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The undesired drill-bit deviation is a source of drilling risks and requires monitoring. Seismic-while-drilling is one potential method to achieve this and has been tested in a number of previous studies. In August 2020 in Örebro, Sweden, we conducted an experiment to test the feasibility of seismic-while-drilling drill-bit positioning and other applications of the method. We used the hammer drill-bit signal generated while drilling a 200 m deep well in hardrock conditions and implemented vertical stacking of the subsequent impulsive signals from the hammer source, generating enhanced direct arrivals from the drill-bit. Then, we used the relative arrival times to estimate the drill-bit position for selected bit depths, confirming our methodology with two numerical studies. We successfully estimated the position of the drill-bit for the numerical examples and for several of the real data examples, with the accuracy dependent on the receiver array geometry and the quality of the data. We conclude that this drill-bit positioning method shows potential for near-real-time monitoring in drilling operations that could be applicable for both impulsive and noise-retrieved drill-bit signals.

Seismic reservoir characterization plays an essential role in the study of integrated reservoirs, with applications from prospect identification to detailed reservoir delineation [...]

Seismic imaging while drilling technology offers possibilities of imaging ahead of the drill-bit, which could be useful for determining when to go from hammer drilling to core drilling. Moreover, seismic images of the surrounding rock can improve geological models which could be then used to guide drilling programs.A seismic imaging while drilling field test was carried out in August 2020 at the I-EDDA Test Center next to the Epiroc factory in Örebro, which is an outcome of the EIT Raw Materials funded project “Innovative Exploration Drilling and Data Acquisition (I-EDDA)”. The purpose of the test presented here was to determine if the signals from hammer drilling can be used for seismic imaging around the drill-bit. The I-EDDA test site has been extensively investigated with geophysical investigations, geological mapping and diamond core drilling, and it therefore represents an ideal location to perform the proposed feasibility study.The data were recorded along a west-east oriented line consisting of 45 active 1C vertical geophones with a spacing of about 2 m and the rig located approximately in the middle of the profile. A reference signal, which is usually recorded by the pilot sensor fixed to the top of the drill string to be used to convert geophone recordings to impulsive-like seismic data, was not available. The passive recordings on the surface were thus correlated with the trace from the geophone closest to the rig.After data pre-processing and cross-correlation, the shot-gathers were vertically stacked over the length of a drill pipe to achieve further signal improvement. A comparison with the results of a modelling study shows certain agreement. However, it has to be noted that the velocity model obtained from earlier studies and used to generate the synthetic data set here is rather a simple one and the noise level in the real data set is still significant, in spite of careful processing. Besides the strong contamination by the rig noise, more typical for data with smaller offsets, the mono-frequency waveform footprints present in the cross-correlograms, which have been observed in similar experiments where a trace from the nearest geophone was used to approximate the bit signal, could also play a role. The recent results from the active seismic studies conducted at the site have not detected any clear reflections within the bedrock, which further hinders the quality assessment of the seismic signal. This work was partly supported by VINNOVA with the project 2019-04832 titled Integrated Smart Test environment for the mining industry - SMIG. We gratefully acknowledge this financial support.

There is a large theoretical capacity to store CO2 in the Palaeozoic sedimentary succession of the Baltic Basin (BB). The most prospective areas for CO2 storage within the BB border several countries such as Sweden, Latvia, Lithuania, Poland and Russia, and include large saline aquifers and oil and gas fields. In recent years, a significant amount of research has been completed in fields related to CCUS in some of the Baltic Sea Region (BSR) countries. The main drivers for implementation of CCUS technology in the BSR are (1) a need to decrease the high CO2 emissions of the region; (2) obligations taken under the Paris Climate Agreement and national strategies up to 2050; (3) European requirements for low-carbon and circular economy; (4) the fact that the BSR has a large potential storage capacity; (5) London Protocol (LP) Parties in October 2019 adopted a resolution to allow provisional application of an amendment to article 6 of the LP to allow sub-seabed geological formations for CO2 storage projects to be shared across national borders; (6) offshore CO2 storage is demonstrated under the North Sea; (7) a well developed natural gas pipeline system exists that can be combined with the a potential CO2 transportation network; (8) good research capacity demonstrated by institutions within the BSR; (9) CO2 injection has been already evaluated experimentally for EOR by oil companies in Lithuania and Russia with positive results. The main barriers for implementation of CCS technology in the BSR are: (1) limitations and bans within the national CCS regulations; (2) not all BSR countries are parties of the LP; (3) amendment to Article 6 of the London Protocol is implemented only by four BSR countries; (4) absence of a CO2 storage atlas of the BSR; (5) public communication and acceptance of CO2 storage options are low in most of the BSR countries; (6) relatively high costs of CCS projects; (7) low or absent national support of CCS research and pilot projects; (8) low public awareness and limited education options for CCS; (9) onshore CO2 storage in saline aquifers is not well established in Europe and not permitted in the BSR. Among positive developments in the BSR are 1) Fortum's plans to develop pilot CO2 capture plants in Sweden, Lithuania and Poland; 2) Willingness has been expressed by the government of Denmark to ratify an amendment to article 6 of the LP and to implement CCS offshore; 3) Several pilot CGS projects have been proposed in the report produced by the CGS Baltic seed project [1]. Among negative developments is a misunderstanding of the role of the EEAP (CO2 tax) in reaching carbon-free targets and banning of any CO2 injection in Lithuania since 2020.

