Sunday, November 23, 2014

DAMAGE INCIDENT INVESTIGATION IN THE GULF - HYDRAULIC WORKOVER UNIT TOPPLED BY WATERSPOUT



DAMAGE INCIDENT INVESTIGATION IN THE GULF  - Hydraulic Workover Unit Toppled by Waterspout








Hydraulic Workover is a well intervention technique which can be used to install or remove tubular in- or out of dead wells.  "Dead" well means that the well has zero surface pressure and has a heavy fluid or mud in the wellbore, or is not capable of sustaining natural flow.












Advantages of Hydraulic Workover






A HWO unit can cover the same working envelope as a workover rig but has advantages over conventional rigs or hoists for certain applications, such as:






•  Small and flexible footprint



•  Small environmental impact



•  It is quickly and easily mobilized to offshore platforms



•  It is quickly and easily mobilized to remote land wells



•  Costs efficient



•  Perfect control over the workstring (tubular) 



•  Custom Rig-up configuration / Modular approach













Hydraulic Power



 The HWO unit (Hydraulic Workover Unit) utilizes hydraulic cylinders to lift the tubular in- or out of the well.  The use of hydraulic cylinders allows control over tubular movements and eliminates the use of a large mast construction which is present on conventional drilling rigs.



Hydraulic cylinders can generate large pull and push forces and give the HWO unit a small footprint and layout. These properties are especially beneficial for offshore operations where space is limited and where weather conditions can be harsh. In general is the running speed of a HWO unit lower than that of conventional workover rig.






Incident Investigation



While conducting workover operations, a Hydraulic Workover (HWO) unit was toppled by strong winds caused by a waterspout that touched down near the platform.  The result was the entire HWO unit collapsing onto the facility, as well as into offshore waters.  The collapse resulted in damage to the lower riser portion of the HWO unit as well as to several other pieces of well servicing equipment located on the platform.  The upper riser portion and the BOP stack of the HWO unit fell into the water resulting in total loss of the BOP stack.  All personnel had been moved from the platform to the supporting lift boat prior to the collapse, and no fatalities or injuries resulted from the incident.



An investigation concluded the following factors contributed to the accident:



       High wind loading was exerted on the unit as a result of the waterspout being so near to the facility. The large surface area presented by the HWO unit, against which the wind could act, and the close proximity of the waterspout resulted in a high wind loading being exerted on the unit.



       The small deck area of the platform caused an increase in the angle(s) of the guy lines used to support the HWO unit.  This increase in angle(s) resulted in diminished stability of the HWO unit during the high wind conditions caused by the waterspout.



       Installation of additional guy lines would have helped to compensate for the increased angle(s) in the guy lines, thus increasing stability and support for the HWO unit in the event of increased wind loading due to the storm, or swaying due to high sea state and possible sway in the platform.


We recommend the following when installing guy lines to support HWO or related well servicing equipment:



       Engineering calculations be performed to determine the correct angle(s) for the guy lines when installing HWO, or related well service equipment.



       Installation of additional guy lines when deck space on the host platform is limited and guy line angle(s) increases.



       Seasonal weather patterns be taken into consideration when installing guy lines and other means of support.



       Guidelines for construction, safety factor, and storm load for wire rope guy lines found in API Spec 4F, Section 8.1.2 and 8.1.3 be followed when selecting wire rope used for the purpose of guy lines.