Patent ID: 6802379
Filing Date: 2004-10-12
Classification: E21B

Abstract:
A method of drilling a well below a body of sea water in which a drill bit is rotated at the end of a drill string, comprising:(a) injecting into the well at a depth below the water surface a liquid having a lower density than a density of a drilling mud producing a mixture of drilling mud and low-density liquid in the well; (b) withdrawing the mixture of drilling mud and low-density liquid from the well wherein the mixture has a density greater than the sea water at the seafloor surrounding the well; (c) separating at least a portion of low-density liquid from the mixture of drilling mud and low-density liquid, thereby producing a drilling mud depleted of low-density liquid; (d) returning at least a portion of the separated low-density liquid to the depth below the water surface; and (e) returning at least a portion of the drilling mud depleted of low-density liquid to an upper end of the drill string.