WOPyrIGM 19% OFFSHORE TECHNOLOGY CONFERENCE nw$ papaf was pmpafad w pfesenlabm al ha Offshore Techc@Y Confererca kkl m HwstcfI, Texas, 6-9 May 19% TM papa was salauad for presantalm by an OTC Prcgmm Commit-folknwng rav!ew c+ mlcwnattof ontaned m an abstracl submrtted by the autkf(s) Ccmtents of the P&PC as wwanmd me nol been revwed by the OIWWe T@WWWY @ WE S* tO W*M by U-m author(s) The materkl as presmtad tis nd recassaniy rafkd my POsrbcn ot ttw 0iT5P0re TechmMgy Ccdarenm c+ m o%cm PanmssIwI to cmpy @ feemchd to an Astrad d nd mcfe man 303 words lllustfat~s may cot b-a copwd TM *SW sti cmiam CZXMPKUMIS aduwu-ent of~re and by whom W p-ape IS pfesanted AbstractAn Operator wanted to drill one or two additional delineation wells in 3,200 feet of water at Green Canyon 254. Because there were no MODUs capable of this water depth available to fit the Operator's schedule, the Operator elected to increase the water depth capability of an existing Ocean Victory Class MODU. The modification consisted of increasing the number of riser tensioners, installing longer BOP control hoses, guidelines and television cable, and using pre-laid moorings to enhance the mooring capability. This paper describes the pre-laid mooring procedures. Each prelaid mooring leg consisted of one 10 metric ton anchor, 1,000 feet of ground wire, 2,500 feet of dip-zone chain and 3,@30 feet of catenary wire. Prior to the arrival of the MODU, each leg also had 3,500 feet of 2 inch riser wire and a surface buoy. The moorings were laid using a single 6,140 brake-horsepower, anchor-handling, towing, supply vessel with a large A-frame at the stern. This same vessel was used to connect the chain from the MODU to the pre-laid moorings.Using pre-laid moorings to extend water depth capability gives the Operator greater flexibility in selecting MODU'S for deep water drilling and can solve scheduling problems. The use of an A-frame and a ground wire adjacent to the anchor allowed use of a smaller vessel than would otherwise be required. The MODU can be moved to nearby deepwater locations without fully recovering the pre-laid moorings.This operation demonstrates that the water depth capability of an all chain MODU, normally capable of 2,000 feet of water, can lx. extended to over 3,000 feet by using wire inserts and pre-laid moorings.

A large~ independent Operator drilled three discovery wells and installed a 24 well template at Garden Banks 388. Two 12 inch pipelines were laid to the location. The Operator also designed a Floating Production Facility (FPF) which consisted of an Ocean Victory class semi-submersible moored to a permanent~ 12 leg, catenary mooring system. The FPF conversion, due for completion in January, 1995, fell behind schedule. The Operator desired to stay as close to schedule as possible by temporarily substituting a semisubmersible drilling unit to complete the discovery wells and tieing them back to the 24 well template.Each pre-laid mooring leg consisted of a 25 metric ton anchor, a spiral-strand ground wire, a dip-zone chain, a spiral-strand catenary wire, and a submersible buoy assembly. First, laying additional mooring legs between the twelve pre .. laid legs was considered. This was ruled out because of the danger of tangling mooting legs and damaging the relatively fragile spiral-strand construction wire ropes in the pre-laid mooring legs. Second, mooring a semisubmersible MODU to the existing pte-laid mooring legs was evaluated and selected. The MODU Ocean Voyager, similar to the FPF prior to conversion, was used. One advantage of using the pre-laid moorings and a similar unit was that the hook-up and disconnect procedures could be tested prior to the arrival of the FPF. These procedures were refined considerably. 457The initial hook-up was completed in December, 1994. Two similar 6140 BHP anchor-handling, towing, supply (AHTS) vessels were rigged with an additional two drum winch and a shallow-depth, diving spread to connect the legs. Four of the pre-laid mooring legs were left idle. Despite some difficulties, the hook-up was completed in nine and one-half days which included four days of weather delay. Disconnecting the moorings was completed in May, 1995. A single AHTS vessel was rigged with an additional two drum winch and a large A-frame over the stern. Because of the revised procedures, considerably less diving was required. Using only one AHTS vessel further reduced costs and required only seven days, including two days of weather delay, to disconnect the moorings.Using the temporary semi-submersible MODU allowed the Operator t<> complete and test two wells and connect the wells to the template with jumpers. Thus, although the FPF arrived five months late, getting production on stream should be only two months behind schedule.Temporary Need for MODU at FPF Site Three discovery wells were drilled at Garden Banks Block 388 during 1989. A semi-submersible MODU, the Penrod 76, was used to drill these wells. As the wells were productive, the Operator set a large 24 well template at the site using the Derrick Barge (DB) 50. Two 12 inch pipelines, each 47 miles long, were laid from the site to a production platform at Eugene Island Block 315 using the DB 22.