Bi Center Bit

DPI PRODUCT BULLETIN PDC/BI-CENTER PDC BIT OPERATING PROCEDURES

September 25, 2003 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 ♦ Lithology ♦ Length/depth of Interval ♦ Directional objectives ♦ Drilling Fluids ♦ Stabilization/BHA ♦ Casing design/objectives

♦ Drilling modes – rotary or positive displacement motor (PDM)

♦ 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 downhole. PREPARATION AT JOBSITE Steps Prior to Making Up Bi-Center Drill Bits 1. Hydraulic calculations must be performed to optimize the Bi-Center performance. See Product

Bulletin No. 004 for Bi-Center nozzle selection. 2. Bottom hole assembly must be agreed upon with well objectives. See Product Bulletin No. 005 for

Bi-Center BHA recommendations. This is especially important when drilling with a PDM. Confirm that largest OD tool +/- 30ft above bi-center bit is less than the maximum tool size.

3. On casing drill outs followed with a vertical section application pass through size stabilizers are recommended at 60ft and 90ft. This BHA provides flex above the bit reducing damage in the drill out stage. On vertical non-drill out applications pass through stabilizers are recommended at 30ft, 60ft and 90ft above the bit. This provides maximum BHA stiffness.

4. Detailed directional BHA’s are recommended later in these procedures. 5. Confirm that the stabilizer O.D.’s have been checked with a “GO” Ring Gage. 6. Previous bits must be inspected for gage wear, broken teeth, or junk damage. If any previous bit is

under gage, then a reaming trip 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.

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Making Up the Bi-Center Drill Bit 1. 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.

2. 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.

3. For larger sizes, the Bi-Center Bit Breaker Box open end should be oriented away from the draw works.

4. Clean, check for connection damage and dope the pin. 5. Lower the drill string to the top of the pin and engage threads. 6. Remove bit breaker and carefully lower the bit and drill string through rotary table. 7. Guide the bit and drill string through the BOP and wellhead. The bit should not take any weight or be

obstructed in any way. 8. Trip slowly through casing shoes, liner hangers, doglegs, tight spots, or ledges. 9. When filling drill pipe (when a PDM is attached), reduce flow to a minimum to avoid rotation of the

motor. Recommended Make Up Torque

Tool Joint Size DPI

Nominal OD Ft-lbs N-m

2.3/8 API Reg 3 ¼” *

3,085 4,182

2.7/8 API Reg 3 7/8”

4,658 6,315

3.1/2 API Reg 4 ¾”

7,660 10,385

4.1/2 API Reg 6”

17,551 23,794

6.5/8 API Reg 8”

38,193 51,778

7.5/8 API Reg 9”

59,966 81,296 Notes:

1) Thread compound composition and application may affect torque values. These values assume use of a thread compound containing 40 to 60% by weight of metallic zinc.

2) Normal torque "range" is the tabulated value plus 10% 3) Torque values are based on the API-RP7G recommendation. 4) *-Indicates box is the weaker member for corresponding OD.

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DRILL OUT RECOMMENDATIONS ♦ When drilling out casing shoe joints with PDC bits, use only PDC Compatible Float/Shoe & Liner

Equipment. Non-rotating cementing plugs are recommended as a way to prevent plug rotation during drill out.

♦ Upon arriving on location, obtain the casing tally and verify the location of all cementing equipment

within the string. Try to determine and record the manufacturer and model number of all cementing equipment that will be drilled out. Again, verify that all equipment is PDC drillable.

♦ Field personnel have determined that composite float equipment is easier to drill out with PDC bits.

Rubber Plugs and Aluminum landing collars have presented the most problems when drilling out. It is very important to know what type of equipment is to be drilled out in order to anticipate problems before they occur. Equipment with aluminum components must be drilled carefully to avoid damaging the bit.

♦ Casing liner jobs typically cause the most problems. The hanger assembly or baffle plate will usually

contain aluminum so it must be drilled out carefully. The landing collar and wiper plug also usually contain aluminum components.

♦ When drilling out, cement will usually be encountered first.

1. While drilling cement, WOB should be kept between 2,000 to 8,000 pounds. 2. It is important to keep a constant ROP while drilling cement in order to avoid rotating in one

place without penetration. WOB can be higher than mentioned in order to achieve this. ♦ When approaching any float, liner, or shoe equipment it is important to back off of the WOB and

approach this equipment with the recommended parameters. ♦ As a general rule the following should be adhered to:

1. Approach any float, liner, or shoe equipment slowly and drill out using the following parameters: 2. WOB should be kept between 2,000 to 6,000 pounds, 3. RPM should be kept at or above the recommended minimum RPM (see following table), 4. When drilling float, liner, or shoe equipment ROP should be controlled between 3 to 6 feet per

hour; however, as long as the WOB is kept light and the recommended RPM is adhered to, the ROP can be higher without damaging the bit. Newer equipment utilizing composite components will typically drill at higher rates and not cause bit damage.

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♦ Many times operators are hesitant to allow higher RPM’s while in the casing in order to avoid casing

damage from stabilizers and other BHA components. When drilling out in rotary applications, DPI strongly recommends adhering to the minimum RPM guidelines. The following reasons justify this recommendation. 1. It is important to keep WOB light when drilling float, liner, or shoe equipment. In so doing the

depth of cut is kept to a minimum. This aids in preventing damage to the cutters as well as preventing rotation of plugs and other equipment. By adhering to the recommended RPM guidelines, penetrations rates through the casing equipment can be kept higher. It is important to keep the BHA drilling ahead to avoid rotating in one place for extended periods, which can cause casing damage.

