Patent Publication Number: US-2022221440-A1

Title: High temperature high pressure (hthp) cell in sum frequency generation (sfg) spectroscopy for oil/brine interface analysis with reservoir conditions and dynamic compositions

Description:
BACKGROUND 
     Water injection is a common technique used in oil production to increase the yield of hydrocarbons from a reservoir. The interactions between the various phases in the reservoir (e.g., oil, water, brines, calcite rock, and gas) can greatly affect yield of the recovered hydrocarbons. For example, by controlling the salinity and the ionic strength of the injected solution, the wettability of rock formations in the reservoir can be changed to improve recovery. To further improve the yield of hydrocarbons, various spectroscopic techniques such as SFG spectroscopy have been used to understand the nature of the interactions between the phases in the reservoir and characterize the chemical and molecular structure and interfaces of the phases. 
     SUMMARY 
     In one aspect, one or more embodiments disclosed herein relate to a pressure cell for SFG spectroscopy. The pressure cell includes a metal pressure chamber that includes a liquid sample holder that retains a liquid sample, a removable lid that seals against a base to enclose the liquid sample holder in an interior of the metal pressure chamber, a window in the removable lid that allows the liquid sample to be optically accessed from an exterior of the metal pressure chamber, a sample inlet that flows the liquid sample from the exterior of the metal pressure chamber to the liquid sample holder in the interior of the metal pressure chamber at a predetermined flow rate, and a sample outlet that flows the liquid sample from the liquid sample holder to the exterior of the metal pressure chamber. The pressure cell further includes: a heating stage, disposed in the interior of the metal pressure chamber, that heats the liquid sample; an ultrasonic stage, disposed in the interior of the metal pressure chamber, that emulsifies the liquid sample; a chamber pump, connected to the interior of the metal pressure chamber, that pressurizes the interior of the metal pressure chamber; and a controller that controls the chamber pump, the ultrasonic stage, and the heating stage to control a pressure of the interior of the metal pressure chamber, an emulsification of the liquid sample, and a temperature of the liquid sample, respectively. 
     In another aspect, one or more embodiments disclosed herein relate to a system for performing SFG spectroscopy. The system includes: a pressure cell and a sum frequency generation microscope. The pressure cell includes a metal pressure chamber that includes a liquid sample holder that retains a liquid sample, a removable lid that seals against a base to enclose the liquid sample holder in an interior of the metal pressure chamber, a window in the removable lid that allows the liquid sample to be optically accessed from an exterior of the metal pressure chamber, a sample inlet that flows the liquid sample from the exterior of the metal pressure chamber to the liquid sample holder in the interior of the metal pressure chamber at a predetermined flow rate, and a sample outlet that flows the liquid sample from the liquid sample holder to the exterior of the metal pressure chamber. The pressure cell further includes: a heating stage, disposed in the interior of the metal pressure chamber, that heats the liquid sample; an ultrasonic stage, disposed in the interior of the metal pressure chamber, that emulsifies the liquid sample; a chamber pump, connected to the interior of the metal pressure chamber, that pressurizes the interior of the metal pressure chamber; and a controller that controls the chamber pump, the ultrasonic stage, and the heating stage to control a pressure of the interior of the metal pressure chamber, an emulsification of the liquid sample, and a temperature of the liquid sample, respectively. The sum frequency generation microscope includes: a first light source that generates light of a first variable frequency; a second light source that generates light of a second frequency; and a detector that detects light. 
     In another aspect, one or more embodiments disclosed herein relate to a method of performing SFG spectroscopy. The method includes: sealing a liquid sample holder in an interior of a metal pressure chamber that includes a base and a removable lid; flowing a liquid sample from an exterior of the metal pressure chamber, thorough a sample inlet, to the liquid sample holder in the interior of the metal pressure chamber at a predetermined flow rate; emulsifying the liquid sample with an ultrasonic stage; heating the liquid sample with a heating stage; pressurizing the interior of the metal pressure chamber with a chamber pump that is connected to the interior of the metal pressure chamber; illuminating a surface of the liquid sample with light of a first variable frequency and light of a second frequency through a window of the metal pressure chamber; collecting, through the window, light of a third frequency that is the sum of the first variable frequency and the second frequency from the surface of the liquid sample; and flowing the liquid sample from the liquid sample holder, through a sample outlet, to the exterior of the metal pressure chamber. 
     Other aspects and advantages will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  shows an oil and gas production facility. 
         FIG. 1B  shows a schematic of a sum frequency generation system. 
         FIG. 2  shows an open pressure cell for SFG spectroscopy according to one or more embodiments. 
         FIG. 3  shows a sealed pressure cell for SFG spectroscopy according to one or more embodiments. 
         FIG. 4  shows a schematic of a controller according to one or more embodiments. 
         FIG. 5  shows a system for performing SFG spectroscopy according to one or more embodiments. 
         FIGS. 6A and 6B  show a method for performing SFG spectroscopy according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Specific embodiments of the present disclosure will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. 
     Numerous specific details are set forth in the following detailed description in order to provide a more thorough understanding of embodiments of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. 
     Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create a particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as by the use of the terms “before,” “after,” “single,” and other such terminology. Rather the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements. 
     In general, embodiments disclosed herein provide an apparatus, a system, and a method for performing sum frequency generation (SFG) spectroscopy under simulated reservoir and dynamic conditions to characterize the molecular and chemical structures and interfaces of an oil/brine sample. For example, as shown in  FIG. 1 , an oil production facility  100  located above a hydrocarbon reservoir  102  may include an oil rig  104  and an oil well  106  to extract hydrocarbons  108 . The hydrocarbons  108  may be extracted by pressurizing the reservoir  102  with an injection solution (e.g., conventional water injection, specialized aqueous solution injection) from a second well (not shown). 
