Automatic chemical treatment system with liquid level sensor in chemical tank for calibration and chemical dispensing rate control

A wellbore chemical treating system include a storage vessel for containing a treating chemical. A chemical dispenser is in fluid communication between an outlet of the vessel and a well for selectively controlling the flow of the chemical from the vessel to the well. A liquid level sensor is disposed in the storage vessel. A controller is in signal communication with the liquid level sensor and is configured to operate the chemical dispenser. The controller is configured to adjust an operating time of the chemical dispenser based on changes in a liquid level measured by the liquid level sensor over a selected period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

Not applicable.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to the field of chemical treatment systems for use with hydrocarbon producing wells. More specifically, the invention relates to chemical treatment systems which inject chemicals into the well.

2. Background Art

Chemical treatment systems are used in hydrocarbon producing wells to introduce various chemicals into such wells to, for example, control or prevent buildup of scale from water produced from subsurface formations, reduce or remove solid hydrocarbon deposits and to inhibit corrosion of metal components in the wellbore, among other purposes. Chemical treatment systems known in the art include chemical pumps that withdraw chemical from a storage tank and introduce the treatment chemical(s) into the wellbore.

One device known in the art for providing controllable, continuous chemical treatment for well production equipment is disclosed in U.S. Pat. No. 5,209,300 issued to Ayres. An apparatus and method described in the Ayres '300 patent include a vessel which holds the chemical and a pressurized gas which exerts a pressure on the chemical. A pressure regulator and a valve selectively control the injection of the chemical into the well as the pressurized gas urges the chemical out of the vessel. The pressurized gas drives the chemical through the regulator, valve, and into the well without venting the chemical or pressurized gas into the ambient environment. The apparatus described in the Ayres '300 patent is adapted to inject chemicals into the well in essentially undiluted form. Another chemical treatment system known in the art is described, for example in U.S. Pat. No. 7,721,806 issued to Ayres.

Chemical treatment systems known in the art dispense a selected amount of chemical with each treatment cycle by operating a valve to release chemical under pressure, or by operating an injection pump. The valve of pump may be operated for a selected period of time, either by an electromechanical timing device, an electronically programmed controller, or by signals conducted to a controller from a flow meter or similar device to measure the amount of chemical moved from a storage tank to the well. It has been observed that accuracy of such devices when dealing with small total volumes, yet at relatively high flow rates may be inadequate. Further, an amount of chemical remaining in the storage tank is typically indicated by a visual indicator, such as a sight glass. Thus, the amount of chemical may be insufficient or excessive for any particular well, and it is typically necessary for a human operator to observe the indicator to determine when it is necessary to refill the storage tank with chemical. What is needed is a system to more accurately determine the amount of treatment chemical dispensed into a wellbore, and to provide indication of an amount of chemical in the storage tank that may be interrogated remotely.

SUMMARY OF INVENTION

A wellbore chemical treating system according to one aspect of the invention includes a storage vessel for containing a treating chemical. A chemical dispenser is in fluid communication between an outlet of the vessel and a well for selectively controlling the flow of the chemical from the vessel to the well. A liquid level sensor is disposed in the storage vessel. A controller is in signal communication with the liquid level sensor and is configured to operate the chemical dispenser. The controller is configured to adjust an operating time of the chemical dispenser based on changes in a liquid level measured by the liquid level sensor over a selected period of time.

A method for displacing treatment chemical in liquid form into a well according to another aspect of the invention includes displacing a selected amount of the treatment chemical into the interior of the well from a storage vessel at selected times. An amount of the treatment chemical in the storage vessel is automatically measured. At selected times the selected amount of the chemical displaced into the well at is adjusted based on a rate of change in the measured amount of chemical in the storage vessel.

