CA2359522A1 - Sample catcher for underbalanced drilling operations - Google Patents

Abstract

A sample catching apparatus includes an intake manifold, an outflow manifold, a first screening chamber and a second screening chamber. The sample catcher receives the returning drill stream from a manifold shack and directs the drill stream into a separation vessel.
Removable pails within the screening chambers retain a portion of the solids in the drill stream, while allowing fluids to pass through.

Description

CA. PATENT
Docket No. 48194.1 SAMPLE CATCHER FOR UNDERBALANCED DRILLING OPERATIONS
Inventors: Albert Cerenzie FIELD OF THE INVENTION
The present invention relates to a sample catcher for capturing solids from a returning drill stream from an underbalanced drilling operation.
BACKGROUND OF THE INVENTION
In underbalanced drilling, as opposed to conventional drilling, down-hole well pressure at the formation is maintained below the formation pressure by the utilization of a relatively light base drilling fluid. The underbalanced condition avoids contamination of the formation by reducing the chances that the drilling fluids and the "cuttings," suspended solids produced by the action of the drill bit, will be forced into the permeable reservoir formation. Several types of base drilling fluid may be used in underbalanced drilling. Water-based and oil-based drilling muds may be used, however, water and lighter oil-based fluids, such as diesel fuel and crude oil, are more commonly used. In some situations the base drilling fluid will have a specific gravity too high to successfully use in an under-balanced well. In such situations, the controlled mixture of additives, such as nitrogen gas, to the base drilling fluid produces an operating fluid of a specific gravity selected to maintain an under-balanced well.
The higher formation pressures usually result in well formation fluids, such as hydrocarbon oil, hydrocarbon gas and well water, flowing into the well and mixing with the operating fluid and cuttings. The returning drilling stream reaches the surface well:head as a mixture of formation oil, formation gas, well water, solid cuttings and operating fluid.
In underbalanced drilling the returning drilling stream is at elevated pressures and when separation of the stream elements is desired, separation must bc~ performed in a closed container or tank. Separation of the well formation fluids from the base f.rilling fluids is necessary before the base drilling fluids may be returned to the well and is accomplished by processing the returning stream through a separation system. Complicating matters, the separation system must handle typical wellhead pressures of the returning stream, which during underbalanced drilling can range from 25 psi to 3000 psi. Wellhead pressures are typically maintained as low as possible but still high enough to handle the returning stream volume. During drilling a large volume of heavy cuttings is produced and returned to the surface wellhea.d in the returning stream. In conventional drilling the returning stream is treated with shale shakers and mud pits. In under-balanced drilling it is necessary to remove the cuttings, or solids produced during drilling, from the returning stream mixture in the pressurized tanks to prevent clogging of the tanks. For safety reasons, in underbalanced drilling, it is first necessary to remove the gases from the returning stream. Removal of the solids from the pressurized chambers without shutting down the drilling operation presents difficulties.
Therefore, it is difficult and inconvenient to remove solids from the pressurized chambers in order to monitor the type of solids being returned. Experienced drillers may be able to determine whether the well is in the "pay zone" by the type of solids being returned to the surface as cuttings.
Therefore, there is a need in the art for methods and apparatuses for conveniently and safely removing solids samples from a returning drilling stream.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus for sampling the solids being returned from an underbalanced drilling operation. Accordingly, in one aspect of the invention, the invention comprises a solids sample catcher for use in an oil or gas well being drilled underbalanced, said well including a wellhead and a separation vessel and producing a returning drilling stream comprising fluids and solids, said sample catcher disposed between the wellhead and the separation vessel and comprising:
(a) an intake manifold for receiving the returning dlrilling stream;

(b) an outflow manifold for directing the drilling si:ream to the separation vessel;
(c) a first solids screening chamber having an inlet connected to the intake manifold and an outlet connected to the outflow manifold;
(d) a first screen disposed within the first screenin~; chamber;
(e) a second solids screening chamber having an inlet connected to the intake manifold and an outlet connected to the outflow manifold;
(f) a second screen disposed within the second screening chamber; and (g) valve means for diverting the drilling stream into the first and second screening chambers, or either of them.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. Figure 1 is a schematic representation of one embodiment of the present invention. Fiigure 2 is a view of a pail screen of one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for a sample catcher for use in underbalanced drilling operations. When describing the present invention, all terms not defined herein have their common art-recognized meanings. As used herein, "fluids" includes gases and liquids, including drilling fluids and gases and production fluids and gases.
The apparatus or sample catcher (10) depicted in the Fiigures comprises an intake manifold ( 12), an outflow manifold ( 14), a first screening chamber ( 16) and a second screening chamber ( 18). The sample catcher ( 10) receives the returning drill stream from the manifold shack (not shown) and directs the drill stream on to a separation vessel (not shown).

