What Have We Learned from Small-scale Injection Projects?

A review has been undertaken of small scale injection projects of less than 100,000 tonnes (t) of CO2 from around the world, with the objective of assisting countries or organisations wishing to embark on their first CO2 injection test, in a cost effective, time efficient and safe manner. The mean amount of CO2 injected per project was approximately 1,000 t; only 9 out of the 45 projects had injected more than 10,000 t. Costs varied greatly from less than $1 million to $100 million, with the mean total cost in the range of $10-20 million. Half of the projects were based on injection into sandstone reservoirs, although a significant number (28%) involved injection into coals. The source of the CO2 was quite variable; the majority of the CO2 was transported by truck to the site. The depth of injection ranged from approximately 300m to over 4,000m but averaged around 1,200m. The time taken from making the preliminary decision to undertake a project to injection of the first molecule of CO2 was variable but averaged approximately three years. Generally, small scale projects are opportunistic, typically initiated by research organisations; they rely on an alliance with industrial partners for operational expertise and access to suitable locations. In most small scale projects, pre-drill reservoir characterisation consists of the integration of pre-existing geological and hydrological data. Saline reservoir sites are usually data deficient. Reservoir simulations are performed routinely, using a variety of codes, to assess CO2 injection tests and provide valuable information for system design, permitting, and monitoring. The simulations are also useful for providing a systematic framework for integrating site characterisation data, visualisation of model results provide a valuable communication tool. Documentation of storage risk assessment by projects was limited. Monitoring programs for the test injection projects were opportunistic to some degree, utilising existing data to help in establishing a baseline and commonly utilising existing wells for down-hole observations and monitoring-based sampling. Nearly all projects undertook pressure and temperature monitoring as a standard. These small scale projects offer a cost effective way of demonstrating storage technologies in CCS, assisting the progression towards large scale injections.