FILED OF THE INVENTION
- BACKGROUND OF THE INVENTION
The present invention relates generally to the pumping of fluid from a well, and more particularly, relating to an apparatus for mounting to the wellhead of a low producing oil and/or gas well for use in producing hydrocarbons from the well.
When an oil and/or gas well no longer produces hydrocarbons naturally, artificial lift systems are commonly used to continue hydrocarbon production from the well. Artificial lift systems include some sort of mechanical device that is inserted into the well to lift fluid from the bottom of the well to the surface.
One of the most commonly used systems for artificial lift in oil production is a combination of a pumpjack (also know as horse head pump, a beam pump, and sucker rod pump), and piston pump installed in downhole in the wellbore. A pumpjack is the above ground drive for reciprocating the plunger of the piston pump. The pumpjack is connected to the plunger of the piston pump through a series of sucker rods connected end-to-end from the pumpjack to the plunger. The pumpjack converts rotary motion of a prime mover, such as an electric motor or a combustion engine, into a vertical reciprocating motion to drive the sucker rods up and down. The piston pump is connected to the end of a production string, which includes numerous separate segments of rigid pipe connected end-to-end that is lowered into the wellbore of the well to position the pump at a location where well fluid will be drawn in by the piston pump. The production string is typically secured at the wellhead by a tubing hanger which supports the production string in the wellbore.
The pumpjack system has many drawbacks including the diameter of the sucker rods being limited by well conditions, and as load is imposed on the sucker rods during the upstroke of the plunger, the rods stretch due to their elasticity. With relatively new sucker rods, this stretch is taken up at the beginning of the down stroke of the plunger. However, with older sucker rods the continuous stretching and relaxing of the rods results in fatigue and plastic deformation and permanent elongation. The amount of elongate of the sucker rods is indefinite and uncertain, but in deep wells it may become so great that nearly the entire stroke of the plunger is taken up in stretching and releasing of the sucker rods, which greatly reduces the efficiency of the pump system. Additionally, installation of rigid segments of production tubing is time consuming, dangerous, and expensive. Also, because this conventional pumping system generally has large dimensions and relatively high weights, it needs a robust foundation and therefore a relatively high capital investment. Furthermore, the labor intensity involved in carrying out periodic parameter adjustments, balance adjustments and costs of operation are relatively high.
- SUMMARY OF THE INVENTION
Another problem with hydrocarbon production is the environmental impact of producing the hydrocarbons. The seal between the polished rod (upper most sucker rod) and the wellhead in pumpjack systems has a tendency to leak, resulting in higher environmental impact and lost of usable oil. To reduce this impact, pumpjack systems need to be frequently inspected to ensure leaking is not occurring.
In general, in one aspect, an apparatus for pumping fluids from a well is provided. The apparatus includes a production tubing extending from a wellhead of the well downhole to a downhole location. A pump having a pump barrel connected to a bottom of the production tubing, and a plunger reciprocable within the pump barrel for lifting fluid from the bottom of the well up through the production tubing and to the wellhead as the plunger upstrokes, and for filling the barrel below the plunger as the plunger upstrokes. A sealed housing attached to the wellhead with the production tubing in fluid communication with the interior of the sealed housing. A cable drum positioned within the interior of the sealed housing. A prime mover operably connected to the cable drum for rotating the cable drum and a cable wound on the cable drum for winding and unwinding by rotating the cable drum. The cable extending downwardly through the production tubing and attached to the plunger. Controls for operating the prime mover for rotating the cable drum to reciprocate the plunger within the pump barrel.
The prime mover can be positioned within the interior of the sealed housing. The prime mover can be a hydraulic motor. A flowline can be connected in fluid communication with the interior of the housing for receiving fluid from the production tubing during reciprocation of the plunger. The controls can include a programmable logic controller programmed for the operation of the prime mover for rotating the cable drum. A means to determine the angular position of the cable drum and outputting a signal to the programmable logic controller can be provided. A means to determine elongation of the cable can be provided. The production tubing can be a continuous, non-segmented length of coiled tubing. A means to determine fluid production from the well can be provided.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.
Numerous objects, features and advantages of the present invention will be readily apparent to those of ordinary skill in the art upon a reading of the following detailed description of presently preferred, but nonetheless illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of descriptions and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention.
The accompanying drawings, which are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and together with the description serve to explain the principles of the invention, in which:
FIG. 1 is a front elevation diagram of the apparatus for pumping fluids from a well constructed in accordance with the principles of the present invention, and installed on a typical oil well;
FIG. 2 is a side elevation diagram of FIG. 1;
FIG. 3 is an enlarged detail view of FIG. 1;
FIG. 4 is a schematic diagram of a control system of the apparatus; and
DETAILED DESCRIPTION OF THE INVENTION
FIG. 5 is a front elevation diagram of the apparatus for pumping fluids from a well with an alternative flowline connection arrangement.
