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TECHNICAL FIELD OF THE INVENTION 
       [0001]    This invention relates in general to optimizing the production of hydrocarbons from oil or gas wells and in particular to a system and method for regulating the flow of injection gas into the production tubing of one or more gas-lift wells. 
       BACKGROUND OF THE INVENTION 
       [0002]    Without limiting the scope of the present invention, its background is described with reference to optimizing the production of hydrocarbons from a well that uses gas injection to artificially lift the fluid contained in the wellbore. 
         [0003]    It is well known in the subterranean well operation arts that the natural pressure of the formation in which the well is completed may be or may become insufficient to produce fluids out of the wellbore, such that the fluids do not flow to the surface at an optimal volume flow rate or do not flow at all. In order to restore production to the optimal volume flow rate, therefore, an artificial method of producing the fluids through the wellbore must be implemented. 
         [0004]    A common method used to increase or restore production to a well is a gas-lift system, whereby some of the gas produced from one or more wells is injected back into the production tubing of the well at one or more downhole locations. This effectively reduces the density of the fluid column in the wellbore, allowing the reservoir pressure to lift the fluid out of the wellbore. 
         [0005]    In typical gas-lift wells, fluids produced from the production wellbore are routed into a separator tank on the surface. The separator may be fed by one or more production wells. Once separated from the water, oil, and other fluids produced from the reservoir, the gas is usually then routed to a compressor to increase its pressure. After the compression stage, the gas may be sent to a sales line, a gas-injection line, or both. Gas that is routed into the gas-injection line is injected into the fluid column in the production tubing of the wellbore of the gas-lift well. This is usually accomplished by installing gas-lift valves on the production tubing that allow the injection gas to be forced into the annulus and pass into the production tubing and the fluid column contained therein. 
         [0006]    To maximize fluid production from a gas-lift well, the volume flow rate of the injection gas must be maintained at an optimum level. In typical gas lift systems, however, some gas is sent to the sales line even if the optimum volume flow rate of injection gas has not been reached. Thus, the well may produce below the optimum level for an extended time. Further, because both sales gas and injection gas are compressed, the power requirements of the compressor fluctuate with fluctuations in the volume flow rate of gas produced by the well. 
         [0007]    It is an object of the present invention, therefore, to prioritize maintaining the optimum level of gas production using the gas-lift process over sending gas into the sales line when the well is not producing gas at the optimum rate due to decreases in formation pressure. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention provides a system and method for regulating the flow of injection gas into the production tubing of a gas-lift well. 
         [0009]    In one aspect, the present invention is directed to a system and method for regulating the flow of injection gas into the fluid column within the production tubing of the gas-lift well when the volume flow rate of gas flowing from the well into the separator equals or exceeds the desired volume flow rate of gas entering the gas-injection line for injecting into the production tubing, and the non-gaseous fluid level of the separator is below a predetermined maximum level. Gas is constantly sent from the separator into the gas-injection line at the desired volume flow rate for injection gas, and if the volume flow rate of gas flowing from the well into the separator exceeds the desired volume flow rate of injection gas, the remaining gas and other fluids produced by the well are sent into a sales line. 
         [0010]    In another aspect, the present invention is directed to a system and method for regulating the flow of injection gas into the fluid column within the production tubing of the gas-lift well when the volume flow rate of gas flowing from the well into the separator is less than the desired volume flow rate of gas entering the gas-injection line for injecting into the production tubing, and the non-gaseous fluid level of the separator is below a predetermined maximum level. Some gas is constantly sent from the separator into the gas-injection line at less than the desired volume flow rate for injection gas, and the remaining gas is sent from the separator into a make-up gas line that routs the gas back into the separator. 
