Patent Publication Number: US-2017370200-A1

Title: Bubble enhanced downhole oil water separation

Description:
BACKGROUND 
     The subject matter disclosed herein relates to separation of fluids in an industrial setting. 
     In various industrial contexts and resource production contexts the separation of differing fluid materials may be part of a production or treatment process. By way of example, in an oil or gas production context, the production fluid present in a subterranean production bore may be mixed with water also present in the ground. 
     Thus, in typical oil production wells, both oil and water are pumped to the surface, where the oil is then separated from the water for further refining. The process wastes energy in lifting produced water from the downhole environment and, additionally, incurs additional costs in managing water, which is not of commercial interest typically. 
     In some conventional approaches, attempts have been made to separate oil from water downhole, such as using a downhole oil-water separation (DOWS) device. Such DOWS devices typically are mechanical rotating devices that rely on centrifugal forces to separate oil (lighter fluid) from the heavier water. However, when the density difference between oil and water is not large enough (i.e., the oil density is close to water) the separation process is not effective and oil-laden water may be inadvertently injected into a subterranean reservoir or formation. 
     BRIEF DESCRIPTION 
     In one embodiment, a downhole tool assembly is provided. In accordance with this embodiment, the downhole tool assembly includes at least one pump configured to pump a target fluid from a target-fluid rich zone of a production environment. The production environment contains both the target fluid and a non-target fluid. The downhole tool assembly also includes a bubble generator configured to inject gas bubbles into the production environment. The gas bubbles are sized so as to associate with droplets of the target fluid to decrease the apparent density of the target fluid relative to the non-target fluid. 
     In a further embodiment, a method for separating a target fluid from water in a downhole environment is provided. In accordance with this method, a plurality of bubbles are generated in a mixture of a target fluid and water present in a production environment. The bubbles bond with droplets of the target fluid to decrease the apparent density of the droplets. Target fluid is pumped to the surface from a first zone of the production environment having an increased concentration of the target fluid due to the decreased apparent density of the droplets. 
     In an additional embodiment, a method for purging settled fines in a downhole environment is provided. In accordance with this method, a first pump configured to inject water into a downhole formation is operated to instead agitate fines within the downhole environment so as to raise at least a portion of the fines to the level of an inlet to a second pump. The second pump is operated so as to intake the agitated fines and to lift the fines form the downhole environment with a produced fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  depicts a pumping mechanism and downhole environment, in accordance with aspects of the present disclosure; 
         FIG. 2  depicts a downhole tool with a bubble generation apparatus, in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Certain embodiments or implementations illustrating aspects of the present disclosure are described and/or depicted with reference to the present figures. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the present invention. Indeed, the present examples are intended to facilitate and simplify explanation of the present approach and to provide useful context for understanding the disclosed subject matter. These description and example should, therefore, not be read to explicitly or implicitly limit application of the described devices and/or techniques to the contexts of the examples. 
     The terminology used herein is for describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Although the terms first, second, primary, secondary, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, but not limiting to, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments or from the discussion attributed to the respective features. As used herein, the term “and/or” includes any, and all, combinations of one or more of the associated listed items. 
     Certain terminology may be used herein for the convenience of the reader in understanding the relative relationships between components, particularly as they may be illustrated in a given example. However, such terminology is not to be taken as a limitation on the scope of the invention. For example, words such as “upper”, “lower”, “left”, “right”, “front”, “rear”, “top”, “bottom”, “horizontal”, “vertical”, “upstream”, “downstream”, “fore”, “aft”, and the like; merely describe the configuration shown in the figures. Indeed, the element or elements of an embodiment of the present invention may be oriented in other directions and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. 
     The present approaches relate to the separation of fluids (e.g., oil and water) in a production or water treatment environment, such as in a downhole hydrocarbon production context. In one such implementation, oil (or other hydrocarbons) and water are separated in a subterranean production environment and the separated oil or oil-rich fluid (e.g., water-free or water-reduced fluid) is lifted to the surface. The remaining water resulting from the separation process is diverted or injected to geologic formations either above or below the producing oil/gas/water zone. Such an approach is more energy efficient than approaches in which both the oil and water are lifted to the surface without meaningful separation. 
