Experimental device and method for measuring heavy oil saturation based on multi-physical field coupling

Abstract

This invention provides an experimental apparatus and method for measuring heavy oil saturation based on multiphysics coupling, belonging to the field of oil and gas field development. It includes a reservoir simulation system, a reservoir development system, and a remaining oil content measurement and control system. The reservoir simulation system comprises a three-dimensional sand-filled model shell, with the shell filled with a porous medium. The shell is connected to the formation pressure system via pipelines, and an external model communication system connects to the shell. The reservoir development system includes an injection supply system, a metering and control system, and a well network system. The remaining oil content measurement and control system includes a pressure-conducting detection system, a conductivity detection system, a thermal conductivity detection system, and a multiphysics coupling saturation measurement system. This invention, employing the aforementioned experimental apparatus and method for measuring heavy oil saturation based on multiphysics coupling, satisfies the requirement for quantitative evaluation of oil saturation during heavy oil reservoir development simulation experiments.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development, and in particular to an experimental apparatus and method for measuring the saturation of heavy oil based on multi-physics coupling. Background Technology

[0002] Physical simulation development experiments for heavy oil are a key research method for the development of heavy oil reservoirs. For conventional heavy oil thermal recovery development methods such as huff and puff, displacement, and gravity-assisted gravity drainage, the simulation experimental devices mainly include one-dimensional sand-filled pipe models, two-dimensional sand-filled plate models, and three-dimensional sand-filled body models. These models simulate the porous media characteristics of the reservoir by filling it with quartz sand or natural cores.

[0003] Currently, common methods for testing oil saturation in the aforementioned sand-filled models include direct sampling, external auxiliary detection, and indirect probe testing. Direct sampling is primarily used for one-dimensional sand-filled models, where saturation is identified by weighing samples taken along the tubing. However, each sampling significantly interferes with the oil-water distribution within the porous medium, leading to substantial fluid loss. External auxiliary detection is suitable for two-dimensional sand-filled models and small-sized core models, such as using light transmittance combined with Beer-Lambert's law to determine oil saturation in two-dimensional models. However, this method becomes unusable when the model thickens, causing decreased light transmittance. Monitoring the saturation evolution of one-dimensional small-sized core models using CT and NMR methods suffers from limitations such as limited monitoring range and poor adaptability to different model sizes.

[0004] Indirect probe testing is commonly used in three-dimensional sand-filled models and large-scale reservoir simulation devices. The invention patent CN01123944.1, "Method and Probe for Measuring Oil Saturation," uses a conductive probe to test the oil saturation of low-viscosity oils. An external injection agent can easily peel the light oil away from the probe, thus stimulating a change in conductivity and testing the oil saturation. However, heavy oils, due to their high asphaltenes and gum content, form a thick oil adhesion layer on the probe surface, hindering the probe's ability to test conductivity. To overcome the influence of heavy oil adhesion, temperature-sensitive probes are used to test residual oil saturation. However, large-scale temperature monitoring results in low measurement accuracy in laboratory simulation devices, making it impossible to accurately characterize the oil saturation within the advantageous water-drive channels during development.

[0005] In summary, while there are numerous methods for testing oil saturation, a precise quantitative identification method for heavy oil saturation is incomplete. Previous saturation identification methods primarily referenced the conductivity coefficient of low-viscosity, low-adsorption crude oil or assessed the oil-water distribution over a wide range, which is insufficient for the precise identification of heavy oil saturation. Furthermore, limitations in dynamically acquired data result in a lack of continuous data on saturation changes during development, necessitating the development of a method that correlates saturation changes throughout the entire process after different development phases. Simultaneously, accurately characterizing saturation by region and time period, and classifying the resulting potential mining areas, presents significant challenges, requiring focused delineation of potential mining areas after saturation identification. Summary of the Invention

[0006] The purpose of this invention is to provide an experimental device and method for measuring the saturation of heavy oil based on multi-physics coupling. This invention solves the problems of existing oil saturation testing methods in terms of accurate quantitative identification of heavy oil, lack of saturation change data during development, and difficulty in characterizing saturation by region and time period and classifying potential areas.

[0007] To achieve the above objectives, the present invention provides an experimental apparatus for measuring the saturation of heavy oil based on multiphysics coupling. The apparatus includes a reservoir simulation system, a reservoir development system, and a remaining oil content measurement and control system.

[0008] The reservoir simulation system includes a three-dimensional sand-filled model shell, the interior of which is filled with a porous medium, the interior of which is connected to the formation pressure system via pipelines, and the exterior of which is connected to a model communication system.

[0009] The reservoir development system includes an injection supply system, a metering and control system, and a well network system. The output end of the injection supply system is connected to the metering and control system via a pipeline, and the injection supply system is connected to the well network system via a second six-way valve.

[0010] The remaining oil content measurement and control system includes a pressure detection system, a conductivity detection system, a thermal conductivity detection system, and a multi-physics field coupled saturation measurement.

[0011] Preferably, the supply system includes a dual-cylinder plunger displacement pump, a liquid supply intermediate container, a displacement gas cylinder, a gas flow controller, a mixed displacement system generator, and a steam generator. The output end of the dual-cylinder plunger displacement pump is connected to the liquid supply intermediate container via a three-way valve. The output end of the liquid supply intermediate container is connected to the inlet of a first six-way valve. The output end of the displacement gas cylinder is connected to the gas flow controller. The output end of the gas flow controller is connected to the other inlet of the first six-way valve. The input end of the mixed displacement system generator is connected to the outlet of the first six-way valve. The output end of the mixed displacement system generator is connected to the inlet of a second six-way valve. The output end of the steam generator is connected to the other inlet of the second six-way valve. The other outlet of the first six-way valve is connected to the input end of the second six-way valve.