Referring to FIGS. 1-4 of the drawings, reference numeral 10 generally designates the apparatus for pumping fluid from a well in accordance with the principals of the present invention. As shown in the Figures of the drawings, there is broadly disclosed an oil and/or gas well 12 that has the usual borehole, or well-bore 14 having casing 16, formed into the Earth. The borehole 14 extends from the surface, down through a hydrocarbon producing formation 18 from which fluid flows through casing perforations 20 into the casing annulus 22. While specific discussion is made herein with respect to an oil and/or gas well, the pumping apparatus 10 of the present invention can be utilized to pump fluids from other types of wells, such as a water well. Well 12 has a conventional wellhead 24 attached to the surface end of the well casing 16 and including a blowout preventer (BOP) 25. The wellhead 24 configuration can include different components suited for the requirements and/or operation conditions of each particular well.
The pumping apparatus 10 includes a production tube 26 extending from the wellhead 24 down the well casing 16 to a downhole position. The production tube 26 can be retained or secured to the wellhead 24 by a conventional tubing hanger (not shown), which is well known in the art. The production tubing 26 can be a length of coiled tubing for specific advantages over segmented sections of rigid tubing, including being capable of being run into the well without killing the well.
A pump 30 is connected to the bottom 28 of the production tubing 26, and is operable to pump formation fluid from casing 16 into and upwardly through the production tubing to the wellhead 24. Pump 30 can be a conventional down-hole reciprocating piston pump having a pump barrel 32, a piston 34 received within the pump barrel for reciprocation therein, a connecting rod 36 extending upwardly from the piston, a standing ball check valve 38, and a traveling ball check valve (not shown). The pump barrel 32 can be connected to the bottom 28 of the production tubing 26 with the connecting rod 36 extending upwardly in the production tubing. Broadly, in operation, when the piston 34 is pulled upwardly the traveling valve, positioned across a flow passage through the piston, closes and the standing valve 38 opens due to a drop in pressure below the piston in the pump barrel 32. Consequently, the pump barrel 32 fills with formation fluid as the piston 34 is raised and lifts the formation fluid that is above the piston upward through the production tubing 26. When the piston 34 travels downwardly, the traveling valve opens, and the standing valve 38 closes due to an increase in pressure below the piston in the pump barrel 32. The formation fluid in the pump barrel 32, which was drawn during the upstroke of the piston, flows up through the traveling valve in the piston. Once the piston 34 reaches the end of its downward stroke, it begins its upward stroke, repeating the process to pump fluid.
The connecting rod 36 is connected to the end of a cable 48 that is wound on a winch/cable drum 46 that is mounted within a housing 40 attached to the wellhead 24. Cable 48 is wound off the cable drum 46 past a cable guide 52 then down and into the top of the wellhead 24 and production tubing 26. The cable guide 52 is to provide an appropriate fleet angle for the cable 48 to wrap properly and to eliminate the need for an expensive level wind or other tool. Housing 40 is connected to the wellhead 24 with the production tubing 26 in fluid communication with the interior 42 of the housing. The housing 40 is sealed and pressure rated at a pressure rating higher than the shut-in pressure of the well 12, and the working pressure of a production pipeline when production is being produced into a pipeline. Housing 40 may have a removable, sealable hatch 44 to permit access to the interior 42.
An important aspect of the pumping apparatus 10 of the present invention is the sealing of the cable 48 and cable drum 46 within the well environment by being positioned and contained within the housing 40. Undoubtedly, during operation, formation fluid will accumulate on the cable 48, and with the cable being contained within the well environment, the formation fluid is prevented from impacting the ambient environment. Additionally, expensive and leak prone seals that otherwise would be required to seal the cable with wellhead are eliminated, and thus reducing operating expense, and the likely environmental impact due to seal leakage or failure, among other advantages.
A prime mover, such as hydraulic motor 50 is operatively coupled to the cable drum 46 for rotating the cable drum to wind and unwind the cable 48 thereon. An intermediate drive (not shown), such as a transmission or gear box, can be connected between the cable drum 46 and the hydraulic motor 50 as desired or may be required. The intermediate drive could be a variable speed drive to more accurately control the rotation of the cable drum 46. Alternatively, the hydraulic motor could be replaced with an electric motor or a combustion engine. A winch break (not shown) can be provided to help control the winding of the cable 48 under load.
The hydraulic motor 50 can also be positioned and supported within the interior 42 of the housing 40, or alternatively, can be positioned and supported exterior to the housing with its drive shaft extending into the interior of the housing. A shaft seal (not shown) would seal the drive shaft with the wall of the housing 40 to prevent leaking of formation fluid from the housing. The hydraulic motor 50 is connected to a hydraulic circuit comprising a hydraulic pump 54, hydraulic fluid lines 55 and 56, a valve 58, and a hydraulic fluid reservoir 60 containing a quantity of hydraulic fluid. The hydraulic pump 54 is operated to circulate hydraulic fluid within the hydraulic circuit to operate the hydraulic motor 50 driving the cable drum 46. Valve 58 is operated to direct the flow of hydraulic fluid to the hydraulic motor 50 to either operate the hydraulic motor in a forward or reverse direction in order to either wind or unwind the cable 48 onto and from the cable drum 46.
