Electro-Magnetic or EM Techniques and Surveys have been around for decades now and most explorationist's will probably have had some limited exposure to one or more of them. Such EM techniques include land MT, audio MT, marine MT and now Controlled Source EM or CSEM for short. EM methods help the explorationist by measuring the flow of electrical energy passing through the earth which allows us to identify conductor and resistor rocks. MT and MMT have been successful commercial exploration tools for some time now and are very good for answering regional broad brush geological questions. They work by measuring the passive or naturally occurring energy in the earth, and are very good in areas where seismic fails or is ambiguous ... areas such as sub-salt, sub-volcanics sub-carbonates, i.e. poor seismic regions. Electro-Magnetic land MT surveys have taken place in a few areas of onshore Indonesia and the greater Far East island region in the past 20-30 years with varying degrees of results and success. Such areas are usually over-thrust and carbonate regimes where seismic data is poor and EM can work well. Marine Magneto-Telluric methods (MMT) were developed in the early 1990's and made commercial by mid 1995 and have been successfully used in difficult seismic areas around the world since then. To our knowledge, no MMT surveys have yet been carried out around Indonesia, but the method is very applicable in difficult seismic areas such as sub thrust, sub carbonate and sun volcanic zones which are found in Indonesia. Both these methods of MT and MMT are what we term passive methods in that we use the naturally occurring electrical energy in the earth as the input source signal. However now a new EM method is available and has been generating huge interest around the world. This new method is called Controlled Source Electro-Magnetics or CSEM and has been developed over the last 5 years. This new deepwater offshore technique of CSEM is rather different; for although it uses similar receiver technology to the passive MMT method, it combines them with an active electrical dipole EM source. This gives CSEM the ability to image much thinner resistors down to some 10's of meters rather than the 100's of meters of passive EM. Thus CSEM offers an entirely new set of applications for EM. With appropriate offset information the method is now being used to predict hydrocarbon fluid content ahead of the drill bit. To date only one CSEM survey has been done in the Indonesia - Far East region and that was in 2004, although there are today many companies operating in the region who are looking to acquire new CSEM surveys in the near future. The geology of the region includes both good and more challenging type of targets for CSEM. It is believed that the USE of CSEM techniques may help to encourage new exploration in some of the more difficult frontier exploration plays around Indonesia.
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