Patent ID: 9051803
Filing Date: 2015-06-09
Classification: E21B

Abstract:
1. A control apparatus for use in controlling the fluid pressure in a borehole during drilling of the borehole, the apparatus including an inlet suitable for connection to a pump, a main outlet suitable for connection to a drill pipe, and an overflow outlet suitable for connection to a fluid reservoir, the inlet being connected to the main outlet by a main flow conduit, and the overflow outlet being connected to the main flow conduit by means of an overflow conduit, wherein the overflow conduit is provided with a pressure regulator by means of which the pressure of fluid in the main flow conduit may be maintained at or around a predetermined pressure value, wherein the apparatus also includes a further choke which is located in the main flow conduit between the overflow conduit and the main outlet and which is adjustable to vary the degree of restriction of flow of fluid along the main flow conduit.