SlickBore BHA Analysis

SlickBore Output

The SlickBore® matched drilling system consists of a pin down motor, a bit, and associated modeling. Most of the problems we have with the SlickBore ® system are related to the bit design, the modeling and execution of the job.

The use of the long gauge bits generate higher bit torque than conventional bits and this represents one of the key issues for the bit design. As a result, the gauge OD is slightly undergauge (1/8” to 1/32”, depending on the formations, mud type and hole size. Full-gauge sleeves should never be used with SlickBore® system BHA’s.

SlickBore® Analysis

By reducing the Bit to Stb1 distance the effect is to increase the deflection of the BHA.

4.3’ Bit to Stb1

4.3’ Bit to Stb1

6.3’ Bit to Stb1

Bit to Stb1 Dist. EffectsO.52 and 0.64 – 0.12” increased deflection

Bit Tilt -0.056 to 0.086 Force Contact moved to the PAD from Stb1

BHA / BitOriented

6.3’ Bit to Stb1

4.3’ Bit to Stb1

Bit Tilt -0.056 to 0.086 and to 0.160 for SlickBore. Reduced bend to 0.78˚ 0.164

0.8’ Bit to Stb1SlickBore BHA

1.15˚ ABH 0.78˚ ABH

Note above the force interference at the

bit to keep the BHA centralized has the

ability to build

SlickBore®Analysis

To analysis the SlickBore BHA, various details need to be modified.

1. Line #1 Bit – SlickBore PDCa. OD = Motor Diameter – (6.75)b. ID = 2-3” (3.00)c. Gauge = Hole Size (8.5)d. Length = Hole Diameter (0.71)


2. Line #2 PDMa. 6.3/4” Sperrydrill …..b. OD = Motor Diameter – (6.75)c. ID should be automatic (4.465)d. Select detail Y/N – enter the standard

FTC bearing Ft – Bend to Btm Motor (6.69)

e. Check STAB with a distance of 0.1 to represent the Bit Sleeve with a blade OD of 1/16” UG (SlickBore Bit = Bit+Sleeve)

3. Bend angle would be set one setting below what was run previously or in an offset well. If no previous information is available then use one bend size less than you would use for the required build rate expected with a conventional steerable assembly.


4. Ideally the bit interference should be between 0 and 1. If it is too high the ABH will drag in the wellbore and the fulcrum at the heel of the bit will not react as required. The calculations are on pages C.1.20 and C.1.21 in the Sperrydrill® Technical Information Handbook

5. Select the second stabilizer and ensure the Blade Gauge is UG by 5-10% of the hole size 8.50” would be 8” - (8.00)

6. The second stabilizer can be entered into the BHA Detailed listing and therefore should be left blank in the Motor Configuration table. If it is in both tables, then a third stabilizer will appear in the calculations.


7. Set the inclination to 15˚, the Formation Index to 1.

8. Run the “Force Analysis” calculation, oriented – highside making sure the WOB and other parameters are realistic (as programmed in the drilling plan). Rerun later at higher values as required fir Inclination and Formation Index and see how these affect the results

SlickBore® Analysis - Force

9. The profile should show the BHA centered in the hole and no contact between the bend and the wellbore. The BHA should not exceed thewellbore. The black vertical “stabilizer” line in the graphic is the heel of the SlickBore® system bit (the fulcrum).


10.The bending moment will be high and concentrated at the bit sleeve, which is right where you want it to be. This is the force that makes steering of the SlickBore® system possible. Note also that there are no indications of anyabrupt changes in the bending forces over the rest of the BHA (apart from a deflection at the second motor top stabilizer) which is relatively relaxed.


11.The slope curve change at the bend should be nearly equally distributed across the zero point of the Y axis. If this shows a change in slope that is too negative, there is a serious bend or stabilization problem that needs to be addressed. Check the bit displacement and interference calculation.

12.Not repeat using the “Equilibrium Rate” calculation.

SlickBore® Analysis - Equilibrium

13. In most applications, the “Equilibrium Rate” will be near neutral, indicating neither a build or drop tendency while rotating. If a build or drop tendency while rotating is desirable, this is where you can make the necessary adjustments to “balance” the assembly. This BUR can most effectively be adjusted by making slight changes to the gauge and / or position of the second stabilizer – 8.0 to 8.1/4” changed build to drop.

SlickBore® Analysis - Equilibrium

14. Finally check the Oriented Highside build rates. These should be compared to build rates on previous runs and the Formation Index can then be changed to reflect this difference but remember this also affects the rotary rates and you may have to change the top stabilizer again. This is a repetitive system and it will take a number of iterations to complete your analysis. Once that is complete, you need to run Whirl and check Vibration.

SlickBore® Analysis – Force – 2 String Stbs

Do not use Full Gauge stabilizers. If an AGS is to be run above the mudmotor – run for retracted and expanded positions.

SlickBore® Analysis – Field Application1. Trust the Model

a) If a stabilizer – bend configuration models correctly, then run this assemblyb) Any time you change the BHA configuration, you must re-run the modelc) Small changes can create large changes in output and this is true in practice too.d) If you are limited by stabilizer placement, then model this to know what can be expected.

2. When kicking off be patienta) Low WOB and controlled drilling should be planned for the first 90-180 ft or so, to get the

assembly to establish its build tendency – this is true of all assemblies, not just SlickBore.b) Expect to see gradual increases in build tendency until it reaches Equilibrium around the 15-20

inclination range.3. Stabilizers

a) Straight bladed stabilizers should be avoided since they do not provide full diameter support for the BHA. The gaps between the blade create low spots especially when drilling in oriented mode and the DLS response not be planned.

b) Watermelon stile stabilizers are also not recommended as they induce whirl into the systemc) The preference is to use spiral integral bladed stabilizers to maximize the support of the BHA.

4. Bit Selectiona) Bit selection is critical. Maximize the number of blades on fixed cutter bits and reduce the

aggressiveness using smaller cutters – this will reduce bit bounce, whirl and vibration.b) Over aggressive bits will also cause toolface control issues. Work with SDBS to solve this.

5. Dimensional checksa) Double check the bit sleeve diameter – it should be 1/8 to 1/32” Undergauge (profiled). b) DO NOT RUN FULL GAUGE SLEEVES

SlickBore® Analysis – Post Well AnalysisPost Well analysis will provide valuable information on BHA performance. Review actual results against the plan and remodel the BHA and rerun.

Do not be in too much of a hurry to improve the bit with only one run – it is not economic to do so and adjusting the BHA may improve the performance without any changes to the bit. By changing the bit and the BHA you introduce too many variables on the next run. The bit should only be considered for modification if it is trashed or causes related problems with equipment due to vibration and high torque. Again small changes affect results but significantly increase costs and supply delays due to production times.

It may take a number of runs in a field to find the solution to the hole section and formation types. Once the model is calibrated for Formation Index and drilling parameters, adjustments to the stabilizers-bends will be more accurate.

Always remember SlickBore modeling must be performed for ALL planned runs: directional or vertical. Cutting corners only damages the reputation of the system which works well and is a “Game Changer”.

SlickBore BHA Analysis

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