Seismic reflection data (normal incidence and wide-angle) are unique assets for Solid Earth Science. They provide critical information about the physical properties and structure of the lithosphere, and are useful to understand the geometry and evolution of the tectonic plates, and for exploration of natural resources, civil engineering, characterization of seismogenic zones and hazard assessment. The resolution of seismic reflection data is highly appreciated for basic and applied Earth Sciences. However, these datasets are logistically complex and expensive to acquire, and their geographical coverage is limited. In addition, legacy seismic reflection data also have an added value as new information can be retrieved by applying new processing approaches. The preservation and dissemination of seismic open access data is an asset to promote accurate and innovative research. Here, we present the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open access online databases that stores seismic data registered with a permanent digital object identifier (DOI). The datasets included here are accessible online and guarantee the FAIR (Findable, Accessible, Interoperable, Reusable) principles of data management, so that each dataset enters into a statistics referencing database and its impact can be measured. This database has been built thanks to a network of several institutions, promoting a multidisciplinary research, and is open for international data exchange and collaborations. SeisDARE includes deep seismic sounding and high resolution data acquired in the last three decades in the Iberian Peninsula and Morocco. In addition, as result of fruitful collaborations, we are starting to host data acquired worldwide. Our first incorporation of this kind are seismic profiles recorded in Hardeman County, Texas, within the COCORP project. SeisDARE aims to make easily accessible legacy and recently acquired seismic data and establish a framework for future seismic data management plans. The datasets are available at https://digital.csic.es/handle/10261/101879, bringing endless opportunities to the scientific, industrial and educational communities., This research has been funded by EPOS IP 676564 and SP 871121, EIT Raw Materials 17024-SIT4ME and SERA 730900.

Seismic reflection data (normal incidence and wide-angle) are unique assets for Solid Earth Science as they provide critical information about the physical properties and structure of the lithosphere, as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated, however they are logistically complex and expensive to acquire and their geographical coverage is limited. Therefore, it is essential to make the most of the data that has already been acquired. The collation and dissemination of seismic open access data is then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (Findable, Accessible, Interoperable, Reusable) principles of data management, granting the inclusion of each dataset into a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last four decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins; the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution; and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research, and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. The SeisDARE is freely available at https://digital.csic.es/handle/10261/101879, bringing endless research and teaching opportunities to the scientific, industrial and educational communities.

The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630–650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post-injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time-lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post-injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%–60% are similar to those obtained earlier from pulsed neutron-gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.

The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a ...

EGU2020: Sharing Geoscience Online, 4-8 may 2020, Controlled source seismic data acquisition experiments have produced a vast amount of Deep Seismic Sounding (DSS) data since its development in the late 50¿s. These datasets provide critical information on the structure and nature of the crust and the lithosphere, which constitutes a fundamental research tool within Solid Earth Sciences. The DSS datasets are unique and constitute the output of an expensive (in time, effort and cost) scientific process, which evidences the need for their preservation, both the recently acquired and the legacy data. Furthermore, the new developments in processing and imaging techniques generate new possibilities for re-use of the vintage datasets. The availability and accessibility of these datasets, therefore, is of foremost importance for scientists, decision-makers and the general public. The research community, aware of the value of these data, has pushed forward Open Data policies based on the FAIR principles of data management (Findable, Accessible, Interoperable and Reusable). In this respect, a long-term plan has been launched by the European Plate Observation System (EPOS, https://www.epos-ip.org/) e-infrastructure. The focus is to streamline the integrated use of scientific data, data products and services. In close link with EPOS, the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA, http://www.sera-eu.org/home, a Horizon 2020 project) includes a working package to set up a network on DSS data and products management. This initiative ensures the traceability of the data allowing that third parties can freely access, exploit and disseminate the data by means of permanent, international identifiers: a Digital Object Identifier (DOI) and a Uniform Resource Identifier (URI) or handle. Furthermore, the current aim is to go beyond the FAIR principles by linking the data with its related peer-reviewed publications, other scientific contributions and technical reports, facilitating its re-use. A prototype DSS data exchange system has been developed jointly between the DIGITAL.CSIC (the Spanish National Research Council) services and the Institute of Earth Sciences Jaume Almera-CSIC (https://digital.csic.es/handle/10261/101879, last access January 2020). Within the platform, each dataset includes the acquired raw data and a metadata file. The metadata provides information of the nature of the data itself, list of authors, the context of the data (time and location of the experiments), funding agencies and other relevant legal aspects. The technical information includes the acquisition parameters, data processing and format of the data (SEGY standard in this case - www.seg.org-, broadly used in the geophysics community). In the developed storage protocol, a permanent identifier is assigned once it has been checked that the data meets all the described requirements. This permanent identifier ensures that any visit or download is accounted for. This information is entered into a statistics referencing database and can also be used as a measure of the impact of the data and/or data product., This work is funded by the European Commission (Grant Agreement no: 676564-EPOS IP, Call H2020-INFRADEV-2014-2015/H2020-INFRADEV-1-2015-1, SERA 730900).

