Method and system for testing inflection point temperature of super heavy oil in porous medium

Abstract

The invention discloses a method and a system for testing inflection point temperature of super heavy oil in a porous medium, and the method comprises the following steps: presetting core models with different permeability, and recording corresponding core length; using the crude oil sample to saturate and age any rock core model; by controlling the injection speed of crude oil into the rock core model, shear stress of different strengths borne by the thickened oil is simulated, and effective starting pressure gradients of the thickened oil under the conditions of different temperatures and different permeability are obtained; and calculating inflection point temperatures of the target thickened oil under different permeability based on the fluidity and the effective starting pressure gradient. The problem that in the experiment process, the seepage resistance of the mode of generating simple shearing through rotation motion is very different from the seepage resistance of thick oil in an actual stratum when the thick oil flows in a porous medium is solved. And moreover, the shearing force action on the thickened oil under different stratum conditions can be accurately quantified, and the flowable limit of the thickened oil is determined by comprehensively considering factors such as temperature and pressure.

Description

Technical Field

[0001] The invention relates to the technical field of thermal oil recovery, and in particular to a method and a system for testing the inflection point temperature of super-heavy oil in a porous medium. Background Art

[0002] With the gradual reduction of conventional oil reserves, the development of heavy oil resources has attracted more and more attention. my country's heavy oil reserves are rich and have great development potential. Heavy oil thermal recovery is the world's largest and most widely used heavy oil recovery technology. By injecting hot fluids, the formation temperature is increased, the viscosity of crude oil is reduced, and the seepage capacity is increased, so that heavy oil can be produced smoothly. At present, the main means of thermal recovery of heavy oil are: steam stimulation, steam drive, steam-assisted gravity drainage, and fire burning of oil layers. Heavy oil with a viscosity greater than 50,000 mPa·s is called super-heavy oil. Compared with ordinary heavy oil, it has greater viscosity and more complex geological conditions. The main characteristics of super-heavy oil are high content of large molecules with large mass and strong polarity such as colloids, asphaltene, and paraffin; under the joint influence of van der Waals forces, hydrogen bonds, and other molecular effects, each component forms a compact multi-level planar structure, resulting in high viscosity and non-Newtonian fluid characteristics of super-heavy oil.

[0003] Heavy oil can only flow in porous media when the pressure gradient is greater than the starting pressure gradient. The flow ability of heavy oil in the reservoir is affected by multiple factors such as temperature and pressure. There are currently two main methods to determine the inflection point temperature. One method is to make two tangents based on the shape of the viscosity-temperature curve, and take the temperature corresponding to the intersection of the two tangents as the inflection point temperature. This method is not suitable for ultra-heavy oil with very high viscosity, because as the temperature rises, the viscosity of ultra-heavy oil changes greatly, and it is impossible to accurately draw two tangents based on the shape of the curve. Another method is to test the rheological curve at different temperatures to obtain the relationship between the yield value and temperature of the heavy oil, and take the temperature point where the yield value is 0 as the inflection point temperature. This method cannot be applied to reservoirs with different permeabilities, cannot be universally promoted, and can only be applied within certain specific ranges.

[0004] In the prior art, for example, the invention patent with publication number: CN103048230A proposes a method for determining the relationship between the yield value of heavy oil and temperature. The method mainly tests the heavy oil with a thermometer and a rheometer, draws a curve graph, and analyzes the relationship between the yield value of heavy oil and temperature. However, the inflection point temperature obtained by this method can only obtain a temperature range, and the inflection point temperature of the heavy oil reservoir cannot be quantitatively obtained. When the viscosity reaches the super-heavy oil range, this method is not applicable.

[0005] Another prior art, such as the invention patent with publication number: CN112324427A, provides a method for quantitatively obtaining the inflection point temperature of a heavy oil reservoir. The method converts the experimentally measured temperature into the inverse of the absolute temperature, and then uses the viscosity-temperature data to calculate the viscosity value of the degassed crude oil at different temperatures. In the rectangular coordinate system, 1000 / T is used as the horizontal coordinate, and the natural logarithm of the degassed crude oil viscosity value is used as the vertical coordinate. The slope value between two adjacent temperature test points is calculated according to the formula. Finally, a scatter plot of the slope value versus temperature is drawn with the temperature value T of the viscosity-temperature data test point as the horizontal coordinate and the slope value B as the vertical coordinate. The temperature point where the slope value jumps down is the rheological inflection point temperature of the heavy oil sample. However, the experimental data tested in this method is the viscosity-temperature curve of the heavy oil, which only takes into account one temperature variable, and does not consider the effect of pressure on the start-up of the heavy oil; and the fluid can only flow when the shear stress experienced by the fluid is greater than the yield stress, but the shearing mode of the viscometer used in the experiment is far different from the shear force experienced by the heavy oil in the actual formation. Summary of the invention

