Abstract: The invention relates to methods and apparatus for determining a downhole parameter in an underbalanced drilling environment which include: selectively activating a first fluid flowing from the formation through a wellbore while under balanced drilled; detecting the activated first fluid, and determining a depth at which said fluid enters the wellbore.

Abstract: A sampling apparatus for sampling a fluid enriched in a selected phase from a multiphase fluid mixture flowing into a main pipe, the multiphase fluid mixture containing at least the selected phase and one other phase, the apparatus comprising: —a sampling arrangement: for taking a fluid sample of the multiphase fluid mixture flowing into the main pipe, —a sample chamber having a variable volume for collecting the fluid sample of the multiphase fluid mixture and letting settle by gravity the fluid sample into the fluid enriched in the selected phase and at least another phase enriched fluid, and —a valve manifold coupling the sampling arrangement to the sample chamber for driving the fluid sample in the sample chamber and for driving the fluid enriched in the selected phase to a sample outlet and the other phase enriched fluid back to the main pipe.

Abstract: The present invention provides a method and apparatus for casing while drilling without the use of an underreamer. In one aspect, the invention provides a flexible drill collar that enables drilling of a large enough borehole for passage of the casing string therethrough.