METHOD AND SYSTEM FOR OPERATING A WELL TREATMENT CHEMICAL PUMP

Abstract

A method for chemical treatment includes operating a chemical pump having a flow rate capacity of a selected multiple of a flow rate of a chemical required to treat at least one of a well and surface equipment associated therewith. The operating is performed at at least one selected time and for at least one selected duration inversely proportional to the flow rate capacity such that a volume of the chemical pumped in a predetermined time interval substantially equals a required volume of the chemical during the predetermined time interval.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND

This disclosure relates to the field of chemical pumps used to introduce treatment chemicals into subsurface wells used for production of fluids, e.g., hydrocarbons, from subsurface reservoirs and for injection of fluids into such wells, e.g., for disposal of produced fluids such as water or for maintenance of fluid pressure in a reservoir.

The nature of fluids contained in subsurface reservoirs, combined with conditions of high heat, high fluid pressure, and turbulence to which the fluids are often subjected, contribute to the formation and deposition of contaminants in wells drilled into subsurface reservoirs. Such contaminants include, for example and without limitation, scales, salts, paraffins, and asphaltenes. Salts in water extracted from a reservoir, combined with dissolved gases such as carbon dioxide and/or hydrogen sulfide, acidify the extracted water, which then can become corrosive to steel piping and equipment disposed in a well and at the surface.

Bacterial growth is also often present in oil and gas wells. Bacteria growth can lead to souring of produced fluids as a result hydrogen sulfide formed by metabolic processes of the bacteria. Bacteria can also produce other acids which can lead to corrosive attack to metal piping and equipment in a well and at the surface.

A number of approaches have been used to inhibit corrosion damage to assets and or remove deposits. For example, in oil and gas production, the technique of “batch treating” is commonly used to reduce corrosion, wherein a slug of a chemical having a selected composition is injected into a well at selected time. A typical treatment schedule may comprise one treatment every week or every two weeks, first dispensing into a well a treatment chemical of predetermined volume, followed by a separate flush treatment, typically water. The foregoing introduction of treatment chemical and flush may require that fluid production from the well or injection into the well is stopped and the treatment is completed before the well can be returned to its regular operation. Flush fluid is introduced into the well to help disperse the chemical treatment to the pipe internal surfaces in the well. The above-described treatment/flush process may require a large amount of fluid and such large amounts of fluid can reduce the treated well's fluid producing potential as a result of increased hydrostatic pressure in the well caused by the large volume of introduced fluid. By applying a chemical treatment to protect well tubulars (casing and/or production tubing) from corrosion, one may actually be inhibiting the treated well's financial value. In many low pressure gas producing wells, for example, corrosion control batch treatments can cause substantial reductions in oil and gas production volumes for days and even weeks following a corrosion control treatment as described above. In extreme examples where the chemical treatment represents a steep enough economic loss, producers may choose to halt corrosion protection treatment.

Another means of performing chemical treatments is using a process called “squeezing”, where a large volume of chemical is introduced into the reservoir formation such that the treatment chemical binds to the formation rock grains (either chemically or by surface tension) where it is slowly released as fluid is extracted from the formation and moved into the well to provide a chemical treatment that may remain effective over an extended period of time. The cost of using large amounts of chemical required for squeeze treatment in extended length wells, such as horizontal wells, could be cost prohibitive. Many such chemical treatments require displacement of fluids from the well into the formation with the risk of well damage and/or damage to the permeability of the formation and resulting loss of economic value of the well.

In addition to treating wells for corrosion with a batch or squeeze treatment, another method of treating corrosion is to pump chemicals directly into a well tubular, for example in an annular space between a production tubing and a well casing. Such treatments are commonly introduced into the well through the tubing or casing in wells using artificial lift (e.g., rod pumps or electric submersible pumps) substantially continuously. Introduction of the treatment chemical may be either directly into the well at the surface or through a separate capillary chemical injection line. Continuous chemical injection may be preferred because treatment chemical is consistently present in the well.

