp. 603-619, pp. B05318, (ISSN: 1340-4202)

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Publication Date: 2000

Keywords: Fluids ; Physical properties of rocks ; FractureT

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BIBLIOGRAPHY SEISMOLOGY

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Variation of Permeability with Porosity in Sandstone Diagenesis Interpreted with a Fractal Pore Space Model (2000)

Pape, H. ; Clauser, C. ; Iffland, J.

Springer

Pure and applied geophysics 157 (2000), S. 603-619

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ISSN: 1420-9136

Keywords: Key Words: Permeability, sandstone, fractals, diagenesis.

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract —Permeability is one of the key rock properties for the management of hydrocarbon and geothermal reservoirs as well as for aquifers. The fundamental equation for estimating permeability is the Kozeny-Carman equation. It is based on a capillary bundle model and relates permeability to porosity, tortuosity and an effective hydraulic pore radius which is defined by this equation. Whereas in clean sands the effective pore radius can be replaced by the specific surface or by the grain radius in a simple way, the resulting equations for permeability cannot be applied to consolidated rocks. Based on a fractal model for porous media, equations were therefore developed which adjust the measure of the specific surface and of the grain radius to the resolution length appropriate for the hydraulic process. These equations are calibrated by a large data set for permeability, formation factor, and porosity determined on sedimentary rocks. This fractal model yields tortuosity and effective pore radius as functions of porosity as well as a general permeability-porosity relationship, the coefficients of which are characteristic for different rock types. It can be applied to interpret the diagenetic evolution of the pore space of sedimentary rocks due to mechanical and chemical compaction with respect to porosity and permeability.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/PL00001110

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Modeling chemical brine-rock interaction in geothermal reservoirs (2002)

Kühn, M. ; Bartels, J. ; Pape, H. ; [et al.]

In: Water-Rock Interaction

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Publication Date: 2020-02-12

Description: Application of the Debye-Hückel theory for chemical reaction modeling of geothermal brines does not yield sufficiently accurate results. Thus, for the development of a new chemical reaction module for the numerical simulation model SHEMAT (Clauser and Villinger, 1990), the Pitzer formalism (Pitzer, 1991) is used to calculate aqueous speciation and mineral solubilities. It is based on an extended code of PHRQPITZ (Plummer et al., 1988). Using temperature dependent Pitzer coefficients, the system Na- K-Mg-Ca-Ba-Sr-Si-H-Cl-SO4-OH-(HCO3-CO3-CO2)-H2O can be modeled with sufficient accuracy for temperatures from 0° to 150°C. The incorporated carbonic acid system (set in parentheses in the list above) is valid for temperatures from 0 to 90°C, only. Flow, heat transfer, species transport, and geochemical reactions are mutually coupled for modeling reactive flow. Changes in porosity and permeability influence the flow and transport properties of the reservoir. These changes are taken into account by a relation derived from a fractal model of the pore space structure (Pape et al., 1999). A conceptual case study of the injection behavior of a geothermal installation focuses on the immediate vicinity of the well. The injection of cold water has a great influence firstly on the hydraulic conductivity of the aquifer indicated by continuous head pressure increase at the well and secondly on the equilibria between the minerals of the formation and the geothermal fluid. Reservoir changes are studied for the two cases of temperature dependence of solubility, prograde (i.e. barite) and retrograde (i.e. anhydrite). Dissolution of anhydrite induced by cooling down increases the permeability of the formation in a growing region around the borehole and precipitation at the temperature front decreases it. During the initial period of reinjection considered in this study, the negative effect on the injectivity by the colder water is partially compensated by the dissolution of anhydrite. Precipitation of barite around the borehole does not alter the permeability of the formation significantly because the volume of relocated mineral is too small.

Keywords: 550 - Earth sciences

Type: info:eu-repo/semantics/bookPart

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Core flooding laboratory experiment validates numerical simulation of induced permeability change in reservoir sandstone (2002)

Bartels, J. ; Kühn, M. ; Schneider, W. ; [et al.]

In: Geophysical Research Letters

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Publication Date: 2020-02-12

Description: Numerical simulation of reactive transport was validated in a core flooding experiment simulating conditions in a managed geothermal reservoir. Permeability was measured along a sandstone core prepared with anhydrite and subjected to a temperature gradient. Anhydrite was dissolved and precipitated in the cold upstream and hot downstream regions of the core, respectively. The numerical code SHEMAT was used to simulate coupled transport and chemical reactions at the temperature front. It comprises an extended version of the geochemical speciation code PHRQPITZ for calculating chemical reactions in brines of low-high ionic strength and temperatures of 0-150 °C. Permeability is updated to porosity via a novel, calibrated power-law based on a fractal pore-space model resulting in a large exponent of 11.3. Simulation results agree well with measured permeability. This both validates the model and demonstrates that the fractal relationship is crucial for a successful simulation of this type of reactive transport.

Keywords: 550 - Earth sciences

Type: info:eu-repo/semantics/article

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