[0012] Preferably, the measurement and control system includes a first measuring cylinder, a first electronic balance, a second measuring cylinder, and a second electronic balance. The first measuring cylinder is connected to the outlet of a second six-way valve. The first electronic balance is installed at the lower end of the first measuring cylinder. The output end of the reservoir simulation system is connected to the second measuring cylinder through a back pressure valve. The second electronic balance is installed at the lower end of the second measuring cylinder.

[0013] Preferably, the well network system includes a wellbore structure and a sand-proof spring structure. The wellbore structure includes a wellbore mechanism and a well location fixing mechanism. The well location fixing mechanism enables the exchange of materials between external fluids and the reservoir simulation system.

[0014] Preferably, the pressure detection system includes a pressure detection array and an electronic pressure gauge; the electrical conductivity detection system includes a high-precision DC power supply, an electric field controller, and a potential detection array; and the thermal conductivity detection system includes a base plate heating device, a temperature detection array, and a heat flux density measuring device.

[0015] A method for measuring heavy oil saturation based on multiphysics coupling includes the following steps:

[0016] S1. Construct a reservoir physical model and select a suitable sand-proof spring structure based on the diameter of the porous medium filling material and the external fluid impact force.

[0017] S2. Multi-parameter synchronous acquisition: The pressure conductivity coefficient, electrical conductivity coefficient, and thermal conductivity coefficient are acquired in the pressure conductivity detection system, electrical conductivity detection system, and thermal conductivity detection system, respectively.

[0018] S3. Multiphysics field coupling calculation of heavy oil saturation is based on the changes in physical properties derived from three physical fields: pressure conductivity, electrical conductivity, and thermal conductivity. The identification of saturation is corrected and supplemented by pressure conductivity, electrical conductivity, and thermal conductivity.

[0019] S4. Verify the saturation of heavy oil, calculate the mass deviation between the experimental oil production and the oil production calculated using the saturation. If the calculated mass deviation is within the allowable error range, the calculated value is considered to conform to the law of conservation of mass and has high accuracy.

[0020] Preferably, the spring selection expression for the sand-resistant spring structure is:

[0021]

[0022] Where l0 is the spring pitch, d s θ is the diameter of the spring wire, θ is the angle between the main current direction and the spring axis, k is the radial stiffness coefficient of the spring, n is the number of coils in the spring, and D is the diameter of the gravel.

[0023] Preferably, the expression for the pressure conductivity coefficient is:

[0024]

[0025] Where k1 and k2 are undetermined coefficients of pressure conductivity, φ is the porosity of the porous medium, K is the permeability, and S is the undetermined coefficient of pressure conductivity. o c represents oil saturation. t The core's overall compressibility coefficient;

[0026] The expression for conductivity is:

[0027]

[0028] Where k3, k4, and k5 are all undetermined coefficients related to the conductivity properties of saturated fluid porous media, R w The resistivity of the formation water;

[0029] The expression for thermal conductivity is:

[0030]

[0031] Among them, c p ρ is the specific heat capacity, Q is the internal heat source, ρ is the density, T is the temperature, t is the time, and λ is the thermal conductivity coefficient.

[0032] Preferably, the expression for calculating oil production based on saturation is:

[0033]

[0034] Wherein, ρ o S is the density of crude oil. oi V represents oil saturation. i,j,k This represents the apparent volume of the porous medium within the model.

[0035] Therefore, the present invention employs the above-described experimental apparatus and method for measuring heavy oil saturation based on multi-physics coupling, and the technical effects are as follows:

[0036] 1. Strong structural stability and reusable disassembly: The sand-filled model shell is made of heat-resistant, pressure-resistant and insulating polyetheretherketone material, which can maintain the integrity and stability of the model under high temperature and high pressure environment. The need for reusability is taken into account, so that the experimental device can be used multiple times and the experimental cost is reduced.

[0037] 2. Comprehensive Heavy Oil Saturation Measurement Experimental Device: A comprehensive measurement system was constructed that includes multiple physical fields such as flow field, electric field and temperature field. It can simultaneously acquire parameters of multiple physical fields and achieve efficient and accurate measurement of heavy oil saturation through coupling analysis of multiple physical fields.

[0038] 3. Applicable to heavy oil reservoirs using thermal development methods: It can accurately measure the saturation of heavy oil and the effective operating distance of the injected thermal fluid during thermal recovery, providing important data support for the optimization of thermal development methods. Attached Figure Description

[0039] Figure 1 This is a logic flowchart of the experimental apparatus and method for measuring heavy oil saturation based on multi-physics field coupling of the present invention.

[0040] Figure 2 A schematic diagram showing the connection between the reservoir simulation system and the reservoir development system;

[0041] Figure 3 Three-dimensional views of a sand-filled shell in a reservoir simulation system;

[0042] Figure 4 A schematic diagram illustrating the logic for calculating saturation through inversion of various physical fields;

[0043] Figure 5 To generate an oil saturation distribution field map for pressure field inversion;

[0044] Figure 6 To generate an oil saturation distribution field map for electric field inversion;

[0045] Figure 7 To generate an oil saturation distribution field map for temperature field inversion;

[0046] Figure 8 To generate an oil saturation distribution field map for multi-physics field collaborative inversion.

