Patent Application
20150136389
The disclosure generally relates to optimizing oil production by employing logic steps in a plunger lift controller to adjust cycle parameters in such a way so as to minimize bottom hole pressure and maximize production (i.e. optimize the plunger lift cycle).
As natural gas is produced from gas wells, the pressure in the formation will decrease, resulting in a reduction in gas flow rate and associated gas velocity. Before the natural drive pressure is reduced, the flow rate and velocity of produced gas may be sufficient to remove the liquids from the well with the gas. However, at some point the flow rate of gas will be insufficient to carry liquids out of the well. As a result, the liquid loading in the well will increase, and liquid will collect in the bottom of the well further reducing its output.
When production by natural reservoir pressure becomes uneconomical, artificial lift techniques can be utilized to increase well production. A number of artificial lift systems are known in the industry, including sucker rod pumps, gas lift techniques and plunger lift techniques.
A plunger lift is an artificial lift method used to de-liquefy natural gas wells and high gas-to-liquid ratio oil wells. A plunger is used to remove contaminants from productive natural gas wells, such as water (as a liquid or mist), oil, condensate and wax.
The basic function of the plunge lift controller is to open and close the well shutoff valve at the optimum times, to bring up the plunger and the contaminants and maximize natural gas production. A well without a de-liquefaction technique will stop flowing or slow down and become a non-productive well, long before a properly de-liquefied well will.
Conventional plunger lift systems, which are also known as free piston systems, utilize a plunger (piston). The well is shut in and the plunger falls to the bottom of the tubing and onto a bumper spring, seating nipple or stop near the bottom of the tubing (
Automatic control of plungers used in plunger lift systems is known in the art. Generally, an electronic controller can be utilized that is able to control all of the various valves required to open and close the well, monitor the position of the plunger, and if the well is equipped with a plunger catcher, catch the plunger at the surface. Such controllers may, for example, use pressure within the well, production flow rate, or travel time of the plunger in order to determine when to perform various operations. Alternatively, an electronic controller may simply operate based on a preset, timed schedule.
U.S. Pat. No. 7,681,641, for example, describes a self-adjusting process to adjust thresholds based on plunger arrival. In turn, those thresholds are used as open and close triggers that open and close the sales valve (i.e. determine how long it is shut-in or flows).
U.S. Pat. No. 7,464,753 describes the use of non-linear (fuzzy logic) to make adjustments to open and close triggers based on looking at plunger arrival time for previous cycles, with the previous cycle data stored in the micro-processor memory. This is an attempt to improve the efficiency of the self-adjust process by allowing for variable sized changes to control thresholds.
U.S. Pat. No. 6,241,014 uses dampened response and exponential response as a method to determine how much to adjust open and close triggers, with all references being made to time-based triggers.
U.S. Pat. No. 5,957,200 uses a microprocessor to evaluate tubing and casing pressures as open and close triggers.
Even though each of these patents discusses adjustments made to open and close triggers and that making such adjustments are necessary to optimize production from a plunger lift well, none of them ever describe what constitutes an optimized plunger cycle or what logic is required to achieve that optimization. It is quite possible the patents use purposefully vague language, because it was not understood what an optimized plunger cycle looks like, nor which parameters should be modified and how for optimization purposes.
This invention provides these missing components.
Most wells currently using plunger lift employ micro-processors that evaluate various well conditions and make determinations as to how long the well is shut-in and how long it flows. There are several patents describing which parameters are used, the analysis done, and how those parameters should be changed (self-adjusted) while well conditions are changing. Many of these patents mention that the intent is to optimize production from the well, but they never address what optimization looks like, nor do they incorporate the precise steps required to reach that optimized state. Instead, they use verbiage like “because each well will have its own unique properties, the automatic controller closing and opening the plunger lift control valve must be suitable for use on a wide variety of wells and be flexible enough to adjust to the changes that often occur during the life of the well to provide on going optimum production”. However, the actual details needed to optimize plunger lift control in various conditions are never provided.
In contrast, this disclosure describes a set of logic steps that will modify the close trigger and open trigger set points that determine the length of flow and length of shut-in of a plunger lift well so to achieve the combination that minimizes bottom hole pressure, there by maximizing production. The logic steps are capable of being integrated into existing controllers that use time to determine the length of flow and length of shut-in as well as controllers that use a combination of rates and pressures to determine when to open and close the sales valve (i.e. open and close triggers).