DETAILED DESCRIPTION

An example embodiment of a chemical treating system according to the invention is shown schematically inFIG. 1. A chemical dispenser vessel10, substantially as described in U.S. Pat. No. 5,209,300 to Ayres, incorporated herein by reference, includes a container which is capable of holding an internal pressure without failure. The chemical dispenser vessel10is distinguishable from containers such as tanks which may only be designed to withstand the hydrostatic pressure exerted by fluid in the tank. Preferably, the chemical dispenser vessel10is made from glass, carbon fiber or composite fiber reinforced plastic, from stainless steel, or from any other material which is resistant to degradation induced by chemicals and corrosive gases. Alternatively, the chemical dispenser vessel10can include an inner lining (not shown) resistant to chemical degradation. A first control valve12, which in the present embodiment may be actuated by an electrically operated actuator12A, for example, a solenoid or the like, has an inlet end14in fluid communication with the interior of the chemical dispenser vessel10. An outlet end16of the valve12may be connected to one end of a fluid injection line18. The other end of the fluid injection line18may coupled to a hydrocarbon producing well20. Alternatively, the actuator12A can be a motor/gear set.

Although the well20is typically a hydrocarbon producing well, the present invention is useful in other wells relating to the production of hydrocarbons such as injection wells used in enhanced recovery operations. As used throughout this disclosure, the terms “well” and “hydrocarbon producing well” can include all wells directly or incidentally associated with the production from or injection of fluids into subsurface formations.

A treating chemical22is typically contained in the chemical dispenser vessel10in liquid form. It is within the scope of the invention that the chemical22can comprise any liquid compound or material that can be injected into a well. As representative examples, without limiting the scope of the invention, the chemical22can comprise chemicals generally identified as corrosion/scale inhibitors, water clarifiers, demulsifiers, and other chemicals which inhibit the formation of chemical, organic, or metallic compounds in hydrocarbon producing wells.

As shown inFIG. 1, a pressurized gas24is also disposed in the chemical dispenser vessel10. The pressurized gas24preferably includes one or more chemically inert gases, which do not chemically react with the chemical22. The gas24may comprise readily available gases such as nitrogen, helium, argon or carbon dioxide. The pressurized gas24may be initially charged to a pressure which is less than the condensation pressure for such gas. The condensation pressures are commonly known for each gas, and are not exceeded within the chemical dispenser vessel10to prevent the mixing, in the liquid phase, of the pressurized gas24with the chemical22. In addition, the density of pressurized gas24is preferably less than the density of the chemical22so that the chemical22is concentrated toward the bottom end of chemical dispenser vessel10, and the pressurized gas24is concentrated toward the upper end of the chemical dispenser vessel10. As shown inFIG. 1, the pressurized gas24is in contact with the chemical22at an interface25and pressurizes the chemical22to the same pressure as that of the pressurized gas24.

As shown inFIG. 1, a pressure regulator32may be installed between the outlet of the chemical dispenser vessel10and an inlet14of the control valve12. The pressure regulator32controls the pressure of the chemical22which is communicated to the inlet14of the valve12. For example, if the pressure of the pressurized gas24and the chemical22in the chemical dispenser vessel10is 500 pounds per square inch (psi), the regulator32can reduce the pressure of the chemical22at the inlet14of the valve12to a selected pressure that is greater than the well20pressure. As a representative example, if the pressure in the well20is 90 pounds per square inch (psi), and the desired pressure differential across the valve12is 10 psi, then the regulator32may be set to reduce the discharge pressure of the chemical22from 500 psi to about 100 psi. The regulator32should not reduce the pressure of the chemical22below the pressure in the well20because this would prevent the chemical22from entering the well20. A fluid line18may conduct the chemical to the well20.

To prevent inadvertent backflow of well fluids into fluid line18, a check valve36may be installed in the line18. The control of the pressure differential across valve12can be important because the flow rate through certain types of valves is dependent on the size of the valve orifice and the pressure differential between the valve inlet and outlet ports. As the pressure differential across a valve increases, the flow rate through the valve will typically increase unless the valve is designed to maintain a steady flow rate in response to varying flow pressures. As steady rate valves are more expensive than other valves which do not have a pressure compensation feature, the pressure regulator32may provide an inexpensive solution for controlling the flow rate of chemical through the valve12. The regulator32is also useful because the use of the regulator32in conjunction with the valve12permits the precise metering of small quantities of the chemical22.

