Turbulent device to prevent phase separation

A mixer for use in a transmission pipeline and a wellbore fluids pipeline having a mixing device. The pipeline extends from a well head to a processing facility. The mixer perturbs the flow into a non-laminar state. Mixer embodiments include a body having a cone shaped leading edge and a hemi-spherical end. Other embodiments include a double cone having a series of helical fins on the trailing end of the double cone and fins extending perpendicular to the pipeline axis having a triangular cross section. The fins may be staggered with a mix of vertically and horizontally orientations.

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' 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.

DETAIL DESCRIPTION

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 toFIG. 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 wellbore5, directed through a wellbore assembly7, and directed into a pipeline10. Thus, the pipeline10entrance is connected with the wellhead assembly7. The pipeline10may include one or more pumps11for pumping the wellbore fluid within the pipeline10to its terminal destination. In the embodiment ofFIG. 1, the terminal destination comprises a processing facility12. Facility equipment14is shown connected to the terminal end of the pipeline10, the facility equipment14may 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 pipeline10is a mixing device20having a mixing member30therein shown in a dashed outline. For the purposes of disclosure herein, the outer housing of the mixing device20is referred to as a spool21, wherein the spool is coupled with the remaining portion of the pipeline10via respective flanges22. Thus when disposed within the pipeline10, the spool21may be considered as part of the pipeline10.

FIGS. 2aand2billustrate in a side and an end view an embodiment of a mixing device20a. The mixing device20acomprises a spool21aflanked by flanges22a. The flanges22aprovide a connection means for connecting the mixing device20awithin an associated pipeline. The mixing device20aincludes a mixing member30ahaving a front end32and a rear end34. The front end32cross-sectional area increases with distance from the tip31of its leading edge along its length. Along the increase the front end32has a profile angled (not parallel) with the spool21ainner circumference. One embodiment of supports36illustrates structural members that support the mixing member30awithin the spool21a. The supports36also orient the mixing member30awithin a flow field of wellbore fluid flow. Fluid flow is illustrated by arrows on the upstream portion of the mixing device20a.

The front end32comprises a generally conical shape converging to a tip31at a forward portion of its leading edge and a rear end34(also referred to as a trailing edge) with a generally semi-hemispherical shape. In the embodiment shown, the mixing member30ais 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 member30a. Flow arrows depicting a flow path over the member30aare directed around the outer surface of the flow member30aat an angle oblique to the axis of the mixing device20a.

In one mode of operation, fluid entering the mixing device20ais 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 flange22a. The flow field here is denoted by FL, where the subscript “L” represents laminar flow. As noted above, upon reaching the front end32the flow field splits and flows along the outer surface of the mixing member30. The region where the mixing member30cross sectional area is at a maximum is referred to as its crest. Along the crest region the annulus area between the mixing member30outer surface and spool21ainner diameter is minimized thus producing a localized maximum in fluid velocity. The flow field redirection by the front end32is relatively gradual. In contrast, as the flow passes across the rear end34, its profile abruptly truncates which creates a low pressure field just downstream of the rear end34. The low pressure field directs the flow field towards the mixing device20aaxis 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 FT, 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. 3aillustrates in side cross sectional view another embodiment of a mixing device20bcomprising a mixing member30bcoaxially disposed within a spool piece21b. Flanges22bare disposed on the ends of the spool piece21b. The mixing member30bcomprises a front end32aand a rear end34a. The front end and rear end (32a,34a) both have a substantially conical shape and are mated at their respective base ends. Supports36aextend from the spool21bto the outer surface of the mixing member30bfor maintaining the mixing member30bwithin the wellbore fluid flow. Fins38are helically arranged on the rear end34a. The fins38each have a width that exceeds its thickness and form corresponding helical channels39that run from the base35of the rear end34atoward the downstream tip37of the mixing member30b. The helically shaped channels39, in combination with the alternating higher fluid velocity adjacent the front end/back end juncture, creates a fluid mixing zone downstream of the mixing member30b. 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. 3bis a view from downstream of the mixing member30billustrating a fin arrangement.

FIG. 4aillustrates yet another embodiment of a mixing device20chaving a mixing member30cdisposed within a spool21c. The spool includes flanges22con its ends for connection within an associated pipeline. The mixing member30cofFIG. 4ais not a single member but comprises multiple mixing members41. These members41are arranged in a forward row40and a rearward row42. The forward row40comprises members disposed within the mixing device20cupstream of the rearward row42. Each member41comprises a front end32band a rear end34b, wherein the front end32bhas a generally triangular cross section that increases in height and area with distance away from the leading edge of the front end32b. The rear end34bterminates in a generally planar configuration at the downstream end of the member41. Similar to the other mixing members, the gradual widening of the mixing members41directs 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 ofFIG. 4a, the forward row40is staggered with respect to the rearward row42. That is, at least one member of the rearward row42is aligned with a gap43separating members41of the forward row40. Similarly a member of the forward row40is aligned with a gap45separating members41of the rearward row42. 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 device20cis not limited to staggered adjacent rows, but includes adjacent rows having members substantially aligned with one another. Although the members41are 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. 4bprovides an axial view of the mixing member30cofFIG. 4adepicting the generally horizontal arrangement of the individual elements41along the height of the spool21c.

FIGS. 5aand5billustrate a side overhead and an axial view of a mixing device20bhaving individual mixing members41adisposed within the device. The mixing device20dis equipped with flanges22don its ends for attachment within a pipeline. Some of the members41aare vertically arranged and some are horizontally arranged. With reference now toFIG. 5a, the mixing device20bcomprises a forward row40aand a rearward row42a, each row (40a,42a) comprises vertical elements44intersecting horizontal members46.FIG. 5a, which is a side view of the mixing device20d, illustrates that the horizontal members46are staggered with respect to corresponding horizontal members46of the different row.FIG. 5b, which is an overhead cross sectional view of the mixing device20d, illustrates that the vertical members44are 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. 5cillustrates an axial view of the mixing device20dcircumscribed by the spool21d.

FIGS. 6a-6cillustrate yet another embodiment of a mixing device20e. In this embodiment, the mixing device comprises a mixing member30edisposed within a spool21ehaving flanges22at its respective ends. The mixing member30ecomprises mixing members, some of which are horizontal and some vertical. As illustrated byFIGS. 6aand6c, vertical members (48,50) are located at different distances lateral from the spool axis A. For example, an outer vertical element48is proximate to the outer radius of the spool21eon either side of the mixing member30eand inner vertical members50are disposed in closer proximity to the spool21eaxis A. Also, the inner vertical members50are longer than the outer vertical members48. Horizontal elements46are horizontally arranged within the mixing device20eat different elevations within the spool21e. As seen in the side view ofFIG. 6aand the overhead view ofFIG. 6b, both the horizontal and vertical members the first row40bare staggered with respect to the members of the second row42b.