# C.2.1. Seismic Surveys

Seismic acquisitions will be needed during exploration and characterization phase. However, the number of kilometres that needs to be acquired depends greatly upon the global knowledge of the underground in the studied area (that is to say, the possibility to obtain data from previous underground exploration). Indeed, fewer acquisitions will generally be needed in heavily explored area than within area where limited exploration took place.

The models developed take into account the suitability of the area (detailed in Appendix A) where the project is developed. We supposed that due to a better geological knowledge, less data acquisitions is necessary in highly suitable area than in possible areas.

Similarly, there are fewer contingencies to drill in heavily explored Oil and Gas areas since geological context is already quite well characterized.

## C.2.1.1. 2D Seismic Surveys

2D seismic is needed to improve structural model definition. Depending on the area where the project is located, 2D seismic acquisitions might have been partially or totally performed over the storage complex (area of review).

In order to determine a probability distribution of the number of kilometres generally acquired during a 2D seismic survey, Geogreen used APPEA^{60} data base of Australian 2D seismic campaigns from 1993 to 2009. After appropriate data processing, the acquisitions length (in km) distribution is presented in Figure 70 below:

Source APPEA

According to Figure 14, the sedimentary basins in Australia (where the data come from) are ranked mainly as being highly suitable to suitable for CO_{2} storage. Geogreen decided to define the Australian available data as a basis for suitable area. From the historical distribution, an analysis allowed defining a model distribution for the length of seismic acquisitions in suitable area. A lognormal distribution with a mean of 147 (same as the historical one) and with 10th and 90th percentiles equalling 20 and 328 respectively seems to fit well the historical data as shown in Figure 71.

To finally represent actual 2D seismic acquisitions length in function of the “area suitability status”, the distribution mean is simply shifted between the different areas. In highly suitable areas, the distribution has been shifted by 25km below the “moderately explored” average. For the possible suitability status categories, the distribution has been shifted by 100km above the “suitable area” average. Figure 72 gives the main parameters of the four distributions as well as the shape of the distribution.

The 2D seismic acquisition cost has been calculated from recent 2D surveys costs in Europe. A normal distribution with the following properties has been chosen to model cost variation:

- 10th percentiles – corresponding to low range encountered: 11 000€/km
- Mean – corresponding to average cost encountered: 13 000€/km
- 90th percentiles – corresponding to high range encountered: 15 000€/km

These costs include equipment mobilization/demobilization. This hypothesis introduces a small distortion since it tends to underestimate the cost for small acquisitions while it slightly overestimates it for large ones. Cost factors have been introduced to take into account the regional differences (see Appendix F).

## C.2.1.2. 3D Seismic Survey

A 3D seismic survey will also be needed to fully characterize the structure of the storage complex (area of review). Geogreen used the same data base (APPEA data base) as for the 2D seismic surveys. The onshore 3D seismic acquisition size is given below for Australia between 2000 and 2009.

Source APPEA

One can see on this figure that the main part of the distribution is located below 125km2. The use of 3D seismic for CO_{2} storage site characterization makes it difficult to imagine that less than 100km2 (square of 10km*10km) are acquired. Indeed, this acquisition will be used as a baseline for storage site monitoring (on top of structural characterization needs). For the same reason, this acquisition is independent to the fact that the area is suitable or not.

Taking into account the fact that the plume might extend over few kilometres, a 100km2 3-D seismic acquisition is a minimum. In order to take into account this parameter, the original distribution has been shifted to place its 10th percentiles to 100km^{2}.

Figure 74 shows the probability density and gives the main properties of the chosen model for 3D seismic acquisition sizes.

Figure 75 shows the comparison between the model and Australian historical data (2000-2009) for 3D acquisition sizes onshore.

As for 2D seismic costs, 3D seismic costs have been calculated from recent surveys in Europe. A normal distribution with the following properties has been chosen to model cost variations:

- 10th percentiles – corresponding to low range encountered: 30 000€/km
- Mean – corresponding to average cost encountered: 40 000€/km
- 90th percentiles – corresponding to high range encountered: 50 000€/km

These costs include equipment mobilization/demobilization. As for 2D seismic acquisition, this hypothesis introduces a small distortion since it has a tendency to underestimate the cost for small acquisitions while it slightly overestimates it for large ones.