Drilling with a Bi Center drill bit is similar to that of a conventional PDC drill bit, but certain steps must be undertaken to properly prepare and operate the Bi Center drill bit.
First and foremost is preplanning of the well with all concerned parties. Depending on the application, this can involve numerous service company personnel with the Operator. Items of importance are:
- Hydraulic Properties (See Also Our Drilling Hydraulics Guide )
- Length / depth of Interval
- Directional objectives
- Drilling Fluids
- Drill String Stabilization / Bottom Hole Assembly Components
- Casing design / objectives
- Drilling modes – Bottom hole Assembly Types – Positive Displacement Motor (PDM) – Non-rotary Steerable System – Rotary Steerable System
- An understanding of how the Bi Center operates and enlarges the wellbore
All of these items must be discussed and agreed upon before the application of a Bi Center drill bit down hole.
Preparation At Jobsite
- Casing Tally Preparations & Excel Sheets Download
- Drill Pipe Washout Operations & Calculations Sheet
- Casing Repair In Operations & Procedure
- Casing Patch Types And Operations Full Guide
- Coiled Tubing Complete Guide
Steps Prior to Making Up Bi Center Drill Bits
- Hydraulic calculations must be performed to optimize the Bi Center performance.
- Bottom hole assembly must be agreed upon with well objectives.This is especially important when drilling with a PDM.
- Previous bits must be inspected for gage wear, broken teeth, or junk damage (See also Our Bit grading Guide). If any previous bit is under gage, then a reaming operation trip (check also: Tripping pipe procedures) must be done to insure a full gage hole. Reaming with a Bi Center bit is not advisable, due to the design characteristics of the Bi Center drill bit.
Making Up the Bi Center Drill Bit
- Rig floor handling of a Bi Center drill bit is similar to that of a conventional PDC drill bit. Under no circumstances should the Bi Center drill bit be placed on the steel floor. Use a wooden pad or rubber mat. Damage to the PDC cutters could occur and hinder performance if placed on the metal floor. Also see SPE/IADC paper no. 16144 for bit handling and operation.
- Locate the bit breaker and attach to the Bi Center drill bit. Engage latch on bit breaker and carefully lower the Bi Center drill bit with bit breaker into the rotary table. Try to avoid any contact of the PDC cutters with the rotary table. Position the bit breaker so that the open end of the breaker is opposite the make-up line.
- Clean and dope the pin.
- Lower the drill string to the top of the pin and engage threads.
- Make-up the bit to the same recommended torque as that of the drill collars directly above the bit.
- Remove bit breaker and carefully lower the bit and drill string through rotary table.
- Guide the bit and drill string through the blowout preventers and wellhead. The bit should not take any weight or be obstructed in any way.
- Trip slowly through casing shoes, liner hangers, Ledges & Doglegs or tight spots.
- When filling drill pipe (when a PDM is attached), reduce flow to a minimum to avoid rotation of the motor.
Drill Out Recommendations
- When drilling out casing shoe joints with PDC bits, use only PDC Compatible Float Shoe & casing liner (One of Types Of Casing) Equipment. Non-rotating cementing plugs are recommended as a way to prevent plug rotation during drill out.
- As a general rule the following should be adhered to as it will help prevent bit damage during the drill out.:
- While drilling cement, WOB to be kept between 2 and 8 thousand pounds. While drilling any float, liner or shoe equipment, ROP should be kept to a maximum of 3 feet per hour.
- Avoid sudden impact with the various components.
- It is advisable to maintain as minimal amount of WOB to drill out the cement and float equipment. Adhering to this procedure
Problems Inside Casing
Any problems encountered inside casing should be handled by reciprocating while continuing circulation and rotation to help clear debris from the bit. Maintain the same bit speed during this operation. Whenever penetration stops prematurely, repeat this step until penetration resumes. This step is especially helpful in removing cementing plug wipers as they are drilled up.
