slide 1 introduction to directional drilling wayne longstreet drilling manager - dragon oil...

Introduction to

Directional Drilling

Wayne LongstreetDrilling Manager - Dragon Oil (Turkmenistan) Ltd

Wayne LongstreetDrilling Manager - Dragon Oil (Turkmenistan) Ltd

Objective of Directional Drilling

Controlled directional drilling is

the science of deviating a

wellbore along a planned course

to a subsurface

target whose location

is a given lateral

distance and direction

from the vertical.

Historical Background

• Originally only as a remedial operation.

• Now primarily a reservoir optimization tool.

• First well surveying in 1920’s in Oklahoma. Acid Bottle Inclinometer.

• 1929 a directional inclinometer with magnetic needle first used. Acid bottle technique proved to have error margin of @10 degrees (low).

Historical Background (cont’d)

• As more accurate survey tools developed, it was found most boreholes were “crooked”.

• Thus the emerging science of geology as given a boost when it was realized that the measured depth of producing zones was in many cases different from the vertical depth.

Historical background (cont’d)

• 1930’s saw the first controlled directional well drilled in Huntington Beach, California. 1933 used to drill under Sunnyside Cemetery in Long Beach.

• 1934 first relief well drilled in Conroe, Texas.

Historical background (cont’d)

• Today the technology incorporates:

Horizontal, EM-MWD, SAG-D, Multi-Laterals,

Extended Reach Drilling, Downhole

Adjustable Gauge Stabilizers, Downhole

Adjustable Motors, Bicentric Bits, 3D Wells,

Underbalanced Wells, River Crossings, CTU

Drilling.

Reasons for Drilling Directional Wells

Reasons for Drilling Directional Wells

Relief Wells

Faulted Formations

Multiple Wells from a Single Structure

Reach Inaccessible Locations

Straight Hole Control & Sidetracking

Horizontal and Multi-Laterals

Steam Assisted Gravity Drainage

Up and Down Dip Laterals

Draining Multiple Reservoirs

More Efficient Drainage of a Single Reservoir

Geological Considerations

• Knowledge of the local geology is essential to the directional driller.

Where Under theEarth Are We?

Where Under theEarth Are We?

Surveying

• Regardless of the type of survey instrument (single-shot, multishot, steering tool, SRO Gyro, MWD, EM-

MWD) three pieces of information are known.

– Survey Measured Depth.

– Borehole Inclination.

– Borehole Azimuth (corrected for true north).

Directional Surveying Permits

• The determination of the bottomhole location

relative to the surface location or another

reference system.

• The location of excessive doglegs or hole

curvature.

• The monitoring of inclination and azimuth

during drilling.

• The orientation of deflection tools.

Survey Calculation Methods

• Average Angle

• Radius of Curvature.

• Minimum Radius of Curvature.

Average Angle

• Calculates the average of the angles at the top and bottom of the course section and assumes this to be the inclination and direction of the wellbore.

• Oldest and least accurate method.

• Easiest to calculate by hand.

• Accurate when BUR is small and survey stations are close together.

Radius of Curvature

• Each course length is defined by points at the top and bottom, and the wellbore is assumed to be curved in either or both the vertical and horizontal projections.

• More complex calculations than average angle.

• Accurate when stations are far apart with higher rates of curvature.

Minimum Radius of Curvature

• Projects the actual dogleg and accounts for the severity of the dogleg on the drillstring.

• Most accurate method of calculation in use today.

• The use of computers and programmable calculators have made this the only real tool used today.

Radius of Uncertainty

• All tools have a range of accuracy.

• The assumption is made that errors will average out, but this still leaves us with a cone of potential error.

• Critical in thin sections and extended horizontal wells.

• Use of LWD, Geosteering, and geology help the directional driller.

Relative Accuracy of Methods

CalculationMethod

Error on TVD(ft)

Error onDisplacement

Tangential -25.38 +43.09Balanced Tangential -0.38 -0.21Average Angle +0.19 +0.11Radius of Curvature 0.00 0.00Minimum Radius 0.00 0.00Mercury (STL = 15’) -0.37 -0.04

The Earth’s Magnetic Field

• Theory #1: Rotation of the earth’s mantle in relation to the liquid core is thought to produce electrical currents.