The returning drill stream is directed into the main inlet pipe (20) through main valve (22). The inlet pipe (20) leads to the intake manifold (12) which connects to both the first and second screening chambers ( 16, 18). Isolation valve (24) shuts off flow the first screening chamber (16) when closed and isolation valve (26) shuts off flow to the second screening chamber (18) when closed. The isolation valves (24, 26) should have an adjustable choke.
Each screening chamber is hollow and cylindrical and encloses a pail-like screen (28).
The screen is formed from a relatively fine mesh which retain:. a substantial portion of the solids in the drill stream while allowing fluids to pass through. The jFluids leave the screening chambers into the outflow manifold, through outflow valves (25, 27), and into the main outlet pipe (30) which leads to the separation vessel.
The tops of each screening chamber are capped with a removeable cap (32) which threads on to the screening chamber. Removal of the cap (32) permits easy removal of the screen (28) by grasping and lifting the screen handle (34). The cap (32) may be reinforced by brace (36) which includes a threaded collar (38). The cap (32) may include a threaded post (40) which engages the collar (38). The brace (36) increases the pressure capability of the screening chamber. The brace may include a pivot (not shown) which permits the cap (32) to be swung away from the top of the screening chamber once disengaged.
In operation, the main intake valve (22) may be opened. to divert flow of all or a portion of the drill stream to the sample catcher. One or both of the intake manifold isolation valves (24, 26) may be opened, as well as the outflow valves (25, 27). All other valves should be closed. If both sets of valves are opened, a sample will be caught in both screening chambers. As is readily apparent to those skilled in the art, the two screening chamber may be operated independently of the other by manipulating the isolation and outflow valves (24-~27).
Once a sample is caught, the main flow valve (22) may be closed, or alternatively, one of the isolation valves may be closed to shut off flow to one or both of the screening chambers. The pressure in the screening chamber may be blown down and than the screening chamber may then be purged with compressed air or propane to drain all fluids and purge any hydrogen disulfide which may have accumulated in the screening chamber. Purge lines and valves (42, 43, 44, 45) may be provided for this purpose. The cap (32) may then be knocked off and the pail screen (28) removed to obtain the sample. While a sample is being retrieved from one screening chamber, there may still be flow through the other screening chamber. As well, spigots (48) may be provided to provide additional means for draining fluid from the screening chambers.
Pressure gauges (50, 52) may also be provided to monitor pressure upstream and downstream from the sample catcher ( 10).
The sample catcher (10) may be assembled with an appropriate pressure rating, as is well known in the industry and may be adapted for either sweet or sour gas service.
All fittings may be adapted to either flange fitting or NPT threads. The catcher (10) may conveniently be mounted on a small skid for portability and convenient use in i:he field.
As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein.

Claims (7)

1. A solids sample catcher for use in an oil or gas well being drilled underbalanced, said well including a wellhead and a separation vessel and producing a returning drilling stream comprising fluids and solids, said sample catcher disposed between the wellhead and the separation vessel and comprising:
(a) an intake manifold for receiving the returning drilling stream;
(b) an outflow manifold for directing the drilling stream to the separation vessel;
(c) a first solids screening chamber having an inlet connected to the intake manifold and an outlet connected to the outflow manifold;
(d) a first screen disposed within the first screening; chamber;
(e) a second solids screening chamber having an inlet connected to the intake manifold and an outlet connected to the outflow manifold;
(f) a second screen disposed within the second screening chamber;
(g) valve means for diverting the drilling stream into the first and/or second screening chambers.

2. The sample catcher of claim 1 wherein the valve means comprises a first valve disposed between the intake manifold and the first screening chamber intake, and a second valve disposed between the intake manifold and the second screening chamber intake.

3. The sample catcher of claim 1 wherein the first and second screening chambers each comprises access means for removing and reinserting the first and second screens.

4. The sample catcher of claim 3 wherein the first and second screens each comprise a cylindrical container having an open top and defining a plurality of openings such that the fluid components of the drilling stream may pass through the container, while solids are retained.

5. The sample catcher of claim 4 wherein each of the first and second screens comprises a handle.

6. The sample catcher of claim 4 wherein the first and second screening chambers comprise a cylindrical chamber having an open top end and the access means comprises a removable lid which securely engages the top end of the chamber.

7. The sample catcher of claim 6 wherein the access means further comprises a brace securely attached to the screening chamber, said brace comprising a threaded collar, a threaded post extending upwardly from the lid, wherein the threaded post engages the threaded collar.