[0047] Figure Labels

[0048] 10. Dual-cylinder plunger displacement pump; 11. Three-way valve for liquid distribution; 12. Intermediate liquid supply container; 13. Displacement gas cylinder; 14. Gas flow meter; 15. First six-way valve; 16. Mixed displacement system generator; 17. Steam generator; 18. Second six-way valve; 19. First measuring cylinder; 20. First electronic balance; 21. Pressure detection array; 22. Potential detection array; 23. Temperature detection array; 24. Three-dimensional sand-filled model; 25. Back pressure valve; 26. Single-cylinder plunger confining pressure pump; 27. Second measuring cylinder; 28. Second electronic balance; 29. ​​Data processing computer. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0050] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0051] Example 1

[0052] like Figure 1 As shown, this invention provides an experimental device and method for measuring heavy oil saturation based on multi-physics field coupling. It is a comprehensive reservoir simulation, development and evaluation method based on reservoir simulation system and its associated reservoir development system, with remaining oil content measurement and control system as the core and heavy oil saturation identification process as an extension.

[0053] like Figures 2-3 As shown, the device includes a reservoir simulation system, a reservoir development system, and a remaining oil content monitoring and control system. The reservoir simulation system includes a three-dimensional sand-filled model shell, a porous medium filling material, a formation pressure system, and a model communication system.

[0054] The three-dimensional sand-filled shell is made of polyetheretherketone (PEEK) material, which can maintain good mechanical properties and dimensional stability at high temperatures. It can adapt to the requirements of different temperature conditions in reservoir development physical simulation. The tensile strength of this material can reach more than 90 MPa and the flexural strength can reach 150 MPa. It can maintain the integrity and stability of the model under high pressure and is not easily deformed or damaged.

[0055] The porous media filler consists of a quartz particle skeleton and clay mineral interstitial material. The clay minerals need to adhere to the surface of the quartz sand. The porous media filler mainly relies on an ultrasonic oscillating suspender and NaOH alkaline solution to promote the mixing of clay minerals and quartz particles.

[0056] The formation pressure system consists of a back pressure valve 25 and a single-cylinder plunger confining pressure pump 26. The single-cylinder plunger confining pressure pump 26 supplies distilled water to the back pressure valve 25 to maintain a certain level of formation start-up pressure and prevent fluid inside the reservoir simulation system from easily leaking out from the output end.

[0057] The model communication system consists of an internal through-hole and an external fixed valve. The reserved through-hole can provide a communication channel between the reservoir system and the outside world for injection and production wells and saturation monitoring and control systems, while preventing quality loss inside the reservoir.

[0058] The supply system includes a dual-cylinder plunger displacement pump 10, a liquid supply intermediate container 12, a displacement gas cylinder 13, a gas flow controller 14, a mixing displacement system generator 16, and a steam generator 17. The output of the dual-cylinder plunger displacement pump 10 is connected to the liquid supply intermediate container 12 via a three-way valve 11. The output of the liquid supply intermediate container 12 is connected to the inlet of a first six-way valve 15, supplying injection energy to each injected component. The output of the displacement gas cylinder 13 is connected to the gas flow controller 14, and the output of the gas flow controller 14 is connected to another inlet of the first six-way valve 15, injecting gas into the reservoir simulation system at a constant speed and pressure. The input of the mixing displacement system generator 16 is connected to the outlet of the first six-way valve 15, and the output of the mixing displacement system generator 16 is connected to the inlet of a second six-way valve 18, generating a two-phase mixed fluid such as emulsion / foam in a porous medium and then injecting it into the reservoir simulation system. The output of the steam generator 17 is connected to the other inlet of the second six-way valve 18, directly injecting high-temperature steam into the reservoir simulation system. The other outlet of the first six-way valve 15 is connected to the input of the second six-way valve 18, directly injecting the component fluids into the reservoir simulation system.

[0059] The measurement and control system includes a first measuring cylinder 19, a first electronic balance 20, a second measuring cylinder 27, and a second electronic balance 28. The first measuring cylinder 19 is connected to the outlet of the second six-way valve 18. The lower end of the first measuring cylinder 19 is equipped with a first electronic balance 20 with a base heating function to simulate the fluid production changes during the development of heavy oil reservoirs or the backflow of fluids from other nearby fluid input ends. The output end of the reservoir simulation system is connected to the second measuring cylinder 27 through a back pressure valve 25. The lower end of the second measuring cylinder 27 is equipped with a second electronic balance 28 to simulate the fluid production changes during the development of heavy oil reservoirs or the displacement of fluids from other fluid input ends.

[0060] The well network system includes different types of wellbore structures and sand-control spring structures, and designs and arranges the distribution of injection and production wells according to various well layout structures, such as the five-point method, seven-point method, or nine-point method well network. The wellbore structure is mainly divided into the wellbore mechanism and the well location fixing mechanism. The well location fixing mechanism is a threaded fastening structure, which is tightly fitted into the in-shell through-type wellbore. This branch line aims to achieve material exchange between the external fluid and the reservoir simulation system. The selection of the sand-control spring structure needs to consider the influence of the particle size of the porous media filler and the impact force generated by the injected fluid. The spring selection expression for the sand-control spring structure is:

[0061]

[0062] Among them, l0 is the pitch of the spring, d s is the wire diameter of the spring, θ is the angle between the main streamline direction and the spring axis, k is the radial stiffness coefficient of the spring, n is the number of coils of the spring, and D is the diameter of the sand grains.

[0063] When the spring is compressed by an external force F, according to Hooke's law F = kx, the wire diameter of the spring can be expressed as d s , the compression amount of the spring spacing is x, the number of coils of the spring is n, and the actual interval l between the coils after the spring is compressed can be expressed as:

[0064] <L

[0065] To achieve the purpose of effective sand control, it is required that l < D, where D is the diameter of the sand grains. Selecting the radial stiffness coefficient k and the initial interval l0 of the spring can, to a certain extent, ensure that even in the case of lateral impact of rock particles, the sand control requirements can still be met.

