CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/568,233 entitled "Pump for Liquid Evacuation," filed May 6, 2004, and a U.S. Non-Provisional Application entitled "Pump For Evacuation of Viscous Liquids," filed May 5, 2005, both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to the pumping of wells such as oil wells, and in particular to oil pumping equipment for evacuating heavy oil containing mechanical impurities and embedded in strata.

Description of the Related Art A plunger-diaphragm pump (PDP) has been previously developed to facilitate extraction of abrasive-containing, aggressive and salt-containing bedded liquids such as petroleum from steep wells. Conventional PDPs for evacuation of oil from wells have increased mean-time-between-repair due to elimination of direct contact between the pump's mechanical surfaces - such as the hydraulic plunger and cylinder - and the impurities in the extracted oil. Statistics show that the prevailing cause of failure in these oil pumps is plunger wear. Pump repair or scheduled maintenance that requires removal of the pump from the well greatly reduces the efficiency and increases the cost of the oil extraction effort.

Conventional PDPs avoid interaction between a mechanical plunger pair and the impurity-laden oil by utilizing tanks divided by flexible membranes. A hydraulic drive (e.g., a plunger in a cylinder) cycles to force operating liquid against a surface of the membrane upon a downward stroke and creates suction against the surface of the membrane upon an upward stroke.

In conventional PDPs, operating liquid is pushed out to the tank by a plunger. The plunger, as with all plungers in oil pumps, has significant length and requires a precision bore diameter to limit seepage between the plunger and the sidewall of the cylinder. The plunger is connected to a hollow rod that extends down a cavity opening from the top of the pump. Any operating liquid that does seep past the plunger to the above cavity passes through openings in the hollow rod and flows back through to the hollow plunger. The bottom of the plunger includes an unloading valve through which the leaked operating liquid returns to the cavity under the plunger.

The existing PDP designs as described above are not optimal. The length of the plunger contributes to an undesirable increase in the overall length of the pump. Length becomes a problem in applications where a well may contain bends or protrusions preventing an extended straight path for the pump. Conversely, shortening the travel length of the plunger to decrease the overall length results in reduced pump capacity. Thus, there remains a need for a shorter PDP pump that can maintain the same capacity of current PDP pumps.

Furthermore, the precise bore required for the plunger to prevent seepage and the addition of an unloading valve in the plunger add a significant increased cost to the pump. There is a need for a more cost effective means to apply hydraulic forces to the PDP tank membranes. Another disadvantage of the existing PDP is the possibility of slippage of the rod when it is screwed together with the rod column and the possibility of an unexpected rod exit when the pump is being lowered into a well or during transport. Thus, there is a need for improving the connection of the rod at the entrance to the pump. Finally, tank assembly methods typically require connecting tank collector branch pipes by linking branch pipes in a process that requires expensive welding and accessories to assure concentricity of the various pipes. There is a need for a PDP that can utilize less expensive, yet fully effective, branch pipe connection techniques.

SUMMARY Accordingly, the invention is directed to pumping equipment for evacuating heavy oil containing mechanical impurities and embedded in strata that improves upon the aforementioned deficiencies of conventional plunger-diaphragm pumps (PDP).

The present invention seeks to improve serviceability and mean-time-between failure of the typical PDP while reducing the manufacturing cost. In particular, the design of the connection of the hydraulic rod to the rod column in accordance with the invention prevents inadvertent exit of the rod. Also, the overall length of the pump is reduced - and the capacity maintained - by eliminating use of a plunger, thus allowing use of the pump in wells with shorter straight-line runs than previously were possible. The elimination of the plunger also saves production costs by eliminating plunger materials and avoiding use of precision boring techniques in the cylinder.

The production cost of a pump according to the present invention is reduced due to a change in how the operating fluid is delivered to the cavity against the tank's flexible membrane. The operating fluid is displaced from the cylinder by a conditional rod, eliminating the need for a plunger and the unloading valve required in typical PDPs. Further cost savings are achieved by eliminating welded kinked branch pipes and replacing them with branch pipes without welded seams.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, according to the disclosed embodiments, a pump for evacuating heavy oil containing mechanical impurities and embedded in strata is disclosed. The pump includes one or more tanks, each with a flexible membrane, situated in an external pump casing. Each flexible membrane divides each tank into two compartments. The first compartment of each tank is in fluid communication with a collector cavity. The second compartment of each tank is in fluid communication with a suction cavity. The suction cavity includes a suction valve and a forcing valve. The pump also includes a hydraulic drive connected with the collection cavity so that operational fluid from the hydraulic drive is forced against the membrane upon insertion of a hydraulic rod and creates suction against the membrane upon extraction of the rod. The external pump casing also includes a change lever for connecting to external pipes.