     To improve the effectiveness of the injection recovery technique, the microscopic characteristics of, and interactions between, the hydrocarbons  108 , the injection solution, and the rock formations of the reservoir  102  may be studied. Examples of such interactions may include surface charge interaction, ionic exchange, and rock dissolution. SFG spectroscopy may be used to probe the fluid/fluid or fluid/rock interactions and to characterize the chemical and molecular structures and interfaces of a liquid sample, discussed in further detail below. Accordingly, one or more embodiments disclosed herein relate to an apparatus, a system, and a method of studying a liquid sample with SFG spectroscopy in a simulated high temperature and high pressure reservoir environment. Alternatively, other optical techniques (e.g., difference frequency generation (DFG) spectroscopy, Raman spectroscopy) may be used in conjunction with embodiments disclosed herein. 
     In one or more embodiments, a liquid sample may be extracted from a subsurface facility (e.g., the reservoir  102 ). For example, a live oil sample may be obtained from the oil well  106 . Furthermore, to more closely recreate the actual fluids found downhole in the well (e.g., compositions previously determined using a modular formation dynamic tester (MDT) technique), gases such as gaseous hydrocarbons, hydrogen sulfide, and the like may be remixed into the live oil sample. Alternatively, or in addition, aqueous solutions may be remixed into the live oil sample to recreate the actual fluids found downhole in the well, as described below. 
     In one or more embodiments, liquid samples collected from the reservoir may be separated into two phases: an organic phase (i.e., primarily hydrocarbons  108  of the live oil sample) and the second component includes an aqueous phase (i.e., primarily water). Then, the two phases may be remixed with a predetermined ratio and/or predetermine level of emulsification. Thus, the liquid sample to be studied may be a synthetic brine (i.e., prepared in a laboratory) comprising the remixed hydrocarbons  108  and an aqueous solution. 
     The term “brine” is defined as a mixture comprising two or more immiscible liquids. A first component of the brine is dispersed in a second component of the brine. In one or more embodiments, the dispersed first component includes an organic phase (i.e., primarily hydrocarbons) and the second component includes an aqueous phase (i.e., primarily water). Alternatively, the phases of the first and second components may be reversed. In one or more embodiments, the liquid sample may be a brine comprising gaseous hydrocarbons, liquid hydrocarbons, solid hydrocarbons, salts, metals, impurities, water, an aqueous solution, and any combination thereof. 
       FIG. 1B  shows a schematic of a sum frequency generation system. In sum frequency generation, a sample is probed with two incident light beams that overlap in space (i.e., both beams converge at a coincidence point on the sample) and time (i.e., the pulses from both beams are incident on the sample at the same time). The size of the coincidence point that is probed corresponds to the spot size of the two incident light beams which may be around 150 microns in diameter. 
     The first light beam is centered at a first variable frequency f 1  that may correspond with an energy level of a molecular vibrational mode that occurs in the sample (e.g., corresponds to an infrared wavelength of light). The first variable frequency f 1  may be continuously or discretely changed (e.g., with a tunable light source, a filtered light source, a spectrometer, or the like) to probe different energy levels of different molecular vibrational modes in the sample. The first light beam may be incident at an angle of 60° with respect to the normal vector of the sample surface. 
     The second light beam is centered at a second frequency f 2  that is different from the first variable frequency f 1  and may correspond to a virtual energy state (e.g., corresponds to a visible wavelength of light). The second light beam may be incident at an angle of 55° with respect to the normal vector of the sample surface. After absorbing the two coincident light pulses, non-linear effects induced by the non-linear susceptibility of the sample causes the surface of the sample to emit light of a third frequency f 3  that is the sum of the first and second frequencies f 1 , f 2  (i.e., an SFG signal). 
     In one or more embodiments, an SFG spectrum is generated by scanning the first variable frequency f 1  across a range of frequencies that span an energy level of a molecular vibrational mode of interest. When the first variable frequency f 1  corresponds to the energy level of the molecular vibrational mode, the intensity of the emitted SFG light at the third frequency f 3  will increase due to a resonant effect of the first light beam exciting the molecular vibrational mode. By analyzing the intensity of the detected third frequency of light f 3 , the vibrational modes in the sample may be identified from the resonant frequencies. Furthermore, the directional dependence of the non-linear susceptibility of the sample allows a user to derive information about the orientation of molecules in the sample from the polarization of the collected SFG signal. 
     In one or more embodiments, the first light beam may be a spectrally broadband light beam that includes a plurality of frequencies f 1  while the second light beam remains at a single fixed frequency f 2 . Accordingly, the emitted SFG light from the sample would include a plurality of third frequencies f 3  that may be collected simultaneously for faster data acquisition. 
       FIGS. 2 and 3  show a pressure cell  200  for SFG spectroscopy according different embodiments of the present invention. The pressure cell  200  simulates conditions that occur in the reservoir  102  ( FIG. 1 ). The pressure cell  200  includes a metal pressure chamber  202  that encloses a liquid sample holder  204  that retains a liquid sample  206  (e.g., a brine). In one or more embodiments, the liquid sample holder  204  may include a rock interface  207  (e.g., a calcite rock sample, a dolomite rock sample, an anhydrite mineral sample, a part of a carbonite rock sample, or any combination thereof) or any other appropriate material to interact with the liquid sample  206  to further simulate interactions that occur in the reservoir  102  ( FIG. 1 ). 
