Patent Publication Number: US-2021189849-A1

Title: System for producing fluid from hydrocarbon wells

Description:
TECHNICAL FIELD 
     This relates to a system for producing fluids from a hydrocarbon well, and in particular, a system that uses a pump that pressurizes a combination of production fluids including gas and liquid phases. 
     BACKGROUND 
     In an oil-producing well, gas may be built up in the casing, which surrounds the production tubing string. Higher casing gas pressure acts against the reservoir, and can reduce the rate at which oil is produced. To reduce the pressure, it is common to use a compressor to remove gas from the casing. U.S. Pat. No. 9,528,355 describes a system for producing oil from a well that includes having an outlet for the casing gas that can be selectively opened and closed to alter the pressure of the casing gas within the well. 
     SUMMARY 
     According to an aspect, there is provided a system for compressing casing gas from a hydrocarbon well. The hydrocarbon well has a wellhead, a production string that produces fluids from a hydrocarbon formation, and a casing string that receives the production string. The wellhead is connected to a pipeline that transports the produced fluids. The system comprises a liquid conduit that receives liquids from a source of liquids, a casing gas conduit that receives casing gas from the casing string, an outlet conduit, and a pump that is capable of pumping a liquid/gas mixture. The pump comprises an inlet that is in fluid communication with the liquid conduit and the casing gas conduit, such that the inlet receives liquid from the liquid conduit and casing gas from the casing gas conduit, and an outlet connected to the pipeline. 
     According to other aspects, the system may comprise one or more of the following features, alone or in combination: the pump may be a positive displacement pump; the pump may be a lobe pump; the pump may be a rotary pump; the liquid conduit may be in fluid communication with the pipeline and the source of liquid may comprise the pipeline; the liquid conduit may be in fluid communication with the hydrocarbon well and the source of liquid may comprise the hydrocarbon well; an outlet line may connect the outlet of the pump to the pipeline, wherein the outlet line may comprise a liquid port that delivers a liquid component to the pipeline and a gas port that delivers a gas component to the pipeline; the liquid conduit may be in fluid communication with the pipeline; the pipeline may be the source of liquid; the gas port may be downstream from the liquid conduit; the liquid port may be upstream from the liquid conduit; the fluid at the inlet of the pump may be more than thirty percent liquid; the outlet of the pump may be connected to a separator, the separator may comprise a separator gas outlet that is in fluid communication with the pipeline and a separator liquid outlet that is in fluid communication with the inlet of the pump, wherein the source of liquid may comprise the separator; the separator may be a separator vessel or a three port connector; and the casing gas conduit may be connected to receive casing gas from a plurality of casing strings from a plurality of hydrocarbon wells. 
     According to an aspect there is provided a method for compressing casing gas from a hydrocarbon well. The hydrocarbon well comprises a wellhead, a production string, and a casing string that receives the production string. The hydrocarbon well is used to produce fluid from a hydrocarbon reservoir, the method comprises the steps of: producing fluid from the hydrocarbon reservoir and transporting the produced fluid in a pipeline connected to the hydrocarbon well; 
     inputting a fluid mixture into a pump, the fluid mixture comprising casing gas from the casing string, and liquid from a source of liquid;
 
pressurizing the fluid mixture in the pump; and
 
introducing the pressurized fluid mixture into the pipeline.
 
     According to other aspects, the method may comprise one or more of the following features, alone or in combination: the pump may be a positive displacement pump; the pump may be a lobe pump; the pump may be a rotary pump; the source of liquid for the fluid mixture may be a diverted stream from the pipeline; the source of liquid for the fluid mixture may be a diverted stream from the hydrocarbon well; the pressurized fluid mixture may be separated into a gas component and a liquid component, and the gas component may be introduced into the pipeline separately from the liquid component; the source of liquid for the fluid mixture may be a stream of liquid from a pipeline port of the pipeline; the liquid component may be introduced into the pipeline upstream of the pipeline port; the gas component may be introduced into the pipeline downstream from the pipeline port; the fluid mixture may be at least thirty percent liquid; the pressurized fluid mixture may be separated into a gas component and a liquid component in a separating vessel, the gas may be component into the pipeline, and at least a portion of the liquid component may be input from the separating vessel to the inlet of the pump; the separator may be a separating vessel or a three-way connector; and the fluid mixture may comprise casing gas from a plurality of casing strings from a plurality of hydrocarbon wells. 
     In other aspects, the features described above may be combined together in any reasonable combination as will be recognized by those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a schematic diagram of a system for producing fluid from a hydrocarbon well that combines a casing gas stream and a slipstream of liquid obtained from a pipeline. 
         FIG. 2  is a schematic diagram of a system for producing fluid from a hydrocarbon well that combines a casing gas stream and a slipstream of liquid obtained from a production string of a wellhead. 
