Combined µ-CT and Pore Network Modeling Dedicated to Quantitative Rock-Typing

De Boever, Eva ²; Varloteaux, Clément ¹; Foubert, Anneleen ³; Nader, Fadi H.²; Youssef, Souhail ¹; Bekri, Samir ¹; Rosenberg, Elisabeth ¹
(1)Reservoir Engineering, IFP Energies nouvelles, Rueil-Malmaison, France. (2) Sedimentology - Stratigraphy, IFP Energies nouvelles, Rueil-Malmaison, Belgium. (3) Earth and Environmental Sciences, K.U.Leuven, Heverlee (Leuven), Belgium.

Carbonate rocks enclose several of the worlds important petroleum reservoirs, but tend to have complicated porosity-permeability relationships. The latter results from their heterogeneous fabric; controlled by depositional textures, but often strongly modified during diagenesis. As a consequence, difficulties arise when rock-types and reservoir properties are to be predicted. Moreover, quantification of diagenetic processes responsible for the alteration of the pore space and associated changes in petrophysical properties are vital in reservoir quality prediction.

In this study, we try to shed more light on the pore network properties of carbonate rocks. We present an integrated methodology of computed micro-tomography (µ-CT) and pore network modeling to reconstruct the evolution of the 3D pore network at different diagenetic time steps. Two case-studies involving well core data are introduced: dolostones of the Middle East Khuff and Arab Formations, being representative of excellent oil and gas reservoirs.

Standard microscopy indicates a first important event of porosity creation by leaching, creating vuggy porosity, followed by porosity destruction due to late anhydrite cementation. µ-CT then allows a more accurate quantification of mineral components (dolomite, anhydrite) and porosity and the reconstruction of a realistic, 3D pore network. Quantification results are in satisfying agreement with classical porosity and quantitative XRD measurements.

The reconstructed 3D pore network is validated by confronting permeability and mercury injection measurements on adjacent plug material with values obtained by pore network transport simulations (PNM). A good agreement was found for both parameters, indicating that we achieved a realistic description of the geometry and topology of the pore network.

As carbonate rocks are often the product of diagenesis, fluids might have migrated through varying pore networks. We therefore reconstructed the pore space before dolomite dissolution and anhydrite precipitation, from µ-CT images. Using the latter as input for PNMs finally permits to quantify phi-K changes as result of these diagenetic processes.

The results of this study show how changes in the pore structure and petrophysical properties as a result of diagenetic phenomena can be quantified and simulated. The integration of µ-CT and pore network models provides a tool for quantitative rock-typing of reservoir rocks throughout their diagenetic history.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.