Neil Burnside

Man-made versus natural CO2 leakage: a 400 k.y. history of an analogue for engineered geological storage of CO2

To evaluate sites for long-term geological storage of CO2 and optimize techniques for monitoring the fate of injected CO2, it is crucial to investigate potential CO2 migration pathways out of a reservoir and surface leakage magnitudes. For the first time, we calculate CO2 leakage rates and volumes from ancient fault-related travertines and from an abandoned borehole. U-Th–dated travertine along two faults near Green River, Utah (western United States), shows that leakage has occurred in this area for over 400 k.y. and has switched location repeatedly over kilometer-scale distances. One individual travertine was active for at least 11 k.y. Modern leakage is predominantly through the active Crystal Geyser, which erupts from an abandoned exploration well. Using age data and travertine volume, we calculate magnitudes and rates of CO2 emission. Fault-focused leakage volume is twice as great than diffuse leakage through unconfined aquifers. The leakage rate from a poorly completed borehole is 13 times greater than the long-term time averaged fault-focused leakage. Although magnitudes and rates of any leakage from future storage sites will be highly dependent on local geology and pressure regime, our results highlight that leakage from abandoned wells is likely to be more significant than through faults. INTRODUCTION Carbon dioxide could potentially migrate from underground storage sites through boreholes, poor cap rocks, or faults and fractures. Storage formation integrity, and effects of leaking CO2 on the surface environment, is commonly investigated (Stevens et al., 2001; Kirk, 2011); however, the overburden between the storage formation and the surface is a poorly studied part of the CO2 storage system (Gaus, 2010). Understanding flow through potential migration pathways in the overburden, such as faults or high-permeability strata is crucial for evaluating long-term storage security. The integrity of well bores and their long-term ability to retain CO2 has also been recognized as a significant risk to the long-term security of geological storage (IEAGHG, 2005). Storage operators will be legally required to monitor the fate of injected CO2 (European Commission, 2009). Effective monitoring and engineered remediation depends on the likely nature of migration pathways through the overburden, and on the locations and likely fluxes of CO2 shallow leakage pathways (Cortis et al., 2008; Benson and Hepple, 2005). We investigate a unique location in the Paradox Basin, Utah, (western United States) where fossil travertine mounds allow us to compare ancient CO2 flux via fault-associated fracturing and diffuse leakage through an aquifer, with modern leakage from abandoned wells. The Paradox Basin hosts at least nine natural CO2 accumulations, most of which have contained CO2 for millennia (Gilfillan et al., 2008). CO2-charged springs along the Little Grand Wash (LGW) and Salt Wash Graben (SWG) normal faults (Fig. 1) demonstrate that CO2 is leaking to the surface through fault zones and abandoned wells (Doelling, 1994). The springs are fed from a shallow aquifer, overlain by low-permeability siltstones and shales and charged by CO2 from depth—making this setting analogous to heterogeneous and variably permeable overburden above a geological CO2 storage site. We use U-Th dating of travertine formed by out-gassing of CO2 from springwater to determine flow history along the faults. Combining travertine age and volume allows us to estimate volumes and rates of CO2 emission to the surface through time and compare fault-focused, diffuse and borehole leakage, in a single hydrogeological setting.

Rapid river incision across an inactive fault: implications for patterns of erosion and deformation in the central Colorado Plateau

The Colorado Plateau presents a contrast between deep and seemingly recent erosion and apparently only mild late Cenozoic tectonic activity. Researchers have recently proposed multiple sources of epeirogenic uplift and intriguing patterns of differential incision, yet little or no quantitative constraints exist in the heart of the plateau to test these ideas. Here, we use both optically stimulated luminescence (OSL) and uranium-series dating to delimit the record of fluvial strath terraces at Crystal Geyser in southeastern Utah, where the Little Grand Wash fault crosses the Green River in the broad Mancos Shale badlands of the central plateau. Results indicate there has been no deformation of terraces or surface rupture of the fault in the past 100 k.y. The Green River, on the other hand, has incised at a relatively rapid pace of 45 cm/k.y. (450 m/m.y.) over that same time, following a regional pattern of focused incision in the “bull’s-eye” of the central plateau. The Little Grand Wash fault may have initiated during Early Tertiary Laramide tectonism, but it contrasts with related structures of the ancestral Paradox Basin that are presently active due to salt dissolution and focused differential erosion. We also hypothesize there may be a Pliocene component of fault slip in the region linked to broad-wavelength erosional unloading, domal rebound, and extension. An apparent rapid decrease in incision rates just upstream through Desolation Canyon suggests the Green River here may have recently experienced an upstream-migrating wave of incision.

CO2 leakage from geological storage facilities: environmental, societal and economic impacts, monitoring and research strategies

Carbon capture and storage (CCS) has the potential to significantly limit CO 2 emissions to the atmosphere; however a leakage of CO 2 from transport or storage could have environmental and safety implications. Monitoring of CCS storage is a further challenge, both to assure the public and, should leakage occur, to enable mitigation and verification. This chapter reviews the current state of knowledge regarding environmental sensitivities and monitoring and outlines the challenges for research over the next few years. The current hypothesis is that significantly large leaks would be required to cause noticeable damage in the ecosystem.

Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22°C) and increases with depth, so, considering the available flow (>100Ls-1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use.

Water from abandoned mines as a heat source: practical experiences of open- and closed-loop strategies, United Kingdom

Pilot heat pump systems have been installed at two former collieries in Yorkshire/Derbyshire, England, to extract heat from mine water. The installations represent three fundamental configurations of heat exchanger. At Caphouse Colliery, mine water is pumped through a heat exchanger coupled to a heat pump and then discharged to waste (an open-loop heat exchange system). The system performs with high thermal efficiency, but the drawbacks are: (1) it can only be operated when mine water is being actively pumped from the colliery shaft for the purposes of regional water-level management, and (2) the fact that the water is partially oxygenated means that iron oxyhydroxide precipitation occurs, necessitating regular removal of filters for cleaning. At Markham Colliery, near Bolsover, a small amount of mine water is pumped from depth in a flooded shaft, circulated through a heat exchanger coupled to a heat pump and then returned to the same mine shaft at a slightly different depth (a standing column arrangement). This system’s fundamental thermal efficiency is negatively impacted by the electrical power required to run the shaft submersible pump, but clogging issues are not significant. In the third system, at Caphouse, a heat exchanger is submerged in a mine water treatment pond (a closed-loop system). This can be run at any time, irrespective of mine pumping regime, and being a closed-loop system, is not susceptible to clogging issues.