Fluid injection monitoring using electrical resistivity tomography — five years of injection at Ketzin, Germany

Abstract

Between the years 2008 and 2013, approximately 67 kilotons of CO2 have been injected at the Ketzin site, Germany. As part of the geophysical monitoring programme, time‐lapse electrical resistivity tomography has been applied using crosshole and surface‐downhole measurements of electrical resistivity tomography. The data collection of electrical resistivity tomography is partly based on electrodes that are permanently installed in three wells at the site (one injection well and two observation wells). Both types of ERT measurements consistently show the build‐up of a CO2‐related resistivity signature near the injection point. Based on the imaged resistivity changes and a petrophysical model, CO2 saturation levels are estimated. These CO2 saturations are interpreted in conjunction with CO2 saturations inferred from neutron‐gamma loggings. Apart from the CO2–brine substitution response in the observed resistivity changes, significant imprints from the dynamic behaviour of the CO2 in the reservoir are observed.

Fully coupled inversion on a multi-physical reservoir model – Part II: The Ketzin CO2 storage reservoir

“…Crosshole electrical resistivity measurements are conducted on a weekly basis since the beginning of injection in June 2008 (Bergmann et al, 2017). Data acquisition is realised with the aid of a permanently installed vertical electrical resistivity array (VERA) consisting of 45 ringshaped stainless steel electrodes mounted on the electrically insulated borehole casings of the injection well and the first two observation wells.…”

“…The authors state the hypothesis of a large barrier zone between injection well Ktzi201 and observation wells Ktzi200 and Ktzi202 and as consequence strongly channeled flow inbetween, but conclude that only limited information at the inter-well scale can be extracted from the pumping test data. The standalone geoelectrical inversions provide certain support for the barrier hypothesis, but information remains ambiguous (Schmidt-Hattenberger et al, 2011Bergmann et al, 2017). Chen et al (2014) suggest a joint inversion of hydraulic and CO 2 injection data to achieve a better characterisation of the subsurface.…”

Large-scale electrical resistivity tomography in the Cheb Basin (Eger Rift) at an ICDP monitoring drill site to image fluid-related structures

“…There are still two white stripes for a dipole with a missing registration. 15 The aim of the inverse modeling is to find a subsurface resistivity distribution that is able to reproduce the measured data. We use a smoothness-constrained Gauss-Newton inversion (Günther et al, 2006) Figure 7.…”

“…described how a fault zone can be imaged with large-scale ERT and additional structural information from seismics along a 2.5 15 km long profile. Bergmann et al (2017) used a surface-downhole ERT survey line (≈4-5 km) for monitoring the progress of carbon dioxide sequestration at Ketzin, Germany. Ronczka et al (2015) used iron boreholes as long electrodes to investigate inland saltwater intrusion into a 4x4 km wide area.…”

“…The occurrence of volumetric and non-double-couple source components of individual earthquakes is discussed as evidence for fluid influences on focal processes (Horálek and Fischer, 2008;Horálek and Šílený, 2013). Most of the micro-earthquakes hypocenters are aligned in a N-S direction and thus follow the course of 15 the PPZ, whereas the NNW-SSE striking MLF seems to be only partially seismically active (Bankwitz et al, 2003b;Fischer et al, 2014). The PPZ forms an escarpment of more than 20 m height in Pliocene/Pleistocene sediments and has probably been active since the late Pleistocene time (Bankwitz et al, 2003b;Peterek et al, 2011;Bussert et al, 2017).…”