Abstract:
A system and method for optimizing transferred fluid volume during an oil well pumping cycle. The speed of a traveling valve, which lifts the petroleum from the well, is monitored to determine at what point during its downstroke the traveling valve contacts the hydrocarbon fluid that has accumulated in the bottom of a petroleum pipe. The system then analyzes speed data returned by a lift sensor and adjusts the speed of the traveling valve either upward or downward during the next upstroke to optimize the amount of hydrocarbon fluid transferred. The system can be configured to handle different ascent speeds, and chooses the most suitable speed depending on the petroleum level detected within the production pipe during the route of the traveling valve downwards.

Description:
REFERENCE TO A RELATED APPLICATION  
       [0001]     This is a non-provisional application relating to the content of, and claiming priority to, Mexican Patent Application No. NL/a/2005/000053, filed Jun. 22, 2005, which is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention.  
         [0003]     The present invention relates to the field of crude oil production and, more specifically, to a system and method for optimizing transferred fluid volume by a traveling valve during a pumping cycle.  
         [0004]     2. Background of the Invention.  
         [0005]     In its broadest definition, an oil well is a perforation into the earth aimed to producing hydrocarbon liquids and gases. The life of a well typically has four stages: drilling, completion, production, and abandonment. The well is created by using a rig that turns a drill bit to drill into the earth. A casing pipe slightly smaller than the drilled hole is then run into the hole and cemented thereto. This casing provides structural support for the hole, which is subjected to a number of violent compressive forces and caustic chemicals during the drilling process. The casing also serves to isolate potentially dangerous high pressure zones from each other and from the surface. Wells frequently have multiple sets of progressively smaller hole sizes nested inside one another, each cemented with casing.  
         [0006]     After drilling, the well is “completed,” which means that well is made capable of producing hydrocarbon products. In cased well bores, a section of the casing in the hydrocarbon producing zone is often perforated to allow the oil and gas to flow into the well bore from the surrounding formation. When a hole is not cased, which is called an open hole completion, a filter material such as sand or gravel may be used with the hole to facilitate the flow of oil and gas into the hole.  
         [0007]     After completion, the drilling and completion tools are removed from the drill site, and the production tubing is connected to a collection of valves for regulating pressure and flow. This network of valves, sometimes called a “Christmas tree,” allows the hydrocarbons to be routed in a plethora of directions that may lead to different pipelines for moving the product off site.  
         [0008]     Ideally, the well will produce hydrocarbons for a very long time, but inevitably, during the abandonment phase of the well&#39;s life, it becomes uneconomical to produce from the well. In most wells, the natural pressure of the subsurface reservoir is high enough to push the oil or gas to the surface, but this is not always the case. In depleted fields, such as fields with a high density of wells that causes the overall pressure to be widely disbursed, decreasing the production tubing diameter may be enough to help the production, but other types of artificial lift might also be used, such as downhole pumps or surface pumpjacks.  
         [0009]     Real time monitoring of the upstroke and downstroke of an oil well is not new, but the primary focus of such applications have been directed toward minimizing or eliminating conditions known as “pump off” and “fluid pound.” See, e.g., U.S. Pat. No. 4,594,665; U.S. Pat. No. 4,666,375. Pump off occurs in depleted wells when fluid is withdrawn from the well at a rate greater than the rate at which fluid enters the well from the formation. In other words, the upstroke of the pump is removing the oil faster than the oil is produced by the formation. When pump off occurs, the subsequent down strokes begin to pound the fluid in the well, which causes severe jarring of the entire pumping unit potentially resulting in damage to the well equipment.  
         [0010]     Other methods are directed primarily toward increasing the efficiency of the well. For example, U.S. Pat. No. 6,854,518 discloses a method for enhancing production of oil that reduces the pressure at the top of the well. The resulting increased difference between the well pressure at the surface and the well pressure at the formation results in a higher production flow.  
         [0011]     U.S. Pat. No. 5,064,349 addresses both the pump-off and optimization problems by providing a method that includes measuring the displacement and the load on a rod string, determining when the well is pumped off due to stoppage of fluid flow, and subsequently adjusting the delay between each pumping cycle, meaning one upstroke and one downstroke. The delay time between cycles is determined from measuring the rod load during the downstroke until the rod load reaches a point of substantial stabilization.  
         [0012]     Similarly, U.S. Pat. No. 6,497,281 also addresses both the pump-off and optimization problems by providing a “smart pump” that adjusts the rate of the well&#39;s pumping cycle to coincide with the well&#39;s production history. The invention uses stored production data to time the cycle appropriately for the rate of fluid produced from the formation.  
         [0013]     In contrast to the prior art, the present invention optimizes the volume of hydrocarbons transferred during the upstroke of the pumping cycle. This allows a well operator to recover hydrocarbons from wells from which production would otherwise not be economically viable.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a method and system for optimizing the amount of fluid transferred during the upstroke of a pumping cycle. The system comprises a casing pipe. disposed in the ground and extending from the surface of the well to beneath a hydrocarbon production zone. The casing pipe has a perforated section for permitting petroleum to flow into the casing pipe from the surrounding hydrocarbon production zone. According to the preferred embodiment of the invention, a filtering material surrounds the casing pipe from the bottom of the well to a level above the production zone, thus requires any hydrocarbons flowing into the casing pipe to move through this filtering material. Concrete encircles the remainder of the casing pipe from the level of the filtering material to the surface.  