An optimized conventional plunger lift well will fit one of two different criteria, that of having the length of off-time be at the ‘Minimum-OFF’ time (e.g., length of time just long enough for the plunger to reach the bottom of the well, see
In order for a conventional plunger lift well to be optimized, it must be either a Minimum-OFF well, a Minimum-ON well, or occasionally one that meets both criteria (
To achieve and maintain a plunger lift well in an optimized state, even with the most sophisticated plunger lift controller (micro-processor and program logic), requires someone knowledgeable in plunger lift optimization to monitor and adjust the control parameters of the plunger lift controller as well conditions change.
Many people do not understand the cycle related changes required to achieve and maintain the shut-in and flow combination that minimizes the bottom hole pressure and maximizes production from the well. Even if people have that knowledge, many times they do not always have easy access to the information required to do the analysis or time to optimize the well. And, since optimization can be an iterative process, by allowing it to be done by the controller on every cycle, makes it much faster than having a person periodically make adjustments.
To date, no one has automated the optimization process. Engineers have refined the techniques plunger controllers used to make changes, but they have never incorporated the steps required to reach and maintain the optimized state. When a well is not optimized, the current process consists of manually changing settings in a controller so as to drive the well to one of the two optimized types. Thus, time and money is spent on training people on plunger lift optimization principles and implementing these principles to reach an optimized well status.
The new logic described herein eliminates the need for continual human intervention and potential misinterpretations of plunger optimization principles, as those principles relate to how the well should be cycled to achieve an optimized state. This logic will adjust the flow period and shut-in periods automatically so as to minimize bottom hole pressure and maximize producing rate. It will also change the cycle characteristics of the well to maintain the minimum bottom hole pressure as reservoir, surface conditions, and equipment related items change. Once properly setup, it will essentially do this with minimal human intervention.
Thus, the present disclosure also minimizes the need to train people in plunger lift optimization as it relates to how the well should be cycled. Training for other aspects of the optimization process, such as surface and down hole equipment maintenance and surface pressure settings, is still necessary. However, since training on the principals of how to cycle a well is often the most difficult and time consuming, the presently disclosure logic will save time and cost.
Current plunger lift controllers compare conditions to certain thresholds and open and close the well when those thresholds are met. Many controllers monitor plunger arrival velocity, or time and adjust those thresholds to achieve a desired result. However, to optimize a well that is not a Minimum-OFF well or a Minimum-ON well requires that someone knowledgeable in plunger lift optimization continually monitor and adjust those settings/thresholds to drive the well to become one of those two characteristic well types. The proposed logic eliminates the need for an individual to make adjustments to the settings to achieve an optimized well (e.g., Minimum-OFF well or Minimum-ON well).
The logic shown in
This logic could potentially be used on some micro-processors by itself, but in most cases will be added to existing plunger lift control logic, so it can take advantage of the other functionality that those controllers bring to the operation.
The logic/process can generally be described as follows:
Information Needed (Controller Source):
Calculations Needed:
The above calculations are directed towards plunger arrival and plunger velocity. The actual plunger velocity needs to be within the upper and lower velocity limits for the type of plunger (i.e. target plunger arrival velocity) being used to prevent wear and damage to the well.
Settings (Either Added to Current Controller Settings or from Controller Current Settings):
Potential Enhancements to the System can Include the Following:
As used herein, “Open Time” or “ON Time” means the rise/lift time for the plunger plus any afterflow time.
As used herein, “Close Time” or “OFF Time” means the fall time for the plunger plus any extra time to allow pressure to build in the well.
As used herein, “Open Trigger” means thresholds that trigger the opening of the well (e.g., the beginning of “ON time”).
As used herein, “Close Trigger” means thresholds that trigger the closing of the well (e.g., the beginning of “OFF time”).
As used herein, “Open Trigger Set Point” refers to the threshold value for the open trigger above which, if the Minimum-OFF time is satisfied, the flow/on portion of the cycle will begin.
As used herein, “Closed Trigger Set Point” refers to the threshold value for the closed trigger above which will cause the well to shut-in starting the off time portion of the next cycle.
As used herein “Afterflow Length” refers to the length of time during a cycle that the well flows after the plunger has arrived at the surface. “OFF Time Length” refers to length of time during a cycle while the well is shut-in (not flowing). “ON Time Length” refers to the length of time during a cycle that the well flows. This includes the time when the plunger is traveling to the surface and any afterflow.
As used herein, “Minimum-ON Maximum Afterflow Set Point” refers to the number of minutes of afterflow above which the well is not considered a Minimum-ON well.
As used herein, “Minimum-OFF Time” refers to a controller setting (usually in minutes) before which the controller will not start the open portion of the cycle. It is intended to insure sufficient closed time has occurred for the plunger to reach the bottom of the well and is often equal to the plunger travel time to the bottom.
As used herein, “High Line Delay” refers to a delay feature used when line pressure exceeds a pre-set limit. This delay causes the well to stop cycling until the line pressure falls below a pre-determined setting. In some controllers, if the line pressure remains high, the delay times out and the well will remain shut in.
As used herein, “Non-arrivals” refers to failed plunger arrivals and “Consecutive Non-arrivals” refers to the number (two or more) of failed arrivals in a row of plunger runs.
As used herein, “Consecutive Non-arrival Shut-in” refers to the number of consecutive cycles the plunger does not arrive, which causes the controller to stop cycling the well until an operator manually re-starts the cycling process.
As used herein, “High Line Delay Recovery Auto-adjust Pause” or “HLDRAP” means the number of full cycles since the most recent cycle pause because of a high line delay.
As used herein, “Auto-Tune Value” means the increment or decrement made to the open and close trigger set points when the plunger arrival velocity is outside of the range set in the controller. The increment and decrement values are settings that are set for each trigger. (e.g. C/L, % critical lift, etc.).
As used herein, “Non-arrival Open Trigger Auto-tune Multiplier” or “NAOTAM” is a number which is multiplied times the open trigger increment value and added to the open trigger setting when the number of consecutive non-arrivals exceeded a set point, resulting in additional off time to recover from an abnormal set of conditions. The purpose of the NAOTAM is to help accumulate more energy (through increasing shut-in time and therefore accumulated pressure/energy) during the off cycle than a normal incremental (or decremental) change. Typically, the multiplier can be any value, normally 1.5-6, preferable 2-4, and most preferably 2-3.
As used herein, “Close Trigger Auto-Tune Increment” and “Open Trigger Auto-Tune Increment” are the amount of adjustment made to the close or open trigger thresholds if the plunger arrival velocity is below the Target Plunger Arrival Velocity Lower Limit.
As an example of the auto-tune increment, if the close trigger being used is % critical lift rate and the controller is using 1.9 or 190% of critical lift rate to close the well, the auto-tune increment might be 0.1. When the controller detects a slow plunger arrival, the trigger set point would be changed to 2.0 or 200% of critical lift for the next cycle, causing the well to close sooner resulting in the accumulation of a smaller fluid slug which requires less energy to lift. Also, if the open trigger being used is C/L (casing pressure divided by line pressure), and the controller is using 1.6, the auto-tune increment might be 0.2. This would cause the trigger value to be changed to 1.8 if the controller detected a slow plunger arrival. This would allow more build up pressure to accumulate prior to opening the well thereby causing the plunger to rise at a higher velocity during the next cycle.
As used herein, “Open Trigger Auto-Tune Decrement” and “Close Trigger Auto-Tune Decrement” are the amount of adjustment made to the open or trigger thresholds if the plunger arrival velocity is above the Target Plunger Arrival Velocity Upper Limit.
As an example of an auto-tune decrement, if the close trigger being used is % critical lift rate and the controller is using 1.9 or 190% of critical lift rate to close the well, the auto-tune decrement might be 0.1 or 10%, so when the controller detects a fast plunger arrival, the trigger set point would be changed to 1.8 or 180% of critical lift for the next cycle causing the well to flow longer resulting in the accumulation of a larger fluid slug which requires more energy to lift. Also if the open trigger being used is C/L (casing pressure divided by line pressure), and the controller is using 1.8, the auto-tune decrement might be 0.2 which would cause the trigger value to be changed to 1.6 if the controller detected a fast plunger arrival. This would result in a lower build up pressure required prior to the well opening thereby causing the plunger to rise at a lower velocity during the next cycle.
