Quantification and Prediction of the 3D Pore Network Evolution in Carbonate Reservoir Rocks

E De Boever,E Rosenberg,A Foubert,C Varloteaux,F.H Nader,S Youssef,S Békri

doi:10.2516/ogst/2011170

Abstract

This study presents an integrated approach that allows the reconstruction and prediction of 3D pore structure modifications and porosity/permeability development throughout carbonate diagenesis. Reactive Pore Network Models (PNM-R) can predict changes in the transport properties of porous media, resulting from dissolution/cementation phenomena. The validity and predictability of these models however depend on the representativeness of the equivalent pore networks used and on the equations and parameters used to model the diagenetic events. The developed approach is applied to a real case of a dolostone rock of the Middle East Arab Formation. Standard 2D microscopy shows that the main process affecting the reservoir quality is dolomitisation, followed by porosity enhancement due to dolomite dissolution and secondary porosity destruction by cementation of late diagenetic anhydrite. X-ray μ -CT allows quantifying the 3D volume and distribution of the different sample constituents. Results are compared with lab measurements. Equivalent pore networks before dolomite dissolution and prior to late anhydrite precipitation are reconstructed and used to simulate the porosity, permeability characteristics at these diagenetic steps. Using these 3D pore structures, PNM-R can trace plausible porosity-permeability evolution paths between these steps. The flow conditions and reaction rates obtained by geochemical reaction path modeling can be used as reference to define PNM-R model parameters. The approach can be used in dynamic rock typing and the upscaling of petrophysical properties, necessary for reservoir modeling.

Highlights

Carbonates hold about half of the world’s oil and gas reservoirs
A dolostone reservoir rock (Jurassic Arab Formation, Arabian Gulf region) was subjected to an integrated approach to quantify changes in pore structure and predict the evolution of petrophysical properties throughout its diagenetic history: – classical 2D microscopy shows that processes that affected the reservoir quality are porosity enhancement by dolomite dissolution and porosity destruction by cementation of late anhydrite; – X-ray μ-Computer Tomography (CT) imaging permits the 3D quantification of the volume and distribution of the different sample constituents
The reliability of the reconstructed 3D pore network is validated by comparing permeability and mercury injection capillary pressure measurements with values obtained by pore network transport simulations

Summary

Introduction

Carbonates hold about half of the world’s oil and gas reservoirs. Porous and permeable carbonate reservoir rocks are known to be heterogeneous in terms of the spatial distribution of their petrophysical properties, which makes production and secondary recovery a challenging task (Ehrenberg, 2006; Lucia, 2007). Dissolution and replacement processes like dolomitisation may successively create, destroy or redistribute the pore space available for oil, gas, water or CO2 storage. This often results in the presence of multiple pore systems that are variously interconnected. Difficulties, typically, arise when rock-types and reservoir properties are to be defined and predicted

Methods

Findings

Discussion

Conclusion