According to another embodiment of the invention, the hydraulic drive includes a hydrocylinder so that the displacement of the flexible membranes is caused by the change in volume of operational fluid in the hydrocylinder when a rod is cyclically inserted into and extracted from the hydrocylinder. According to another embodiment, the number of tanks in the pump may vary from as few as one to any suitable larger number.

According to another embodiment of the invention, the change lever on the external pump casing has at least one opening for a fastening screw and at least one slot for securing the tail unit of the rod. The tail unit of the rod includes an annular groove to receive the fastening screw and at least one overhang (or cam) to engage the slot. The fastening screw inserted through the change lever and into the annular grove prevents inadvertent exiting of the rod. The engagement of the overhang with the slot prevents inadvertent rotation of the rod. According to a further embodiment of the invention, the tanks are connected to branch pipes without the use of welded kink branch pipe connections so as to enable mounting into the pump casing as a single unit.

According to another embodiment of the invention, the geometric properties of the hydraulic drive are selected based on the size of the tank or set of tanks so as to prevent membrane damage due to the membrane being forced through openings in the tanks.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the figures: FIG. 1 illustrates a cross-sectional view of one embodiment of the improved plunger- diaphragm pump (PDP) in accordance with the present invention; FIG. 2 illustrates an enlarged view of a portion of the pump header section showing the entry point of the rod to the pump housing; FIG. 3 illustrates an enlarged view of the pump header section showing the end portion of the hydraulic rod and sealing rings at the entrance of the hydraulic drive cavity; and FIG. 4 illustrates an enlarged view of a portion of the pump tail section showing branch pipes without welded seams.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. FIG. 1 provides a schematic cross-sectional view of a pump according to the present invention. As shown in FIG. 1, the pump includes a two part hydraulic drive, including a header section 1 and a tail section 2. The header section 1 serves as a suction cavity and is hermetically sealed to the tail section 2, which serves as a hydraulic drive cavity.

Inside the header section 1 are an encasement 3 and a plurality of tanks 4. Each tank 4 is divided into two hermetically sealed compartments 26 and 27 divided by an elastic membrane 5. The first compartment 26 of each tank 4 is provided with a hole or set of holes 28 (FIG. 4) to enable fluid communication with a branch pipe 8. A plurality of the branch pipes 8 are connected and form, along with the connected compartment of each tank 4, a collector cavity 25.

The second compartment 27 of each tank 4 is provided with a set of holes to enable fluid communication with the cavity 29 formed by the encasement 3. The encasement 3 forms, along with the connected compartment of each tank 4, a suction cavity 29. The tanks 4 serve as a means to secure the flexible membrane 5 and, thus, to protect the hydraulic drive from contact with the extracted impurity-laden fluids.

The encasement 3 has two openings 6, 7 to connect to the space outside the encasement 3. A suction valve 6 may be located at the bottom of the encasement 3, as shown in FIG. 1, to allow liquid to enter the suction cavity 29. A forcing valve 7 may be located at the top of the encasement 3 to expel the liquid.

Inside the hydraulic drive cavity of the tail section 2, a hydrocylinder 9 is connected to a rod 10; and a change lever 12 is mounted on a casing 11 for connection to external pump and compressor pipes (not shown). The cavity of the hydrocylinder 9 is filled with a working medium or operation fluid (for example, hydraulic oil). Because of the connection between the hydrocylinder 9 and the collection cavity 25 formed by the branch pipes 8 and the associated compartment of each of the tanks 4, the tanks 4 may be partially filled with operational fluid as well. The lower portion of the rod 10, at its downward-most stroke, does not adjoin the opening to the branch pipe 8. Contact with the opening to the branch pipe 8 is prevented because the rod 10 is fitted with a tail unit 15 (FIG. 2) to which the rod column is connected. As shown in FIG. 3, the change lever 12 is fitted with a fastening screws 14 that are screwed into the change lever 12 to avoid slipping of the rod 10 (shown in FIG. 2) during connection to the rod column. The tail unit 15 of the rod 10 has an annular groove, into which the fastening screws 14 can be inserted. Also, two overhangs (or cams) 17 are included on a bearing flange 16. By means of the overhangs 17, the tail unit 15 enters the slots on the face end of the change lever 12. Use of the fastening screws 14 and the overhangs 17, ensure that the rod 10 (FIG. 2) is securely locked from unwanted shifts and slipping caused by rotation of the rod column.

Returning to FIG. 1, the suction cavity 29 of the header section 1 is connected to the pressurization cavity of the tail section 2 by the hydraulic drive, where the hydrocyilinder 9 forms an annular channel with the external casing through which the impurity-laden oil flows into lifting pipes (not shown).

