Method for combined jet and mechanical drilling

A method for drilling a hole in an earthen formation, comprising:

• (a) conducting a first fluid down said hole;
• (b) separately conducting a second fluid down said hole;
• (c) mixing said first and second fluids within said hole;
• (d) conducting said fluid mixture back up the hole to the surface;
• (e) segregating and substantially clarifying a portion of said fluid mixture;
• (f) pressurizing the remainder of said fluid mixture;
• (g) pressurizing said segregated portion of said fluid mixture to a pressure greater than said fluid mixture;
• and
• (h) separately re-conducting said pressurized fluids down said hole as said first and second fluids.

A method for circulating drilling fluid in a drilling fluid circuit in connection with the drilling of a hole in an earthen formation, comprising:

• a. circulating a first, substantially clarified fluid stream at a lower flow rate;
• b. circulating a second fluid stream at a higher flow rate;
• c. mixing said first and second fluid streams;
• d. separating said first and second fluid streams from one another;
• and
• e. re-establishing the respective flow rates of said first and second fluid streams.

A system for drilling a hole in an earthen formation, comprising:

• a. a drill bit;
• b. a first substantially closed fluid circuit for circulating a drilling fluid stream;
• c. a second substantially closed fluid circuit for circulating a second fluid stream;
• d. at least one jet in said second fluid circuit adjacent said drill bit for directing a jet of said second fluid adjacent said drill bit;
• e. said second fluid jet stream and said drilling fluid stream being effluent at said drill bit to form a common stream;
• f. means for segregating a portion of said common stream;
• and
• g. means for pressurizing said portion to a level greater than said common stream, said pressurized portion forming said second fluid jet stream.

A method for conducting fluid in connection with the drilling of a hole in an earthen formation, comprising:

• (a) highly pressurizing a first fluid stream at the surface of said formation in order to avoid the adverse effect of extreme downhole conditions on the pressurizing means;
• (b) conducting said first highly pressurized fluid stream down said hole;
• (c) directing said first highly pressurized fluid stream against said formation to assist in drilling said hole;
• (e) conducting a second fluid stream down said hole to provide well control in drilling said hole, said second fluid stream having a higher volume and lower pressure than that of said first fluid stream;
• and
• (f) mixing said first and second fluid streams to remove cuttings and other solids from the hole.