Patent ID: 8813872

Claim:
A method of delivering drilling fluid for use in drilling boreholes with a drill bit, the method comprising: transferring drilling fluid to and from the drill bit by means of a primary flow circuit having a first flow rate; transferring drilling fluid to and from the primary flow circuit by means of a secondary flow circuit having a second flow rate, wherein the first flow rate is higher than the second flow rate; receiving fluid containing cuttings from the primary circuit in a cuttings transfer system between the primary and secondary flow circuits; separating the fluid in the cuttings transfer system into a first stream that contains substantially no cuttings and a second stream containing cuttings; returning the first stream to the primary flow circuit; and directing the second stream to the secondary flow circuit; wherein the step of separating the fluid into first and second streams comprises directing fluid from the primary circuit into a hydrocyclone having a primary vortex and a secondary vortex, directing fluid containing cuttings in the primary vortex to the secondary circuit, and directing fluid that is substantially free of cuttings in the secondary vortex to the primary circuit.