Quartz School for Well Site Supervisors Module – 8 Directional Drilling
Section – 5a Bottom Hole Assemblies for Directional Drilling
Objectives 1.
Describe the minimum number of BHA changes needed in: - a slant directional well - an “S” type directional well
2.
Describe what is meant by: - bit side force - fulcrum effect - pendulum effect
3.
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Explain the effect of drill collar stiffness in BHA design
Objectives 4.
Explain why minimizing the number of DC's and stabilizers is advisable in directional BHA's
5.
Describe the effect of an under gauge near-bit stabilizer in: - drop-off BHA's - build-up BHA's
6.
Show why an under gauge second is used in a locked BHA for tangent section
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Describe the effect of hole washout on BHA behavior
Objectives 8.
Describe the effect of drilling parameters have on inclination & direction with each type of BHA
9.
Explain why frequent surveys is advisable when an MWD tool is available
10.
Give examples of typical BHA designed to build and drop inclination at various rates
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Deflection Devices Tools & Techniques to deflect the course of the well in a controlled manner, (overcoming “natural” tendencies) eg., to: Kick-off, nudge (build angle from vertical to a desired direction) Trajectory correction (turn, build, drop to the desired trajectory) Sidetrack (deflect the well from it’s original course)
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Rotary Bottom Hole Assemblies
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BHA Side Force BHA’s cause a side force at the bit that makes the bit build, drop or hold angle
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Definitions All BHAs cause a side force at the bit, leading to change hole inclination Positive side force-Build Inc. Zero Net Side force-Hold Inc. Negative Side force-Drop Inc. Fulcrum Effect: Builds Inclination Packed Effect: Holds Inclination Pendulum Effect: Drops Inclination
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Factors affecting bit side force The side force is affected in three different ways: By the mechanical characteristics of the BHA The gauge and placement of stabilizers and other BHA components The diameter, length and material of the BHA components Bit type By the drilling parameters applied to the BHA Weight on bit Rotary Speed Circulation or flow rate 9 10/23/2009
By the formation being drilled
The Principles Bar of mass M
Weight of 1/2 M
Weight of 1/2 M
When we consider the side force, we are only able to use the unsupported unsupported weight that lies between the tangent and the bit. Because the weight is supported at each end, only half of the weight is available at the bit as sideside-force.
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Side Force Forces acting on a bit in an inclined hole Side force with zero WOB: H = w x L x BF x sin(inc)/2 Where: H is side force w is weight per unit length of the DCs L is the length of unsupported DCs below the Tangent BF is the buoyancy factor
Pendulum force (negative side force)
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Slick Assembly – Pendulum Force If WOB = 0, only pendulum force applies (-ve side force) The max. pendulum force at bit is given by: H = (Wc x L x BF x sin(inc) ÷ 2
If WOB is applied a Positive bending force is introduced. Tangency Point moves closer to the bit And pendulum effect decreases
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Negative Side Force Increased WOB results in a shorter tangent to bit distance. This reduces the pendulum effect and increases bit tilt, resulting in greater positive side force
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Positive Side Force Weight on Bit With WOB we can induce Bit Tilt by moving the tangent closer to the bit and thus generate a Build Force (positive side force). If the Build Force is great enough it will become greater than the pendulum force and an increase in hole angle will result. Bit Tilt Hole Direction 14 10/23/2009
Single Stabilizer The effect of a single stabilizer changes with it’s proximity to the bit. As the distance reduces it’s effect goes from none, when the tangent is the same distance as if no stabilizer was run, to maximum build when it becomes a Near Bit Stabilizer.
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Single Stabilizer BHA As the stabilizer moves closer to the bit the
tangency point changes. There is a point of maximum negative side force. Moving the stabilizer closer to the bit reduces side force. Eventually reach a point of zero side force. Moving stabilizer closer will result in a positive side force – collar above the stabilizer bends forcing the bit upwards – Fulcrum Effect. Increase in WOB, increase in build rate. The more limber the collar above the stabilizer the greater the build rate 16 10/23/2009
Two stabilizers With Two stabilizers, by controlling their relative position to the bit create almost any behavioral tendency that we require. The spacing in this example is twice that of the Tangent point from the first stabilizer, so there is no effect from the second stabilizer.
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Two Stabilizer BHA’s
Simplest BHA has a NB Stabilizer and a
second stabilizer some distance above this.
For a given WOB the distance from bit to first stabilizer (L1) and between the stabilizers (L2) determines the tangency point.
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Principles of Rotary BHA
NMDC
PowerPulse Stabilizer Pony NMDC
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Stabilization
Build
Hold
Drop
Stabilizer Placement and resultant side forces 20 10/23/2009
Drop
2 Stabilizer - 90’ Build Assembly Tangency occurs between the stabilizers. Various bits and collar sizes with 30 Klbs WOB Smaller hole size – more flexible collars – bigger side force
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Effect of WOB
• What is the effect of increasing WOB? - to a building BHA - to a dropping BHA
• What are the limits? 22 10/23/2009
Effect of WOB on 2 Stabilizer Assembly
Increase WOB
Induce Tangency point Increase Side Force
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Effects of Stabilizer Gauge
• Full Gauge Vs Under Gauge for Near Bit Stabiliser • Full Gauge vs Under Gauge for second Stabiliser
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Under gauge Near-bit Stabilizer • Results in changes of bit
side force • Build BHA will have less build
• Lock-up BHA will drop • More under gauge = greater effect
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Under gauge Second Stabilizer • Becomes easier to get a
tangency point below it. • More under gauge = greater
effect • Hold assembly = try to get zero net side force
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Effects of Hole Gauge • How does hole gauge effect: - a building BHA - a dropping BHA
• Considerations:
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Hole Washout • Dealing with soft formations
• Loss of bit side force • May be necessary to drop flow rate • May be necessary to run a more limber collar between NB and string Stabilizer • May need to pick up motor 28 10/23/2009
Fulcrum / Build Assemblies
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Standard Fulcrum Assemblies (Build)
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Standard Fulcrum Assemblies (Build)
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Fullcrum (Build) Assemblies - Summary
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For increasing the build rate of a fulcrum BHA: Increase in WOB Reduction in size of the top Stabilizer Increase in distance between the bottom and top stabilizer Reduction in RPM Increase in hole inclination Reduction in flowrate (soft formations)
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Standard Packed Assemblies (Hold)
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Standard Packed Assemblies (Hold)
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Standard Packed Assemblies (Hold)
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Typical locked up BHA for 12-1/4 in. hole
The response of this type of BHA is determined by: 1. Hole size 2. Distance between near-bit and lower string stabilizers 3. Stiffness of the collar directly above the near bit 4. Gauge of the stabilizers 5. Drilling parameters 37 10/23/2009
Packed (Hold) Assemblies - Summary
UG
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Standard Pendulum (Drop) Assemblies
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Standard Pendulum (Drop) Assemblies
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Standard Pendulum (Drop) Assemblies
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Semi-drop BHA
- is a lock-up BHA incorporating an under gauge near-bit
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Pendulum (drop) Assemblies - Summary
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For increasing the drop rate of a pendulum BHA: Decrease in WOB Increase in RPM Increase in flow (soft formations) Reduction in size of NB Stabilizer Increase spacing between bit and first string stabilizer
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How do bits affect the BHA Tendency !
Roller Cone Bits Tendency to walk Right Long tooth bits in soft to medium formation have greater walk Short tooth in hard formation have less walk Higher rotary speed more walk (less bearing life)
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PDC Bits Almost no walk tendency Long gauge PDC hold inclination and direction Short gauge PDC can provide better build/drop rates Higher rotary speed more walk Higher RPM and low WOB can affect Build rate
How does the formation Dip affect the BHA tendency!
Generally when the apparent o angle of Dip is below 45 the bit follows the easiest path and drills up-dip
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Stabilization
• Stabilized BHA can be designed to build, hold or drop inclination • Critical elements: -Stabilizer gauge -Stabilizer position -Drill collar OD/weight/moment of inertia -Hole inclination -WOB, RPM, flow rates -Hole gauge -Bit Type
• Prediction issues (formation effects, bit walk, hole washout.…) 47 10/23/2009
Neutral Point (Vertical Hole) • Is the point where the drill string
transitions from tension to compression • Needs to be kept in the BHA
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• Enough DC and HWDP picked up to ensure enough weight is available
Neutral Point (Inclined Hole) • For an inclined hole the
inclination has to be taken into account. • For a well at 45° only 71% of BHA weight is available in air.
