RIASSUNTO
Abstract
A new concept, which combines existing fieldproven technology with newinnovative features, has been evaluated as an attractive technique forcollection and retrieval of top-hole drill cuttings, excavated during offshoredrilling.Simplified, the presented technique is based on using a collarthat is thread on the drill string prior to the spudding in commences.Thecollar is fitted with a connecting hose and a pump that help suck the fluid andthe excavated drill cuttings into settling and filtration bags.Aftercollection of solids the bags are easily displaced.By its simplicity andefficiency the technology appears as an attractive solution for drilling wellsin sensitive areas where a zero discharge regime of drill cuttings prevail.
Introduction
Prior to installation of a riser general operating procedure in offshoredrilling is to leave the excavated drill cuttings on the seabed.This isacknowledged as a safe and sound environmental practice due to the benignproperties of the material that is deposited, and the overall Health Safety andEnvironmental benefits connected to it.Once a riser is installed, drillcuttings and drilling fluid is returned to the rig for further handling.However, in some cases even benign material from the excavation, i.e the solidsper se, may have detrimental impacts on the near well bore area.Suchcases may be where a smothering effect of a sludge blanket causes damage tospawning grounds and where the dispersion of small particles in the watercolumn impairs sensitive marine organisms like corals and other filterfeeders.
In many countries restrictions to drilling activity in environmentallysensitive areas are enforced.Seabed deposition of top hole drill cuttingsis often denied in such cases.Moreover, the precautionary principle isfrequently applied to justify a rejection of a seabed drill cuttings disposaloption.It is on the backdrop of these facts the interest and thetechnology development presented in this paper can be recognised. The presentedtechnique has gone through different stages of trial and error, followingimprovements, to prepare for a field trial.This paper presents the entireconcept, the benefits of using it, and the experience and results acquired sofar.
Challenges and success criteria
Collection of tophole drill cuttings and following removal to the surface iscontroversial both from an environmental point of view and from the perspectivethat several risk factors are introduced when the well return is lifted to thesurface.Large circulation volumes are generated at a high rate duringdrilling of top hole sections.The water content of the well return ishigh and accordingly unpractical to handle and separate from the solids at thesurface.A rig based handling system would require extensive equipmentinstallation, along with intermittent storage capacity and logisticchallenges.
Recognising that the most widely used fluid in top hole drilling isbasically seawater added some bentonite high viscosity pills, it is arguablyjustified to waste this fluid, both from a cost and environmentalperspective.In typical cases this reasoning appears valid.The realchallenge, as we perceive it, really is to collect and confine the excavatedsolids not allowing them to disperse and impair the ambientenvironment.Moreover, a technique to collect the solids should preferablynot introduce new and/or increase risks of jeopardizing the drillingprogress.Concerns related to shallow gas during top hole drilling shouldalso be adequately dealt with. Usually drilling installation rental costis a major concern and care should be taken to prevent extension of the rentalperiod.