Patent Publication Number: US-7721806-B2

Title: Automatic chemical treatment system with integral flush fluid dispenser and method for using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Continuation of application Ser. No. 10/990,617 filed on Nov. 16, 2004, now U.S. Pat. No. 7,318,476 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   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 “pre flushed” or diluted treatment chemicals into the well. 
   2. Background Art 
   In wellbores drilled through the Earth and then used for production of hydrocarbons, a pipe or casing is disposed in the wellbore from the Earth&#39;s surface to the bottom of the well. The casing serves to hydraulically isolate the various Earth formations penetrated by the wellbore and to provide the wellbore with a degree of mechanical stability. Typically a tubing string, which is a pipe of considerably lesser diameter than the casing, is positioned within the well casing. The purpose of the tubing string is to enable produced fluids to move to the Earth&#39;s surface at greater velocity than would be possible within the casing. The hydrocarbons, and in many cases a considerable amount of connate water, enter the tubing through perforations located at the lower end of the casing, travel through the tubing, to a wellhead at the Earth&#39;s surface. In some wells, where the natural fluid pressure in the Earth&#39;s subsurface is not sufficient to lift the produced fluids to the Earth&#39;s surface, the fluids are pumped to the surface with a “sucker rod” pump or with a downhole electrical submersible pump. 
   At the Earth&#39;s surface, various production equipment directs the produced fluids to holding tanks and/or to a pipeline. The production equipment typically comprises tubing, valves, piping, and other components. The produced fluids typically contain numerous compounds which adversely affect the production equipment. For example, paraffins and water/oil emulsions can coat well production equipment and can eventually plug off the tubing and/or plug the perforations in the casing. In addition, chemical reactions between the produced fluids and metallic equipment can cause scale to be formed on the well production equipment, and some compounds in the produced fluids can corrode the well production equipment. 
   Various techniques are known in the art to treat these well conditions to extend the useful life of the well production equipment, tubing and casing. In wells susceptible to paraffin build-up, for example, “treater trucks” or “hot oil trucks” are regularly dispatched to pump heated oil and/or heated water into the well. The heated oil and/or water is pumped into the well through the annular space between the tubing and the casing, travels down through the annulus to melt the paraffin deposits in the well production equipment, and the returns to the surface through the tubing. In wells susceptible to corrosion and scale problems, high pressure injection treater trucks pump batches of chemicals into the well to chemically remove the scale, and to inhibit the causes of corrosion. All of these techniques require regular maintenance services which are costly and which do not continuously treat the well. Treater truck or batch treatment of wells is less efficient than continuous treatments because more chemicals are typically injected in batch treatment operations. 
   To avoid inefficiencies associated with treater truck maintenance of hydrocarbon producing wells, it is known in the art to use mechanical pumps to inject chemicals into a well. Typically, mechanical pumps are supplied from a storage tank which holds the chemicals. The mechanical pumps and storage tanks are located adjacent the well for several reasons, such as for reducing the length of power cable or piping that connects the pump to a power source such as electricity or natural gas. The tanks are located above the pump and the chemical is gravity fed to the intake port of the pump. The tanks include a vent at the upper end of the tank to prevent a vacuum from developing in the tank as the pump draws chemical from the tank. In addition, the vent releases excess pressure within the tank caused by thermal expansion of the chemical. Such thermal expansion can cause the chemical vapors to be released into the environment through the vent. In addition, thermal expansion can cause the chemical to be ejected through the vent or through the sight glass used to indicate the chemical level in the tank. In either event, chemical vapors or the chemical fluids are released in an uncontrolled manner and can pose a hazard to personnel and to the environment. 
   The mechanical pumps used in typical chemical injection systems are powered by electricity or gas and include numerous moving components. It is customary to inspect these pumps on a regular basis, sometimes daily, to verify the operability of the pumps. Because the chemical is gravity fed to the intake of the chemical pump, sediment in the tank or the chemical settles toward the pump intake and can interfere with the operation of the pump In addition, the presence of an air bubble in the intake line may impede the operation of the pump because of a vapor lock. In such event, maintenance personnel routinely open a bleeder valve on the pump and release chemical from the pump until the air bubble has been cleared. This practice is undesirable because it releases chemical into the environment. An additional consideration with respect to venting a chemical pump system to the atmosphere is introduction of moisture into the chemical system, which may condense and foul the chemical. 