As used herein “Load Ratio” means a ratio of casing pressure minus tubing pressure divided by casing pressure minus line pressure, i.e. (CP−TP)/(CP−LP). This ratio is often used as an open trigger.
The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise.
The term “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated.
The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive.
The terms “comprise”, “have”, “include” and “contain” (and their variants) are open-ended linking verbs and allow the addition of other elements when used in a claim.
The phrase “consisting of” is closed, and excludes all additional elements.
The phrase “consisting essentially of” excludes additional material elements, but allows the inclusions of non-material elements that do not substantially change the nature of the invention, such as instructions for use, sensors, and the like.
The following abbreviations are used herein:
The disclosure provides novel control logic used to control a plunger lift system to maximize hydrocarbon recovery from a well. The invention comprises any of the following embodiments in any combination thereof:
The following examples are intended to be illustrative only, and not unduly limit the scope of the appended claims.
With reference to
In a typical arrangement, the well production will flow through the tubing 14 to the wellhead 16. For plunger lift operations the tubing 14 can be provided with a stop 18 or seating nipple 19 at the lower end of the tubing 14, and a plunger 20 which travels in the tubing 14 to the wellhead 16. In a typical arrangement, a manifold 22 is provided at the wellhead 16, which can have a plunger catch 30 to hold the plunger in place, a lubricator 32, and a control box 34 to control the flow of gas and liquid from the well by operating the valves 24, 26, 28 and 250 and related conduits.
Stop 18 is provided to prevent plunger 20 from falling below the position of the stop 18. The stop 18 can include a spring 36 or other shock-absorbing device to reduce the impact of the falling plunger 20. The plunger 20 can be of any of the numerous designs that are known in the art or another delivery system as described herein.
The plunger 20 provides a mechanical interface between the gas 38 and the liquid 40 present in the well. After shutting the well off at the surface, plunger 20 is allowed to fall to the bottom of the well and rest on the stop 18. After pressure builds in wellbore 10, the well is opened and the pressure will push plunger 20 and liquid 40 on top of plunger 20 up the tubing 14 to the surface.
When plunger 20 reaches the top of the well it enters or is received by a manifold 22. Manifold 22 can include a shock absorbing spring 42 or other mechanism to reduce the impact of the plunger. A plunger arrival sensor 41 is provided to detect arrival of the plunger 20 at the surface and if the well is equipped with one, to activate plunger catcher 30, which holds the plunger 20 until a signal is received to release plunger 20. In many cases no automated plunger catcher exists so the plunger remains at the surface until flow ceases or is sufficiently reduced to allow the plunger to fall. Control box 34 contains circuitry for opening and closing the appropriate valves 24, 26, 28, and 250 during the different phases of the lift process.
However, even with the above data gathering and self-adjusting by the control box, the well conditions may not be optimized. Currently, no automated optimization system exists, thus, someone knowledgeable in plunger lift optimization must still monitor the unit and manually adjust parameters to insure the well reaches and maintains an optimized state. This could lead to potential misinterpretations of what adjustments should be made and result in the well spending more time in an un-optimized, and thus less efficient, state.
The present disclosure is directed to control box logic that can be implemented with existing plunger lift control logic to automate the optimization process with minimal human intervention. This novel control box logic is exemplified in
In contrast, an optimized Minimum-OFF well is shown in
As reservoir pressure declines, less buildup pressure/energy is available for lift from the Minimum-OFF time, so ON times must be shorter so as to accumulate smaller fluid slugs. Over the life of the well, while maintaining a minimum shut in time, the slug size (and afterflow) gets smaller and smaller until there is no afterflow time at all. At this point, the well is a “both”, i.e. both a Minimum-OFF and a Minimum-ON well (
As the well continues to be produced, reservoir pressure continues to decline, making less energy available with the shut-in in being the Minimum-OFF time. At that point, the OFF time has to be increased beyond the minimum to accumulate energy to lift the smallest fluid slug possible (afterflow time has been reduced to zero), thus creating a Minimum-ON well (
To illustrate the difference another way, early in the life of the well, the number of cycles per day start out being very few in a Minimum-OFF well because a larger afterflow time is needed to produce the largest slug size for the corresponding lift pressure accumulated during the Minimum-OFF time. Because the lift energy accumulated during the Minimum-OFF time declines with reservoir pressure, the number of cycles increases until it reaches a maximum when the well is a “both” because no afterflow time is needed to produce the largest slug size possible, although very small for the corresponding lower lift pressure.