In some embodiments, such as shown inFIG. 1, a flow meter34can be located between the valve12and the well20. The valve12, the first regulator32, and the flow meter34are each in fluid communication with the interior of the chemical dispenser vessel10and the well20through the line18. In the present embodiment, any pressure fluctuations in the chemical dispenser vessel10and in the well20are thus isolated from the valve12. Consequently, the pressure differential acting across the valve12can be precisely controlled, thereby permitting effective control over the flow rate of the chemical22through the valve12. The present embodiment permits the flow rate of the chemical22to be controlled to a very precise rate, even substantially less than one one-thousandth of a gallon per day.

In operation, the valve12is initially closed to prevent the release of the chemical22from the chemical dispenser vessel10. The valve12is then selectively opened and the pressurized gas24urges the chemical22through the first regulator32, the valve12, the second regulator34through the line18, and into the well20.

Preferably, the opening of the valve12is timed to selectively control the flow of chemical22into well20. The valve12can be operated at particular open durations to selectively increase or decrease the amount of the chemical22injected into the well20. The precise injection amount of the chemical22accomplishes several objectives. Certain wells may require large volumes of chemicals to accomplish the desired function. Other wells may require only relatively small quantities of chemicals to accomplish the desired results. For example, certain wells may require only a fraction of a gallon per day to accomplish the desired result, and the injection of additional chemicals is unnecessary to the operation of the well. If more chemical than required is injected into the well, then the excess chemical is superfluous to the operation of the well and results in additional cost to the operator. The present invention selectively controls the flow amount of the chemical22and eliminates unnecessary chemical use.

The apparatus of the present invention can be configured to control the flow of chemical22by selecting the operating time and frequency of operation of the valve12from any chemical amount, ranging from essentially a continuous discharge of the chemical22from the chemical dispenser vessel10, to any amount even as small as one one-thousandth of a gallon per day or less.

As previously explained, the check valve36may also be installed in the injection line18to prevent the backflow of fluids in the well20into the valve12or the chemical dispenser vessel10. This feature is desirable because a well operator could accidentally pressurize well20to a pressure higher than that of the chemical22in the chemical dispenser vessel10. Alternatively, this function could be incorporated into the design of the valve12.

In some embodiments, a float37or similar means can be located in the chemical dispenser vessel10to prevent the pressurized gas24from exiting the chemical dispenser vessel10. The float37has a density less than that of the chemical22and is buoyant therein. As the level of chemical22is lowered in the chemical dispenser vessel10by releasing the chemical22through the valve12, the float37will be lowered in the chemical dispenser vessel10. When the float37reaches a selected position within the chemical dispenser vessel10, the float37seals the outlet of the chemical dispenser vessel10to prevent the release of the pressurized gas24from the chemical dispenser vessel10. This function can be performed other than by using the float37. For example, a liquid level gauge42could be used to indicate the level of the chemical22within the chemical dispenser vessel10so that an operator could visually check the level of the chemical22. In other embodiments, mechanical, electrical, or electronic equipment could be used to indicate the level of the chemical22within the chemical dispenser vessel10or, alternatively, to seal the outlet when the level of the chemical22in the chemical dispenser vessel10is lowered to a certain position. A pressure gauge40can be attached to chemical dispenser vessel10to measure the pressure of the pressurized gas24. The gauge42can be attached to the chemical dispenser vessel10for measuring the quantity of the chemical22in the chemical dispenser vessel10. The gauge42can comprise many different embodiments such as sight glasses, electromagnetic switches, and other devices well-known in the art. In addition, the gauge42could comprise a flow meter which measures the quantity of liquid flowing from the chemical dispenser vessel10. When the liquid quantity flowing from the chemical dispenser vessel10is compared to the quantity of the chemical22initially installed in the chemical dispenser vessel10, the quantity of the chemical22in the chemical dispenser vessel10at any point in time can be determined.

