Wellbore Sidetracking Guidelines

The following guidelines are used to aid in understanding and in establishing some protocol in the event of having to sidetrack while drilling. Although this may not cover all circumstances, it gives useful information for both the desk and field engineer.

General Principles

Sidetracking a Harder Target Formation - a diamond sidetrack bit should be employed. Caution needs to be exercised when using a diamond sidetrack bit as, it can produce very high doglegs. Motor settings typically used with sidetrack bits should be between 2-2.5. Sidetrack bits are used only to establish the “ledge”.

Generally only 5-6m is cut with a sidetrack bit, as this is the distance that the ledge will be the same width as the bit face (typically—the actual amount drilled will vary). Once the entire bit face is off, and is cutting new hole, the bit will generally stop drilling, and typically an increase in SPP will be seen. These two signs indicate that a good ledge is started, and the assembly should be pulled out in favour of a traditional Directional Drilling assembly. Sidetracking from a Cement Plug - a new bit of the same type used to drill the original wellbore should be used. The ideal situation is the cement plug is harder (drills slower) than the formation, for the natural tendency is drilling in the path of least resistance. Should the formation be harder, than the cement plug, a higher motor setting, and a less aggressive (slower) time drilling program should be considered.

The type of PDM ideally to use is a medium speed configuration, as higher bit speeds typically result in easier sidetracking. Bit and formation types need to be considered when making this decision.

Sidetracking Horizontals - it is important not to begin drilling out of the bottom of the wellbore (180 toolface), as is the natural tendency. A setting of approximately 125º either left or right toolface will work. Using gravity somewhat and a sharp directional change in either direction will aid in the process. This scenario allows a greater ability to return to either wellbore.

Exercise extreme caution when exiting out of casing. Sidetracking should not be commenced less than 15-20m out of the Hz casing shoe. This ensures there is no magnetic interference and to eliminate any damage to the casing.

Maintain a distance of 15-20m separation between multi-lateral KOP’s, This distance allows an easier determination of which sidetrack you are re-entering.

Prior to beginning your sidetrack and when re entering, always re-strap, and check pipe tally to be assured of bit depth. Double checking measurements will ensure confidence that the sidetrack is being initiated in the proper place.

Once a sidetrack ledge is established, it is very important not to drill ahead aggressively, for the ledge may break off and one would have to re start the entire process again.

Higher than normal doglegs are typically experienced when sidetracking, so exercise caution when sidetracking.

Sidetracking off Cement Plugs

A minimum of 100m of cement should be used. Keep a minimum of 50m above and 50m below the estimated sidetrack point.

To begin drilling (polishing) the cement plug, a “slick” assembly can be used or to begin faster a PDM can be employed to drill up the cement. If using a slick assembly to polish the plug, follow the rule of 5’s for drilling a hard cement plug – with 5000daN WOB, and rotary table at 50RPM, ROP should be +/-5min/meter. If polishing with a PDM, noticeable weight and differential pressure should be observed, and ROP should be somewhat close to formation ROP when originally drilled.

Drill up 10-15m to polish the plug while the cement is somewhat soft to be just above the proposed sidetrack point or Kick Off Point (KOP). If polishing cement with an MWD system in the hole be aware

that this may damage and/or plug up the MWD tool. Carefully monitor samples to determine amount of cement returns – onsite geology should be consulted for this information. Anything less than 90% cement returns and the assembly should be changed out for directional equipment.

With the directional assembly in the hole begin drilling the last 10-15m of cement in a staged approach to the KOP. For high compressive strength formations a diamond sidetrack bit should be used. Patience is critical in this hole section as, one can easily, rush the process and waste the cement plug. With the motor setting set between 1.83º and 2.8º begin time drilling. The ideal motor is a medium speed or 4:5 Lobe configuration. The motor type and motor setting will be dictated by the bit type being, used, formation hardness, aggressiveness tendency to come off the cement plug and build requirement.

Time Drill in a staged approach.

Staged Approach to Sidetracking off Cement Plugs

Survey frequently and closely observe tool face as WOB is increased. Steer accordingly to establish correct azimuth for sidetrack.

Do not increase weight on bit until completely off plug to minimize the breaking of established ledge, and falling back into softer cement.