[0006] The embodiment of the present invention provides a method and system for testing the inflection point temperature of super heavy oil in porous media, which at least partially solves the technical problem that the shear stress input method in the prior art is inconsistent with the actual displacement process, and achieves the technical effect of accurately and quantitatively obtaining the inflection point temperature of the heavy oil from a non-Newtonian fluid to a Newtonian fluid.

[0007] In the first aspect, to solve the above technical problems, the embodiments of the present invention provide the following technical solutions:

[0008] A method for testing the inflection point temperature of super heavy oil in porous media, comprising:

[0009] Preset core models with different permeabilities and record the corresponding core lengths;

[0010] Saturating and aging any of the above core models with crude oil samples;

[0011] By controlling the injection rate of crude oil into the core model, the shear stress of different strengths on the heavy oil is simulated, and the effective starting pressure gradient of the heavy oil under different temperatures and permeabilities is obtained;

[0012] Based on the mobility and the above effective starting pressure gradient, the inflection point temperature of the target heavy oil at different permeabilities is calculated.

[0013] Optionally, the step of saturating and aging any of the core models using a crude oil sample further includes:

[0014] Crude oil is injected into the core model using a constant speed pump and allowed to stand for a preset time.

[0015] Optionally, the step of obtaining the effective starting pressure gradient of heavy oil under different temperatures and different permeabilities may further include:

[0016] The viscosity of crude oil at different temperatures is tested using a viscometer to establish the first relationship between viscosity and temperature;

[0017] Based on the first relationship, the pressure rise law of the heavy oil in the core with preset permeability at the first preset temperature is monitored to obtain the effective pressure gradient when the heavy oil flows stably at different flow rates;

[0018] The effective starting pressure gradient is obtained based on the above effective pressure gradient and temperature difference.

[0019] Optionally, before using a viscometer to test the viscosity of crude oil at different temperatures, the method further comprises:

[0020] The crude oil sample is filtered through a stainless steel mesh with a preset aperture at a second preset temperature, and then dehydrated to a preset water content in a crude oil dehydrator.

[0021] Optionally, the step of calculating the inflection point temperature of the target heavy oil at different permeabilities further includes:

[0022] Based on the physical law of mobility and the above effective starting pressure gradient, a second relationship between the effective starting pressure gradient, reservoir permeability and reservoir temperature is established;

[0023] Based on the second relational expression, the inflection point temperature of the heavy oil at different permeabilities is obtained.

[0024] Optionally, the second relational expression includes:

[0025]

[0026] In the formula, is the pressure gradient; k is the reservoir permeability; T is the reservoir temperature.

[0027] Optionally, the step of simulating shear stresses of different intensities to which the heavy oil is subjected further comprises:

[0028] Different displacement flow rates were used to simulate the shear stress of different intensities on the heavy oil, and the start-up pressure gradient was measured.

[0029] In a second aspect, a system for testing the inflection point temperature of super heavy oil in a porous medium is provided, comprising:

[0030] The model body module is used to preset core models with different permeabilities and record the corresponding core lengths;

[0031] An aging module for saturating and aging any of the above core models using crude oil samples;

[0032] A simulation module is used to simulate the shear stress of different strengths on the heavy oil by controlling the injection rate of crude oil into the core model, and obtain the effective starting pressure gradient of the heavy oil under different temperatures and permeabilities;

[0033] The calculation module calculates the inflection point temperature of the target heavy oil at different permeabilities based on the mobility and the above-mentioned effective starting pressure gradient.

[0034] In a third aspect, an experimental device for testing the inflection point temperature of super heavy oil in a porous medium is provided, comprising a constant speed pump, a piston container and a core model placement container which are sequentially connected by pipelines; the piston container and the core model placement container are arranged in a constant temperature box; the core model placement container acquires data in real time under the monitoring of a pressure sensor and transmits the data to a processing terminal; the processing terminal executes a preset computer program to implement the steps corresponding to the method in the first aspect.

[0035] In a fourth aspect, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the steps corresponding to the above method in the first aspect are implemented.

