Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/152

The Resources of the Niger Delta: Minerals

*Petroleum Jelly (Vaseline) - octadecane
 * Paraffin Wax - pentacosane
 * Bitumen (Tar)

Also, being water resistant, hydrocarbons, mainly as ethylene (CH₃ molecules) are the basis of the plastics industry. For instance, polythene is simply a very long chain of ethylene molecules.

14.3.3 SEISMIC PROSPECTING FOR OIL

When oil companies decide that the basic geological conditions are right (as Shell did in the North-western Niger Delta in 1937) they undertake Seismic surveying in order to identify the composition of the rock strata, and the existence of folds and faults, as potential oil traps.

Seismic prospecting enables energy waves (rather like the shock from the shot of a gun) to be directed into the ground. The return times of the vibration, like an echo, identifies the nature of the rock and its configuration. The vibration is recorded on a microphone called a Geophone.

Thus onshore in the Niger Delta, Seismic prospecting involves laying cables and geophones along previously surveyed receiver lines that are linked by source lines. These lines may be several tens to hundreds of metres apart. The geophones pick up and relay along the cables several shocks set up by Seismogelite explosives shots. There are a number of shots on each source line and each shot consists of in excess of ten kilograms of explosive set in bore holes that are from three to tens of metres deep.

It should be noted that the technology of seismic surveying is a rapidly developing one. For instance, since the late 1980s, oil companies have increasingly used 3Dimensioonal seismic survey instead of the 2-Dimensional processes previously used.

The seismic lines have only to be clear enough to allow sight-lines, safe access, the drilling of the shot-holes (usually by hand with steel tubes that take out a plug of soil) and the laying of the cable. Thus a line that is no more than a metre in width and often less is sufficient, and does not have to be absolutely clear.

Offshore, floating Hydrophones are either hung on cables that are laid on the seabed or towed behind a ship. Energy waves are produced by a compressed air shot, the return vibration being picked up by the hydrophones, indicating the geological conditions.

14.3.4 DRILLING FOR OIL – THE EXPLORATION WELL

If seismic prospecting suggests that there may be commercially exploitable accumulations of hydrocarbons, an exploration well has to be drilled. 150