Drill Pipe Jumps
If the drill pipe and/or rotary table should start to jump, back-lash or act erratically, temporarily change one or more of the following drill out parameters: weight-on-bit, circulation rate on bit speed. (It is important to maintain a certain bit speed to ensure cutter depth of cut.)
At the current PDC bit Technology Level and a normal cement job, drill outs should take approximately two (2) to three (3) hours.
If the penetration rate ceases and cannot be reinstated using the above procedures, it would be advisable to recover the bit for inspection.
PDC/CSD Inside Pipe
|Cutter Size||Depth of cut||Rotary Min. RPM||Motor & Rotary Rotary/ Min. Mtr. / Min. Bit|
|3/8” – 8mm||.15”||140||40-60 / 140 / 180|
|1/2” – 13mm||.20”||100||40-60 / 130 / 170|
|3/4” – 19mm||.30”||80||40-60 / 120 / 160|
PDC/Bi Center PDC Bit Break-In in Formation
- Circulating to bottom is preferable prior to tagging bottom. The pilot bit must be in contact with the bottom of the hole so that it can be anchored to the formation and the reamer section can pivot around the wellbore and enlarge the hole once rotation is started.
- Use low weight on bit (drilling conditions dictate) and 80 to 100 rpm on rotary applications and 30 to 60 rotary on motor applications with full flow rates to establish a new bottom hole patterns.
- Record pump strokes and standpipe pressure and compare with expected vs. actual hydraulics.
- Slowly break the bit in, drilling at least three (3) feet in this mannar.
- Increase rotary speeds and add weight in 2,000 pound increments to determine the optimum drilling weight on bit.
- Perform drill off tests to determine optimum drilling parameters. Care should be taken with Bi- Center drill bits of large diameters in determining maximum rpm to avoid heat damage to the reamer section. (formation hardness dictates) If in doubt, contact your local DPI representative for recommendations.
- Before and after making connections, observe the following guidelines:
- Check pump strokes and standpipe pressure.
- After connections, add weight slowly to attain the previous weight on bit and maintain previous parameters.
- Rotary and weight on bit parameters should be adjusted to maintain optimum drilling parameters as formation changes, directional requirements and hole conditions. See also (Drill Off Test Procedure)
PDC / Bi Center in Formation
|Cutter Size||Depth of cut||Rotary Min. RPM||Motor & Rotary Rotary/ Min. Mtr. / Min. Bit|
|3/8” – 8mm||.15”||140||30-140 / 140 / 170|
|1/2” – 13mm||.20”||110||30-140 / 130 / 160|
|3/4” – 19mm||.30”||100||30-140 / 120 / 150|
- Reaming long sections of undergage hole is not recommended, but has been accomplished successfully with varying degrees of damage to the bit.
- If reaming is absolutely necessary, observe the following guidelines:
Without a Mud Motor
- Ream with full flow.
- Use 40 to 60 RPM and 2,000 to 4,000 lbs. weight on bit.
- Ream slowly and avoid high torque.
With a Mud Motor
- Ream with full flow.
- Use 20 to 40 RPM in low dogleg situations, use 20 to 40 RPM.
- In high dogleg situations keep tool face aligned to hole direction and do not rotate.
- For either case, use only 2,000 to 4,000 lbs. weight on bit and ream slowly to avoid high torque and possible sidetracking of hole (check also: sidetracking well).
Guidelines To Prevent Bi Center Drill Bit Balling
Bit Balling is a serious problem that may cause pulling out of holes and waste a lot of the rig time, especially in high depth wells.
- Find out if there were any previous tight spots. If so, circulate with as much flow as possible through these intervals.
- Establish new bottom hole pattern.
- In sticky (Gumbo) type formations, keep the pumps on at full throttle whenever the drill string is moving (connections and short trips).
- Pump Low/High (Thin/Thick) viscosity sweeps as necessary to keep well bore clean of cuttings (especially true when drilling with Bi Center drill bits).
