The underbalanced drilling campaign undertaken by Shell U.K. Exploration and Production (Shell Expro) offshore in the Southern North Sea has been on the cutting edge of UBD technology since its inception in 1997. Electromagnetic (EM) telemetry systems were incapable of performing in the Southern North Sea due to the depth and nature of the formations. However, recent enhancements to the technology have greatly expanded the scope of EM telemetry. The use of this technology has potential for expanding the scope of underbalanced operations possible in the Southern North Sea.

A fundamental advantage of the EM telemetry system is the capability to transmit data independently of wellbore hydraulics. For example, down-hole pressure data can be transmitted to surface during pressure buildup tests and flow tests. Data can also be transmitted during trips, during connections, with pumps on or off, etc. The transmission of data is unaffected by loss of drilling fluid returns, the use of air, air-mist, foam or other multi-phase drilling fluid mediums generally associated with underbalanced drilling practices. The down-hole instrumentation can also be interrogated or reprogrammed at any time by direct communications protocol, which is completely independent of the rig or drilling activity.

A new, innovative twist to enhance the use of EM telemetry involves the use of insulated casing to reduce signal attenuation and further expand the application of the technology where it has been previously out of reach. This paper discusses rationale for the use of EM telemetry in the Southern North Sea basin and the results of a recent successful field trial of the technology.

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