RIASSUNTO
SPE Member
Abstract
Several North Sea Operators are now using Snubbing Units to undertake operations previously regarded as only within the scope of a drilling rig (such as the running of 7"" completions and the undertaking of gravel-packing operations).
Snubbing Units are also increasingly being used to access and service horizontal and extended reach wells which coiled tubing cannot access.
With the use of a Snubbing Unit, through-tubing side-tracking and underbalanced drilling is no longer limited by the technology of Coiled Tubing Drilling. Additional margins are available if a `Snubdrill' option is adopted and these are quantified with the presentation of the results a `Snubdrill' Case Study.
Snubbing Units can therefore now be regarded as an established means of providing an Operators with a versatile and unique device which offers many advantages over both Derrick Equipment Sets and Coiled Tubing Units.
Introduction
A Snubbing System is basically a well servicing system capable of running and retrieving jointed pipe under live wells conditions. A typical Snubbing System is illustrated in Figure 1.
The use of a Snubbing Unit is not only already providing cost effective technology for a wide range of Drilling and Well Servicing applications but also has the potential for providing an alternative way to optimally develop future fields.
Present Snubbing and Hydraulic Workover applications include the undertaking of remedial well work without resorting to the use of kill fluids or lost circulation material and the performing of conventional tubing replacement workovers Snubbing well intervention operations are also now routine where coiled tubing operations are not feasible due to well bore geometry or length and should be considered where platform facilities are unable to handle the weights of larger coiled tubing reels.
Historically, workovers performed through existing tubing (`through-tubing workovers') have been undertaken with wireline or coiled tubing equipment, often supported by the use of a derrick equipment set. Snubbing systems are now performing similar work and are proving to be far more versatile than wireline coiled tubing and conventional workover rigs with the additional ability of being able to run and rotate tubulars while there is pressure on the well. Although certain workover situations will still call for wireline coiled tubing or workover rigs, there are now many situations where a Snubbing Unit is the logical choice. In principle, all of the downhole work that can be carried out by standard rig or through-tubing workover equipment can also be completed by Snubbing Units, with the (current) exception of running large >10 3/4"") tubulars.
Future applications for the technology include the horizontal side-tracking of existing wells (which could be performed conventionally or underbalanced). Such operations can either be undertaken through the existing tubing or, where such operations are not deemed feasible, the Snubbing Unit can be used to pull the existing completion prior to the side-track and used for the subsequent running of the liner and completion after drilling.
One of the main advantages of utilising Snubbing equipment is the ability to undertake a whole variety of operations and hence supply the versatility that has, up to now, only been regarded as available from a full derrick equipment set in combination with wireline or coiled tubing equipment.
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