Abstract:
A system for detecting and controlling a slug event in a flow through a pipeline is provided. The system includes multiple sensors configured to indicate one or more parameters of the flow for a slug at multiple locations in the pipeline. The system also includes a controller configured to receive one or more response signals corresponding to at least one of the parameters from the sensors. The system further includes a variable speed drive system electrically coupled to the controller and a compressor pumping fluid in the pipeline such that a ratio of liquid to gas is within an acceptable range, wherein the variable speed drive is configured to receive one or more signals from the controller and further configured to regulate at least one of a translational or a rotational speed or a power of the compressor based upon the signals. The system also includes a display unit coupled to the controller, the display unit configured to output the plurality of signals received from the controller.

Description:
BACKGROUND 
       [0001]    The invention relates generally to oil field operations, and more particularly, to controlling slugs in pipelines. 
         [0002]    Pipelines are widely used in a variety of industries, allowing a large amount of material to be transported from one place to another. A variety of fluids, such as oil and/or gas, particulate, and other small solids suspended in fluids, are transported cheaply and efficiently using underground pipelines. Pipelines may be subterranean, submarine, on the surface of the earth, and even suspended above the earth. The pipelines carry enormous quantities of oil and gas products indispensable to energy-related industries, commonly under tremendous pressure and at low temperatures, and at high flow rates. 
         [0003]    Typically, in oil fields, pipelines are used to transport multiphase mixtures such as, gas, oil, and water mixtures produced from individual oil wells to common gathering lines and to also transport the multiphase mixtures recovered from a common gathering point to a treatment facility such as a separator or like. In such a case, the multiphase mixtures frequently tend to separate during transportation to the pipeline so that there are intermittent slugs of liquid followed by slugs of gas, in a non-limiting example. The formation of such slugs in the pipelines result in severe stress on the pipelines and erratic operation of an equipment into which the pipelines discharge. Furthermore, the slugs result in flow distortions that are characterized by more or less rapid changes in pressure, temperature, density and other variables that may in turn, lead to surpassing straining limits of materials of components used for displacement of flows. Some examples of such components include blades, and impellers common to turbomachinery. 
         [0004]    Therefore, there is a need for an improved system and method for avoiding flow instabilities caused by the slugs. 
       BRIEF DESCRIPTION 
       [0005]    In accordance with an aspect of the invention, a system for detecting and controlling a slug event in a flow through a pipeline is provided. The system includes multiple sensors configured to indicate one or more parameters of the flow for a slug at multiple locations in the pipeline. The system also includes a controller configured to receive one or more response signals corresponding to at least one of the parameters from the sensors. The system further includes a variable speed drive system electrically coupled to the controller and a compressor pumping fluid in the pipeline such that a ratio of liquid to gas is within an acceptable range, wherein the variable speed drive is configured to receive one or more signals from the controller and further configured to regulate at least one of a translational or a rotational speed or a power of the compressor based upon the signals. The system also includes a display unit coupled to the controller, the display unit configured to output the plurality of signals received from the controller. 
         [0006]    In accordance with another aspect of the invention, a method for controlling a slug event in a flow through a pipeline is provided. The method includes sensing one or more parameters of the flow for the slug via multiple sensors disposed at a plurality of locations in the pipeline. The method also includes transmitting one or more signals corresponding to the parameters sensed to a controller. The method further includes regulating at least one of a translational or a rotational speed or power of a compressor pumping fluid into the pipeline via the controller based upon the signals and a detection of the slug in order to create an unsteady flow oscillation to affect a flow of the slug. The method also includes regulating multiple valves via the controller upon detection of the slug. 
