MEC&F Expert Engineers : 11/23/14

Sunday, November 23, 2014

WHAT IS HYDRAULIC WORK OVER (HWO) AT OIL AND GAS WELLS?



WHAT IS Hydraulic Work Over (HWO) AT OIL AND GAS WELLS?

Hydraulic Workover is a versatile, cost-saving and safe technique for repair- and remedial work on all types of wells.



Hydraulic Workover may include:

     Completing or re-completing wells
     Installation of ESP pumps
     Tubing conveyed perforations
     Installation of liners and sand screens
     Repair of down hole safety valves (scsssv)
     Drilling over small distances
     Fishing/ (production) Packer Milling operations
     Casing milling, milling bridge plugs, etc.
     Casing repairs
     Well Clean outs / Cleaning, Stimulations
     Cementing
     Abandonments

Why HWO?
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 perfect 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.


 



HOW SNUBBING UNITS WORK IN THE OIL AND GAS INDUSTRY



How Snubbing Units Work IN THE OIL AND GAS INDUSTRY

History of Snubbing Units
Snubbing units have evolved into one of the most capable and efficient well servicing tools in the oil & gas industry.  In the 1920's, the need for a rig to work with pressures at surface drove the invention of the snubbing unit.  The first snubbing unit was primarily designed to work in well control situations to "snub" drill pipe and or casing into, or out of, a well bore when conventional well killing methods could not be used.  The first snubbing unit relied on the draw works of the companion rig to supply its' power.  A series of sheaves, cables and counter weights were rigged up so that as the rig's traveling blocks hoisted up, the snubbing unit would snub in the hole.  Conversely, when the traveling blocks on the rig were lowered, the snubbing unit would snub out of the hole. As you can imagine, this required close communication with several different contractors in order to perform the work safely and efficiently.


Components of a Snubbing Unit
One of the main components of a snubbing unit is the slip.  Stationary and travelling slips are operated in sequence to grip the pipe as it is snubbed into the well.  Typically, a minimum of four slip bowls are used in snubbing operations.  Two slip bowls are designated for "pipe light" operations. Pipe light is when the well bore forces are greater than the tubular weight in the well bore.  The other two slip bowls are designated for "pipe heavy" operations.  Pipe heavy occurs when either enough pipe has been snubbed into the well bore and fluid weight inside of the pipe is greater than the snub forces acting against the pipe in the well bore.

While snubbing into the hole, there is a transition point the tubular goes through from being pipe light, to pipe heavy.  This transition is an equilibrium typically referred to as the "balance point".  The balance point occurs when there is enough pipe weight in the wellbore to equal the snub forces generated against the pipe.  In certain instances, thousands of feet of pipe can be moved with minimal effort since the pipe weight is at an equal state with the snub forces.  Snubbing contractors calculate this snub force and add in a friction factor from the BOP and wall contact on either a casing or tubing string.  If done correctly, the snubbing contractor can predict when this balance point will take place and can properly prepare for it.



Modern snubbing units are powered by sophisticated hydraulic systems. These hydraulic units typically supply all power required by the components of a snubbing operation. With a better understanding of hydraulics and modern advances, companies have been able to harness this hydraulic energy to develop precision controlled snubbing units. These units move tubulars into and out of a well bore by use of a "multi cylinder jack"; a snubbing jack comes in many sizes depending on the task at hand. They are usually denoted in size by the snubbing unit description (i.e. 460K, 340K, 200K, etc). The 460K snubbing unit has the ability to lift 460,000 LBS and a snubbing capacity of 230,000 LBS. Most snubbing units can typically snub half of their lift rating. Assume you had a well with 10,000 PSI at surface and wished to snub in a string of 2 3/8" tubing.  The snubbing contractor can calculate the snub force, add in their respective friction calculations and project the snub force to overcome will be approximately 51,000 LBS.  This would put a 120K snubbing unit to close to its maximum capacity of 60,000 LBS snub loading.  The safest bet would be a 150K or 235K snubbing unit.