Upon initiation of the pump cycle, the rod 10 is released from its secured position (in which the tail unit 15 is engaged by the fastening screws 14). This motion determines the lower point of movement of the rod 10. During the subsequent upward motion of the rod 10, a vacuum is created inside the hydrocylinder 9 and the collector cavity 25 formed by the branch pipes 8 and the tanks 4. Under this vacuum, the impurity-laden oil that was filling the header section 2 via the suction valve 6, displaces the membranes 5 and fills up the tanks 4.

During the downward motion of the rod 10 from the upper position, the volume of the cavity in the hydrocylinder 9 decreases due to the insertion of the rod 10. Thus, operational fluid inside the collector cavity 25 is swept into the tanks 4 and against the membranes 5. During this process, each of the membranes 5 is displaced and the impurity- laden oil is forced out of the tanks 4 and passes through the forcing valve 7 (shown in FIG. 1) and subsequently past the change lever 12 into the external lifting pipes (not shown). During the pressurization process the suction valve 6 stops any liquid from flowing back into the well until the pump cycle repeats.

While a conventional PDP uses a plunger to force hydraulic fluid against a membrane, that plunger must be of substantial length to reduce potential leaks past the plunger into the cylinder above the plunger. From FIG. 2 it can be seen that an end portion 18 of the rod 10 does not counteract with a surface 19 of the hydrocylinder 9. Instead a gap exists between the hydrocylinder 9 and the rod 10 allowing fluid flow around the hydrocylinder 9. Thus, the interior surface of the hydrocylinder 9 and the rod 10 of the present invention do not work as an adjoining pair, which allows for less stringent tolerances in the manufacture and assembly of the hydrocylinder 9 and the rod 10 when compared with traditional hydraulic plungers. Also the need for an unloading valve in traditional hydraulic plungers is eliminated.

As shown in FIG. 2, at the end portion 18, a bearing plate 20 is fitted. The bearing plate 20 can serve as a stopper to prevent accidental exit of the rod 10 from the hydrocylinder 9. The bearing plate 20 may be in the form of a multi-lobe centering cam that allows fluid flow past the bearing plate. The bearing plate 20 can be used as a centering device for the rod 10. However, there is no need to use the bearing plate 20 as a centering element if the sealing base of the rod 10 in a box 21 is sufficient (e.g., normally between 5-6 diameters of the rod).

A set of sealing rings 22 is located inside the box 21. The outer-most ring serves as a wiper. Rubber, fluoroplastic or a combination of the two is preferably used as a material for the sealing rings 22. However, any suitable material may be used. Using a larger number of the sealing rings 22 than shown in FIG. 3, with at least one of them serving as a wiper ring, may increase reliability and leakage prevention.

Filing the pump with operation fluid (for example, oil) can be performed during or after the pump assembly. After assembly, a drainage pipeline 24 (FIG. 1), which enables bleed air to be released during filing, is fitted with a safety valve 23. In case of overfilling in the event that the hermetic seal is lost, the valve protects parts of the pump from destruction, enabling further operation of the pump until the termination of feed.

During the pump operation, the existence of hydro-pads (not shown) or other means of stabilization between the tanks 4 and the membranes 5 is important to ensure the membranes 5 are not squeezed out through openings in the tanks 4. Such an occurrence would result in damage or premature wear of the membranes. Using the proper ratio between volumes of the tanks 4, volume of the branch pipes 8, and volume of the hydrocylinder 9 can also prevent membrane damage.

To avoid the membranes 5 from being squeezed out through openings in the tanks 4, a working formula is used. The geometry of the tanks 4 and the hydraulic drive, as well as the amount of working fluid are related. The necessary data is calculated by the following formula: (nVT+ Vcv) > Qt> VAM

pt = tmax-t0 VAM - V0"1 fHmax, where VAM hydrocylinder cavity volume filled by actuating medium Qt actuating medium volume under to temperature VT full volume of tank n number of tanks Vcv tanks collector cavity volume to entry into hydrocylinder V0 hydrocylinder liquid volume at the most bottom active position Qo operating liquid volume under to filling indoors to oil temperature indoors β coefficient of oil volume expansivity f area of the cylinder Hmax maximum movement range of the rod Additional cost savings in manufacturing of the present pump may be realized by eliminating welded kinks in the branch pipe 8 that are typically used in PDPs and using non- welded links instead. FIG. 4 shows the branch pipe 8 connection between the two tanks 4 that utilizes a mechanical fastener. Any suitable mechanical pipe fastener may be used, including sleeves, collars, and threaded connections. The capacity of the pump can thus be expanded by simply connecting additional branch pipe 8 and tank 4 segments. Also, repairs to damages branch pipes or tanks can be accomplished by exchanging components between the non-welded links, rather than replacing an entire set of welded tanks and branch pipes.

While exemplary embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous insubstantial variations, changes, and substitutions will now be apparent to those skilled in the art without departing from the scope of the invention disclosed herein by the Applicants. Accordingly, it is intended that the invention be limited only by the spirit and scope of the claims, as they will be allowed.