Calculation of CO2 column heights in depleted gas fields from known pre-production gas column heights

Abstract

a b s t r a c tDepleted gas fields have been identified as potential targets for CO 2 storage. In order to maximise storage capacity, a target field must be deep enough to ensure that the CO 2 is in a dense phase (either liquid or supercritical). Accurate assessment of the storage capacity also requires an estimation of the amount of CO 2 that can be safely stored beneath the reservoir seal which can be estimated in several ways. In this paper we develop a methodology to convert known pre-production gas column heights into CO 2 column heights in order to estimate storage capacities. Several authors have correctly identified that the differences in interfacial tension and wettability act to reduce the threshold capillary entry pressure for CO 2 compared to natural gas, consequently reducing column height estimates. However, under reservoir conditions the density of CO 2 is substantially higher than natural gas so the buoyancy force on the seal for a fixed column height is much lower for dense phase CO 2 increasing column height estimates; we investigate the effects of this trade off on storage estimates and apply it to a typical dataset, in this case the UK North Sea.

Are rocks still water‐wet in the presence of dense CO2 or H2S?

“…The latter parameter provides an indication on the gas leakage rate through the seal if breakthrough is to occur: effective gas permeabilities in the range of 10 )7 to 10 )9 Darcy, typical for instance of caprocks from the Alberta Basin (Bennion & Bachu 2007), correspond to acceptable leakage rates; whereas values in the range of 10 )4 to 10 )5 Darcy, encountered for instance in the caprock of the Weyburn EOR and storage site, lead to significant leakage rates (Li et al 2006). The gas breakthrough pressure, or maximum bottomhole pressure, can be transformed into a maximum height of acid gas that can be stored in the depleted hydrocarbon reservoir, that is, into a storage capacity (Daniel & Kaldi 2008;Naylor et al 2011). When the storage formation is a deep saline aquifer, the ability of the overlying layers (usually referred to as aquitard or aquiclude) to confine a buoyant nonwetting fluid is not known in the first place, and this breakthrough pressure must therefore be determined with care prior to any storage project.…”

Influence of CO2‐wettability on CO2 migration and trapping capacity in deep saline aquifers

“…6,9 For safety and efficiency reasons, CO 2 is injected at depths greater than 800 m, so that CO 2 remains in a supercritical (sc) note that CO 2 -rock wettability can vary tremendously. 12,13 However, despite this laboratory-scale evidence, the effect of wettability on reservoir-scale processes and associated storage capacity and containment security predictions has received little attention 27 and generally, though the wettability is incorporated in the pilot projects modeling via relative permeability curves and multiphase flow, the values are poorly constrained. 13,27,[29][30][31][32][33][34][35][36][37][38][39] Wettability, as has been previously shown in laboratory experiments (at the mm to cm scale), has a significant effect on residual trapping 15,[40][41][42] and structural trapping.…”

Molecular dynamics computations of brine–CO2 interfacial tensions and brine–CO2–quartz contact angles and their effects on structural and residual trapping mechanisms in carbon geo-sequestration

“…The column height h (i.e. volume) of CO 2 immobilized beneath such a caprock is directly proportional to the cosine of the contact angle between water, scCO 2 and the caprock [12] (measured through the water):…”