         [0011]    In a further aspect, the present invention is directed to a system and method for regulating the flow of injection gas into the fluid column within the production tubing of the gas-lift well when the non-gaseous fluid level of the separator is above a predetermined maximum level. The gas lift process is temporarily suspended to dump the excess non-gaseous fluid from the separator into a sales line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
           [0013]      FIGS. 1 and 2  are schematic illustrations of an apparatus for separating and compressing gas produced from a single well and injecting it back into the fluid column within the production tubing of the well of the present invention; 
           [0014]      FIG. 3  is a flow chart depicting the method of the present invention when the volume flow rate of gas flowing from the well into the separator equals or exceeds the desired volume flow rate of gas entering the gas-injection line, and the non-gaseous fluid level of the separator is below a predetermined maximum level and in which the preferred volume flow rate of injection gas is 500 thousand cubic feet per day. 
           [0015]      FIG. 4  is a flow chart depicting the method of the present invention when the volume flow rate of gas flowing from the well into the separator is less than the desired volume flow rate of gas entering the gas-injection line, and the non-gaseous fluid level of the separator is below a predetermined maximum level and in which the preferred volume flow rate of injection gas is 500 thousand cubic feet per day. 
           [0016]      FIG. 5  is a flow chart depicting the method of the present invention when the non-gaseous fluid level of the separator is above a predetermined maximum level and in which the preferred volume flow rate of injection gas is 500 thousand cubic feet per day. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention. 
         [0018]    Referring initially to  FIGS. 1 and 2 , an apparatus for separating gas produced from a single production and gas-lift well and injecting gas into the fluid column within the production tubing of the gas-lift well is schematically illustrated and generally designated at  10 . Gas, oil, saltwater, and other fluids produced in production casing  12  are transported to the surface inside production tubing  14 , which is supported by wellhead  16 . At wellhead  16 , the fluids are directed into separator  18  through inlet line  20  that connects to inlet  22 . Separator  18  is equipped with first outlet  24  for directing gas into compressor line  26  and second outlet  28  for directing gas into sales line  30 . Compressor line  26  directs gas into compressor  32 . Pressure sensor  34  located on compressor line  26  measures the suction pressure of compressor  32 . 
         [0019]    Still referring to  FIGS. 1 and 2 , and as further explained in more detail below, gas exiting compressor  32  may be routed through gas-injection line  36 , which directs the gas back into production tubing  14  through one or more gas lift valves  38  located on production tubing  14 . Gas lift meter  40  records the pressure and volume flow rate of gas that is injected for gas lift via gas-injection line  36 . Gas exiting compressor  32  may also be routed through make-up gas line  42  that feeds back into separator  18  via make-up gas inlet  44 . Dump valve  46  is located on make-up gas line  42  and is actuated by level controller  48 , which measures the non-gaseous fluid level in separator  18 . Make-up gas valve  50  is located on make-up gas line  42  in parallel with dump valve  46 . Make-up gas valve  50  is actuated by pressure sensor  34 , which measures the suction pressure of compressor  32 , which is approximately equal to the pressure within separator  18 . 
         [0020]    Even though  FIG. 1  depicts a single well that supplies produced or production fluids (production well) and is the recipient of injected gas (gas-lift well), it should be noted by those skilled in the art that the system and method for regulating the flow of injection gas of the present invention are equally well-suited for use in systems wherein production from multiple wells flows into a single separator or where a single separator and/or compressor supplies gas to multiple gas-lift wells Further, even though  FIG. 1  depicts a vertical well, it should be noted by those skilled in the art that the system and method for regulating the flow of injection gas of the present invention are equally well-suited for use in deviated wells, inclined wells, or horizontal wells. Still further, even though  FIG. 1  depicts an onshore operation, it should be noted by those skilled in the art that the system and method for regulating the flow of injection gas of the present invention are equally well-suited for offshore operations. 
