MWD North Sea Field Use, Aug. 1978-Feb. 1979 (With 1982 Update) (includes associated papers 11865 and 11929 )
Authors: Griffin W.H. , Keith F.A.J. 
Published: December 2007

1982 Update
The use of the Teleco Oilfield Services Ltd.measurement-while-drilling(MWD) system has grownfivefold in the North Sea since 1979, when this paper was written. As of Sept. 1982. our service has beenprovided to more than 400 wells drilled by 17 operatorsfrom some 60 rigs in the U.K., Norwegian, Danish, andDutch sectors.The operational procedures, case examples, and thelike are still accurate as presented in the paper in 1979, but, of course, a wider range of drilling conditions hasbeen experienced since. For instance, surveys have beentransmitted from measured depths greater than 16,800 ft, inclinations higher than 72 degrees, and at flow rates exceeding 1,000 gal/min.As we have gained more experience and understanding of the North Sea drilling environment, the reliability ofour system has nearly doubled. On the average, only onetool failure per 250 circulating hours is experienced inNorth Sea operations now.From the operators'standpoint, the direct time savingsresulting from MWD have materialized as expected.Second-tier benefits also have been revealed andquantified.The years between 1979 and 1982 mark a turning pointin directional surveying. During this period, MWDmade the transition from being simply a new way ofsurveying to becoming the standard way of surveying inthe North Sea. Our system now is being used on nearlyevery North Sea platform where directional wells aredrilled.The remainder of the paper appears as originally presented.

Introduction
Teleco Oilfield Services Ltd. was formed in May 1978as a subsidiary of Teleco Oilfield Services Inc., a jointventure of Raymond Industries Inc., and Soc. Natl. ElfAquitaine. The firm's primary function is to provide adirectional drilling MWD service to customers in theNorth Sea. We began commercial service in the NorthSea in Aug. 1978 and in the Gulf of Mexico in Sept.1978.

The MWD System
This system uses mud-pulse telemetry to transmit data;hence, there is no wireline. Mud-pulse telemetry is amethod of transmitting information from the bottom of aborehole to the surface by using a downhole valve to induce coded pressure pulses in the mud.The MWD system consists of a downhole assemblycontaining a sensor and transmitter mounted in anonmagnetic drill collar (Fig. 1) and surface displayequipment (Fig. 2) located on the drilling platform. The collaris a self-contained unit that remains in the drillstring nearthe drill bit. The sensor incorporates a magnetometer tomeasure direction and accelerometers to measureinclination and tool facing. Electrical power for thedownhole assembly is produced by a mud-driven turbinein the transmitter. After taking a survey, the sensor tellsthe transmitter to encode the directional data into a seriesof positive pressure pulses by periodically moving avalve that partially restricts mud flow. The increase inpressure propagates upward inside the drillstring through the mud to the surface, where it is detected by a pressuretransducer in the standpipe. The presence or absence of apulse in a given time interval forms a binary numbercode that is decoded into a directional angle and displayed on the surface equipment.
JPT
P. 2888^