This chapter provides a review of the life-cycle operations at the Ketzin pilot site for CO2 storage. The injection phase at the Ketzin site lasted from 2008 to 2013 and a comprehensive geophysical monitoring program was applied, including seismic and geoelectric surface and surface-downhole measurements, as well as crosshole tomographic investigations. Furthermore, borehole logging campaigns using the pulsed-neutron-gamma method and permanent pressure and temperature sensing were applied. The geophysical data were used to set up and iteratively optimize the reservoir model for simulating the storage behavior over a wide range of scales, including the long-term stabilization of the reservoir in the postinjection phase.

Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time-lapse three-dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero-offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal-to-noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site.

The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 migration into thin layers, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 migrating into thin layer and being dissolved was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.

The goal of the dip-moveout correction (DMO) is to eliminate velocity bias when stacking. DMO processing is tested in order to account for variable dips at the Ketzin CO2 storage pilot site. In this study, 3D Squeezing DMO is applied to seismic data to study the impact of DMO on seismic imaging and to investigate if it enhances the CO2 seismic monitoring technique. We compare the data with and without DMO processing by utilizing quantitative and qualitative analysis. Our results indicate its effectiveness with applications to the 3D seismic data at the Ketzin site.

Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time-lapse three-dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero-offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal-to-noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site. © 2016 European Association of Geoscientists & Engineers.

At the Ketzin pilot site for geological CO2 storage, about 67,000 tons of CO2 were injected during the period June 2008 – August 2013. Since August 2013, the site is in its post-closure phase. Before and during the injection phase, a comprehensive monitoring programme was established. In the early post-injection phase, a majority of the monitoring activities have continued. The stepwise abandonment of the pilot site, which is planned to be accomplished in 2018, marks also the termination of most monitoring activities. Four 3D seismic surveys were acquired between 2005 and 2015 for characterizing the reservoir structure and its overburden and for monitoring the propagation of the injected CO2 in the storage formation. The first and second repeat surveys revealed the lateral extension of the CO2 plume after injecting 22 and 61 ktons, respectively. In autumn 2015, the third 3D repeat seismic survey, serving as the first post-injection survey, was acquired. The survey was acquired using the same acquisition geometry as for previous surveys, consisting of 33 templates with five receiver lines and twelve source profiles perpendicular to the receiver lines. Seismic processing of the recently acquired data has resulted in preliminary observations which can be summarized as follows: As in previous seismic repeat surveys, a clear CO2 signature is observed at the top of the storage formation. No systematic amplitude changes are observed above the reservoir which might indicate leakage. Compared to the second repeat survey acquired in 2012, the lateral extent of the CO2 plume seems to have been reduced, which may be an indication for ongoing (and relatively fast) dissolution of the CO2 in the formation brine and diffusion into very thin layers indicating pressure release.

The injection of CO2 at the Ketzin pilot site started in June 2008 and ended in August 2013. A total amount of about 67 kt of CO2 was injected into a saline aquifer. Aiming to investigate post-injection movement of the injected CO2, a third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015. Consistent with the previous two monitoring surveys, a predominantly WNW migration of the gaseous CO2 plume in the updip direction within the reservoir is inferred in this first post-injection survey. There are no systematic anomalies detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost the same as that one found in the 2012 second repeat survey (after injection of 61 kt). But there is a significant decrease in its size east of the injection site. The percentage of detected CO2 mass for the three seismic repeat surveys estimated using consistent input parameters shows a dramatically lower result for the third repeat than for the two surveys acquired during the injection period. Decrease in the size of the seismic anomaly may be explained as to be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 migration into thin layers, in addition to the effects of ambient noise. The assessments of various performance parameters comparing seismic monitoring and reservoir simulation results generally showed better conformance for the 2009 dataset than for the 2012 and 2015 datasets. The conformance assessment will be repeated with updated models after incorporating various new up-to-date monitoring data.

