Carbonate cements in Miller field of the UK North Sea: a natural analog for mineral trapping in CO2 geological storage

Abstract

Miller field of the North Sea has had high concentrations of natural CO 2 for *70 Ma. It is an ideal analog for the long-term fate of CO 2 during engineered storage, particularly for formation of carbonate minerals that permanently lock up CO 2 in solid form. The Brae Formation reservoir sandstone contains an unusually high quantity of calcite concretions; however, C and O stable isotopic signatures suggest that these are not related to the present-day CO 2 charge. Margins of the concretions are corroded, probably because of reduced pH due to CO 2 influx. Dispersed calcite cements are also present, some of which postdate the CO 2 charge and, therefore, are the products of mineral trapping. It is calculated that only a minority of the reservoired CO 2 in Miller (6-24%) has been sequestrated in carbonates, even after 70 Ma of CO 2 emplacement. Most of the CO 2 accumulation is dissolved in pore fluids. Therefore, in a reservoir similar to the Brae Formation, engineered CO 2 storage must rely on physical retention mechanisms because mineral trapping is both incomplete and slow.

A new stratigraphic trap for CO2 in the UK North Sea: Appraisal using legacy information

“…We suggest that significant volumes of minerals will not form, as in the UK North Sea there are several oil and gas fields with exceptionally high levels of CO 2 that have been present in the reservoirs for 10's of millions of years. There are almost no detectable minerals precipitated within these reservoirs from the CO 2 (Wilkinson et al, 2009;Lu et al, 2011). We conclude that it is unlikely that there will be sufficient chemical reaction between the reservoir sandstone and the injected CO 2 to significantly alter the mass of free-phase CO 2 within the reservoir, and so this is neglected in the preliminary modelling.…”

How important is carbonate dissolution in buried sandstones: evidences from petrography, porosity, experiments, and geochemical calculations

“…Some studies with convincing petrographic evidence of the dissolution of carbonate cements in buried sandstones have been published. Review of these works suggests that most of the extensive dissolutions were related to deep hot fluids (Taylor 1996;Taylor et al 2010) and cold meteoric fresh water (Bouch et al 2006;Cavazza et al 2009;Khidir and Catuneanu 2003;Poursoltani and Gibling 2011;Yuan et al 2017;Zaid 2012), while organic CO 2 leaching resulting in very limited dissolution (Lu et al 2011;Weedman et al 1996).…”

“…Some authors have presented convincing petrographic evidence of carbonate dissolution that was induced by organic CO 2 originating from the thermal evolution of kerogen. The authors, however, also stated that only a small amount of carbonate minerals were dissolved under the constraints of fluid chemistry modeling or mass balance calculation (Lu et al 2011;Weedman et al 1996).…”

The Stable Isotope Composition of the Calcite Cement in the Fluvio-Deltaic Reservoir Sandstones of the Lower Acacus Formation, Ghadames (Hamada) Basin, NW Libya

“…The negative δ 13 C values probably record the increasing importance with depth of bicarbonate production by thermal decarboxylation (e.g. [8]; [15]). …”