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A proof-of-concept demonstration using a scalable, automated, semipermanent, seismic array (SASSA) is being conducted to test a novel seismic method for detecting and tracking an injected CO 2 plume as it traverses discreet points within a reservoir in southeastern Montana at Bell Creek oil field which is undergoing commercial CO 2 enhanced oil recovery (EOR). This document serves to describe the technical design of the project infrastructure, the operational approach, corresponding data collection, and data-processing activities. [ABSTRACT FROM AUTHOR]

Acquiring multi-scale seismic measurements – 3D surface seismic, vertical seismic profiles (VSPs), and cross-well seismic data – comes with high cost and can be an operationally challenging endeavour, particularly in an oilfield under active enhanced oil recovery (EOR) management, as is the case with the Farnsworth Unit (FWU) EOR Field Project. The three aforementioned measurements were implemented in the FWU geophysical program, and utilized in conjunction with downhole measurements to address multiple site characterization and monitoring objectives for both EOR optimization and carbon dioxide (CO 2 ) sequestration and monitoring. The three geophysical methods will be discussed in this paper. [ABSTRACT FROM AUTHOR]

Hydrocarbon extraction from unconventional reservoirs demands ever-increasing technological effort, for better understanding phenomena occurring within the reservoir. We review currently available geophysical techniques for reservoir monitoring. First, we describe basic characteristics of geophysical monitoring, identifying properties and their associated monitored quantities, according to the different fields of analysis in reservoir. Second, we present an overview of current monitoring techniques associating them to monitored quantities. Monitoring is extremely important in understanding how the reservoir reacts to external or internal perturbation of its state; secondly, monitoring is one of the first steps in preventing and addressing key environmental issues. [ABSTRACT FROM AUTHOR]

Subsurface monitoring is essential for the successful implementation and public acceptance of CO 2 storage. Injected CO 2 will need to be monitored to verify the successful containment within its intended formation, and to ensure no loss of containment within the storage complex. The ability for seismic techniques to monitor structurally trapped CO 2 has been successfully demonstrated due to the changes in the acoustic properties of the reservoir produced by the displacement of brine by less dense and more compressible CO 2 . However, the ability for seismic methods to detect free-phase migrating CO 2 is still moderately understood. In order to assess the feasibility for seismic monitoring of a migrating front, we estimate the time-lapse signal over a theoretical, clean, homogeneous sandstone reservoir through the application of a three-stage model-driven workflow consisting of fluid-flow, rock physics and seismic forward modelling. To capture the range of responses which could be encountered, two end-member fluid distribution models were used: uniform saturation and the modified patchy saturation model. Analysis of the time- lapse survey highlights the importance of determining and understanding the fluid distribution model impacting the range of velocities prior to generating and interpreting the seismic response. This change in velocity is shown to be directly related to the volume of CO 2 occupying the pore-space of a migrating plume front. This highlights the fact that the detectability of a migrating front is a site specific issue which not only depends on the geophysical parameters of the seismic survey but also on the geological variations and spatial distribution in the reservoir. [ABSTRACT FROM AUTHOR]

Abstract: Time lapse seismic surveys covering the CO2 injection plume at Sleipner are used to test novel techniques which estimate the thickness of a spreading CO2 layer. Utilising the spectral content of the data, the methods extend the limited vertical resolution encountered with time domain data. Spectral decomposition using the smoothed pseudo Wigner-Ville distribution extracts monochromatic reflection amplitudes from the topmost CO2 layer and is used to assess the lateral variation in peak tuning frequency. This provides a direct proxy for temporal thickness which show consistency with true layer thicknesses derived from structural analysis. A spectral inversion method is also applied to a subset of the upper layer, with limited success. It is noted that high signal-to-noise ratios and the absence of overlying and underlying reflections are required to utilize the technique fully. [Copyright &y& Elsevier]

Abstract: A key objective of Stage 2 of the CO2CRC Otway Project is to explore the ability of geophysical methods to detect and monitor injection of greenhouse gas into a saline formation. For this purpose, injection o f some 10,000 30,000 tonnes of CO2-rich mixture into the Paaratte formation, a saline aquifer located at a depth of about 1,400 m, is planned. Before such an injection experiment is undertaken, we assess the feasibility of geophysical monitoring using computer modelling. To examine the detectability of the plume we need to estimate the time-lapse signal and time- lapse noise. The time lapse signal is modelled using flow simulations, fluid substitution and seismic forward modelling. In order to assess the applicability of time-lapse seismic to monitor the injection, the predicted signal is compared to the time-lapse noise level from the recent 4D seismic survey acquired at the Otway site in 2009-2010. The methodology is applied to two alternative reservoir intervals located at a depth of 1392-1399 m and 1445-1465 m below the sea level, respectively. These intervals are considered to be the two possible options for the injection. The results show that injection into the lower interval will produce a plume of a larger thickness and smaller lateral extent, and a seismic response that is more likely to be detectable. The developed feasibility assessment workflow, and the results of its application to the Otway site, can be used to assess the ability of seismic methods to detect and monitor greenhouse gas leakage in other CCS projects. [Copyright &y& Elsevier]

