Contents
Introduction………………………………………………………………………………..04
Definition of Directional Drilling……………………………………………..…………..04
Description of Directional Drilling………………………………………………………..04
1-Directional Well Application…………………………………………………………....04
Sidetracking……………………………………………………………………..…04
Inaccessible Locations……………………………………………………………..05
Salt Dome Drilling…………………………………………………….…………..05
Fault Controlling…………………………………………………………………..06
Multiple Exploration Wells from A Single Wellbore……………………….…….06
Onshore Drilling to Offshore Locations…………………………………………..07
Offshore Multi-well Drilling………………………………………………………07
Relief Wells……………………………………………………………….……….08
Horizontal Wells…………………………………………………………………..08
Extended Reach Wells………………………………………………………….....09
Multilateral Wells………………………………………………….………………10
Short, Medium, and Long Radius Wells…………………………………..………10
2- Directional Well Profile……………………………………………………...…………11
Features of a Directional Well Profile………………………………………….....11
Kickoff Point (KOP)………………………………………………………………11
Well Inclination…………………………………………………………...……….11
End of Buildup (EOB)………………………………………………………….…12
Hold Angle…………………………………………………………………….…..12
Tangent Section…………………………………………………………………....13
Start of Drop……………………………………………………………………….13
End of Drop (EOD)…………………………………………..……………………14
Target Displacement………………………………………………………………14
Target Location……………………………………………………………………15
Drop Off Rate (DOR)……………………………………………………………...15
Buildup Rate (BUR)……………………………………………………………….16
Turn Rate…………………………………………………………………………..16
True Vertical Depth (TVD)………………………………………………………..16
Measured Depth (MD)…………………………………………………………….16
Horizontal Displacement (HD)……………………………………………………17
Vertical Section (VS)……………………………………………………………...17
Azimuth……………………………………………………………………………18
Quadrant…………………………………………………………………………...19
3- Types of Profiles………………………………………………………………………..19
Type 1 (Build and Hold)…………………………………………………………..19
Type II (Build, Hold and Drop)…………………………………….……………..20
Type III (Deep Kick-off and Build)…………………………………………...…..21
Horizontal Wells……………………………….………………………………….21
Horizontal Drain holes…………………………………………………………….22
4- Directional Well Planning………………………………………………………………22
Location ……………………………………..…………………………………….22
Target Size …………………………………………..…………………………….23
Cost versus Accuracy………………………………………….…………………..23
Good Communication …………………………………………...………………..23
Formation Characteristics…………………………………………………………23
Deflecting Tools Available……………….……………………………………….24
Location of Adjacent ………………………….………………………………….24
Choice of Build-up Rate………………………………….……………………….25
5-Types Of Directional Wells……………………………………..………………………25
Type I Well………………………………………………………..………………25
Type II Well…………….……………………………………………………….. 26
Type III Well ………………...……………………………………………………27
Type IV Wells ………………………..…………………………………………. 28
6- Drilling Tools & Deflection Methods…………………………………………………..29
6.1 Drilling Tools…………………………………….……………………………………30
Drill Collar (DC)………………………………..…………………………………30
Short Drill Collar (SDC)…………………………………………………………..30
Non-Magnetic Drill Collar (NMDC)…………………………..………………….30
Short Non-Magnetic Drill Collar (SNMDC)……………...………………………31
Float Sub……………………………………………………………….………….31
Bit Sub………………………………………………….………………………….31
Junk Sub………………………………………………………………………...…31
Extension Sub………………………………………………………….…………..32
Heavyweight Drill Pipe (HWDP)………………………………………………....32
Stabilizer…………………………………………………………………………...32
Welded-blade Stabilizer…………………………………………………………...32
Integral-blade Stabilizer (I.B.)…………………………………………………….33
Non-rotating Rubber Sleeve stabilizer…………………………………………….34
Replaceable Wear Pad stabilizer (RWP)…………………………………………..34
Underguage stabilizer………………………………………………………...……34
Roller Reamer……………………………………………………………………..35
Under Reamer……………………………………………………………………..35
String Reamer……………………………………………………………….……..36
Key-seat Wiper…………………………………………………………….………37
Turbine…………………………………………………………………………….37
Bent Sub…………………………………………………………………………...37
Orienting Sub……………………………………………………………………...38
Features of a Directional Well Profile………………………………………….….39
Hole Opener……………………………………………………………………….39
Bull nose…………………………………………………………………………...39
Section Mill………………………………………………………………………..39
Whip-stock………………………………………………………………………...40
Drilling Jars………………………………………………………………………..40
Shock Absorber/Shock Sub………………………………………………………..40
Rebel Tool…………………………………………………………………………41
6.2 Deflection Methods……………………………………………………………………42
Whip stock…………………………………………………………………………42
Jetting……………………………………………………………………………...43
PDM (or Turbine) With Bent Sub…………………………………………………44
Steerable Positive Displacement Motor…………………………………………...45
Specified Deflection Techniques………………………………………………….46
Curved Conductors………………………………………………………………..46
Slant Hole Drilling………………………………………………………………...47
Rotary Assembly…………………………………………………………………..48
Building Assembly………………………………………………………………...48
Holding Assemblies……………………………………………………………….49
Dropping Assemblies………………………………………………………..…….50
DIRECTIONAL DRILLING
Introduction
Directional drilling has become a very important tool in the development of oil and gas deposits. Current expenditures for hydrocarbon production have dictated the necessity of controlled directional drilling to a much larger extent than previously. Probably the most important aspect of controlled directional drilling is that it enables producers all over the world to develop subsurface deposits that could never be reached economically in any other manner. In this module a number of topics will be covered that must be understood by the directional driller. The various types of wells and applications of directional wells will be touched upon along with well profiles and well planning.