     
    
     
       DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  is a diagrammatical illustration of an exemplary slug flow regime in accordance with an embodiment of the invention; 
           [0009]      FIG. 2  is a schematic illustration of an exemplary system employing an external supply for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0010]      FIG. 3  is a schematic illustration of another exemplary system employing an external supply of fluid for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0011]      FIG. 4  is a schematic illustration of an exemplary system employing an internal supply and a storage facility for fluid for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0012]      FIG. 5  is a schematic illustration of an exemplary system including a pump installed at a shore for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0013]      FIG. 6  is a schematic illustration of an exemplary system including additional valves for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0014]      FIG. 7  is a schematic illustration of an exemplary system including an adjustable speed electronic drive for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0015]      FIG. 8  is a schematic illustration of an exemplary system including a recirculation equipment for stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0016]      FIG. 9  is a schematic illustration of an exemplary system including a control system for a pump installed for detecting a slug event and stabilizing multiphase flow in a pipeline according to an embodiment of the invention; 
           [0017]      FIG. 10  is a schematic illustration of an exemplary system including backward facing elements installed in the system of  FIG. 8 ; 
           [0018]      FIG. 11  is a flow chart representing steps in an exemplary method for stabilizing flow in a pipeline according to an embodiment of the invention; and 
           [0019]      FIG. 12  is a flow chart representing steps in another exemplary method for stabilizing flow in a pipeline according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    As discussed in detail below, embodiments of the invention include a system and method for eliminating slugs. As used herein the term ‘slug’ refers to multiphase mixtures including, but not limited to, oil, gas, water, and sand that flow typically in pipelines, and subsea wells in the oil and the gas industry. The flow in a slug regime may lead to instabilities leading to negative consequences for pipelines, downstream equipment and overall plant throughput. Various systems and methods for avoiding such slugs are disclosed herein. As used herein, the term ‘sensors’ refer to direct or indirect measurements. Non-limiting examples of the sensors include wire mesh sensors, pressure, temperature, density, conductivity, mass flow, ultrasound, optical waves, with continuous variable outputs, and binary specialized sensors with discrete output like presence/no presence. Further, the term ‘compressor’ refers generally to pumps, translational and rotatory organs. 
         [0021]    In one exemplary embodiment, the pipeline is a flowline that is an element of subsea oil and gas production, collection, and shipping facility, including an offloading system, such as a buoy or platform offloading system. In another embodiment, the fluid may be transported in subsea wells or a manifold from which flowlines transport the fluid to a buoy or platform. Non-limiting examples of the flowline are metal pipes that are equipped with floatation devices located along lengths of the flowlines, to provide a suitable contour or configuration to the flowlines. In another embodiment, the pipes may include carbon fiber composite material. In yet another embodiment, the pipeline is land-based and receives production flow from a surface wellhead or other source. 
         [0022]    Turning to the drawings,  FIG. 1  is a diagrammatic illustration of an exemplary slug flow regime  12  in an infrastructure such as, but not limited to, a pipeline  14 . In the illustrated embodiment, the slug flow regime  12  includes a liquid phase  11  and a gaseous phase  17 . It is desirable to minimize slug events or damage caused to the infrastructure by formation of the slug flow regime  12 . 
         [0023]      FIG. 2  is a schematic illustration of an exemplary system  10  for stabilizing fluid flow  12 , as referenced in  FIG. 1 , in a pipeline  14 . Fluid flow  12  originates from a wellhead  13 . It will be appreciated that the wellhead is a non-limiting example and may include other sources of flow. The fluid flow  12  includes multiphase flows or slugs that may be unsteady and proportions of the phases may change with time. It is desirable to minimize damage caused by the slugs or slug flow. In the illustrated embodiment, the fluid flow  12  includes a two phase flow of liquid and gas. In operation, a ratio of the liquid to gas in the flow  12  is monitored and accordingly, gas or liquid supply is provided to obtain a desirable ratio that is at least above a threshold value that minimizes slug formation. An external supply  15  provides the gas or liquid supply and is coupled to the wellhead. In the presently contemplated embodiment, the external supply is a pump or compressor  16  located above the sea surface  19 . At least one sensor  18  detects a ratio of liquid to gas in the flow  12 . The compressor  16  operates at a set point to ensure that a ratio of liquid to gas is at least above a threshold value that minimizes slug formation in the multiphase flow  12 . The set point will tend to change over time as it follows changes in the ratio of liquid to gas in the flow that is detected by the sensor  18 . Valves  21  and  20  regulate motion of the flow within the pipeline to ensure elimination of the slug. 
         [0024]      FIG. 3  is a schematic illustration of another exemplary system  30  for stabilizing multiphase flow  32  employing a pump  16  on a seabed near a wellhead  13 , as referred to in  FIG. 1 . The system  30  includes the pump  16  (as referred to in  FIG. 2 ) installed on or near the seabed. A large pressure exists at the source or wellhead  13  that is utilized by the pump  16  to force the fluid flow  12 . Advantageously, the large pressure already existing at the wellhead is utilized by the pump and helps improve efficiency of the system  30 . 
