Environmental Impact of the Oil Industry
15.5 SPECIFIC IMPACTS
15.5.1 SEISMIC PROSPECTING ACTIVITY
Interfaces of seismic activities and the environment (from an SPDC fact book of 1993):
| Seismic Activity | Interface | Potential Environmental Impact |
| Line cutting | Disturbance | Cleared vegetation Expelled fauna Affected ecosystem |
| Source operation (i.e. preparing for the soundings) | Soil Water |
Soil structure/erosion Disturbance of sea-mammals (offshore) |
| Recording (i.e. the soundings) | Disturbance Soil |
Soil structure/erosion Soil pollution by explosives |
| Presence Crew/accommodation |
Disturbance Water |
Impact communities Expelled fauna Undegradable waste pits in the field |
SPDC Eastern Division Seismic Activity from (from an SPDC fact book of 1993):
| Parameter | 2D | 3D |
| Area covered onshore | Entire Eastern Division | 5,000 km² |
| Length seismic lines | 60,000 km | 31,380 km |
| Length seismic lines in mangroves | in 39,000 km (=39 km²) | 17,400 km (=17.4 km²) |
| Area covered offshore | — | 3,100 km² |
There are five main specific impacts of seismic surveying.
Seismic Prospecting - Extent
As shown in the table above, the lines cleared for seismic surveying cover great distances, often giving access to otherwise relatively inaccessible areas.
Seismic Prospecting - Explosions
Onshore, these can set up shock waves strong enough to damage buildings and certainly have a compacting effect upon soil structure. Also, if the boreholes are not back-filled with the same material that came out of them and compacted to a natural state, localised drainage and or water-logging problems can arise.
Seismic Prospecting - Damage to Vegetation
Although seismic prospecting is only a temporary exercise and much of the damaged vegetation recovers, some economic tree crops may be irrecoverably damaged or lost, while mangrove forests seem to be especially damaged with survey lines remaining
177
