CTD is another drilling technique used for sidetracking wells. It has potential to save cost over conventional rotary rig operations particularly if the CTD sidetracks can be performed through the existing production tubing (saving decomplete and recomplete costs) and if the kickoff window can occur within the target reservoir thus avoiding overlying cap rock shales.
CTD’s high dogleg severity drilling capability of 45°/100 feet or more consumes less TVD in getting to horizontal and gets to the target quicker. Also, CTD’s continuous drillpipe (the coil) can really be a benefit for areas that require UBD or MPD operations.
On the other hand, CTD needs a relatively stable formation to drill in. For example, it will struggle through formations that contain reactive shales due to the inability to rotate and marginal overpull capability.
CTD sidetracking operations have been very successful in Alaska, UAE and Russia. Since it is a relatively uncommon technique that requires a thorough assessment of applicability for each area.
Limitations:
- Restricted hole sizes
- Limitations in BHA power
- Bits are typically frail
- Directional oriented holes limited to 3.5’’ TBG and larger
Three Basic Techniques:
- In TBG Whipstock
- Thru TBG Whipstock
- CMT Kick-off (time drill or whipstock in pilot hole)