Patent Publication Number: US-11656211-B2

Title: Systems and methods for identifying gas migration using helium

Description:
BACKGROUND 
     The present disclosure relates generally to gas migration and, more specifically, to identifying natural gas migration direction via a noble gas. 
     BRIEF SUMMARY 
     According to the subject matter of the present disclosure, a system for identifying migration direction of natural gases from source to reservoir in a petroleum exploration environment may comprise a network of  4 He gas sensors and a migration monitoring hub. The network of  4 He gas sensors may be positioned at a plurality of reservoir wells in the petroleum exploration environment and may be operable to identify a  4 He concentration in gas samples at the reservoir wells. The migration monitoring hub may be in communication with the network of  4 He gas sensors and may comprise a user interface and a processor in communication with the network of  4 He gas sensors. The processor may be operable to determine a direction of increasing  4 He concentration between selected ones of the reservoir wells based on the identified  4 He concentration at the reservoir wells and map increasing  4 He concentration in the petroleum exploration environment based on the direction of increasing  4 He concentration between selected ones of the reservoir wells. The user interface may be in communication with the processor and may be operable to display migration information based on the mapped increasing  4 He concentration in the petroleum exploration environment. 
     In accordance with one embodiment of the present disclosure, a method for identifying migration direction of natural gases from source to reservoir in a petroleum exploration environment may comprise isolating a target portion of the petroleum exploration environment, detecting gas samples from a network of  4 He gas sensors positioned at a plurality of reservoir wells in the target portion of the petroleum exploration environment, identifying a  4 He concentration in the gas samples at the plurality of reservoir wells, and determining a direction of increasing  4 He concentration in the gas samples between the plurality of wells in the target portion of the petroleum exploration environment. 
     Although the concepts of the present disclosure are described herein with primary reference to natural gas, it is contemplated that the concepts will enjoy applicability to any hydrocarbon. For example, and not by way of limitation, it is contemplated that the concepts of the present disclosure will enjoy applicability to oil such as, but not limited to, crude oil. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG.  1    schematically depicts a user interface in accordance with one or more embodiments of the present disclosure; 
         FIG.  2    schematically depicts a network of  4 He gas sensors and a migration monitoring hub in accordance with one or more embodiments of the present disclosure; and 
         FIG.  3    schematically depicts a reservoir well in accordance with one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     During the formation of gases, gases that are produced in source rocks migrate to reservoirs within petroleum exploration environments. The migration of gases in petroleum exploration environments is a little-understood process of the petroleum system. However, the migration of gases is also a critical process in the petroleum system. While efforts have been made to better understand the migration of gases from source rock to reservoir, few, if any, methods have proven to be consistent and verifiable. An identification of the migration of gases may prove valuable for assessing hydrocarbon origin, hydrocarbon characteristics, and reserves in potential petroleum exploration environments. Accordingly, there is an ongoing need for identifying the migration of gases from source rock to reservoir. 
     The migration of gases from source rock in petroleum exploration environments may include both primary migration and secondary migration. Primary migration may include the expulsion of the gases from a fine-grained source rock to a coarse-grained carrier bed, while secondary migration may include the passage of gasses from the coarse-grained carrier bed to a reservoir in the petroleum exploration environment. Occasionally, the migration of gases may include tertiary migration, which occurs when the gases migrate from a first reservoir to a second reservoir. 
     Natural gas production may span a certain geological time, for example, from t 1  to t 3 , During production, the production rate may increase quickly between t 1  and t 2 , where t 2  is somewhere between t 1  and t 3 . The production rate may then decrease increase between t 2  and t 3 . 
     The present inventors have identified that noble gases such as, but not limited to, helium may be used as an identifier of gas migration. Helium is highly inert and may generally be immune to subsurface geochemical reactions that may occur during migration from source rock to reservoir. Additionally, helium is readily detectable and may be measured at low concentrations (e.g., a few parts per million (ppm)). While there are nine helium isotopes, there are only two stable helium isotopes,  3 He and  4 He. These helium isotopes may be distributed mainly in the atmosphere, the water, the crust, and the mantle. In each of the atmosphere, the water, the crust, and the mantle,  3 He and  4 He comprise different concentrations and ratios. For example, in the atmosphere, the helium concentration may be about 5.24 ppm, 99.99986% of which may be  4 He, and the rest (0.00014%) may be  3 He. Additionally, the ratio of  3 He/ 4 He in the atmosphere may be about 4×10 −4 . In the crust, the helium concentration may be about 8 ppb. Accordingly, helium concentration and stable isotopic ratio ( 3 He/ 4 He) may indicate the origin of the helium gas. 
     In the crust,  4 He gas may be predominantly radiogenic. That is, the  4 He gas may be a product of alpha decay of radioactive elements such as, but not limited to, Uranium (U) and Thorium (Th). The production rate per gram of specimen  4 He gas that originates from the crust may be calculated using Equations (1) and (2), where P is the production rate (measured in cubic centimeters at standard temperature and pressure per gram per year) and U and Th are the concentrations of Uranium and Thorium, respectively (measured in parts per million): 
     
       
         
           
             
               
                 
                   
                     P 
                     ⁡ 
                     
                       ( 
                       
                         
                             
                           4 
                         
                         ⁢ 
                         He 
                       
                       ) 
                     
                   
                   = 
                   
                     0.2355 
                     × 
                     
                       10 
                       
                         
                           - 
                           1 
                         
                         ⁢ 
                         2 
                       
                     
                     ⁢ 
                     
                       U 
                       * 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
             
               
                 
                   
                     U 
                     * 
                   
                   = 
                   
                     U 
                     ⁢ 
                     
                       { 
                       
                         1 
                         + 
                         
                           0. 
                           ⁢ 
                           1 
                           ⁢ 
                           23 
                           ⁢ 
                           
                             ( 
                             
                               Th 
                               
                                 U 
                                 - 
                                 4 
                               
                             
                             ) 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
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     Similar to the natural gas,  4 He gas production may span a certain geological time. However, the production rate of  4 He gas may generally be fixed and slows marginally as the radioactive elements continue to decay. In-situ curst-derived  4 He gas may be absorbed onto mineral grains or dissolved in water. Moving fluids, such as water, gas, and oil may pick up noble gases from their sources, along their migration pathways, and carry the noble gases to their reservoirs where the fluids may accumulate. 
     In addition to crust-derived helium produced through radioactive decay, atmospheric helium may also end up in the crust. The atmospheric helium may be carried by meteoric water in aquifers. However, there is usually little atmospheric helium observed in the crust. In fact, atmospheric helium is typically only observed in the top few meters of the subsurface. 
     Referring initially to  FIGS.  1  and  2   , a system  200  for identifying migration direction of natural gases from source to reservoir in a petroleum exploration environment may comprise a network of  4 He gas sensors  204  and a migration monitoring hub  201 .  FIG.  1    illustrates the user interface  100  of the migration monitoring hub  201 , while  FIG.  2    schematically depicts a network of  4 He gas sensors  204  and the migration monitoring hub  201 . The user interface  100  of  FIG.  1    illustrates a plurality of reservoir wells  101 - 118  and migration lines  120 - 125  identifying the migration direction of natural gases from source to reservoir in the petroleum exploration environment. 
     Referring again to  FIGS.  1     2 , and  3 , the network of  4 He gas sensors  204  may be positioned at a plurality of reservoir wells  300  in the petroleum exploration environment and may be operable to identify a  4 He concentration in gas samples at the reservoir wells  300 . Referring now to  FIG.  2   , the migration monitoring hub  201  may be in communication with the network of  4 He gas sensors  204  and may comprise a user interface  100  and a processor  202  in communication with the network of  4 He gas sensors  204 . The processor  202  may be operable to determine a direction of increasing  4 He concentration between selected ones of the reservoir wells  300  based on the identified  4 He concentration at the reservoir wells  300  and map increasing  4 He concentration in the petroleum exploration environment based on the direction of increasing  4 He concentration between selected ones of the reservoir wells  300 . The user interface  100  may be in communication with the processor  202  and may be operable to display migration information based on the mapped increasing  4 He concentration in the petroleum exploration environment. 
     In the system  200 , the natural gases may comprise both hydrocarbons and helium, as helium may serve as a migration identifier, as detailed above. According to one or more embodiments, the petroleum exploration environment and the natural gases may be free of helium injection. As used throughout the present disclosure, “helium injection” may refer to the introduction of any additional helium, i.e., helium that is not naturally produced through radioactive decay or cosmogenic helium that is introduced to the petroleum exploration environment via, for example, meteoric water. 
     Referring to  FIGS.  1  and  3   , the  4 He gas sensors  204  may identify the  4 He concentration in gas samples in production flow lines at the plurality of reservoir wells  300 . According to one or more embodiments, the reservoir wells  300  may be in fluid communication with dedicated fluid control trees. The dedicated fluid control trees may be in fluid communication with corresponding production flow lines. The  4 He gas sensors  204  may be configured to identify  4 He concentrations in the production flow lines in fluid communication with the dedicated fluid control trees. The  4 He gas sensors  204  may be operable to detect  4 He concentration in the gas samples that may be consistent with levels of radiogenic helium. According to one or more embodiments, the  4 He gas sensors  204  may be operable to detect  4 He concentration in an amount of less than 10 ppm. In embodiments, the  4 He gas sensors  204  may be operable to detect  4 He concentration in the gas samples in a range from 1 ppm to 3,000 ppm. For example, the  4 He gas sensors  204  may be operable to detect  4 He concentration in the gas samples in a range from 10 ppm to 2,500 ppm. 
     According to one or more embodiments, the  4 He gas sensors  204  may identify the  4 He concentration in gas samples in real time. That is, the  4 He gas sensors  204  may identify the  4 He concentration in gas samples in production flow lines at the plurality of reservoir wells  300  in real time. As used throughout the present disclosure, “real time” may refer to an instantaneous reading, such that the gas samples do not need further testing or analysis to determine the  4 He concentration. 
     Referring again to  FIG.  1 - 2   , the communication between migration monitoring hub  201  and the  4 He gas sensors  204  enables the migration monitoring hub  201  to gather, collect, receive, or otherwise process  4 He concentration generated by the network of  4 He gas sensors  204 . Similarly, the communication between the user interface  100 , which may comprise, for example, a touch screen input/output (I/O) device, or any type of conventional or yet to be developed visual display and I/O device, enables the user interface  100  to gather, collect, receive, or otherwise process, mapped  4 He concentration data for manipulation and display 
     According to one or more embodiments, the user interface  100  of the migration monitoring hub  201  may comprise prompts configured to allow a user to select certain ones of the network of  4 He gas sensors  204  for the processor  202  to consider in mapping increasing  4 He concentration in the petroleum exploration environment. In embodiments, the user may selectively choose individual  4 He gas sensors  204  to be considered. The user may focus on a specific area within the petroleum exploration environment by selecting a few local  4 He gas sensors  204 . Alternatively, the user may focus on the petroleum exploration environment as a whole on a more global level. 
     Referring again to  FIG.  1   , as previously detailed, the user interface  100  may be operable to display migration information. According to one or more embodiments, the migration information may comprise migration trends. Migration trends may include the path (i.e., the direction) that the natural gases follow from source rock to reservoir. The migration information may provide a better understanding of the migration of the natural gas. 
     Referring now to  FIG.  3   , one embodiment of a reservoir well  300  is schematically depicted. It should be noted that other types and configurations of reservoir wells  300  are contemplated and that  FIG.  3    is an example of just one type and configuration of a reservoir well  300  that may be used with the embodiments described herein. The reservoir well  300  may comprise a fluid control tree  310  of the reservoir well  300  that may be above the surface, and a subsurface portion  330  of the reservoir well  300 . 
     The fluid control tree  310  may generally comprise a number of valves, spools, and fittings that regulate and control the flow of pipes in a reservoir well  300 . As seen in  FIG.  3   , the fluid control tree  310  may comprise a tree cap  311 , a tree adapter  312 , a swab valve  313 , a kill wing valve  314 , a kill wing connection  315 , a production wing valve  316 , a surface choke  317 , a production line  318 , the  4 He gas sensor  204 , an upper master valve  321 , a lower master valve  322 , and a tubing head adapter  323 . 
     The fluid control tree  310  may be in fluid communication with a casing  331 . A production tubing  332  may also be in fluid communication with the fluid control tree  310  and may be positioned within an annular space of the casing  331 . A rod string  333  may be connected to a production pump  334 . The production pump  334  may be operable to direct natural gases from the reservoir to the surface via the production tubing  332 . The production pump  334  may direct natural gases from the reservoir to the reservoir well  300  via casing perforations  335 , which may fluidly connect the reservoir to the reservoir well  300 . 
     In another embodiment, a method for identifying migration direction of natural gases from source to reservoir in a petroleum exploration environment may comprise isolating a target portion of the petroleum exploration environment from helium injection, detecting gas samples from a network of  4 He gas sensors  204  positioned at a plurality of reservoir wells  300  in the target portion of the petroleum exploration environment, identifying a  4 He concentration in the gas samples at the plurality of reservoir wells  300 , determining a direction of increasing  4 He concentration in the gas samples between the plurality of wells in the target portion of the petroleum exploration environment, and mapping an increase of  4 He concentration in the target portion of the petroleum exploration environment. It is noted that an environment where a statistically insignificant amount of helium is injected may still be considered as isolated from helium injection. 
     According to one or more embodiments, identifying the  4 He concentration in the gas samples may comprise  4 He gas sensors identifying  4 He concentrations in production flow lines at the plurality of reservoir wells  101 . It is contemplated that identifying the  4 He concentration in the gas samples may comprise identifying the  4 He concentration in gas samples in real time. 
     According to one or more embodiments, the method may further comprise displaying migration information based on increasing  4 He concentration in the petroleum exploration environment on a user interface  100 . Additionally, the method may further comprise identifying migration information comprising migration trends, compound compositions, isotopic compositions, or combinations thereof. 
     In preparing the user interface schematically depicted in  FIG.  1   , gas samples were obtained from an Aeolian sandstone reservoir. In the gas samples, the  3 He/ 4 He ratio ranged from 1.5-4.4×10 −8 . As the atmospheric  3 He/ 4 He ratio may be about 1.384×10 −6 , cosmogenic and radiogenic  3 He/ 4 He ratios are 4×10 −4  and 1×10 −8 , respectively. Therefore, it can be concluded that the helium in the gas samples is about 99% radiogenic helium. As shown in Table 1,  4 He concentrations were measured at a plurality of reservoir wells, 101-118. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Reservoir Well 
                   4 He Concentration (ppm) 
               
               
                   
                   
               
             
            
               
                   
                 101 
                 923 
               
               
                   
                 102 
                 607 
               
               
                   
                 103 
                 533 
               
               
                   
                 104 
                 847 
               
               
                   
                 105 
                 719 
               
               
                   
                 106 
                 462 
               
               
                   
                 107 
                 485 
               
               
                   
                 108 
                 642 
               
               
                   
                 109 
                 523 
               
               
                   
                 110 
                 549 
               
               
                   
                 111 
                 349 
               
               
                   
                 112 
                 321 
               
               
                   
                 113 
                 376 
               
               
                   
                 114 
                 442 
               
               
                   
                 115 
                 322 
               
               
                   
                 116 
                 488 
               
               
                   
                 117 
                 626 
               
               
                   
                 118 
                 394 
               
               
                   
                   
               
            
           
         
       
     
     Still referring to  FIG.  1   , once the  4 He concentrations were measured at the plurality of reservoir wells, the processor identified migration direction of the natural gas by way of increasing  4 He concentrations and displayed on the user interface. Migration lines  120 - 125  show the general migration direction of the natural gases, as determined by increasing  4 He concentration in the gas samples obtained at the plurality of reservoir wells. 
     It is noted that recitations herein of a component of the present disclosure being “configured” or “programmed” in a particular way, to embody a particular property, or to function in a particular manner, are structural recitations, as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is “configured” or “programmed” denotes an existing physical condition of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component. 
     It is noted that terms like “preferably,” “commonly,” and “typically,” when utilized herein, are not utilized to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to identify particular aspects of an embodiment of the present disclosure or to emphasize alternative or additional features that may or may not be utilized in a particular embodiment of the present disclosure. 
     Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects. 
     It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”