     The metal pressure chamber  202  includes a base  208  and a removable lid that enclose the liquid sample holder  204  within the metal pressure chamber  202 . The base  208  and the removable lid  210  are formed from a metal and may be aluminum, stainless steel, or any other appropriate metal with sufficient strength to withstand the temperatures and pressures of a simulated reservoir environment. In one or more embodiments, the metal pressure chamber  202  may have a circular cross-section and a diameter of at least 20 cm. Alternatively, the metal pressure chamber may have a rectangular cross-section. However, the metal pressure chamber  202  is not limited to these shapes or dimensions and any appropriate size or shape may be used. 
     As shown in  FIG. 2 , in one or more embodiments, the base  208  may comprise a horizontal base plate  208   a  and a vertical wall(s)  208   b  that extends in a direction perpendicular to the base plate  208   a . The base plate  208   a  and wall(s)  208   b  define a cavity  208   c  that retains the liquid sample holder  204 . The base  208  includes an interior surface that is exposed to the simulated environment created in an interior of the metal pressure chamber  202  and an exterior surface that is exposed to an external environment of the metal pressure chamber  202 . In one or more embodiments, the base  208  may further include one or more feedthroughs  208   d  that communicate between the interior surface and the exterior surface of the base  208 . 
     A feedthrough  208   d  may be a channel, a port, a fluid path, a length of tubing, an electrical line, an electrical conduit, an electrical plug, or any combination thereof depending on the material or signal being passed through the base  208 . For example, one or more feedthroughs  208   d  may be electrical conduits that pass signals (e.g., control signals) or power to equipment inside the metal pressure chamber  202 , as described below. In addition, one or more feedthroughs  208   d  may include a channel connected to a chamber pump  230 , described below, that pressurizes the interior of the metal pressure chamber  202 . Further still, one or more feedthroughs  208   d  may include various tubes that introduce and remove the liquids sample  206  to and from the interior of the metal pressure chamber  202 . 
     As discussed above, the removable lid  210  cooperates with the base  208  to form the metal pressure chamber  202  that encloses the liquid sample holder  204 . The removable lid  210  may be a planar plate that seals against an upper surface of the wall(s)  208   b  of the base  208 . The removable lid  210  may attach to the base  208  by a set of cooperating threads (i.e., screws onto the base  208 ), one or more clips (i.e., clipped onto the base  208 ), or by fastening one or more fasteners (e.g., bolts, screws). However, the removable lid  210  may attach to the base  208  by any appropriate means that provides a seal to contain the pressure of the simulated reservoir environment. As shown in  FIG. 2 , in one or more embodiments, a seal  212  may be disposed between the base  208  and the removable lid  210  to isolate the simulated environment inside the metal pressure chamber  202  from the external environment of the metal pressure chamber  202 . The seal  212  may be an elastomer O-ring, a copper gasket, any other appropriate sealing material, or any combination thereof. 
     In one or more embodiments, the removable lid  210  comprises a window  214  that allows the liquid sample  206  to be optically accessed from the exterior of the metal pressure chamber  202  (e.g., to allow light from an external source to access the liquid sample  206 ). The window  214  may be transparent to a first, a second, and a third frequency of light (i.e., frequencies f 1 , f 2 , and f 3 ), where the third frequency f 3  is the sum of the first and second frequencies f 1 , f 2 . The window  214  may be made of glass (e.g., a silica based glass, a calcium fluoride based glass, or the like) that is transparent enough to allow the liquid sample  206  to be illuminated with light of the first and second frequencies f 1 , f 2  from a source disposed outside of the metal pressure chamber  202 . The window  214  may also be transparent enough to pass the generated SFG signal comprising light of the third frequency f 3  from the liquid sample  206  to a detector disposed outside of the metal pressure chamber  202 . The window  214  may have a refractive index of approximately 1.5. The window  214  may be coated with an antireflection coating. 
     In one or more embodiments, the window  214  may comprise multiple transparent windows. For example, the removable lid  210  may comprise three distinct windows  214 , wherein the optical properties (e.g., transmission coefficient) of each window  214  is tuned to a corresponding first, second, and third frequency f 1 , f 2 , f 3  of light, respectively. 
     In general, the base  208  and the removable lid  210  cooperate to enclose the liquid sample holder  204  and the window  214  allows external light to access the liquid sample  206 . However, other embodiments may be devised without departing from the scope of embodiments disclosed herein. For example, the base  208  may comprise only a base plate  208   a  while the wall(s) that define the cavity  208   c  of the metal pressure chamber  202  may be disposed on the removable lid  210 . In this configuration, the base  208  may be removable from the lid  210 . Accordingly, the one or more feedthroughs  208   d  may be disposed on the lid  210  rather than the base  208 . 
     As discussed above, the metal pressure chamber  202  encloses a liquid sample holder  204  that retains the liquid sample  206 . The liquid sample holder  204  may be made of any appropriate material that retains the liquid sample  206 . In one or more embodiments, the liquid sample holder  204  is made of a non-corrosive material (e.g., a stainless steel, a polymer, TEFLON, or the like) that can be easily cleaned of the liquid sample  206  and reused. For example, the liquid sample holder  204  may be made of TEFLON which exhibits excellent chemical and temperature resistance up to 250° C. 
     The liquid sample holder  204  may be any shape (e.g., circular cross-section, non-circular cross-section) provided that the liquid sample  206  retained by the liquid sample holder  204  is exposed to the interior of the metal pressure chamber  202 . In one or more embodiments, the liquid sample holder  204  may be an open cylinder with a circular cross-section and a diameter of 10-15 cm. The liquid sample holder  204  may retain 15-20 mL of the liquid sample  206 . However, any appropriate size or shape may be used to retain the liquid sample  206  provided the liquid sample holder  204  fits within the metal pressure chamber  202 . 