[0066] The remaining oil content measurement and control system includes a pressure conduction detection system, a conductivity detection system, a heat conduction detection system, and the determination of multi-physical field coupling saturation.

[0067] The pressure conduction detection system includes a pressure detection array 21 and an electronic pressure gauge, which can record pressure data in real time. The injection supply system is adjusted to supply fluid for developing heavy oil. Pressure fluctuations are obtained through the pressure detection array, and the pressure conduction coefficient is calculated based on the diffusion equation of pressure propagation:

[0068]

[0069] The discretization process of the above diffusion equation:

[0070]

[0071] The pressure conduction coefficient of each phase fluid in the porous medium is pre-determined by using a prefabricated small-size three-dimensional sand-packed model 24 of the saturation water-phase fluid to measure the pressure conduction coefficient when the water-phase fluid is saturated, and then the small-size three-dimensional sand-packed model 24 is injected with oil-water two phases in equal proportion until stable liquid production to measure the pressure conduction coefficient at different saturations, and a correlation function χ = g(S o ) of the pressure conduction coefficient - oil saturation is constructed. Under the combined influence of the porosity φ and permeability K in the porous medium, the correction formula of the pressure conduction coefficient in the porous medium can be expressed as:

[0072]

[0073] Among them, k1 and k2 are undetermined coefficients of pressure conductivity, which need to be generated by data fitting with small-scale three-dimensional sand-filled model experiments; φ is the porosity in the porous medium, K is the permeability, S0 is the oil saturation, and ct is the core comprehensive compressibility coefficient.

[0074] The conductivity detection system comprises a high-precision DC power supply, an electric field controller, and a potential detection array 22. It can determine the oil saturation field map based on the electric field using a conductivity coefficient interpolation algorithm. The high-precision DC power supply provides a stable, adjustable voltage with an output voltage range of 0–100V and an accuracy of 0.1V. The electric field controller can precisely control the magnitude and direction of the DC power supply output voltage according to measurement requirements, forming a uniform or specifically distributed electric field within the sand-filled model. The electrodes of the potential detection array 22 are cylindrical, made of a corrosion-resistant, highly conductive platinum-iridium alloy. These electrodes are installed on the sides and bottom of the three-dimensional sand-filled shell through a through-hole within the shell, forming a three-dimensional electrode array. The electrodes are connected to an external circuit via wires for measuring voltage signals.

[0075] The conductivity interpolation algorithm for determining the oil saturation field map based on the electric field involves applying current to different electrode pairs using an electrode array system and measuring the voltage between the corresponding electrode pairs. Based on the reciprocal relationship between resistivity and conductivity, the conductivity can be expressed as:

[0076]

[0077] Where I is the current, S is the contact area between the electrode and the porous medium, U is the voltage, and l is the electrode spacing.

[0078] The number of conductivity coefficients obtained is limited by the number of electrode arrays, and only discrete data points can be obtained. The measurement points of eight adjacent electrodes of the micro-grid unit in the sand-filled model are calculated. Based on the coordinates and conductivity values ​​of these eight points, the conductivity coefficient σ(x,y,z) of the grid unit is calculated using the trilinear interpolation formula. Color and transparency mapping are set according to the conductivity coefficient values ​​to form a conductivity coefficient distribution map in the three-dimensional sand-filled model.

[0079] The oil saturation field map based on the electric field is established based on the differences in conductivity of oil, gas, and water, and the correspondence between conductivity coefficient and fluid type: under certain experimental conditions, the region with conductivity coefficient greater than σ1 can be identified as water, the region with conductivity coefficient less than σ2 (σ2<σ1) can be identified as oil, and the region with conductivity coefficient close to zero can be identified as gas. Finally, based on the above correspondence between conductivity coefficient and fluid type, the generated conductivity coefficient distribution map is divided into oil saturation values.

[0080] The numerical classification of oil saturation in porous media is based on the Archie formula. Under the combined influence of porosity φ and permeability K in porous media, the modified form of conductivity in porous media can be expressed as:

[0081]

[0082] Where k3, k4, and k5 are all undetermined coefficients related to the conductivity properties of saturated fluid porous media, R w The resistivity of the formation water.

[0083] The thermal conductivity detection system includes a base plate heating device, a temperature detection array 23, and a heat flux density measuring device.

[0084] The temperature detection array 23 uses a distributed temperature-sensitive fiber optic temperature sensor, which uses the backscattering Raman effect of light in the fiber to achieve temperature measurement. The temperature measurement accuracy can reach ±0.2℃ and the spatial resolution can reach 0.5m. The fiber optics are laid in a grid pattern inside the three-dimensional sand-filled model body, on the four sides, the bottom, and the planes at different heights inside.

[0085] The base heating device consists of a heating base plate, a temperature controller, and an insulation layer. The heating base plate is made of 10mm thick high-temperature resistant stainless steel, with resistance heating wires evenly embedded inside to provide stable heat output. The heating base plate is installed on the bottom surface of the 3D sand-filled model 24, fitting tightly against the model to ensure effective heat transfer to its interior. The temperature controller monitors the temperature in real time via a temperature sensor mounted on the heating base plate and automatically adjusts the heating power according to the set value. The insulation layer, made of high-temperature resistant and heat-insulating ceramic fiber material, is 20mm thick and laid under and around the heating base plate to prevent heat loss and improve heating efficiency.

[0086] The heat flux density measuring device consists of heat flux density meters based on thin-film sensor technology installed on the four sides and the outer bottom surface of the three-dimensional sand-filled model 24, and connected to the data processing computer 29 via data cables.