With reference back to FIG. 1, the wellhead 24 can be provided with a flowline connections 70 and 71 for fluid and/or gas flow. Appropriate pipelines 72 and 73 are connected to the flowline connections 70 and 71 respectively for conveying fluid and/or gas to collection tanks, separators, and/or production pipelines. Flowline connection 70 can be provided with a one-way check valve 74, a valve 76, and fluid flow switch 66. Similarly, flowline connection 71 can be provided with a one-way check valve 75, a valve 77, and a fluid flow switch 67. While only two flowline connections are illustrated the wellhead 24 may be configured to have as many as required by the operating conditions of the well 12. As shown in FIG. 5, alternatively or in addition to, the housing 40 can be provided with a flowline connection, such as flowline connection 70 in fluid communication with the interior of the housing.
Numerous different control methods and apparatuses can be employed to control the operation of the hydraulic motor 50 to affect the reciprocation of the piston 34 of the pump 30 through the winding of the cable 48. An exemplary control, can include a rotary position encoder 62, a fluid pressure sensor 64, a fluid flow switch 66, valve 58, and a programmable logic controller (PLC) 68. The rotary position encoder 62 can be operatively coupled to the drive shaft of the hydraulic motor 50 to determine the angular position of the shaft and ultimately the angular position of the cable drum 48. A rotary position encoder, also called a shaft encoder, is an electro -mechanical device used to convert the angular position of a shaft or axle to an analog or digital code, making it an angle transducer. These devices are routinely used in industrial controls and robotics, and are readily available and are easily implemented into control logic. The fluid pressure sensor 64 can be installed on hydraulic fluid line 56 to measure the pressure of the hydraulic fluid in the fluid line to determine the load on the hydraulic motor 50. The fluid flow switch 66 can be installed in flowline 68 connected to wellhead 24 for sensing pumped fluid flow through the flowline from the wellhead. The rotary position encoder 62, the fluid pressure sensor 64, the fluid flow switch 66, the valve 58, a winch brake (if provided), and pump 54 are each operatively coupled to the PLC 68.
After initial installation, operation of one cycle of the pumping apparatus 10 that is installed on well 12 is as follows. When the piston 34 is at the bottom of its stroke in the pump barrel 32 as indicated by the rotary position encoder 62, the PLC 68 operates valve 58 to direct hydraulic fluid to the hydraulic motor 50 to wind the cable 48 onto the cable drum 46 to raise piston upward. The position of piston 34 along its stroke is continuously measured by the rotary position encoder 62 and reported to the PLC 68. As the piston 34 is raised fluid pressure sensor 64 continuously monitors the fluid pressure within the hydraulic line and reports this to the PLC 68. The PLC 68 uses this pressure signal to monitor load on the piston and cable 48. The piston 34 is determined to be at the top of its stroke as indicated by the rotary position encoder 62. As a fail-safe, an abnormal increase in hydraulic line pressure as measured by the pressure sensor 64 can be used to indicate the piston 34 is being pulled upward against the top of the pump barrel 32. Once it is determined the piston 34 is at the top of its stroke, the PLC 68 commands valve 58 to reverse fluid flow to the hydraulic motor 50 to unwind the cable 48 from the cable drum 46 to lower the piston. The piston 34 will reset to the bottom of its stroke under gravitational force of the weight of the piston and the weight of the cable 34 acting on the piston. Once the piston 34 is determined to be at the bottom of its stroke, the cycle repeats to produce formation fluid up through the production tubing 26 into the wellhead 24 and through the flowline connection 70.
The PLC 68 can be programmed to determine an estimation of elongation of the cable 48 in real-time as a result of the load of the column of formation fluid using Hooke's Law of elasticity. The elongate of the cable is directly proportional to the tensile force and the length of the cable and inversely proportional to the cross-sectional area of the cable and the modulus of elasticity of the material of the cable. Tensile force on the cable can be calculated by determining the hydrostatic head of the column of formation fluid and knowing the diameter of the piston and the diameter of the cable. The length of the cable between the cable drum 46 and the connecting rod 36 can be easily determined from the rotary position encoder 62 and other known constants of the well geometry, such as well depth. The cross-sectional area of the cable and the modulus of elasticity of the material of the cable are also known. The elongate of the cable 48 can be used to more accurately determine the position of the piston 34 along its stroke.
Output from the fluid flow switch 66 can be used by the PLC 68 to determine if formation fluid is being produced by operation of the pumping apparatus 1O. To prevent dry running of the pumping apparatus 10, the PLC 68 will cause the pumping apparatus to operate in a shut-down mode for a predetermined period of time upon the sensing of no fluid being produced by the fluid flow switch 66.
A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.