Practical Directional Drilling
Problems and Solutions
Practical Directional Drilling
Problems and Solutions
At the end of this lecture, YOU should be able to:
1. List common problems encountered in directional drilling 2. Propose solutions to these problems
Problems and Solutions 1
Costs related to directional versus vertical well
Rule of thumb – 1.50 to 1.75 times the cost of vertical well Proper planning and communication is essential to reducing
costs costs
Problems and Solutions 2
Torque
Caused by dog-leg severity, keyseating, balled-up drilling
assemblies, poor mud properties and well path.
Some corrective measures are: use HWDP, minimize dog- Some corrective measures are: use HWDP, minimize
dog-leg severity, and maintain drill fluid properties (mud weight, viscosity, filtrate and lubricity).
Problems and Solutions 3
Drag - related to torque
Clean hole properly
Make short trips to reduce total drag (trip every ~300 mtrs of
drilled hole, or every ~18 hours of drilling time) drilled hole, or every ~18 hours of drilling time)
Optimize BHA design
Optimize drillstring design Use drilling fluid lubricants
Problems and Solutions 4
Dog legs - lead to torque
Shorten interval between surveys when drilling with limber
hookups. This takes more time to survey.
Do not assume that dog-leg is removed by reaming. Make Do not assume that dog-leg is removed by reaming. Make
sure by re-surveying at same depth.
Plug back and sidetrack well if an excessive dog-leg cannot
Problems and Solutions 5
Key seats - more problematic in soft formations
Keep dog-legs to minimum
Design well KOP either deeper in well or in firm formation
Use keyseat wipers (hard formations) and string reamers
Use keyseat wipers (hard formations) and string reamers
(soft formations)
Run stabilizer near top of drillcollars Make daily wiper trips
Problems and Solutions 6
Differential sticking (wall sticking) – a potential problem when drill string is stationary, for instance during surveys and sliding portion of motor runs
Add lubricant (oil, surfactant, gel, etc,) to the mud system
Minimize time pipe is stationary
Reduce wall contact area - Use HWDP and spiral DC
Use stabilizers to prevent wall contact
Problems and Solutions 7
Hydraulics
Reduce bit hydraulic energy while building angle in soft
formation
Control erosion with nozzle design and nozzle type selection Control erosion with nozzle design and nozzle type selection High annular velocities may erode hole while jetting
Do not circulate without moving location of pipe, avoid
keeping bit at same location while circulating especially at high flow rates
Problems and Solutions 8
Lateral drift
Normally influenced by bedding planes, hence use geologic
structural maps for pre-planning
Use true rolling-cone bit (zero offset) Use true rolling-cone bit (zero offset) Use rebel tool (azimuth control tool) Jet with packed BHA
Problems and Solutions 9
Small Hole and Ream Vs. One Pass
Larger holes are more difficult to control the direction Dog-legs for larger hole are often not uniform
Small hole needs to be opened up to larger hole and adds to
Small hole needs to be opened up to larger hole and adds to
drilling time
Two BHA assemblies may be needed adding to handling
time and tool rental
Problems and Solutions 10
Plan Vs Actual
Plan the well will a lead to the left so as to anticipate normal
right hand bit walk
Design left hand lead so that if no walk occurs, only one Design left hand lead so that if no walk occurs, only one
deflection tool run will bring it back to desired direction/inclination
Problems and Solutions 11
Weight on Bit and Rotary Speed
Variation is used to control angle & walk
Because WOB & RPM are reduced, this method is not
always conducive to maximum penetration rates always conducive to maximum penetration rates
Varying WOB or RPM may introduce doglegs
Plan to maximize ROP by designing for high WOB with
Problems and Solutions 12
Off-bottom Rotation
Creates a ledge and may lead to sidetrack Aggravates and initiates keyseating
Increases cyclic stress on drillstring and may lead to
Increases cyclic stress on drillstring and may lead to
drillstring fatigue failure
Unless pipe is reciprocated may lead to localized erosion
Problems and Solutions 13
Well Collision
Common consideration for multi-platform or drilling pads –
develop structural plots (spider diagram)
Project radius of uncertainty and traveling cylinder Project radius of uncertainty and traveling cylinder Curved conductors may be necessary
Magnetic interference very likely, use gyro orientation survey
and short course lengths between surveys
Problems and Solutions 14
Target Definition - Hard & Soft Lines
Soft lines ( e.g. target radius, target intersection requirement,
etc.) are preferred because hard lines cannot be changed, varied, or extended (lease or fixed areas). Select big target varied, or extended (lease or fixed areas). Select big target size
Problems and Solutions 15
Casing Wear
Use drillstring protectors on the drill string Slow rotary and tripping speeds
Monitor torque and drag in casing Monitor torque and drag in casing
Use ditch magnets to monitor wear rates Run casing inspection logs
Reduce low gravity solids content in mud
Directional Drilling
Problems and Solutions
Now, YOU should be able to:
1. List common problems encountered in directional drilling 2. Propose solutions to these problems