[0036] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0037] The starting pressure of the heavy oil in the reservoir in the cores with different permeabilities is more realistically reflected, and the starting temperature of the heavy oil can be calculated quantitatively and accurately. It breaks through the limitations of two conventional testing methods (i.e., the viscosity change of the heavy oil is tested by a viscometer and the change tends to be flat, or the temperature point when the yield stress of the heavy oil is 0 is tested by a rheometer to obtain its inflection point temperature). In addition, the present application comprehensively considers the shear force that the heavy oil in the cores with different permeabilities can smoothly flow through the pore throat, avoiding the use of a viscometer and a rheometer, etc., which leads to problems such as "the shear stress input method does not match the actual displacement process", and realizes accurate and quantitative acquisition of the inflection point temperature of the heavy oil from a non-Newtonian fluid to a Newtonian fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A flow chart of a method for testing the inflection point temperature of super heavy oil in porous media provided by the present invention;

[0040] Figure 2It is a schematic diagram of the curve results of viscosity and temperature fitting in the present invention;

[0041] Figure 3 It is a schematic diagram of the pressure changing with time in the present invention;

[0042] Figure 4 It is a schematic diagram of the relationship between pressure gradient and flow rate in the present invention;

[0043] Figure 5 It is a schematic diagram of the relationship between the effective flow pressure gradient and fluidity in the present invention;

[0044] Figure 6 A schematic diagram of the structure of a system for testing the inflection point temperature of super-heavy oil in porous media provided by the present invention;

[0045] Figure 7 A schematic structural diagram of an experimental device for testing the inflection point temperature of super heavy oil in a porous medium provided by the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0049] It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations of the technical solutions of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0050] The technical solution of the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0051] A 10cm core was used to simulate porous media for a single-phase seepage experiment of heavy oil. The injection rate of crude oil was controlled to simulate the shear stress of different intensities on the heavy oil, and the effective starting pressure gradient of the heavy oil under different temperatures and permeabilities was obtained. When the shear stress on the heavy oil was greater than the effective starting pressure gradient, the heavy oil could flow smoothly in the porous medium. Mobility can characterize the flow characteristics of heavy oil in porous media. According to the functional relationship between the effective starting pressure and mobility, the inflection point temperature of heavy oil in cores with different permeabilities was obtained.

[0052] In an embodiment of the present invention, there is provided Figure 1 A method for testing the inflection point temperature of super heavy oil in porous media is shown, the method comprising steps S101 to S104:

[0053] Step S101, presetting core models with different permeabilities and recording corresponding core lengths;

[0054] It should be noted that a core model with a length of about 10 cm is selected, wherein the core can be an artificial core or a natural core model of various sizes, and the core length △ L is recorded. In addition, the core model can also be replaced by a sand filling tube, a flow dispersion device, and other equipment with similar principles.

[0055] Step S102, saturating and aging any core model using a crude oil sample;

[0056] Specifically, the piston container is filled with crude oil, and the crude oil is injected into the core using a constant speed pump and left to stand for 24 hours for full aging.

[0057] Step S103, by controlling the injection rate of crude oil into the core model, simulating the shear stress of different strengths on the heavy oil, and obtaining the effective starting pressure gradient of the heavy oil under different temperatures and different permeabilities;

[0058] It should be noted that the simulation of different shear stresses on heavy oil is mainly to use different displacement flow rates to simulate different shear stresses on heavy oil, and to perform startup pressure gradient measurement. Specifically, the temperature is set to the preset experimental temperature. When the temperature reaches the set value and stabilizes, the temperature is kept constant for two hours; the liquid is displaced to the inlet end of the core under ultra-low speed conditions, and the inlet pressure is gradually established. When the pressure data shows stability, the outlet pressure P0 at this time is recorded; at the same time, the pressure value of the injection pressure is recorded, the core is left to age for 8 hours, and the startup pressure gradient measurement is continued with different displacement flow rates.

[0059] The steps of obtaining the effective starting pressure gradient of heavy oil under different temperatures and different permeabilities also include: using a viscometer to test the viscosity of crude oil at different temperatures, and establishing a first relationship between viscosity and temperature; based on the first relationship, monitoring the pressure rise law of heavy oil in a core with a preset permeability at a first preset temperature, and obtaining the effective pressure gradient when the heavy oil flows stably under different flow rates; and obtaining the effective starting pressure gradient based on the effective pressure gradient and temperature difference. Taking the super-heavy oil in a block of Liaohe Oilfield as an example:

[0060] like Figure 2 As shown, the first relationship between the fitted viscosity and temperature is:

[0061]

[0062] The core displacement experiment was conducted in a single-phase seepage experiment at a measurement temperature range of 55°C-135°C. The parameters of the core model used in the experiment are shown in Table 1.