Abstract: Our purpose is development of a monitoring method for both lowering costs and increasing the safety in CO2 sequestration by complementing standard seismic survey with various other geophysical techniques, especially gravity monitoring. In many cases reservoirs are relatively thin and deep, resulting in subtle time-lapse gravity signals at the earth's surface. These signals must be separated from gravity signals generated by near-surface hydrological sources, in which case it would be effective to monitor continuously with a superconducting gravimeter. We have started gravity monitoring at a CO2 sequestration field in Utah in collaboration with the US project of Southwest Regional Partnership. [Copyright &y& Elsevier]

Abstract: The CO2 plume at Sleipner has been imaged on 3D seismic surveys as a series of bright sub-horizontal reflections. Nine discrete CO2 rich layers are inferred to have accumulated between a series of intra-reservoir mudstones beneath a substantial reservoir topseal. Time-lapse changes in reflectivity and in the lateral extent of these layers provide useful information about CO2 flow within the reservoir. The deepest CO2 layers within the growing plume have acoustically dimmed, stopped growing, and some have shrunk. Shallower layers have continued to grow. A combination of numerical flow models and analytical solutions of layer spreading yields useful insights into plume development. The observed seismic dimming and shrinkage of the deeper layers are, at least in part, caused by a reduction in the amount of CO2 trapped in the deeper plume. This is probably due to increases in the effective permeability of thin intra-reservoir mudstones. These changes reduce net flux of CO2 into the deeper layers of the plume with a corresponding increase of CO2 flux towards the top of the reservoir [Copyright &y& Elsevier]

Abstract: The use of depleted gas fields for CO2 storage as well as CO2-based enhanced gas recovery are of global importance. Thus, the CO2CRC Otway Basin Pilot Project provides important experience in establishing whether such scenarios can be monitored by geophysical techniques, in particular seismic time-lapse methodology. Injection of CO2 into a depleted gas reservoir (with residual gas in the Otway case) does not present favourable conditions for the application of geophysical monitoring techniques. Simulation of the CO2 injection process at Otway shows that changes in elasticity of the reservoir rock will be quite small and difficult to monitor even with the most powerful time-lapse (TL) seismic methodologies. Consequently, the design and implementation of the monitoring program had to address these issues. To increase the sensitivity of TL seismic we combined 3D VSP with 3D surface seismic. For land seismic case, we achieved excellent repeatability with 3D time lapse surveys, which at the reservoir level produced normalised RMS difference values of about 20% for surface seismic and 10% for 3D VSP, respectively. Still due to very small time lapse signal, the primary use of 3D surface seismic was for assurance monitoring. Borehole seismic measurements confirmed that time-lapse is too small to be reliably estimated and analysed from repeated seismic measurements. Finally, post-injection reservoir simulation and accompanying seismic modelling suggest that a prolonged CO2/CH4 injection should produce only negligible change of the elastic properties of the Naylor reservoir. [Copyright &y& Elsevier]

Abstract: The Penn West enhanced oil recovery pilot project is located in the Pembina Oil Field in west-central Alberta, Canada, with CO2 injection into the 20 m thick Cretaceous Cardium Formation at a depth of 1650 m below surface. Time-lapse processing of the surface seismic monitoring data collected between March 2005 and March 2007 yielded no significant changes in P-wave seismic amplitudes or traveltimes between monitor and baseline surveys after ∼40,000 t of CO2 had been injected. A small amplitude change in the Cardium Formation and deeper events were detected by a fixed geophone array in an observation well. We conclude that partial or full saturation of the reservoir pore space was restricted to the most permeable sandstone members of the Cardium Formation. The seismic data indicates that no leakage of CO2 has occurred into shallow aquifers. [Copyright &y& Elsevier]

Abstract: Designing a seismic characterization and monitoring program for a site with high levels of industrial and cultural infrastructure is by not trivial. At the MGSC Phase III project site, a combination of 3D surface seismic and VSP surveys will be used for site characterization and to monitor the injected CO2. The sparse existing data have been carefully analyzed to design 3D surface seismic and VSP surveys that will fit within the surface constraints at the site and meet the greater objectives of the project. The seismic data will be used to map formation heterogeneities and characterize fractures. [Copyright &y& Elsevier]