Storage of CO2 in saline aquifers–Lessons learned from 10 years of injection into the Utsira Formation in the Sleipner area

AbstractThe ongoing CO2 injection at Sleipner has demonstrated that 2/3 of the injected CO2 has not reached the top of the Utsira Formation, but has instead migrated laterally below imperfect intra-reservoir seals. The CO2 trapping below the structural spill point in the Utsira Formation is due to local mini traps, capillary flow resistance, and the hydrodynamic drive of the injection. About 40% of the CO2 that has entered the pore systems will remain as residually trapped CO2, whereas an unknown fraction of the remaining CO2 will migrate towards the top of the reservoir

Field-case simulation of CO2-plume migration using vertical-equilibrium models

When injected in deep saline aquifers, CO2 moves radially away from the injection well and progressively higher in the formation because of buoyancy forces. Analyzes have shown that after the injection period, CO2 will potentially migrate over several kilometers in the horizontal direction but only tens of meters in the vertical direction, limited by the aquifer caprock. Because of the large horizontal plume dimensions, three-dimensional numerical simulations of the plume migration over long periods of time are computationally intensive. Thus, to get results within a reasonable time frame, one is typically forced to use coarse meshes and long time steps which result in inaccurate results because of numerical errors in resolving the plume tip. Given the large aspect ratio between the vertical and horizontal plume dimensions, it is reasonable to approximate the CO2 migration using vertically averaged models. Such models can, in many cases, be more accurate than coarse three-dimensional computations. In particular, models based on vertical equilibrium (VE) are attractive to simulate the long-term fate of CO2 sequestered into deep saline aquifers. The reduced spatial dimensionality resulting from the vertical integration ensures that the computational performance of VE models exceeds the performance of standard three-dimensional models. Thus, VE models are suitable to study the long-time and large-scale behavior of plumes in real large-scale CO2-injection projects. We investigate the use of VE models to simulate CO2 migration in a real large-scale field case based on data from the Sleipner site in the North Sea. We discuss the potential and limitations of VE models and show how VE models can be used to give reliable estimates of long-term CO2 migration. In particular, we focus on a VE formulation that incorporates the aquifer geometry and heterogeneity, and that considers the effects of hydrodynamic and residual trapping. We compare the results of VE simulations with standard reservoir simulation tools on test cases and discuss their advantages and limitations and show how, provided that certain conditions are met, they can be used to give reliable estimates of long-term CO2 migration.publishedVersio

Active and passive damping systems for vibration control of metal machining equipment

Passive damping is used to reduce vibrations of machining tools. The drawback with the passive damping system is that it is adjusted to damp out vibrations in one restricted frequency range. Active damping uses real time measurements to dampen the vibrations and is not tuned for one specific frequency range. Teeness AS wants to be able to investigate different ways of regulating an active damping system on a physical test bench and to investigate if an Arduino is suited for regulating the system. This paper presents the design development of the physical test bench, simulations of the designed test bench and an electrical setup with Arduino as the regulating controller. Actuators were evaluated and purchased. The test bench was designed to fit the actuators using Siemens NX as CAD program. The components of the test bench were produced by Teeness AS. Simulations of the designed test bench were conducted using FEDEM to investigate the dynamics of the system. Requirements for the Arduino were investigated and regulating scripts were coded, tested and evaluated. The simulated test bench was able to significantly reduce the vibrations investigated. However there were some behaviors of the simulated test bench that differ from the measurements made of the physical test bench. This was most likely a result of the modeling of actuators. The results from the simulations give an indication of the general behavior of the test bench, but the use of exact values should be avoided. To improve the validity of the simulations, further work with the simulation of the actuators should be conducted. Using an Arduino as a control mechanism seems promising, but further work needs to be done to reduce the noise of the sensor data and the regulating script presented in this paper should be improved

(Table 1) Gravity and pressure within the Sleipner area relative to ones at the reference station in 2002 and 2005

At Sleipner, CO2 is being separated from natural gas and injected into an underground saline aquifer for environmental purposes. Uncertainty in the aquifer temperature leads to uncertainty in the in situ density of CO2. In this study, gravity measurements were made over the injection site in 2002 and 2005 on top of 30 concrete benchmarks on the seafloor in order to constrain the in situ CO2 density. The gravity measurements have a repeatability of 4.3 µGal for 2003 and 3.5 µGal for 2005. The resulting time-lapse uncertainty is 5.3 µGal. Unexpected benchmark motions due to local sediment scouring contribute to the uncertainty. Forward gravity models are calculated based on both 3D seismic data and reservoir simulation models. The time-lapse gravity observations best fit a high temperature forward model based on the time-lapse 3D seismics, suggesting that the average in situ CO2 density is about to 530kg/m**3. Uncertainty in determining the average density is estimated to be ±65 kg/m**3 (95% confidence), however, this does not include uncertainties in the modeling. Additional seismic surveys and future gravity measurements will put better constraints on the CO2 density and continue to map out the CO2 flow