• Theory #2: The internal circulation currents (similar to phenomenon observed at the periphery of the sun) of the liquid iron in the earth’s core acts as the source according to the principle of a self-excited dynamo.

Magnetic Declination

• The angle between magnetic north and geographic north (true north) is defined as the angle of declination.

• All surveys are converted to true north.

• Angles of declination to the west of true north can be written as negative numbers, to the east as positive numbers.

Visual

True NorthMagnetic North

Angle ofDeclination

Magnetic Interference

• Caused by:

– Drill String.

– Fish left in hole.

– Nearby casing.

– Geology (Iron Pyrite, Hematite)

– Magnetic “hot spot” in Drill Collar.

– Fluctuations in the earth’s magnetic field. (minor)

Minimizing Drill String Interference

• Eliminate magnetism by using “non-mag” collars (monel).

– The connection area can be magnetized due to mechanical torque. (azimuth errors in 10’s of degrees) Never space within 2’ of connection.

– Do not space in the center. Collars are bored from both ends leaving a ridge in center and potential magnetic hot spot.

Drill String Interference (cont’d)

• Non-mag stabilizers are magnetic near the blades (hard facing can be very magnetic).

• Amount of non-mag BHA is affected by:

– Latitude.

– Hole Inclination.

– Distance from North/South hole azimuth.

– Location (Alaska has used as much as 165 ft above magnetometer).

True Vertical Depth vs Measured Depth

MD

TVD

Vertical Section and Closure

• VS is the length of the horizontal

displacement defined by it’s azimuth in

relation to the target.

• Closure is the length of the horizontal

displacement passing through the survey

point.

Azimuth

• Wellbore direction measured in the

horizontal plane and expressed in degrees

from the North direction starting at 0 and

continuing clockwise to 360.

Dog Leg Severity

• AKA BUR.

• Expressed in degrees per unit of length.

Basic Well PlanningBasic Well Planning

Defining Objectives

• Careful planning is essential for success.

• Each well will have specific objectives defined by the reservoir or business units.

• The design must be tailored to meet all of the objectives.

Location

• DD involves drilling a hole from one point in space (surface location) to another point in space (target).

• Local coordinate system must be known so the target can be accurately correlated to the target.

• Most directional plans will use wellhead location as 0.

Target Size

• During drilling the trajectory is constantly monitored in relation to the target.

• Costly decisions are constantly being made to ensure that the well objectives are met.

• Today’s technology allows us to drill extremely accurate wells.

• Cost of the well is largely dependent upon accuracy required.

Cost vs Accuracy

• Operators often adopt arbitrary target sizes or tolerances which do not reflect the geological realities of the reservoir.

• Many needless correction runs have been made.

• Hard Boundaries must be clearly defined. Legal limits, fault lines, pinch outs.

• Communication and Team Work required.

Wellbore Profile

• Given surface location, target location, target tvd, and rectangular coordinates, it is possible to determine the geometric well profile from surface to bottomhole target.

• General directional well types:

– Straight, Build and Hold, “S” Wells, Slant Wells, Horizontal, and Multi-Lateral.

Determining KOP

• Kick Off Point is the depth at which the well will be deviated off the vertical.

• Selection of KOP is made by considering the geometrical wellpath and geological characteristics.

• Optimum inclination is determined by maximum permissible BUR and location of the target.

Determining Build & Drop Rates

• Maximum permissible build/drop rate is determined by:

– Total depth of well, and hole size.

– Torque & Drag limitations. High DLS results in higher T&D except in horizontal wells.

– Geology - high bur’s not always possible in soft formations.

– Limitations of tools, casing, drill strings.

Types of Directional Wells

• Build and Hold

• “S” Wells

• Slant Wells

• Horizontal Wells

• Multi-Laterals

Anti-Collision

• As platform and pad drilling becomes more popular anti-collision planning is critical.