     In one or more embodiments, the metal pressure chamber  202  further includes a sample inlet  216  that flows the liquid sample  206  from the exterior of the metal pressure chamber  202  to the liquid sample holder  204  in the interior of the metal pressure chamber  202 . The sample inlet  216  may include a sample inlet path  218  connected to the liquid sample holder  204  and a sample pump  220  that pumps the liquid sample  206  through the sample inlet path  218  and into the liquid sample holder  204 . 
     The sample inlet path  218  may be a rigid or flexible tubing that passes through the base  208  via a feedthrough  208   d  and directly connects to the liquid sample holder  204 . The sample inlet path  218  may be disposed to flow the liquid sample  206  directly into the liquid sample holder  204  (e.g., one end of the sample inlet path is directly connected to a wall of the liquid sample holder). In one or more embodiments, the sample inlet path  218  is disposed to flow the liquid sample  206  onto the rock interface  207  disposed in the liquid sample holder  204 . 
     The sample pump  220  may be a metering pump that generates a predetermined flow rate of the liquid sample  206  in the sample inlet path  218 . For example, the sample pump  220  may generate a maximum inlet flow rate of 50 mL/min and a minimum inlet flow rate of 0.001 mL/min. However, depending on the reservoir conditions that are being simulated, other flow rates may be used. The sample pump  220  may be a Quizix Q6000 high pressure syringe pump (Chandler Engineering). In one or more embodiments, the sample pump  220  may include a sample storage container or a sample preparation device (e.g., a mixer that combines an organic phase and an aqueous phase to create the liquid sample  206 ). 
     In one or more embodiments, the sample inlet  216  may further comprise an inlet valve that seals the sample inlet path  218 . The inlet valve may completely seal the sample inlet path  218  to prevent the pressurized environment in the interior of the metal pressure chamber  202  from forcing the liquid sample  206  back into the sample pump  220 . Alternatively, the inlet valve may be controlled to partially seal the sample inlet path  218  to regulate the flow rate of the liquid sample  206  from the sample pump  220 . 
     As shown in  FIG. 3 , in one or more embodiments where the liquid sample  206  is a brine, the sample inlet  216  may include a plurality of sample inlet paths  218   a ,  218   b , each with a corresponding sample pump  220   a ,  220   b  that pumps a portion of the liquid sample  206  into the liquid sample holder  204 . For example, a first sample inlet path  218   a  may flow an aqueous phase of the liquid sample  206  into the liquid sample holder  204  at a first partial flow rate. A second sample inlet path  218   b  may flow an organic phase of the liquid sample  206  into the liquid sample holder  204  at a second partial flow rate. In other words, the liquid sample  206  may be a brine that is mixed inside of the pressure cell  200 . As discussed in further detail below, an ultrasonic stage  228  may prepare the liquid sample  206  for study by emulsifying (i.e., mixing) the organic and aqueous phases to more accurately recreate sample compositions and liquid/liquid or liquid/solid interfaces found in the reservoir  102  ( FIG. 1 ). 
     The metal pressure chamber  202  further includes a sample outlet  222  that flows the liquid sample  206  from the liquid sample holder  204  in the interior of the metal pressure chamber  202  to the exterior of the metal pressure chamber  202 . The sample outlet  222  may include a sample outlet path  224  connected to the liquid sample holder  204  and a sample drain  226  that removes the liquid sample  206  from the metal pressure chamber  202 . 
     The sample outlet path  224  may be a rigid or flexible tubing that passes through the base  208  via a feedthrough  208   d  and directly connects to the liquid sample holder  204 . In one or more embodiments, the sample outlet path  218  may the same type of tubing as the sample inlet path  218 . 
     The sample drain  226  may be a sample storage container or a sample disposal container. In one or more embodiments, the flow in the sample outlet path  224  and out of the sample drain  226  may be passively generated by the sample pump  220  introducing a new portion of the liquid sample  206  into the liquid sample holder  204 . Alternatively, the sample drain  226  may also include a pump (e.g., a syringe pump) to actively extract the liquid sample  206  from the metal pressure chamber  202 . 
     In one or more embodiments, the sample drain  226  may further comprise an outlet valve that seals the sample outlet path  224 . The outlet valve may completely seal the sample outlet path  224  to prevent the pressurized environment in the interior of the metal pressure chamber  202  from forcing the liquid sample  206  out of the pressure cell. Alternatively, the outlet valve may be controlled to partially seal the sample outlet path  224  to regulate the flow of the liquid sample  206  through the sample drain  226 . 
     The combination of the sample inlet  216  and the sample outlet  222  allows the composition of the liquid sample  206  in the metal pressure chamber  202  to be changed in situ. In other words, the composition of the liquid sample  206  and the liquid/liquid or liquid/solid interfaces found in the liquid sample holder  204  may be actively changed and manipulated to simulate dynamic conditions of the reservoir  102 . For example, the liquid sample  206  may be diluted by introducing an aqueous injection solution via the sample inlet  216  to simulate the displacement of an oil/brine sample by conventional water injection recovery techniques. 
