Patent ID: 7278497
Filing Date: 2007-10-09
Classification: E21B

Abstract:
1. A method for drilling a lateral wellbore from a main wellbore, comprising: running a string of casing with an injection line connected thereto into the main wellbore, wherein the injection line is disposed along an outer side of the casing and a portion of the casing corresponding to a starting depth of the lateral wellbore is made from a drillable material; running a drillstring through the casing to the starting depth of the lateral wellbore, wherein the drillstring comprises a drill bit; injecting drilling fluid through the drill sting; and injecting a second fluid, having a density less than that of the drilling fluid, through the injection line at a rate corresponding to an injection rate of the drilling fluid to control hydrostatic pressure exerted by a column of the drilling fluid and the second fluid returning through the casing.