         [0025]      FIG. 4  is a schematic illustration of a system  50  for stabilizing multiphase flow  52  employing an internal supply of liquid and gas such as a wellhead  54 . The fluid flow  52  includes multiphase flows or slugs that may be unsteady and proportions of the phases may change with time. It is desirable to minimize damage caused by the slugs or slug flow. In the illustrated embodiment, the fluid flow  52  includes a two phase flow of liquid and gas. In operation, the liquid and gas in the flow  52  is separated and stored in a storage facility. A ratio of the liquid to gas in the flow  52  is monitored and accordingly, gas or liquid is released from the storage facility to obtain a desirable ratio that is at least above a threshold value that minimizes slug formation and moves the flow outside the slug flow regime. Accordingly, a gas/liquid separator  56  is employed to isolate liquid and gaseous phases of a flow  60  that further propagates the liquid phase  62  and gaseous phase  64  into a liquid storage facility  66  and a gas storage facility  68  respectively. At least one sensor  70  is employed to detect the ratio of liquid to gas entering the multiphase flow  52 . Valves  72  further regulate the flow of the liquid phases and the gaseous phases into the multiphase flow  52  such that a ratio of liquid to gas is within an acceptable range. 
         [0026]      FIG. 5  is a schematic illustration of another exemplary embodiment of a system  90  controlling a multiphase flow  92 . A pump  94  is installed prior to an existing valve  96  on a platform or shore  98  of a well  100 . The pump  94  operates in a reverse mode such that the liquid/gas mixture is pumped in a reverse direction referenced by numeral  102 . A secondary valve  104  is installed on a seabed of the well  100  to regulate a reverse flow from the pump  94 . 
         [0027]      FIG. 6  is a schematic illustration of yet another exemplary embodiment of a system  120  controlling a multiphase flow employing additional valves  124 . Further, a pump  126  installed at a shore delivers liquid from a storage facility  128 . In a particular embodiment, the liquid is water. The liquid is pumped upstream against a wellhead or against a secondary valve  130  that is entirely or partially closed. In case of pressure of the liquid being desirably large enough such that a multiphase mixture moves out of a slug regime or a slug is destroyed, the pump  126  is returned to normal operation by closing the valve upstream and stopping injection of the liquid. 
         [0028]    In another illustrated embodiment of the invention, a system  140  including adjustable speed electronics  142  as an antislug mechanism is depicted in  FIG. 7 . A pump  144  is installed at a seabed and is coupled to the adjustable speed electronics  142 . In a particular embodiment, the electronics  142  includes a variable speed electronic drive  150 , an electric motor  152  and a controller  154 . The electronics  142  allows for flow reversal using the pump  144 . In one embodiment, slug destruction is possible via closing an upstream valve  156  and operating the pump  144  in a reverse direction. In another embodiment, a downstream valve  158  is closed and the pump  144  is operated in a normal flow direction with the upstream valve  156  open. 
         [0029]      FIG. 8  is a schematic illustration of an antislug system  170  including a recirculation equipment  172 . A liquid pump  174  is employed to recirculate liquid from a location  176  where slugs typically occur in a pipeline  178  to a comparably gas rich region  180  upstream of the location  176 . The liquid pump  174  ensures continuous movement of a liquid phase through critical parts of the pipeline  178  preventing blockage. Slug prone locations where local recirculation is to be applied is estimated from flow parameters and a geographic signature of the pipeline  178 . The recirculation equipment  172  is installed in the slug prone locations. 
         [0030]      FIG. 9  is a schematic illustration of an exemplary embodiment of a system  190  that provides protection to ensure extended operation of a pipeline  192 . Accordingly, multiple slug indicators  194  are installed at upstream locations to measure flow characteristics. In a presently contemplated embodiment, three sensors  200 ,  204 ,  206  are installed at the upstream locations. A non-limiting example of the sensors  200 ,  204  and  206  include a wire mesh sensor that measures a local gas volume fraction and phase distribution of a flow across a section of the pipeline  192 . The sensors  200 ,  204 ,  206  may be pressure, temperature, density, conductivity, mass flow, ultrasound, and optical waves, with continuous variable outputs. In another embodiment, the sensors  200 ,  204 ,  206  are binary specialized sensors with discrete output like presence/no presence. A mounting distance between the sensors  200 ,  204 ,  206 , as well as between the sensors and the pump  208  are pre-determined. The distances also depend upon characteristics of the pipelines and type of material flowing through the pipelines. When the sensor  200  detects a slug, a pressure wave oscillation is created to destroy or dilute the slug. The pressure wave distortion is created by controlling torque, speed or power of a pump or compressor  208 . In a case of a mild slug, a driving torque in the pump  208  is changed to destroy the slug. The torque is changed via electronics  210  coupled with a control system  212 . In a particular embodiment, the electronics  210  is a power converter coupled to an electric motor. The control system  212  performs functions such as anti slug, modulation of torque to obtain a mild slug pass through the pump  208 , and to shut off the pump  208  in an emergency situation such as, when a torque above an acceptable limit is required to eliminate the slug. A set of valves  214  and drain lines  216  are installed after sensors  200  and  204 . The drain lines  216  coalesce into a mixing point  217 , separate of the pipeline  192 , and the mixing point  217  is fed back through a tertiary valve  219  to the pipeline  192  at a point after the sensor  206 . 
