2-Well Control & Directional Drilling
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Transcript of 2-Well Control & Directional Drilling
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FORMATION PRESSURE,
WELL CONTROL &DIRECTIONAL DRILLING
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Pressure Relations• Overburden Pressure
– Total weight of the rock and fluid above the depth of material (total weight of material)
– Assume overburden pressure is 1psi/ft
• Formation Pressure
- The pressure of the fluid (Oil/gas/water) existing within thepore space of a rock formation. Also called Rock orReservoir pressure
Formation Pressure Classification
• Normal pressure
• Subnormal pressure
• Abnormal pressure
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Formation Pressure Classification
• Normal Pressure
– Hydrostatic pressure exerted by all fluids in the formation
above a depth of interest.• Gulf of Mexico = 0.465 psi/ft
• Niger Delta = 0.442 psi/ft
• Subnormal Pressure
– Pressure that is lower than the actual pressure expected inthe area
Problems of subnormal pressure
– Lost Circulation
– Pipe stickingReasons for Subnormal Pressure
– Tectonic Movement
– Depletion Reservoir
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Formation Pressure Classification• Abnormal Pressure
–
Pressure gradient is greater than expected/actualpressure in that area
Problems of Abnormal Pressure
– Kick
– Blowout
Reasons For Abnormal Pressure
– Earthquakes
–
Tectonic movements – Stresses in the subsurface
– Casing leakage in nearby area
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Importance of Formation Pressure
determination
• Essential for proper well planning and drillingpractises
• Lessens the frequency and severity of kicks
and blowouts• Reduces differential pipe sticking
• Maximizes Penetration rate
• Reduces formation damage
• Minimizes drilling cost
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Formation Fracture Gradient• The pressure at which an increase in the mud
will fracture the formation.
Reasons for Determining Formation Fracture Pressure
• Minimizes or avoids lost circulation problem
• Proper selection of casing seat depth (casing shoe)
* Field Determination – Leak-off test or Pressure
Integrity Test
* Leakoff Pressure – The point at which an increase inpressure pump into the well will tear and there will a
decrease in pressure
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WELL CONTROL
•
Kick : It is an flux of formation fluids into theborehole that causes an unequal volume of
drilling fluids to be displaced from the drilling
hole.
• Blow out: It is an uncontrolled flow of
formation fluid from the borehole
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STAGES OF WELL CONTROL• Primary control
– The pressure exerted by drilling fluid to hold backformation fluid from entering the borehole beforecasing
• Secondary control
– It arises from the failure from primary control – Surface equipment is closed to stop further entry
of formation fluids. Use BOP
• Tertiary control
– Techniques to control blow-out when it hasoccurred
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CAUSES OF KICK• Reduction on the mud hydrostatics which could arise as
failure to fill hole during pull-out
•
Drop in level of mud weight in the hole• Low density of formation fluids being swabbed in during
tripping
SWABBING FACTORS• Pulling too fast
• High viscosity mud
• Small collar to hole clearance
• Balling up of bit
• Increased in formation pressure
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KICK WARNING SIGNS• Improper fillup or displacement during trips
• Connection gas (gas caught mud)
• Increased drill rate
• Flowline mud temperature increase
•
Increased drillstring torque&drag• Increased number and quantity of cutting
• Decreasing shale density
• Lost circulation
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SURFACE KICK INDICATOR• Excess flow from the well when tripping
• Return flow rate increase when pumping
• Pit gain
• Drilling break
• Flow from the well when pumps are shutoff
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KILL METHODS
• Driller’s method
• Wait and weight method• Concurrent method
• Volumetric method
SHUTTING THE WELL
– Any further influx of formation fluid into the well
to be stopped
– To determine the pressure of the formation fluidso that the well can be killed with a heavier mud.
– This is done using BOP
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DIRECTIONAL DRILLING
•This is the process of directing the wellborealong a specific trajectory to reach a specific
depth.
• Deviation control is the process of keeping the
wellbore contained within prescribed limit
relative to inclination angle and the horizontalextension from the vertical.
