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A detailed test program was performed with an eccentric tool at the Baker Hughes Experimental Test Area (BETA) field research facility to evaluate the feasibility of its use in an Expandable Tubular Technology application in the North Sea. The testing used a 9–7/8" Drill Out Steerable Ream While Drilling (DOSRWD) tool in conjunction with 6–1/2" pilot bits (both PDC and roller cone). Motor bent housing settings included 1.0°, 1.5°, 1.75° and 2.0° bends to evaluate directional and stability response. Surface speeds were varied from 0, 35, 50 and 75 rpm at each motor housing setting. Caliper logs including four and six-arm and ultrasonic borehole imaging (UBI) tools were used to characterize the borehole under all conditions. The analysis included directional tendencies, down hole vibration monitoring and borehole diameter, quality and degradation over time. The test results show the 9–7/8" DOSRWD system is capable of providing the high quality wellbore required for expandable tubular technology, ensuring the casing can be run, expanded and isolated across the formation. Introduction Expandable tubular technology has the potential to significantly reduce well construction costs. Conventional well construction results in telescoping of the well size from the wellhead down to the reservoir. Apart from resulting in large expensive surface casing, wellheads, trees and operating equipment, the method can result in an unworkable small hole size at the required depth. This could then lead to compromises in well operability or in worst case failure to reach the final objective. Expandable tubulars can help solve difficult drilling challenges posed by high-pressure zones, deepwater environments and troublesome sub-salt plays.1,2,3,4,5 Its innovative characteristics allow operators to explore in remote geologic regions and exploit reserves once considered unprofitable if drilled with conventional technology. Instead of using progressively smaller diameter pipe as drilling progresses deeper, Expandable Tubular Technology allows tubular diameters to be expanded with specially designed "pigs," or mandrels. This reduces well tapering while preserving borehole size. Expandable technology can also extend the profitable life of mature fields by internally cladding existing wellbores to isolate troublesome zones. This developing technology has created a need for improved understanding of the directional tendencies of eccentric drilling tools run on steerable assemblies and the wellbore geometry and quality that can be achieved with these tools. Consistent wellbore diameter is of particular concern for expandable tubulars. If the wellbore diameter is too small, expansion of the pipe with a fixed diameter cone might not proceed properly across sections of firm formation. Worse yet, the expansion cone could become stuck requiring remediation or sidetrack of the well. A wellbore that is too large could affect the sealing effectiveness depending on the sealing system used. For example, a closer diameter tolerance would be required if the seal mechanism is an integral part of the casing (elastomer bonded to the outside of the casing).

This paper was prepared for presentation at the 1999 Offshore Europe Conference held in Aberdeen, Scotland, 7–9 September 1999.

Through bit logging is a method for data acquisition using the drill string and bit as a conduit to the well bore. Two case studies are presented demonstrating the unique capabilities of this technology to obtain data in difficult and troublesome well situations. Both cases were recent (early 2004) wells, offshore North Sea. Case study 1 concerns an exploration well with a large open salt interval open above the reservoir. Conventional logging tools could not pass the squeezing salt interval, and TBL was used to get past the troublesome interval and successfully obtain quad combo and pressure data. Subsequently, the cement stinger could not pass the same interval, and the TBL bit was again used, this time to cement through. Case study 2 describes a well drilled into a nearby block, suspected of being depleted. After loosing the BHA, the operator wanted to reduce the risk of getting stuck with an RFT and decided to use TBL to successfully obtain wireline pressure data in the subsequent side track. Recent developments include a new type of Side Entry Sub System to enable easy surface deployment as well as providing a rapid easy fishing method in case the logging tools were to get stuck during TBL operations. Compatibility with rotary steering and MWD is under development, delivering the concept of ‘Through Bore Drilling’, the ultimate low cost drilling system. This will allow directional drilling in combination with open hole logging and other operations through the bit, in a single trip. Conclusion: TBL opens up new low cost/low risk options for data acquisition (and other through bore operations) during well construction. It gives both drilling and petroleum engineers new and low cost options to choose from to optimise well construction and data acquisition. TBL is a first significant step on the way to Through Bore Drilling and has already proven its versatility in a number of ‘difficult well’ cases. Introduction Data acquisition in oil and gas wells has evolved over the last century since the Schlumberger brothers performed their first well bore profiling in 1927. Wireline logging is now fully mature, and logging-while-drilling (LWD) is being developed rapidly, giving the end user options to perform data acquisition either during the drilling phase, post drilling in the open hole, or subsequently in cased hole. All options have advantages and disadvantages, and a balance needs to be struck between cost, quality, risk and timing of data acquisition. As a major operator, Shell has from time to time experienced difficulties obtaining data with existing methods, and was motivated to seek alternatives. Through Bit Logging (TBL) has been developed over the last few years by Shell and Reeves Logging Services (now part of Precision Energy Services) together with other industry partners, as a cost-effective and operationally efficient alternative to standard open hole wireline logging and LWD. In the new system the logging tools are conveyed via the drill string and pass into open hole through a specially designed bit, with formation evaluation data being acquired with either wireline or memory tools; in the latter case while tripping drill pipe out of the well, thus improving rig efficiency. Acquiring log data with through bit logging - how does it work? The logging tools are lowered down the drill string and pass through the bit into the open hole (figure 1) below. The TBL bit is a conventional PDC design modified with a removable central section (figure 2) leaving a 2.5" passage way.

Application of multi-lateral well engineering has been successfully applied as an emerging technology in the Northern North Sea to drain more marginal reservoirs which would otherwise be uneconomic. Calibration of the technique to local conditions is vital and the success in the North Sea offers tremendous follow-on opportunities for global applications. Following a successful onshore trial, Shell Expro's Northern Business Unit and their lead well engineering contractor, KCA Drilling Ltd, drilled and completed TA-14, a cased hole multi-lateral. This consisted of an appraisal and subsequent abandonment of the Triassic formation, followed by the drilling of two geosteered horizontal laterals into the shallower Brent reservoir. Techniques developed on TA-14 were then employed on an existing well. TA-19, to suspend the mainbore, side-track and recomplete as a dual lateral. Re-entry exists into the horizontal lateral with continued production available from the mother bore. Recently, TA-17 has been completed as a dual lateral horizontal Triassic oil producer with selective production from, and re-entry capabilities into both cased hole laterals. One lateral developed Triassic reserves proven by TA-14 while the other appraised the neighbouring block. A steep learning curve has been experienced throughout the construction of multi-lateral junctions. This includes the milling and fishing process, management of debris and equipment design. Further well engineering strategies for cementing, clean up, perforating and completions have been developed. Benefits of the multi-lateral technique are pervasive. Savings on TA-14 type wells can be achieved by applying the technique in a combination of variable and low quality reservoirs in one single well. Slot constraints can be alleviated using the TA-19 technique by side-tracking existing producers at an earlier stage. This strongly accelerates production whilst safeguarding the often underestimated tail production from the mother borehole. By using the TA-17 technique, two objectives can be met from one borehole, which would have otherwise required two new wells. Lessons learnt have accelerated the evolution of multilateral systems on the Tern and applications have been identified for multi-laterals in early and mid 1998. Other future applications of the multi-lateral methods are expected to involve coiled tubing drilling and water injection wells with a very large economic window of opportunity. P. 523