         FIG. 3  is a schematic diagram of a system for producing fluid from a hydrocarbon well that combines a casing gas stream and a slipstream of liquid obtained from a liquid source and introduced pressurized gas into a pipeline separately from pressurized liquid. 
         FIG. 4  is a schematic diagram of a system for producing fluid from a hydrocarbon well that combines a casing gas stream and a slipstream of liquid obtained by separating a pressurized fluid mixture in a separating vessel. 
         FIG. 5  is a schematic diagram of a system for producing fluid from a hydrocarbon well that combines a casing gas stream and a slipstream of liquid obtained by separating a pressurized fluid mixture in three way connector. 
         FIG. 6  is a schematic diagram of a system for producing fluid from a hydrocarbon well that has a separating vessel that can be filled with liquid directly from a production string of a wellhead. 
         FIG. 7  is a schematic diagram of a system for producing fluid from a hydrocarbon well that compresses gas and liquid from a plurality of hydrocarbon wells. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A system for producing fluid from a hydrocarbon well, generally identified by reference numeral  10 , will now be described with reference to  FIGS. 1 to 3 . System  10  is used to produce fluid, including casing gas, from hydrocarbon well  12  that has a wellhead  14  with a casing string  16  and production string  18  that extends between wellhead  14  and a hydrocarbon reservoir  20 . Casing gas may be drawn from casing string  16  via casing gas outlet  17 . Production string  18  sits within casing string  16  and is used to pump production liquid  22  from reservoir  20  to a pipeline  24 . Fluid is produced through production string  18  via production outlet  19  using a downhole pump (not shown). The fluid produced from the reservoir may be a mixture of gas, oil, and water and is communicated to a pipeline  24  via outlet line  21 . While the relative amounts vary from well to well, and depend on the formation under consideration, system  10  is primarily suited for wells where the fluid that is pumped up through production tubing string  18  is primarily liquid, and gas tends to accumulate in casing string  16 . As shown, fluid produced from well  12  is transported in pipeline  24  for downstream processing. Other transport or collection methods may also be used, as is known in the art. Pipeline  24  may be connected to and receive fluid from multiple hydrocarbon wells  12 , and typically has an operating pressure. Fluids produced from well  12  must be pressurized to this pipeline pressure in order to be transported via pipeline  24 . 
     Casing gas is removed from casing string  16  and pressurized to a desired pressure for transport or storage. In some cases, and as shown in  FIGS. 1 to 3 , the casing gas may be injected into pipeline  24  by pressurizing the gas to the pipeline pressure. Casing gas may include a liquid component, or a liquid component may develop as the pressure and temperature conditions of the casing gas change as the casing gas is removed and compressed. To address this, system  10  uses a pump  30  that is capable of pumping and pressurizing a liquid/gas mixture. 
     In one example, referring to  FIG. 1 , pump  30  has an inlet  36  connected to casing string  16  by way of a casing gas conduit  34 . A liquid conduit  38  is also connected to inlet  36  and, provides a source of production liquid  22  to pump  30 . The source of production liquid  22  may be pipeline  24 , wellhead  14  via production string  18 , or other suitable sources of liquid. In some cases, the fluid mixture in pump  30  may be 30% or more, 50% or more, or 70% or more liquid. The minimum amounts of liquid or gas in pump  30  will generally be defined by the specifications of the pump, as the amount of gas that can be handled by a particular pump may vary. By way of example, pump  30  may be a positive displacement pump or any other suitable pump capable of handling a mixture of liquid and gas and pressurizing the fluid mixture to the necessary output pressures. Examples of suitable positive displacement pumps include rotary lobe pumps, or other types of positive displacement pumps known to those skilled in the art. As will be described herein, steps may be taken to ensure a suitable proportion of liquid and gas is present in pump  30  during operation. Prior to starting system  10 , it may be beneficial to flood pump  30  and the associated lines with liquid to ensure that there will always be a suitable amount of liquid present within pump  30 . This is particularly useful if inlet  36  of pump  30  receives liquid from pipeline  24  as shown in  FIG. 3 , where the liquid is drawn off downstream of line  31 , as this ensures there will be sufficient liquid in the pipeline at all times to be sent to pump  30 . 
     Once pressurized, the gas/liquid mixture is ejected from pump  30  via an outlet  32  to the destination, such as pipeline  24 . This may be done directly or through other intermediate components, such as a shutoff valve  80  and check valve  82  as shown, or other components as may be present in any given well location. 