[0087] The oil saturation field diagram based on the temperature field is derived from the differences in heat transfer properties such as thermal conductivity and specific heat capacity of oil, gas, and water. The heat transfer properties of different regions are directly related to the multiphase saturation of that region. Based on mixture theory, the thermal conductivity λ of the mixed fluid can be established. mix and specific heat capacity c mix With oil saturation S o The relationship between them can be obtained using the weighted average method:

[0088] λ mix =S o λ o +S w λ w +Ss λ s ;

[0089] c mix =S o c o +S w c w +S s c s ;

[0090] Where, λ o , λ w , λ s The thermal conductivity values ​​are, in order, those of the oil phase, water phase, and solid phase.

[0091] Based on Fourier's law of thermal conductivity, the heat conduction equation within the three-dimensional sand-filled model is established as follows:

[0092]

[0093] Among them, c p ρ is the specific heat capacity, Q is the internal heat source, ρ is the density, T is the temperature, t is the time, and λ is the thermal conductivity coefficient.

[0094] After the base heating device is turned on, the entire model is heated from the bottom. The real-time temperature data of each area after heating is obtained by the temperature-sensitive fiber optic temperature sensor array. The thermal conductivity at each point is calculated according to the Fourier heat conduction equation mentioned above. The thermal conductivity λ(x,y,z) of the micro-grid unit in the three-dimensional sand-filled model 24 is calculated by the trilinear interpolation formula using the temperature measurement data of eight adjacent micro-grid units in the three-dimensional sand-filled model 24. The color and transparency mapping are set according to the heat transfer coefficient value to form a thermal conductivity distribution map in the three-dimensional sand-filled model.

[0095] The thermal conductivity of each phase fluid in the porous medium was determined by pre-measuring the heat transfer coefficient at an oil saturation of 0 using a prefabricated small-scale three-dimensional sand-filled model 24 of the saturated aqueous phase fluid. Then, oil and water phases were injected into the small-scale three-dimensional sand-filled model 24 in equal proportions until stable liquid discharge, at which point the thermal conductivity at different saturation levels was measured. A correlation function λ = f(S) was constructed to determine the correlation between thermal conductivity and oil saturation. o ).

[0096] The heavy oil saturation identification process is based on the changes in physical properties derived from three physical fields: pressure conductivity, electrical conductivity, and thermal conductivity. It uses pressure conductivity, electrical conductivity, and thermal conductivity to correct and supplement the identification of saturation.

[0097] Within the pressure conductivity distribution field, regions with significantly higher pressure conductivity indicate that the fluid flow resistance is significantly lower and cannot weaken the injection pressure. Therefore, this region can be identified as a strong spillover development area with high water phase saturation and a large space occupied by the water phase fluid. The difference in conductivity after applying an electric field is more obvious. Therefore, the saturation identification based on the pressure field and electric field can be carried out in the low oil saturation region (i.e., the "spreadover region").

[0098] The coordinated identification of oil saturation using pressure and electric fields is considered a good match when the difference between the single-point saturation values ​​obtained from the inversion of the pressure coefficient and conductivity coefficient within the high-efficiency sweep area is less than 5%. The oil saturation value at this point can then be calculated using the average value. However, when the oil saturation measured by the pressure coefficient is lower than that measured by the conductivity coefficient, and the difference exceeds 5%, the electrode probe at that point is largely surrounded by heavy oil, making it impossible to accurately measure the surrounding oil saturation. In this case, the oil saturation value obtained from the pressure coefficient inversion is more accurate.

[0099] The calculation of oil saturation is dominated by the pressure conductivity coefficient, while the conductivity coefficient is used to assist in the calculation. It is necessary to determine the weight coefficients of the two. The first weight ω1 of the pressure conductivity coefficient can be preset to 0.7 to 0.8, and the weight ω2 of the conductivity coefficient can be preset to 0.2 to 0.3. The small-scale three-dimensional sand-filled model 24 is used for verification first. By continuously adjusting the weight coefficients, the error is minimized.

[0100] When the oil saturation measured by the pressure conductivity coefficient is higher than that measured by the conductivity coefficient and the difference between the two exceeds 5%, the electrode probe at that point has many continuous initial saturated water channels in the oil saturation process. There is no heavy oil adhering to its surface, and its conductivity is likely to greatly exceed the pressure conductivity performance. The oil saturation in this area can be accurately characterized in the microporous channel. However, if the effective distance is slightly increased, the oil saturation value fluctuates greatly. The saturation value corresponding to the intersection of the curves of the pressure conductivity coefficient expression and the conductivity coefficient expression is the oil saturation value at each point.

[0101] In regions where the oil saturation obtained from conductivity inversion is significantly low, the electrode probe is surrounded by highly adhesive heavy oil, resulting in high resistance and an inability to accurately reflect changes in the surrounding flow field. Therefore, in regions with insufficient conductivity, the measurement of oil saturation based on the electric field should be ignored. Coordinated identification based on pressure and temperature fields can be conducted in high oil saturation regions (i.e., "unaffected areas") where development effects are weak.

[0102] The coordinated identification of oil saturation using pressure and temperature fields allows for a good match between two fields when the difference in single-point saturation values ​​obtained from pressure and thermal conductivity inversions within the high-efficiency sweep area is less than 5%. In this case, the oil saturation value at that point can be calculated using the average value. However, when the oil saturation measured by the pressure coefficient is lower than that measured by the thermal conductivity, and the difference exceeds 5%, the pressure-sensitive probe at that point detects a narrow, water-driven dominant channel. Due to the narrowness of this channel, the surrounding oil saturation values ​​fluctuate significantly, and the accuracy of temperature measurement is insufficient to effectively cover this. In this situation, the oil saturation value obtained from the pressure coefficient inversion is more accurate.

