RIASSUNTO
Abstract
This paper will discuss the use and advantages of employing snubbing units during and after well control operations. The benefits of snubbing units compared to coiled tubing are widely known and generally accepted in the industry. During some well control operations the advantages a snubbing unit provides can positively impact the outcome of the well.
From its inception solely as a mechanism for handing tubulars during well control operations, snubbing has evolved into a highly versatile technology, offering myriad operational, economic and HSE benefits. To illustrate the versatility of new generation snubbing technology in a variety of well control situations, the authors will present case studies of a number of diverse applications.
The paper is intended to educate operators and service contractors alike by sharing experiences, lessons learned and demonstrating the effectiveness of snubbing units in a variety of hostile well control environments, including its use with gunk squeezes.
Introduction
The evolution of snubbing from a mechanism used solely for running tubing into live or flowing wells into a multipurpose technology offering a host of operational and economic benefits has been well-documented in the literature.1-2 (Wehrenberg, et al, ""Versatile HWO/snubbing units offer multiple benefits over conventional rigs,?? Hart's E&P, May 2009; Blount, et al, ""Dynamic kill: Controlling wild wells a new way,"" World Oil, October 1981). Snubbing has been used since the late 1920s when it was developed out of necessity as the only available means of running tubing into an active well. The original process involved the use of a series of blowout preventers that were engineered to allow the tool joint or coupling to pass through freely when mandated. In those early snubbing units, two sets of slips, positioned upside down, held the pipe in place. One set of slips remained stationary and the other traveled on a set of cables attached to the rig blocks. With the advent of the hydraulic unit in the 1960s, the cable-type began to phase out, although they remained in use well up into the early 1980s.
In some areas, the use of snubbing in workover operations is relatively common, typically in applications where the well is allowed to continue flowing as remedial work is carried out. Moreover, snubbing may be considered for well control operations during drilling operations. Typically, for well control, snubbing is contemplated when it is otherwise impossible to introduce pipe into a well that is under pressure, or in instances where the BOP system is judged inadequate to provide reliable pressure containment during a prolonged stripping operation.
A snubbing unit can be used to introduce a range of sizes of pipe into the well. It can be used to snub tubing, drill pipe and even casing in exceptional circumstances. Today, snubbing units are engineered in a wide range of sizes from smaller through-tubing units to those large enough to effectively run 9 5/8-in. casing handling hook loads of 300 tons (272 metric tons). Generally, hydraulic units can push (snub) about one-half the hook load rating. The units have proven themselves very useful in a multitude of applications from sand washing to the containment and recovery of blown out wells. In a blowout, snubbing units have proven to be invaluable tools. Even while the well is blowing out, a snubbing unit has the capability of entering the well bore with a multitude of tools and either install kill strings or else tie into and recover lost or damaged drill strings or tubing.