Abstract
Making an accurate estimate of the CO2 storage capacity before the commencement of a carbon capture and storage (CCS) project is crucial to the project design and feasibility investigation. We present herein a numerical modelling study on the CO2 storage capacity in depleted gas reservoirs. First, we show a simple volumetric equation that gives the CO2 storage capacity in a depleted gas reservoir, which considers the same volume of CH4 at reservoir pressure and temperature conditions produced from the reservoir. Next, the validity and the limitations of this equation are investigated using a numerical reservoir simulation with the various reservoir characteristics of reservoir heterogeneity, aquifer water encroachment, and rock compaction and its reversibility. Regardless of the reservoir heterogeneity, if a reservoir is subjected to a weak or moderate aquifer support, the volumetric equation provides an estimate of the CO2 storage capacity as structurally trapped gas within 1% of that estimated from numerical simulations. The most significant factor influencing the CO2 storage capacity is the reversibility of rock compaction, rather than the degree of rock compaction. If reservoir rocks have a strong hysteresis in their compaction and expansion behaviour, the material balance equation will overestimate the amount of structural CO2 trapping. All the simulation results show a fairly consistent amount of trapped CO2 as a dissolved component in water, which is 15∼17% of the structurally trapped CO2. Overall, our study presents the validity and the limitation of the simple material balance equation for estimating the CO2 storage capacity, which helps with designing a CCS project at the early stage.
Highlights
The development of natural resources has recently seen an increasing demand for decarbonization, which reduces or eliminates carbon dioxide (CO2 ) from energy sources.Having a good affinity for the development of natural resources, CO2 capture and storage (CCS) in underground geological formations is one of the most promising ways to decarbonaize because, it uses technologies developed for and applied by the natural resources industry.Three types of geological formation are suitable for carbon capture and storage (CCS): deep saline formations, depleted oil and gas reservoirs, and unminable coal beds [1]
We studied the influence of reservoir characteristics on CO2 storage capacity
We have studied the validity and limitations of the simple material balance equation that estimates CO2 storage capacity under various reservoir characteristics
Summary
Three types of geological formation are suitable for CCS: deep saline formations, depleted oil and gas reservoirs, and unminable coal beds [1]. The CO2 injected into these geological formations is securely trapped via the following four major mechanisms: structural (hydrostratigraphic), residual (capillary), solubility, and mineral trapping [2,3]. The first two mechanisms are classified as physical trapping, whereas the latter two are classified as geochemical trapping [3]. The significance of each mechanism depends on the type of geological formation and its changes over time [4]. Physical trapping occurs over a time period of 10∼100 years, while geochemical trapping takes effect over a longer time period of >100 years [1,4]
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