Seismic monitoring of an injected carbon dioxide (CO2) distribution at depth is an important issue in the geological storage of CO2. To help monitor changes in the subsurface during CO2 injection a series of 2D seismic surveys were acquired within the framework of the CO2SINK and CO2MAN projects at Ketzin, Germany at different stages of the injection process. Here we investigate using seismic full waveform inversion as a qualitative tool for time-lapse seismic monitoring given the constraints of the limited maximum offsets of the 2D seismic data. Prior to applying the inversion to the real data we first made a number of benchmark tests on synthetic data using a similar geometry as in the real data. Results from the synthetic benchmark tests show that it is difficult to recover the true value of the velocity anomaly due to the injection but that it is possible to qualitatively locate the distribution of the injected CO2. After the synthetic studies, we applied seismic full waveform inversion on the real time-lapse data from the Ketzin site along with conventional time-lapse processing. Both methods show a similar qualitative distribution of the injected CO2 and agree well with expectations based upon more extensive 3D time-lapse monitoring in the area.

Summary Since the CO2SINK project start in April 2004, different methods involving seismics, geoelectrics and pressure-temperature monitoring have been applied at the Ketzin pilot site to map geological structures and assess CO2 distribution and movement. One 3D baseline seismic survey prior to CO2 injection and two 3D repeat seismic surveys during CO2 injection have proven that the 3D time-lapse surface seismic method is an effective tool for providing good quality images of the CO2 plume. In the autumn of 2015, a third 3D repeat seismic survey, serving as the first post-injection survey, was acquired. The preliminary results show that the predominant westward trend of the CO2 migration is in agreement with the previous results. No CO2 migration upwards through the caprock was detected. The decrease in the size of CO2 plume may be related to ongoing dissolution into the saline formation water.

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.

The Ketzin project provides an experimental test site for the geological storage of CO2 in Germany. During the CO2 injection period, as well as the ongoing post-injection period, a broad range of geophysical monitoring activities was conducted. In particular time-lapse seismic and electrical resistivity tomography (ERT) data sets have been extensively collected. In order to exploit the complementary imaging characteristics of these co-located data sets, we apply a joint inversion algorithm for combined processing. We use for this purpose an approach which enforces common model structure through spatial parameter gradients. Within this ongoing study, this contribution focuses on the validation of the implemented time-lapse joint inversion algorithm by means of two synthetic models. The second model captures the main features of the geology at the site and includes a hypothetical CO2 distribution. The tests are conducted as a benchmark to study how the joint inversion performs in comparison to the individual inversions and to set up the joint inversion for application to the real data sets from the Ketzin site.

Time–lapse 3D surface seismic monitoring at the Ketzin CO2 storage pilot site has provided time–lapse images of the spreading plume, which has been interpreted as being caused by fluid saturation changes only. The integration of seismic AVO/AVA modeling and petrophysical experiments on core samples from the Ketzin reservoir support the interpretation of the field data by demonstrating that pressure has a rather minor impact on the seismic amplitudes at the Ketzin site. In this study Amplitude Variation with Offset (AVO) analysis has been applied to the baseline and the latest 3D repeat data set to investigate the real AVO response from the top of the sandstone reservoir after the injection of ~ 61 kT of CO2. The results show a good agreement with the modeling results, indicating that CO2 saturation effect dominates the time–lapse seismic signature.

The Ketzin pilot site for geological CO2-storage has been operative between June 2008 and August 2013. In this period, 67 kt of CO2 have been injected (Martens et al., this conference). Repeated 3D seismic monitoring surveys were performed before and during CO2 injection. A third repeat survey, providing data from the post-injection phase, is currently being prepared for the autumn of 2015. The large scale 3D surface seismic measurements have been complemented by other geophysical and geochemical monitoring methods, among which are high-resolution seismic surface-downhole observations. These observations have been concentrating on the reservoir area in the vicinity of the injection well and provide high-resolution images as well as data for petrophysical quantification of the CO2 distribution in the reservoir. The Ketzin pilot site is a saline aquifer site in an onshore environment which poses specific challenges for a reliable monitoring of the injection CO2. Although much effort was done to ensure as much as possible identical acquisition conditions, a high degree of repeatability noise was observed, mainly due to varying weather conditions, and also variations in the acquisition geometries due to logistical reasons. Nevertheless, time-lapse processing succeeded in generating 3D time-lapse data sets which could be interpreted in terms of CO2 storage related amplitude variations in the depth range of the storage reservoir. The time-lapse seismic data, pulsed-neutron-gamma logging results (saturation), and petrophysical core measurements were interpreted together in order to estimate the amount of injected carbon dioxide imaged by the seismic repeat data. For the first repeat survey, the mass estimation was summed up to 20.5 ktons, which is approximately 7% less than what had been injected then. For the second repeat survey, the mass estimation was summed up to approximately 10-15% less than what had been injected. The deviations may be explained by several factors of uncertainty, and by partial dissolution of the injected CO2, thus reducing the amount of free gas, which can be detected by seismic time-lapse observations. These quantitative assessment studies have shown that conformity between injected and estimated CO2 quantities can only be achieved with some degree of uncertainty which needs to be quantified for a realistic assessment of conformity studies.