   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 &#39;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 &#39;300 patent is adapted to inject chemicals into the well in essentially undiluted form. As will be explained below, in certain cases it is desirable to pump undiluted chemicals into a wellbore and follow such injection with a water flush. 
   So called “batch treatment” is among the more widely used methods used for downhole treatment of sucker rod pumped wells. A treater truck is dispatched to the well. The chemical is placed into the annulus in undiluted form, and is followed by an “overflush” of water to assure proper treatment of the well, because sucker rod pumped wells are susceptible to “pump off”, whereby the pump is operated at such a rate as to essentially remove all the fluid from the well down to the level of the pump In such cases, there is substantially no fluid to dilute and disperse the treating chemical, making the treatment less effective. The overflush is intended to provide sufficient dispersing fluid for the treatment chemical so that the chemical can reach the bottom of the well. The chemical would otherwise need to travel the entire distance from the surface in undiluted form, often against upward flow of gas in the well. Typically, the chemical can dry out inside the well before ever reaching the bottom when injected in undiluted form. The overflush water, however, is typically taken from storage tanks located near the well for storing, and subsequent environmentally safe disposal, of connate water that is produced from the well along with oil and gas. The water in the tanks is often contaminated with high levels of oxygen and sulfate reducing bacteria. When reinjected into a well, such cross-inoculation of contaminates lessens the effectiveness of typical corrosion inhibitor chemicals, among other problems. The truck batch treatment process in effect provides a recirculation of the corrosive materials through the entire well, and any other wells sharing the same surface production equipment, on a periodic basis. Some method is needed to break this cycle so that the fluid used to protect the system is not part of the problem. 
   SUMMARY OF INVENTION 
   One aspect of the invention is a wellbore chemical treating system. A system according to this aspect of the invention includes a pressure vessel for containing a treating chemical. The pressure vessel is closed to atmospheric pressure. A first controllably operated valve is disposed in fluid communication between an outlet of the pressure vessel and a well for selectively controlling the flow of the chemical from the pressure vessel to the well. A pressurized gas is disposed in the pressure vessel wherein the pressure exerted by the pressurized gas causes the chemical to flow from the pressure vessel to the well through the first valve when the first valve is opened. A second controllably operated valve is disposed in fluid communication between the well and an outlet of a fluid supply tank for selectively controlling flow of fluid in the tank to the well. The system includes a controller for selectively operating the first valve and the second valve. The fluid tank is replenished by fluid produced from the well. 
   Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  shows an automatic treatment system according to one embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   An example embodiment of a chemical treating system according to the invention is shown schematically in  FIG. 1 . A chemical dispenser vessel  10 , 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 vessel  10  is distinguishable from containers such as tanks which may only be designed to withstand the hydrostatic pressure exerted by fluid in the tank. Preferably, the vessel  10  is made from glass, carbon 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 vessel  10  can include an inner lining (not shown) resistant to chemical attack. A first control valve  12 , which in the present embodiment can be actuated by an actuator  12 A, which can be a solenoid or the like, has an inlet end  14  in fluid communication with the interior of the vessel  10 . An outlet end  16  of the valve  12  is connected to one end of a fluid injection line  18 . The other end of the fluid injection line  18  is coupled to a hydrocarbon producing well  20 . Alternatively, the actuator  12 A can be a motor/gear set. 
   Although the well  20  is 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 Earth formations. 
   A treating chemical  22  is typically contained in the vessel  10  in liquid form. It is within the scope of the invention that the chemical  22  can comprise any liquid compound or material that can be injected into a well. As representative examples, without limiting the scope of the invention, the chemical  22  can 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 in  FIG. 1 , a pressurized gas  24  is also disposed in the vessel  10 . The pressurized gas  24  preferably includes one or more chemically inert gases, which do not chemically react with the chemical  22 . The gas  24  may comprise readily available gases such as nitrogen, helium, argon or carbon dioxide. The pressurized gas  24  is 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 vessel  10  to prevent the mixing, in the liquid phase, of the pressurized gas  24  with the chemical  22 . In addition, the density of pressurized gas  24  is preferably less than the density of the chemical  22  so that the chemical  22  is concentrated toward the bottom end of vessel  10 , and the pressurized gas  24  is concentrated toward the upper end of the vessel  10 . As shown in  FIG. 1 , the pressurized gas  24  is in contact with the chemical  22  and pressurizes the chemical  22  to the same pressure as that of the pressurized gas  24 . 