Definition of Directional Drilling
Controlled directional drilling is the science and art of deviating a wellbore along a planned course from a starting location to a target location, both defined with a given coordinate system.
Description of Directional Drilling
Drilling a directional well basically involves drilling a hole from one point in space (the surface location) to another point in space (the target) in such a way that the hole can then be used for its intended purpose. A typical directional well starts off with a vertical hole, then kicks off so that the bottom hole location may end up hundreds or thousands of feet or meters away from its starting point. With the use of directional drilling, several wells can be drilled into a reservoir from a single platform.
Directional Well Applications
1) Sidetracking
Sidetracking was the original directional drilling technique used to get past fish (obstructions). Oriented sidetracks, the most common type of sidetracking, are performed when there are unexpected changes in geology and obstructions in the path of the wellbore
2. Inaccessible Locations
Inaccessible locations such as targets located beneath cities, rivers or environmentally sensitive areas make it necessary to locate the drilling rig some distance away from the target.
3. Salt Dome Drilling
Salt domes have been found to be natural traps of hydrocarbons accumulating beneath the overhanging hard cap. A directional well is used to reach the trapped reservoir to prevent the problems associated with drilling a well through the salt formation.
4. Fault Controlling
Fault controlling is an application used to drill a directional well into faulted subsurface formations without crossing the fault line.
5 Multiple Exploration Wells from A Single Wellbore
Multiple exploration wells from a single wellbore use a single hole to drill multiple new wells by deviating away from the original well at a certain depth. It allows the exploration of structural locations without drilling another complete well.
6. Onshore Drilling to Offshore Locations
Onshore drilling takes place when a reservoir is located below large bodies of water that are within drilling reach of land. The wellheads are located on land, and the borehole is drilled directionally underneath the water to reach the reservoir. This technique saves money because land rigs are much cheaper than offshore rigs.
7. Offshore Multi well Drilling
Offshore multi well drilling is the most economical way to develop offshore fields. Several directional wells are drilled in "clusters" on a multi well offshore platform.
8 .Relief Wells
Relief wells are used to kill wells that are blowing by intercepting the borehole. A carefully planned directional well must be drilled with great precision to locate and intercept the blowing well borehole.
9. Horizontal Wells
Horizontal wells are used to intersect a producing formation horizontally to better produce the reservoir. Horizontal drilling increases the surface area of a producing formation. For
Example, a vertical well may give exposure to a reserve with a depth of 20 to 30 ft (6 to 10 m) while a horizontal well drilled into the same reservoir may give exposure to 2000 to
3000 ft (600 to 1000 m). Horizontal wells can make a platform profitable, where it was not previously.
10. Extended Reach Wells
Extended reach wells are drilled to reach reservoirs that have a horizontal displacement in excess of 16,400 ft (> 5,000
m) From the starting point.
11. Multilateral Wells
Multilateral wells have several wellbores running laterally and originating from one original hole.
12. Short, Medium, and Long Radius Wells
Short radius wells, typically re-entries of old vertical wells, have curves with a 143 ft (44 m) radius or smaller that cannot be drilled with conventional motors. They are used to isolate higher-/lower-pressured production zones or water sands without setting and cementing a liner. Medium radius wells have curves with a 200-500 ft (61-152 m) radius that can be drilled with conventional motors. Long radius wells have curves with a 750 ft (229 m) radius or larger that can also be drilled with conventional motors.
Directional Well Profiles
Features of a Directional Well Profile
A directional well profile is the planned well trajectory from the surface to the final drilling depth by projecting the wellbore onto two plotted planes. In order to determine the best geometric well profile from the surface to the bottom hole target, the following information must be known.
the position of the surface location,
the position of the target location, and
the true vertical depth (TVD).
A directional well profile is the planned well trajectory from the surface to the final drilling depth by projecting the wellbore onto two plotted planes. In order to determine the best geometric well profile from the surface to the bottom hole target, the following information must be known the position of the surface location, the position of the target location, and the true vertical depth (TVD).
Kickoff Point (KOP)
The kickoff point is the location at a given depth below the surface where the wellbore is deviated in a given direction.
Well Inclination
The well inclination is the angle by which the wellbore deviates from the vertical.
End of Buildup (EOB)
The end of buildup is the location where the wellbore has finished increasing.
Hold Angle
The hold angle occurs where the inclination of the borehole is held constant.
Tangent Section
The tangent section (hold section) occurs after a buildup where the inclination of the borehole is held constant for a certain distance. There could be an additional build or drop before reaching the target.
Start of Drop
The start of drop is the location where the wellbore starts dropping inclination.
End of Drop (EOD)
The end of drop is the location where the wellbore finishes dropping inclination.
.
Target Displacement
The target displacement is the lateral distance from the surface location to the target.
Target Location
The target location is a point defined in space by geographical coordinates at a given true vertical depth. A well profile could have multiple targets.
Drop Off Rate (DOR)
The drop off rate is the rate at which the inclination decreases. The rate is usually expressed in degrees per 100 ft or degrees per 30 m of the course length.
Buildup Rate (BUR)
The buildup rate is the change of inclination of a wellbore where the angle is increased. The rate is usually expressed in degrees per 100 ft or angular increase per 30 m of the measured depth.
Turn Rate
The turn rate determines the rate a well profile turns in azimuth direction. Usually expressed in degrees per 100 ft or degrees per 30m.
True Vertical Depth (TVD)
The true vertical depth of any point or station along a wellbore is the vertical distance from the well surface reference point to the station of interest.
Measured Depth (MD)
The measured depth of any point or station along a wellbore is the distance from the well surface reference point to the station of interest along the actual well path.