In this study, we investigated the presence of transverse isotropy at the Ketzin CO2 pilot storage site, Germany. The anisotropy parameter, eta (ŋ), is used as an indicator of anisotropy. Preliminary results show that ŋ ranges from -0.2399 to 0.1341, which indicates weak anisotropy. Introducing ŋ into the velocity estimation and applying the nonhyperbolic moveout correction resulted in an improvement in the continuity of reflections in the shallow part of the final migrated seismic data.

When CO2 replaces brine as a free gas it is well known to affect the elastic properties of porous media considerably. 3D seismic time-lapse surveys (4D seismics) have proven to be a suitable technique for monitoring of injected CO2. Forward modeling of a 4D seismic response to the CO2 fluid substitution in a storage reservoir is an important step in such studies. In order to track the migration of CO2 at the Ketzin pilot site (Germany), 3D time-lapse seismic data were acquired by means of a baseline (pre-injection) survey in 2005 and the monitor surveys in 2009 and 2012. Results of 4D seismic forward modeling with the reflectivity method suggest that effects of the injected CO2 on the 4D seismic data at the Ketzin pilot site are significant regarding both seismic amplitudes and time delays. They prove the corresponding observations in the real 4D seismic data at the Ketzin pilot site. However reservoir heterogeneity and seismic resolution, as well as random and coherent seismic noise are negative factors to be considered while the interpretation. In spite of these negative factors, results of 4D seismic forward modeling with the reflectivity method support the conclusion that the injected CO2 can be monitored at the Ketzin pilot site both qualitatively and quantitatively.

A combination of seismic and geoelectric processing was studied by means of a structurally constrained inversion approach. Structural constraints were interpreted from the seismic data and integrated into the geoelectric inversion through a local regularization, which allowed inverted resistivities to behave discontinuously across defined boundaries. This arranged seismic processing and constrained resistivity inversion in a sequential workflow, making the generic assumption that the petrophysical parameters of both methods change across common lithostructural boundaries. We evaluated the approach using a numerical example and a real data example from the Ketzin [Formula: see text] pilot storage site, Germany. The latter demonstrated the efficiency of this approach for combining 4D seismic and surface-downhole geoelectric data. In consistence with the synthetic example, the constrained resistivity inversions produced clearer delineated images along the boundary between caprock and reservoir formation. Near the [Formula: see text]-flooded reservoir, the seismic and geoelectric time-lapse anomalies correlated well. At some distance to the downhole electrodes, however, the geoelectric images conveyed a notably lower resolution in comparison to the corresponding seismic images. Both methods confirm a northwesterly trend for the [Formula: see text] migration at the Ketzin site, although a rather northerly direction was initially expected. The results demonstrate the relevance of the presented approach for the combination of both methods for integrated geophysical [Formula: see text] storage monitoring.

Changes in the near surface are a major problem for land time-lapse seismic projects. Three seismic surveys at the Ketzin pilot site for CO2 storage in Germany demonstrated the importance of removing the variations in the shallow subsurface by applying spatially variable, relative time shifts to the different vintages prior to 4D interpretation. The main reason for these time shifts is a change in seismic velocities in the ground layer above the water table due to different soil-moisture saturation at the times of acquisition. We compared the variation in precipitation, groundwater level and trace-to-trace time shifts between the baseline and two monitor surveys and revealed that delays in reflected energy are in a qualitative sense, proportional to the moisture content in the soil.

A combination of seismic and geoelectric processing is presented using a structurally constrained inversion approach. Structural constraints are interpreted from seismic data and inserted into the geoelectric inversion through a local regularisation, which allows inverted resistivities to behave also discontinuously across these a priori constraints. This sequential arrangement of seismic processing and constrained resistivity inversion makes the generic assumption that the petrophysical parameters of both methods change across common lithostructural boundaries. We evaluate the approach using a numerical example and a real 4D data example from the CO2 pilot storage site, Ketzin, Germany. The real data case shows that the time-lapse anomalies, which have independently been imaged by surface seismic and surface-downhole geoelectric methods, correlate well at the CO2-flooded reservoir. However, at some distance to the downhole electrodes the geoelectric images provide a notably lower resolution in comparison to the corresponding seismic images. The results demonstrate the relevance of the presented approach for the combination of both methods in geophysical CO2 storage monitoring operations.

A method for static correction of time-lapse differences in reflection arrival times of time-lapse prestack seismic data is presented. These arrival-time differences are typically caused by changes in the near-surface velocities between the acquisitions and had a detrimental impact on time-lapse seismic imaging. Trace-to-trace time shifts of the data sets from different vintages are determined by crosscorrelations. The time shifts are decomposed in a surface-consistent manner, which yields static corrections that tie the repeat data to the baseline data. Hence, this approach implies that new refraction static corrections for the repeat data sets are unnecessary. The approach is demonstrated on a 4D seismic data set from the Ketzin [Formula: see text] pilot storage site, Germany, and is compared with the result of an initial processing that was based on separate refraction static corrections. It is shown that the time-lapse difference static correction approach reduces 4D noise more effectively than separate refraction static corrections and is significantly less labor intensive.

