Advanced and Integrated Petrophysical Characterization for CO2Storage: Application to the Ketzin Site

M Fleury,N Gland,C Schmidt-Hattenberger,S Gautier,P.F Boulin,B Norden

doi:10.2516/ogst/2012084

Abstract

Advanced and Integrated Petrophysical Characterization for CO2 Storage: Application to the Ketzin Site — Reservoir simulations and monitoring of CO2 storage require specific petrophysical data. We show a workflow that can be applied to saline aquifers and caprocks in order to provide the minimum data set for realistic estimations of storage potential and perform pertinent simulations of CO2 injection. The presented series of experiments are fully integrated with quantitative log data analysis to estimate porosity, irreducible saturation, drainage capillary pressure and water relative permeability, residual gas saturation, resistivity-saturation relationships and caprock transport properties (permeability and diffusivity). The case considered is a saline aquifer of the Triassic Stuttgart formation studied in the framework of the CO2SINK onshore research storage, the first in situ testing site of CO2 injection in Germany located near the city of Ketzin.We used petrophysical methods that can provide the required data in a reasonable amount of time while still being representative of the in situ injection process. For two phase transport properties, we used the centrifuge technique. For resistivity measurements, we used the Fast Resistivity Index Measurement (FRIM) method in drainage and imbibition, at ambient and storage conditions. For caprock characterization, we used a fast NMR (Nuclear Magnetic Resonance) deuterium tracer technique to measure diffusivity and a modified steady state innovative technique to determine permeability. Entry pressure has also been evaluated using several methods. Resistivity and NMR logs were analyzed to provide a continuous estimation of irreducible saturation for the entire storage zone and to judge on the representativity of the samples analyzed in the laboratory.For the Ketzin site, the storage zone is a clayey sandstone of fluvial origin locally highly cemented, with porosity around 30% and permeability ranging from 100 to 300 mD. Two zones were identified on the logs characterized by two different irreducible saturation ranging from 15 up to 35%. The measured relative permeability curves show a sharp decrease of the water effective permeability and suggest that a saturation lower than 50% cannot be reached in practice. The exponent of the resistivity index curve is about 1.7, lower than the default value of 2. The caprock has a permeability of 27 nD, a porosity around 15% and a pore diffusivity of 0.8 x 10-9 m2/s

Highlights

Carbon Capture and Sequestration (CCS) is one of the many solutions to limit the current emissions of carbon dioxide into the atmosphere resulting in global warming
As part of the wireline-logging program of the CO2 Ktzi 201/2007 borehole, NMR data were recorded in addition to the performed standard logging measurements of the natural radioactivity (GR-log), acoustic properties, electrical resistivity, bulk density and neutron porosity
The Stuttgart Formation, which was completely cored at the CO2 Ktzi 201/2007 borehole, is lithologically heterogeneous, consisting of sandstone, siltstone, and mudstone intervals, the latter inter-bedded with variable amounts of anhydrite and minor coal (Norden et al, 2010)

Summary

Introduction

Carbon Capture and Sequestration (CCS) is one of the many solutions to limit the current emissions of carbon dioxide into the atmosphere resulting in global warming. Depleted oil and gas reservoirs can be used for CCS, their worldwide capacity and distribution is much less attracting than saline aquifers. Target reservoir is the saline aquifer of the Triassic Stuttgart Formation at a depth of 625 to 700 m at the injection site. Three boreholes were drilled, including coring of the target reservoir, and instrumented in 2007 to realize injection (CO2 Ktzi 201/2007 borehole) and monitoring of CO2 (CO2 Ktzi 200/2007 and CO2 Ktzi 202/2007 boreholes; Prevedel et al, 2008). For monitoring of CO2, the injection well and the two observation wells were equipped with geophysical sensors including e.g. a fiber-optic-sensor cable loop for Distributed Temperature Sensing (DTS; all wells) and a Vertical Electrical Resistivity Array (VERA) consisting of fifteen toroidal steel electrodes per well and 15-line surface connection cables (Prevedel et al, 2009; Giese et al, 2009). Electrical Resistivity Tomography (ERT) based on cross-hole measurements has been evaluated as a suitable method to detect the resistivity changes caused by CO2 injection and migration in geological reservoirs (Ramirez et al, 2003; Christensen et al, 2006)

Methods

Results

Conclusion