   As shown in  FIG. 1 , a pressure regulator  32  can be installed between the outlet of the vessel  10  and an inlet  14  of the control valve  12 . The pressure regulator  32  controls the pressure of the chemical  22  which is communicated to the inlet  14  of the valve  12 . For example, if the pressure of the pressurized gas  24  and the chemical  22  in the vessel  10  is 500 pounds per square inch (psi), the regulator  32  can reduce the pressure of the chemical  22  at the inlet  14  of the valve  12  to a selected pressure that is greater than the well  20  pressure. As a representative example, if the pressure of the well  20  is 90 psi, and the desired pressure differential across the valve  12  is 10 psi, then the regulator  32  can be set to reduce the pressure of the chemical  22  from 500 psi to about 100 psi. The regulator  32  should not reduce the pressure of the chemical  22  below the pressure in well  20  because this would prevent the chemical  22  from entering the well  20 . To prevent the accidental or inadvertent backflow of well fluids into fluid line  18 , a check valve  36  can be installed in the line  18 . The control of the pressure differential across valve  12  can 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 regulator  32  is an inexpensive solution for controlling the flow rate of chemical through the valve  12 . The regulator  32  is also useful because the use of the regulator  32  in conjunction with the valve  12  permits the precise metering of small quantities of the chemical  22 . 
   In some embodiments, such as shown in  FIG. 1 , a second regulator  34  can be located between the valve  12  and the well  20 . The valve  12 , the first regulator  32 , and the second regulator  34  are each in fluid communication with the interior of the vessel  10  and the well  20 . In the present embodiment, any pressure fluctuations in the vessel  10  and in the well  20  are thus isolated from the valve  12 . Consequently, the pressure differential acting across the valve  12  can be precisely controlled, thereby permitting effective control over the flow rate of the chemical  22  through the valve  12 . The present embodiment permits the flow rate of the chemical  22  to be controlled to a very precise rate even substantially less than one one-thousandth of a gallon per day. 
   In operation, the valve  12  is initially closed to prevent the release of the chemical  22  from the vessel  10 . The valve  12  is then selectively opened and the pressurized gas  24  urges the chemical  22  through the first regulator  32 , the valve  12 , the second regulator  34  through the line  18 , and into the well  20 . 
   Preferably, the opening of the valve  12  is timed to selectively control the flow of chemical  22  into well  20 . The valve  12  can be operated at particular open durations to selectively increase or decrease the amount of the chemical  22  injected into the well  20 . The precise injection amount of the chemical  22  accomplishes 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 chemical  22  and eliminates unnecessary chemical use. 
   The apparatus of the present invention can be configured to control the flow of chemical  22  by selecting the operating time and frequency of operation of the valve  12  from any chemical amount, ranging from essentially a continuous discharge of the chemical  22  from the vessel  10 , to any amount even as small as one one-thousandth of a gallon per day or less. 
   As previously explained, the check valve  36  may also be installed in the injection line  18  to prevent the backflow of fluids in the well  20  into the valve  12  or the vessel  10 . This feature is desirable because a well operator could accidentally pressurize well  20  to a pressure higher than that of the chemical  22  in the vessel  10 . Alternatively, this function could be incorporated into the design of the valve  12 . 
   In some embodiments, a float  37  or similar means can be located in the vessel  10  to prevent the pressurized gas  24  from exiting the vessel  10 . The float  37  has a density less than that of the chemical  22  and is buoyant therein. As the level of chemical  22  is lowered in the vessel  10  by releasing the chemical  22  through the valve  12 , the float  37  will be lowered in the vessel  10 . When the float  37  reaches a selected position within the vessel  10 , the float  37  seals the outlet of the vessel  10  to prevent the release of the pressurized gas  24  from the vessel  10 . This function can be performed other than by using the float  37 . For example, a liquid level gauge  42  could be used to indicate the level of the chemical  22  within the vessel  10  so that an operator could visually check the level of the chemical  22 . In other embodiments, mechanical, electrical, or electronic equipment could be used to indicate the level of the chemical  22  within the vessel  10  or, alternatively, to seal the outlet when the level of the chemical  22  in the vessel is lowered to a certain position. A pressure gauge  40  can be attached to vessel  10  to measure the pressure of the pressurized gas  24 . The gauge  42  can be attached to the vessel  10  for measuring the quantity of the chemical  22  in the vessel  10 . The gauge  42  can comprise many different embodiments such as sight glasses, electromagnetic switches, and other devices well-known in the art. In addition, the gauge  42  could comprise a flow meter which measures the quantity of fluid flowing from the vessel  10  When the fluid quantity flowing from the vessel  10  is compared to the quantity of the chemical  22  initially installed in the vessel  10 , the quantity of the chemical  22  in the vessel  10  at any point in time can be determined. 
