Rheometer for drilling-mud viscosity measurements
Described herein is a rheometer comprising a rotor comprising a rotary shaft and at least two screws extending longitudinally along a first portion of said shaft; a motor coupled to said shaft and adapted to rotatably drive said rotor; a stator having a cylindrical shape and adapted to contain a fluid; wherein said at least two screws form a cylindrical twin helix; wherein said cylindrical twin helix has an inside radius of 2 mm to 10 mm and an outside radius of 10 to 20 mm; wherein said stator has a radius which is longer than the outside radius of said cylindrical twin helix.
1. A method for measuring viscosity of a drilling mud, the method comprising:
providing a rheometer, including: a rotor comprising a rotary shaft and at least two screws extending longitudinally along a first portion of said shaft; a motor coupled to said shaft and adapted to rotatably drive said rotor; a stator having a cylindrical shape; wherein said at least two screws form a cylindrical twin helix; wherein said cylindrical twin helix has an inside radius of 2 mm to 10 mm and an outside radius of 10 mm to 20 mm; wherein said stator has an inside radius which is 31% longer than the outside radius of said cylindrical twin helix;
feeding the stator with a drilling mud, said drilling mud comprising cuttings;
activating the motor for rotating the cylindrical twin helix so as to stir the drilling mud;
measuring the viscosity of the drilling mud during stirring.
2. The method according to claim 1 , comprising causing a rotational and convective motion of the drilling mud in the stator by stirring the drilling mud by means of the cylindrical twin helix.
3. The method according to claim 2 , wherein the rotational and convective motion prevents the cuttings included in the drilling mud from sedimenting.
4. The method according to claim 1 , wherein said at least two screws are mutually congruent.
5. The method according to claim 1 , wherein said shaft has a pointed end; wherein said end has a tip angle of 120° to 140°.
6. The method according to claim 1 , wherein said cylindrical twin helix extends longitudinally over a length of 80 mm to 120 mm.
7. The method according to claim 1 , wherein said cylindrical twin helix has a pitch that equals its length.
8. The method according to claim 1 , wherein said shaft has a second portion, along which said two screws do not longitudinally extend, wherein the first portion has a radius smaller than the second portion.
9. The method according to claim 1 , wherein said stator is a cylindrical container, the method comprising providing the cylindrical container with an insulating sleeve associated with a temperature control and recirculation system.
10. The method according to claim 1 , wherein the cuttings have a maximum size which is smaller than the inside radius of the twin helix.
11. The method according to claim 1 , wherein the cuttings have a maximum size of 4 mm.