Well control is taken very seriously by snubbing contractors.  The BOP is the only barrier between the well bore and personnel.  Depending upon well conditions, pressures and work performed, the BOP stack configuration varies greatly; there can be a minimum of three BOP's and in some cases, up to ten.  All of this is determined in the pre-job phase of the operation.

Pipe handling is performed by the snubbing units "gin pole" and "pipe winches".  The gin pole is typically telescoped out in excess of 40ft above the snubbing unit.  With the use of dual tubing winches, multiple joints of pipe can be handled simultaneously, speeding up the operation.



The snubbing "basket" is the platform where the snubbing personnel work.  The basket contains all of the necessary hydraulic controls to operate all the features of the snubbing unit, as well as a large bank of BOP's and hydraulic valve controls.

Snubbing Unit Applications
Today's snubbing units can be employed to provide a wide range of services. In essence, a snubbing unit is a hydraulic rig that can do everything a rig can do, plus it can perform under pressure in an under balanced live well state. This is especially critical to the operators in the Haynesville Shale, which is known for HPHT wells. With the use of the snubbing units' hydraulic rotary, the unit can be employed for fishing, milling, drilling, side tracking or any task needed to remove bridge plugs, cement or deepen wells.



Advantages
The industry has become more aware of damages caused by heavy kill weight fluids and mud. This has helped make snubbing units more popular in a completion and workover role, versus its' traditional use as a well control response tool. With the advances in drilling technologies in the unconventional shale market, the benefits of snubbing units have become very apparent. These types of completions often have laterals extending out thousands of feet. With costly stimulations used to help extract the gas more efficiently, operators often times do not wish to turn around and load the well with heavy fluids to complete the well dead.
Coiled tubing has its limitations in reach, due to wall to wall mechanical friction in horizontal wells. Often times the coiled tubing units cannot reach TD or supply the needed weight on bit to mill up composite plugs typically used in completions.



Another clear advantage to using a snubbing unit is its' small footprint, which is critical on the tight locations in the unconventional shale's. Moreover, the small size and ease of mobilizing is especially useful and cost effective with offshore wells.
In conclusion, with the snubbing unit's size, ability to handle pressure, rotary capabilities, rigidity of jointed tubing and minimal wall contact, snubbing units have become the chosen resource for these types of completions.

OVERLOADING LEADS TO CATASTROPHIC FAILURE OF CRANE BOOM AT AN OIL RIG PLATFORM



Overloading Leads to Catastrophic Failure of Crane Boom AT AN OIL RIG PLATFORM


A lease operator was performing a well permanent abandonment (PA) on an Outer Continental Shelf (OCS) platform.  Operations were being conducted to pull the 3.5" workstring and casing knives from the well after using a power swivel to cut the 9 5/8” and 10 3/4” casings.  The cutter assembly had become stuck while mechanically cutting the casings, and the hydraulic cylinders on the swivel stand were used to free the stuck knives. The cutter came free from the casing and the assembly was ready to be pulled from the well using the crane.  


The workstring and knives weigh approx. 6,600 pounds.  The load line on the platform crane was attached to the workstring using pipe elevators.  The load chart in the crane indicated that the crane could perform a static lift of 21,448 pounds and dynamic lift of 16,780 pounds at a boom angle of 63 degrees.  The boom was raised to a 63 degree angle and the crane operator then proceeded to pull on the workstring until 21,000 pounds was displayed on the weight indicator with no success.  The crane operator stated "looked like workstring was stuck.”  After slacking off on the load, a second attempt was made to pull the workstring and knives from the well.  The crane operator stated that "the weight indicator in the crane cab was displaying 21,000 pounds during the second attempt.”  The operator then stated that "all of the weight fell off of the indicator at which time the crane boom began to fall to the deck of the platform.” 