[0103] The calculation of oil saturation is dominated by the pressure conductivity coefficient, while the thermal conductivity coefficient is used to assist in the calculation. It is necessary to determine the weight coefficients of the two. The second weight ω3 of the pressure conductivity coefficient can be preset to 0.5 to 0.7, and the weight ω4 of the thermal conductivity coefficient can be preset to 0.3 to 0.5. The small-size three-dimensional sand-filled model 24 is used for verification first. By continuously adjusting the weight coefficients, the error is minimized.

[0104] When the oil saturation measured by the pressure conductivity coefficient is higher than that measured by the thermal conductivity coefficient and the difference between the two exceeds 5%, less of the heavy oil around the pressure-sensitive probe is replaced by the injected fluid, and the pressure fluctuation is small, so it cannot accurately reflect the change in oil saturation on its own. Therefore, the saturation value corresponding to the intersection of the curves of the pressure conductivity coefficient and the thermal conductivity coefficient is the oil saturation value at each point.

[0105] The pressure (or "flow field"), electric field, and temperature fields applied in the affected and unaffected regions are ultimately plotted to create an oil saturation field map to represent the zoning of remaining oil. By multiplying the volume of each microgrid cell by its saturation, the oil saturation changes within each microgrid can be summarized as the oil phase mass change within the porous medium using the mass conservation method, expressed as:

[0106]

[0107] Where, ρ o S is the density of crude oil. oi V represents oil saturation. i,j,k This represents the apparent volume of the porous medium within the model.

[0108] The logic for calculating saturation by inverting each physical field is as follows: Figure 4 As shown, the experimental oil production m recorded during the development process... oe The oil production m calculated using saturation as described above oc By comparison, if the calculated mass deviation is within the allowable error range (less than 5%), the calculated value is considered to conform to the law of conservation of mass and has high accuracy; if the calculated mass deviation exceeds the allowable error range, the four weighting coefficients of pressure conductivity, electrical conductivity, and thermal conductivity are readjusted to verify the measured oil production m. oe.

[0109] Using a three-dimensional reservoir simulation device and its development system as the equipment basis for identifying remaining oil saturation, according to Figure 2 The devices are connected in sequence as shown. Inside the three-dimensional sand-filled model 24, a completion wellbore with a screen, a pressure detection array 21, a potential detection array 22, and a temperature detection array 23 are installed sequentially. A bottom plate heating device is evenly laid at the bottom of the model. To adapt to the application of heavy oil thermal recovery, two parallel vertical wells are set in the middle area of ​​the top of the three-dimensional sand-filled model 24.

[0110] The walls of the three-dimensional sand-filled model 24 were covered with clay and ceramic sheets for sealing and insulation. Subsequently, the mass of the pre-prepared mixture of quartz particle framework and clay mineral filler was measured as m. s After being poured into a container filled with heavy oil and thoroughly mixed, oil sands are formed. The solid particles form the rock framework, and their mass can be measured as the total mass m of the oil sands. t The oil sand was filled into a three-dimensional model with heat preservation and monitoring functions.

[0111] A single-cylinder plunger-type confining pressure pump 26 was used to increase the pressure of the back pressure valve 25 to 3.5 MPa. Subsequently, an injection supply system was used to continue saturating the three-dimensional model with heavy oil until the fluid stabilized and oil production was achieved. During this process, the permeability was tested to be 1572 mD. The mass of heavy oil in the oil sand was calculated and divided by its density to obtain the oil-bearing volume V. o The porosity φ is calculated by dividing the oil-bearing volume by the total volume of the reservoir's internal filling space. The volume of the oil phase fluid is 39763 mL, resulting in a porosity of approximately 0.32 and a saturated oil mass of 36582 g. After saturation, the oil is aged in a constant temperature chamber for at least 144 hours to promote pressure equilibrium within the reservoir.

[0112] During the injection of 0.5 PV of 260℃ steam into the reservoir from the injection wellhead, the oil saturation inside the steam cavity undergoes significant changes after full development. During development, pressure readings inside the reservoir are detected by a pressure-sensitive probe array, and the pressure conductivity coefficient is calculated using the diffusion equation of pressure propagation. Then, pressure discretization is performed to obtain a distribution field map of the pressure conductivity coefficient. Finally, a relationship between the pressure conductivity coefficient and oil saturation is constructed by fitting data from a small-scale three-dimensional sand-filled model (24 experiments).

[0113]

[0114] In the formula, K, μ, c t These are expressed as permeability, viscosity, and overall compressibility, respectively. Using the above formula, the original pressure conductivity distribution field diagram can be transformed into an oil saturation field diagram based on pressure conductivity, as shown below. Figure 5 As shown.

[0115] After connecting a high-precision DC power supply and an electric field controller to the simulated oil reservoir, the magnitude and direction of the voltage output are controlled. During development, the conductivity coefficient is obtained by measuring the voltage between corresponding electrode pairs. Then, interpolation is performed on the discrete data points of the conductivity coefficient to obtain a conductivity coefficient distribution field map. Since the conductivity coefficients of water, oil, and gas decrease sequentially within the model, a relationship between conductivity coefficient and oil saturation is constructed with reference to the Archie formula:

[0116]

[0117] In the formula, R w Let be the resistivity of the formation water. Using the above formula, the original conductivity distribution field map can be transformed into an oil saturation field map based on conductivity, such as... Figure 6 As shown.