     In one implementation of the present approach, in-situ well gas (e.g., air, hydrocarbons, CO 2 , and so forth) or an air stream is used to mechanically generate bubbles (e.g., nanobubbles, microbubbles, or macrobubbles), which are injected into a mixture of produced oil and water that is present in a downhole production zone. In one embodiment, the nanobubbles (defined herein as bubbles having a diameter equal to or less than 500 μm) attach to or aggregate with oil droplets, which effectively results in “lighter” oil relative to the water in the mixture. The nanobubble-oil aggregates rise above (i.e., separates from) the produced water and form an oil-rich zone of entirely or predominantly of oil. An artificial lifting means, such as a pumping mechanism, may then be employed in this oil-rich zone to send oil dominant fluid to a wellhead. Water in the non-oil zone (i.e., the water zone, may then be injected into a receiving formation, such as a subterranean reservoir. 
     Turning to the figures,  FIG. 1  depicts a simplified example of a hydrocarbon production system  12  suitable for use with an oil-water separation system as discussed herein. In the illustrated embodiment, the hydrocarbon production system  12  includes an extraction system in the form of a beam pump  14  suitable for use in the extraction of oil or gas from a subterranean reservoir. In such a beam pump example, production fluid is extracted from a downhole reservoir by repeatedly raising and lowering a series of connecting rods  18  coupling the surface beam pump assembly  14  and the downhole pump equipment (discussed in greater detail below). This repetitive motion causes a piston in the downhole pump mechanism to transport production fluids to the surface. 
     The surface equipment associated with the beam pump  14  includes a rocking beam  22  that moves the connecting rods  18  up and down with respect to a bore and the downhole equipment within the bore. In particular, the downhole equipment is coupled to a first end  24  of the rocking beam  14  while a second, opposite end is connected to a crank assembly  30  that is moved by a motor assembly  34 . The second end  26  of the beam is moved up and down based on the operation of the crank assembly  30 , which in this example includes a rotating counterweight  32 . The beam  22  moves (i.e., rocks) relative to a pivot point in this example, resulting in the first end  24  to move up and down in alternation with the second end  26 . 
     While a beam pump is shown by way of example in  FIG. 1 , it should be appreciated that the present fluid separation approach may be suitable for use in other contexts including, but not limited to, other hydrocarbon production pumping mechanisms, mining and resource gathering contexts where separable fluids may be produced, and wastewater treatment contexts where mixtures of fluids may be present. The present hydrocarbon production discussion including this example of a production site provide a useful context for explaining aspects of the present approach. However, it should be understood that this example and the present discussion are merely intended to simplify and facilitate explanation of the present approach and to provide a useful, real-world context for understanding. Thus, the present separation mechanism may be employed in other suitable mechanisms and technologies (including other pumping technologies, such as PCP&#39;s) and should not be understood as being limited to the present examples. 
     With the preceding in mind, a hydrocarbon production site such as that described in  FIG. 1  may be used with a downhole tool in the form of an integral pump-bubble generator module, which may be used to facilitate pumping an oil-rich fluid (e.g., water-free or water-reduced fluid) to the surface (e.g., the wellhead) and leaving produced water underground. As described below, the bubble generator forms or injects bubbles (e.g., nanobubbles, microbubbles, or macrobubbles) into a mixture of oil and water in the downhole environment. The bubbles attach to oil droplets and result in “lighter” bubble-attached oil aggregates, which more readily separate from the produced water, forming two layered fluids, i.e., oil-rich fluid on top and predominantly water beneath. A suitable artificial lifting means (e.g., an electric submersible pump (ESP), rod pump, progressive cavity pump (PCP), turbine pump, and so forth) may then be employed to transport oil-rich fluid (which in an optimal scenario is entirely or predominantly a desired hydrocarbon production fluid or mixture) to the ground surface for further processing. In one implementation the downhole oil-water separation system includes a downhole bubble generator using in-situ well gas (or other gas), an injection mechanism (i.e., an injector) that puts the nanobubbles into produced oil-water to cause separation of the oil and water, an artificial lifting mechanism (e.g., a suitable downhole pump, such as an ESP or PCP) to pump the separated oil to the surface, a water pump to inject the produced water into a water absorbing formation, which may be below the production zone, and a separation device (e.g., an isolation packer) to isolate the production liquid portion from injected water portion. 
     By way of example, and turning to  FIG. 2  a downhole assembly  50  is depicted that is configured to facilitate the separation of oil and water downhole, to pump separated oil-rich fluid to the surface, and to inject separated water into a disposal formation  54  outside the production formation  52 . This is conceptually shown in  FIG. 2  in which a mix of oil and water flow into the wellbore through openings or perforations within a casing  58  (arrows  60 ) from the production formation  52 . Conversely, water is pumped out (arrows  62 ) of the bore through openings or perforations in the casing  58  into the disposal formation  54 , i.e., the water is injected into the disposal formation. In the depicted example, an isolation packer  70  separates the production zone associated with the inflow from the production formation  52  from the disposal formation  54  so as to prevent separated and disposed from freely comingling with the mixture of fluids in the production zone. 
     As depicted in this example, the region of the well bore above the isolation packer  70  and proximate to the production formation  52  fills with a mix of oil and water. To avoid pumping both oil (or other hydrocarbons) and water to the surface when oil is the primary constituent of interest, the present approach uses bubbles (e.g., nanobubbles, microbubbles, or macrobubbles) to facilitate the separation of bubble-associated oil from the water downhole (i.e., in a separation zone), thereby allowing differential treatment of the separated oil and water. 
     With this in mind, a gas bubbling assembly is provided, either as part of the downhole pumping tool or as a separate, distinct downhole assembly. As discussed herein, the gas bubbling assembly injects or emits gas bubbles into the production fluid of oil and water. The bubbles attach to or otherwise associate with the oil droplets to effectively reduce the density of the combined oil/bubble aggregates, thereby causing the oil to rise in the combined fluid and creating separate layers of oil and water or, short of that, a distinct gradient of oil over water which may be leveraged to recover oil in preference to water, as discussed herein. 
     In the depicted example, the gas bubbling assembly includes a bubble pump  84  that pumps a gas (either unpressurized or under pressure) from the surface to the production formation  52 , gas tubing (i.e., bubble line  86 ) through which the gas (e.g., well gas, compressed or uncompressed atmospheric gas (O 2 , CO 2 , N 2 , ambient surface air, etc.)) is pumped by the bubble pump  84  downhole, and a bubble emitter  88  though which gas bubbles (e.g., nanobubbles) are injected or placed into the produced fluids when the gas passes through the emitter  88 . The gas may be compressed or pressurized at one or more points in the fluid flow path (e.g., at the bubble pump  84  or a down hole compressor) if such compression is employed in the bubble formation processes. In one such example, compressed gas may be released or forced through a nozzle (e.g., a ceramic nozzle or tip) provided as part of the emitter  88  and having a plurality of holes or apertures sized to cause the release of bubbles (e.g., nanobubbles) of the gas into the production fluid mixture. 
     Depending on the implementation, the bubbles (e.g., nanobubbles, microbubbles, or macrobubbles) are introduced into the production fluids either continuously or intermittently. In certain implementations, the bubble generator mechanism produces bubbles of gas sized to generally correspond to or be distributed around the size (e.g., the average or median size) of the oil droplets in the produced fluid. Thus, suitable bubble size may be a function of the weight of the oil present in the production zone. 
     As shown in  FIG. 2 , the emitted bubbles  100  (shown in the inset view) flow upward in the production fluid column, shown by direction flow arrows  102 . The bubbles  100  preferentially associate with oil droplets in the mixture of production fluids, effectively decreasing the density of the oil droplets and moving them upward in the column of mixed production fluids, thus creating the separation of oil and water within the fluid column. Once separated the oil and water form a gradient that is primarily oil-rich fluid on top and primarily water on the bottom. Demarcation of an oil-rich region or zone  80  and a water region or zone  82  within this gradient may be sufficiently sharp that these regions essentially constitute distinct and separate layers or may essentially remain a linear or non-linear gradient with oil concentration increasing as depth within the well bore decreases. Thus a greater concentration of water is found at the bottommost region of the production zone and a greater concentration of oil is found at the uppermost region of the production zone. Regardless of whether a sharp demarcation is present, an oil-rich zone  80  is present in the upper portion of the fluid column and a predominantly water zone  82  is present in the lower portion of the fluid column. Above the oil-rich zone  80 , well gas may rise and be vented to the surface. 
     In accordance with the present approach, oil-rich fluid from a resulting oil-rich fluid zone  80  is pumped to the surface, while fluid in a resulting lower water zone  82  is injected into the subterranean formation  54 , such as a formation beneath the production formation  52  that is separated by the isolation packer  70 . In the depicted example, the down-hole tool assembly is depicted partly spanning the packer  74  to allow injection of water in the disposal formation  54 . 
     The down-hole tool in the depicted example includes one or more pumping assemblies used to move oil to the surface and water to the disposal formation. By way of example, the down-hole tool may be implemented as either a single pump having two separate, distinct, and alternating pumping modes of operation (e.g., lifting mode and an injection mode) or as two pumps, one for pumping the produced oil to the surface and the other for pumping the produced water after separation. 
     In the arrangement shown in  FIG. 2  a skimmer basket  110  is positioned within the oil-rich zone  80 . The skimmer basket  110  in this example is positioned in the fluid column gradient so that oil  112  from the top of the separation gradient spills over the upper edge of the skimmer basket  110  such that the fluid within the basket is primarily oil  112 , with little or no water content. The skimmer basket  110  also facilitates the gas bubbles  100  bypassing the skimmer top edge. In such an implementation, the gas content in the oil  112  is minimized. A pumping mechanism  120  (e.g., an electrical submersible pump (ESP), a progressive cavity pump (PCP), a turbine pump, a rod pump, or any other suitable pump mechanism) is positioned to intake and pump fluid within the skimmer basket  110  to the surface. In this manner, the skimmer basket  110  forms a reservoir of the most oil-rich fluid from the top of the oil-rich gradient, which is then pumped to the surface using the pump  120 . 
     Conversely, at the lower, water-rich portion of the production fluid gradient a water pumping mechanism  126  (e.g., an ESP or other suitable pumping mechanism) is used to inject water  62  into the subterranean formation  54 . In such an implementation, the oil and water pumping mechanisms may be connected to one another (such as by drop pipe  128 ) so they can be lowered into the wellbore as a single or combined tool. 
     One or both of the pumping mechanisms may be controlled or operated so as to provide a flow rate of fluid (such as a flow rate of oil-rich fluid to the surface and/or of water into the water injection formation  54 ) that is based on or otherwise takes into account the separation time for the oil and water in the production zone. In one example a sensing mechanism, such as a multiphase flow meter  130  having a downhole sensor  132 , may generate real-time flow readings that may be used as an input in a control loop or control logic used to control one or more of the pumps and/or the bubble emitter. 
     In a final operational aspect, it may be noted that the bubble generation mechanism may periodically be lowered within the production zone, such as to a level proximate to the packer  70  to purge the solid fines  140  that settle on the packer  70 . For example, water from the pumping mechanism  126  may be used to raise the fines to the pumping mechanism  120  inlet. From there, the fines ma be taken in by the inlet and lifted to the surface with the produced fluids. In one implementation, during this purge cycle, the water injection to the aquafer  54  is shut off. 
     Technical effects of the invention include the use of a bubble-generating mechanism in a production environment to facilitate the separation of a target fluid from a non-target fluid, such as by creating a gradient of the fluids or creating separate and distinct zones of the fluids to be separated. The target fluid can then be preferentially recovered from the production environment based on the gradient or distinct zones. The non-target fluid can be left in the production environment or injected into a nearby formation. In one embodiment, the bubbles generated by the bubble generating mechanism are sized to correspond to, or to be distributed around, an average or median size of the droplets of target fluid present in the production environment. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.