Separation of drilling fluid

1. A method for separating by specific gravity barite, drill cuttings, and bentonite from an aqueous drilling fluid comprising barite, drill cuttings, and bentonite recovered from use in drilling a well penetrating a hydrocarbon bearing subterranean formation, the method comprising:

directing from the well the drilling fluid comprising barite, cuttings, and bentonite into a closed pressure vessel positioned horizontally and generally proximate to or near the well, the vessel having a top, an elongated shape, an end proximal the well and an end distal the well, and comprising an inlet port at the proximal end of the vessel, first, second, and third outlet ports serially distributed along the length of the vessel bottom, a vent at the vessel top, and a fourth outlet port at the distal end of the vessel, such that the fluid can flow through the vessel and such that the vessel can be pressurized by gas;

allowing said fluid to flow through the vessel from the inlet port to the first, second, and third outlet ports such that a substantial amount of the barite separates out by specific gravity and exits from the first outlet port, a substantial amount of the cuttings separate out by specific gravity and exit from the second outlet port, and a substantial amount of the bentonite separates out by specific gravity and exits from the third outlet port.

2. The method of claim 1 wherein the drilling fluid comprises hydrocarbon gas and during the flow of the drilling fluid through the vessel, hydrocarbon gas released from the drilling fluid into the vessel exits from the vent in the vessel.

3. The method of claim 1 further comprising allowing the drilling fluid to exit the fourth outlet port of the vessel and reusing the drilling fluid exiting the fourth outlet port in further drilling the well.

4. The method of claim 1 wherein the flow from the well through the vessel is continuous.

5. The method of claim 1 wherein the gas pressure in the vessel is regulated.

6. The method of claim 1 wherein the vessel further comprises a first baffle between the first outlet port and the second outlet port and a second baffle between the second outlet port and the third outlet port.

7. The method of claim 6 wherein the first baffle comprises a plurality of first holes sized to resist passage of barite through the first holes and the second baffle comprises a plurality of second holes sized to resist passage of cuttings through the second holes.

8. The method of claim 7 wherein the first baffle and the second baffle are positioned perpendicular to the outlet ports and generally across at least a portion of the interior of the vessel such that the fluid moves through the baffles in flowing from the inlet port to the fourth outlet port.

9. The method of claim 6 wherein the vessel further comprises a flow diverter between the second baffle and the outlet port for diverting bentonite away from the fourth outlet port and toward the third outlet port.

10. A method of specific gravity separation of barite, drill cuttings and bentonite from a drilling fluid comprising barite, drill cuttings and bentonite and recovered from use in drilling a well penetrating a hydrocarbon bearing subterranean formation, the method comprising:

continuously directing from the well the drilling fluid comprising barite, drill cuttings, and bentonite into a pressurized, horizontal vessel having opposing ends, a top, and a bottom extending the length of the vessel, such that the fluid has a level in the vessel and can flow through the length of the vessel, the vessel further comprising: an inlet port at one end of the vessel; first, second, and third outlet ports serially distributed along the bottom length of the vessel; a vent at the top of the vessel; a fourth outlet port at the opposing end of the vessel; a first baffle positioned in the flow path of the fluid between the first outlet port and the second outlet port and having a plurality of first holes sized to resist passage of barite through the first holes; a second baffle positioned in the flow path of the fluid between the second outlet port and the third outlet port and having a plurality of second holes sized to resist passage of drill cuttings through the second holes; and a fluid diverter for directing bentonite from the fourth outlet port and toward the third outlet port;

allowing the drilling fluid to flow continuously through the vessel from the one end of the vessel to the opposing end of the vessel and out the opposing end of the vessel, while maintaining the fluid level in the vessel, regulating pressure within the vessel, and allowing barite to separate out from the drilling fluid by specific gravity and exit the vessel at the first outlet port, allowing drill cuttings to separate out from the drilling fluid by specific gravity and exit the vessel at the second outlet port, and allowing bentonite to separate out from the drilling fluid and exit the vessel at the third outlet port.

11. The method of claim 10 further comprising recycling barite from the first outlet port, bentonite from the third outlet port, and drilling fluid from the fourth outlet port.

12. The method of claim 1 wherein the drilling fluid has a level in the vessel and that fluid level in the vessel is maintained at a constant level when the fluid flows through the vessel.