Abstract:
A method of producing hydrocarbon includes introducing the hydrocarbons into a tubular for transport to a surface and introducing a gas into the tubular, wherein the gas is introduced as miniature bubbles for mixing with the hydrocarbon. The method also includes mixing the bubbles with the hydrocarbons, thereby reducing a hydrostatic pressure in the tubular and flowing the hydrocarbons toward the surface. In one embodiment, the gas is introduced at one or more gas lift entry points along the tubular.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the present invention generally relate to artificially lifting fluid from a wellbore. More particularly, embodiments of the present invention relate to artificially lifting fluid from a wellbore using a gas lift system.  
         [0003]     2. Description of the Related Art  
         [0004]     To obtain hydrocarbon fluids from an earth formation, a wellbore is drilled into the earth to intersect an area of interest within a formation. The wellbore may then be “completed” by inserting casing within the wellbore and setting the casing therein using cement. In the alternative, the wellbore may remain uncased (an “open hole wellbore”), or may become only partially cased. Regardless of the form of the wellbore, production tubing is typically run into the wellbore primarily to convey production fluid (e.g., hydrocarbon fluid, which may also include water) from the area of interest within the wellbore to the surface of the wellbore.  
         [0005]     Often, pressure within the wellbore is insufficient to cause the production fluid to naturally rise through the production tubing to the surface of the wellbore. Thus, to carry the production fluid from the area of interest within the wellbore to the surface of the wellbore, artificial lift means is sometimes necessary.  
         [0006]     Some artificially-lifted wells are equipped with sucker rod lifting systems. Sucker rod lifting systems generally include a surface drive mechanism, a sucker rod string, and a downhole positive displacement pump. Fluid is brought to the surface of the wellbore by pumping action of the downhole pump, as dictated by the drive mechanism attached to the rod string.  
         [0007]     One type of sucker rod lifting system is a rotary positive displacement pump, typically termed a progressive cavity pump (“PCP”). The progressive cavity pump lifts production fluid by a rotor disposed within a stator. The rotor rotates relative to the stator by use of a sucker rod string.  
         [0008]     An additional type of sucker rod lifting system is a rod lift system, with which fluid is brought to the surface of the wellbore by reciprocating pumping action of the drive mechanism attached to the rod string. Reciprocating pumping action moves a traveling valve on the positive displacement pump, loading it on the down-stroke of the rod string and lifting fluid to the surface on the up-stroke of the rod string.  
         [0009]     Sucker rod lifting systems include several moving mechanical components. Specifically, the rod strings of sucker rod lifting systems must be reciprocated or rotated to operate the lifting systems. In some applications, the moving parts are disadvantageous. When a subsurface safety valve is employed within the wellbore, such as within an offshore well, a sucker rod string cannot be placed through the subsurface safety valve. Additionally, moving parts are susceptible to failure or damage, potentially causing the sucker rod lifting systems to become inoperable.  
         [0010]     An alternative lift system is a gas lift system. In a typical gas lift system  10  shown in  FIG. 1 , compressed gas G is injected into an annulus  15  between the outer diameter of production tubing  20  and the inner diameter of casing  25  within the wellbore  30 . A valve system  35  supplies injection gas G and allows produced fluid to exit the gas lift system  10 .  
         [0011]     The production tubing  20  typically has gas lift mandrels  40  thereon having gas lift valves  45  therein. The gas lift valves  45  are used to allow or disallow gas flow from the annulus  15  into the production tubing  20 . A production packer  50  located at a lower end of the production tubing  20  forces the flow of production fluid P from a reservoir or zone of interest in a formation  55  up through the production tubing  20  instead of up through the annulus  15 .  
         [0012]     In operation, production fluid P flows from the formation  55  into the wellbore  30  through perforations  60  through the casing  25  and the formation  55 . The production fluid P flows into the production tubing  20 . When it is desired to lift the production fluid P with gas G, compressed gas G is introduced into the annulus  15 . Any of the gas lift valves  45  which are in the open position allow the gas G to flow into the production tubing  20  through an opening in the gas lift mandrel  40  to lift the production fluid P to the surface of the wellbore  30 . The injected gas G lowers the hydrostatic pressure in the production tubing  20  to re-establish the required pressure differential between the reservoir and the wellbore  30 , thereby causing the production fluid P to flow to the surface of the wellbore  30 .  
         [0013]     Gas lift systems are often the preferred artificial lifting systems because fewer moving parts exist during the operation of the gas lift systems than during the operation of sucker rod lift systems. Moreover, gas lift systems are sometimes preferred over sucker rod lift systems because no sucker rod is required in the operation of gas lift systems. Because a sucker rod is not used in operating the gas lift system, the gas lift system is usable in offshore wells having subsurface safety valves.  
         [0014]     Although gas lift systems are advantageous in most applications, wells which contain heavier production fluid P (such as heavier oil) are often not effectively served using typical gas lift systems. When heaver oil is present in the well, the gas G tends to channel up the inner diameter of the production tubing  20 . The channeling of the gas G causes a stratified flow of fluid up the production tubing  20 , as the heavier oil sticks against the wall of the production tubing  20  and the gas G flows rapidly up the center portion of the production tubing  20  through the stuck oil.  
         [0015]     Because of these difficulties with using a gas lift system  10  to lift heavier oil up the production tubing  20  for production, gas lift systems are often not utilized when a well contains heavier production fluid P. Therefore, historically, sucker rod lifting systems commonly are resorted to, despite the problems inherent with these sucker rod systems described above, when it is desired to lift heavier production fluid P from a well.  
         [0016]     Therefore, it would be advantageous to provide a gas lift system capable of effectively lifting heavier production fluid from a well. It would be further beneficial to provide a gas lift system capable of lifting production fluid from a well without a stratified flow of gas and production fluid ensuing, regardless of the weight of the production fluid.  
       SUMMARY OF THE INVENTION  
       [0017]     Embodiments of the present invention provide methods of producing hydrocarbon. In one embodiment, the method includes introducing the hydrocarbons into a tubular for transport to a surface and introducing a gas into the tubular, wherein the gas is introduced as miniature bubbles for mixing with the hydrocarbon. The method also includes mixing the bubbles with the hydrocarbons, thereby reducing a hydrostatic pressure in the tubular and flowing the hydrocarbons toward the surface. In another embodiment, the gas is introduced at one or more gas lift entry points along the tubular.  
         [0018]     In another embodiment, the gas is introduced to the tubular using a mixing device. Preferably, the mixing device is adapted to form the miniature bubbles.  
         [0019]     In yet another embodiment, the gas comprises one or more additives for creating smaller or miniaturized bubbles.  
         [0020]     In yet another embodiment, the gas comprises one or more additives for emulsifying the gas and the hydrocarbon.  
         [0021]     In another embodiment, a method of producing hydrocarbon comprises flowing hydrocarbon through a tubular for transport to a surface; introducing gas into the tubular; and generating small bubbles for mixing with the hydrocarbon. The method also includes increasing a pressure differential between an exterior of the tubular and the interior of the tubular and moving the hydrocarbon toward the surface.  
         [0022]     In yet another embodiment, the method also includes increasing a concentration of the gas adjacent a wall of the tubular.  
         [0023]     In yet another embodiment, the gas is introduced using a device selected from the group consisting of venturi nozzle and a vortex nozzle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0025]      FIG. 1  shows a typical gas lifting system.  
         [0026]      FIG. 2  shows an embodiment of a gas lift system of the present invention.  
         [0027]      FIG. 3  is a sectional view of the gas lift system of  FIG. 2 .  
         [0028]      FIG. 3A  is a cross-sectional view of the mixing device of the gas lift system of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0029]     Embodiments of the present invention include methods and apparatuses for lifting production fluid using a gas lift system. Embodiments of the present invention are capable of lifting the production fluid by preventing the stratification of the gas and the production fluid while flowing up through production tubing. In particular, embodiments of the present invention are especially useful to lift heavier oil production fluid without stratification of the flow.  
         [0030]      FIG. 2  shows a first embodiment of a gas lift system  110  for artificially lifting production fluid P using a compressed gas G. The compressed gas G is injected into an annulus  115  between the outer diameter of production tubing  120  and the inner diameter of casing  125  (or the inner diameter of the wellbore  130 , in the case of an open hole wellbore) by a valve system  135  disposed at a surface of the wellbore  130 . The valve system  135  includes a gas injection inlet  114  regulated by a valve  117  which controls gas G flow into the annulus  115 . Also included in the valve system  135  is a production fluid outlet  113  through which production fluid P exits the gas lift system  110 , regulated by a valve  116  which controls production fluid P flow exiting the gas lift system  110 . Either or both of the valves  116  and  117  may include an in-line orifice choke, which is a calibrated, adjustable choke for regulating injection gas or production fluid flow. In the alternative, either or both of the valves  116 ,  117  may include pneumatic motor valves. A pressure gauge  112  may be included with the valve system  135  to indicate the pressure within the gas lift system  110 .  
         [0031]     Extending below the valve system  135  is a wellbore  130  formed in an earth formation  155  by a drilling device such as a drill bit. The wellbore  130  shown in  FIG. 2  is a cased wellbore, as casing  125  is located within the wellbore  130  and set by cement  184 . One or more perforations  160  extend through the casing  125 , cement  184 , and wellbore  130  to allow production fluid P to flow from the formation  155  into the wellbore  130 . Although a cased wellbore is shown in  FIG. 2 , it is contemplated that the wellbore may be an open hole wellbore.  
         [0032]     Production tubing  120  is disposed within the inner diameter of the casing  125 . One or more sealing elements  150 , preferably production packers, are disposed at a portion of the production tubing  120  to seal the annulus  115  so that production fluid P flows from the wellbore  130  up into the inner diameter of the production tubing  120 , rather than flowing up through the annulus  115 .  
         [0033]     In one aspect, one or more mixing devices  180  are disposed at one or more locations of the production tubing  120 . The mixing devices  180  are adapted to cause the compressed gas G and the production fluid P to form a mixture M. In one embodiment, the mixing device  180  is adapted to introduce small or “miniaturized” bubbles into the production tubing  120  to mix with the production fluid P. It is believed that these miniature bubbles provide several advantages for increasing the efficiency of the gas lift system  110 . For example, because smaller bubbles have a larger surface area to volume ratio, smaller bubbles offer more surface area for contacting the production fluid. Another advantage is that smaller bubbles require a longer time period to coalesce into larger bubbles, thus allowing more bubbles to mix with the production fluid. It is also believed that smaller bubbles tend to accumulate near the wall of the tubing  120  while larger bubbles migrate toward the center. Therefore, the smaller bubbles are more adapted to mix with the production fluid near the wall, thereby preventing the stratified flow of gas and production fluid. It must be noted that realization of one or more of these advantages are not prerequisites for the operation of various embodiments of the present invention, and therefore do not limit embodiments of the present invention.  
         [0034]      FIG. 3  shows an exemplary mixing device  180  suitable for supplying small bubbles to the production tubing  120  to provide a better gas and production fluid mixture. As shown, the mixing devices  180  may be housed within one or more side pocket mandrels  122 . The mixing device  180  is preferably generally concentric around the production tubing  120 . Each mixing device  180  includes a gas inlet passage  181  therethrough to allow the gas G to enter from the annulus  115  into the mixing device  180 . A one way valve  183  or check valve may be used to prevent production fluid P from flowing into the annulus  115 . Additionally, the production tubing  120  has a gas inlet passage  182  therethrough to allow the gas to enter the production tubing  120  and mix with the production fluid P within the production tubing  120 . In one embodiment, the mixing device  180  comprises a nozzle  186  adapted to form the small bubbles in the production tubing  120 .  FIG. 3A  is a cross-sectional view of the mixing device  180 . Although four nozzles  186  are shown arranged around the tubing  120 , one or more nozzles  186  may be used. Suitable mixing devices include a venturi nozzle, a vortex venturi, or any other mixing devices capable of creating small bubbles into the production tubing. In another aspect, the mixing device  186  may inject the gas into the production tubing  120  with sufficient velocity or energy such that a turbulent flow is created in the adjacent areas. The turbulent flow acts like an agitator to bring more gas into contact with the oil, thereby increasing gas saturation. In this respect, the turbulent flow, alone or in combination with the smaller bubbles, promotes the formation of a more homogeneous gas and oil mixture. In yet another embodiment, the gas may be injected with sufficient energy to form an emulsion with the oil. As a result, more oil will be lifted toward the surface.  
         [0035]     In operation, referring to both  FIGS. 1 and 2 , compressed gas G is injected through the gas injection inlet  114  into the annulus  115  by manipulating the valve  117  into the open position. The valve system  135  may be controlled electronically or optically by a surface monitoring and control unit (not shown) to control and monitor the amount of gas G supplied into the annulus  115  and the amount of gas needed to lift the production fluid P. The surface monitoring and control unit may operate at the well site or by remote telemetry and may be used to control an individual well or multiple gas lift wells.  
         [0036]     The compressed gas G may be natural gas obtained from the well into which it is injected or from another well, and may be obtained as high pressure natural gas from the well or from a compression source. Other suitable gases such as nitrogen, carbon dioxide, and other compressed gases known to a person of ordinary skill in the art may be used to lighten the oil. The compressed gas G enters the mixing device  180  through the one way valve  183 . In turn, the mixing device  180  injects the gas into the production fluid such that small bubbles are formed to increase mixing of the gas and the production fluid. In this respect, the increased saturation of the gas in the production fluid will resist the stratification of the production fluid flow, thereby causing more production fluid to be lifted toward the surface. In some instances, additional mixing devices may be disposed at one or more gas lift entry points along the production tubing  120  to optimally lift the production fluids to the surface.  
         [0037]     In another embodiment, additives may be employed to facilitate the formation of small bubbles. The additives may also promote a better mixing of the gas and the production fluid. For example, additives such as surfactants may be added to the gas at the surface. Exemplary additives such as sulfur trioxide or sulfonates may be added to the gas to help wet the gas for mixing. It is contemplated any additive suitable for causing the gas to form smaller bubbles as is known to a person of ordinary skill in the art may be used. When the additives are injected into the tubing  120  along with the gas, the additives may cause emulsification of the gas with the oil, thereby preventing the oil from separating from the gas and sticking to the walls of the tubing. In some cases, the emulsion generated from the gas bubbles dispersed in the oil creates a foam. It must be noted that the additives may be utilized separately from or in combination with mechanically generated small bubbles to increase the efficiency of the gas lift system. Also, the additives may be added in the gaseous phase, liquid phase, or combinations thereof.  
         [0038]     Additives may also include emulsifiers that may be classified as amido-esters or esterified amides. Exemplary emulsifiers include oxidized mixtures of vegetable oils, saponified tall oils, crude tall oil oils, distilled tall oil oils, and polyacids thermally produced from the vegetable oils or tall oil fatty acids of linolenic or linoleic acids. They may also be non-oxidized. Further, the additives may be modified. Exemplary modified additives include acrylic adducts or maleic adducts and the like. They may be combinations of the above. The additives may further include mixed amido-esters and distilled talls.  
         [0039]     Other examples of additives include fumaric acid, maleic anhydride modified bis amides or polyamides, the fumaric or maleic adducts of imidazolines, and combinations thereof.  
         [0040]     Other suitable additives are disclosed in U.S. Pat. No. 6,194,361; U.S. Pat. No. 6,489,272; and U.S. patent application Publication No. 2003/0092580, which patents and/or application have been assigned to the assignee of the present application and are herein incorporated by reference in their entirety.  
         [0041]     In one embodiment, the additive is formed by the sequential reaction and subsequent distillation of a tall oil fatty acid having a moderately low rosin content with a fatty alkanolamide, preferably in the presence of methyl ester of fatty acids, and most preferably when further reacted with an emulsifier such as coconut oil diethanolamide or an amide of aminoethylpiperazine (AEP) under distillation conditions facilitating the removal of water and lighter reaction byproducts.  
         [0042]     Fatty acids suitable for use in the compositions of the additive include, for example, disproportionated tall oil fatty acids; distilled tall oil; disproportionated tall oil; resin acids and rosin acids; rosin tall oil; and combinations thereof. Tall oil fatty acids having from  8  to  24  carbon atoms are preferred, with tall oil fatty acids having C 12 , C 14 , C 16 , C 18 , and C 20  fatty acids being most preferred.  
         [0043]     Amide/esters that are suitable for use in the compositions of the additive include, for example, N,N-bis (hydroxyethyl) tall oil fatty amides; reaction products of rosin with diethanolamine; and reaction products of tall oil fatty acids with diethanolamine. The preferred amides for use are most preferably made using diethanolamine (DEA), monoethanolamine (MEA), and other hydroxyethylamines that can undergo low temperature esterification and then interchange during the distillation.  
         [0044]     Amides suitable for use as additives include the reaction product of vegetable oil and an alkanolamine, the reaction product of vegetable oil with a polyethylene amine, the reaction product fo distilled tall oil with AEP, and the reaction product of distilled tall oil with a polyethylene amine, for example, N,N-bis (hydroxyethyl) saturated and unsaturated C 8-18  and C 18  amides; reaction products of coconut oil with diethanolamine; and reaction products of these substituents with AEP and other polyethylene amine homologues.  
         [0045]     Methyl esters suitable for use in the compositions of the additive include, for example, methyl esters of C 16-18  saturated and C 18  unsaturated fatty acids, and methyl esters of tall oil fatty acids.  
         [0046]     In another embodiment, the additive comprises from about 45 to about 90 weight percent of the reaction product of tall oil fatty acid and a fatty alkanolamide, reacted in the presence of from about 5 to about 25 weight percent methyl ester of fatty acids, then further reacted and distilled in the presence of from about 5 to about 30 weight percent of the reaction product of a fatty oil with an alkanolamine. The combined weight of the fatty acid and amide/ester components preferably ranges from about 55 to about 90 weight percent of the total reactants, and the ratio of fatty acid to amide/ester desirably ranges from about 2:1 to about 3:2. Where the fatty alkanolamide is the reaction product of distilled tall oil and diethanolamine, the distilled tall oil and diethanolamine are preferably reacted in a ratio of about 3:1 by weight. According to a preferred embodiment of the invention, from about 5 to about 25 weight percent of methyl ester of fatty acids is also added to the initial reactants.  
         [0047]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.