[0063]

[0064] Table 1

[0065] based on Figure 2 The first relationship and data in the above example monitor the pressure rise law of heavy oil in the core with a permeability of 3025mD at 85℃, as shown in Figure 3 As shown in the figure, the effective starting pressure gradient of heavy oil stable flow at different flow rates is obtained, as Figure 4 As shown, a curve of the relationship between pressure gradient and flow rate was drawn, and it was determined that the minimum starting pressure gradient and the effective starting pressure gradient were 0.025MPa / m and 0.527MPa / m respectively.

[0066] Step S104, calculating the inflection point temperature of the target heavy oil at different permeabilities based on the mobility and the effective starting pressure gradient.

[0067] It should be noted that the temperature is controlled by using a thermostat, and step S103 is repeated to draw a relationship curve between the effective starting pressure and the fluidity, to obtain a relationship between the effective starting pressure and the temperature, and to calculate the temperature point at which the effective starting pressure P≈0 is the inflection point temperature; in detail,

[0068] Based on the mobility and effective starting pressure gradient, the oil sample will flow in the core only when the driving pressure gradient is greater than the effective flow pressure gradient. The second relationship between the effective starting pressure, reservoir permeability and reservoir temperature is established; based on the second relationship, the inflection point temperature of heavy oil at different permeabilities is obtained.

[0069] In the specific calculation, the mobility parameter is introduced, such as the relationship between the effective flow pressure gradient and mobility shown in Figure X; the effective starting pressure gradient at different permeabilities and temperatures is obtained by fitting the experimental results, such as Figure 5 As shown; mobility can characterize the flow characteristics of heavy oil in porous media. The smaller the mobility, the greater the effective flow pressure gradient. The effective flow pressure gradient and mobility are in a power exponential relationship, and the second relationship is established:

[0070]

[0071] In the formula, is the pressure gradient; k is the reservoir permeability; T is the reservoir temperature.

[0072] Let the effective starting pressure be (The pressure gradient value can be brought in according to the needs of the mine, and 0.1MPa / m is taken as an example here). According to the above-mentioned discrimination formula, it is calculated that the inflection point temperatures of the heavy oil in the reservoirs of 928mD, 3025mD and 4632mD in this block of Liaohe Oilfield are 116.36℃, 103.65℃ and 99.07℃ respectively.

[0073] Furthermore, before using the viscometer to test the viscosity of the crude oil at different temperatures, the method further comprises:

[0074] The crude oil sample is filtered through a stainless steel mesh with a preset aperture at a second preset temperature, and then dehydrated to a preset water content in a crude oil dehydrator.

[0075] It should be noted that, in this embodiment, the crude oil sample is filtered through a stainless steel mesh with a pore size of 0.045 mm at 80° C. and then dehydrated in a crude oil dehydrator at a constant temperature for two hours. The water content is qualified when it is less than 0.3%.

[0076] Based on the same inventive concept, an embodiment of the present invention provides a system for testing the inflection point temperature of super heavy oil in porous media, such as Figure 6 As shown, including:

[0077] The model body module 201 is used to preset core models with different permeabilities and record the corresponding core lengths;

[0078] An aging module 202, for saturating and aging any of the core models using crude oil samples;

[0079] The simulation module 203 is used to simulate the shear stress of different strengths on the heavy oil by controlling the injection speed of crude oil into the core model, and obtain the effective starting pressure gradient of the heavy oil under different temperatures and different permeabilities;

[0080] The calculation module 204 calculates the inflection point temperature of the target heavy oil at different permeabilities based on the mobility and the effective starting pressure gradient.

[0081] Based on the same inventive concept, an embodiment of the present invention provides an experimental device for testing the inflection point temperature of super heavy oil in porous media, such as Figure 7 As shown, including:

[0082] A constant speed pump 302, a piston container 301 and a core model placement container 305 are sequentially connected by pipelines; the piston container 301 and the core model placement container 305 are arranged in a constant temperature box 306; the core model placement container 305 obtains data in real time under the monitoring of the pressure sensor 303 and transmits it to the processing terminal 304; the processing terminal 304 executes a preset computer program to implement a method for testing the inflection point temperature of super heavy oil in a porous medium.