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The Principals Forces acting on a Bit in an inclined hole (for a string rotating off bottom).
θ Available weight:
W = w x L x BF x cos(θ θ) Where:
θ is the hole inclination in degrees w is weight per unit length L is the length of DCs below the Tangent BF is the buoyancy factor
Available weight BF = 1-(mwt/65.5) (for ppg)
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Neutral Point Calculations
In deviated wells Available WOB = (Buoyed BHA Weight) x (cos Inclination)
BHA Weight in air =
Available WOB x DF BF x cos α
where DF = Design Factor (usually DF = 10%)
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Neutral Point Calculations Example: Hole Size: 12 ¼ “ Well Inclination: 45° Mud Density: 11 ppg Required WOB : 40,000 lbs Use a design factor of 10% a) How many DC’s (8 ¼ ”,32’, 160 lbs/ft) this BHA will require? b) If the number of DC’s is limited to 6, how many HWDP should be added to the string? (HW= 5”, 31’, 49.7 lbs/ft)
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Neutral Point - answer cos(45) = 0.707 BF for 11ppg = 0.831
Required BHAair WT Number whole DC
• •
8 ¼” DC are 5120 lb/32ft 5” HWDP are 1540 lb/31ft
= (40000 x 1.1)÷(0.831 x 0.707) = 74982 lbs = 74982 ÷ 5120 = 15 DC
There are only 6 DC available; how many HWDP are required? Required BHAair WT 6 x DC Amount HWDP
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= 74982 lbs = 5120 x 6 = 30720 lbs = (74982 – 30720) ÷ 1540 = 29 jts
Special BHA's 1. Tandem Stabilizer 2. Roller Reamers 3. Variable Gauge Stabilizer 4. Jetting BHA 5. Gilligan BHA's 6. Hole Openers 54 10/23/2009
Tandem Stabilizers
• String Stabilizer run directly above near-bit • Normally for directional purposes • May result in high rotary torque • Longer gauge NB Stabilizer may be an alternative
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Stabilizers
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Roller Reamers • Used where there is excessive rotary torque – replaces some or all of the stabilizers • Behave differently to stabilizers with respect to directional response – if used as a Near Bit – tendency is to drop angle • Increase spacing between NB and first string to try and counteract the drop • Important to check roller condition after each run
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Adjustable Gauge Stabilizer
• Various makes & sizes available – D&M, Andergauge, Sperry AGS, TRACS • First Rotary Steerable tool – 2D only • Minimum two position stabilizer • In most cases can be run as a Near Bit or String Stabilizer
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Jetting BHA • is an easy and cost-effective way of kick off a well, in very soft formation - can be used with MWD - safer to use SS
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Gilligan BHA
• Flexible Build-Up BHA • Flexible tubular inserted above NB Stabilizer • BUR’s of 6° - 11° / 100’ are possible – depends on flexibility of tubular. • Vital to take surveys at close intervals to track achieved BUR. • Common before advent of steerable motors as a method to perform a blind side track. 60 10/23/2009
Hole Opening BHA Hole Opener • BHA needs to be stabilized but limber • MWD – yes or no? • Cutter type – various available
Bull Nose • Length:7’ – 9’……size dependant
• Ported or non-ported? 61 10/23/2009
Under Reamer •Bi Center bits •“Ander reamer” – “Andergauge” •DBS NBR Near Bit Reamer – Halliburton Security •DBS URS Under Reamer Services – Halliburton Security •“Reamaster” (XTU) – Smith Services •RWD – Ream While Drilling – Baker Hughes Christensen
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Hole openers and “Anderreamers”
Tri Max Smith Quad BHI Security DBS “Anderreamer” Smith Rhino reamer
8 ½ - 9 7/8, 10 5/8, 12 ¼ 9 7/8 - 10 5/8 12 ¼ - 13 ½, 13 ¾, 14, 14 ¾ 14 ¾ - 17 17 ½ - 24
Considerations Shocks Hydraulics MWD signal
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Motor Design Considerations
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Settings of the motor Bend angle RPM restriction if too high a setting is selected The bend dictates the sliding dogleg capability
If it can give 7o/100ft then it will !!! Sleeve stabilizer position Motor body – bearing housing Drive shaft Slick Sleeve stabilizer size Housing 1/8” under gauge Drive shaft 1/16” under gauge 65 10/23/2009
Motor Stabilization Options
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RSS BHA
Note features
PDC
Bit Selection?
