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Tender assist drilling (TAD) units
Tender Assist Drilling (TADs) units are drilling units constantly challenging the status quo in drilling. By being in a red ocean market, Tender Assisted had to always find its way to evolve to deliver cost efficient drilling and well intervention solution for the operators.
They are focussing mainly on two areas of activity: factory drilling of marginal field and Deepwater Drilling, however due to its flexibility, tender assisted is being considered for various other application.
Factory drilling of marginal field
Marginal oil and gas reservoir requires drilling efficiency and an optimisation of any associated costs. The drilling package are fit-for-purpose and optimized for rig move and skidding and are generally opperated by experienced crews who developed themselves on this type of unit. The drilling package followed the latest inovations in term of automation and equipement with the primary focuss to improve the efficiency for the client. This type of units are as efficient as the latest generation of jack up and in addition, provide large deck space allowing important saving for the operator in logistic cost. Cost to build the tender are lower than jack up, and it reflects in the day rate. We have seen however that since 2014 downturn, some jack up contractors dont hesitate to slash their price, to get their jack up working, which is turning the development drilling segment in shallow water into a highly competitive one.
Tender assisted will however remains the unit of choice when there is:
- risk of punch through for a jack up
- incompatibility of spud can
- pipelines, corral,etc on sea bed
- water depth above 100 meters
- platform out of reach of the jack up cantilever
Over the years, the flat bottom barge concepted evolved toward semi-sub shape design allowing improved motion in rougher weather. It unlocked the restriction on area of operation that the previous design has, an nowadys, tender assisted had been operating in Brazil, North Sea or Vietnam.
Semi Submersible tender operate along side TLP or SPAR thank to a couple body system. It enables important saving for the opperator since the drilling package is not permanent and will be removed at the end of the drilling campaign. It results in saving in construction cost (less weight on the platform translate in less weight for the TLP), saving in maintenance and decommissioning cost ( drilling equipement doesnt need to be decommissioned).
It is not unusual for a platform to deteriorate with age, and then be unable to hold up a standard platform rig when additional wells need to be drilled. The TAD is an option for this situation. Of course, if the platform is in jackup water depth range, the jackup may also do the drilling .
Semi TADs also have the advantage of acting as construction barges for platforms that are commissioning production equipment. They offer a relatively inexpensive construction platform compared with a construction derrick barge due to the following amenities:
- Large rig-up crane
- Open decks where the DES is stored and transported
- General facilities
They are offering an interesting alternative also during platform P&A and decommissioning. Offering enough bed and storage space, to allow P&A and platform removal operation to be performed simultaneously.
Situations favorable to TAD use
They may be particularly attractive for standard platforms in water depths over jackup-rig rating and where space and/or load limits are a major factor, for deepwater spars and TLPs with the right number of wells, and for any platform where weight and space for long ERW are limited. Generally, a TAD costs more than a platform rig when uniquely looking at day rate, especially the modular type. However when looking at the overall cost of operation, especially the additional logistic imposed to the operator, they are a very attractive option.
Recent TAD application
01) West Seno- 1000m WD
02) Kikeh SPAR-1300m WD
03) Tombua Landana-365m WD
04) Okume-500m WD
05) KBB- 137m WD
06) Total-Moho Nord- 650m WD
07) Papa Terra- 1190m WD
08) Malikai- 500m WD
09) [Project] Ca Rong Do - 320 WD
Over 7,000 wells drilled using TAD since 1980's.
Noteworthy papers in Onepetro
Stig Botker, Terje Karp et al. 2001. Wellhead TLP with Tender Assisted Drilling, Offshore Technology Conference, 30 April-3 May 2001, Houston, Texas, 12988-MS, http://dx.doi.org/10.4043/12988-MS
MATHIESEN, R. 1989. The TENDER ASSISTED DRILLING - NPD EXPERIENCE, Offshore Europe, 5-8 September 1989, Aberdeen, United Kingdom, 19248-MS, http://dx.doi.org/10.2118/19248-MS