Patent ID: 9388650
Filing Date: 2016-07-12
CPC Classification: E21B,F15B

Claim Text:
1. A drilling system including a drill string which extends into a borehole, and a well closure system which contains fluid in the annular space in the borehole fluid out of the annular space in the borehole around the drill string is permitted, the side port being connected to a fluid return line which extends from the side port to a fluid reservoir, there being provided in the fluid return line a valve which is operable to restrict flow of fluid along the fluid return line to variable extent, and a flow meter operable to measure the rate of flow of fluid along the fluid return line, the flow meter being located between the valve and the side port, wherein a filter is provided between the flow meter and the side port, the filter including a plurality of apertures which have a smaller cross-sectional area than the smallest fluid flow lines in the flow meter; wherein the flow meter is located in a branch line of the fluid return line which extends between a first portion of the fluid return line and a second portion of the fluid return line, the first portion being located between the side port and the second portion; the filter is located at or adjacent to a junction between the branch line and the first portion of the fluid return line; and the filter has an edge or edges which are located at the junction between the branch line and the first portion of the fluid return line, and a central portion which extends into the branch line.