Flow processes and pressure evolution in aquifers during the injection of supercritical CO ₂ as a greenhouse gas mitigation measure

Abstract

ABSTRACT:Regional saline aquifers offer the greatest potential for very large-scale underground CO 2 storage as a means of mitigating greenhouse gas emissions. Their dynamic storage capacity, in terms of induced increases in formation pressure, will limit the rate at which CO 2 can be injected and may ultimately limit the amount of CO 2 that can be stored. Generic flow models have been generated to examine the effects on pressure evolution of various reservoir parameters (dimensions, permeability, porosity, presence and nature of flow barriers). CO 2 injection involves dominantly hydrogeological (single-phase flow) processes in much of the reservoir and surrounding adjacent strata, with additional two-phase flow effects around the CO 2 plume itself. Large, thick aquifers with no significant flow barriers can accept high injection rates (~10 million tonnes of CO 2 per year) without undue pressure effects. However, flow barriers, such as faults, increase induced pressures considerably; for reservoirs with such features, careful site characterisation and operational planning will be required for large storage projects. The principles established from the generic modelling were then applied to a real aquifer storage operation at Sleipner in the North Sea. Here CO 2 is being injected into the Utsira Sand, a large relatively homogeneous reservoir. Modelling indicates that pressure increase should be negligible. In fact observed wellhead pressures do show a small rise, but this can be attributed to temperature changes in the fluid column in the wellbore. Pressure changes in the reservoir are likely to be very small.

Dynamic modelling of a UK North Sea saline formation for CO 2 sequestration

“…This 547 finding is similar to the results of Chadwick et al (2009a) who showed that near-field pressure 548 (within a 2.5 m radius of the injection well) is inversely proportional to permeability. Increasing 549 storage formation porosity independently of permeability leads to slightly higher pressure at the top 550 of the model (s01a, s01a5).…”

The realities of storing carbon dioxide – A response to CO2 storage capacity issues raised by Ehlig-Economides & Economides

“…In fact, development and migration of the CO 2 plume at Sleipner is very much as predicted, with no migration from the storage reservoir so far detected and no leakage. Simulated pressure increase is negligible and this is supported by the measurements (Chadwick et al 2009). For the record, Sleipner has now injected 12 million tonnes of CO 2 at a rate of about 1 million tonnes per year.…”

Modelling large-scale carbon dioxide injection into the Bunter Sandstone in the UK Southern North Sea

“…In any case it naturally decreases during the injection period as the relative permeability to CO 2 increases (Chadwick et al, 2009). At the end of the injection period there is a rapid pressure fall-off near the injection point as the pressure equilibrates within the model as a whole and a longer term decline due to water leaving the system via the seabed outcrop and the low permeability caprock.…”