• Radius of uncertainty.

• Lead angle for rotary drilling.

• Accurate well plan map essential.

Survey ToolsSurvey Tools

Steering Tools

• Continuous readout when drilling without rotation. Some available now that will allow slow rotation - unreliable.

• Jointed pipe operations require a “wet connect” system.

• Wet connects are unreliable and time consuming.

• System of choice for coil drilling.

Magnetic Single & Multi Shots

• Camera or Electronic (digital).

• Very Accurate.

• Still the basic surveying tool.

• Multi-shot surveys used to legally confirm open hole wells drilled with MWD. Pump down - time out.

Gyroscopes (Gyros)

• Rate Integrating Gyro (North Seeking) most common today.

• Very accurate.

• Used to legally confirm wellbore location of cased holes.

• Most common gyro errors are caused by initial alignment or drift.

Gyro Drift

• Drift values may range as follows:

– 0.5 to 1 degree/min for cheap gyros (toys).

– A few degrees per hour for directional gyros.

– 1/100th degree per hour for inertial gyros using gimbal flotation.

– 1/1000 degree per hour for some inertial gyros with spherical spinning rotors, supported by electrical fields. Used in space flight.

Mud Pulse MWD

• Use coded mud pulses to transmit tool data to surface in digital (binary) form.

• Pulses are converted to electrical energy by a transducer at surface and decoded by computer.

• Three types: Negative Pulse, Positive Pulse, Standing Wave Generator.

EM - MWD

• Uses the same triaxial inclinometers and triaxial magnetometers as conventional MWD.

• Transmits data to surface using Electro-magnetic telemetry.

• Dependent on depth and formation resistivity.

• Two commercial systems available.

Directional Drilling Tools

Directional Drilling Tools

Spiral Drill Collars

• Spiral grooves reduce the wall contact by 40% with a weight reduction of only 4%

• Reduces chances of becoming differentially stuck.

Non-Magnetic Drill Collars

• Usually flush, not spiraled.

• Made from high quality stainless steel.

HWDP

• Less rigid than drill collars.

• More common in the modern era of higher build rates and horizontal wells.

Stabilizers

• Indispensable part of rotary directional BHA’s.

• Non-rotating styles available,

Downhole Adjustable Stabilizers

• Essential for extended reach directional drilling.

• Adjustable by changing pump pressure or by cycling pumps.

Roller Reamer

• Designed to maintain hole gauge.

• Either 3 point or 6 point.

• Near bit roller reamers help prolong bit life, without adding torque associated with near bit stabilizers.

Underreamers & Hole Openers

• Used to wipe out bridges and keyseats, opening directional pilot holes, opening holes for casing, drilling out skin damage.

• Underreamer is hydraulically operated.

Keyseat Wiper

• Run between the top drill collar and the drill pipe.

• Greater diameter than the DC’s.

• If stuck, release, jar out, rotate and back ream to eliminate keyseat.

Bent Sub

• Run on top of a straight motor.

• Not in common use after the advent of steerable assemblies

• If bored for mule shoe it becomes an orienting sub.

Steerable Motor

• Most common tool in use today.

• Versatile. Rotary or slide drilling.

• Saves many trips for BHA changes experienced in the past.

Motor Assembly Cross Section

Dump Valve Assembly

Power Section Assembly

Surface Adjustable Bend

Bearing Assembly

Deflection MethodsDeflection Methods

Whipstocks

• Most commonly used in re-entries.

• Controllable and versatile.

Jetting

• Used in soft formations.

• Erratic results and severe doglegs.

• Not in common use today.

Bent Sub-Straight Motor

• Not commonly used today, since the advent of steerable assemblies.

• Good for low build rates.

• Non-rotatable.

Steerable Assemblies

• Very versatile and controllable.

• Modern method of directional drilling.

• Motor bend less than 2 degrees.

• Offset pads are run for high build rates.

slide 1 introduction to directional drilling wayne longstreet drilling manager - dragon oil...

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