Fig. 8.39: Bent sub unconstrained and constrained in a wellbore. Nonmagnetic Drill Collar Hole Orienting Sub Bent Sub Mud Motor Bent Sub Angle Bit is not necessarily equal to the bent sub angle, but it may be close in (a) above
Problem 1 Determine the effective bent sub response for a 1 1/2 o bent sub in a motor run where at 6,357’, = 1 o and is S85E and at 6,382, = 1 o and is S20E; the tool face is 160 o right of high side.
Solution to Problem 1 Calculate from Eq. 8.53: Dogleg severity:
Solution to Problem 1 - cont’d If the mud motor length is 25 ft from the bit face to the bent sub, the maximum angle change that could be reached if there are no restrictions is: The lower rate of build implies that the formation resisted the maximum rate of build by a factor of: An efficiency factor?
= Bent Sub Angle? Since the value of for any given run may differ from the bent sub angle, it should not surprise us if predicted = measured Let us look at some examples.
Fig. 8.40: Example of three jetting stops while trying to kick off and set the wellbore lead.
Jetted 7’ ’ Surv 1722’: S32W 2.25 o Orient S90E Final 1799’: S30E 2.75 o = -122 o Nozzle Orientation
Jetted 12’ ’ Surv 1814’ S20E 3.0 o Orient N80E Final 1877’ S36E 3.25 o = -80 o
Jetted 6’ ’ Surv 1877’ S36E 3.25 o Orient N70E Final 1940’ S66E 4.75 o = -74 o
Directional Drilling Measurements The trajectory of a wellbore is determined by the measurement of: inclination I direction A measured depth MD, L, L
Directional Drilling Measurements - cont’d A tool-face measurement is required to orient: a whipstock the large nozzle on a jetting bit a bent sub or bent housing
Directional Drilling Measurements - cont’d Tools available single-shot magnetic or gyroscopic multi-shot magnetic or gyroscopic magnetometers, accelerometers, MWD tools
Magnetic Single-Shot Instrument Records –inclination –direction –tool face position on sensitized paper or photographic film Inclination may be determined by –a float on a liquid –a pendulum
Magnetic Single-Shot Instrument Unit may be triggered by: –clock timer. –inertial timer (after stop). Unit may be dropped (pumped down) and later retrieved by wireline or the drillpipe.
Magnetic Single-Shot Instrument Single-shot instruments are used: –to monitor progress of directional- control well. –to monitor progress of deviation-control well. –to help orient tool face for trajectory change.
Magnetic Single-Shot Instrument - cont’d Procedure: –load film into instrument –activate timer (activate stopwatch) –make up the tool –drop the tool –retrieve tool (wireline or drillpipe)
Fig. 8.41: Schematic diagrams of magnetic single-shot angle-compass unit (courtesy Kuster Co.). Light Housing Center Post Float Fluid Reference Mark Main Frame Photographic Disc A o Angle-Compass Unit B o Angle-Compass Unit
Fig. 8.43: Pendulum suspended inclinometer and compass unit for a 0 to 17 o o singe- shot unit. 1. Pendulum 2. Circular Glass 3. Compass 4. Pressure equalization 5. Cover glass Indicated inclination 5 o. Direction of inclination N 45 degrees 0’ or azimuth 45 degrees.
Fig. 8.42: Single-shot film disks (courtesy of Kuster Co.). A/C UnitsPlumb-Bob UnitsIncl. Only Units Inclination Direction Tool Face Angle
Fig. 8.12: Pendulum assembly: a) plumb- bob angle unit b) drift arc inclinometer Pendulum Glass ring Piston (a)(b)
Fig. 8.13: Schematic drawing of magnetic single and multi-shot instruments. Hole direction with reference to Magnetic North N35 o W I = 5.5 o
Fig. 8.44: Cardan suspended compass and inclinometer for a single-shot 5 o to 90 o unit. Compass Inclination Scale
Fig. 8.45: Typical magnetic single-shot tool with landing sub. Rope Socket Swivel Stabilizer Stabilizer Fingers Wire Line Socket Overshot Bottom Landing Assembly Protective Case Mule Shoe Mandrel Bottom Hole Orienting Sub Orienting Anchor & Plug Takes time. Rig time is costly. Temperature limitation. May have to pump down.
Fig. 8.46: Typical single-shot operation. Free Falling to Bottom Tool seated Ready to be Dropped Retrieve single shot
Fig. 8.46: Typical single-shot operation. Compass Unit 3 min. Single Shot Free Falling in Mud to Bottom Non Magnetic Drill Collar Orienting Sub Sleeve *Single Shot Instruments are run on slickline if there is a mule shoe sub in the hole Single Shot Ready to be Dropped Timer On
Fig. 8.46: Typical single-shot operation. 3 min. Overshot Used to Fish Single Shot Tool seated in orienting sleeve or at stop taking picture Wireline unit to retrieve single shot 10 min.
Fig. 8.47: Arrangement of the mule shoe for orienting a mud motor. Fishing Neck Non Magnetic Collar Single Shot Mud Motor Top View Existing Centerline New Centerline Bent Sub Mule Shoe Key Position Mule Shoe Orienting Sub Orienting Sleeve Lined up with Bent Sub Direction of Tool Face Via Bent Sub
Magnetic Multishot Instruments Are capable of taking numerous survey records in one run. May be dropped down the drillpipe or run on wireline in open hole. The unit contains a watch that is spring wound and uses the power of the spring to operate a timer cam.
Fig. 8.48: Typical arrangement for landing a multi-shot instrument. Non-Magnetic Drill Collar(s) Compass Position Multi-shot Instrument Landing Plate
Fig. 8.49: Drop multi-shot survey instrument Angle Unit Rope Socket Bottom Landing Battery Case Battery Connector Bottom Shock Absorber Assembly Stabilizer with Rubber Pins Connector Shock Absorber Barrel Lower Ball Plug Aluminum Spacer Bar Protective Instrument Barrel Watch Assembly
Fig. 8.50: Views of the watch and camera unit of a typical multi-shot tool. Watch SectionMotor Light Switch Lever Geneva Gear Winding Stem Time Cycle Cam Watch Switch Supply Film Spool Takeup Film Spool Film Sprocket Motor Lever Switch Geneva Drive Wheel Assembly Knife Switch Terminal
Magnetic Multishot - cont’d The multishot tool is usually dropped down the drillpipe and landed in the nonmagnetic drill collar. During the trip out, a survey is taken every 90 ft, i.e. every stand.
Magnetic Multishot - cont’d More closely spaced stations could be obtained by stopping the pipe more often, and waiting for a picture. A stopwatch at the surface is synchronized with the instrument watch.
Synchronize with instrument watch by starting at the instant camera lights go on. Fig. 8.51: Use of the surface watch while running a magnetic multi-shot operation.
A. 10 seconds - Lights are on, exposing film B. 15 seconds - Delay before moving. This is an allowance for instrument watch lag during survey. Time Intervals:
C. 20 seconds - Instrument is idle allowing movement of drill string without affecting picture. Most moves require sufficient time for taking one or more shots while moving D.15 seconds - Minimum time for plumb bob and compass to settle for good picture, plus allowance for instrument gain during survey. Time Intervals - cont’d
Fig. 8.52b: Projection of one survey frame for determining inclination and direction.
Steering Tools Used with mud motors and bent sub Can either pull every stand or use a side entry sub for continuous drilling Mud Motor Bent Sub Mule Shoe Monel DC Probe Standard Measuring Cable
Gyroscopic Tools Non-magnetic drill collars used to prevent magnetic interference from drillstring Gyros used if magnetic interference is from non drillstring source