Patent ID: 6065550
Filing Date: 2000-05-23
Classification: E21B

Abstract:
A method of drilling and completing multilateral wells in an underbalanced condition from a principal wellbore, comprising:a) providing an overall system, which comprises:i. a first drilling/completion subsystem, further comprising a drill string assembly having at least a drill bit and guidance system at an end of the drill string assembly;ii. a containment subsystem for maintaining an underbalanced state within the wellbore, the containment system further comprising pressure control means such as a BOP stack, rotating BOP, or snubbing unit;iii. a separation subsystem for separating hydrocarbons that have been co-mingled with drilling fluids as a hydrocarbon/drilling fluid mixture is returned to a surface of the wellbore, so that the hydrocarbons may be collected and separated from other fluids in the system;b) lowering a carrier string into the wellbore, the carrier string having a deflection member on its lower end;c) orienting the deflection member in a pre-selected direction;d) lowering a segmented drill string assembly having a drill bit on its end into the carrier string and drilling a first multilateral well off of the deflection member in the preselected direction;e) simultaneously circulating fluid down the bore of the segmented drill string assembly and an annulus between the carrier string and a wall of the borehole, of sufficient weight to provide an underbalanced state without the fluid entering the formation;f) retrieving the drill string assembly and reorienting the deflection member to drill at least a second multilateral well, while maintaining the first multilateral well as a live well; andg) returning to the surface any hydrocarbons received from any of the multilateral wells through an annulus between the carrier string and the segmented drill string assembly co-mingled with the circulated fluid.