If a lower motor setting, or a bit change is needed, trip out of hole and change BHA including bit. Adjust motor setting to a lower rate for the new bit, formation and well plan. Use a motor with a 7:8 lobe configuration and monitor cuttings for cement percentage.

It is good practice to strap pipe and conduct an additional pipe tally when tripping out of the hole after a sidetrack. Check all physical measurements such as the tool face offset (OTF) as frictional forces along with torque may cause a change in the make up torques of the BHA and drill string. Monitor tool face, and azimuth on any subsequent trips to assure one is in the correct wellbore. Once again, patience is required when returning back into the sidetracked wellbore and you may have to orient the BHA to re-enter the correct path.

Sidetracking in Open Hole Wellbores

Choose an area in the wellbore with a well established dogleg or positive change in angle . Ideally this area would also have a good penetration rate to make for a quicker sidetrack.

Begin to establish a trough. This will be dictated by the type of formation and compressive strength of the rock. Normally a 3-4m slide or stroke is practiced for 0.5 to 1 hour maintaining a constant toolface. Start the sidetrack in the desired direction and time drill @ 4min/inch for 2-3m. A staged approach should be used as below.

Conscientiously add weight conservatively to determine if the ledge has been established. If the sidetrack is able to handle a slight increase in WOB continue to time drill at a reduced weight for another 3-4m, Once the ledge is fully established, resume drilling with normal WOB.

When drilling ahead and making connections always orient the string in the direction of the sidetrack to avoid existing. For the connection, when on bottom, shut off pumps, pull up approximately 1m and set slips on rig. To resume drilling and avoid breaking the ledge, go back to bottom, kick in pumps and

begin drilling. Do not allow the rotation of the drill string out until back on bottom and then turning on pumps.

Trip out of hole to change BHA and bit. Use a motor with a 7:8 Lobe configurations. Adjust motor setting to a lower setting for use with the new bit, and appropriate for the well plan.

Staged Approach to Sidetracking in Open Hole Wellbores

It is good practice to strap pipe and conduct an additional pipe tally when tripping out of the hole after a sidetrack. Check all physical measurements such as the tool face offset (OTF) as frictional forces along with torque may cause a change in the make up torques of the BHA and drill string. Monitor tool face, and azimuth on any subsequent trips to assure one is in the correct wellbore. Once again, patience is required when returning back into the sidetracked wellbore and you may have to orient oneself to re-enter the correct path.

Whipstocking inside of Casing

It is common to come off a “One Trip” whipstock system. When doing so, it is ideal to have a directional driller present when the whipstock is being set in casing. The Directional Driller aids in the orientation of the whipstock to assure it is set at the right azimuth. Whipstocks can be set at upwards of 85º. Whipstocks should be set 2m above casing collars, as recommended by the whipstock manufacturer.

Whipstocks are oriented with reference to high side of the wellbore except for truly vertical wells, which are set by azimuth.

Prior to setting the whipstock it is best to choose a point in the casing which is not at a tool joint or upset in the casing. If there is some angle in the hole it is best to come off the low side of the hole to allow gravitational forces to help in coming off.

For Vertical wells (0-4 degrees) a gyro is used to set the whipstock . As the casing is metal, the use of the gyro is necessary, due to magnetic interference with MWD telemetry. It is always best to set the whipstock, mill, and drill out of the window with the gyro placed directly above, and oriented to the motor. This enables the directional driller to ‘see’ actual angle built, and the resulting dogleg severity sooner, so that a better informed decision can be made regarding motor setting for drilling ahead. In some instances it can beneficial to drill with an MWD with the gyro “piggy backed” on top. Once the window is milled and the MWD is 15-20m out side and away from the casing the MWD begins to function normally and the Gyro can then be pulled and normal drilling operations can continue. Caution must be exercised as the extent of the vibration and the harsh environment may cause a MWD failure when conducting this procedure. It is not always a recommended practice.

Staged Approach to Whipstocking Outside of Casing

Continue drilling ahead, steering high side with MWD surveys and separation is evident from a lack of influence from the casing. The MWD will begin producing valid surveys beyond 3º. The tool goes from gravity toolface to magnetic toolface.

Doglegs produced by Whipstocks can be as high as 14º/30m (or more) for the first 6-8m drilled by the milling assembly.