The number of cycles decreases again as the reservoir pressure continues to decline, because the well must be shut in for additional time to accumulate the pressure (or energy) needed to lift the smaller slugs generated with no afterflow. Finally, the produced gas decreases as the reservoir pressure declines until the well is abandoned.
The logic described herein automatically adjusts for all of these changes over the life of the well. Before proceeding through the logic steps, some information is needed from the controller. This includes the valve on and off time, plunger arrival time, whether plunger actually arrived, and was there a High Line Delay since last flow period. From this information, certain calculations are made to determine consecutive non-arrivals, afterflow length, off time length, plunger arrival velocity and how many cycles have occurred since a High Line Delay. The information and calculations are used by the controller to make adjustments to the system as the controller proceeds through the steps of the logic.
Referring to
In determining a Minimum-ON well (401), if the afterflow is less than the Minimum-ON maximum afterflow set point, the well is a “Minimum-ON well” and the logic proceeds to the next question regarding plunger arrival velocity (411). The actual plunger arrival velocity is compared to the target plunger arrival velocity upper limit. If the actual velocity is larger, then the control box will attempt to slow down the plunger velocity on the next cycle by decreasing the OPEN trigger threshold by the open trigger auto-tune decrement value. This adjustment should result in a shorter shut-in time, thus reducing the amount of pressure built during OFF time. A lower amount of pressure available for lift will result in the plunger having a slower rise velocity.
If the plunger velocity is smaller than the target plunger arrival velocity lower limit (421), the control box will attempt to speed up the plunger on the next cycle by increasing the OPEN trigger threshold by the open trigger auto-tune increment value. This will result in a longer shut-in time, resulting in an increased amount of pressure during the OFF period. A higher pressure will push the plunger at a higher velocity.
The control box makes no changes if the actual plunger velocity falls within the upper/lower limits of the target arrival velocity. This is because the well is meeting the criteria for being a Minimum-ON well with the plunger arriving at the desired velocity. Note, for most open triggers, there exist a proportional relationship between the OPEN trigger and the OFF time. Thus, increasing the OPEN trigger threshold increases the OFF time.
As mentioned previously, if the afterflow is greater than the Minimum-ON maximum afterflow set point, then the actual OFF time is compared with the Minimum-OFF time setting (402) to determine if the well is an optimized Minimum-OFF well. If the actual OFF time that is less than or equal to the Minimum-OFF time setting (i.e. less than 101% of the Minimum-OFF time setting), the well is a “Minimum-OFF well”. Much like before, the controller will then compare the plunger velocity with the upper/lower limits of the target plunger arrival time.
If the actual velocity is larger (412), then the control box will attempt to slow down the plunger velocity on the next cycle by decreasing the CLOSE trigger threshold by the close trigger auto-tune decrement value. This should result in more afterflow time thus increasing the size of the slug to be lifted during the next cycle. If the plunger velocity is smaller than the target plunger arrival velocity lower limit (422), the control box will attempt to speed up the plunger on the next cycle by increasing the CLOSE trigger threshold by the close trigger auto-tune increment value. This should result in less afterflow time thus decreasing the size of the slug to be lifted during the next cycle. Note, for most close triggers there exist an inverse relationship between the CLOSE trigger and the ON time. Thus, increasing the CLOSE trigger threshold decreases the ON time.
The control box makes no changes if the actual plunger velocity falls within the upper/lower limits of the target arrival velocity. This is because the well is meeting the criteria for being a Minimum-OFF well with the plunger arriving at the desired velocity.
It should be noted that logic steps 401 and 402 are interchangeable. In other words, the logic can determine if the well is a Minimum-ON well (401) and if not, check to see if it is a Minimum-OFF well (402), or check to see if it is a Minimum-OFF well (402) and if not, check to see if it is a Minimum-ON well (401). If, in the first step, the well is optimized, then the logic will not check to see if the well meets the other optimize state.