         [0031]    When the sensor  200  detects a slug, the control system  212  creates an unsteady flow oscillation upstream that affects the slug traversing slightly after sensor  200 . In one embodiment, the unsteady oscillation is sufficient to destroy or dilute the slug, which is detected by the sensor  204 . In such a case, the operation is continued as normal. In another embodiment, if the unsteady oscillation does not dilute or destroy the slug, the sensors  200  and  204  are ‘active’, and the third sensor  206  detects the slug. As used herein, the term ‘active’ refers to detection of a slug. In yet another embodiment, the sensors  204  and  206  may be ‘active’, but the sensor  200  may not be ‘active’ implying that the slug is small and may be traversed through the pump  208  with a small enough force or torque such that not to damage the pump. In another exemplary embodiment, when the sensors  200 ,  204 , and  206  remain ‘active’, the slug is considered too large for safe transferal through the pump and a plant shutdown is requested. 
         [0032]    The pipeline  192  is optionally fitted with backward facing elements  220 , as illustrated in  FIG. 10 , inducing a change in diameter of the pipeline. The backward facing elements constrict flow to enable effect of pressure wave initiated at the pump  208  ( FIG. 9 ). Parameters such as volume of the pipeline  192  between the sensors  200 ,  204  and  206  and the pump  208 , and the diameters are critical for determining amount of backward pressure and mass flow waves to be generated at the pump. The parameters sensed upstream are coded and transmitted by electromagnetic means and decoded, amplified and employed in a control algorithm via the control system  212 . The control system  212  further generates controlling actions such as, variations in time of pressure and flow inside the pipeline  192 . The variations are caused by changes in various parameters such as, but not limited to, delivered electric force, torque, shaft speed, displacement speed, and power of the pump  208 . 
         [0033]      FIG. 11  is a flow chart representing steps in an exemplary method  230  for stabilizing flow in a pipeline. The method  230  includes providing fluid into a pipeline in step  232 . In one embodiment, the fluid is pumped via an internal or an external supply. In another embodiment, liquid and gas in the fluid is separated prior to pumping the fluid via a liquid-gas separator. In yet another embodiment, excess liquid and gas are stored in a storage facility. A ratio of liquid to gas of the flow is sensed in step  234 . In a particular embodiment, the ratio is sensed via multiple wire mesh sensors. Further, the ratio is compared to an acceptable range in step  236 . The flow of the fluid is regulated via multiple valves based upon comparison in step  238 . 
         [0034]      FIG. 12  is a flow chart representing steps in another exemplary method  250  for stabilizing flow in a pipeline. The method  250  includes sensing one or more parameters of the flow for the slug in step  252  via multiple sensors disposed at a multiple locations in the pipeline. Signals corresponding to the parameters sensed are transmitted to a controller in step  254 . At least one of a translational or a rotational speed or power of a compressor pumping fluid into the pipeline is regulated in step  256  via the controller based upon the signals and a detection of the slug in order to create an unsteady flow oscillation to affect a flow of the slug. In a particular embodiment, the signals are transmitted from the controller to a variable speed drive system coupled to the compressor, in order to regulate the speed. Motion of multiple valves is further regulated upon detection of the slug in step  258 . In one embodiment, the compressor is powered down in case of an emergency. In another embodiment, multiple drains are installed with multiple drain valves to dispose the slug. 
         [0035]    The various embodiments of a system and method to eliminate flow instabilities or slugs described above thus provide slug free operation of the pipelines resulting in increased production from a wellhead and reduction of undesirable losses. The ability to detect slug events or slug flow regimes and employ protective measures to mitigate the effect of slug events and/or to alter the flow regime helps to avoid damage to the machinery and enables extended lifetime. 
         [0036]    It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0037]    Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. For example, the use of a slug indicator with respect to one embodiment can be adapted for use with recirculation equipment described with respect to another. Similarly, the various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. 
         [0038]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.