The Dip-moveout (DMO) correction is a process which attempts to make the finite offset data closer to zero offset data after the normal-moveout (NMO) correction. The NMO correction is then dip independent and reflections with different dips will stack coherently. DMO plays a critical role in seismic processing by enhancing the final image quality of the seismic data. In this study, we apply 3D Squeezing DMO (Hale and Artley, 1993) to seismic data from the Ketzin pilot CO2 site after NMO to study the impact of DMO on time-lapse seismic imaging and to investigate if it enhances the CO2 seismic monitoring technique. This 3D DMO method is based on an integral approach and incorporates Hale and Artley’s (1993) modifications for variable velocity with time. A constant velocity algorithm is used with a gamma correction function which depends on the velocity function. An anti-alias velocity of 3000 m/s is used for the DMO. After DMO the data are stacked and F-XY deconvolution is applied. Finally, 3D finite-difference migration using the final smoothed NMO velocities is performed for each data set.We then apply a time-lapse analysis to the 3D seismic data sets and compare the results with and without DMO processing. The most important aspect of the DMO processing is determining the velocity field for the NMO step. This is done by using the initial smoothed velocity field obtained from the conventional velocity analysis before DMO as a first estimate. The data are input into the DMO process and then inverse NMO is applied. These data are then subjected to a new velocity analysis and the velocity field is updated and used as input for the NMO process. A number of iterations are generally required until the velocity field does not need further updating. In this study velocities were picked at every 20th CDP in the inline and crossline directions. Compared to the velocity spectrum without DMO processing, the velocity trend is improved and the ambiguity in the velocity picks is eliminated after DMO correction. The improved accuracy of velocity picking makes it easier to interpret the velocity spectrum and obtain correct interval velocities. Considering the stacked section, DMO suppresses the random noise to a greater extent and thus the signal-to-noise ratio is enhanced. From the comparison of the amplitude difference horizon at the reservoir level, the shape of the anomaly observed in the data with DMO processing is similar to that observed in the data without DMO processing. However, the amplitude anomalies of the former are stronger than those of the latter, especially close to the injection well. In addition, one stronger amplitude anomaly in the DMO time-lapse horizon indicates a preferred trend of the CO2 migration in WNW direction due to the reservoir heterogeneity. CO2MAN

A method for correction of time-lapse differences (TLD) in the statics of seismic data from repeated surveys is presented. Such static differences are typically caused by changes in the near-surface velocities between the acquisition repeats and have a deteriorating impact on the time-lapse image. Trace-to-trace time shifts are determined from the pre-stack data sets using cross-correlations. These time shifts are decomposed in a surface-consistent manner, which is providing a static correction that is capable of aligning the repeat data to the baseline data. The approach is demonstrated on a 4D seismic data set from the Ketzin CO2 pilot storage site, Germany, and is compared with results of an initial processing that was based on individual refraction static corrections. It is shown that the proposed TLD static correction reduces 4D noise more effectively than refraction static corrections while being significantly less labor intensive.

Seismic methods have proven to be effective for monitoring the movement and location of injected CO2 within deep saline aquifers. However, a disadvantage of seismic monitoring is the high costs associated with many repeat seismic surveys as part of a long term monitoring strategy of a CO2 storage site. As the cost for the use of the seismic source is often a significant part of the overall survey cost, affordable, smaller sources would increase the potential feasibility of a long term seismic monitoring strategy. A comparison of three land seismic sources is performed at the Ketzin CO2 storage site, Germany. Two of these sources (Vibsist 500 and Bobcat drop hammer) can be considered to be smaller and more affordable sources than those conventionally used in the seismic monitor surveys at Ketzin. In this study these smaller sources are compared to a larger more conventional Vibsist 3000 source. The subsurface target for the three sources in this comparison is the CO2 storage reservoir for the Ketzin site, located within the Triassic Stuttgart formation, which lies at a depth of approximately 600m/500ms. Two of the sources are Swept Impact (SIST) type courses (Vibsist 500 and 3000) which use hydraulic concrete breaking hammers. The third source uses a concrete breaking drop hammer tool mounted on a Bobcat loader. Data were collected along a 984m long profile with 24m receiver spacing and 12m shot spacing in 2011, 2012 and 2013 using the three different sources. A quantitative and qualitative comparison of the raw data from the three sources was performed in order to assess their relative performance. Frequency content, signal to noise ratio and penetration depth curves were calculated for the raw data. Data from the three sources was also processed using a conventional workflow to produce stacked sections which were compared. Based on the results from this study the Bobcat drop hammer source appears to perform better than the Vibsist 500 source. However both of the smaller sources were capable of producing good images of the target CO2 storage reservoir. Hence, both provide viable options as small affordable seismic sources for long term monitoring at the Ketzin site, or other shallow CO2 storage sites.