         [0015]     A production pipe is nested within the casing pipe, and the production pipe further contains a system of valves for moving accumulated petroleum from the bottom to the top of the production pipe. As hydrocarbon fluid flows into the casing pipe through the perforated section thereof, the fluid accumulates at the bottom of the casing and production pipes. The valve assemblies, which are similar to ball-and-seat valves commonly used in the industry, operate to lift the hydrocarbon fluid from the bottom to the top of the production pipe, where it is forced though a first pipe and into a collection reservoir for later retrieval.  
         [0016]     According to the preferred embodiment of the invention, the valve assemblies are functionally connected to a lift assembly located at the surface over the well. The lift assembly comprises a hydraulic lift moveable along a vertical axis that is parallel to the longitudinal axis of a pumping rod attached to a traveling, or moving, valve and a lift anchor affixed to the hydraulic lift. This assembly also includes a lift tower for providing the hydraulic lift with structural support and guidance for the movement of the hydraulic lift and a lift controller functionally connected to the hydraulic lift for controlling the valves according to a predefined program. A lift sensor measures the speed of the hydraulic lift and returns this speed measurement to the lift controller.  
         [0017]     According to the method of the invention, the speed of the traveling valve is monitored to determine at what point during its downstroke the traveling valve contacts the hydrocarbon fluid that has accumulated in the bottom of the petroleum pipe. The system then analyzes speed data returned by the lift sensor and adjusts the speed of the traveling valve either upward or downward during the upstroke to optimize the amount of hydrocarbon fluid transferred. The system can be configured to handle different ascent speeds, and chooses the most suitable speed depending on the petroleum level detected within the production pipe during the route of the traveling valve downwards.  
         [0018]     In the preferred embodiment, the operation of the fixed, traveling, and main valves generally apply typical ball-and-seat valve principles. A ball-and-seat valve is a device used to restrict fluid flow to one direction. It consists of a polished sphere, or ball, usually of metal, and an annular piece—the seat—that is ground and polished to form a seal with the surface of the ball. Gravitational force or the force of a spring holds the ball against the seat. Flow in the direction of the force is prevented, while flow in the opposite direction overcomes the force and unseats the ball. A more detailed description of this ball-and-seat operation as it pertains to the present invention is included herein.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The present invention, as well as further objects and features thereof, is more clearly and fully set forth in the following description of the preferred embodiment, which should be read with reference to the accompanying drawings, wherein:  
         [0020]      FIG. 1  describes operation of the system of the present invention; and  
         [0021]      FIG. 2  describes the pump assembly positioned within a production pipe of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     As shown in  FIG. 1 , the system of the present invention may be installed in a hydrocarbon producing zone  3  by drilling a vertical borehole  2  through the earth&#39;s surface  1  to determine the depth of the producing zone  3 . Thereafter, the borehole  2  is further extended under the producing zone  3  and a casing pipe  4  disposed therein. Filtering material  5  is interposed between the casing pipe  4  and the wall and floor of the borehole  2 . The filtering material  5  fills the space between the casing pipe  4  and borehole until a depth at least sufficient to span the producing zone  3 . Concrete  6  fills the remaining space between the casing pipe  4  and borehole  2  wall above the filtering material  5 .  
         [0023]     The casing pipe  4  comprises a perforated section (not shown) positioned at the depth of the producing zone  3  for providing an ingress path for petroleum  50  that migrates through the filtering material  5 . Petroleum  50  may be forced to the top of the casing pipe  4  by natural well pressure, where the petroleum  50  can flow through a casing unloading pipe  7  to a collection reservoir  8  for storage and later retrieval.  
         [0024]     A production pipe  52  positioned within the casing pipe  4  extends from the bottom  10  of the casing pipe  4  to above the surface  1 . By operating the system, petroleum  50  lifted to a production unloading pipe  11 , which is interposed between the production pipe  52  and the collection reservoir  8 , flows into the collection reservoir  8  for storage and later retrieval. Petroleum  50  is moved to a position where it may flow through the production unloading pipe  11  by a pump assembly  9  substantially contained within the production pipe  52  and operably attached to a lift assembly  54 , the operation of which is described hereinafter.  
         [0025]     A structure  12  affixed to the surface  1  over the casing pipe  4  provides support for the lift system  54 , which drives the pump assembly  9 . The pump assembly  9  is operably connected to a lift anchor  14  through the pumping rod  16 . The lift anchor  14 , in turn, is affixed to a hydraulic lift  13  partially housed within a lift tower  15 , which provides guidance and support for the hydraulic lift  13  during operation. The hydraulic lift  13  vertically moves the lift anchor  14  along the lift tower  15  to cause the attached pumping rod  16  to drive a traveling valve  17  of the pump assembly  9 , the operation of which is more thoroughly shown in  FIG. 2 . Centering bushings  18  are fixed within the production pipe  52  to guide movement of the pumping rod  16  and maintain a centered position thereof within the production pipe  52 .  
