METHOD OF CONSTRUCTING A SIDE WELL SHAFT Russian patent published in 2020 - IPC E21B7/04 E21B33/10 

FIELD: soil or rock drilling.

SUBSTANCE: invention relates to drilling of offshoots of oil and gas wells, namely to methods of prevention of destruction and collapse of well walls at drilling intervals with unstable rocks. Method of constructing a side wellbore, involving preliminary determination of a zone of unstable rocks, cutting an opening in a production string, drilling of the offshoot, attachment of the offshoot with a extreme line tie-back casing in a certain zone of unstable rocks with a drilling shoe installed on the lower end, drilling of the offshoot to the projecting face. A zone of unstable rocks is opened by a lateral shaft in three stages. At the first stage drilling of unstable rock zone to the roof is performed with usage of service water to facilitate pumping through the casing string annulus. Running at the second stage of the unstable rocks on the hydrocarbon-based drilling mud, and expansion of the well shaft at the third stage of unstable rocks on the hydrocarbon-based drilling mud. Expansion is performed to provide laminar flow of liquid in expansion range beyond drilling column and increased static pressure, which allows penetrating drilling fluid deeper into unstable rocks interval. After that it is lowered on the process string with an automatic trailer to the bottomhole and an extreme line tie-back casing is cemented with further disconnection from it of the process string, which is removed to the surface with washing.

EFFECT: reliable isolation is ensured at development of unstable rock formation zone without possible emergency situations due to preliminary reinforcement of well walls with subsequent cementation of extreme line tie-back casing.

3 cl, 3 dwg