A limitation to continuous pumped chemical treatment is that the continuous operation of the chemical delivery pump puts a lot of wear and tear on the moving parts of the pump and therefore chemical injection pumps require frequent maintenance. Also, chemical pumps operate within a predetermined window of efficiency of output. There is an optimum effective flow rate range for any given size pump, discharge pressure, and desired fluid flow rate output. A pump designed to move fluid at high rates is not efficient when delivering fluid at relatively low rates; conversely a pump designed to move fluid at low rates cannot pump large volumes in a short time frame. For example, published literature from Sidewinder Pumps, P.O. Box 80769 Lafayette, La. 70598-0769 shows that typical chemical pumps are designed to operate continuously, require frequent maintenance, and have a specific optimum operating range.

Alternative treatment methods have therefore been sought for introducing treatment agents into oil and/or gas wells as well as flow conduits or other processing equipment used in the production of oil and gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a continuous chemical injection system installed next to a well. Shown in the drawing is a solenoid valve in a gas supply line between a pump operating pressurized gas supply and the pump. Also shown is a control box which can be used to control the operation of the solenoid valve.

DETAILED DESCRIPTION

The present disclosure relates to a method of introducing a chemical treatment composition into a well, e.g., into the annular space between a tubing and casing in the well. The treatment composition may contain a liquid well treatment agent, such as a scale inhibitor, corrosion inhibitor, salt inhibitor, paraffin inhibitor, emulsion breaker, scale remover or biocide. A treatment method according to the present disclosure may be described as a hybrid of those techniques described in the Background section herein and may be described as a “micro-batch” treatment.

A micro-batch treatment is different than chemical delivery techniques known in the art in that treatment chemical is not continuously introduced into the well. In a micro-batch treatment, chemical delivery from a chemical treatment pump is purposely and intentionally started and stopped. A method according to the present disclosure is similar to batch treating in that a selected amount or “batch” of treatment chemical is periodically introduced into a well. The difference between methods according to the present disclosure and batch treatments is that methods according to the present disclosure provide more frequent introduction of treatment chemical into a well, for example, multiple times a day. The treatment volume in each micro batch treatment introduction would be less than that introduced using batch treatment. Individual treatment volumes for a micro batch may range, for example, from a few milliliters to a few pints per treatment, versus a few gallons in a single batch treatment or drums (e.g., 55 gallon drums) for a squeeze.

Chemical treatments supplied from a continuously operated chemical pump typically operate 100% or very nearly 100% of the time. Sidewinder Pumps (referenced in the Background section herein) literature states that one model of chemical treatment pump can operate over a range of for example, 5 strokes per minute to 35 strokes per minute continuously. Even though there may be intermittent brief pauses to the operation od such pumps, the overall operation of the pump would be considered continuous to those skilled in the art of chemical treatments. Such chemical treatment pumps are designed and pump displacement volumes are chosen with continuous operation accounted for in the selection.

In many chemical treatment applications a batch treatment is a preferred method chemical application. Many oil and gas wells produce small volumes of fluid daily and would not require a large amount of chemical in each treatment. A micro-batch treatment, automatically performed in a selectively controlled manner may be a preferred method. For example, a remotely situated well in a difficult to access area producing 1 barrel per day of bacteria laden water may require a periodic batch treatment of bactericide. A required bactericide treatment of 1 quart per day in the water phase of the produced fluid may be required to control bacterial growth. The volume of water produced may make it uneconomical to move a treatment truck the distance and endure off road conditions to the well location to perform a treatment. Also, the low volume of chemical required may be below the efficient operating parameters of a continuous operation chemical pump, resulting in an uneconomical excess volume of treatment chemical introduced into the well and/or surface equipment.

A micro batch treatment of chemical supplied over a short time duration, such as a few hours, may be preferred over a slower rate, continuous introduction of of chemical in some circumstances. Chemical treatments such as bactericide treatments work best by supplying a high dosage of chemical over a relatively short time duration to result in effective sterilization. A slower dosage rate of chemical bactericide supplied continuously may not reach a high enough concentration to result in effective sterilization.

Using a method according to the present disclosure, a switch disposed in a circuit between a power supply and a chemical pump designed for continuous operation may be controllably operated such that the chemical pump does not operate continuously, but when operated, does operate at its designed fluid flow rate. An example of such as switch as applied to a pneumatically operated chemical pump may be a solenoid valve disposed between a pressurized gas supply and the pneumatically operated pump. The solenoid valve can be selectively controlled to operate the chemical pump, wherein the size of the chemical pump is selected to deliver larger fluid volumes than would be required by the particular well if the pump were operated continuously. For example, a chemical pump sold under the model number Model 84 by Sidewinder Pumps may be made to deliver one quart of treatment chemical in a micro-batch technique. Published literature of the Model 84 pump shows it to be effective in an operating range of 20 to 120 quarts per day. 20 quarts per day may be obtained by operating the pump at 5 strokes per minute. Even at one stroke per minute, 4 quarts per day is the output of the foregoing pump and such rate is significantly above the 1 quart per day required for the above example well. It may be inferred that within the published efficient operating rage of such pump it is difficult to deliver a micro batch of one quart per day of treatment chemical to such example well reliably.

Using a method according to the present disclosure, selectively operating a solenoid valve, such as an Asco brand solenoid valve for 24 minutes daily would deliver the proper treatment chemical volume to the well automatically and reliably. Using the foregoing Sidewinder Model 84 pump, one quart per day may be accurately delivered by setting the pump to operate at 15 strokes per minute, which is within the published efficient operating range of the foregoing example pump. If the foregoing example pump were operated at 15 strokes per minute for a full day (1440 minutes), the total fluid volume output would be 60 quarts. Since the example well described above requires only one quart of treatment chemical in one day, such volume may be obtained by operating the pump 24 minutes continuously, and then stopping operation of the pump for the rest of a 24 hour day.

Methods according to the present disclosure differ from batch treatments known in the art by the manner of delivery. Batch treatments known in the art are performed with a purposely built truck which is dispatched to a well at selected times and performs one treatment at each trip to the well. After the treatment, the truck leaves the well location until it is time for another treatment. The process is fully manually performed and each treatment is performed one at a time. There is no automation applied to the process. Methods according to the present disclosure automate the treatment process and allow for a fixed location chemical treatment device to be placed at the well to automatically and economically deliver a desired amount of chemical into a well at selected times.

For continuous chemical injection systems known in the art, equipment used consists of a pneumatic chemical pump, chemical tank, containment, sight glass, hoses and other hardware required to treat an oil and gas well with a chemical additive. The equipment includes a hose or other conduit in communication with a high pressure air or gas source and the chemical pump. The air or gas supply is of a suitable pressure and deliverable volume rate to have the pneumatic chemical pump operate within its designed operating parameters. In a method according to the present disclosure a controllable valve, such as an electrically operated solenoid valve or an electric motor operated valve may be disposed in the gas conduit between the gas source and the chemical pump. The air or gas line would be in communication with the chemical pump when the solenoid or motor valve is open but not in communication when such valve is shut. In the present example embodiment the valve may be one such as an Asco model HV 4270430001 ¼× 3/32 brass solenoid valve.

Because the valve, whether a solenoid valve or motor operated valve, is electrically operated, the valve may be operated by a timer or other control device such as a programmable logic controller to selectively operate opening and shutting of the valve. When the solenoid valve is open, the chemical pump will be in communication with the air or gas supply and the pump will operate within its designed operating parameters. When the solenoid valve is closed, the air or gas supply to the chemical pump will be closed, and therefore chemical delivery would stop.

Starting and stopping the chemical pump may have several advantages and unique features over having the chemical pump operate continuously. By selectively and automatically controlling the operation of the pump, the chemical injection rate can be fine-tuned. Many chemical pumps have difficulty pumping at low rates to treat low production rate wells. By altering the output of the pump in a selectively controlled manner, low injection rates are possible while maintaining operation of the pump within its designed operating parameters when operating. For example, if a pneumatic pump can reliably deliver 4 quarts of chemical daily but operates inefficiently at rates below that, setting the pump output at 4 quarts a day and having the pump only operate 1 minute out of every 4 minutes or one hour out of every four would effectively deliver 1 quart of chemical daily in a reliable manner.