         [0026]     A lift sensor  20  returns the speed and position of the lift anchor  14  to a lift controller  19 . Using the received speed and position information of the lift anchor  14 , the lift controller  19  determines the position of the lift anchor  14  during a downstroke thereof when the traveling valve  17  encounters petroleum  50  within the production pipe  52 . When the downward movement of the traveling valve  17  is impeded by petroleum  50 , this resistance is detected by the lift sensor  20  from the speed reduction of the lift anchor  14 , and the level of petroleum can be calculated. Based on the petroleum level within the production pipe  52 , the lift controller  19  adjusts the speed (if needed) of the anchor  14  during the subsequent upstroke to ensure that the greatest possible volume of petroleum  50  is transferred. The greater the amount of petroleum to be transferred, the faster the anchor  14  must move the pumping rod  16  and traveling valve  17 . The lift controller  19  is configurable to handle different upstroke speeds, from which the controller  19  will choose the most suitable speed depending on the level of petroleum  50  detected within the production pipe  52 .  
         [0027]     The pump assembly  9  comprises a main valve  21  fixed to the production pipe  52  near or at the bottom thereof. As more thoroughly shown by  FIG. 2 , the main valve  21  comprises a metallic main sphere  22  and a metallic main cone  23  having an opened base attached to the production pipe  52  at the circumference thereof and an opened apex of smaller diameter than the main sphere  22 . The apex of the main cone  21  is oriented toward the bottom  10  of the production pipe to allow the main sphere  22  to rest therein. The opened base of a grid code  24  is affixed to the base of the main cone  21  with the apex of the grid cone  24  oriented toward the surface  1  to contain the main sphere  22  therebetween and facilitate the operation of the main valve  21 . To optimize sealability of the main valve  21  and prevent the flow of petroleum  50  from above the main sphere  22  down through the main cone  23 , the main sphere  22  and the main cone  23  are coated with a sealing liquid sprayed on the valve through a washing hose  25 . As petroleum  50  moves from the producing zone  3  through the filtering material  5  and into the casing pipe  4 , the accumulation of petroleum  50  causes the level of petroleum to raise and unseat the main sphere  22  from the apex of the metallic first cone  23  so the petroleum may move therethough.  
         [0028]     The traveling valve  17 , which is attached to the pumping rod  16  and moved by the upstroke and downstroke thereof, collects the petroleum  50  that has moved through the main valve  21  and raises the petroleum  50  to and through a fixed valve  26 . Disposed in the traveling valve  17  are a four traveling cones  28  and traveling spheres  32  that function similarly to the main cone  23  and main sphere  22  described hereinabove, although alternative embodiments of the invention may have more or fewer of these traveling cones  28  and traveling spheres  32 . The traveling cones  28  each have an opened base and an opened apex to allow petroleum communication therethrough. In addition, because the traveling valve  17  moves vertically within the production pipe  52 , the side of the traveling valve is coating with a friction reducing material  27  (shown in  FIG. 1 ).  
         [0029]     As the traveling valve  17  encounters petroleum  50  in the production pipe  52  that has already moved through the main valve  21 , the petroleum  50  is channeled through the opened bases of the traveling cones  28  to contact the traveling spheres  32  seated on the open apexes. This causes the traveling spheres  32  to lift, thereby allowing the petroleum to flow through the apexes to a position above the traveling valve  17 . The transfer process is further facilitated by injecting a liquid flow enhancer (not shown) from the surface through a flow enhancer hose  29 . As the traveling valve  17  initiates an upstroke, the traveling spheres  32  descend by the weight of the petroleum  50  to seal and seat against the apexes of the traveling cones  28 , thereby impeding the exit of transferred petroleum  50  back through the traveling valve  17 . As the traveling valve  17  moves to complete the upstroke, it pushes the collected petroleum  50  through a fixed valve  26 , which also has a plurality of fixed spheres  33  seated on apexes of fixed cones  30  to prevent the petroleum  50  from flowing back through the fixed valve  26  in a downward direction. The fixed spheres  33  are unseated from the apexes of the fixed cones  30  when the petroleum is forced though the bases thereof, then are reseated when the traveling valve  17  initiates its next downstroke.  
         [0030]     The petroleum  50  moved through the fixed valve  26  is pushed upwards by each upstroke of the traveling valve  17  until the level of accumulated petroleum reaches the production unloading pipe  11 , by which the accumulated petroleum will flow through the production unloading pipe  11  to the collection reservoir  8  for storage and later collection.  
         [0031]     The present invention is described in terms of a preferred illustrative embodiment in which a specifically described system is described. Those skilled in the art will recognize that alternative embodiments can be used when carrying out the present invention. Other aspects and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims.