Systems, methods, and apparatus for separating fluid mixtures

Techniques and apparatus for separating a Flowback mixture received from a wellbore. Employing a vessel or system of vessels to receive the fluid mixture and configured to manage the discharge of gases, liquids, and solids to maintain a vapor barrier in the vessel(s) to prevent unwanted release of gas to the atmosphere.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

TECHNICAL FIELD OF THE INVENTION

This disclosure relates generally to techniques for collecting and handling fluid mixtures, and more particularly to vessels or tanks for separating fluid mixtures received from subsurface wellbores.

BACKGROUND

In the oilfield industry, the completion of subsurface wells to produce hydrocarbons entails the insertion of casing tubulars into a wellbore traversing the subsurface formations. Specialized tools are then inserted into the casing to perforate the walls of the tubular at desired subsurface locations in order to allow the hydrocarbons in the surrounding formation to flow into the casing for collection at the surface. Once the casing is perforated, a well stimulation technique known as hydraulic fracturing is applied to create cracks in the rock formations surrounding the wellbore to create fissures or fractures through which natural gas, petroleum, and other fluids can flow more freely. In this process, a fluid is injected into the casing at high pressure to penetrate the formation via the perforations in the casing. Fracturing of a particular stage along the casing requires isolation of casing sections. In this way, the hydraulic fracture is created at the location of the perforations. In such operations, a “plug” is set in the casing to seal off the casing section to receive the high-pressure fluid. Once the fracture is initiated, a propping agent, such as sand, is added to the fluid injected into the wellbore.

After all the stages along the casing have been fractured, the series of plugs are removed so that the well can be produced via the perforations from all the stages. It is common during this drill out process to utilize a coil tubing unit or work over rig to remove the plugs placed in the well during the fracturing process. A shortcoming of plugs that are drilled out is that they leave debris in the wellbore. This debris can create problems with subsequent operations in the well, or at the surface, should it be produced. As oil and gas begin to flow into the wellbore, unwanted fluids and gasses, as well as unwanted particulates from the strata (including, sand, salts, etc.), combine with the plug debris forming a fluid mixture in the wellbore.

The fluid mixture is brought to the surface through a hydraulic process and the fluid is separated into hydrocarbon and water streams and the water is recirculated as part of the drill out process. The combined stream of Gas/Liquid Hydrocarbon/Solids/Water are generally referred to as “Flowback.” Simple frac tanks are commonly used to collect the unwanted Flowback from the wellbore. When the frac tank is full of collected fluids, sand, salts, gasses, etc., different techniques are used to process its contents. The collection, removal, and decontamination of the Flowback is an expensive process. In some cases, environmentally approved services are employed to remove the Flowback collected in the tank.

Thus, a need remains for improved techniques for separating and reclaiming Flowback arriving at the surface from a wellbore.

SUMMARY

According to an aspect of the invention, an apparatus for separating a fluid mixture includes a sealed vessel having a chamber to collect a fluid mixture received from a wellbore, the vessel including: at least one inlet conduit proximate a middle section of the vessel to admit the fluid mixture into the vessel; a liquids discharge line, including: a standpipe disposed within the vessel, the standpipe having an opening at an upper end to receive and transport liquids from within the vessel to a discharge port proximate a lower section of the vessel; a liquids discharge pipe exiting the vessel at the discharge port and having a curved section, wherein the standpipe and liquids discharge pipe form a P trap; and a vacuum breaker valve mounted on the liquids discharge pipe. The vessel also including a gas discharge conduit coupled to a gas discharge port proximate an upper section of the vessel; and a valve coupled to a solids discharge port, the valve configured to permit discharge of solids from within the vessel.

According to another aspect of the invention, a method for separating a fluid mixture includes collecting a fluid mixture from a wellbore within a sealed vessel having a chamber, the vessel including: at least one inlet conduit proximate a middle section of the vessel to admit the fluid mixture into the vessel; a liquids discharge line, including: a standpipe disposed within the vessel, the standpipe having an opening at an upper end to receive and transport liquids from within the vessel to a discharge port proximate a lower section of the vessel; a liquids discharge pipe exiting the vessel at the discharge port and having a curved section, wherein the standpipe and liquids discharge pipe form a P trap; and a vacuum breaker valve mounted on the fluid discharge pipe; a gas discharge conduit coupled to a gas discharge port proximate an upper section of the vessel; and a solids discharge port at the bottom of the vessel. The method also including discharging gas within the vessel out the gas discharge conduit; discharging liquids within the vessel out the liquids discharge line; and operating a valve coupled to the solids discharge port to permit discharge of solids from within the vessel.

According to another aspect of the invention, a system for separating a fluid mixture includes a plurality of vessels to collect a fluid mixture received from a wellbore. Each vessel including: at least one inlet conduit proximate a middle section of the vessel to admit the fluid mixture into the vessel; a liquids discharge line, comprising: a standpipe disposed within the vessel, the standpipe having an opening at an upper end to receive and transport liquids from within the vessel to a discharge port proximate a lower section of the vessel; a liquids discharge pipe exiting the vessel at the discharge port and having a curved section, wherein the standpipe and liquids discharge pipe form a P trap; and a vacuum breaker valve mounted on the liquids discharge pipe. Each vessel also includes a valve coupled to a solids discharge port, the valve configured to permit discharge of solids from within the vessel; and a gas discharge port proximate an upper section of the vessel. The system also includes: a gas discharge conduit coupled to the gas discharge port of each vessel; and a valve mechanism to selectively isolate fluid mixture flow into one or more of the vessels.

DETAILED DESCRIPTION

The foregoing description of the figures is provided for the convenience of the reader. It should be understood, however, that the embodiments are not limited to the precise arrangements and configurations shown in the figures. Also, the figures are not necessarily drawn to scale, and certain features may be shown exaggerated in scale or in generalized or schematic form, in the interest of clarity and conciseness.

While various embodiments are described herein, it should be appreciated that the present invention encompasses many inventive concepts that may be embodied in a wide variety of contexts. The following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings, is merely illustrative and is not to be taken as limiting the scope of the invention, as it would be impossible or impractical to include all of the possible embodiments and contexts of the invention in this disclosure. Upon reading this disclosure, many alternative embodiments of the present invention will be apparent to persons of ordinary skill in the art. The scope of the invention is defined by the appended claims and equivalents thereof.

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. In the development of any such actual embodiment, numerous implementation-specific decisions may need to be made to achieve the design-specific goals, which may vary from one implementation to another. It will be appreciated that such a development effort, while possibly complex and time-consuming, would nevertheless be a routine undertaking for persons of ordinary skill in the art having the benefit of this disclosure.

Once the Flowback arrives at the surface it presents a four-phase fluid mixture that requires separation into distinct streams: Gas/Liquid Hydrocarbon/Solids/Water. An effective way to separate these streams is to first address the removal of the gas phase from the other three phases. At this point in the development of the well, the quantity of the gas phase is very small, but still requires special handling. The gas should enter a sealed vessel for separation and not find release to the atmosphere. Embodiments of this disclosure perform the action of separating the gas phase prior to releasing the other three phases for additional processing.

FIG. 1depicts an embodiment of this disclosure. An apparatus10for separating the Flowback from the wellbore consists of a sealed vessel12. The vessel12has a single inner chamber14to collect the fluid mixture received from a wellbore (not shown). It will be appreciated by those skilled in the art that the vessel12may be manufactured via conventional tank manufacturing processes. It will also be appreciated that the vessel12may be produced from suitable materials depending on the specific application and fluid mixtures to be collected and processed by the vessel12. For example, the vessel12may be produced using metals (e.g. stainless steel, alloys, etc.), non-metallic materials (e.g. PVC, carbon fiber composites, etc.), or a combination of metallic and non-metallic materials. Although a cylindrical vessel12is depicted inFIG. 1, other embodiments may be produced with vessels12having different shapes (e.g. oblong, spherical, square, rectangular, etc.). The dimensions of the vessel12may also vary in height, width, and internal chamber14volume depending on the desired application. Some embodiments may be implemented with a conventional digital level readout11mounted at the top of the vessel12.

InFIG. 1the vessel12is depicted supported by a frame16. In one embodiment the frame16is configured with a square base and four support legs extending from the base to engage with the lower outer section of the vessel12. The frame16may be produced using any suitable materials that will support the weight of the vessel12and its contents when the vessel is in operation. The vessel12may be permanently coupled to the frame16using conventional means (e.g. welding, fasteners, etc.) or temporarily disposed on the frame, depending on the desired application. For example, if the vessel12is to be used as a stand-alone unit, the frame16provides a suitable means to set the vessel in place. In some applications, the frame16provides a convenient stand to set the vessel12atop a discharge receiving tank. Other applications of the vessel12embodiments may be set or carried on trailers, vehicles, or linked with other vessels, as desired for the particular use and environment of operation.

Flowback fluid mixture from the wellbore is admitted into the vessel12chamber14by one or more inlet conduits18mounted proximate a middle section of the vessel. Each inlet conduit18is passed through the vessel12, entering one side of the vessel and exiting at another side of the vessel via apertures20formed in the vessel walls. Similar to the vessel12, the inlet conduit(s)18may be made from any suitable materials depending on the specific application and fluid mixtures to be collected and processed by the vessel. The inlet conduit18dimensions (inside diameter and outside diameter) may vary depending on the desired application. To maintain a sealed chamber14, the pass-through junctions of the inlet conduit18and apertures20may be sealed using suitable conventional means as known in the art (e.g. gaskets, O-rings, sealing compounds, etc.).

The Flowback mixture to be treated in the vessel12is transported to the inlet conduit(s)18from the wellbore via conventional fluid transport systems used in oilfield operations (not shown). Such fluid transport systems include means to connect to one or both open ends of the inlet conduit(s)18extending out from the vessel12wall at the apertures20. If only one open end of an inlet conduit18is coupled to the wellbore fluid transport system, the other end of the conduit may be capped to close it off.

FIG. 2depicts a cutaway cross-section of an inlet conduit18embodiment mounted within a vessel12. The conduit18is configured with a plurality of apertures22spaced along the conduit body. As Flowback fluid mixture is received at one or both open ends24of the inlet conduit18, the mixture is dispersed throughout the vessel12chamber14via the apertures22.FIG. 2also depicts the inlet conduit18passing through a tubular sleeve26disposed inside the vessel12. The tubular sleeve26may be made from any suitable materials depending on the specific application and fluid mixtures to be collected and processed by the vessel12. The tubular sleeve is also configured with a plurality of apertures28spaced along the sleeve body to disperse the fluid mixture throughout the vessel12chamber14. The inside diameter of the sleeve26is greater than the outside diameter of the inlet conduit18, allowing the inlet fluid mixture to flow through the annulus between the two concentric tubes and out the sleeve apertures and into the vessel12. In some embodiments, the inlet conduit18and the tubular sleeve26have the same number of apertures22,28formed thereon such that the apertures of both tubes align with one another along the length of tube bodies. In this manner, the concentric tubes form a baffle30for the fluid mixture stream entering the vessel12. Vessel12embodiments may be implemented with a single baffle30or multiple baffles mounted on the vessel to admit and disperse the fluid mixture into the vessel. Other embodiments may also be implemented with multiple baffles30mounted at different heights on the vessel12body. It will be appreciated by those skilled in the art that the tubular sleeve26may be positioned within the vessel12for passage of the inlet conduit18therethrough during assembly of the vessel.

The gas in the incoming Flowback stream rapidly separates from the solids and liquids streams due to a differential in density. Turning toFIG. 3, a side view of the apparatus10for separating the Flowback from the wellbore is depicted. A gas discharge conduit32is coupled to a gas discharge port34proximate an upper section of the vessel12via a bolted flange36. Gas in the vessel12exits through the discharge port34and flows along the conduit32. The gas discharge conduit32extends along the exterior wall of the vessel12and is configured with a first discharge port38proximate an upper end of the vessel and a second discharge port40proximate a lower end of the vessel. Depending on the application and types of gases involved, the first and/or second discharge ports38,40may be linked to vent the gas to a flare stack for burn off or to vent the gas safely to the atmosphere. The gas discharge conduit32may be made from any suitable materials depending on the specific application and gases to be discharged by the vessel. In some embodiments, an upper section of the gas discharge conduit32is configured with a lifting eye42to facilitate lifting and movement of the apparatus10. In other embodiments, the vessel12may be configured with a blind hatch44proximate a lower section of the vessel. The blind hatch44provides redundancy to permit manual disposal of liquids and solids from within the vessel12if desired. In other embodiments the vessel12may be configured with an inspection hatch45proximate a middle section of the vessel (SeeFIG. 4).

Except for gas discharge via the gas discharge conduit32, the vessel12is otherwise sealed from the atmosphere due to vapor barriers at fluids and solids exit points. The presence of discharge ports on the vessel12for liquids and solids creates specific problems in the management of a vapor barrier. If not managed properly, the gas will escape through the discharge ports and release potentially harmful substances to the atmosphere and in the presence of personnel. The apparatus10is configured to address the potential problems.FIG. 4depicts the apparatus10configured with a liquids discharge line46. The discharge line46includes a vertical standpipe48disposed within the vessel12. The standpipe48has an opening50at an upper end to receive and transport liquids from within the vessel12to a discharge port52(SeeFIG. 4) proximate a lower section of the vessel. The standpipe48is coupled to a liquids discharge pipe54exiting the vessel12at the discharge port52. The liquids discharge pipe54is configured with a curved section (SeeFIG. 3). The standpipe48and the liquids discharge pipe54configuration forms a P trap as known in the art. The liquids discharge line46may be formed from any suitable materials depending on the specific application and fluid mixtures to be collected and processed by the vessel12.

The curved liquids discharge pipe54exiting the vessel12is equipped with a vacuum breaker valve56(SeeFIG. 3). In the event the liquids discharge line46is completely charged with fluids and potentially empties all fluids to the top level of the standpipe48, the breaker valve56equalizes the pressure with the atmosphere and prevents the line from creating a siphon within the vessel12. A conventional vacuum breaker valve56may be used. For example, vacuum breaker valves available from Kadant Inc. (https://kadant.com) may be used in implementations of the disclosed embodiments.

As the incoming Flowback mixture is dispersed into the vessel12from the baffle(s)30, solids in the mixture may fall directly into the opening50at the upper end of the standpipe48, clogging the pipe.FIG. 5depicts a cone-shaped cover51mounted at the standpipe opening50to shield and prevent solids from48falling into the opening while permitting fluids to flow into the opening.

The solids that arrive in the Flowback mixture accumulate in the bottom of the vessel12and require discharge into another vessel (not shown). The solids and liquids from the Flowback tend to aggregate at the bottom of the vessel12with the liquids occupying a layer on top of the solids. This presence of the liquids creates the vapor barrier and needs to be maintained. This requires management of the rate at which the solids are discharged in order to preserve the vapor barrier above the solids and prevent the release of gas to the atmosphere. An electric rotary valve58is coupled to a solids discharge port60on the bottom of the vessel12. The rotary valve58is operated to manage the solids discharge from the vessel12. The rotary valve58is configured with a rotor entailing a series of paddles to remove solids at a determined rate and prevent fluids from escaping through the solids discharge port60. Each revolution of the rotary valve58removes a specific quantity of solids from within the vessel12and discharges them into a receiving tank (not shown). Operation of the rotary valve58delivers a consistent solids stream into the receiving tank and maintains the vapor barrier in the vessel12. Conventional rotary valves58as known in the art may be used in implementations of the apparatus10. For example, rotary valves available from ACS Valves (www.acsvalves.com) may be used in implementations of the disclosed embodiments. The combination of the anti-siphon breaker valve56to manage liquids discharge and the rotary valve58to manage solids/liquids discharge allow the regulation of the vessel12in a unique manner.

In some embodiments, the rotary valve58may be configured with conventional electronics and computer technology59including a processor and an antenna to provide for wired or wireless control and operation of the valve. Performance and operation of the rotary valve58may be monitored and controlled using a computing device17(SeeFIG. 1). In other embodiments, the digital level readout11mounted at the top of the vessel12may be configured with conventional electronics including a processor and an antenna to wirelessly transmit data representing the mixture level in the vessel to the computing device17(SeeFIG. 4). The computing device17may include, for example, a mobile phone, a tablet, a laptop computer, a desktop computer, an electronic notepad, a server computing device, etc. In some implementations, the rotary valve58and computing device17can be implemented for remote valve monitoring and control via a cloud-computing architecture. In yet other embodiments, the computing device17may be programmed to automatically control the valve58to adjust the volume of solids discharge from the vessel12depending on the mixture level data wirelessly received from the digital level readout11. It will be appreciated by those skilled in the art that the processors in the digital level readout11and the rotary valve58may be configured to perform as described herein using conventional software using any suitable computer language and electronics protocols.

FIG. 6depicts another embodiment of this disclosure. In this implementation, a series of vessels12are linked together to form a system13for separating fluid mixtures. The vessels12operate in a similar manner and are configured similarly to the other vessel embodiments12disclosed herein, with minor differences. A gas discharge conduit62is coupled to the gas discharge port34of each vessel. One end of the discharge conduit62may be configured to vent the gas safely to the atmosphere and the other end to vent the gas to a flare stack for burn off. The gas discharge conduit62includes valves64at each end of the conduit62, with the vessels12linked into the conduit in between the valves. In this manner, either valve64may be closed to shut off gas flow through either or both ends of the conduit62. The valves64may be conventional valves configured for manual operation or with electronics for automatic or remotely controlled operation.

The system13ofFIG. 6offers the ability to process large volumes of Flowback mixtures, where the flow rate may exceed the capacity of a single vessel12. Some vessel12embodiments (whether implemented as stand-alone units or in a multi-unit system), may be configured with internal plates66or extensions affixed to the inner walls at the upper end of the vessel, above the inlet conduit(s)18to provide baffling to prevent solid or liquid splash into the gas discharge conduit32,62. The multi-unit system13employs a valve mechanism68to selectively isolate fluid mixture flow into one or more of the vessels12. The valve mechanism68may use conventional tubing70and one or more valves configured for manual operation or with electronics for automatic or remotely controlled operation. The Flowback mixture to be treated in the vessel(s)12is transported to a primary inlet65from the wellbore via conventional fluid transport systems used in oilfield operations. Embodiments may also be implemented with some vessels12configured with conventional hand-operated valves72and other vessels with mechanized rotary valves58.

In accordance with some embodiments,FIG. 7is a flow chart illustrating a process for separating a fluid mixture. At step100, a fluid mixture from a wellbore is collected within a sealed vessel, the vessel including: at least one inlet conduit proximate a middle section of the vessel to admit the fluid mixture into the vessel; a liquids discharge line, comprising: a standpipe disposed within the vessel, the standpipe having an opening at an upper end to receive and transport liquids from within the vessel to a discharge port proximate a lower section of the vessel; a liquids discharge pipe exiting the vessel at the discharge port and having a curved section, wherein the standpipe and liquids discharge pipe form a P trap; and a vacuum breaker valve mounted on the fluid discharge pipe; a gas discharge conduit coupled to a gas discharge port proximate an upper section of the vessel; and a solids discharge port at the bottom of the vessel. At step105, gas within the vessel is discharged out the gas discharge conduit. At step110, liquids within the vessel are discharged out the liquids discharge line. At step115, a valve coupled to the solids discharge port is operated to permit discharge of solids from within the vessel. This process may be implemented using the techniques and embodiments disclosed herein.

In light of the principles and example embodiments described and depicted herein, it will be recognized that the example embodiments can be modified in arrangement and detail without departing from such principles. Also, the foregoing discussion has focused on particular embodiments, but other configurations are also contemplated. Even though expressions such as “in one embodiment,” “in another embodiment,” or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the invention to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. As a rule, any embodiment referenced herein is freely combinable with any one or more of the other embodiments referenced herein, and any number of features of different embodiments are combinable with one another, unless indicated otherwise. The terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” The term “processor” may refer to one or more processors.

In view of the wide variety of useful permutations that may be readily derived from the example embodiments described herein, this detailed description is intended to be illustrative only, and should not be taken as limiting the scope of the invention. What is claimed as the invention, therefore, are all implementations that come within the scope of the following claims, and all equivalents to such implementations.