Continuous functioning of a chemical pump causes excessive wear and tear on many parts of the pump. By minimizing the number of pump strokes the pump makes, less wear and tear is put on the pump. Using the example above, a pump set on an injection rate of 4 quarts per day but only operating 1 minute out of every 4 (or ¼ the total elapsed time) would result in 75% reduction of the operating time of the pump and therefore 75% reduction in wear and tear on moving parts. Decreasing the wear and tear and associated maintenance and replaced parts may be an additional benefit of a method according to the present disclosure.

FIG. 1 shows a schematic diagram of example parts used for a pneumatic air or gas operated chemical pump using methods according to the present disclosure. The example embodiment in FIG. 1 includes additional parts not ordinarily used in a chemical pump-operated treatment system. In FIG. 1, an electric solenoid valve in the pressurized gas line required to make the chemical pump function has been added. Also included is a control box which allows for the programming of operation of the solenoid valve. Programming the functioning of the solenoid valve allows automatic control of when the solenoid opens and shuts and the duration of the opening. The control box could be any mechanism used to control the functioning of an electric solenoid valve. Examples of such devices may include, without limitation, a timer or programmable logic controller.

The solenoid valve may be a fail open valve or a fail closed valve. A fail open valve is one which is open if no power is supplied to it to allow it to open or shut. A fail closed valve would be one that is closed when no power is supplied to the solenoid. In the present example embodiment, the solenoid valve may be a fail closed valve such as an Asco model HV 4270430001 ¼× 3/32 brass valve.

EXAMPLE

A field installation is provided herein as an example. A chemical injection system was set up on a pumping well near Caldwell, Texas which had a low pressure annulus. The objective of the field installation was to determine if a pneumatic chemical pump could be made to deliver reliably 1 quart per day liquid output. There are numerous wells in the geographic area of the field installation which produce low fluid volumes, so a low chemical pump output is desirable. Chemical pumps known in the art, however, are not reliable over time at delivering a quart of liquid per day. A prototype chemical delivery system was developed. A regular industry standard continuous injection chemical delivery system was built which included the additional equipment of a programmable electric solenoid valve in the gas supply line between the pump and the gas supply source. A control box with power supplied from a solar panel and rechargeable 12 volt battery was included to control the operation of the solenoid. Pictures of the prototype system are included separately.

FIG. 1 shows a schematic of the parts of an embodiment of a chemical pump system that may operate according to the present disclosure. A chemical tank or reservoir, sight glass, hoses and fittings 1 were set up to treat a pumping well 20 with a low pressure annulus 7 using a corrosion inhibitor treatment chemical. The chemical tank 1 outlet may be connected to a manually controlled valve 2. The manually controlled valve 2 may be provided to avoid spillage or loss of chemical during servicing of the system. The manually controlled valve 2 may be connected to the suction side of a chemical pump 6, in the present example a pneumatically operated, positive displacement chemical pump. An injection rate of one quart of treatment chemical per day was a desired chemical output. The chemical pump 6 is designed to deliver 7 quarts per day under full speed continuous injection.

A selectively operated (e.g., Asco model HV 4270430001 ¼× 3/32 brass solenoid valve) valve 4 may be placed in the gas supply line between a gas supply source 3 and the chemical pump 6. A controller 5, for example, containing a programmable logic controller was programmed to operate the valve 4 at selected times. The valve 4 was operated to open and supply gas from the source 3 to the chemical pump 6 for 7½ minutes every 3 hours. Chemical outputs were measured periodically and it was determined the chemical pump output was 150 milliliters every 7½ minute cycle. Every three hours 150 milliliters of chemical was introduced into the well 20 in a micro-batch fashion. An output of 0.3 gallons per day or just over a quart per day was the daily output. Modifying the time sequence or frequency or operating the valve 4 could further optimize the chemical output. The result of the prototype equipment and the field example showed that a selectively operated solenoid using a programmable logic controller could control the chemical delivery volumes of a pneumatic pump.

Other components of the system may include a chemical supply line 6A that may be coupled to a casing valve 7 on a wellhead 8 affixed to the top of the well 20. The casing valve 7 is opened into the annular space 9 between the well casing 12 and a production tubing 10. The production tubing 10 may be sealingly seated in the wellhead 8 and have a wing valve 11 or other fluid control valve in a flow line 13 that discharges produced fluid from the well. In some embodiments, the chemical supply line 6A may be in hydraulic communication with the flow line 13, and/or fluid processing equipment (not shown) disposed at the surface and connected to the flow line 13.