     The pressure cell  200  further includes an ultrasonic stage  228  that is directly connected to the liquid sample holder  204 . The ultrasonic stage  228  may be a vibrating table, a vibrating probe, an ultrasonic bath, or any other appropriate mechanism that sonicates the liquid sample  206  in the liquid sample holder  204 . In one or more embodiments, the ultrasonic stage  228  may be vibrationally isolated from the metal pressure chamber  202  (e.g., to prevent misalignment of the incident light beams at the surface of the liquid sample  206  or to prevent loosening of the sealed connection between the base  208  and removable lid  210 ). For example, a thermal isolation layer  240 , discussed in further detail below, may absorb mechanical vibrations from the ultrasonic stage  228 . 
     The ultrasonic stage  228  may be connected to a controller  232  that provides power and control signals to the ultrasonic stage  228 . The controller  232 , described in further detail below with respect to  FIG. 4 , may control the ultrasonic stage  228  based information from the sample inlet  216  and sample outlet  222 . For example, the controller  232  may control the ultrasonic stage  228  to emulsify the liquid sample  206  only when the sample inlet  216  and sample outlet  222  have completed setting or altering of the composition of the liquid sample  206 . In one or more embodiments, the ultrasonic stage  228  may emulsify an aqueous phase and an organic phase of the liquid sample  206  for 30 seconds to generate a brine, an oil/water emulsion, or a nano-sized oil emulsion. 
     The pressure cell  200  further includes a chamber pump  230  that is connected to, and pressurizes, the interior of the metal pressure chamber  202 . The chamber pump  230  may be a vacuum pump, a compressor, a pneumatic compressor, a hydraulic compressor, any other appropriate mechanism that generates a pressurized environment in the interior of the metal pressure chamber  202 , or any combination thereof. In one or more embodiments, the chamber pump  230  may be vibrationally isolated from the metal pressure chamber  202  (e.g., to prevent misalignment of the incident light beams at the surface of the liquid sample  206  or to prevent loosening of the sealed connection between the base  208  and removable lid  210 ). For example, the feedthrough  208   d  and/or the tubing that connects the chamber pump  230  and the metal pressure chamber  202  may absorb mechanical vibrations from the chamber pump  230 . 
     The pressure range of the chamber pump  230  may be between ambient atmospheric pressure (e.g., around 14.7 psi) to approximately 3000 psi. However, as conditions in a reservoir  102  ( FIG. 1 ) may vary according to many parameters (e.g., depth, geographic location, rock composition), the pressure range of the chamber pump  230  is not limited to this approximate value and pressures greater than 3000 psi may be implemented. In one or more embodiments, the chamber pump  230  may further comprise a vacuum pump that evacuates the metal pressure chamber  202  (e.g., to outgas components). 
     The chamber pump  230  may be connected to a controller  232  that provides power and control signals to the chamber pump  230 . The controller  232 , described in further detail below with respect to  FIG. 4 , may control the chamber pump  230  based upon a pressure gauge  234  that measures a pressure of the interior of the metal pressure chamber  202 . Furthermore, the controller  232  may also control a control valve  236  that seals the metal pressure chamber  202  from the chamber pump  230 . Furthermore, the controller  232  may open the control valve  236  to release pressure from the interior of the metal pressure chamber  202 . In other words, the controller  232  may control the chamber pump  230  and the control valve  236  to control (e.g., increase, decrease, maintain) the pressure in the metal pressure chamber  202 . 
     The pressure cell  200  further includes a heating stage  238  (e.g., a heating element) that heats the liquid sample  206 . In one or more embodiments, the heating stage  238  is an electric heater (e.g., electrical joule heater, ohmic heater), however any appropriate heating element may be used to heat the liquid sample  206 . The heating stage  238  may be directly connected to the liquid sample holder  204 . In some embodiments, a thermal isolation layer  240  may be disposed on the heating stage  238  (e.g., between the heating stage  238  and the metal pressure chamber  202 ) to thermally isolate the heating stage  238  from the metal pressure chamber (i.e., prevent the metal pressure chamber  202  from unnecessarily heating during operation). The thermal isolation layer  240  may be made of mica. Alternatively, the thermal insulation layer may a ceramic that includes one or more of aluminum oxide (Al 2 O 3 ), silica (SiO 2 ), magnesium oxide (MgO), or any combination thereof. 
     The temperature range of the heating stage  238  may be between 25-100 C.° to simulate the temperatures of the reservoir  102 . However, as conditions in a reservoir  102  ( FIG. 1 ) may vary according to many parameters (e.g., depth, geographic location, rock composition), the temperature range of the heating stage  238  is not limited to this range and temperatures greater than 100 C.° may be implemented. 
     The heating stage  238  may be connected to a temperature controller  242  disposed outside of the metal pressure chamber  202 . The temperature controller  242  may be a hardware or software component of the controller  232  or may be a distinct controller apparatus. The temperature controller  242  provides power and control signals to the heating stage  238  through one or more feedthroughs  208   d  in the metal pressure chamber  202 . The temperature controller  242  may control the heating stage  238  based on a temperature of the liquid sample  206  that is measured by a thermocouple  244  connected to the liquid sample holder  204 . 
     In one or more embodiments, the pressure cell  200  further includes a positioning stage  246  that controls a position of a surface of the liquid sample  206 . The positioning stage  246  may include one or more actuators (e.g., an electric actuator, a pneumatic actuator, a hydraulic actuator, a piezoelectric actuator, or any combination thereof) that translates the base  208  or the liquid sample holder  204  in one or more dimensions (e.g., a vertical direction) to align the surface of the liquid sample  206  with the incident light beams. The positioning stage  246  may automatically position the surface of the liquid sample  206  based on optical feedback from the surface of the liquid sample  206 , as described in further detail below with respect to  FIG. 5 . The positioning stage  246  may be controlled by the controller  232 . 
     In one or more embodiments, the positioning stage  246  may be disposed on an interior surface of base  208 , as shown in  FIG. 2 . The positioning stage  246  may translate the liquid sample holder  204 , the heating stage  238 , and the ultrasonic stage  228  to align the surface of the liquid sample with respect to the incident light. The positioning stage  246  may be separated from the heating stage  238  by the thermal insulation layer  224  that prevents the positioning stage  246  from unnecessarily heating up during operation. 
     In another embodiment, as shown in  FIG. 3 , the positioning stage  246  may be disposed exteriorly to the metal pressure chamber  202  while the heating stage  238  is disposed in the interior of the metal pressure chamber  202 . The positioning stage  246  may translate the metal pressure chamber  202  and the entire contents thereof to align the surface of the liquid sample  206  with respect to the incident light. An external positioning stage  246  advantageously reduces the number of feedthroughs  208   d  and the possibility of leaks from the metal pressure chamber  202 . 
       FIG. 4  shows a schematic of a controller  232  according to one or more embodiments. As discussed above, in one or more embodiments, the controller  232  may control the chamber pump  230 , the heating stage  238 , and the ultrasonic stage  228  to control a pressure of the interior of the metal pressure chamber  202 , a temperature of the liquid sample  206 , and an emulsification of the liquid sample  206 , respectively. The controller  232  may be implemented on virtually any type of computing system, regardless of the platform being used. For example, the computing system may be one or more mobile devices (e.g., laptop computer, smart phone, personal digital assistant, tablet computer, or other mobile device), desktop computers, servers, blades in a server chassis, or any other type of computing device or devices that includes at least the minimum processing power, memory, and input and output device(s) to perform one or more embodiments disclosed herein. For example, as shown in  FIG. 4  the controller  232  may include one or more computer processor(s)  402 , associated memory  404  (e.g., random access memory (RAM), cache memory, flash memory), one or more storage device(s)  406  (e.g., a hard disk, an optical drive such as a compact disk (CD) drive or digital versatile disk (DVD) drive, a flash memory stick), and numerous other elements and functionalities. The computer processor(s)  402  may be an integrated circuit for processing instructions. For example, the computer processor(s) may be one or more cores, or micro-cores of a processor. 
     The controller  232  may also include one or more input device(s)  408 , such as a pressure gauge  234 , thermocouple  244 , SFG microscope  500  (discussed in further detail with respect to  FIG. 5 ), camera, imager, touchscreen, keyboard, mouse, microphone, touchpad, electronic pen, or any other type of input device. Further, the controller  232  may include one or more output device(s)  410 , such as a screen (e.g., a liquid crystal display (LCD), a plasma display, touchscreen, cathode ray tube (CRT) monitor, or other display device), a printer, external storage, or any other output device. One or more of the output device(s) may be the same or different from the input device(s). The controller  232  may be connected to a network  412  (e.g., a local area network (LAN), a wide area network (WAN) such as the Internet, mobile network, or any other type of network) via a network interface connection (not shown). The input and output device(s) may be locally or remotely (e.g., via the network  412 ) connected to the computer processor(s)  402 , memory  404 , and storage device(s)  406 . Many different types of computing systems exist, and the aforementioned input and output device(s)  408 ,  410  may take other forms. 
     Further, one or more elements of the controller  232  may be located at a remote location and be connected to the other elements over a network  412 . Further, one or more embodiments may be implemented on a distributed system having a plurality of nodes, where each portion of the embodiment may be located on a different node within the distributed system. In one embodiment, the node corresponds to a distinct computing device. In other embodiments, the node may correspond to a computer processor with associated physical memory. In yet other embodiments, the node may correspond to a computer processor or micro-core of a computer processor with shared memory and/or resources. 
       FIG. 5  shows a system  500  for performing SFG spectroscopy according to one or more embodiments. A system  500  for performing SFG spectroscopy may include a pressure cell  200 , as previously described with respect to the embodiments of  FIGS. 2-3 , and an SFG microscope  501 . The SFG microscope  501  may be an SFG vibrational spectrometer (Ekspla), for example. 
     The SFG microscope  501  includes a first light source  502  that generates light of the first variable frequency f 1 . The range of the first variable frequency f 1  may correspond to the vibrational energy of a molecule in the liquid sample (e.g., corresponds to an infrared wavelength of light). The first light source  502  may be disposed to focus the light of the first variable frequency f 1  on the surface of the liquid sample  206  with an incidence angle of 60° with respect to a surface normal vector. In one or more embodiments, the first light source  502  is pulsed laser source with a pulse energy of 2.7-35 mJ and a pulse duration of 28+/−10 picoseconds. For example, the first light source  502  may comprise a PL2231-50 picosecond laser centered at 1064 nm (Ekspla) that feeds into a SFGH500 multichannel beam delivery unit (Ekspla) that feeds a PG501-DFGx optical parametric generator (Ekspla) that outputs a variable IR wavelength ranging of 2300-16000 nm. The first light source may further include a visible laser to aid in focusing the light of the variable frequency f 1 . 
     The SFG microscope  501  further includes a second light source  504  that generates light of the second frequency f 2 . The second frequency f 2  is different from the first variable frequency f 1  and may correspond to a virtual energy state (e.g., may correspond to a visible wavelength of light). The second light source  504  may be disposed to focus the light of the second frequency f 2  on the surface of the liquid sample  206  with an incidence angle of 55° with respect to a surface normal vector. In one or more embodiments, the second light source  504  is pulsed laser source with a pulse energy of 2.7-35 mJ and a pulse duration of 28+/−10 picoseconds. For example, the second light source  502  may be a second output of the PG501-DFGx optical parametric generator (Ekspla) that outputs a fixed 532 nm wavelength. 