     The fluid provided to pump  30  may be provided in different ways. As shown in  FIG. 1 , liquid conduit  38  communicates fluids, typically liquids, from a pipeline  24 . Referring to  FIG. 2 , the liquid may be provided directly from the production flow from the wellhead. As shown, liquid conduit  38  is connected to a secondary production outlet  22 , although it may also be connected to production outlet  19 , as shown in  FIG. 3 . Liquid may also be provided to pump  30  via different means, such as a tank of liquid, by recirculating liquid using a separator as will be discussed below, etc. In some examples, the liquid and gas phases may be communicated to pump  30  using the same conduit, which may receive both gas and liquid from a wellhead or downstream of the wellhead using different ports. In that situation, the gas and liquid would be combined at the wellhead or any suitable point downstream of the wellhead and communicated to the pump in a single conduit, or connected with other conduits connected to other wells prior to being received by the pump. In that case, the downhole pump typically provides the pressure required to transfer the liquid, and the casing gas is drawn into the conduit as the liquid is pumped through the conduit. 
     In some cases, it may be beneficial to separate the pressurized fluid from outlet  32  of pump  30 . Referring to  FIG. 3 , the pressurized fluid from outlet  32  is separated into a liquid line  31  and gas line  33  before ejection into pipeline  24 . Separation may occur with the help of a separator vessel (not shown). Depending on the circumstances, the separation may result in fluid streams that are primarily liquid in line  31 , and primarily gas in line  33 , rather than attempting to achieve a high degree of separation before being injected into pipeline  24 , which may be a group line connected to multiple wells, or a line connected to a single well as shown. As noted above, the example shown in  FIG. 3  uses pipeline  24  as the source of production liquid for liquid conduit  38 . By separating liquid and gas into lines  31  and  33 , respectively, liquid conduit  38  may be connected downstream of liquid line  31  and upstream of gas line  33  to pipeline  24  to provide a stream of fluid that is primarily liquid into liquid conduit  38 . It will be understood that this may result in production liquid recirculating through pump  30  any number of times. The mixture may also be injected into other storage or transport equipment, as will be recognized by those skilled in the art. 
     Production liquid that is provided via line  38  to inlet  36  of pump  30  may be liquid that originates from hydrocarbon reservoir  20 . In the examples depicted in  FIGS. 1 and 3 , liquid conduit  38  draws liquid from pipeline  24  and provides the liquid to pump inlet  36  where it is pressurized along with casing gas. The pressurized fluid is then injected into pipeline  24 . Where liquid conduit  38  draws liquid from pipeline  24 , this preferably happens upstream of the point at which gas is injected into pipeline  24  to reduce the amount of gas drawn out of pipeline and into liquid line  38 . Even if the connection is downstream of this point, some separation in pipeline  24  will occur due to gravity, such that drawing fluid out from the bottom of pipeline  24  may also assist in reducing the amount of gas drawn from pipeline  24 . It may be possible to connect liquid conduit  38  upstream of the point at which liquid is injected from pump  30  into pipeline  24  if pipeline  24  is transporting fluid from wells upstream of hydrocarbon well  12 , or if well  12  produces sufficient liquid to supply pump  30  with the necessary amount of liquid. In another example, depicted in  FIG. 2 , liquid conduit  38  may be connected to receive liquid directly from well  12 , such as via a secondary production outlet  22  on wellhead  14  that is in communication with production tubing  18 , or other suitable connection from production string  18 . This approach may be used if well  12  produces sufficient liquid and pump  30  is only used when this is the case. In other examples, pump  30  may be connected to receive liquid from both wellhead  14  and pipeline  24 , with the ability to switch between the two sources, as needed. 
     In other examples, the liquid mixed with casing gas in pump  30  may be a recirculated stream obtained from the outlet of pump  30 . In one example, referring to  FIG. 4 , system  10  may include a separator vessel  42  that is connected to pump outlet  32  and receives the pressurized fluid mixture. Separator  42  is a tank with an upper outlet  44  on top of the tank, and a liquid outlet  46  located at the bottom of the tank. Upper outlet  44  is connected to inject pressurized fluid into pipeline  24  at pipeline pressure. Liquid outlet  46  is connected to a liquid conduit  38   b , which provides the liquid source for the pump  30  at pump inlet  36 . One benefit of using separator  42  is the ability to maintain a liquid level in separator  42  that is available to be recirculated through pump  30  with the casing gas. Generally, gas will flow to the top of separator  42  and will exit via upper outlet  44 . As liquid builds up in separator  42 , liquid will exit separator  42  via upper outlet  44  along with the gas. Alternatively, there may be a separate dump valve or bypass valve to reduce the liquid level in separator  42 . As shown in  FIG. 4 , a separate liquid conduit  38   a  may also be provided through which liquid may be redirected from wellhead  14  to pump  30  if there is insufficient liquid in separator  42 , such as during the initial start-up procedure, or if the fluid level in separator  42  is insufficient. For example, liquid conduit  38   a  may be used initially to provide a liquid source to pump  30  until a sufficient volume of liquid has been collected in separator  42 . When a sufficient volume has been reached, a valve  80   a  along liquid conduit  38   a  may be closed and a valve  80   b  along liquid conduit  38   b  may be opened to switch the source of liquid. Alternatively, liquid conduit  38   a  may be the primary supply of liquid to pump  30 , with liquid conduit  38   b  making liquid from separator  42  available in the event that the amount of liquid in liquid conduit  38   a  is insufficient. System  10  in may also have a liquid fill bypass conduit (not shown) that runs between production outlet line  21  and separator  42 , which may be used to fill separator  42 , such as during the initial start-up procedure, to ensure a reservoir of liquid is made available to pump  30 . Separator  42  may have other connections that are not shown in  FIG. 4 , such as a connection between liquid outlet  46  and a pipeline  24 , or an additional inlet for filling separator vessel  42  with liquid hydrocarbons, water, or other fluid from an external source. 
