• Energy Research

AbstractThe multiphase flow properties of CO2 water systems in permeable rocks control the engineering design and management of industrial CO2 sequestration projects. The relative permeability, capillary pressure, and residual trapping determine the rate of CO2 injection, the spread of injected CO2 in subsurface storage formations, and the long-term immobilization of injected fluid after injection has completed. Due to difficulties in working with CO2 brine systems, however, few observations have been made of these properties at pressure, temperature, and fluid salinities that exist in target reservoirs. In this paper we report on measurements of relative permeability and residual trapping made in a Berea sandstone rock core at reservoir conditions. The drainage relative permeability and residual trapping are characteristic of multiphase flow in a strongly water-wet system.

Abstract Global decarbonisation scenarios include Carbon Capture and Storage (CCS) as a key technology to reduce carbon dioxide (CO2) emissions from the power and industrial sectors. However, few large scale CCS plants are operating worldwide. This mismatch between expectations and reality is caused by a series of barriers which are preventing this technology from being adopted more widely. The goal of this paper is to identify and review the barriers to CCS development, with a focus on recent cost estimates, and to assess the potential of CCS to enable access to fossil fuels without causing dangerous levels of climate change. The result of the review shows that no CCS barriers are exclusively technical, with CCS cost being the most significant hurdle in the short to medium term. In the long term, CCS is found to be very cost effective when compared with other mitigation options. Cost estimates exhibit a high range, which depends on process type, separation technology, CO2 transport technique and storage site. CCS potential has been quantified by comparing the amount of fossil fuels that could be used globally with and without CCS. In modelled energy system transition pathways that limit global warming to less than 2 °C, scenarios without CCS result in 26% of fossil fuel reserves being consumed by 2050, against 37% being consumed when CCS is available. However, by 2100, the scenarios without CCS have only consumed slightly more fossil fuel reserves (33%), whereas scenarios with CCS available end up consuming 65% of reserves. It was also shown that the residual emissions from CCS facilities is the key factor limiting long term uptake, rather than cost. Overall, the results show that worldwide CCS adoption will be critical if fossil fuel reserves are to continue to be substantively accessed whilst still meeting climate targets.

Abstract We quantify the impact of mobility, simple heterogeneities and grid orientation error on the performance of first contact miscible gas flooding in a quarter five spot configuration by comparing the outputs from experimental and numerical models. The aim is to quantify the errors that may arise during simulation and to identify a workflow for minimizing these when conducting field scale fingering studies. A commercial reservoir simulator was validated by comparing its predictions with the results obtained from physical experiments. An uncorrelated, random permeability distribution was used to trigger fingering in the simulations. The physical experiments were carried out using a Hele-Shaw cell (40×40cm) designed and constructed for this study. The impact of a square low permeability inclusion (20×20cm) on flow was investigated by varying its permeability, location and orientation. For lower mobility ratios (M=2 to M=10) the commercial numerical simulator was able to reproduce the experimental observations within the uncertainty range of the permeability distribution used to trigger the fingers, provided a nine-point scheme was used for the pressure solution. At higher mobility ratios (M=20 to M=100) the grid orientation effect meant that the simulator overestimated the areal sweep even when a nine-point scheme was used. The introduction of a square, low permeability inclusion near the injection well reduced the discrepancy between experimental and numerical results, bringing it back within uncertainty limits in some of the cases. This was mainly because the real flow was then forced to move parallel to the edges of the Hele-Shaw cell and thus parallel to the simulation grid. Breakthrough times were well predicted by the numerical simulator at all mobility ratios.

AbstractWe demonstrate experimentally, that the spatial distribution of fluids in the pore space is the primary control on CO2 relative permeability, and that the importance of spatial heterogeneity in rock properties such as capillarity, porosity and permeability on fluid distributions is controlled by viscous forces. The importance of viscous forces during drainage core floods is evaluated using fluid viscosity as the varying parameter in CO2-brine core floods, and flow rate in N2-water core floods. A transition from a heterogeneous to a homogeneous displacement is observed with increasing viscous force applied to the core. During capillary dominated core flooding the relative permeability is sensitive to flow rate and viscosity. Homogeneous displacements have an invariant relative permeability and as such are a measure of the true relative permeability of the rock.

