Patent Publication Number: US-8122947-B2

Title: Turbulent device to prevent phase separation

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure generally relates to the field of transmitting produced fluids extracted from a subterranean wellbore. The disclosure more specifically relates to a pipeline for transmitting wet crude with a mixing device for sustaining an oil and water emulsion within the wet crude. 
     2. Description of the Related Art 
     Crude oil from a subterranean formation generally comprises water along with liquid hydrocarbons. Crude oil having a discernable water fraction is herein referred to as wet-crude. After being extracted from the formation, the wet crude is transmitted to a processing facility typically through one or more transmission pipelines. Examples of a processing facility include refineries, water separation units, treatment facilities, and any other unit that refines or otherwise treats the crude oil. While flowing through the pipeline, the wet crude flow regime generally remains in a laminar flow region. 
     Transmission pipelines typically extend in a horizontal orientation that can run for many miles. The pipelines&#39; long run combined with the wet crude laminar flow allows water to separate from the crude oil and contact the inner pipeline surface. Since the common material for pipelines is carbon steel, being directly subjected to a water fraction over time will corrode the inside of the pipeline. This may be exacerbated in situations when the water has a high metal salt content. This problem has been addressed by either providing a coating on the inner surface of the piping as well as injecting additives into the wet crude to maintain the water fraction in solution and dispersed within the crude fraction. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a method for transmitting a wellbore fluid through a pipeline, wherein the wellbore fluid comprises wet crude having liquid hydrocarbon and water. The method comprises directing a controlled stream of the wellbore fluid into the pipeline to produce a flowfield of wellbore fluid through the pipeline and creating non-laminar flow of the wellbore fluid in at least a portion of the pipeline with a mixing device. Use of the mixing device forms a sustaining water-in-oil emulsion of the wellbore fluid. The mixing device is disposed in the wellbore fluid flowpath and comprises a member within the pipeline. The member comprises a leading edge with a tip at one end and a crest at another end, the contour of the member between the tip and the crest being largely non-parallel to the pipeline, and wherein the member cross-section increases with distance away from the tip. The member also may comprise a rear or trailing end comprising a hemi-sphere, a body having fins helically arranged on its outer surface, a body having a terminal end substantially perpendicular to the pipeline axis, or combinations thereof. 
     Also disclosed herein is a pipeline for transmitting wet crude. The pipeline comprises an inlet in fluid communication with a hydrocarbon producing wellhead, wherein the inlet is formed to receive wellbore fluid from the wellhead thereby creating wellbore fluid flowfield in the pipeline. The wellbore fluid comprises wet crude having liquid hydrocarbon and water. The pipeline includes an exit in fluid communication with a wellbore fluid processing facility and a mixing device. The mixing device comprises a mixing member having a front end and a backend disposed downstream of the front end. The front end converges to a point at its leading edge and has a cross sectional area that increases with distance from the leading edge to the backend. Flowing wellbore fluid across the mixing member trips the wellbore fluid flowfield into a non-laminar state and suspends the water within the liquid hydrocarbon. In one embodiment, the front end comprises a cone and the backend comprises a shape selected from the group consisting of a hemi-sphere and a cone having helically disposed fins thereon. Optionally, the pipeline may comprise multiple members in its mixing device, where the members have a front end with a triangular cross section and a substantially planar backend that is perpendicular to the pipeline axis. The members may be vertically oriented members, horizontally oriented members, or a combination. The members may be arranged in rows that are disposed at different axial locations in the pipeline, wherein members of one row are staggered with respect to members of another row. The pipeline may include more than one mixing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention&#39;s scope as it may admit to other equally effective embodiments. 
         FIG. 1  is a schematical view illustrating flow of wellbore fluid to the wellhead and pipeline and to a processing facility. 
         FIG. 2   a  is a side partial cross sectional view of an embodiment of a mixing device. 
         FIG. 2   b  is an axial view of the mixing device of  FIG. 2   a.    
         FIG. 3   a  is a side partial cross sectional view of an embodiment of a mixing device. 
         FIG. 3   b  is axial view of the mixing device of  FIG. 3   a.    
         FIG. 4   a  is a side cross sectional view of an embodiment of a mixing device. 
         FIG. 4   b  is an axial view of the mixing device of  FIG. 4   a.    
         FIG. 5   a  is a side partial cross sectional view of an embodiment of a mixing device. 
         FIG. 5   b  is an overhead view of the mixing device of  FIG. 5   a.    
         FIG. 5   c  is an axial view of the mixing device of  FIGS. 5   a  and  5   b.    
         FIG. 6   a  is a side partial cross sectional view of an embodiment of a mixing device. 
         FIG. 6   b  is an overhead view of the embodiment of the mixing device of  FIG. 6   a.    
         FIG. 6   c  is an axial view of the mixing device of  FIGS. 6   a  and  6   b.    
