RIASSUNTO
Summary
Aluminum drillpipe was used to drill the first five directional wells from aNorth Sea platform. A comparison with steel drillpipe showed that theoperational problems of using the aluminum drillpipe outweighed the benefits inthe directional wells drilled. Therefore, steel drillpipe was specified forsubsequent, similar platform wells.
Introduction
In 1971, Mobil North Sea Ltd. became the operator of Block 9/13 in the U.K.sector of the North Sea. The block is located 215 miles northeast of Aberdeen.The Beryl field was discovered in Block 9/13 in 1972 in water depths from 350to 400 ft. The Beryl A production platform, a concrete gravity structureequipped with production platform, a concrete gravity structure equipped withtwo drilling rigs, was installed in 1975, and oil production began in 1976. TheBeryl B production platform, a steel-jacket structure equipped with a singledrilling rig, was installed over a drilling template in 1983, and oilproduction began in 1984. Six wells had been predrilled through the 21-slotBeryl B drilling template, so the first job of the platform drilling rig was totie back and complete these wells. Aluminum drillpipe and a top drive wereincorporated into the Beryl B drilling rig as a result of recommendations froma jointindustry extended-reach-drilling (ERD) project and the local drillingmanager's experience with using aluminum drillpipe in remote land operations.This paper presents information on aluminum drillpipe selection, required rigmodifications, establishing operating limits, operational benefits andproblems, and ways to extend service life. A comparison with steel drillpipeprovides a frame of reference, and the results from a drillstring simulatorquantify the surface torque reduction achieved in an example Beryl B well.Aluminum drillpipe was used during a series of casing-repair workovers on thepredrilled wells and to drill five directional wells from mid-May 1984 tomid-Nov. 1986 (see Fig. 1). The pipe was then taken out of service for a fullinspection and was found to require extensive tool-joint rebuilding that couldnot be done in the U.K. Pending the decision to drill any long-reach wells thatrequired the special attributes of aluminum drillpipe, we stored the pipe andused a string of steel drillpipe for continuing operations pipe and used astring of steel drillpipe for continuing operations on Beryl B. (A steeldrillstring was available at no additional cost because only one rig on theBeryl A platform was being used for drilling operations.)
Selection and Preparation of Aluminum Drillpipe
Selection. The 21,000 ft of 5-in. aluminum drillpipe with extra-long 51/2-in. full-hole (FH) tool joints purchased for use on the Beryl B rig waschosen because it was comparable to the 5-in., Grade G steel drillpipe used onthe Beryl A platform rigs. As the buoyed-weight and available-pull data inTable 1 show, the pull capacity of aluminum drillpipe exceeds that of Grade Edrillpipe and compares very favorably with that of Grade G drillpipe. Note thatthe buoyed weights in 10-lbm/gal fluid and 90% of the new pipe tensile ratingswere used to calculate the available pull values at the vertical depths listed.pull values at the vertical depths listed. The extra-long tooljoints werespecified to permit two thread recuts because replacing individual steeltooljoints was considered to be a special repair best left to the pipemanufacturers. Hard or soft banding was considered but was not thoughtnecessary because the lower buoyed weight of pipe produced lower wellborecontact forces than steel pipe. Fig. 2 shows the aluminum drillpipe purchasedfor the Beryl B rig. purchased for the Beryl B rig. Preparation. Only minorequipment changes were required to use Preparation. Only minor equipmentchanges were required to use aluminum drillpipe on the Beryl B platform. First,we used 5- to 7-in. variable-bore rams to accommodate the nonuniform OD of thealuminum-drillpipe tube section. (This also enabled us to close on thetooljoint OD without damaging the rams.) Second, we used special tapereddrillpipe slips with blunted slip elements to match the taper of thealuminum-drillpipe tube. Third, the rig-floor automated make-and-breakequipment was modified to accept the extralong tooljoints. Fourth, crossoverswere provided on the rig floor for circulating swages and stabbing valves tomatch the 5 1/2-in. FH connections. One important procedural change wasnecessitated by the wellknown sparking hazard associated with a steel objectstriking a rusty surface smeared with aluminum. Rusty metal is one requirementfor the sparking hazard, so a regular inspection program was introduced to backup the drilling crew's routine wire brushing and painting. Also, wood cappingwas added to the pipe storage racks. painting. Also, wood capping was added tothe pipe storage racks. No U.K. offshore legislation regarding the control ofthe sparking hazard associated with the use of aluminum drillpipe existed;however, we discussed control procedures with the certifying authority.
Establishment of Operating Parameters
Aluminum drillpipe is not fully covered in API specifications or recommendedpractices, so the manufacturer must be relied on for specific operatingprocedures and limits. Engineering data and reports on limited operationalexperience with 5-in. aluminum drillpipe have been published, but the drillpipeused on the Beryl B rig had nonstandard, extra-long tooljoints that gave it anumber of unique parameters. Table 2 lists the material properties and theparameters obtained from weighing joints and from detailed calculations basedon the dimensions shown in Fig. 2. Note that unlike those of steel drillpipe,the lengths of individual aluminum-drillpipe joints are the same for everyjoint supplied. Thus, the calculated average weight per unit length will notvary from joint to joint.