The crane boom, as well as a power pack, came to rest on the power swivel stand that had been used for the cutting operation.  The tip section of the boom came to rest at approximately 90 degrees to the right side of the main stem of the crane boom.  No personnel were injured, and all were accounted for immediately following the incident.
An investigation of the incident concluded that the following factors contributed to the accident:
     Incorrect load chart was used at the time of the incident.
     The crane operator used static load limits when pulling cutter assembly from the well instead of using the dynamic load limits as required by the contractor’s SOP.
     The bore holes of the pin connections in the boom showed excess wear thus causing slack in the connections and improper load distribution in the boom.
     The diagonal lacing, boom cords, and pin connections of the middle boom sections were found to be corroded.

We recommend the following prior to use of cranes on OCS platforms:
       Conduct proper crane pre-use inspections as per API RP 2D, C.4.1.2a which should include proper load chart verification.
       Conduct proper crane maintenance inspections as per API RP 2D, C.4.1.2 which should include thorough inspection of boom connections and proper load chart verification.
       Adherence to the SOPs and procedures put forth by both the operator and contractor while conducting lifting operations.
       Use the load chart for the dynamic load limits when pulling tubulars from wells instead of using the static load limits.
       The Crane Operator shall verify that the hook load is within the crane’s applicable static or dynamic rated load at the radius for which the load is to be lifted.
       Crane boom pull shall never exceed the calculated weight of the hook load, block, and rigging.


SAFETY ALERT AT OIL RIG PLATFORMS: MISUSE OF BEAM CLAMPS AS GROUND THAT CAN CAUSE FIRES AND OTHER ELECTRIC HAZARDS







SAFETY ALERT AT OIL RIG PLATFORMS:  Misuse of Beam Clamps as Ground THAT CAN CAUSE FIRES AND OTHER ELECTRIC HAZARDS



The Bureau of Safety and Environmental Enforcement (BSEE) has identified a potential safety issue in regard to the use of beam clamps on many Outer Continental Shelf (OCS) facilities.  It is determined that the use of beam clamps as grounding conductors could potentially cause fires  and present electrical hazards to personnel.



Many OCS facilities are utilizing beam clamps as current carrying external ground to meet the requirements in the API RP 14F.  The beam clamps are approved by Underwriters Laboratories (UL) and FactoryMutual Research Corporation (FM) to mount and support conduit and cable from structural beams, not as temporary or permanent external equipment grounding conductors.  Examples of beam clamps are shown below:













API RP 14F & 14FZ § 6.10.3.1 states: “Grounding of electrical equipment on fixed and floating offshore petroleum facilities in a positive manner is of particular importance because personnel standing on steel decks or in contact with steel framing present a low impedance path to ground, effectively grounded. In addition, the dampness and salt spray contribute to the breakdown of insulation and to the possibility of leakage on the surface of insulators and similar devices. On platforms with wooden or concrete decks, equipment-grounding conductors should be installed between electrical equipment and a grounding network.



It is recommended that all metal equipment, such as buildings, skids, and vessels be grounded to the steel structure or grounding network. Exposed, noncurrent-carrying metal parts of fixed equipment that may become energized because of any condition shall be grounded. Equipment that is welded to the structure or deck is considered to be adequately grounded. The physical contact obtained when equipment is bolted to a steel structure is not necessarily an adequate effective ground because of paint and possible corrosion. Exposed, noncurrent-carrying metal parts of portable electrical equipment shall be grounded through a conductor in the supply cable to the grounding pole in the receptacle.”





These grounding jumpers do not meet the requirements in API RP 14F/API RP 14FZ.




API RP 14F & 14FZ both make a clear requirement that any equipment that has exposed, noncurrent-carrying metal parts that may become energized because of any condition shall be grounded. In this requirement, it is clear that during a fault condition this grounding means must be capable of reliably conducting the ground fault current back to the source of electrical power to activate or trip the electrical circuit protective device. To further clarify, if the equipment is not electrically powered and the metal parts associated with that equipment become energized due to no association with electrically operated equipment, controls, devices, or lighting, then the requirement for approved current carrying conductors, lugs, terminals, etc. should not apply.








 



Operators, as well as contractors, are advised to review your facilities in comparison with these best practices and guidelines.