2. WOB must be kept light to avoid causing large pieces of the equipment from becoming dislodged and becoming stuck around the pilot or in the reamer blades. Again, higher RPM’s will enhance the ROP while drilling with lightweight.

3. When drilling equipment with aluminum components, it is very important to keep cutting size to a minimum. When drilling aluminum it is typical to create long strings of aluminum typical to lathe cuttings. If these become too large they can become lodged in the area between the pilot and reamer or in the blades of either part. By keeping the WOB light and the RPM high this can be avoided while still maintaining a constant ROP. Some casing equipment is designed to cause an interrupted cut when drilling the aluminum components. It is still important to keep the depth of cut to a minimum to avoid damage to the cutters.

4. Since drilling the float, liner, and shoe equipment requires using minimal WOB, it is important to keep the RPM high to achieve a constant penetration rate. This helps to avoid staying in one place too long and decreases the overall time spent in the casing.

♦ If the operator insists on using slower than recommended RPM, try and negotiate the use of higher

RPM’s while drilling float and liner equipment. It is not as important to have higher RPM’s when drilling cement and shoe equipment.

PDC/CSD Inside Pipe

Cutter Size Rotary Min. RPM

Motor & Rotary Rotary/ Min. Mtr. / Min. Bit

3/8in – 8mm 120 40-60 / 140 / 180 0.4in - 10.5mm 1/2in - 13mm

110

40-60 / 130 / 170

5/8in – 16mm 3/4in - 19mm

100

40-60 / 120 / 160

♦ When approaching the shoe equipment it is important to slack off on the WOB and drill the shoe with

light WOB. If the shoe is encountered with too much WOB, the bottom of the shoe can be sheared allowing it to drop to the bottom of the hole where it can be difficult to drill.

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♦ Avoid sudden impact with any of the various components. ♦ Many problems can occur when drilling float, liner, and shoe equipment. The most typical problems

occur when drilling components with aluminum or while drilling rubber plugs. As mentioned, long strings of aluminum can become lodged in the bit stopping or slowing ROP. Likewise as rubber plugs break up the pieces can become lodged in the bit stopping or slowing ROP.

♦ 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. Many times when picking up off of bottom increased drag will occur. This is a clear indication that debris is lodged in the bit. Continue to reciprocate the pipe until the drag returns to normal or until penetration resumes.

♦ 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 or bit speed. (It is important to maintain a certain bit speed to ensure a proper depth of cut.)

♦ When drilling float, liner, and shoe equipment with a PDC bit it is not unusual to see metal shavings

in the returns. This is normal but should be monitored and kept to a minimum. Adhering to these guidelines and keeping a constant ROP while drilling out should keep metal shavings kept to a minimum. New bit technology is helping to reduce this occurrence.

♦ Rotating and drilling out in casing in one place is not advisable for long periods of time. ♦ It is normally good practice to back ream and ream through any float, liner, and shoe equipment after

the drill out is complete. This simply insures everything has been drilled and is cleaned out. ♦ 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/Bi-Center PDC Bit Break-In in Formation 1. 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.

2. Use low weight on bit (drilling conditions dictate) and a minimum 100-rpm on rotary applications and

30 to 60 rotary speeds on motor applications with full flow rates to establish a new bottom hole pattern.

3. Record pump-strokes and standpipe pressure and compare with expected vs. actual hydraulics.

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4. Slowly break the bit in, drilling at least three (3) feet in this manner. 5. Increase rotary speeds and add weight in 2,000-pound increments to determine the optimum drilling

weight on bit. 6. 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.

Drilling Ahead 1. 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.

2. Rotary and weight on bit parameters should be adjusted to maintain optimum drilling parameters as formation changes, directional requirements and hole conditions.

PDC/Bi-Center in Formation

Cutter Size Rotary Min. RPM

Motor & Rotary Rotary/ Min. Mtr. / Min. Bit

3/8in – 8mm 120 30-140 / 140 / 170 0.4in - 10.5mm 115 30-140 / 135 / 165 1/2in - 13mm 110 30-140 / 130 / 160 5/8in – 16mm 3/4in - 19mm

100

30-140 / 120 / 150

Generally recommended mud motor speeds have been 120+RPM. Recent testing in vertical applications has suggested that in 30fph or slower drilling and higher ROP (150fph+) drilling applications a slower speed motor will increase ROP and reduce damage to the bit. (In the higher ROP applications increased weight is required with slower RPM.) Reaming 1. Reaming long sections of undergage hole is not recommended, but has been accomplished

successfully with varying degrees of damage to the bit. 2. 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.

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With a Mud Motor ♦ Ream with full flow. ♦ In low dogleg situations, use 20 to 40 RPM. ♦ In high dogleg situations keep toolface aligned to hole direction and do not rotate. ♦ In 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. GUIDELINES TO PREVENT BIT BALLING

♦ 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., and minimized number of drill collars (increase heavy weight drill pipe) are possible alternatives to increase available flow rates in marginal flow applications.

GUIDELINES TO BIT CLEANING 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). To clean the bit, raise the bit off-bottom, and then go back to just above 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.

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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, 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.

Optimum Rotary Speed for Build-30-40 RPM Optimum Rotary Speed for Hold-40-50 RPM Optimum Rotary Speed for Drop-50-60 RPM

BI-CENTER SIZE (inches)

STABILIZER SIZE (inches)

% 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 UTILIZATION OF PERFORMANCE MOTORS, WHICH WERE IN THE 30-FOOT RANGE. THE MORE SUCCESSFUL RUNS PLACED THE STABILIZER 40 TO 60 FEET 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.

Bi Center Bit

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