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Abstract

A central challenge of both scientific and regulatory interest is how to ensure carbon dioxide (CO₂) is securely contained within a storage site. The fate of CO₂ in the subsurface describes the range of processes that progressively trap the CO₂. Pure phase CO₂ can be trapped within the pore space as (i) residual saturation, and (ii) capillary trapping where the buoyancy forces exerted by a vertical column of CO₂ are not sufficient to overcome the capillary forces either within the reservouir rock or to overcome the caprock. Aside from the physical trapping of free CO₂, it can be trapped as an aqueous phase. An alternative to injection of pure phase CO₂ is to inject CO₂ saturated waters which are denser than the unsaturated formation waters thus eliminating the problems associated with buoyancy. Further, in order for the CO₂ to be locked away geochemically as mineral trapping, it must first enter an aqueous phase in order for it to be reactive.

Here we explore engineering technologies for enhancing the dissolution of CO₂ in formation fluids to mitigate leakage and minimise the risk of CO₂ escaping from the storage site. Conceptual process engineering and design of CO₂ injection systems downstream were performed with primary aim of rendering integrated injection strategies suitable for use in enhancing permanent storage of CO₂ in deep geological formations.

The results of the application indicate that the strategies speed up CO₂ dissolution and immobilisation as the period of time needed to achieve immobilisation in the subsurface formation is enhanced by the surface processes engineering. The immobilised CO₂ will remain indefinitely in the storage zone even if the integrity of the caprock is not intact.

These innovative engineering technologies provide leakage prevention opportunities which are fundamental to addressing long-term risk management and monitoring issues for CO₂ storage sites.

Introduction

Carbon capture and storage (CCS) is capable of reducing atmospheric emissions of greenhouse gases from coal or gas fired power plants.  The technologies for capturing, transporting, and injecting carbon dioxide (CO₂)  from industrial facilities draw upon a large body of existing research and field experience in the energy industry which are generally well understood [1, 2]. Moreover, there are a number of on-going researches and demonstration efforts to improve and refine these existing technologies to be more suitable for large-scale CCS implementation (for example; Sleipner field [3] and Weyburn [4]). Injecting CO₂ into an underground formation is literally the reverse of producing oil or water from a confined aquifer. Virtually all production facilities use separator as first vessel for converting the reserviour fluids to a state where they can be safely delivered to the market, likewise CCS requires surface processes engineering technologies for treating CO₂ to a state where it can be suitable to enhance permanent storage of CO₂ in deep geological formations. Hence, special design considerations need to be implemented when constructing facilities for downstream processing and injecting CO₂ into underground formations.