     However, the present disclosure is not limited to this configuration and any appropriate light sources for generating an SFG signal (i.e., light of the third frequency f 3  that is the sum of the first and second frequencies f 1 , f 2 ) may be used. The first and second light sources  502 ,  504  are configured to spatially and temporally overlap the first and second light beams at the surface of the liquid sample  206  to generate the SFG signal. The SFG signal may be a pulsed signal with a pulse energy of 0.52-5.3 mJ and a pulse duration of 28+/−10 picoseconds. 
     The SFG microscope  501  further comprises a detector  506  that detects light. The detector  506  is offset from the light sources  502 ,  504  of the SFG microscope  501  to collect the SFG signal emitted from the liquid sample  206 . The detector  506  may include additional optical elements (e.g., lens, spatial filter, frequency filter, spectrometer, power meter) to control, measure, and manipulate the detected light. For example, in one or more embodiments where multiple vibrational frequencies are probed simultaneously, the detector  506  may be a monochromator that collects and spectrally separates different frequencies of light in the collected signal. 
     In one or more embodiments, the SFG microscope  501  may further include additional optical elements (e.g., mirror, lens, spatial filter, frequency filter, delay line, spectrometer, power meter) to control, measure, and manipulate the emitted and detected light. 
     In one or more embodiments, the SFG microscope  501  may be controlled by the controller  232 . For example, the controller  232  may instruct the SFG microscope  501  to begin data acquisition once the chamber pump  230  has pressurized the metal pressure chamber  202  to a predetermined pressure, the heating stage  238  has heated the liquid sample  206  to a predetermined temperature measured by the thermocouple  228 , and the ultrasonic stage  228  has emulsified the liquid sample  206  to a predetermined degree of emulsification. 
     In one or more embodiments, the controller  232  may halt data acquisition while the sample inlet  216  and sample outlet  222  control the composition of the liquid sample  206  in the liquid sample holder  204 . Specifically, adjusting the flow rate of the liquid sample  206  or adding/removing a quantity of the liquid sample  206  may modify the position of the surface of the liquid sample  206  and disrupt the spatial overlap of the first and second light beams at the surface. Furthermore, the controller  232  may halt data acquisition while the liquid sample  206  is being emulsified because the surface of the liquid sample  206 , and thus the spatial overlap of the first and second light beams, may be disrupted by the ultrasonic stage  228  process. 
     Furthermore, the controller  232  may use one or more of the first and second light sources  502 ,  504  to illuminate the liquid sample  206  to align the liquid sample holder  204  using the positioning stage  246 . For example, a portion of the light emitted by the first light source  502  (e.g., the light of the first variable frequency f 1  or the visible alignment laser) may reflect off of the surface of the liquid sample  206  and be detected by the detector  506  or a second detector (not shown) of the SFG microscope  501 . Alternatively, the detector  506  may detect the SFG signal. Based on a position or an intensity of the detected signal, the controller  232  controls the positioning stage  246  to align the liquid sample  206  with the convergence point of the spatially and temporally overlapped first and second light beams. 
       FIGS. 6A and 6B  show a flowchart according to one or more embodiments. The flowchart depicts a method for performing SFG spectroscopy that may be performed using the pressure cell  200  described above in reference to  FIGS. 2, 3, and 5 . In one or more embodiments, one or more of the steps shown in  FIGS. 6A and 6B  may be combined, omitted, repeated, and/or performed in a different order than the order shown in  FIGS. 6A and 6B . Accordingly, the scope of the present disclosure should not be considered limited to the specific arrangement of steps shown in  FIGS. 6A and 6B . 
     At  600 , a rock interface  207  is loaded into a liquid sample holder  204  disposed inside of a metal pressure chamber  202  that includes a base  208  and a removable lid  210 . The rock interface  207  may be a calcite rock sample or any other appropriate material that may simulate liquid/solid interactions or liquid/solid interfaces that occurring in a reservoir  102  ( FIG. 1 ). 
     At  602 , the removable lid  210  is sealed onto the base  208  to seal the liquid sample holder  204  in an interior of the metal pressure chamber  202 . The seal may be formed by screwing, clipping, mechanical fastening (e.g., with bolts, screws) the removable lid  210  onto the base  208 . However, the removable lid  210  may be sealed to the base  208  by any appropriate means that provides a seal to contain the pressure of the simulated reservoir environment. In one or more embodiments, a seal  212  (e.g., elastomeric O-ring, copper gasket, or other seal) may be disposed between the base  208  and the removable lid  210  to seal the metal pressure chamber  202 . 
     At  604 , a liquid sample  206  is flowed from an exterior of the metal pressure chamber  202 , through a sample inlet  216 , to the liquid sample holder  204 . In one or more embodiments, the liquid sample  206  may be a brine comprising a mixture of an aqueous phase and an organic phase that is flowed through a single sample inlet path  218 . The flow of the liquid sample  206  in the sample inlet path  218  may be generated by a sample pump  220 . 
     In another embodiment, the aqueous phase and organic phase of the liquid sample  206  may be separate liquids that are flowed into the liquid sample holder  204  by separate sample inlet paths  218   a ,  218   b . The relative proportions of the aqueous and organic phases introduced into the liquid sample holder  204  may be controlled by separate sample pumps  220   a ,  220   b  that are connected to the corresponding sample inlet paths  218   a ,  218   b.    
     At  606 , an ultrasonic stage  228  emulsifies the liquid sample  206 . In one or more embodiments including a mixture of an aqueous phase and an organic phase (e.g., a brine) as the liquid sample  206 , the ultrasonic stage  228  may sonicate the liquid sample  206  to emulsify the two phases. 