Rockbit
WOB requirements
Note features WOB requirements
Run BHA software Insert bit
RSS BHA design
Insert Camco Bias Unit Insert Camco Control Unit Insert Full Gauge Stab
DLS>3°/30 in
Yes
Insert flex
No Insert MWD Insert U/G Stab Insert DCs stabilised every 60 feet
Yes
DC?
Sufficient weight from WOB x buoyancy
No
No Insert HWDP Yes
No
Sufficient weight from WOB x buoyancy
Insert Jar / Acc above neutral points
Yes
Review RSS configuration / stab configuration
Insert HWPP for transition
Insert drill pipe available
Run tendency / prediction PowerPlan
Exit
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Yes
Model work?
No
BHA Design - Client’s expectations
Shocks and vibration management (CBT certification) Dog Leg capability (need to liaise with DE) Rate of penetration
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BHA Design – Key factors
Bit design Stabilizer Flex Hydraulics
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Bit design features Stability Minimize Shocks (Highest percentage, ref. FFM) Minimize vibration Minimize Stick slip
Steerability (around 5% failure in 2004 YTD) Gauge length Aggressive side cutting ability
Durability Shoe to TD
Rate of penetration 70 10/23/2009
Short gauge
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Example of “gauge” configurations Active Gauge
Dual Action Gauge
Steering Wheel Gauge
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Stabilized Control Collar (IBS or Sleeve)
Reducing stabiliser to bias unit spacing Reduced drop tendency in neutral, improved DLS / BUR Should allow lower bias settings, improve seal life Sleeve Left Hand Thread 73 10/23/2009
Stabilization Control Stabilizer Non magnetic melon shaped profile Spiral blade RAB (GVR) stabilizer Motor stabilizer (vorteX)
Control Collar IBS or sleeve type Reduces drop tendency in neutral: - Lower bias settings in soft formations - Improved seal life / reduced pad wear 74 10/23/2009
Flex Joints Flex joints are normally used on a profile requiring greater than 2°/100’ DLS (PD675) Downside: Assembly may be sensitive to changes in formation, esp. non-homogeneous rock or stringer zones Length, diameters & materials Non-mag / “flex joint”or short DC
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Dog Leg capability
Theoretical DLS Range: PD475: 0 to 8+ deg/100’ PD675: 0 to 5 deg/100’ (with flex up to 8 deg) PD900: 0 to 3 deg/100’ (with flex up to 5 deg) PD1100: 0 to 2 deg/100’ (with flex up to 4 deg)
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RSS Tip-Stabilizer Type and Placement Where is the good place for Stabilizer? a) Above Control Unit b) On the Control Unit c) It depends
Which Stab gauge is good? a) Full gauge b) Under gauge c) It depends
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PowerDrive vorteX BHA configurations * Bit – PowerDrive – X/O – Stab - Motor ? * Bit – PowerDrive – NMStab - Flex Joint – Motor ? (AIM) * Bit – PowerDrive – x/o - Motor (sleeve) Considerations Hydraulics, DLS Limitations of surface RPM PowerDrive 475 vorteX ? No E-Mag (C-Link ?) vorteX motor vs PowerPak (with 0° bent, kink) 78 10/23/2009
PowerDrive VorteX Applications Environmental (Noise reduction) Reduction of stick-slip Rig limitations (top drive rating – torque / RPM output) Improved drilling performance (ROP) Less casing wear Motor selection – requirement for low speed, high torque PowerEdge (no ABH, angular bearing assembly) GT option (700GT 7:8/ 962GT 7:8) used on most runs XP option has also been used (675XP 7:8) 79 10/23/2009
RSS-PD Xceed Looks and acts like a motor (No formation depended) 2 Sleeve-type spiral stabilizers -First Stabilizer 1/8 UG -Second Stabilizer ¼ UG BHA tendency is neutral Bi-center Bit 8 ½ x 9 1/4 can be used on regular CRS tool with both slick stabilizer 8 1/2 x 9 7/8 needs to be run with a special collar and steering section design
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Common BHA Problems 1. Formation Effects 2. Worn Bits 3. Accidental Side Track 4. Pinched Bit 5. Differential Sticking 6. Drilling Parameters
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