In some embodiments, the chemical pump 6 may have a rated flow capacity at least four times the required treatment chemical flow rate into the well 20. The valve 4 may be operated such that the chemical pump 6 operates only ¼ of the total time in any selected time interval, e.g., 24 hours. In some embodiments, the chemical pump 6 may have a rated flow capacity of at least 10 times the required treatment chemical flow rate into the well 20. The valve 4 in such embodiments may be operated 1/10 of the total time. Expressed more generally, the chemical pump 6 may have a designed flow rate capacity that is a selected multiple of the required flow rate of treatment chemical, and the pump 6 is operated for an inversely proportional fraction of the total time to provide the required flow rate of treatment chemical into a well or into production equipment in fluid communication with a fluid outlet of a well.

It will be appreciated by those skilled in the art that a pneumatically operated chemical pump is only one example of a chemical pump that may be used in accordance with the present disclosure. In other embodiments, the chemical pump 6 may be an hydraulically operated pump in fluid communication with its drive side to a source of pressurized hydraulic fluid. The hydraulic fluid may be pressurized continuously and selectively applied to the drive side of the chemical pump 6 using a solenoid valve as shown in FIG. 1. In other embodiments, a motor used to drive an hydraulic fluid pump (not shown) may be operated for the selected times and selected durations for which the chemical pump 6 is to be operated. In other embodiments, the chemical pump 6 may be operated by an electric motor. In such embodiments, the control box 5 may directly operate the chemical pump 6 and the solenoid valve may be eliminated or substituted by a low pressure check valve to reduce the possibility of chemical leakage from the tank 1 through the pump 6 and into the well 20 when the pump is switched off.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

1. A method for chemical treatment, comprising:

operating a chemical pump having a flow rate capacity of a selected multiple of a flow rate of a chemical required to treat at least one of a well and surface equipment associated therewith, the operating performed at at least one selected time and for at least one selected duration inversely proportional to the flow rate capacity such that a volume of the chemical pumped in a predetermined time interval substantially equals a required volume of the chemical during the predetermined time interval.

2. The method of claim 1 wherein the chemical pump has a flow rate capacity of at least four times the flow rate of the chemical required to treat the at least one of the well and the surface equipment.

3. The method of claim 1 wherein the chemical pump has a flow rate capacity of at least ten times the flow rate of the chemical required to treat the at least one of the well and the surface equipment.

4. The method of claim 1 wherein the chemical pump comprises a pneumatically operated pump, and the operating comprises automatically opening a valve between a pressurized gas source and the pneumatic pump.

5. The method of claim 3 wherein the valve comprises an electrically operated solenoid valve.

6. The method of claim 4 wherein the electrically operated solenoid valve is controlled by at least one of a timer and a programmable logic controller.

7. The method of claim 1 wherein a chemical output of the chemical pump is connected to an annular space in a well.

8. The method of claim 1 wherein a chemical output of the chemical pump is connected to a flow conduit in fluid communication with an outlet of a well.

9. A chemical treatment system, comprising:

a chemical treatment pump in fluid communication at an outlet thereof with at least one of a well and surface equipment connected to an outlet of a well, the chemical treatment pump having a flow rate capacity of a selected multiple of a flow rate of chemical required to treat the at least one of a well and surface equipment; and

a controller connected between a power supply used to operate the chemical treatment pump and the chemical treatment pump, the controller programmed to operate the chemical treatment pump for time intervals inversely proportional to the selected multiple of the flow rate.

10. The system of claim 9 wherein the controller comprises a valve and the power supply comprises a pressurized gas source.

11. The system of claim 10 wherein the valve comprises an electrically operated solenoid valve.

12. The system of claim 11 wherein the electrically operated solenoid valve is controlled by at least one of a timer and a programmable logic controller.

13. The system of claim 9 wherein a chemical output of the chemical treatment pump is connected to an annular space in a well.

14. The system of claim 9 wherein a chemical output of the chemical treatment pump is connected to a flow conduit in fluid communication with an outlet of a well.