Time Coded Impulse Seismic Technique for Marine Reservoir Monitoring

Various methods have been used in order to generate the signal that is transmitted into the ground and provides mapping of a reservoir by means of seismic reflection. ?Air-gun? is the most commonly used seismic source. The principle of an ?Air-gun? is som ewhat similar to an explosion in the way that an high pressure gas bubble is released in to the water and the rapid expansion of this bubble generates a shock pulse. The use of ?Air-gun? has to main disadvantages: ?The deeper one wants to penetrate into t he ground with a seismic survey, the more powerful the airgun has to be, i.e. higher peak pressure in the surrounding water. However, a high peak pressure and especially the negative pressure caused by the air bubble when it collapses, is known to impact on marine life. ?An ?Air-gun? system is large and expensive due to the requirement for supply of high pressure air and thereby the need of large compressors. On land, seismic methods utilising a pulse type source in a more sophisticated manner have been developed and taken successfully into use. The principle of these may be loosely described as follows; instead of using a high impact these methods apply a series of moderate energy pulses according to a Time Coding scheme. Even though the signal to nois e ratio for the reflections from the moderate impacts are less than for a single high impact, the overall result is comparable after processing. Different methods for Time Coding are used (SIST and Mini-Sosie), but as a generic term we will call this met hod Time Coded Impulse Seismic Technique (TCIST). Unfortunately, TCIST is not compatible with the use of ?Air-gun?. However, a new type of seismic source called LACS (Low Frequency Acoustic Combustion Source) has the potential to be used together with T CIST. The objective of this project is two fold: ?Develop a Time Coded Impulse Seismic Technique (TCIST) for Marine Reservoir Monitoring ?Optimise and qualify the LACS concept for TCIST