Automated, Trajectory Controlled Whipstock Exit
Publication Date: 2017-Mar-31
The IP.com Prior Art Database
This publication describes an advanced whipstock/milling assembly that features a keyseated guidance along the whip for the milling BHA and a hydraulic piston in the milling BHA that controls distance of whip to milling BHA in order to adjust BHA curvature and milling trajectory. It also describes the control mechanism for automating this process.
Automated, trajectory controlled whipstock exit
Abstract: This publication describes an advanced whipstock/milling assembly that features a keyseated
guidance along the whip for the milling BHA and a hydraulic piston in the milling BHA that controls
distance of whip to milling BHA in order to adjust BHA curvature and milling trajectory. It also
describes the control mechanism for automating this process.
Novel features and problems solved: There are two novelties:
- Active trajectory guiding of a milling BHA
- Automated control / feedback loop of the trajectory creation of the rathole created by a
Rathole curvature can be extreme and so far is unknown in direction and extend until it is too late.
This regularly causes
- challenges to achieve tight directional targets - especially not to exceed the TVD of the
wellbore beyond the reservoir depth
- in extreme cases with weak cement, the casing below the whipstock may be damaged from a
milling assembly following the outside the of casing
- limitations to the length of the rathole chosen to avoid such issues above. This often leaves
no other choice than rotating a stiff BHA through the high DLS of the whip and the rathole,
causing excessive bending fatigue. With this idea, the rathole could be the length of the
subsequent drilling BHA – giving more choice for its design, which is often badly needed.
The concept in detail:
Aspect A – mechanical refinements of whipstock design that allow a more
consistent way of drilling the rathole
There are 3 design options discussed here that can lead to a guiding of the starter mill (and possibly
Option 1 – placing a non-rotating sleeve in the flex section between the two watermelon mills.
The non-rotating sleeve slides along the whip with the BHA and is connected to the ramp via a
keyseat. The depth of the keyseat varies and the sleeve is either pulled towards (at first; when the
watermelon mill is still on the ramp) or pushed away from the ramp surface (when the watermelon
mill is inside the rathole. This causes the BHA to bend and in both cases pushes the pilot mill away
from the casing. In effect, it prevents the rathole to stay inside the soft cement. It also guides the
pilot BHA to stay somewhat straight and walk neither right nor left.
The non-rotating sleeve possibly will have journal rather than ball bearings. As the watermelon mills
will have stronger than normal contact forces on the ramp, the ramp may require special hardfacing
and/or the watermelon mills minimal aggressiveness on the OD (and greater aggressiveness on the
As cuttings etc. may make it difficult to slide the key inside the keyseat, it may be beneficial to fill the
keyseat with non-bonded-rubber or a similar easy-to-remove material until it is pushed out by the
non-rotating sleeve at the respective position.
Possible geometry of the keyseat and non-rotating sleeve:
Possible depth-distribution of the groove/keyseat along the ramp: