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FIELD 
       [0001]    The present disclosure relates to production of formation fluids, and, in particular, separating gaseous material that is entrained within the formation fluids. 
       BACKGROUND 
       [0002]    Gas lock is a problem encountered while producing wells, especially wells with horizontal portions. Packer-type gas anchors are provided to remedy gas lock. However, packer-type gas anchors are relatively expensive. Further, the packers on packer-type gas anchors are susceptible to having debris accumulate thereon and, as a result, becoming stuck within the wellbore tubular against which it forms a seal. This makes it difficult to remove production tubing from the wellbore, such as during a workover. Such attempt at removal may also damage the packer, thereby rendering the packer-type gas anchor unusable for future production. 
       SUMMARY 
       [0003]    In one aspect there is provided a system for effecting production of formation fluid from a subterranean formation, comprising: 
         [0000]    a wellbore tubular disposed within a wellbore, wherein the wellbore tubular includes a receptacle portion, wherein the receptacle portion includes a receptacle sealing surface;
 
a production tubular, disposed within the wellbore tubular, including:
 
         [0004]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing member-engaging surface portion; 
         [0005]    a gas separator portion configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid; 
         [0006]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and 
         [0007]    a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    and
 
a sealing member disposed between the sealing member-engaging surface portion and the receptacle sealing surface for effecting a seal between at least the sealing member-engaging surface portion and the receptacle sealing surface, for preventing, or substantially preventing, flow of the formation fluid between at least the sealing member-engaging external surface portion and the receptacle sealing surface;
 
wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the effected seal between at least the sealing member-engaging surface portion of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus;
 
and wherein the receptacle sealing surface is disposed less than a distance “D” of 2.5 millimetres from the sealing member-engaging surface portion.
 
         [0008]    In another aspect there is provided a system for effecting production of formation fluids from a subterranean formation, comprising: 
         [0000]    a wellbore tubular disposed within a wellbore, wherein the wellbore tubular includes: 
         [0009]    a casing string; 
         [0010]    a liner string, coupled to the casing string, the liner string including:
       a polished bore receptacle that includes a receptacle portion, wherein the receptacle portion includes a receptacle sealing surface; and   a sealing surface, sealingly engaged to the casing string for preventing, or substantially preventing, flow of formation fluid between the sealing surface and the casing string; and
 
a production tubular, disposed within the wellbore tubular, including:
       
 
         [0013]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing surface disposed in sealing engagement with the receptacle sealing surface for preventing, or substantially preventing, flow of the formation fluids between the sealing surface and the receptacle sealing surface; 
         [0014]    a gas separator portion configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid; 
         [0015]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and 
         [0016]    a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by at least the sealing engagement between the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus. 
         [0017]    In another aspect there is provided a system for effecting production of formation fluids from a subterranean formation, comprising: 
         [0000]    a wellbore tubular disposed within a wellbore, wherein the wellbore tubular includes a casing, wherein the casing includes a receptacle portion, wherein the receptacle portion is defined by an inwardly extending protrusion of the casing and includes a receptacle sealing surface; and
 
a production tubular, disposed within the wellbore tubular, including:
 
         [0018]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing surface disposed in sealing engagement with the receptacle sealing surface for preventing, or substantially preventing, flow of the formation fluids between the sealing surface and the receptacle sealing surface; 
         [0019]    a gas separator portion configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid; 
         [0020]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by at least the sealing engagement between the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus. 
         [0021]    In another aspect there is provided a process for effecting production of formation fluids from a subterranean formation, comprising: 
         [0000]    positioning a wellbore tubular within a wellbore, wherein the wellbore tubular includes a receptacle portion, wherein the receptacle portion includes a receptacle sealing surface;
 
providing a production tubular, wherein the production tubular includes:
 
         [0022]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing member-engaging surface portion; 
         [0023]    a gas separator portion; 
         [0024]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and 
         [0025]    a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    and
 
a sealing member disposable between the sealing member-engaging surface portion and the receptacle sealing surface for effecting a seal between at least the sealing member-engaging surface portion and the receptacle sealing surface, for preventing, or substantially preventing, flow of the formation fluid between at least the sealing member-engaging surface portion and the receptacle sealing surface;
 
wherein, while the production tubular is positioned within the wellbore tubular such that the seal between at least the sealing member-engaging surface portion and the receptacle sealing surface is being effected, the gas separator portion is configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid;
 
and wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the effected seal between at least the sealing member-engaging surface portion of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus, and the receptacle sealing surface is disposed less than a distance “D” of 2.5 millimetres from the sealing member-engaging surface portion.
 
positioning the production tubular within the wellbore tubular such that the seal between at least the sealing member-engaging surface portion and the receptacle sealing surface is being effected;
 
inducing flow of the formation fluid, from a treated subterranean formation to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the prime mover;
 
directing flow of the received formation fluid through the gas separator annulus, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the co-operating of the gas separator with the wellbore tubular;
 
preventing, or substantially preventing, the received formation fluid, that is flowing through the gas separator annulus, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the seal effected between at least the seal member-engaging sealing surface portion of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular;
 
while the flow of the received formation fluid is being directed through the gas separator annulus, effecting separation, in response to buoyancy forces, of at least a fraction of gaseous material entrained within the formation fluid flow being flowed through the gas separator annulus to generate a gaseous material-depleted formation fluid flow;
 
energizing the gaseous material-depleted formation fluid flow with the prime mover for flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular; and
 
conducting the energized gaseous material-depleted formation fluid flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular.
 
         [0026]    In another aspect there is provided a process for effecting production of formation fluids from a subterranean formation, comprising: 
         [0000]    positioning a wellbore tubular within a wellbore, wherein the wellbore tubular includes: 
         [0027]    a casing string; 
         [0028]    a liner string, coupled to the casing string, the liner string including:
       a polished bore receptacle that includes a receptacle portion, wherein the receptacle portion includes a receptacle sealing surface; and   a sealing surface, sealingly engaged to the casing string for preventing, or substantially preventing, flow of formation fluid between the sealing surface and the casing string;
 
providing a production tubular, wherein the production tubular includes:
       
 
         [0031]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing surface disposable for sealing engagement with the receptacle sealing surface for preventing, or substantially preventing, flow of the formation fluids between the sealing surface and the receptacle sealing surface; 
         [0032]    a gas separator portion; 
         [0033]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and 
         [0034]    a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    wherein, while the production tubular is positioned within the wellbore tubular such that the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion and the receptacle sealing surface of the receptacle portion is being effected, the gas separator portion is configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid;
 
and wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus;
 
positioning the production tubular within the wellbore tubular such that the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular is being effected;
 
inducing flow of the formation fluid, from a treated subterranean formation to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the prime mover;
 
directing flow of the received formation fluid through the gas separator annulus, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the co-operating of the gas separator with the wellbore tubular;
 
preventing, or substantially preventing, the received formation fluid, that is flowing through the gas separator annulus, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle portion of the wellbore tubular;
 
while the flow of the received formation fluid is being directed through the gas separator annulus, effecting separation, in response to buoyancy forces, of at least a fraction of gaseous material entrained within the formation fluid flow being flowed through the gas separator annulus to generate a gaseous material-depleted formation fluid flow;
 
energizing the gaseous material-depleted formation fluid flow with the prime mover for flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular; and
 
conducting the energized gaseous material-depleted formation fluid flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular.
 
         [0035]    In another aspect there is provided a process for effecting production of formation fluids from a subterranean formation, comprising: 
         [0000]    positioning a wellbore tubular within a wellbore, wherein the wellbore tubular includes a casing, wherein the casing includes a receptacle portion, wherein the receptacle portion is defined by an inwardly extending protrusion of the casing and includes a receptacle sealing surface;
 
providing a production tubular, wherein the production tubular includes:
 
         [0036]    a formation fluid-receiving conduit portion, defining a formation fluid-receiving fluid passage portion for receiving the formation fluid, and including a sealing surface disposable for sealing engagement with the receptacle sealing surface for preventing, or substantially preventing, flow of the formation fluids between the sealing surface and the receptacle sealing surface; 
         [0037]    a gas separator portion; 
         [0038]    a gaseous material-depleted fluid formation conduit defining a gaseous material-depleted formation fluid conducting-fluid passage portion for conducting a flow of the gaseous material-depleted formation fluid to the surface; and 
         [0039]    a prime mover disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion, and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion to the surface; 
         [0000]    wherein, while the production tubular is positioned within the wellbore tubular such that the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion and the receptacle sealing surface of the receptacle portion is being effected, the gas separator portion is configured to co-operate with at least the wellbore tubular for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid;
 
and wherein the co-operation between the gas separator portion and at least the wellbore tubular is with effect that, while the flow of the formation fluid is being induced by the prime mover and received through the formation fluid-receiving fluid passage portion, flowing of the received formation fluid is directed through a gas separator annulus disposed between the gas separator portion and the wellbore tubular, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, prior to being received by the prime mover, and the formation fluid flowing through the gas separator annulus is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular, wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus, the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus;
 
positioning the production tubular within the wellbore tubular such that the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle sealing surface of the receptacle portion of the wellbore tubular is being effected;
 
inducing flow of the formation fluid, from a treated subterranean formation to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the prime mover;
 
directing flow of the received formation fluid through the gas separator annulus, in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular, by the co-operating of the gas separator with the wellbore tubular;
 
preventing, or substantially preventing, the received formation fluid, that is flowing through the gas separator annulus, from returning to the formation fluid-receiving fluid passage portion of the formation fluid-receiving conduit portion of the production tubular by the sealing engagement between at least the sealing surface of the formation fluid-receiving conduit portion of the production tubular and the receptacle portion of the wellbore tubular;
 
while the flow of the received formation fluid is being directed through the gas separator annulus, effecting separation, in response to buoyancy forces, of at least a fraction of gaseous material entrained within the formation fluid flow being flowed through the gas separator annulus to generate a gaseous material-depleted formation fluid flow;
 
energizing the gaseous material-depleted formation fluid flow with the prime mover for flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular; and
 
conducting the energized gaseous material-depleted formation fluid flow to the surface through the gaseous material-depleted fluid formation conduit of the production tubular.
 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0040]    The preferred embodiments will now be described with the following accompanying drawings, in which: 
           [0041]      FIG. 1  is a schematic illustration of an embodiment of the present disclosure, illustrating fluid flowpath through the gas separator; 
           [0042]      FIG. 2  is a schematic illustration of an enlarged portion of the embodiment illustrated in  FIG. 1 , in the region of the gas separator; 
           [0043]      FIG. 2A  is a schematic illustration of a further enlarged portion of the embodiment illustrated in  FIG. 1 , in the region of the gas separator, and specifically illustrating the relative spatial disposition between a receptacle sealing surface of the wellbore tubular and the sealing member-engaging surface portion of the production tubular; 
           [0044]      FIG. 3  is a schematic illustration of another embodiment of the present disclosure, also illustrating fluid flowpath through the gas separator; and 
           [0045]      FIG. 4  is a schematic illustration of an enlarged portion of the embodiment illustrated in  FIG. 1 , in the region of the gas separator. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    The term “upwardly” means, in a spatial context, from a lower position to an upper position. The lower and upper positions do not necessarily need to be in perfect vertical alignment, but this possibility is not excluded. 
         [0047]    The term “downardly” means, in a spatial context, from an upper position to a lower position. The upper and lower position do not necessarily need to be in perfect vertical alignment, but this possibility is not excluded. 
         [0048]    The term “tubular” refers to any generally tubular conduit (not necessarily cylindrical in cross-section) for transporting fluid, into or from a subterranean formation. A “tubular”, as deployed in a wellbore, may be formed from individual, discrete lengths of generally tubular conduit that are joined together to form, for example a tubing string, drill string, casing string, or liner. In this respect, a tubular may be a tubing string, drill string, casing string, or liner. Any of these structures are positioned within a wellbore and utilized, at least in part, to transport fluids. The tubular may have a bore of a generally uniform diameter throughout the length thereof or may have two or more sections having bores of different diameters. In some embodiments, for example, one or more downhole tools may be secured to the tubular. 
         [0049]    “Formation fluid” is fluid that is contained within a subterranean formation. Formation fluid may be liquid material, gaseous material, or a mixture of liquid material and gaseous material. In some embodiments, for example, the formation fluid includes hydrocarbonaceous material, such as oil, natural gas, or combinations thereof. 
         [0050]    Referring to  FIGS. 1 to 4 , there is provided a system  10  for effecting production of formation fluids from a subterranean formation  50 . The system includes a wellbore tubular  20  and a production tubular  30 . The wellbore tubular  20  and the production tubular  30  extend from a wellhead  15  that is supported on the ground surface  16 . 
         [0051]    The wellbore tubular  20  is disposed or positioned within a wellbore  40 . The wellbore tubular  20  includes a receptacle portion  22 . The receptacle portion  22  includes a receptacle sealing surface  21 . 
         [0052]    The wellbore  40  can be straight, curved, or branched. The wellbore can have various wellbore portions. A wellbore portion is an axial length of a wellbore. A wellbore portion can be characterized as “vertical” or “horizontal” even though the actual axial orientation can vary from true vertical or true horizontal, and even though the axial path can tend to “corkscrew” or otherwise vary. The term “horizontal”, when used to describe a wellbore portion, refers to a horizontal or highly deviated wellbore portion as understood in the art, such as, for example, a wellbore portion having a longitudinal axis that is between 70 and 110 degrees from vertical. 
         [0053]    In some embodiments, for example, the wellbore tubular  20  includes a casing. The casing isolates certain zones of the subterranean formation  50  from the formation fluid being produced from another zone of the subterranean formation. In some embodiments, for example, the casing stabilizes the subterranean formation during drilling of the wellbore, as well as after the wellbore has been completed, by preventing the collapse of the subterranean formation that is defining the wellbore. 
         [0054]    In some embodiments, for example, the casing  20  includes one or more casing strings, each of which is positioned within the well bore, having one end extending from the well head, either surface or subsea. The casing strings may be cemented to the wellbore. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the subterranean formation behind the casing for the production of formation fluids. In some embodiments, for example and referring to  FIG. 1 , the casing, including one or more casing strings, is connected at its other end to a liner string  26 . The liner string extends only a short distance above the lower end of the previously installed casing string and is suspended within the wellbore by a liner hanger connected to the previously installed casing string. The liner string can be made from the same material as the casing string, but, unlike the casing string, the liner string does not extend back to the wellhead. The liner string may be cemented to the wellbore, or remain uncemented. 
         [0055]    In some embodiments, for example and referring to  FIGS. 3 and 4 , the casing may include one or more expandable liner strings. During assembly of the casing, and after being disposed in the wellbore, the expandable liner string is expanded diametrically into frictional engagement with the previous string of casing or liner (which could also have been expanded diametrically into frictional engagement with a further previous string of casing or liner). The expanded string may be cemented to the wellbore, or remain uncemented. The assembly of the casing, using such expandable liner strings, effects production of at least a casing section generally described as a “monobore” casing or casing section. 
         [0056]    In some embodiments, for example, the production tubular may be a tubular string that includes several “joints” (a “joint” is a length of pipe) or other tubular members assembled to create the string. 
         [0057]    The production tubular  30  is disposed within the wellbore tubular  20 . The production tubular includes a formation fluid-receiving conduit portion  32 , a gas separator portion  38 , a gaseous material-depleted fluid formation conduit portion  34 , and a prime mover  36 . 
         [0058]    The formation fluid-receiving conduit portion  32  includes a formation fluid-receiving fluid passage-defining surface  323  that defines a formation fluid-receiving fluid passage portion  3231  for receiving the formation fluid. 
         [0059]    In one aspect, the formation fluid-receiving conduit portion includes a sealing surface  321  disposed in sealing engagement with the receptacle sealing surface  21  for preventing, or substantially preventing, flow of the formation fluids between the sealing surface  321  and the receptacle sealing surface  21 . The sealing engagement effects a seal between the sealing surface  321  and the receptacle sealing surface  21 . In some embodiments, for example, one of the sealing surfaces  21  or  321  is defined by a sealing member  400  that is disposed between the formation fluid-receiving conduit portion  32  and the receptacle portion  22  for effecting the seal between the formation fluid-receiving conduit portion  32  and the receptacle portion  22 . 
         [0060]    In some embodiments, for example, the sealing member  400  includes resilient material, such as elastomeric material. In some embodiments, for example, the sealing member  400  includes deformable metallic materials. 
         [0061]    The gas separator portion  38  is configured to co-operate with at least the wellbore tubular  20  for effecting separation of at least a fraction of gaseous material, that is entrained within the received formation fluid, from the received formation fluid to generate a gaseous material-depleted formation fluid. 
         [0062]    The gaseous material-depleted fluid formation conduit portion  34  defines a gaseous material-depleted formation fluid conducting-fluid passage portion  341  for conducting a flow of the gaseous material-depleted formation fluid to the surface. 
         [0063]    The prime mover  36  is disposed for inducing flow of the formation fluid from a subterranean formation and into the formation fluid-receiving fluid passage portion  3231 , and for receiving and energizing the gaseous material-depleted formation fluid to flow through the gaseous material-depleted formation fluid conducting-fluid passage portion  341  to the surface. In some embodiments, for example, the prime mover  36  is a fluid propeller. In some of these embodiments, for example, the prime mover is a pump, such as a downhole pump. In some embodiments, for example, the pump is a rod pump, such as a sucker rod pump. 
         [0064]    The co-operation between the gas separator portion  38  and at least the wellbore tubular  20  is with effect that, while the flow of the formation fluid is being induced by the prime mover  36  and received through the formation fluid-receiving fluid passage portion  3231 , flowing of the received formation fluid is directed through a gas separator annulus  381  disposed between the gas separator portion  38  and the wellbore tubular  20 , in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion  3231  of the formation fluid-receiving conduit portion  32  of the production tubular  30 , prior to being received by the prime mover  36 , and the formation fluid flowing through the gas separator annulus  381  is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion  3231  of the formation fluid-receiving conduit portion  32  of the production tubular  30  by at least the seal formed (as above-described) between the formation fluid-receiving conduit portion  32  of the production tubular  30  and the receptacle portion  22  of the wellbore tubular  20 , wherein, while the flowing of the received formation fluid is being directed through the gas separator annulus  381 , the at least a fraction of the entrained gaseous material becomes separated, in response to buoyancy forces, from the received formation fluid that is being directed through the gas separator annulus  381 . 
         [0065]    Referring to  FIG. 2A , in another aspect, the formation fluid-receiving conduit portion  32  includes a sealing member-engaging surface portion  325 , and a sealing member  400  is disposed between a sealing member-engaging surface portion  325  of the formation fluid-receiving conduit portion  32  and the receptacle sealing surface  21  for effecting the seal between at least the sealing member-engaging surface portion  325  and the receptacle sealing surface  21 , for preventing, or substantially preventing, flow of the formation fluid between at least the sealing member-engaging surface portion  325  and the receptacle sealing surface  21 . In some of these embodiments, for example, the sealing member  400  is coupled to, or carried, by the formation fluid-receiving conduit portion  32 . The receptacle sealing surface  21  is disposed less than a distance “D” of 2.5 millimetres from the sealing member-engaging surface portion  325 . In some embodiments, for example, the distance “D” is one (1) millimetre, such that the receptacle sealing surface  21  is disposed less than one (1) millimetre from the sealing member-engaging surface portion  325 . This distance “D” is selected so as to minimize debris accumulation but still permit the in installation of the sealing member  400 . 
         [0066]    By effecting separation of at least a fraction of gaseous material, that is entrained within the received flow of formation fluid, from the received formation fluid, the gas lock phenomena is at least partially mitigated by the co-operation of the gas separator  38  and the wellbore tubular  20 . Unlike existing packer-type gas anchors, by co-operatively configuring the wellbore tubular  20  and the production tubular  30  such that the provided spacing between the receptacle sealing surface  21 , of the wellbore tubular  20 , and the sealing member-engaging surface portion  325 , of the production tubular  30 , is below a predetermined distance (as defined above), the amount of space to be dedicated for effecting the sealing engagement between the receptacle sealing surface  21  and the sealing member-engaging surface portion  325  can be minimized such that conventional packers are not required to be used associated with the gas separator portion  38  to effect the necessary sealing for preventing, or substantially preventing flow between the tubulars  20 ,  30  in order for the removal of the entrained gases to be effected. Because this is the case, the problem of debris accumulation on the packer, which would otherwise make it more difficult to remove the production tubular  30 , from the wellbore tubular  20 , owing to the fact that such accumulated debris may cause the packer associated with a gas separator, disposed on the production tubular  30 , to be stuck against the wellbore tubular  20 , is eliminated or mitigated, at least as it relates to its relevance to removability of the production tubular  30  from the wellbore, such as during workovers. 
         [0067]    In some embodiments, for example, the production tubular  30  is releasably secured to the wellbore tubular  20 . In some of these embodiments, for example, the production tubular is disposed in an interference fit relationship (such as a press-fit relationship) with the wellbore tubular  20 . In some of these embodiments, for example, the interference fit relationship is effected between the sealing surface  321  of the formation fluid-receiving conduit portion  32  of the production tubular  30  and the receptacle sealing surface  21  of the receptacle portion  22  of the wellbore tubular  20 . 
         [0068]    Referring to  FIGS. 1 and 2 , in some embodiments, for example, the wellbore tubular  20  includes a casing  2 , and the casing includes a casing string  201  and a liner string  26 . In some embodiments, for example, the liner string  26  is hung from the casing string  201 . The liner string  26  includes a polished bore receptacle  261  and an external sealing surface  262 . The polished bore receptacle  261  includes the receptacle portion  22 . The external sealing surface  262  is sealingly engaged to the casing string  201  for preventing, or substantially preventing, flow of formation fluid between the external sealing surface  262  and the casing string  201 . In some embodiments, for example, the sealing engagement between the surface  262  and the casing string  201  is effected by a packer  24  mounted to the casing string  201 . The production tubular  30  is disposed within the polished bore receptacle  261 , and urging of the sealing engagement between the sealing surface  321  of the production tubular  30  and the receptacle sealing surface  21  of the receptacle portion  22  of the polished bore receptacle  261  is effected with a seal latch assembly that releasably secures the production tubular  30  to the polished bore receptacle  261 . In some embodiments, for example, the production tubular  30  is releasably coupled or releasably secured to the polished bore receptacle  261 . In some of these embodiments, for example, the releasable coupling (or the releasable securement) is effected by way of an interference fit engagement (such as a press-fit engagement) between the production tubular  30  and the receptacle portion  22  of the polished bore receptacle  261 . 
         [0069]    Referring to  FIGS. 3 and 4 , in some embodiments, for example, the wellbore tubular  20  includes a casing  2 , and the receptacle portion  22  extends inwardly from the casing  2 . In some embodiments, for example, the receptacle portion  22  defines a constricted portion  221  of the casing  2 . In some embodiments, for example, the production tubular  30  is releasably coupled or releasably secured to the receptacle portion  22 . In some of these embodiments, for example, the releasable coupling (or the releasable securement) is effected by way of an interference fit engagement (such as a press-fit engagement) between the production tubular  30  and the receptacle portion  22 . In this respect, the extending inward receptacle portion  22  is permanently affixed to the casing  2 , thus any accumulation of debris will not prevent removal of the production tubular  30  and the sealing member-engaging surface portion  325 . 
         [0070]    In some embodiments, for example, the system further includes a conducting annulus  382  disposed between the production tubular  30  and the wellbore tubular  20 . The conducting annulus  382  is configured to receive and conduct the separated gaseous material to the surface. The gas separator annulus  381  is disposed in vertical alignment with the conducting annulus  382 . 
         [0071]    In some embodiments, for example, the gas separator  38  further co-operates with the wellbore tubular  20  with effect that the received formation fluid flow being flowed through the gas separator annulus  381  is flowing in a downwardly direction. 
         [0072]    In some embodiments, for example, the disposition of the wellbore tubular  20  relative to the wellbore is with effect that the effected fluid communication between the formation fluid-receiving fluid passage portion  3231  of the production tubular  30  and the subterranean formation treatment zone is isolated, or substantially isolated, from at least one other zone of the subterranean formation (such as, in  FIG. 1 , by another packer  501 ). 
         [0073]    In some embodiments, for example, the prime mover  36  is disposed within a horizontal wellbore portion of the wellbore  40 . 
         [0074]    In some embodiments, for example, a mechanical filter  327  (such as a sand screen) is disposed within the production tubular  30 , upstream of the gas separator  38  for filtering solids from the formation fluid whose flow has been induced into the formation fluid-receiving conduit portion  32 . Intermittently, the solids, retained by the mechanical filter  327  can be purged by pumping a fluid downhole through the annulus  382 . 
         [0075]    In some of these embodiments, for example, a check valve may be disposed within the production tubular, upstream of the inlet, for enabling fluid circulation of a purging fluid that may be used for cleaning out debris within the production tubular, while preventing fluid communication with the production zone. 
         [0076]    There is also provided a process for effecting production of formation fluids from a subterranean formation. 
         [0077]    The process includes positioning the wellbore tubular  20  within the wellbore, and then positioning the production tubular  30  within the wellbore tubular  20 . 
         [0078]    Flow of the formation fluid, from a treated subterranean formation  50  to the formation fluid-receiving conduit portion  32  of the production tubular  30 , is then induced by the prime mover  36 . The flow of the received formation fluid is directed through the gas separator annulus  381 , in a direction opposite to that which the formation fluid is flowing while being received by the formation fluid-receiving fluid passage portion  3231  of the production tubular  30 , by the co-operating of the gas separator  38  with the wellbore tubular  20 . The received formation fluid, that is flowing through the gas separator annulus  381 , is prevented, or substantially prevented, from returning to the formation fluid-receiving fluid passage portion  3231  of the production tubular  30  by at least the sealing engagement between the formation fluid-receiving fluid passage portion  3231  of the formation fluid-receiving conduit portion  32  of the production tubular  30  and the receptacle sealing surface  21  of the receptacle portion  22  of the wellbore tubular  20 . While the flow of the received formation fluid is being directed through the gas separator annulus  381 , separation, of at least a fraction of gaseous material entrained within the formation fluid flow being flowed through the gas separator annulus  381 , in response to buoyancy forces, is effected to generate a gaseous material-depleted formation fluid flow. The gaseous material-depleted formation fluid flow is energized with the prime mover  36  for flow to the surface through the gaseous material-depleted formation fluid conducting-fluid passage portion  341  of the production tubular  30 . The energized gaseous material-depleted formation fluid flow is conducted to the surface through the gaseous material-depleted formation fluid conducting-fluid passage portion  341 . 
         [0079]    In some embodiments, for example, the received formation fluid flow, being flowed through the gas separator annulus  381 , is flowing, in a downwardly direction. 
         [0080]    In some embodiments, for example, while the flow of the formation fluid, for receiving by the formation fluid-receiving fluid passage portion  3231  of the production tubular  30 , is being induced, the formation fluid is flowing in an upwardly direction. 
         [0081]    In some embodiments, for example, the inducing flow of formation fluid includes effecting the development of a sufficient pressure differential, between the suction of the prime mover  36  and the subterranean formation  50 , by the prime mover  36 . 
         [0082]    In some embodiments, for example, the positioning of the production tubular  30  includes positioning the prime mover  36  within a horizontal wellbore portion of the wellbore  40 . 
         [0083]    In some embodiments, for example, the process further includes flowing the separated gaseous material to the surface through a conducting annulus  382  disposed between the production tubular  30  and the wellbore tubular  20 . In some of these embodiments, for example, the gas separator annulus  381  is disposed in vertical alignment with the conducting annulus  382 . In some of these embodiments, for example, the flowing of the separated gaseous material is in a direction opposite to that of the flow of the received formation fluid through the gas separator annulus  381 . 
         [0084]    In some embodiments, for example, the process further includes, prior to the positioning of a production tubular  30  within the wellbore tubular  20 , the steps of: delivering a wellbore treatment fluid to a treatment zone of the subterranean formation  50  to effect treatment of the subterranean formation treatment zone, and then suspending the delivering of the wellbore treatment fluid. The formation fluid is derived from the subterranean formation treatment zone. In some of these embodiments, the process further includes, prior to the delivering of the wellbore treatment fluid to the subterranean formation treatment zone, the step of positioning the wellbore treatment tubular into fluid communication with the subterranean formation treatment zone with effect that the wellbore treatment tubular is disposed for conducting wellbore treatment fluid to the subterranean formation treatment zone, and also further includes, after the delivering of the wellbore treatment fluid, repositioning the wellbore treatment tubular with effect that fluid communication between the wellbore treatment tubular and the receptacle portion becomes suspended. After the repositioning, the production tubular  30  is positioned within the wellbore tubular  20 . 
         [0085]    “Wellbore treatment fluid” refers to fluid used in treatment (such as stimulation) of a subterranean formation. Stimulation is a type of treatment performed on a subterranean formation to restore or enhance the productivity of oil or gas or other fluid within the subterranean formation. Stimulation includes hydraulic fracturing. Nonlimiting examples of a suitable wellbore servicing fluid include but are not limited to a fracturing fluid, a perforating or hydrajetting fluid, an acidizing fluid, or combinations thereof. 
         [0086]    In some embodiments, for example, while the delivering of the wellbore treatment fluid is being effected, the receptacle  22  is sealingly engaging the wellbore treatment tubular. 
         [0087]    The wellbore treatment tubular includes a fluid passage for conducting wellbore treatment fluid from a wellbore treatment fluid supply source disposed on the surface to the subterranean formation  50 . In some embodiments, for example, The wellbore treatment tubular may be a tubular string that includes several “joints” (a “joint” is a length of pipe) or other tubular members assembled to create the string. In some embodiments, for example, the wellbore treatment tubular includes one or more downhole tools for effecting fracturing of the subterranean formation with which the one or more downhole tools is disposed in fracture-effecting communication with when disposed within the wellbore. 
         [0088]    One or more flow control devices may be provided for selectively effecting fluid communication between the receptacle portion and a subterranean formation. In some modes of operation, the effecting of fluid communication between the wellbore treatment tubular and a treatment zone of a subterranean formation  50 , by the one or more flow control valves, provides a flowpath for the delivery of wellbore treatment fluid. In other modes of operation, the effecting of fluid communication between the formation fluid-receiving fluid passage portion  3231  of the production tubular  30  and a subterranean formation, by the one or more flow control valves, provides a flowpath for conducting of formation fluid from the subterranean formation to the production tubular  30 . 
         [0089]    In some embodiments, for example, the one or more flow control devices are integrated within the wellbore tubular  20 . For those embodiments where the one or more flow control devices are provided by the wellbore tubular, in some of these embodiments, for example, the wellbore treatment tubular includes a tool for selectively effecting opening and closing of the one or more flow control devices integrated within the wellbore tubular for effecting fluid communication between a selected zone of the subterranean formation  50  and the wellbore treatment tubular, and thereby facilitating the delivery of the wellbore treatment fluid to the selected zone of the subterranean formation  50  to effect treatment of the selected zone of the subterranean formation, independently of other zones of the subterranean formation. Also for those embodiments where the one or more flow control devices are provided by the wellbore tubular, in some of these embodiments, for example, the production tubular  30  includes a tool for selectively effecting opening and closing of the one or more flow control devices integrated within the wellbore tubular for effecting fluid communication between a selected zone of the treated subterranean formation  50  and the formation fluid-receiving fluid passage portion  3231  of the production tubular  30 , while isolating other ones of the zones of the treated subterranean formation, and thereby facilitating flow of the formation fluid from the selected zone of the treated subterranean formation, to the formation fluid-receiving fluid passage portion  3231 , while isolating other ones of the zones of the treated subterranean formation from the formation fluid being flowed from the selected zone. 
         [0090]    The flow control devices may comprise sliding sleeves, valves, and other types of flow control devices which may be actuated by a member dropped down through the associated tubular. 
         [0091]    In the above description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present disclosure. Although certain dimensions and materials are described for implementing the disclosed example embodiments, other suitable dimensions and/or materials may be used within the scope of this disclosure. All such modifications and variations, including all suitable current and future changes in technology, are believed to be within the sphere and scope of the present disclosure. All references mentioned are hereby incorporated by reference in their entirety.

Summary:
There is provided a system for effecting production of formation fluids from a subterranean formation. The system includes a gas anchor for mitigating gas lock. Sealing engagement of the gas anchor against the wellbore tubular is effected without use of a conventional packer, which would otherwise be susceptible to receiving debris deposited from the formation fluid, which thereby results in the packer, as well as the gas anchor, becoming vulnerable to becoming stuck within the wellbore tubular.