Directive 2009/31/EC of the European Parliament and of the CouncilShow full title

Step 3: Characterisation of the storage dynamic behaviour, sensitivity characterisation, risk assessment

The characterisations and assessment shall be based on dynamic modelling, comprising a variety of time-step simulations of CO₂ injection into the storage site using the three-dimensional static geological earth model(s) in the computerised storage complex simulator constructed under Step 2.

Step 3.1: Characterisation of the storage dynamic behaviour

At least the following factors shall be considered:

(a)

possible injection rates and CO₂ stream properties;

(b)

the efficacy of coupled process modelling (that is, the way various single effects in the simulator(s) interact);

(c)

reactive processes (that is, the way reactions of the injected CO₂ with in situ minerals feedback in the model);

(d)

the reservoir simulator used (multiple simulations may be required in order to validate certain findings);

(e)

short and long-term simulations (to establish CO₂ fate and behaviour over decades and millennia, including the rate of dissolution of CO₂ in water).

The dynamic modelling shall provide insight into:

(f)

pressure and temperature of the storage formation as a function of injection rate and accumulative injection amount over time;

(g)

areal and vertical extent of CO₂ vs time;

(h)

the nature of CO₂ flow in the reservoir, including phase behaviour;

(i)

CO₂ trapping mechanisms and rates (including spill points and lateral and vertical seals);

(j)

secondary containment systems in the overall storage complex;

(k)

storage capacity and pressure gradients in the storage site;

(l)

the risk of fracturing the storage formation(s) and caprock;

(m)

the risk of CO₂ entry into the caprock;

(n)

the risk of leakage from the storage site (for example, through abandoned or inadequately sealed wells);

(o)

the rate of migration (in open-ended reservoirs);

(p)

fracture sealing rates;

(q)

changes in formation(s) fluid chemistry and subsequent reactions (for example, pH change, mineral formation) and inclusion of reactive modelling to assess affects;

(r)

displacement of formation fluids;

(s)

increased seismicity and elevation at surface level.

Step 3.2: Sensitivity characterisation

Multiple simulations shall be undertaken to identify the sensitivity of the assessment to assumptions made about particular parameters. The simulations shall be based on altering parameters in the static geological earth model(s), and changing rate functions and assumptions in the dynamic modelling exercise. Any significant sensitivity shall be taken into account in the risk assessment.

Step 3.3: Risk assessment

The risk assessment shall comprise, inter alia, the following:

3.3.1. Hazard characterisation

Hazard characterisation shall be undertaken by characterising the potential for leakage from the storage complex, as established through dynamic modelling and security characterisation described above. This shall include consideration of, inter alia:

(a)

potential leakage pathways;

(b)

potential magnitude of leakage events for identified leakage pathways (flux rates);

(c)

critical parameters affecting potential leakage (for example maximum reservoir pressure, maximum injection rate, temperature, sensitivity to various assumptions in the static geological Earth model(s));

(d)

secondary effects of storage of CO₂, including displaced formation fluids and new substances created by the storing of CO₂;

(e)

any other factors which could pose a hazard to human health or the environment (for example physical structures associated with the project).

The hazard characterisation shall cover the full range of potential operating conditions to test the security of the storage complex.

3.3.2. Exposure assessment — based on the characteristics of the environment and the distribution and activities of the human population above the storage complex, and the potential behaviour and fate of leaking CO₂ from potential pathways identified under Step 3.3.1.

3.3.3. Effects assessment — based on the sensitivity of particular species, communities or habitats linked to potential leakage events identified under Step 3.3.1. Where relevant it shall include effects of exposure to elevated CO₂ concentrations in the biosphere (including soils, marine sediments and benthic waters (asphyxiation; hypercapnia) and reduced pH in those environments as a consequence of leaking CO₂). It shall also include an assessment of the effects of other substances that may be present in leaking CO₂ streams (either impurities present in the injection stream or new substances formed through storage of CO₂). These effects shall be considered at a range of temporal and spatial scales, and linked to a range of different magnitudes of leakage events.

3.3.4. Risk characterisation — this shall comprise an assessment of the safety and integrity of the site in the short and long term, including an assessment of the risk of leakage under the proposed conditions of use, and of the worst-case environment and health impacts. The risk characterisation shall be conducted based on the hazard, exposure and effects assessment. It shall include an assessment of the sources of uncertainty identified during the steps of characterisation and assessment of storage site and when feasible, a description of the possibilities to reduce uncertainty.