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Transcript of Directional Drilling
Definition by Schulemberger
"The intentional deviation of a wellbore from the path it would naturally take."
Deflection Tools and Techniques
Positive Displacement Motors (PDM)
Multiple Wells from Offshore Structure
TYPES OF WELLS
Measured Depth (MD):
The distance measured along the actual course of the borehole from the surface reference point to the survey point.
True Vertical Depth (TVD):
The vertical distance from the depth reference level to a point on the borehole course.
The angle (in degrees) between the vertical and the well bore axis at a particular point.
The depth of the well in which the deflection tool is placed and the inclination is begun.
End of Build Up:
The location where the wellbore inclination has finished increasing.
The angle that occurs where the inclination of the wellbore is held constant.
The section between the end of build up and the drop-off, where the hold angle occurs.
The location where the wellbore starts dropping inclination.
End Of Drop (EOD):
The location where the wellbore finishes dropping inclination.
The lateral distance from the surface location to the target.
A point defined in space by geographical coordinates at a given TVD.
The angle in the horizontal plane measured from a fixed reference direction (such as True North), generally measured clockwise.
Build and Hold "J"
This type of directional well has one straight section, one build section and one tangent section straight to the target. It has a shallow kick-off point.
These slant wells are drilled where it is not desirable or possible to locate the surface location directly above the target.
There are two types of 'S' Wells
This type of well has a straight section, a build section, a tangent section and a drop section that reaches cero degrees of inclination, entering vertically to the target.
Is similar to the convention 'S' type, but in this type the drop section does not reach cero degrees. Instead it reaches certain angle and then maintains it, entering to the target.
Deep Kick-Off and Build
This type of well has a deep KOP and enters to the target with a build section. It may also have a short tangent section (optional).
These types of wells have a straight section, a build section, a target section, then another build section (most of the time), and a horizontal section.
This type of well is drilled from surface with an inclination degree between 45° and 90°, and requires an inclined derrick to work.
Basically the idea of downhole motors is to rotate the bit without necessarily rotating the whole drillstem.
A hydraulically driven downhole motor that uses the Moineau principle (a helical rotor with one or more lobes will rotate eccentrically when the stator contains more lobes than the rotor) to rotate the bit, independent of drill string rotation. The flow of the fluid transmits power allowing the assembly to rotate and turn the bit.
It allows fluid to fill the drill string while tripping in the hole and to drain while tripping out.
As mud is pumped through the motor, it fills the cavities between the dissimilar shapes of the rotor and stator. The rotor is forced to give way by turning or, in other words, is displaced (hence the name). It is the rotation of the rotor shaft which is eventually transmitted to the bit.
The stator will always have one more lobe than the rotor. Therefore motors will be described as 1/2, 3/4, 5/6 or 9/10 motors.
Connecting Rod Assemblies
Since the rotor is spiral shaped, it does not rotate concentrically, rather it traces a back and forth motion. This motion must be converted to a concentric motion to be transmitted to the bit via the drive sub. This is achieved by a connecting rod assembly.
These bearings support the concentrically rotating drive shaft against lateral loads. A typical positive displacement motor utilizes three sets of bearings attached to a drive shaft, but the number of these bearings will vary, depending on the size of the tool.
It has a series of rotors/stators (stages) connected to a shaft.As the drilling fluid is pumped through the turbine, the stators deflect the fluid against the rotors, forcing the rotors to rotate the drive shaft to which they are connected.
Downhole Motor with a Bent Sub
A bent sub is a short cylindrical device installed in the drill stem between the bottom drill collar and a downhole motor. Its purpose is to deflect the downhole motor off vertical to drill a directional hole. The 'dogleg' severity depends on the bent sub angle and the OD of the motor, drill collars in relation to the diameter of the hole, and also on the length of the motor.
Historically, it has always been possible to control the angle (inclination) of directional wells during rotary drilling by correct design of the assembly and use of suitable drilling parameters. However, the control of hole direction has traditionally been poor. Roller cone bits usually walk to the right, and directional control was formerly limited to using well-stabilized assemblies to reduce this tendency. Until the eighties it was standard practice to give wells a lead angle to the left of the proposal to compensate for this right hand walk.
Factors affecting Bit Trajectory
Gauge and placement of stabilizers
Diameter and length of drill collars
Weight on bit
Directional Control Principles
• The Fulcrum Principle is used to build angle (increase borehole inclination).
• The Stabilization Principle is used to hold (maintain) angle and direction.
• The Pendulum Principle is used to drop (reduce) angle.
An assembly with a full gauge near-bit stabilizer, followed by 40 to 120 feet of drill collars, before the first string stabilizer, or no string stabilizer at all, will build angle when weight-on bit is applied.