Difficulties encountered during the processing of the timelapse 3D land-seismic data at the CO2 geological storage site at Ketzin, Germany, were to a large extent attributed to changes in near-surface velocities. Two workflows for processing of the 4D data were tested. The first one included re-calculation of the refraction static corrections based on new information about the near-surface from first breaks. This workflow showed that the near-surface changes could only imperfectly be resolved by new refraction static corrections. The second workflow included cross-correlation of the traces acquired at the same locations but during different campaigns and calculation of the prestack time shifts between the surveys. Both workflows demonstrated their capability to minimize the time-lapse noise and enhance the time-lapse reservoir signature. They provide similar time-lapse results, except that the cross-correlation workflow is quicker, more accurate and displays less time-lapse noise.

Various geophysical methods applied at the Ketzin storage site have successfully imaged migration of the injected CO2 within the target reservoir zone of the ~ 650-680 m deep saline aquifer. Results from the first 3D repeat seismic survey conducted in 2009, after about 15 months of injection (~22,000 t), showed that the CO2 plume was concentrated around the injection well with a lateral extent of approximately 300-400 m and a thickness of about 5–20 m. The plume, however, was not radially symmetric, but had a rather westerly trending tendency, revealing the heterogeneous nature of the reservoir. A second 3D repeat seismic survey was acquired in the Summer/Fall of 2012, when ~ 61,000 tons of CO2 had been injected. Preliminary results show further growth and migration of the anomaly which has been interpreted to be induced by the CO2 injection. It is similar in shape to the one observed at the time of the first repeat survey, but larger by approximately 100-200 m and much stronger with the highest amplitudes nearly centered at the injection well. There is still a pronounced westward propagating tendency. The new seismic data show no indication of upward migration into the caprock.

Summary Seismic monitoring of the injected carbon dioxide (CO2) distribution at depth is an important issue in the geological storage of CO2. To help monitor changes in the subsurface during CO2 injection a series of 2D seismic surveys were acquired within the framework of the CO2SINK and CO2MAN projects at Ketzin, Germany, at different stages of the injection process. Here we investigate the use of seismic waveform tomography as a qualitative tool for time-lapse seismic monitoring given the constraints of the limited maximum offsets of the 2D seismic data. We applied seismic waveform tomography to the real timelapse data from the Ketzin site along with conventional seismic time-lapse processing. Both methods show a similar qualitative distribution of the injected CO2 and compare well with the results of more extensive 3D timelapse monitoring in the area.

Summary Difficulties encountered during the processing of the timelapse 3D land-seismic data at the CO2 geological storage site at Ketzin, Germany, were to a large extent attributed to changes in near-surface velocities. Two workflows for processing of the 4D data were tested. The first one included re-calculation of the refraction static corrections based on new information about the near-surface from first breaks. This workflow showed that the near-surface changes could only imperfectly be resolved by new refraction static corrections. The second workflow included cross-correlation of the traces acquired at the same locations but during different campaigns and calculation of the prestack time shifts between the surveys. Both workflows demonstrated their capability to minimize the time-lapse noise and enhance the time-lapse reservoir signature. They provide similar time-lapse results, except that the cross-correlation workflow is quicker, more accurate and displays less time-lapse noise.

In April 2004, a research pilot project in the German town of Ketzin started as the first onshore CO2 storage project in Europe. Injection started in June 2008 and until the latest repeat survey in February 2011 around 45 kilotons of CO2 had been injected into a saline aquifer at approximately 630 m depth. Different seismic methods, such as time-lapse Vertical Seismic Profiling, Crosswell, Moving Source Profiling and surface seismics have been employed to detect and monitor changes in the reservoir. We present here time-lapse results from sparse pseudo-3D seismic surveying with a radial distribution of acquisition profiles directed towards the approximate location of the injection well, which were acquired to link downhole surveys with full 3D surface seismic surveys. The results are consistent with the 3D seismic time-lapse studies over the injection site and show that the sparse 3D geometry can be used to qualitatively map the CO2 in the reservoir at a significantly lower effort than the full 3D surveying. The last repeat survey indicates preferential migration of the CO2 to the west. There are no indications of migration into the caprock on either of the repeat surveys. The same observation was obtained from the full 3D dataset.

Geophysical monitoring at the CO2 pilot storage Ketzin comprises time-lapse seismic and geoelectric (ERT) measurements. Both types of measurements are known to image geological structures differently, in particular for a variable saturation of CO2. We present a combination of both methods by means of a structural constrained inversion approach. Structural constraints are implemented in the geoelectric inversion by a local regularization. This allows model parameters to behave discontinuously across prominent geological boundaries. A tetrahedral finite-element parametrization is used to closely follow geometric a priori structures interpreted from seismic reflection data. Thus, seismics and geoelectrics are arranged in a sequential workflow which is based on a structural similarity. Practical application is performed on the Ketzin datasets which comprise repeated 3D seismic surveys, as well as repeated surface-downhole geoelectric surveys, providing different illumination/coverage and time-lapse signals. However, application of a local regularization for the caprock-reservoir boundary yields a more consistent image and reduces some of the ill-posedness in the ERT inversion. We compare the result with that of an unconstrained inversion and discuss its potential for CO2 migration imaging.

