Oilfield Review April 1993


New Lease on Life for the 704

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Rig

The world's aging semisubmersible fleet poses a dilemma for drilling contractors. Most semis were built in the mid-1970s and are nearing the end of their prescribed 20-year life span. Replacement cost is estimated at up to $200 million per unit, too expensive in today's business climate. An alternative solution is to renew. We follow how Sedco Forex engineers recently extended the life of the 704 semisubmersible another 20 years, and at a stroke streamlined the annual inspection process so that this semi could be used as a long-term drilling tender in the North Sea.


Drilling and Testing Hot, High-Pressure Wells

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HotHeight Pressure Well

Meticulous planning and careful control of operations are needed to safely drill and test high-temperature, high-pressure (HTHP) wells. This article examines the techniques employed in the Central Graben in the UK sector of the North Sea where about 50 HTHP wells have been drilled. This comprehensive review covers three main areas of activity: drilling safety, casing and cementation, and testing. We also detail how this North Sea experience has been used to help plan a jackup rig modification for hot, high-pressure drilling off Brunei.


The Quest for Borehole Stability in the Cusiana Field, Colombia

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Borehole Stability

The newly discovered Cusiana field in Colombia may be one 50 largest oil fields in the world. But the rewards are providing hard to get at. Compressed by the southeast thrust of the Pacific and Caribbean plates, the field is abnormally stressed with horizontal stress exceeding vertical stress. This causes severe borehole insability and makes wells tough to drill—10% of well costs are spent dealing with mechanical borehole problems. We follow efforts to understand the field-s stress and see how it may affect field development.


Measurements at the Bit: A New Generation of MWD Tools

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MWD Tools

With sensors at least 50 feet behind the bit, conventional MWD measurements are retrospective rather than prospective—they look back where the bit has been, rather than foreward to where it's going. Recently, technologic innovation has relocated sensors to the bit itself, providing geologist and drillers with immediate information on how to maximize drilling efficiency and where to steer the well.


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