The collars above the near-bit stabilizer bend, partly due to their own weight and partly because of the applied WOB. The near-bit stabilizer acts as the pivot, or fulcrum, of a lever and the bit is pushed to the high side of the hole. The bit therefore drills a path which is gradually curving upwards.
The rate of build will increase by...
• Increasing the distance from the near-bit stabilizer to the first string stabilizer
• Increase in hole inclination
• Reduction of drill collar diameter
• Increase in weight on bit
• Reduction in rotary speed
• Reduction in flow rate (in soft formations)
Stabilization (Packed Hole) Principle
This principle states that if there are three stabilizers in quick succession behind the bit separated by short, stiff drill collar sections, then the three stabilizers will resist going around a curve and force the bit to drill a straight path.
Assemblies which utilize this principle are called packed hole assemblies and are used to drill the tangent sections of directional wells, maintaining angle and direction. High rotary speed (120-160+) will assist the tendency to drill straight.
The portion of the BHA from the bit to the first string stabilizer hangs like a pendulum and, because of its own weight, presses the bit towards the low side of the hole. The major design feature of a pendulum assembly is that there is either no near-bit stabilizer or an undergauge near- bit stabilizer. The length of collars from the bit to the first string stabilizer (the “pendulum”) must not be allowed to bend too much towards the low side of the hole.
It is recommended...
• The assembly should have two string stabilizers with the second stabilizer not more than 30 feet above the first.
• Initially use low WOB until the dropping tendency is established, then gradually increase bit weight until an acceptable penetration rate is achieved.
• Use high rotary speed, depending on bit type.
• If possible, do not plan drop sections in hard formations.
Standard Removable Whipstock
Mainly used to Kick of wells
The concave side holds and guides the assembly
A chisel point at the bottom prevents the tool from turning
Simple to use
Requires little maintenance
Has no temperature limitations
Number of trips
Produces a sudden deflection
(Severe dog leg)
It has the same functional principle as the standard removable one
Drilling mud flows to the bottom of the whipstock
It allows a more efficient cleaning, ensuring a clean seat for the tool
Permanent Casing Whipstock
Is designed to remain permanently in the well
A window is to be cut in the casing for a sidetrack
It has a packer and an aligning key which ensures seal and orientation of the whipstock
Orientate the packer and whipstock, settle in place
A starting mill cuts through the casing 2 ft of the window
A tungsten carbide or diamond bit drills the rest of the window
5 ft of formation is cut
A taper mill with a watermelon mill cleans the window
The assembly is changed over to the one which will be used to continue drilling
Advantages and Disadvantages
Is simple to use
Ideal for sidetracking
Requires several trips
Is not recommended if there is a considerable distance to drill below the sidetrack; Problems when trying to pull accessories back through the window
Formations soft enough to be eroded by the mud.
ROP of 80 ft/hr
Shallow, sandy formations
Adequate rig hydraulic HP.
Mud velocity of at least 500 ft/sec
Used in soft formations, mainly used to kick off wells
A cone can be replaced by a nozzle, it can use a very large one with two smaller ones, or it can block the flow of two jets
Orientate the large jet in the required direction
A controlled washout is effected
The drill string moves up and down (Without rotation) until several ft (3-8) have been made
A rotary table can turn a maximum of 15º left and right to enhance the operation
Continue drilling for 10 ft with 50% of circulation rate, WOB 40 - 45 Klb, RPM 60-70,this will guarantee that the assembly follows the trend established
Re-orientate the nozzle and start jetting
Repeat until sufficient angle has been built in the desired direction
The mud washes out the formation and creates a pocket
Once the drill string rotates and a higher WOB is applied, the bit works its way into the pocket (Path of least resistance)
The BHA bends and acts as a pivot or fulcrum, pushing the bit harder into the pocket
Simple and cheap
Dogleg is controlled with the ft jetted each time
Orientation is easy
There is no need for an special BHA
Only works in soft formations and shallow depths
Deviation is not a smooth continuous change
The normal practice is to jet a undergauge hole, and then open it to full gauge
Hostile Environment Logging (HEL)
Multi-Frequency Resistivity (MFR)
Measurement while drilling (MWD)
Logging while drilling (LWD)
Drilling on Gauge sub (DOG)
Bibliography and Webgraphy
Baker Hughes. (1995). Drilling Engineering Workbook. Houston, TX: Baker Hughes INTEQ.
Bourgoyne, A., Millheim, K., Chenevert, M., & Young, F. S. (1991). Applied Drilling Engineering. Richardson, TX: Society of Petroleum Engineers.