[0118] After the steam displacement stage is completed, the bottom of the 3D sand-filled model 24 is heated using a heating base plate and temperature controller, and temperature changes are monitored using a temperature-sensitive fiber optic temperature sensor array. After development is complete, the base plate heating device is activated to heat the entire model from the bottom. Real-time temperature data for each region after heating is obtained using the temperature-sensitive fiber optic temperature sensor array, and the thermal conductivity at each point is calculated based on the Fourier heat conduction equation.

[0119]

[0120] In the formula, λ and c are the thermal conductivity and specific heat capacity, respectively.

[0121] The thermal conductivity and specific heat capacity at each node are caused by the differences in heat transfer properties such as thermal conductivity and specific heat capacity of oil, gas, and water, and can be expressed as:

[0122] λ mix =S o λ o +S w λ w +S s λ s ;

[0123] c mix =S o c o +S w c w +S s c s ;

[0124] Using temperature measurements from eight adjacent microgrid cells in the 3D sand-filled model 24, the thermal conductivity λ(x,y,z) of the grid cell was calculated using a trilinear interpolation formula. Color and transparency mapping were then applied based on the thermal conductivity value to create a thermal conductivity distribution map within the 3D sand-filled model 24. Data from experiments using a small-scale 3D sand-filled model were used to construct a relationship function between the pressure conductivity and oil saturation.

[0125]

[0126] Using the above formula, the original thermal conductivity distribution field diagram can be transformed into an oil saturation field diagram based on thermal conductivity, such as... Figure 7 As shown.

[0127] The oil saturation fields derived from pressure conduction, electrical conduction, and heat transfer exhibit significant differences, reflecting the varying sensitivity of each physical field to the oil saturation value. Therefore, in regions where the measured saturation differs considerably across the three physical fields, it is necessary to consider the reasons for these measurement discrepancies and make targeted corrections to the measured oil saturation. The detailed correction process is as follows:

[0128] In areas with significantly higher strong waves and development zones, characterized by both conductivity and pressure conductivity, steam condensate occupies a larger portion of the pore space, resulting in lower oil saturation values. The oil saturation can be determined jointly by the inversion values ​​from conductivity and pressure conductivity. When the difference between the single-point saturation values ​​obtained from the inversion of pressure and conductivity is less than 5%, the two values ​​are considered to match, and the oil saturation value at that point can be calculated using the average. When the oil saturation measured by the pressure conductivity is lower than that measured by the conductivity, and the difference exceeds 5%, the electrode probe at that point is mostly surrounded by heavy oil, making it impossible to accurately measure the surrounding oil saturation. In this case, the oil saturation inverted by the pressure conductivity is more accurate. In regions where the oil saturation inverted by the pressure conductivity is significantly lower than that inverted by the conductivity, the first weight ω1 of the pressure conductivity can be preset to 0.7–0.8, and the weight ω2 of the conductivity can be preset to 0.2–0.3. Using a small ruler… The three-dimensional sand-filled model was first verified. After multiple trials, it was found that when ω1 and ω2 were 0.75 and 0.25 respectively, the average error of the inversion result was the smallest, which can be used as the optimal weight value. In the region where the oil saturation inverted by the pressure conductivity coefficient is significantly higher than that inverted by the conductivity coefficient, the electrode probe at this point has many continuous initial saturated water channels in the oil saturation process. There is no heavy oil adhering to its surface, and its conductivity is likely to significantly exceed the pressure conductivity performance. The oil saturation in this region can be accurately characterized in the microporous channels. The saturation value corresponding to the intersection of the curves of the pressure conductivity coefficient-oil saturation relationship and the conductivity coefficient-oil saturation relationship is the oil saturation value at each point.

[0129] In regions where the conductivity coefficient inversion saturation is significantly low, the electrode probe is surrounded by highly adhesive heavy oil, resulting in high resistance and an inability to accurately reflect changes in the surrounding flow field. Therefore, alternative methods are needed to supplement the accurate measurement of oil saturation in areas with insufficient conductivity. Thus, the synergistic identification based on pressure and temperature fields can be used to develop areas with high conductivity. When the difference between the single-point saturation values ​​obtained from the inversion of pressure and thermal conductivity is less than 5%, the two field values ​​are considered to match, and the oil saturation value at this point can be calculated using the average. In regions where the oil saturation measured by the pressure coefficient is lower than that measured by the thermal conductivity, and the difference exceeds 5%, the pressure-sensitive probe at this point detects a narrow, water-driven dominant channel. Due to the narrowness of the channel, the surrounding oil saturation values ​​fluctuate significantly, and the accuracy of temperature measurement is insufficient to effectively cover this. In this case, the oil saturation inversion using the pressure coefficient is more accurate. In regions where the oil saturation inversion using the pressure coefficient is significantly low, the thermal conductivity plays an auxiliary role in the calculation, and the second weight ω3 of the pressure coefficient can be preset to 0.5. The thermal conductivity weight ω4 can be preset to 0.3-0.5. Using a small-scale three-dimensional sand-filled model for initial verification, after multiple trials, it was found that when ω3 and ω4 were 0.65 and 0.35 respectively, the average error of the inversion result was the smallest, and these can be considered the optimal weight values. In areas where the oil saturation measured by the pressure conductivity is higher than that measured by the thermal conductivity, and the difference exceeds 5%, less heavy oil around the pressure-sensitive probe is replaced by the injected fluid, resulting in smaller pressure fluctuations that cannot accurately reflect changes in oil saturation. Therefore, the saturation value corresponding to the intersection of the curves of the pressure conductivity-oil saturation relationship and the thermal conductivity-oil saturation relationship is the oil saturation value at each point. Figure 8 Place.