         [0021]    Referring now to  FIG. 3 , therein is depicted an aspect of the present invention in which the well is in the “unloaded condition,” that is, when the volume flow rate of gas flowing from the well into separator  18  equals or exceeds the desired volume flow rate of gas in gas-injection line  36  for injecting into production tubing  14  and the non-gaseous fluid level of separator  18  is below a predetermined maximum level. In a preferred embodiment, the unloaded condition is indicated when the pressure of separator  18  as indicated by pressure sensor  34  equals or exceeds a predetermined minimum value and the non-gaseous fluid level of separator  18  measured by level controller  48  is below a predetermined maximum level. It should be apparent to those skilled in the art, however, that the unloaded condition may be indicated by a variety of means. 
         [0022]    When the well of the present invention is in the unloaded condition, gas produced from the well is routed into separator  18 . Gas exits separator  18  via first outlet  24  and is directed through compressor line  26  into compressor  32 . In a preferred embodiment, compressor  32  is sized or configured such that its maximum discharge volume flow rate equals the desired volume flow rate of gas in gas-injection line  36  to be injected into production tubing  14 . Dump valve  46  is closed, and make-up gas valve  50  is closed. Thus, compressor  32  will constantly send gas into gas-injection line  36  at the desired injection volume flow rate as long as the volume flow rate of fluids produced by the well equals or exceeds the desired injection volume flow rate. If the volume flow rate of gas entering separator  18  equals the maximum discharge volume flow rate of compressor  32 , then no fluids in separator  18  enter sales line  30 . If the volume flow rate of gas entering separator  18  exceeds the maximum discharge volume flow rate of compressor  32 , then the fluids remaining in separator  18  exit separator  18  via second outlet  28  and into sales line  30 . 
         [0023]    In the example of  FIG. 3 , the desired volume flow rate of gas in gas-injection line  36  for injecting into production tubing  14  is about 500 thousand cubic feet per day (“MCFD”). In the example depicted, the volume flow rate of gas flowing from the well into separator  18  is about 700 MCFD, the volume flow rate of saltwater produced is about 50 barrels of saltwater per day (“BWPD”), and the volume flow rate of oil produced is about 5 barrels of oil per day (“BOPD”). In the example depicted, the predetermined maximum level of non-gaseous fluids in separator  18  is not exceeded. The pressure of separator  18  is about 160 psig, which exceeds the predetermined minimum value for maintaining the unloaded condition in the embodiment depicted. Compressor  32  is sized or configured such that its maximum discharge flow rate equals 500 MCFD, which corresponds to the desired injection flow rate. 
         [0024]    Again, because the unloaded condition exists in the example depicted in  FIG. 4 , dump valve  46  is closed and make-up gas valve  50  is closed. Thus, compressor  32  will constantly send gas into gas-injection line  36  at about 500 MCFD as long as the volume flow rate of gas produced by the well equals or exceeds said desired injection volume flow rate of 500 MCFD. In the example depicted, the volume flow rate of gas produced at wellhead  16  is about 700 MCFD, therefore, the remaining gas in separator  18 , equal to about 200 MCFD, is sent to sales line  30 , along with the saltwater and oil in separator  18 . 
         [0025]      FIG. 4  depicts a second aspect of the present invention in which the well is in the “loaded condition,” that is, when the volume flow rate of gas flowing from the well into separator  18  is less than the desired volume flow rate of gas in gas-injection line  36  and the non-gaseous fluid level of separator  18  is below a predetermined maximum level. In a preferred embodiment, the loaded condition is indicated when the suction pressure of compressor  32  as indicated by pressure sensor  34  is below a predetermined minimum value and the non-gaseous fluid level of separator  18  measured by level controller  48  is below a predetermined maximum level. It should be apparent to those skilled in the art, however, that the loaded condition may be indicated by a variety of means. 