     At  608 , a heating stage  238  heats the liquid sample  206  to a simulated reservoir temperature. In one or more embodiments, the temperature of the liquid sample  206  is raised to approximately 90-100 C°. However, as discussed above, the present disclosure is not limited to this temperature range because conditions of a reservoir  102  may vary according to many parameters (e.g., depth, geographic location, rock composition). The temperature of the liquid sample  206  may be monitored by a thermocouple  244  that is connected to the liquid sample holder  204 . The thermocouple  244  may send temperature information to a temperature controller  242 , or alternatively a controller  232 , that sends power and control signals to the heating stage  238 . 
     At  610 , a chamber pump  230  connected to the interior of the metal pressure chamber  202  increases the pressure inside the metal pressure chamber  202  to a simulated reservoir pressure. In one or more embodiments, the pressure of the liquid sample  206  is raised to approximately 3000 psi. However, as discussed above, the present disclosure is not limited to this approximate pressure value because conditions of a reservoir  102  may vary according to many parameters (e.g., depth, geographic location, rock composition). The pressure of the interior of the metal pressure chamber  202  may be monitored by a pressure gauge  234 . The pressure gauge  234  may send pressure information to the controller  232  that sends power and control signals to the chamber pump  230 . Furthermore, the controller  232  may control a control valve  236  to seal the metal pressure chamber  202  from the chamber pump  230  or release pressure from the interior of the metal pressure chamber  202 . 
     At  612 , a surface of the liquid sample  206  is illuminated with light of a first variable frequency f 1  and light of a second frequency f 2  through a window  214  of the metal pressure chamber  202 . The incident light beams of the first and second frequencies f 1 , f 2  are spatially and temporally overlapped at the surface of the liquid sample  206  to generate an SFG signal (i.e., light of the third frequency f 3  that is the sum of the first and second frequencies f 1 , f 2 ). 
     In one or more embodiments, a positioning stage  246  may translate the surface of the liquid sample  206  to align the surface of the liquid sample  206  with the incident first and second light beams. The positioning stage  246  may automatically position the surface of the liquid sample  206  based on a reflected signal from the surface of the liquid sample  206  (e.g., alignment with the surface of the liquid sample  206  is achieved when the reflected signal exceeds a predetermined threshold or reaches a predetermined position on a detector  506 ). Alternatively, the positioning stage  246  may automatically position the surface of the liquid sample  206  based on an intensity of the generated SFG signal (e.g., alignment with the surface of the liquid sample  206  is achieved when the SFG signal is maximized or exceeds a predetermined threshold). In yet another embodiment, the positioning stage  246  may be controlled manually. 
     At  614 , the SFG signal comprising light of a third frequency f 3  is collected from the surface of the liquid sample  206  for analysis. 
     At  616 , the liquid sample  206  is flowed from the liquid sample holder  204 , through a sample outlet  222 , to the exterior of the metal pressure chamber  202 . In one or more embodiments, the liquid sample  206  that is removed from the metal pressure chamber may be replace by a new liquid sample  206  from the sample inlet path  218 . 
     In other words, in one or more embodiments, the composition of the liquid sample  206  may be altered in situ by flowing different solutions or different proportions of the aqueous phase and organic phase into the liquid sample holder  204  and removing the liquid sample  206  that has already been studied. Thus, the liquid sample  206  may be characterized in both static and dynamic reservoir compositions (e.g., stable live oil compositions or dynamically changing compositions that may model displacement of hydrocarbons by an injection fluid). 
     In one or more embodiments, In one or more embodiments, the heating stage  238  and the chamber pump  230  may dynamically change the temperature and pressure inside the metal pressure chamber  202  during acquisition of the SFG signal. For example, the controller  232  may ramp the temperature or pressure to different values in response to data collected from the pressure gauge  234 , the control valve  236 , the thermocouple  244 , the detector  706 , or any combination thereof. Thus, the liquid sample  206  may be characterized in both static and dynamic reservoir environments (e.g., stable temperature and pressure conditions or dynamically changing temperature and/or pressure conditions). 
     In one or more embodiments, the first variable frequency f 1  may be continuously or discretely changed to obtain a spectrum of SFG signals from the liquid sample  206 . In another embodiment, first variable frequency f 1  may be a spectrally broadband frequency range that includes a plurality of frequencies. Accordingly, a spectrum of SFG signals from the liquid sample  206  may be obtain at one time. 
     Software instructions in the form of computer readable program code to perform embodiments of the present disclosure may be stored, in whole or in part, temporarily or permanently, on a non-transitory computer readable medium such as a CD, DVD, storage device, a diskette, a tape, flash memory, physical memory, or any other computer readable storage medium. Specifically, the software instructions may correspond to computer readable program code that when executed by a processor(s), is configured to perform embodiments disclosed herein. 
     One or more of the embodiments disclosed herein may have one or more of the following advantages and improvements over conventional SFG spectroscopy techniques: simulating reservoir conditions (e.g., high pressure, high temperature environments); simulating reservoir interactions for study in a controlled environment; SFG spectroscopy under static and dynamic temperature and/or pressure conditions; SFG spectroscopy with dynamic sample compositions to analyze more accurate liquid/liquid and liquid/solid interfaces that occur in hydrocarbon reservoirs. One or more of the above advantages may improve a user&#39;s understanding of the chemical and molecular structures and interfaces that occur in a reservoir and improve the effectiveness of hydrocarbon recovery techniques. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the disclosure should be limited only by the attached claims.