[0130] Finally, using the mass conservation method, the oil saturation values ​​within each grid were calculated and compared with the final recovery rate of the experiment for verification. The mass extracted based on oil saturation in the model can be expressed as:

[0131]

[0132] The volume of oil produced during the experimental process, as recorded during development, was 7157 mL, and the mass was m. oe It is 6585g. This is compared to the oil production m calculated using saturation. oc By comparing (6724g), if the calculated mass deviation value is within the allowable error range (less than 5%), the comparison results show that the oil saturation field identified by the multiphysics field has high accuracy.

[0133] Therefore, this invention employs the aforementioned experimental device and method for measuring heavy oil saturation based on multi-physics field coupling. A sand-filled model shell is constructed using a temperature- and pressure-resistant, pressure-resistant, and insulating polyetheretherketone (PEEK) material. This builds a comprehensive experimental device for measuring heavy oil saturation, incorporating multiple physical fields such as flow, electric, and temperature fields. While accurately measuring heavy oil saturation, it can also measure the effective operating distance of the injected hot fluid during thermal recovery. This provides an efficient and systematic method for accurately measuring the saturation of heavy oil in indoor experiments and guides the detection of potential for exploitation during the physical simulation and thermal recovery development of heavy oil reservoirs.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for measuring heavy oil saturation based on multi-physics coupling, which applies a multi-physics coupling-based experimental apparatus for measuring heavy oil saturation to the measurement, characterized in that... The device includes a reservoir simulation system, a reservoir development system, and a remaining oil content monitoring and control system. The reservoir simulation system includes a three-dimensional sand-filled model shell, the interior of which is filled with a porous medium, the interior of which is connected to the formation pressure system via pipelines, and the exterior of which is connected to a model communication system. The reservoir development system includes an injection supply system, a metering and control system, and a well network system. The output end of the injection supply system is connected to the metering and control system via a pipeline, and the injection supply system is connected to the well network system via a second six-way valve. The remaining oil content measurement and control system includes a pressure detection system, a conductivity detection system, a thermal conductivity detection system, and a multi-physics field coupled saturation measurement system. The well network system includes a wellbore structure and a sand-proof spring structure. The wellbore structure includes a wellbore mechanism and a well location fixing mechanism. The well location fixing mechanism realizes the material exchange between external fluids and the reservoir simulation system. The method includes the following steps: S1. Construct a reservoir physical model and select a sand-proof spring structure based on the diameter of the porous medium filling material and the external fluid impact force. S2. Multi-parameter synchronous acquisition: The pressure conductivity coefficient, electrical conductivity coefficient, and thermal conductivity coefficient are acquired in the pressure conductivity detection system, electrical conductivity detection system, and thermal conductivity detection system, respectively. S3. Multiphysics field coupling calculation of heavy oil saturation is based on the changes in physical properties derived from three physical fields: pressure conductivity, electrical conductivity, and thermal conductivity. The identification of saturation is corrected and supplemented by pressure conductivity, electrical conductivity, and thermal conductivity. S4. Verify the saturation of heavy oil, calculate the mass deviation between the experimental oil production and the oil production calculated using the saturation. If the calculated mass deviation is within the allowable error range, the calculated value is considered to conform to the law of conservation of mass and has high accuracy. The expression for the pressure conductivity coefficient is: ； in, k 1. k Both 2 are undetermined coefficients of pressure conductivity. Porosity within porous media K For penetration rate, S o Oil saturation c t The core's overall compressibility coefficient; The expression for conductivity is: ； in, k 3. k 4 and k 5 are all undetermined coefficients related to the electrical conductivity of saturated fluid porous media. R w The resistivity of the formation water; The expression for thermal conductivity is: ； in, c p For specific heat capacity, Q As an internal heat source, ρ For density, T For temperature, t For time, λ The thermal conductivity coefficient; The expression for calculating oil production using saturation is as follows: ； in, ρ o The density of crude oil, S oi Oil saturation V i,j,k Let i be the apparent volume of the porous medium within the model, and i, j, k be the microgrid elements of the model.

2. The method for measuring heavy oil saturation based on multiphysics coupling according to claim 1, characterized in that, The supply system includes a dual-cylinder plunger displacement pump, a liquid supply intermediate container, a displacement gas cylinder, a gas flow controller, a mixed displacement system generator, and a steam generator. The output end of the dual-cylinder plunger displacement pump is connected to the liquid supply intermediate container via a three-way valve. The output end of the liquid supply intermediate container is connected to the inlet of a first six-way valve. The output end of the displacement gas cylinder is connected to the gas flow controller. The output end of the gas flow controller is connected to the other inlet of the first six-way valve. The input end of the mixed displacement system generator is connected to the outlet of the first six-way valve. The output end of the mixed displacement system generator is connected to the inlet of a second six-way valve. The output end of the steam generator is connected to the other inlet of the second six-way valve. The other outlet of the first six-way valve is connected to the input end of the second six-way valve.

3. The method for measuring heavy oil saturation based on multiphysics coupling according to claim 1, characterized in that, The measurement and control system includes a first measuring cylinder, a first electronic balance, a second measuring cylinder, and a second electronic balance. The first measuring cylinder is connected to the outlet of a second six-way valve. The first electronic balance is installed at the lower end of the first measuring cylinder. The output end of the reservoir simulation system is connected to the second measuring cylinder through a back pressure valve. The second electronic balance is installed at the lower end of the second measuring cylinder.

4. The method for measuring heavy oil saturation based on multiphysics coupling according to claim 1, characterized in that, The pressure detection system includes a pressure detection array and an electronic pressure gauge; the electrical conductivity detection system includes a high-precision DC power supply, an electric field controller, and a potential detection array; and the thermal conductivity detection system includes a base plate heating device, a temperature detection array, and a heat flux density measuring device.

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