Drilling fluid filter screen and method of use

1. A method for filtering drill bit cuttings and other abrasive debris and contaminants from a drilling mud that is circulated from a surface mud tank through an oil or gas well drilling system located on a well drilling rig having a rig floor and a rig derrick, the method comprising the steps of:

providing a drill string;

providing a drilling system supported by the well derrick that rotatably drives the drill string for drilling a well bore, the drill string having a drilling mud fluid passageway;

providing an interconnecting conduit downstream of the mud circulating pump for communicating with the drilling mud fluid passage in the drill string;

wherein the drilling system includes a stand pipe that is located in the interconnecting conduit between a discharge outlet of the mud pump and the remainder of the drilling system on the derrick, the stand pipe being positioned in a generally upright position;

providing a mud filter screen assembly for filtering the drilling mud, the mud filter screen assembly being positioned in the interconnecting conduit adjacent the discharge outlet of the mud pump at ground level and prior to the stand pipe;

the mud filter screen assembly comprising a porous structure made of metal having a plurality of openings formed along a length thereof which allows a flow of drilling mud through the filter screen section while trapping drill bit cuttings and other abrasive debris;

wherein the mud filter screen assembly includes a filter screen section having a longitudinal axis, the filter screen section being mounted within an outer tubular member, whereby an annular passageway exists between the filter screen section and the outer tubular member, the filter screen assembly having a filter inlet for receiving mud flow from the discharge outlet of the mud pump and a filter outlet, and wherein drilling mud enters the filter inlet in an in-line direction and continues axially through the mud filter screen assembly and through the annular passageway, parallel to the longitudinal axis of the filter screen section and to the outer tubular member, the flow continuing to the filter outlet where it passes through the interconnecting conduit and from there through the drilling mud fluid passageway of the drilling system; and

wherein the mud filter screen assembly has an inlet piece provided with at least one by-pass outlet which allows the flow of mud to continue outside the filter screen section in the annular passageway between the filter screen section and the outer tubular member and thereafter along the longitudinal axis of the outer tubular member to the filter outlet in the event the filter screen section itself should become clogged or inoperative.

2. The method of claim 1 , wherein the filter screen section porous structure is selected from the group consisting of metal mesh material, a plurality of welded metal bars, a generally solid metal material having a plurality of openings machined therein, Nylon and hard plastic materials.

3. The method of claim 2 , wherein the derrick and drilling system includes a rotary hose, a swivel and a Kelly, the Kelly being positioned at an elevated level above one end of the string of drill pipe, the filter screen assembly being located upstream of the rotary hose, swivel and Kelly.

4. The method of claim 3 , wherein the drilling rig has a floor level and a substructure and wherein the filter screen assembly is located at ground level as a part of the substructure of the drilling rig.

5. A mud filter system for filtering drill bit cuttings and other abrasive debris and contaminants from a drilling mud that is circulated from a surface mud tank through an oil or gas well drilling system located on a well drilling rig having a rig floor and a rig derrick with a rig floor substructure, the drilling system further including as components thereof a drill string on the derrick with a rotatable drive for driving the drill string for drilling a well bore, the drill string having a drilling mud fluid passageway, and at least one mud pump having an inlet and a discharge outlet, the mud pump being located at a well surface level on or partly below the rig floor for circulating the drilling mud from a mud tank to the drilling mud fluid passageway of the drill string, the mud filter system comprising:

an interconnecting conduit between the discharge outlet of the mud circulating pump and the drill string;

a mud filter screen assembly for filtering the drilling mud, the mud filter screen being positioned in the interconnecting conduit adjacent the discharge outlet of the mud pump at ground level as a part of the rig substructure;

wherein the mud filter screen assembly includes a filter screen section which is a porous structure made of metal having a plurality of openings along a length thereof which allows a flow of drilling mud through the filter screen section while trapping drill bit cuttings and other abrasive debris;

wherein the mud filter screen assembly includes a filter screen section having a longitudinal axis, the filter screen section being mounted within an outer tubular member, whereby an annular passageway exists between the filter screen section and the outer tubular member, the filter screen assembly having a filter inlet for receiving mud flow from the discharge outlet of the mud pump and a filter outlet, and wherein drilling mud enters the filter inlet in an in-line direction and continues axially through the mud filter screen assembly and through the annular passageway, parallel to the longitudinal axis of the filter screen section and to the outer tubular member, the flow continuing to the filter outlet where it passes through the interconnecting conduit and from there through the drilling mud fluid passageway of the drilling system; and

wherein the mud filter screen assembly has an inlet piece provided with at least one by-pass outlet which allows the flow of mud to continue outside the filter screen section in the annular passageway between the filter screen section and the outer tubular member and thereafter along the longitudinal axis of the outer tubular member to the filter outlet in the event the filter screen section itself should become clogged or inoperative.

6. The mud filter system of claim 5 , wherein the drilling system includes a stand pipe that is located in the interconnecting conduit between a discharge outlet of the mud pump and the remainder of the drilling system on the derrick, the stand pipe being positioned in a generally upright position relative to the derrick, and wherein the filter screen assembly is located prior to the stand pipe.

7. The mud filter system of claim 6 , wherein the derrick and well drilling system includes a swivel, a rotary hose and a Kelly connecting the drill string to the stand pipe, the mud screen filter being located upstream of the swivel, rotary hose and Kelly.

8. The mud filter system of claim 5 , wherein the filter screen porous structure is selected from the group consisting of metal mesh material, a plurality of welded metal bars, a generally solid metal material having a plurality of openings machined therein, Nylon and plastic materials.