[0083] It should be noted that the piston container is used to load crude oil, and the saturated crude oil is injected into the core under the drive of the constant speed pump; the thermostat is used to control the temperature. The pressure data is monitored in real time by the pressure sensor, and the inflection point temperature is calculated on the processing terminal using the above-mentioned method for testing the inflection point temperature of super-heavy oil in porous media.

[0084] Based on the same inventive concept, this embodiment provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the program is executed by a processor, a method for testing the inflection point temperature of super-heavy oil in a porous medium is implemented.

[0085] In summary, the present invention provides a method and system for testing the inflection point temperature of super heavy oil in porous media, which uses cores to create a restricted space, directly simulates the shear stress of crude oil passing through the pore throat of porous media, and solves the problem that the method of generating simple shear by rotating motion during the experiment is far from the seepage resistance of heavy oil flowing in porous media in actual formations. In addition, by establishing the relationship between mobility parameters and starting pressure gradient, the inflection point temperature of heavy oil under different permeabilities is calculated, the shear force effect on heavy oil under different formation conditions is accurately quantified, and the flow limit of heavy oil is determined by comprehensively considering factors such as temperature and pressure.

[0086] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0087] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0088] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for testing the inflection point temperature of super heavy oil in porous media, characterized in that: The method comprises: Preset core models with different permeabilities and record the corresponding core lengths; Saturating and aging any of the core models with a crude oil sample; By controlling the injection rate of crude oil into the core model, the shear stress of different strengths on the heavy oil is simulated to obtain the effective starting pressure gradient of the heavy oil under different temperatures and different permeabilities; Based on the mobility and the effective starting pressure gradient, the inflection point temperature of the target heavy oil at different permeabilities is calculated.

2. The method according to claim 1, characterized in that The step of saturating and aging any of the core models using a crude oil sample also includes: Crude oil is injected into the core model using a constant speed pump and left to stand for a preset time.

3. The method according to claim 1, characterized in that The step of obtaining an effective starting pressure gradient for heavy oil under conditions of different temperatures and different permeabilities also includes: The viscosity of crude oil at different temperatures is tested using a viscometer to establish the first relationship between viscosity and temperature; Based on the first relationship, monitoring the pressure rise law of the heavy oil in the core with preset permeability at a first preset temperature, and obtaining the effective pressure gradient when the heavy oil flows stably at different flow rates; An effective starting pressure gradient is obtained based on the effective pressure gradient and the temperature difference.

4. The method according to claim 3, characterized in that Before using the viscometer to test the viscosity of crude oil at different temperatures, the method further includes: The crude oil sample is filtered through a stainless steel mesh with a preset aperture at a second preset temperature, and then dehydrated to a preset water content in a crude oil dehydrator.

5. The method according to claim 1, characterized in that The step of calculating the inflection point temperature of the target heavy oil at different permeabilities also includes: Based on the physical law of mobility and the effective starting pressure gradient, a second relationship between the effective starting pressure gradient, the reservoir permeability and the reservoir temperature is established; The inflection point temperature of the heavy oil at different permeabilities is obtained based on the second relationship.

6. The method according to claim 5, characterized in that The second relational expression includes: In the formula, is the pressure gradient; k is the reservoir permeability; T is the reservoir temperature.

7. The method according to claim 1, characterized in that The step of simulating shear stresses of different intensities to which heavy oil is subjected also includes: Different displacement flow rates were used to simulate the shear stress of different intensities on the heavy oil, and the start-up pressure gradient was measured.

8. A system for testing the inflection point temperature of super heavy oil in porous media, characterized in that: The system comprises: The model body module is used to preset core models with different permeabilities and record the corresponding core lengths; An aging module, for saturating and aging any of the core models using crude oil samples; A simulation module, used for simulating the shear stress of different strengths on the heavy oil by controlling the injection speed of crude oil into the core model, and obtaining the effective starting pressure gradient of the heavy oil under different temperatures and different permeabilities; The calculation module calculates the inflection point temperature of the target heavy oil at different permeabilities based on the mobility and the effective starting pressure gradient.

9. An experimental device for testing the inflection point temperature of super heavy oil in porous media, characterized in that: The device comprises: a constant speed pump, a piston container and a core model placement container which are connected in sequence by pipelines; the piston container and the core model placement container are arranged in a constant temperature box; the core model placement container acquires data in real time under the monitoring of a pressure sensor and transmits the data to a processing terminal; the processing terminal executes a preset computer program to implement any method step described in claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps corresponding to the method according to any one of claims 1 to 7 are implemented.

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