DEFINITION OF SIDETRACKING. To drill a secondary wellbore away from an original wellbore. A sidetracking operation may be done intentionally or may occur accidentally. Intentional sidetracks might bypass an unusable section of the original wellbore or explore a geologic feature nearby. In the bypass case, the secondary wellbore is usually drilled substantially parallel to the original well, which may be inaccessible due to an irretrievable fish, junk in the hole, or a collapsed wellbore.
There are times when it is necessary to abandon or bypass the lower portion of a well.
there are many reason for sidetracking: the casing is damaged or collapsed, junk may be lost in the hole, the production zone may have been damaged in the original well, or to tap into another less-depleted drainage area.
If a window is to be cut in casing, cement is first circulated back to a point just above the kickoff point. Cement is then dressed back to the point of the kickoff. The kickoff can be accomplished with a bent sub and downhole motor, whipstock or a combination. Once the window has been cut and properly dressed, the drillstring can be removed. Proper design of the new bottomhole assemply is crucial. Should the present angle of the well be maintained, a packed hole assemply (numerous stabilizers) is runb. If hole angle is to be dropped, (pendulum) stabilizers are placed above the bit at crucial points. if the well is to be horizontal and desired angle has yet to be reached, a build (fulcrum) assembly is run with stabilizers near the bit. Several angle changes may take place during course of drilling before desired depth and target are reached. Depending on the type of completion to be performed, the new section of hole may be logged, the liner run and the new interval may now be perforated and productiob resumed.
- SIDETRACKING CUTS THROUGH CASING AND EXPOSES FORMATION.