Drilling fluid circulation system

Claim 1

In a drilling system comprising (1) a drill unit for drilling from an underground room and for providing horizontal thrust to a drill bit, and (2) a drilling fluid circulation system for providing liquid drilling fluid through a drill string to a drill bit and for returning said fluid, cuttings and produced gas through a borehole to a gas and cuttings separation system, the improvement wherein said gas and cuttings separation system is a closed loop system comprising: (a) a first compartment for storing clean liquid drilling fluid; (b) a second compartment having an inlet for receiving drilling fluid, drilling cuttings and produced gas from said drilling fluid circulation system and said second compartment including a plurality of baffles therein; (c) connecting means between said first and second compartments, said connecting means including fluid passage means allowing liquid drilling fluid to flow from said second compartment to said first compartment; (d) liquid level control means for maintaining a minimum liquid level in said compartments; (e) liquid level control means for limiting the upper level of liquid in said compartments; (f) gas-containing sections in the upper part of said compartments; (g) gas communication means providing for free passage of gas between the said gas-containing sections; (h) gas exhaust means for removing gas from said gas-containing sections and exhausting it at a location outside said underground room; (i) cuttings removal means comprising an auger positioned in the bottom of said second compartment and including a cuttings discharge outlet for removing settled cuttings from said second compartment; and (j) outlet means for returning said liquid drilling fluid to said drilling fluid circulation system.