         [0026]    When the well of the present invention is in the loaded condition, fluids produced from the well are routed into separator  18 . Gas exits separator  18  via first outlet  24  and is directed through compressor line  26  into compressor  32 . Dump valve  46  is closed and make-up gas valve  50  is open. Thus, gas exits compressor  32  to both gas-injection line  36  and make-up gas line  42 . Gas entering gas-injection line  36  is routed into production tubing  14  through gas lift valves  38 . Gas entering make-up gas line  42  is routed into separator  18  via make-up gas inlet  44 . Once the volume flow rate of gas produced by the well and flowing into separator  18  equals or exceeds the desired volume flow rate of gas for injecting into production tubing  14 , make-up gas valve  50  is closed, thereby cutting off the gas flow from compressor  32  to make-up gas line  42 , and the well of the present invention is again in the “unloaded” condition. 
         [0027]    In the example of  FIG. 4 , the desired volume flow rate of gas for injecting into production tubing  14  is about 500 MCFD. In the example depicted, the volume flow rate of gas flowing from the well into separator  18  is about 200 MCFD. The predetermined maximum level of non-gaseous fluids in separator  18  is not exceeded, however, the pressure of separator  18  is about 40 psig, which is less than the predetermined minimum value for maintaining the unloaded condition in the preferred embodiment depicted in  FIG. 4 . 
         [0028]    Because the loaded condition exists, make-up gas valve  50  is open. Dump valve  46  is closed. Gas flows through gas-injection line  36  at about 100 MCFD and make-up gas line  42  at about 100 MCFD. Gas entering gas-injection line  36  is routed into production tubing  14  through gas lift valves  38 . Gas entering make-up gas line  42  is routed into separator  18  via make-up gas inlet  44 . Once the volume flow rate of gas produced by the well and flowing into separator  18  equals or exceeds 500 MCFD, make-up gas valve  50  is closed, and the well is again in the “unloaded” condition. 
         [0029]      FIG. 5  depicts a third aspect of the present invention in which the well is in the “unloading condition,” that is, when the non-gaseous fluid level of separator  18  exceeds a desired maximum non-gaseous fluid level. When the unloading condition exists, the gas lift process is temporarily suspended to dump the excess non-gaseous fluids from separator  18 . In a preferred embodiment, the unloading condition is indicated when the non-gaseous fluid level of separator  18  measured by level controller  48  is above a predetermined maximum level. It should be apparent to those skilled in the art, however, that the unloading condition may be indicated by a variety of means. 
         [0030]    When the well of the present invention is in the unloading condition, fluids produced from the well are routed into separator  18 . Gas exits separator  18  via first outlet  24  and is directed through compressor line  26  into compressor  32 . Make-up gas valve  50  is open and dump valve  46  is open. Thus, gas exits compressor  32  only to make-up gas line  42  and is routed into separator  18  via make-up gas inlet  44 , and excess non-gaseous fluids are continually dumped from separator  18  into sales line  30 . This process continues until the non-gaseous fluid level of separator  18  is equal to or below a predetermined maximum level, at which point dump valve  46  is closed. 
         [0031]    In the example of  FIG. 5 , the volume flow rate of gas flowing from the well into separator  18  is about 50 MCFD, the volume flow rate of saltwater produced at wellhead  16  is about 100 BWPD, and the volume flow rate of oil produced at wellhead  16  is about 10 BOPD. In the present example, the unloading condition is indicated by level controller  48 , which detects that the level of non-gaseous fluids in separator  18  is above a predetermined maximum level. 
         [0032]    Because the unloading condition exists in the example depicted, dump valve  46  is open. Make-up gas is continually routed into separator  18  via make-up gas inlet  44  and excess non-gaseous fluids are continually dumped from separator  18  into sales line  30 . This process continues until the non-gaseous fluid level of separator  18  is equal to or below the predetermined maximum level, at which point dump valve  46  is closed. 
         [0033]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
The system and method are utilized to control the flow of crude oil, natural gas, and field produced salt water to optimize production from an oil or gas well. The invention is suitable for use with a well that utilizes gas-lift as artificial lift. The equipment is designed to regulate the flow of injection gas into the production tubing to optimize production of the well.