     
    
    
     DETAIL DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     The method and device disclosed herein provides a manner of transmitting produced wet crude through a pipeline, wherein the fluid contains a hydrocarbon and a liquid water fraction. During the fluid transmission, the method maintains the water fraction in the wet crude. More specifically, the system and method included herein incorporates a mixing device within the pipeline, wherein the mixing device perturbs the wellbore fluid into a non-laminar flow regime. The step of perturbing the wellbore fluid flow prevents water within the wet crude from coalescing and separating from within the hydrocarbon fraction thereby substantially reducing direct exposure of the inner surface of a pipeline with water contained in wet crude. 
     With reference now to  FIG. 1 , one embodiment of a transmission system for transmitting a wellbore fluid is shown. In this embodiment, wellbore fluid, that comprises wet crude, is being produced from within a wellbore  5 , directed through a wellbore assembly  7 , and directed into a pipeline  10 . Thus, the pipeline  10  entrance is connected with the wellhead assembly  7 . The pipeline  10  may include one or more pumps  11  for pumping the wellbore fluid within the pipeline  10  to its terminal destination. In the embodiment of  FIG. 1 , the terminal destination comprises a processing facility  12 . Facility equipment  14  is shown connected to the terminal end of the pipeline  10 , the facility equipment  14  may be any type of fluids handling equipment. Examples of facility equipment includes a heat exchanger, a separator, a coalescer, and rotating equipment, such as a pump. 
     Also included within the pipeline  10  is a mixing device  20  having a mixing member  30  therein shown in a dashed outline. For the purposes of disclosure herein, the outer housing of the mixing device  20  is referred to as a spool  21 , wherein the spool is coupled with the remaining portion of the pipeline  10  via respective flanges  22 . Thus when disposed within the pipeline  10 , the spool  21  may be considered as part of the pipeline  10 . 
       FIGS. 2   a  and  2   b  illustrate in a side and an end view an embodiment of a mixing device  20   a . The mixing device  20   a  comprises a spool  21   a  flanked by flanges  22   a . The flanges  22   a  provide a connection means for connecting the mixing device  20   a  within an associated pipeline. The mixing device  20   a  includes a mixing member  30   a  having a front end  32  and a rear end  34 . The front end  32  cross-sectional area increases with distance from the tip  31  of its leading edge along its length. Along the increase the front end  32  has a profile angled (not parallel) with the spool  21   a  inner circumference. One embodiment of supports  36  illustrates structural members that support the mixing member  30   a  within the spool  21   a . The supports  36  also orient the mixing member  30   a  within a flow field of wellbore fluid flow. Fluid flow is illustrated by arrows on the upstream portion of the mixing device  20   a.    
     The front end  32  comprises a generally conical shape converging to a tip  31  at a forward portion of its leading edge and a rear end  34  (also referred to as a trailing edge) with a generally semi-hemispherical shape. In the embodiment shown, the mixing member  30   a  is oriented so the leading edge is directed opposite the fluid flow direction. Accordingly, particles in the fluid flow encounter the leading edge before passing over the remaining portion of the mixing member  30   a . Flow arrows depicting a flow path over the member  30   a  are directed around the outer surface of the flow member  30   a  at an angle oblique to the axis of the mixing device  20   a.    
     In one mode of operation, fluid entering the mixing device  20   a  is in a generally laminar flow regime. The laminar flow regime is illustrated by the uniform length and distribution of the arrows proximate to the entrance flange  22   a . The flow field here is denoted by F L , where the subscript “L” represents laminar flow. As noted above, upon reaching the front end  32  the flow field splits and flows along the outer surface of the mixing member  30 . The region where the mixing member  30  cross sectional area is at a maximum is referred to as its crest. Along the crest region the annulus area between the mixing member  30  outer surface and spool  21   a  inner diameter is minimized thus producing a localized maximum in fluid velocity. The flow field redirection by the front end  32  is relatively gradual. In contrast, as the flow passes across the rear end  34 , its profile abruptly truncates which creates a low pressure field just downstream of the rear end  34 . The low pressure field directs the flow field towards the mixing device  20   a  axis A. The abrupt redirection of flow thereby trips the flow field from a laminar state into a non-laminar state and sufficiently perturbs the wet crude to suspend its water fraction therein. The flow field is identified by F T , where the subscript “T” represents transitional flow. Moreover, the non-laminar transition sustains the water and oil emulsion of the wellbore fluid within the pipeline having the mixing device. 