More than 50 000 tons of CO2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1 st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO2 had been injected. We show here that rather complex time-lapse signatures of this CO2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow an estimate of the total amount of CO2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO2 storage site using seismic methods.

SUMMARY Recent seismic evidence suggested that most oceanic plate hydration is associated with trenchouter rise faulting prior to subduction. Hydration at trenches may have a significant impact on the subduction zone water cycle. Previous seismic experiments conducted to the northwest of Nicoya Peninsula, Northern Costa Rica, have shown that the subducting Cocos lithosphere is pervasively altered, which was interpreted to be due to both hydration (serpentinization) and fracturing of the crustal and upper-mantle rocks. New seismic wide-angle reflection and refraction data were collected along two profiles, running parallel to the Middle American trench axis offshore of central Nicaragua, revealing lateral changes of the seismic properties of the subducting lithosphere. Seismic structure along both profiles is characterized by low velocities both in the crust and upper mantle. Velocities in the uppermost mantle are found to be in the range 7.3–7.5 km s −1 ; thus are 8–10 per cent lower than velocities typical for unaltered peridotites and hence confirm the assumption that serpentinization is a common process at the trench-outer rise area offshore of Nicaragua. In addition, a prominent velocity anomaly occurred within the crust beneath two seamounts. Here, velocity reduction may indicate increased porosity and perhaps permeability, supporting the idea that seamounts serve as sites for water percolation and circulation.

A seismic wide‐angle and refraction experiment was conducted offshore of Nicaragua in the Middle American Trench to investigate the impact of bending‐related normal faulting on the seismic properties of the oceanic lithosphere prior to subduction. On the basis of the reflectivity pattern of multichannel seismic reflection (MCS) data it has been suggested that bending‐related faulting facilitates hydration and serpentinization of the incoming oceanic lithosphere. Seismic wide‐angle and refraction data were collected along a transect which extends from the outer rise region not yet affected by subduction into the trench northwest of the Nicoya Peninsula, where multibeam bathymetric data show prominent normal faults on the seaward trench slope. A tomographic joint inversion of seismic refraction and wide‐angle reflection data yield anomalously low seismic P wave velocities in the crust and uppermost mantle seaward of the trench axis. Crustal velocities are reduced by 0.2–0.5 km s−1 compared to normal mature oceanic crust. Seismic velocities of the uppermost mantle are 7.6–7.8 km s−1 and hence 5–7% lower than the typical velocity of mantle peridotite. These systematic changes in P wave velocity from the outer rise toward the trench axis indicate an evolutionary process in the subducting slab consistent with percolation of seawater through the faulted and fractured lithosphere and serpentinization of mantle peridotites. If hydration is indeed affecting the seismic properties of the mantle, serpentinization might be reaching 12–17% in the uppermost 3–4 km of the mantle, depending on the unknown degree of fracturing and its impact on the elastic properties of the subducting lithosphere.

TOUGH2/ECO2N was used to simulate CO2 injection into a saline aquifer in the Baltic Sea and the effect of different amounts of CO2 injection on the seismic response. The Biot-Gassmann model was used to convert the simulated saturation and densities to seismic velocities and synthetic seismic responses before and after injection were compared. The results show that the amplitude changes in the seismic response are detectable even for small amounts of injected CO2, while noticeable signs of velocity pushdown, as a signature of the CO2 substitution, could only be observed if the injection rate is high enough.

article i nfo We apply a range of quantitative pre-stack analysis techniques to assess the feasibility of using smaller and cheaper seismic sources, than those currently used at the Ketzin CO2 storage site. Results from two smaller land sources are presented alongside those from a larger, more powerful source, typically utilized for seismic acquisition at the Ketzin. The geological target for the study is the Triassic Stuttgart Formation which contains a saline aquifer currently used for CO2 storage. The reservoir lies at a depth of approximately 630 m, equivalent to a travel time of 500 ms along the study profile. The three sources discussed in the study are the Vibsist 3000, Vibsist 500 (using industrial hydraulic driven concrete breaking hammers) and a drop hammer source. Data were collected for the comparison using the three sources in 2011, 2012 and 2013 along a 984 m long line with 24m receiver spacingand 12m shotspacing.Initiallya quantitative analysis isperformedof thenoise levels between the 3 surveys. The raw shot gathers are then analyzed quantitatively to investigate the relative energy output, signal to noise ratio, penetration depth, repeatability and frequency content for the different sources. The performance of the sources is also assessed based on stacked seismic sections. Based on the results from this study it appears that both of the smaller sources are capable of producing good images of the target reservoir and can both be considered suitable as lower cost, less invasive sources for use at the Ketzin site or other shallow CO2 storage projects. Finally, the results from the various pre-stack analysis techniques are discussed in terms of how representative they are of the final stacked sections. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license