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DIRECTIONAL WELL• Long radius well
–
Well achieves a large horizontal displacementbefore reaching the target.
– Inclination angle - 2o – 6o/100’
– Radius – 1000 – 3000’
• Medium radius well
- Well turns from vertical to horizontal at
- Inclination angle – 8o – 20o/100’
- Radius – 285 – 700’
- Most commonly used because most tools can pass throughit and very effective for horizontal drilling
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DIRECTIONAL WELL
•
Short radius wells – Inclination angle – 1.5 – 3o/ft
– Can reach 90o in 20 – 60’ of hole
–
Horizontal length are limited to few hundred feet – There are difficulties to pass completion tools
through the tight radius
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DEFINITIONS
• Measured depth (MD) :
– Actual drill string measurement
• Drift/inclination angle:
- Deviation from vertical in degrees
• Kick off point: – Well depth at which inclination is initiated
• Build Section:
- Deviated length of the well from the kick off point
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DEFINITIONS
• Build up rate:
- Rate at which the well deviates
• Tangent
- Length of the straight section of the well after thebuild section
• True vertical depth – The true vertical depth as calculated from the directional
survey
• Azimuth
- Direction of the well with respect to the true north
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APPLICATIONS OF DIRECTIONAL DRILLING
• Side tracking
• Inaccessible locations
• Fault control
• Multi Exploration wells from single wellbore
• Onshore drilling to offshore location
• Relief well
•
Extended reach wells• Offshore multi well drilling
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DIRECTIONAL WELL PLANNING
• Factors consider
– Design trajectory
– Geology of the area
– Bottom hole assemblies
• Well Trajectories:
– Build and hold
– Build hold and drop (“S” type)
– Modified “S”
– Continous build
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DEFECTION TOOLSDrill string device that causes the bit to drill at an
angle to the existing hole
• Badger Bit
– Technique uses the fluid power direct through an enlarged
bit nozzle
– Used in soft formation and requires close control
• Whip Stock
- Steel wedge which is run in hole and set at the kick off
point- Wedge makes the deflection in the required direction
- Once deflection is made, whipstock is retrieved and hole
reamed to full guage
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DEFECTION TOOLS• Rebel Tool
– Designed to make lateral push to either left or right
ADVANTAGES
- Makes gradual change in direction
- Allows normal drilling to continue
- Cheaper than using down hole motor
- Bent Sub- Short length of collar size pipe specially designed so that the axis of
the lower connection is offset from the vertical
- Available in ranges 1 – 3o
• Navigation Sub (Steerable system)• Standard mud motor converted to steerable motor by tilting the bit
at a predetermined angle (Positive displacement motor)
• Ensures deflection forces are applied to the face of the bit.
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HORIZONTAL DRILLING•
Refers to well at 90o
to the vertical (parallel tobedding plane)
• A special aspect of directional drilling
•
HD is a procedure for drilling and completingoil and gas well with improved productivity
MAJOR REASON FOR HORIZONTAL DRILLING
•
Increase rate of return on investment (bettereconomics)
• Productivity increase
C O /C S C O O
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APPLICATION/CANDIDATE SELECTION OF
HORIZONTAL WELLS
• Gas or water coning
• Tight Reservoirs
• Inaccessible reservoirs
• Heavy oil recovery
• Thin reservoir
• Reduced number of platforms and wells
needed to develop a field and better coverageof the reservoir from existing platform
O S
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LIMITATIONS
• Only one payzone can be drained perhorizontal section
• Cost 1.4 – 3 times vertical wells
• High production related problems
• Well spacing
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DESIGN FACTORS
• Rig sizing
• Drill string capacity• Directional well planning
• Plan for drilling hydraulics (hole cleaning, flow rate,rheology)
• Tortuosity consideration
– Hole drag & torque• Solid control
• Casing consideration – Geology at the point of target
– Interference with other wells
– Torque and drag as it affects casing
– Wear consideration and bending stress