If neither the afterflow or OFF time is below their minimum set point, then the actual plunger arrival velocity is checked against the upper (403) and lower set limits (404). If the plunger velocity is outside the target limits, then steps are taken to decrease/increase the velocity in an effort to move towards one of the optimized states. If the actual plunger arrival velocity falls above the upper limit (403), then the OPEN trigger is reduced by the open trigger auto-tune decrement, and subsequently, the OFF time is decreased. If the actual plunger arrival velocity falls below the lower limit (404), then the CLOSE trigger is increased by the CLOSE trigger auto-tune increment, and subsequently, the ON time is decreased.
If the plunger velocity is within the target limits, yet is neither a Minimum-ON or Minimum-OFF well, then the logic moves the cycle toward one of those two states (405) by either taking a less conservative approach by decreasing the OPEN trigger by the open trigger auto-tune decrement value and slowing the plunger arrival velocity to a value below the plunger arrival velocity lower limit, or it can be set to take a more conservative approach by increasing the CLOSE trigger by the CLOSE trigger auto-tune increment value and speed up the plunger arrival velocity above the plunger arrival velocity upper limit.
Then after the next cycle, the logic will adjust to either the OPEN or CLOSE trigger to bring the velocity back between the upper and lower plunger arrival velocity limits. After several cycles (iterations) the well will be moved to either a Minimum-OFF well or a Minimum-ON well, or in a rare occasion both a Minimum-OFF and a Minimum-ON well with the plunger arrival velocity within the desired limits.
It should be noted that the adjustments, increments/decrements (i.e. auto tune value), can be preprogramed into the logic. Exemplary numbers will vary depending on the trigger used (e.g. C/L, T/L, LR, flow rate, % critical lift rate, etc.) and just how big of adjustments the operator wants the controller to make (see the examples under [0050] and [0052]. These are typically a set number (e.g. a setting in the controller). However, it may be possible to incorporate a variable approach to the increment and decrement as a future enhancement. In fact, some controllers already allow for a variable increment or decrement depending on how far the plunger speed is from the desired range.
The logic displayed in
However, there can also be certain “exception” events that can occur requiring specific action. Examples of these events include high line pressure events and plunger non-arrivals. If the plunger lift system is having issues such as these, then specific problems can be addressed by a simple addition on the front of the logic, as shown in
If there has been a high-line pressure delay, then the logic determines if the plunger has arrived. If the plunger has not arrived, it checks to see if there has been more than the allowable number (X) of consecutive non-arrivals (521). If the allowable number is exceeded, the well is shut in to allow the line pressure to lower. Once lower, then the well cycle will restart. If the allowable number of consecutive non-arrivals has not occurred, then OPEN trigger is increased to increase the OFF time. The amount that the trigger is increased is equal to (open trigger auto-tune increment value)*(non-arrival multiplier). The non-arrival multiplier is simply a way to increase the adjustment such that more energy can be accumulated in an attempt to get the well back on track and prevent it from logging off, which may result if the adjustment is only equal to the auto-tune value. A typical multiplier is any value between 2-6, preferably 2-4, and most preferably 2-3. If the plunger did arrive, no action is taken and the system is allowed to reset.
When the well is recovering from a high line pressure event, the logic halts any optimization adjustments until the cycle count since the last high line pressure delay has exceeded a set point value (HLDRAP) (502). Once the target number of cycles is reached, the control will essentially perform a systems check to make sure the plunger is arriving 503. It if is, then the control will move through the decision tree displayed in
The novel logic described above provides an automated method of optimizing the well and maintaining the optimized status. Also, because the logic is automating the process, it will seamlessly change the cycle characteristics to maintain the minimum bottom hole pressure as reservoir, surface conditions, and equipment related items change.
It is well understood by those familiar with well optimization principles, that uplift is dependent on the change in bottom hole pressure and current reservoir pressure. Experiments showed that use of the aforementioned logic results in a lower bottom hole pressure and therefore uplift values in the ranges expected.
The present invention is exemplified with respect to
All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience:
This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/907,227 filed Nov. 21, 2013, entitled “PLUNGER LIFT OPTIMIZATION,” which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61907227 | Nov 2013 | US |
