underbalance drilling

Underbalance DrillingRotating Heads&Rotating BOPs

Rotating HeadsRotating BOPsUsed to divert the return flow stream down the blooey line, flow line or to the choke manifold.

Rotating Drilling HeadsTwo types of systems; hydraulic active (RBOP) and mechanical sealing (RH)Both are used successfully in air and underbalanced wells

Rotating HeadMechanical Sealing Type

Gas and Air Drilling

Rotating Head Mechanical Sealing Mechanism

Drilling Fluid Description

Rotating BOPHydraulic ActiveRBOPTM Kelly Packer

Closing Unit

ManufacturersWilliamsSmith GrantShaffer RSBOP (Varco) Northland Inter-Tech RBOPTESCO1Alpine - TechnicorpLynn InternationalOthers

Mechanical Seal Rotating HeadsPressure RangesLow 300psiMedium 700psiHigh 1500psiVery High 3000psiStatic pressure ranges are twice as high

Mechanical Sealing Rotating HeadsKelly BushingDrive BushingSwing Bolt ClampStripper Rubber

Grant - Smith

Conventional Rotating HeadWilliams Model 9000 Kelly DriverBearing AssemblyStripper RubberBowl500 psi rotating1000 psi staticUp to 200 rpmGeothermal model - two stripper rubbers


Negative Impact to Stripper Rubber ElementsThe purpose of the stripper rubber is to provide a seal around the kelly as it rotates and to seal around the drill pipe while tripping in or out of the hole.

Stripper Rubber CompositionNatural- Air, Mist, Foam, GasPolyurethane- Oil Based below 140 FNitrile - Oil Based above 140 FButyl - Geothermal and H2S

Negative Impact to Stripper Rubber ElementsKelly condition is critical.Surface condition- check wear pattern on cornersBent Kellys

AlignmentRig to Stack Alignment is criticalCheck DailySuspect to excessive element usage

Other Negative ImpactsDrill pipe identification groovesPitting and abrasion on drill pipeTong and slip die damageSome hardbandingMills and bits

Other Negative ImpactsExtreme cold Extreme heatAge Sun light

Low Pressure Rotating Head

Gas and Air Drilling

Medium Pressure RDHPressure to 700 psi Single or Dual ElementLower Mounting Spools from 7 1/16 2000 psi to 13 5/8- 5000 psi.Outlet Flanges are 7 1/16-2000/3000 psiGrant - Smith

High Pressure MODEL 7000For use on rigs withtop drives or Kellys CALL FOR SIZES AVAILABLE

MODEL 7000 COMPONENTSMODEL 7000 ROTATINGCONTROL HEADREMOTE MODULAR POWER UNITREMOTE MONITORINGCONTROL CONSOLEMODEL 7000 EXPLODEDCUT-AWAY VIEWU.S. Patent No.5,662,181Rotating Blowout Preventer

Rotating Head SchematicsSingle ElementDual Element

Main ComponentsHydraulic Oiler Lubricator/ And cooling System Heavy Duty Rotating Drilling Head

Bearing AssemblyContains large heavy duty tapered roller bearingsBearing Chamber sealed with low pressure seals against atmospheric pressureSeparate high pressure seal assembly to contain wellbore pressure

Drive Assembly andStripper RubberElastomers available for oil, gas or geothermal drillingAvailable in single or dual element systemsCombination one piece drive assembly and stripper rubber

KELLY DRIVERS

MODEL 8000/9000 STRIPPER RUBBERSStripper rubber usage is determined by the operating pressures, Kelly and drill pipe conditions and stack alignment. Standard Heavy duty Oil resistant

MODEL 9200 GEOTHERMAL STRIPPER RUBBERSStripper rubber usage is determined by the operating pressures, Kelly and drill pipe conditions and stack alignment.Drill collar (1) Drill pipe (2)

7000 SERIES STRIPPER RUBBERSStripper rubber usage is determined by the operating pressures, Kelly and drill pipe conditions and stack alignment.

CASING STRIPPER RUBBERSAvailable for all models

LOGGING ADAPTERAvailable for all models

SPACER SPOOLSAvailable in all sizesSpecify flange series and height when orderingTO ONLY BE USED ABOVE ANNULAR BOP

FLOWLINE FLANGESUsed to connect flowline to Rotating Head7 1/16" - 3000 - w / swages from 6" - 12" 11" - 3000 - w / swages from 6" - 12"Available for all models

PIPE WIPER HOLDERAvailable for all models

OILER - LUBRICATOR

DRILLING NIPPLEAvailable for all models

SNUBBING ADAPTER

BLANKED FLANGES

TEST PLUGAvailable for all models

RBOP - Oil Tools InternationalDeveloped by SealTech, Oryx Energy, Clayton Williams and ExxonDesigned for use in High GOR wells, Wells With H2S and High Pressure Wells.


Wellhead Pressure Control

Active pressure unitMultiple pressure settingsSimple quick packer change2000 psi static pressure11 ID capabilities

RBOP Schematic

Wellhead Pressure ControlBottom FlangeQuick-ChangePacker AssemblyHydraulic Fluid InletInner PackerOuter PackerSealOutlet FlangeBearingKelly DriveAssemblySurgeBottle

Wellhead Pressure ControlSimple quick packer changeRedundant element sealing11 ID capabilities

Multiple pressure settingsRig floor operation

RBOP Closing Unit

Shaffer Rotating Blow-Out Preventer 2,500 psi rotating - 5,000 psi static

Shaffer PCWD


Passing a Tool Joint

Techcorp 3000

Inner Replaceable Element

TESCO DOUBLE ANNULARNot a rotating preventerUses two small modified Shafer packersUsed like a rotating preventor

Rotating Heads and Rotating Blow Our Preventers

SUMMARY

Rotating Drilling HeadsLow - High Pressure Systems Hydraulic Activated SystemsNot API certified as a blowout preventerSealability is electronically hydraulically actuated as a function of wellbore pressureShop serviced bearing assemblyMechanical Interface SystemsNot API certified as a blowout preventerStretch-interface seal maintained, assisted with wellbore pressureWellsite replaceable bearing assembly

Hydraulic Lubricator SystemsHydraulic Active SystemSeal is hydraulically actuated as a function of wellbore pressure and lubricates the bearingUsually a common oil reservoir cools bearing Mechanical Interface System Seal is activated by well pressureCirculating system for high pressure used to lubricate and cool bearing -does not activate elements

Rotating Drilling HeadsHigh Pressure SystemsHydraulic Activated Systems Pressure to activate is controlled by sensor or manually.Seal is totally controllable.Mechanical Interface SystemsSeal is always active and increases with increasing well pressure.No pressure seal is function of stretch fit.

END

Probably the basic tool for UB drilling is the rotating head or rotating blow out preventer. This is not a new tool as you can see by this old catalog from 1937. This model, which has no model number, was made for 13-3/8 casing and from 2 to 6 drill pipe.It is essentially the same in principle as the Rotating Heads used today.This is the 1954 catalog, and now they call it the Model 50 rotating and stripping head. I saw what appeared to bean old model 50 just a few years ago in Mexico. The Rotating head or rotating bop is a diverter by definition. Sometimes we confuse it with a blow out preventor, and the trend is towards making them true annular blowout preventors..There are two types of systems available on the commercial market today. They are a hydraulic actuated system and a mechanical seal system. Both refer to the system used to achieve a seal around the drill string. Both are used successfully in air, gas or underbalanced applications in low or high pressure regimes.Hydraulic active systems use hydraulic closure, often electronically controlled. They are essentially active systems.Mechanical sealing systems utilize the memory of a stretch fit stripper rubber assisted by well bore pressure. These are essentially passive systemsSection of a mechanical sealing system (Williams, Smith). The whole sleeve assembly rotates.On the left we see the tight stretch seal of the rubberOn the right, well bore pressure makes the seal tighter in direct response tothe unit pressure in the well bore- psi, kPa, kG/m2 The hydraulically active Rotating blow Out Preventor uses hydraulic fluid to push a packer closed around the pipe. The closing pressure is set to be some amount higher than the well pressure. The whole packer assembly rotates.Here is the view of a hydraulic closing unit in a portable building. (Schaefer RBOP)The white names are rotating heads. The yellow are Rotating Blow Out PreventorsTESCO has a hydraulically closed annular preventor that does not rotate.Static ranges are higher than rotating ranges. This is mostly a convention. Rotating at higher pressures causes more wear.The split kelly bushing is made up with a loose fit around the kelly. When the kelly is run in, this bushing automatically indexes itself inside the Drive Bushing. The rotary action of the kelly turns the bushing. The bushing turns the Drive Bushing, and consequently, the attached Stripper Rubber. When the kelly is picked up, the shoulder on the lower kelly upset lifts the bushing with it. This automatically disengages the bushing from the drive bushing , and the bushing remains with the kelly in the rathole. The stripper rubber is designed to seal off on all drill string components. The rubber expands and contracts (breathes) as the pipe, kelly, and tool joints are stripped in and out of the hole. Stands of drill pipe may be added or removed during tripping without loss of time since the drive bushing assembly is removed only for drill bits or special tools. The better the pipe condition supplied the more life can be expected in the stripper rubbers. Drillpipe condition is critical to a long lasting seal. Similar to tire wear, where pavement travel is less damaging to tires than travelling on gravel roads. More meterage of drill pipe can be tripped safely with good pipe and kelly conditions.One or two steel reinforced stretch-fit self actuating stripper rubber elements provide a robust seal around the drill string or kelly which allows annular fluids to be diverted to the flow line or a choke manifold. Rubber selection is varied based on drilling medium and dynamic pressures found on the drilling location, as well as temperature of drilling muds. Here we show the low pressure elements in natural rubber good to 500 psi dynamic rating. The composition of the elastomer can be varied to provide optimal protection from wellbore fluids, pressure and temperature. Both low pressure and high pressure elements are available in natural, nitrile, butyl, or polyurethane compositions.The shape of the element is also designed to cause the closing force wellbore pressures to assist in a seal against the drill pipe, kelly or BHA from the wellbore pressure. The inside diameter of a stripper rubber element is considerably smaller than the outside diameter of the drill pipe or diameter of the kelly. In this way the stretching force applied around the drill string provides a positive seal. Wellbore pressure applies a closing force on the cone shaped element and provides the self actuating seal. The greater the well bore pressure, the greater the closing force pressing the stripper rubber against the drill string or kelly. In this way no hydraulic pressure is required to activate a seal in low or high pressure regimes. In low pressure or no pressure scenarios, the predominate seal, with stretching force from the element itself, is safe and reliable. A misunderstanding that seems to persist is that wellbore pressure in low or high pressure environments creates a seal. Or that wellbore pressure only maintains a seal. Neither is correct. Before picking up the new kelly, check the kelly bushing. The rollers, pins, or bearings may need replacing to return the drive assembly to like new status. Check the bushing body for journal area wear ,and body spreading. A loose fitting drive unit can badly damage a new kelly on the first well drilled. Remember to lubricate kelly drive surfaces.Check wear pattern on the corners of the kelly.The major cause for kelly wear is the rounding off or sharpening of the drive corners. This rate of wear is a function of the clearance fit between the kelly and the rollers in the kelly bushing. The wear is usually caused by rig to stack misalignment, and/or an improper kelly drive roller fit.Stack alignment is critical to the performance and life of the rotating drilling head bearings and stripper rubber. Check alignment by lowering the kelly until kelly bushing engages in the rotating drilling head. The kelly drive bushing should go into the drive bushing freely without having to force the kelly sideways. If the kelly drive bushing does not freely engage into the drive bushing of the rotating drilling head, then BOP stack and rig rotary should be properly aligned.Check kelly by running your hands up it full length for sharpness.Most stripper rubber elements used in the oil and gas industry are designed with a 60-90 durometer hardness. The palm of your hand is approximately a 45 durometer. Your sneaker soles are a 60 durometer. If you feel that the palm of your hand could be cut or damaged by running it over the surface that the elastomers will travel. Then simply the elastomer will be damaged also in the same fashion. As higher pressure operations are extended the condition of drill pipe against which the seal is being made becomes more important. The seal life may vary widely for different pipe condition. The following practices will extend the life of the seal when operating in high pressure environments. Maintain proper rig to stack alignment.Inspect drill pipe regularly and clean up all tong marks and sharp edges.Use low tapered tool joints on both box and pin ends (18 degrees)Lubricate exterior surface of drill pipe and tool joint before stripping into the well.Avoid use of tool joints with rough hard-banding surfaces and identification grooves cut into the tool joints. Avoid tripping out of the well with pressures higher than required for the underbalanced needs. element life increases rapidly as pressure decreases. Inspect the seal at regular intervals, and change when significant wear is noticed. Operating the rotating head to the point of seal failure is not a good drilling practice. Frequency of the inspections should be based on pressure and the number of tool joints tripped in or out of the well.Store elements that are not in use in a warm area. (boiler or doghouse) Elastomers become very brittle in extremely cold climates. They should be sufficiently warmed up prior to drill pipe being started in the element. .Operation of the hydraulic unit is automatic. The high pressure system will increase or decrease hydraulic pressure when the well bore pressure increases or decreases. The low pressure system continuously circulates oil through the bearings. The hydraulic reservoir levels should be checked daily.Oil contiously circulates through bearing assembly to lubricate and cool bearings and seals.Separate lubricator system for high pressure seal assemblyRotating test pressures of 1500 psi.If necassary the drilling head can be changed by removing 3 quick release line to the bearing assembly and the high pressure seal assembly, unbolt the lower clamp and remove the bearing assembly in minutes.NotesOn of the two packers in the TESCO double annular packer discarded after use. Note the wear on the upper outside of the rubber finders. There is steel inside the fingers. Thisis essentially small Shaffer spherical annular Bearing assemblies and stripper rubber elements must operate and resist heavy upward thrust caused by wellbore pressures. Therefore oil lubricator systems must maintain a constant flow of oil through the bearing to lubricate and cool the bearing assemblies. This is also true of R.B.O.P.s. Some systems also cool their bearings with water or antifreeze. A hydraulic unit or power unit contains both the oil cooling and lubricating reservoirs, circulating pumps, and controls. Hydraulic and manual operated clamps at the top of the rotating drilling head allows the bearings or stripper rubber assemblies to be removed quickly. The assemblies are lowered into place through the rotary table by riding on the last joint of drill pipe when the drill string is run in the hole.

underbalance drilling

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