In the present invention, the control valve12can be operated electrically, such as by the actuator12A. The actuator12A can be operated by a controller54of any type known in the art, such as a programmable logic controller, for electronic control of operation of a process operating device. The controller54may be supplied with electrical power by a battery56. The battery56may be recharged by a solar cell58. The foregoing electrical power to operate the controller54and the actuator12A are not intended to ultimately limit the scope of the invention, but are preferred for economy and reliability of operation.

The present example embodiment may include a fluid storage tank44. The fluid storage tank44may receive produced fluid from the well20through a flowline50coupled to an outlet of the well20. The fluid storage tank44may be made so that it can hold internal pressure equal to the pressure at the outlet of the well20. As fluid is produced from the well20, some of it will enter the flowline50and ultimately fill the tank44. The fluid storage tank44may include at its discharge end a float52similar in operation to the float37on the chemical dispenser vessel10. The outlet of the fluid storage tank44is in hydraulic communication with the well20through a flush control valve46operated by a motor/gear set46A. It has been determined through experimentation with various types of valve actuators that using a motor/gear set to actuate the flush valve46reduces the incidence of improper valve operation due to contamination of the valve from materials present in the fluid produced from the well20. A motor/gear set is also less susceptible to the valve46being improperly opened by high pressures extant on the outlet side of the flush control valve46. The motor/gear set46A can also be operated by the controller54. When the flush control valve46is operated, fluid in the tank44may flow into the well20. By having equal pressure on the well20and the tank44, fluid in the tank44may simply flow by gravity into the well20.

In the present embodiment, the controller54may be programmed to operate the control valve12to selectively discharge the chemical22, and the flush control valve46for the fluid stored in the fluid storage tank44at selected times and durations. Operating the first control valve12, as previously explained, causes injection of a selected amount of the chemical22into the well20. At substantially the same time, operation of the second control valve46causes the contents of the fluid storage tank44to flow by gravity into the well20. Thus, a chemical treatment is supplied to the well20that is already dispersed in fluid (which may include oil and/or water) prior to reaching the bottom of the well20, in the event the fluid level in the well20is too low to properly disperse the chemical22by itself.

In some embodiments, the float52may include a switch (not shown separately) so that the controller54will not operate the valves12,46if the level of water in the water tank44falls below a selected level. In some embodiments, the flush control valve46can be operated to discharge essentially the entire contents of the fluid storage tank44at each operation. In other embodiments, the flush control valve46can be operated to discharge a selected amount of the contents of the fluid storage tank44. In other embodiments, the flowmeter34and the check valve36may be omitted. Additionally, the controller54can be programmed to operate the control valve12and the flush control valve46with respect to any timing reference, such as during periods of time in which a pump (not shown) is operating to lift fluids out of the well20, or at times during which the pump (not shown) is not operating. Alternatively, the controller54can be programmed to operate the control and flush control valves,12,46simultaneously, or at different times from each other.

As explained in the Background section herein, the accuracy with which the amount of chemical dispensed during each operation of the control valve12, even when measured using a device such as the flowmeter34may be limited. Further, and as explained in the Background section herein, the amount of chemical actually present in the chemical dispenser vessel10may be determined at any time by visual observation of the level gauge42. Visual observation requires that a human operator be sent to the location of the chemical dispenser vessel10to observe the level. The foregoing may add substantial operating expense to the well. In the present invention, a liquid level sensor62may be disposed inside the chemical dispenser vessel10. The liquid level sensor62may be in signal communication with the controller54and provide the controller54with an electrical or optical signal related to the level of the interface25inside the chemical dispenser vessel10. The interface level25may be used as a proxy for the volume of chemical remaining in the chemical dispenser vessel10at any time. Various examples of liquid level sensor62will be explained below with reference toFIGS. 2,3and4.