- Keep weight on bit constant; don’t let the weight drill off. Avoid unnecessary fluctuations of drilling weight. A constant-steady feed of weight to bit is preferable to the drilling methods used with roller cone drill bits.
- After connections and short trips, proceed to bottom with caution. Avoid spudding of the bit. Again, make sure the pumps are at full throttle when encountering the bottom of the hole. Dropping the kelly quickly and then stopping the drill string suddenly can cause the bit to hit bottom and damaged or balled due to pipe stretch.
- Review previous offset bit records, morning reports, mud logs and other related information to locate sticky / balling intervals.
- Optimize hydraulics to provide maximum flow rate. Changing of liners to increase available standpipe pressure, usage of a rotor nozzle with a motor, larger drill pipe O.D., minimize number of drill collars design (increase heavy weight drill pipe) are possible alternatives to increase available flow rates in marginal flow applications.
Guidelines To Bit Cleaning With Bi Center Drill Bits
Bit balling sometimes occurs when drilling in soft/sticky formations with a water base drilling fluid. The usual indications are a sudden decrease in the penetration rate and rotary torque and an increase in on- bottom standpipe pressure (which disappears when off-bottom).
Cleaning the bit
To clean the bit, raise the bit off-bottom, and then go back to just above the bottom while running full pumps and normal bit speed. The bit should be held there for 10 to 15 minutes, giving the fluid flow across the bit face an opportunity to clean the bit face while no new cuttings are being generated. Very high rotary speeds off-bottom for short periods of time while circulating can be tried in an attempt to “sling” the balled-up formation off the bit face. WARNING: This may cause holes with angle to undercut or wash on the low side.
If balling continues to be a problem and the flow rate of the drilling fluid cannot be increased, it might be best to limit the penetration rate to one where balling is not a problem. If repeated cleaning is needed or the penetration rate falls to the point where the bit can no longer drill economically, then it will be advisable to pull the bit. Other bit styles designed for better cleaning should then be considered.
In the event a nozzle becomes plugged, the indication is an increase in standpipe pressure with the same amount of flow previously. One method is to use the same circulation technique as described above. Another method of cleaning a plugged nozzle is to lift the bit 30 to 40 feet off-bottom, and then drop the kelly 5 to 10 feet and stop it suddenly to surge the fluid through the bit.
If it is not possible to clear the nozzle, but the bit still drills at an acceptable penetration rate and no other problem is experienced, the bit should be left on bottom. Bits with a single plugged nozzle often make economical runs, and plugging material will sometimes wash away given time. The pumping of nut plug (Lost Circulation Material), Low/High (Thin/Thick) viscosity sweeps will also aid in unplugging nozzles and bit face balling
Bi Center Directional Tendencies
For Build, Hold Or Drop Runs Utilizing Rotary Speed To Control Inclination.
- For Building, Optimum Rotary Speed will be 30-40 RPM
- Optimum Rotary Speed for Hold-40-50 RPM
- Incase Of dropping, Optimum Rotary Speed will be 50-60 RPM
|BI CENTER SIZE||STABILIZER SIZE||% DRILL SIZE|
|17” X 20”||14.5||72|
|14.5” X 17.5”||13||74|
|12.25” X 14.75”||11.5||78|
|12.25” X 13.5”||10.5||78|
|10.625” X 11.5”||9.25||80|
|10.625” X 12.25”||10||82|
|8.5” X 9.875”||8.25||84|
|6.5” X 7.5”||6.5||86|
|6” X 7”||6||86|
Note: a high % of the runs this data was extracted from utilized performance motors, which were in the 30’ range. The more successful runs placed the stabilizer 40 to 60 ft. From the bit; used a 1.75° or greater bent housing motor and a minimum motor speed of 120 rpm.
Suggested Operating Parameters are based on case histories to date and have provided proven results. Recommendations are however, general guidelines only and will vary with application. DPI assumes no liability from the use of recommendations or suggestions contained herein.