   In the present invention, the control valve  12  can be operated electrically, such as by the actuator  12 A. The actuator  12 A can be operated by a controller  54  of any type known in the art, such as a programmable logic controller, for electronic control of operation of a process operating device. The controller  54  may be supplied with electrical power by a battery  56 . The battery  56  may be recharged by a solar cell  58 . The foregoing electrical power to operate the controller  54  and the actuator  12 A are not intended to ultimately limit the scope of the invention, but are preferred for economy and reliability of operation. 
   The present invention includes a fluid storage tank  44 . The fluid storage tank  44  receives produced fluid from the well  20  through a flowline  50  coupled to an outlet of the well  20 . The fluid storage tank  44  is preferably made so that it can hold internal pressure equal to the pressure at the outlet of the well  20 . As fluid is produced from the well  20 , some of it will enter the flowline  50  and ultimately fill the tank  44 . The fluid storage tank  44  may include at its discharge end a float  52  similar in operation to the float  37  on the vessel  10 . The outlet of the fluid tank  44  is in hydraulic communication with the well  20  through a second control valve  46  operated by a motor/gear set  46 A. It has been determined through experimentation with various types of valve actuators that using a motor/gear set to actuate the second valve  46  reduces the incidence of improper valve operation due to contamination of the valve from materials present in the fluid produced from the well. A motor/gear set is also less susceptible to the valve  46  being improperly opened by high pressures extant on the outlet side of the valve  46 . The motor/gear set  46 A can also be operated by the controller  54 . As will be explained below, when the valve  46  is operated, fluid in the tank  44  may flow into the well  20 . By having equal pressure on the well  20  and the tank  44 , fluid in the tank  44  may simply flow by gravity into the well  20 . 
   In the present embodiment, the controller  54  may be programmed to operate the first control valve  12  to selectively discharge the chemical  22 , and the control valve  46  for the fluid stored in the fluid storage tank  44  at selected times and durations. Operating the first control valve  12 , as previously explained, causes injection of a selected amount of the chemical  22  into the well  20 . At substantially the same time, operation of the second control valve  46  causes the contents of the fluid storage tank  44  to flow by gravity into the well  20 . Thus, a chemical treatment is supplied to the well  20  that is already dispersed in fluid (which may include oil and/or water) prior to reaching the bottom of the well  20 , in the event the fluid level in the well  20  is too low to properly disperse the chemical  22  by itself. 
   In some embodiments, the float  52  may include a switch (not shown separately) so that the controller  54  will not operate the valves  12 ,  46  if the level of water in the water tank  44  falls below a selected level. In some embodiments, the second valve  46  can be operated to discharge essentially the entire contents of the fluid storage tank  44  at each operation. In other embodiments, the second valve  46  can be operated to discharge a selected amount of the contents of the fluid storage tank  44 . In other embodiments, the second regulator  34  and the check valve  36  may be omitted. Additionally, the controller  54  can be programmed to operate the first valve  12  and the second vale  46  with 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 well  20 , or at times during which the pump (not shown) is not operating. Alternatively, the controller  54  can be programmed to operate the valves  12 ,  46  simultaneously, or at different times from each other. 
   Embodiments of the invention provide a system for automatic chemical treatment of a well in which the treating chemical is pre-dispersed in a fluid obtainable from the well itself. Embodiments of the invention can provide properly dispersed treatment chemical for a well even in the event the well is “pumped off” (meaning that the fluid level is insufficient for a downhole pump to lift fluid to the Earth&#39;s surface). 
   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.