Oil/ Gas Wells may require sidetracking in order to re-drill the well to a new target, may be to past a fish or because of hole problems.
To sidetrack any Oil / Gas well, you have to develop a lateral force to allow the drilling bit to cut on the side of the hole. This force will be provided by the drilling BHA geometry.
The most reliable drilling BHA configuration to perform a successful sidetrack kick off is the mud motor with bent sub.
2 Main Issues to consider when select Kick-off Point.Ok let's understand how we select the kickoff point in simple steps
- Choose a soft or soft to medium formation so that you can increase the chances of a successful kick-off. However, if only medium to hard formations exist at the required sidetrack depth, you will need to be more patient.
- Control your ROP till it is confirmed that you got a successful kick-off.
Consider The Following When you Set A Kick-off plug
- SET a 300 - 500 ft NEAT CMT PLUG (Class G in the production hole section) at 17.0 ppg (batch mixer will be more reliable in this situation if possible).
- WOC WAIT ON CMT for 12 hours minimum.
- DRESS OFF 20 ft with low parameters, and WEIGHT TEST the plug
- Now you have 2 possibilities
- Plug is firm : DRESS OFF a further 20-30 ft comparing drillability with that of the original hole
- Plug appears good: WAIT a further 12 hours before attempting to kick-off
- Plug has no signs of compressive strength: Then WASH DOWN more CMT to be able to place second 300 ft plug at a suitable depth for sidetracking.
Take Care While Cutting Casing Windows.When it is about initial cut, try to avoid casing collars and centralizers (minimum of 8 ft above a casing collar).
Generally the lengths of window to facilitate an effective sidetrack are:
Choose Adaptable Drilling BHA To Perform Successful Hole SidetrackA suitable assembly shall be agreed between the Directional Driller in consultation with the Drilling Supervisor. The number of non-magnetic components can usually be reduced by applying a survey correction algorithm to survey data.
Simple Tips To Consider While Sidetracking A Well:
- bent sub size will depend on the drilling hole size, formation hardness and required deviation.
don't forget to check the geometry of the assembly to ensure that there is a lateral loading with the motor length and bent sub for the hole size that will be sidetracked.
- Mud Motor / Bent Sub combination is the most economical choice for well sidetrack then you can change to a more optimum drilling BH.
- If you consider to drill ahead after the kick-off with the same drilling BHA, it is much better to choose a motor bearing bit.
- You can run MWD tool directly above the bent sub and utilize survey correction algorithms.
- In-case of sidetracking through a casing window, orient the string using tool face high side readings or a UBHO with steering tool above the MWD.
Sidetracking Through the Low Side of the Drilling Hole
- The low side hole sidetrack have higher risk of creating high doglegs as it allow you to take off rapidly. So that it is much better to come off low side to the right / left than purely low side.
- Once the new hole has been cut, lateral separation should be maintained to prevent collapse of the old hole into the new hole.
Maximizing Kick-off Success
- If there are external factors which may reduce the chances of performing successful kick-off such as (Eg., hard formations, deep kick-offs, or restricted window lengths), you will have to consider the following drilling BHA to maximise kick-off probability:
PDC Sidetracking bit, mud motor, 1.5 degree bent housing, MWD, UBHO sub, DC’s.
- Initially, the assembly shall be time drilled until approximately 30 ft with 100 % formation returns, then the BHA shall be pulled to reset the deflection.