CO2 Migration Monitoring by Means of Electrical Resistivity Tomography (ERT) – Review on Five Years of Operation of a Permanent ERT System at the Ketzin Pilot Site

At the Ketzin pilot site, Germany, electrical resistivity tomography (ERT) is a substantial component in a multi-disciplinary monitoring concept established in order to image CO2 injected in a saline aquifer. Since more than five years, crosshole ERT data sets have repeatedly been collected using a borehole electrode array acting as a permanent reservoir monitoring tool. This contribution summarizes the aspects being essential for a successful deployment and operation of such a downhole installation. It is shown that the presented installation can facilitate stable and reliable data collection at least throughout the investigated five- year period of ongoing CO2 injection. Based on the experiences being gained so far, it is concluded that a properly calibrated and integrated downhole ERT system allows for mapping of quantitative CO2 saturation estimates in the subsurface.ISSN:1876-610

Electrical Resistivity Tomography (ERT) for Monitoring of CO2 Migration - from Tool Development to Reservoir Surveillance at the Ketzin Pilot Site

Since more than four years of operation, the Ketzin pilot site is successfully demonstrating a multi-disciplinary monitoring concept for detecting and tracking the CO2 distribution in the subsurface. In this research frame, the electrical resistivity tomography (ERT) is part of the geophysical measurement program and contributes to the observation of the pore fluid changes due to the CO2/brine displacement process in the reservoir zone. Our work demonstrates the feasibility of a permanently installed geoelectrical array and its potential for providing frequently acquired time-lapse results as well as for supporting periodical surface-downhole surveys. Based on standardized technical components and equipped with a sequence of suitable data evaluation tools, this permanent reservoir monitoring system aims to support subsurface management solutions.ISSN:1876-610

A qualitative risk assessment methodology for scientific expert panels.

Risk assessment can be either quantitative, i.e. providing a numeric estimate of the probability of risk and the magnitude of the consequences, or qualitative, using a descriptive approach. The French Agency for Food, Environmental and Occupational Health and Safety (ANSES), formerly the French Food Safety Agency (AFSSA), bases its assessments on the opinions of scientific panels, such as the ANSES Animal Health Scientific Panel (AH-SP). Owing to the lack of relevant data and the very short period of time usually allowed to assess animal health risks on particular topics, this panel has been using a qualitative risk method for evaluating animal health risks or crises for the past few years. Some experts have drawn attention to the limitations of this method, such as the need to extend the range of adjectives used for the lower probabilities and to develop a way to assess consequences. The aim of this paper is to describe the improved method now established by the AH-SP, taking into account the limitations of the first version. The authors describe a new set of levels for probabilities, as well as the items considered when addressing either animal or human health consequences

Review on geophysical monitoring of CO2 injection at Ketzin, Germany

Geophysical monitoring activities were an important component of the CO2 injection program at the Ketzin site, Germany. Here we report on the seismic and electrical resistivity tomography (ERT) measurements performed during the period of the site development and CO2 injection. Details on the site geology, the history of the CO2 injection operation, and petrophysical models relevant for the interpretation of the geophysical data are presented. The seismic measurements comprise 2D and 3D surface seismic surveys, vertical seismic profilings, and crosshole measurements. Apart from the measurements, results from advanced processing methods, such as impedance inversion and full-waveform inversion are also presented. In addition, results from crosshole ERT and surface-downhole ERT are presented. If operational efforts are taken into consideration we conclude that a combination of several geophysical methods is preferable given the demands of a spatiotemporally comprehensive monitoring program. We base this conclusion on that the different imaging characteristics and petrophysical sensitivities of different methods can complement each other. An important finding is, based on signal quality and reduced operational costs, that the use of permanent installations is promising. Generally, specific monitoring layouts will depend on site-specific characteristics, such as reservoir depth, availability of wells, petrophysical characteristics, and accessibility of surface locations. Given the comprehensive range of methods applied, the reported results are not only relevant to the operation of CO2 storage sites, but are also of interest to other monitoring projects dealing with fluid injection or production. © 2015 Elsevier B.V

Geo-electrical Characterisation for CO2 Sequestration in Porous Media

This is a post-peer-review, pre-copyedit version of an article published in Environmental Processes. The final authenticated version is available online at: http://dx.doi.org/10.1007/s40710-017-0222-2.Developing monitoring strategies for the detection and monitoring of possible CO2 leakage or migration from existing and anticipated storage media are important because they can provide an early warning of unplanned CO2 leakage from a storage site. While previous works have concentrated on silicate and carbonate porous media, this work explores geoelectrical techniques in basalt medium in a series of well-defined laboratory experiments. These were carried out to identify the key factors which affect geoelectrical monitoring technique of CO2 in porous media using low cost and efficient time domain reflectometry (TDR). The system has been set up for simultaneous measurement of the bulk electrical conductivity and bulk dielectric permittivity of CO2-water-porous media system in silica sand, basalt and limestone. Factors investigated include pH, pressure, temperature, salinity, salt type and the materials of the porous media. Results show that the bulk electrical conductivity and dielectric permittivity decrease as water saturation decreases. Noticeably, electrical conductivity and permittivity decrease due to the changes in water saturation and the relationship remains the highest in limestone except at the start of the experiment. Also, an increase in temperature, pressure and salinity tend to increase the bulk electrical conductivity (σb) and permittivity (εb) of the CO2-water-porous media system during the drainage experiment. On the other hand, pH and concentrations of different types of salt do not seem to have significant effect on the geoelectrical characteristics of the system. It was evident that Archie’s equation fit the experimental results well and the parameters obtained were in good agreement with those in the literatures. The regression shows a good reliability in the prediction of electrical properties during the monitoring process of CO2 sequestration