     Referring to  FIG. 5 , a three port connector  43  may be used instead of separator vessel  42 , such as a tee connector, wye connector, etc. that has one inlet and two outlets. If configured properly, such as with a lower outlet  47  that will have less gas contend passing through than an upper outlet  45 , three port connector  43  may be used to provide a sufficient amount of liquid to inlet  36  of pump  30  via line  38   b , even if some gas is recirculated along with the liquid. Three port connector  43  may be designed with baffles, larger inner diameters, etc. to encourage separation. 
     Referring to  FIG. 6 , another example is shown in which both liquid and gas phases are introduced into system  10  using a common line  35 . Common line  35  may be passed through a strainer  54  before it is connected to liquid conduit  38   a . System  10  in  FIG. 6  may also have a liquid bypass conduit  48  that runs between common line  35  and pipeline  24  or other outlet. System  10  may also have multiple liquid conduits  38   a  and  38   b  that supply liquid to pump  30 , where liquid conduit  38   a  communicates liquid from common line  35 , and liquid conduit  38   b  communicates liquid from lower outlet  47  of three port connector  43 . In this way, the source of liquid provided to pump  30  may be varied, depending on the operation of the well. Liquid from lower outlet  47  may pass through an orifice plate  52  to help control the flow rate of liquid through liquid conduit  38   b  into pump  30 . A bypass line  53  with a valve  80   c  may be provided around orifice plate  52 . As depicted in  FIG. 6 , mixed stream  35  is connected to inlet  36  of pump  30 . It will be understood that other arrangements may also be made, such as mixing liquid with casing gas immediately prior to pump  30  (not depicted), or adding an additional liquid slipstream line (not shown), which may be combined with line  34  shortly before pump  30 . This may be useful to increase the liquid content within pump  30 , if the liquid component in mixed fluid stream  35  is insufficient. 
     Referring to  FIG. 7 , common line  35  may be produced fluids from more than one well  12 . Production liquid and casing gas may be drawn from each well  12  ports  22  and  17  into a mixed fluid streams  37 , such that production outlet  19  and casing gas outlet  17  (shown in  FIG. 1 ) are at substantially the same pressure. These mixed fluid streams  37  are then combined into a common line  35  that is then communicated to system  10 . In this configuration, the pumpjack (not shown) pressurizes the produced fluid to the same pressure as the casing gas stream, and pump  30  pressurizes the mixture to the pipeline pressure. It will also be understood that common line  35  may also be pressurized fluids from other upstream systems, where multiple system  10  are connected in a cascading arrangement, such as to increase the pressure and/or flow rate as produced fluids are transported or to reach a desired pressure within a transportation system. System  10  may also be used to “draw down” the pressure within a well. This allow the formation pressure to be reduced and may result in higher production rates. 
     As will be understood, other connections may also be provided to allow for different options for communicating production fluids to a pipeline  24 , depending on the preferences of the user, and the expected well production fluids. For example, secondary casing outlet  40  may be provided that allows casing gas to be injected directly into pipeline  24  if the pressure within casing  16  is sufficiently high. System  10  may include pressure sustaining valves  76  along any of the liquid or gas lines in system  10  that open and route fluid directly to production pipeline  24  when a predetermined pressure is reached to limit the build-up of pressure within system  10 . System  10  may include relief valves  86 , such as those shown in  FIG. 4  to  FIG. 6 , which can be opened to prevent a dangerous pressure build up. Relief valves may be connected to safely vent the fluids, such as to atmosphere, to holding tanks, to flare stacks, as may be required and as is known in the art. Other components may also be included, such as pressure gauges  78 , shutoff valves  80 , check valves  82 , pressure regulator  84 , etc. These other components may be connected to and operate with a controller that automatically regulates the operation of system  10  in response to measured pressures, flow rates, fluid composition etc. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. 
     The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.