       FIG. 3   a  illustrates in side cross sectional view another embodiment of a mixing device  20   b  comprising a mixing member  30   b  coaxially disposed within a spool piece  21   b . Flanges  22   b  are disposed on the ends of the spool piece  21   b . The mixing member  30   b  comprises a front end  32   a  and a rear end  34   a . The front end and rear end ( 32   a ,  34   a ) both have a substantially conical shape and are mated at their respective base ends. Supports  36   a  extend from the spool  21   b  to the outer surface of the mixing member  30   b  for maintaining the mixing member  30   b  within the wellbore fluid flow. Fins  38  are helically arranged on the rear end  34   a . The fins  38  each have a width that exceeds its thickness and form corresponding helical channels  39  that run from the base  35  of the rear end  34   a  toward the downstream tip  37  of the mixing member  30   b . The helically shaped channels  39 , in combination with the alternating higher fluid velocity adjacent the front end/back end juncture, creates a fluid mixing zone downstream of the mixing member  30   b . As noted above, the zone produces a perturbing mixing action and may trip laminar fluid flow into non-laminar flow that suspends the water components within the liquid hydrocarbon.  FIG. 3   b  is a view from downstream of the mixing member  30   b  illustrating a fin arrangement. 
       FIG. 4   a  illustrates yet another embodiment of a mixing device  20   c  having a mixing member  30   c  disposed within a spool  21   c . The spool includes flanges  22   c  on its ends for connection within an associated pipeline. The mixing member  30   c  of  FIG. 4   a  is not a single member but comprises multiple mixing members  41 . These members  41  are arranged in a forward row  40  and a rearward row  42 . The forward row  40  comprises members disposed within the mixing device  20   c  upstream of the rearward row  42 . Each member  41  comprises a front end  32   b  and a rear end  34   b , wherein the front end  32   b  has a generally triangular cross section that increases in height and area with distance away from the leading edge of the front end  32   b . The rear end  34   b  terminates in a generally planar configuration at the downstream end of the member  41 . Similar to the other mixing members, the gradual widening of the mixing members  41  directs flow away from its middle and then the abrupt absence of material allows for a low pressure zone downstream of the member. The low pressure zone draws in flow elements from the flow field thereby providing a mixing effect in the zone. 
     In the embodiment of  FIG. 4   a , the forward row  40  is staggered with respect to the rearward row  42 . That is, at least one member of the rearward row  42  is aligned with a gap  43  separating members  41  of the forward row  40 . Similarly a member of the forward row  40  is aligned with a gap  45  separating members  41  of the rearward row  42 . Accordingly, enhanced mixing and perturbation is produced by staggering members of adjacent rows and aligning a member of a row with a gap of an adjacent row. Optionally, additional rows of individual mixing elements may be included within this mixing device. However the mixing device  20   c  is not limited to staggered adjacent rows, but includes adjacent rows having members substantially aligned with one another. Although the members  41  are shown as aligned with the spool axis, they can be oriented at an angle to the axis. This orientation applies to any of the mixing members disclosed herein.  FIG. 4   b  provides an axial view of the mixing member  30   c  of  FIG. 4   a  depicting the generally horizontal arrangement of the individual elements  41  along the height of the spool  21   c.    
       FIGS. 5   a  and  5   b  illustrate a side overhead and an axial view of a mixing device  20   b  having individual mixing members  41   a  disposed within the device. The mixing device  20   d  is equipped with flanges  22   d  on its ends for attachment within a pipeline. Some of the members  41   a  are vertically arranged and some are horizontally arranged. With reference now to  FIG. 5   a , the mixing device  20   b  comprises a forward row  40   a  and a rearward row  42   a , each row ( 40   a ,  42   a ) comprises vertical elements  44  intersecting horizontal members  46 .  FIG. 5   a , which is a side view of the mixing device  20   d , illustrates that the horizontal members  46  are staggered with respect to corresponding horizontal members  46  of the different row.  FIG. 5   b , which is an overhead cross sectional view of the mixing device  20   d , illustrates that the vertical members  44  are generally aligned with corresponding elements from different rows. Optionally, the vertical members may be staggered with the horizontal members aligned, the horizontal and vertical members may be staggered, or the horizontal and vertical members may be aligned. Further illustrating the cross hatch arrangement of the vertical and horizontal members ( 44 ,  46 ),  FIG. 5   c  illustrates an axial view of the mixing device  20   d  circumscribed by the spool  21   d.    
       FIGS. 6   a - 6   c  illustrate yet another embodiment of a mixing device  20   e . In this embodiment, the mixing device comprises a mixing member  30   e  disposed within a spool  21   e  having flanges  22  at its respective ends. The mixing member  30   e  comprises mixing members, some of which are horizontal and some vertical. As illustrated by  FIGS. 6   a  and  6   c , vertical members ( 48 ,  50 ) are located at different distances lateral from the spool axis A. For example, an outer vertical element  48  is proximate to the outer radius of the spool  21   e  on either side of the mixing member  30   e  and inner vertical members  50  are disposed in closer proximity to the spool  21   e  axis A. Also, the inner vertical members  50  are longer than the outer vertical members  48 . Horizontal elements  46  are horizontally arranged within the mixing device  20   e  at different elevations within the spool  21   e . As seen in the side view of  FIG. 6   a  and the overhead view of  FIG. 6   b , both the horizontal and vertical members the first row  40   b  are staggered with respect to the members of the second row  42   b.    
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.