CONTROLLED-SOURCE ELECTROMAGNETIC (CSEM): A GAME CHANGING TECHNOLOGY FOR FRONTIER DEEPWATER EXPLORATION? A USER'S PERSPECTIVE

摘要

Marine Controlled-Source Electromagnetic (CSEM) technology is a non-invasive geophysical method using an active source to probe the subsurface for thin, high resistive bodies. It employs a vessel-towed Horizontal Electric Dipole (HED) source over an array of seabed receivers which record electric fields in inline and broadside geometry. The CSEM measurement is sensitive to resistivity contrasts, and therefore can potentially differentiate between hydrocarbon saturated reservoirs (highly resistive) and the surrounding conductive sediments, given the right condition.One of the more recent applications of CSEM in the offshore Sabah area is to distinguish "fizz" gas from commercially saturated reservoirs, where both situations may create an AVO anomaly. A case study will be demonstrated where one prospect in a frontier deepwater area, that lacks of well control, is identified and derisked by utilising a combined AVO-CSEM interpretation.In other areas, where pre-acquisition modelling suggests that the CSEM technology is feasible, it nevertheless fails to deliver expected responses due to a high noise floor. Several other situations where CSEM is considered unsuccessful will be described, e.g. as a result of rugose bathymetry, water depth less than 600m, limited target size and shallow highly resistive anomalies such as hydrates.Having identified the CSEM limitation and its applications, it is postulated here that the combined AVO-CSEM technique is a compelling prospect qualifier in the Sabah deepwater, hence CSEM is a potential game changing application, particularly when utilised in combination with other seismic-based interpretation techniques. Some hurdles stillremain, given that this technology is still in its infancy. However, future development in the acquisition techniques and advancements in equipment, i.e. source and receiver capabilities, coupled with processing improvements such as 3D inversion, may overcome such obstacles and further strengthen this technology for prospect derisking in the frontier deepwater exploration.