In the present embodiment, the controller54may include a communication transceiver (not shown separately) coupled to an antenna60. The antenna60may be configured to communicate with a communications satellite in Earth orbit, or to another communications device (not shown) located away from the geodetic position of the well20such that signals related to the position of the liquid level sensor62may be communicated to a remote location, e.g., a headquarters office of the well operator. Such signals may be communicated on the basis, for example, of a selected time interval (e.g., hourly, daily, weekly, etc.), when a selected amount of level change occurs, or when the liquid level drops to a selected position within the chemical dispenser vessel10, e.g., when chemical recharge would be expected within a selected time span.

In some embodiments, signals from the liquid level sensor62may be used in the controller54periodically or continuously such that the operating time of the control valve12and/or the flush control valve46may be adjusted. For example, if the initial programming of the controller54is set to operate the control valve12for a time interval selected to dispense a selected amount of treatment chemical into the well20, (or to operate the control valve in response to a liquid volume measured by the flow meter34) over an extended number of operations of the control valve12, a corresponding change in the level of the interface25may be expected, such change depending on the volume of the chemical dispensing vessel10, the geometry of the chemical dispensing vessel10and the expected amount of chemical dispensed in each operation of the control valve12. If the signals from the liquid level sensor62indicate a different liquid level than that expected based on the controller54programming for operating the control valve12, instructions in the controller54may be provided to automatically adjust the operating time of the control valve12such that the rate of change of the liquid level as measured by the liquid level sensor62is made to correspond to the expected rate of change. Thus, any inaccuracy in the liquid flow rate through the control valve12and/or liquid flow rate as measured by the flow meter34. Alternatively, signals from the liquid level sensor62may be communicated to a remote location (e.g., using antenna60) and a remotely located operator or electronic controller (not shown) may adjust the operating time of the control valve12to adjust for differences between expected total chemical volume dispensed and the actual chemical volume dispensed. The controller54may be programmed to operate the flush control valve46proportionately with the control valve12.

Various examples of a liquid level sensor that may be used in accordance with the invention may be better understood with reference toFIGS. 2,3and4. InFIG. 2, a float66may rest on or about the liquid/gas interface (see25inFIG. 1). The float66may be coupled as shown by an arm67to a rotary position encoder64of any type known in the art, for example a variable resistor, photoelectric encoder or magnetic position transducer.

Another example liquid level sensor is shown inFIG. 3. A float66may be substantially as explained with reference toFIG. 2, but may move along a substantially vertically disposed rod66A. Position of the float66may be measured by a linear position transducer69such as a variable resistor or a linear variable differential transformer (LVDT).

Another example liquid level sensor is shown inFIG. 4. An acoustic transducer68may be used to determine a two-way sound wave travel time between the transducer68and the interface25. The two-way travel time may be inversely related to the level of the interface in the vessel (10inFIG. 1).

The example system shown inFIG. 1is explained in terms of a pressurized chemical dispensing vessel as described in the Ayres patents referenced herein above. It should be clearly understood that a system according to the invention may also be used with unpressurized chemical storage vessels using chemical treatment pumps to move treatment chemical from the storage vessel to the well. In such examples, a controller (e.g.,54inFIG. 1) may operate an electrically powered chemical pump for a selected time to move chemical to the well in the desired quantity. The operating time of such chemical pump may be adjusted substantially as explained above with reference to the control valve (12inFIG. 1) to change the amount of dispensed chemical in response to changes in the stored chemical level over time as measured by the liquid level sensor.

It is also to be understood that the automatic flush components shown in and explained with reference toFIG. 1may provide a system according to the invention with certain advantages over systems not having such components.

Embodiments of the invention provide a system for automatic chemical treatment of a well in which the treating chemical injection rate can be adjusted to compensate for inaccuracies in dispensing control components, and can provide the well operator with remote indication of the amount of chemical stored in a storage vessel so that visual observation of the storage vessel is not required.