Single and Multishot
Magnetic Toolface (MTF) and Gravity Toolface (GTF)
A single shot is a magnetic instrument capable of one survey per trip, it identifies course and position in order to determine deviation; Is ideal when a survey is carried out periodically
A Multi shot is a magnetic instrument that can produce several surveys per trip, with a control on the frequency. Is ideal when doglegs have to be identified and when the position of the hole must be known
Method to obtain variables needed to plot the well path 3D (MD, Inclination, Direction
Most of the variables are obtained from MWD tools
Is best to have surveys from at least two different sources with different sensor types, such as magnetic and gyroscopic
Mechanical compass (floating device)
Inertial navigation systems (group of gyros)
As the measurements are taken, they must be transmitted to surface. This is done via:
Wireline: Employs an electrical cable to lower the tools and transmit data
Mud: Mud Pulse Telemetry (MPT), which modulates the flow of mud generating pulses that are detected by transducers at surface
Non magnetic material and tool that corrects earth's magnetic field effects and in drill collars allows measurements without magnetic interference. Magnetic instruments must be locate in non magnetic drill collars
TOTCO or totco barrel is a single-shot inclination indicator.
It consists of a mechanical timer and an angle unit. The timer is set assuming a descent rate of 300 ft/min that presses a calibrated paper disc against a pendulum which records the inclination
Tools that measure direction relative to the magnetic north are MTF, and can be corrected to a reference or geographical north. Usually MTF is used when the inclination is low (less than 5º)
If it is measured from the high side of the borehole in a plane perpendicular to the axis of the hole is a GTF
Sensor that provides formation resistivity measurements, it provides 12 independent resistivity measurements.
It can operate under high temperature, pressure and flow-rates
Can work using radio waves, MPT, or Wirleline
Evaluation of the wellbore including but not limited to:
Vertical and horizontal sections
Direction, Inclination, Azimuth
It can use radio waves, MPT, High-speed telemetry systems, acoustic systems, among others that provide fast information to surface
Guarantees the safety and trajectory of the operation
Measurements of the formation made while drilling, including but not limited to:
It can use electromagnetic,induction, acoustic and nuclear tools
The data is usually transmitted via MPT providing real-time information
Equipment designed to withstand harsh conditions such as extreme pressures and temperatures (More than 400 ºF and 20,000 PSI and deeper than 20,000 ft)
It allows operations of MWD and LWD to run smoothly under severe conditions
Tool used to deliver an impact load on a downhole component, especially if it's stuck.
It can be hydraulic or mechanical
It works as a hammer that stores kinetic energy and releases it as a strike, either up, down or both
Optimal to avoid stuck pipe and dogleg problems
Component used to stabilize the BHA, control deviation, avoid severe doglegs
The number of stabilizers on the BHA will determine the deviation:
Fulcrum (Build up angle): 1 or 2 (1 near bit and 1 optional string)
Packed Hole (Maintaining angle): At least 3
Pendulum (Dropping angle): 2 or 3 (1 optional near bit and 2 string)
Component that maintains gauge and removes ledges, avoiding stuck pipe situations
Usually located on top of LWD tools
Tool specially designed for directional operations that works as a near bit reamer so it can be placed between the bit and the motor, providing a smother build section
Doesn't needs moving parts, ensuring reliability
Used when maintaining the hole gauge is critical
It also works as a stabilizer, thus being ideal for packed-hole assemblies
(ROTARY STEERABLE SYSTEM)
A tool designed to drill directionally with continuous rotation from the surface, eliminating the need to slide a steerable motor. Rotary steerable systems typically are deployed when drilling directional, horizontal, or extended-reach wells.
Point The Bit
The point-the-bit system uses the same principle employed in the bent-housing motor systems. Point-the-bit technologies cause the direction of the bit to change relative to the rest of the tool by bending the main shaft running through it.
Push The Bit
The push-the-bit system uses the principle of applying side force to the bit, pushing it against the borehole wall to achieve the desired trajectory. Push-the-bit tools use pads on the outside of the tool which press against the well bore thereby causing the bit to press on the opposite side causing a direction change.
Curvature of a particularly abrupt crooked place in the well, expressed in degrees per 100 feet (#º/100ft) (Degrees per 30 mts).
Force necessary to move the drillstring along the wellbore
Force necessary to rotate the drillstring.
*Drag and torque changes result from frictional forces, so they should be carefully monitored as the well is drilled.
The act of measuring the characteristics of an area, and the results of such. This allows the measurement of the direction of the borehole as is drilled, including data such as: MD, TVD, Inclination, Azimuth, Dogleg severity, among others.
Survey that takes into account earth's curvature, allowing a higher accuracy of the measurements.