Abstract A portable stable carbon isotope ratio analyzer for carbon dioxide, based on wavelength scanned cavity ringdown spectroscopy, has been used to detect, locate, and characterize an intentional leakage of CO2 from an underground pipeline at the ZERT experimental facility in Bozeman, Montana. Rapid (1 h) walking surveys of the 100 m × 100 m site surrounding the pipeline were collected using this mobile, real-time instrument. The resulting concentration and 13C isotopic abundance maps were analyzed using Keeling plots, permitting not only the identification of specific leakage locations, but providing the ability to distinguish petrogenic sources of CO2 from biogenic sources. The ability to rapidly and reliably detect 12CO2 and 13CO2 concentration anomalies and identify the isotopic composition of the source flux provides a powerful and practical tool for detecting leakage from CO2 sequestration projects.

The ultimate composition of the CO2 stream captured from fossil fuel power plants or other CO2 intensive industries and transported to a storage site using high pressure pipelines will be governed by safety, environmental and economic considerations. So far, most of the studies performed on this topic have been limited in scope, primarily focusing on investigating the impact of the CO2 stream impurities on each part of the Carbon Capture and Sequestration (CCS) chain in isolation. This is a significant drawback given the markedly different sensitivities of the pipeline, well bore materials and storage sites to the various impurities. For example, given the risk of water table contamination, trace elements such as Lead, Mercury and Arsenic in the CO2 stream are of far greater concern in an aquifer storage site than compared to the pipeline. On the other hand, even small concentrations of water in the CO2 stream are detrimental to the pipeline due to corrosion, but of benefit even at high concentrations during storage given the immobilisation effect of water on CO2. 'What is good for the pipeline is not necessarily good for storage'. It is clear that the optimum composition and concentration of the impurities in the captured CO2 stream involves a delicate balance between the different requirements within the CCS chain, spanning capture, transportation and storage, with cost and safety implications being the over-arching factor. Pivotal to these considerations is an understanding of the impact of the impurities on the physico-chemical properties of CO2 and its hazard profile. This paper presents and overview of the current FP7 European Commission CO2QUEST project involving the collaboration of 12 industry and academic partners in Europe, China and Canada aimed at addressing fundamentally important and urgent issues regarding the impact of the typical CO2 streams impurities captured from fossil fuel power plants on its safe and economic transportation and storage. The work programme, spanning 36 months, focuses on the development of state-of-the-art mathematical models, backed, by laboratory and industrial-scale experimentation using unique EC-funded test facilities to perform a comprehensive techno-economic, risk-based assessment of the impact of the CO2 stream impurities on the phase behaviour and the physico-chemical reactions governing the pipeline and storage site integrities. The above involves the determination of the important CO2 mixtures that have the most profound impact upon the pipeline pressure drop, compressor power requirements, pipeline propensity to ductile and brittle facture propagation, corrosion of the pipeline and well bore materials, geochemical interactions within the well bore and storage site, and the ensuing health and environmental hazards. Based on a cost/benefit analysis and whole system approach, the results will in turn be used to provide recommendations for tolerance levels, mixing protocols and control measures for pipeline networks and storage infrastructure thus contributing to the development of relevant standards for the safe design and operation of CCS. Acknowledgement: The CO2QUEST project has received funding from the European Union 7th Framework Programme FP7-ENERGY-2012-1-2STAGE under grant agreement number 309102.

Abstract A significant uncertainty which remains for CO 2 sequestration, is the effect of natural geological heterogeneities and hysteresis on capillary trapping over different length scales. This paper uses laboratory data measured in cores from the Goldeneye formation of the Captain D Sandstone, North Sea in 1D numerical simulations to evaluate the potential capillary trapping from natural rock heterogeneities across a range of scales, from cm to 65m. The impact of different geological realisations, as well as uncertainty in petrophysical properties, on the amount of capillary heterogeneity trapping is estimated. In addition, the validity of upscaling trapping characteristics in terms of the Land trapping parameter is assessed. The numerical models show that the capillary heterogeneity trapped CO 2 saturation may vary between 0 and 14% of the total trapped saturation, depending upon the geological realisation and petrophysical uncertainty. When upscaling the Land model from core-scale experimental data, using the maximum experimental Land trapping parameter could increase the expected heterogeneity trapping by a factor of 3. Conversely, depending on the form of the imbibition capillary pressure curve used in the numerical model, including capillary pressure hysteresis may reduce the heterogeneity trapping by up to 70%.