Katriona Edlmann

Appraisal of global CO2 storage opportunities using the geomechanical facies approach

Different tectonic settings exert different depositional process controls within the tectonic basin which influence CO2 storage site suitability in terms of basin architecture, caprock architecture, reservoir quality, stress state, mechanical characteristics, fractures, burial depth, geothermal gradient, risk of orogenic modification, structural stability and preservation potential. We apply the concept of geomechanical facies; where deposits are grouped together on the basis of engineering parameters that fulfil a specific role within the storage system, e.g. reservoir, caprock, overburden; to provide an assessment of CO2 storage suitability for seven different tectonic settings. The geomechanical facies data were analysed using two different multiple attribute decision analysis methodologies and the results show that foreland basins are likely to be the most suitable for CO2 storage, followed by passive continental margins, terrestrial rift basins, Strike-slip basins, Back-arc basins, with oceanic basins, forearc basins and trench basins expected to be the least suitable. The geomechanical facies approach was compared with two current storage projects (Sleipner and In Salah) and a natural CO2 storage analogue (Miller) to build confidence in the methodology. Finally the global distribution of the most likely CO2 storage basins based on their geomechanical facies was mapped and correlated with CO2 emission sources.

Permeability prediction using stress sensitive petrophysical properties

The correlation of stress sensitivity to various petrophysical parameters was studied by analysis of experimental results from a range of sandstone core plugs tested hydrostatically at room temperature. The parameters measured were: compressional wave velocity, porosity, permeability and electrical resistivity. More detailed information on the effects of sorting and grain size distributions was obtained from experiments on artificial, unconsolidated sandstone cores. The measurements showed a high degree of stress sensitivity, which was different for each core but, broadly, could be classified as either high or low stress sensitivity. Cores from the high permeability clean sand were less stress sensitive than the cores from the low permeability coarsening-upwards sequence and the petrophysical values when combined into a synthetic log distinguished between the two lithologies. The results were compared to the predictions of a simple asperity deformation model. The experimental results and the model suggested a possible logging strategy to deduce permeability, by varying wellbore pressure.

Estimating geological CO2 storage security to deliver on climate mitigation

Carbon capture and storage (CCS) can help nations meet their Paris CO2 reduction commitments cost-effectively. However, lack of confidence in geologic CO2 storage security remains a barrier to CCS implementation. Here we present a numerical program that calculates CO2 storage security and leakage to the atmosphere over 10,000 years. This combines quantitative estimates of geological subsurface CO2 retention, and of surface CO2 leakage. We calculate that realistically well-regulated storage in regions with moderate well densities has a 50% probability that leakage remains below 0.0008% per year, with over 98% of the injected CO2 retained in the subsurface over 10,000 years. An unrealistic scenario, where CO2 storage is inadequately regulated, estimates that more than 78% will be retained over 10,000 years. Our modelling results suggest that geological storage of CO2 can be a secure climate change mitigation option, but we note that long-term behaviour of CO2 in the subsurface remains a key uncertainty.Carbon capture and storage can help reduce CO2 emissions but the confidence in geologic CO2 storage security is uncertain. Here the authors present a numerical programme to estimate leakage from wells and find that under appropriate regulation 98% of injected CO2 will be retained over 10,000 years.

Wastewater from hydraulic fracturing in the UK: assessing the viability and cost of management

The safe and effective management of wastewaters from unconventional hydrocarbon production using the hydraulic fracturing (fracking) process poses a major challenge. Exploitation of unconventional hydrocarbons, such as shale gas, remains controversial in the UK primarily due to concerns surrounding the hydraulic fracturing process required to extract the resource. The key issue of how waste fluids produced by hydraulic fracturing in the UK will be safely managed has yet to be adequately addressed, and the capacity for the specialist treatment required is currently uncertain. To address this critical knowledge gap we review, for the first time, the available management options for these waste fluids in the UK. We find that these are limited in comparison to the options available in the U.S., due to uncertainty surrounding whether wastewater injection wells will be permitted in the UK. Consequently, it is highly probable that these fluids will need to be treated and safely disposed of at the surface. In order to constrain the composition of wastewater which will require treatment in the UK, we analyse the only existing data set of returned waters from hydraulic fracturing (n = 31). We supplement this with measurements of wastewater from UK conventional onshore hydrocarbon (n = 3), and offshore hydrocarbon (n = 14), operations which produce water from similar formations as those currently targeted for shale gas exploration. Comparison of this limited UK data to the more extensive unconventional production dataset from the United States (n = 3092) provides confidence in our projected UK wastewater compositions. We find that the high level of salinity and concentration of naturally occurring radioactive material (NORM) in UK wastewaters will be problematic to treat for disposal into a freshwater environment. We use our data compilation to estimate costs of treating such wastewaters in a number of relevant scenarios. We find that the projected salinity in FP waters from UK hydraulic fracturing operations can be treated at a cost of between

Natural Analogue Studies

2701 (∼£2000) and

Risk Management for CO 2 Geological Storage Projects

1 376 093 (∼£1 047 000) per well, requiring between 2 and 26% of expected revenue. Additional costs, specific to the UK of up to £163 450 per well, will be incurred due to the legislative requirement for disposal of NORM concentrated sludge in permitted landfill sites. We find that existing capacity to receive NORM waste at currently permitted UK treatment facilities is limited, and that this will pose management problems if wastewaters are generated from multiple unconventional wells simultaneously.

Experimental investigation into the sealing capability of naturally fractured shale caprocks to supercritical carbon dioxide flow

Lessons learned from sites where CO2 has naturally been stored for long geologic periods of time provides valuable information for assessing proposed anthropogenic storage sites. This chapter discusses the natural CO2 storage analogue sites and looks at them worldwide to determine which geological characteristics are preferable for natural CO2 storage and which are not. Following this, an approach is presented based on geomechanical facies, for a comparative assessment of storage sites, accounting for features observed in the natural analogue sites. Finally, a number of anthropogenic storage sites are classified according to the characterization criteria and a detailed description of a number of natural and anthropogenic storage sites are presented.

Heletz experimental site overview, characterization and data analysis for CO2 injection and geological storage

A number of key challenges relating to potential CO2 reservoir capacity, injectivity and confinement need to be overcome when validating the performance of a storage system for its lifecycle. In the case of a failure of a storage operation, the environment, investments, and human health and safety, may be at risk. It is therefore important to use risk management methods to ensure that the project will meet its objectives in all aspects. The aims of risk management are both to identify and evaluate all the risks that could impact the project objectives, and to establish treatment, monitoring actions and plans to reduce the impact of risks thereby ensuring the project performance. This Chapter discusses the implementation of risk management for a CO2 geological storage project.