Method for simultaneously evaluating shale oil reservoir CO2 diffusion characteristics and storage state and experimental device thereof

Abstract

The invention belongs to the technical field of oil and gas field development, and particularly relates to a method for simultaneously evaluating shale oil reservoir CO2 diffusion characteristics and storage states and an experimental device thereof. The method comprises the steps that firstly, a sampled shale core is subjected to artificial fracture forming, and the basic physical property of the shale core is measured; sequentially saturating formation water and oil; obtaining T1 and T2 maps of the shale core by utilizing nuclear magnetic resonance; and finally, according to corresponding formulas, calculating the effective diffusion coefficient De of the CO2, the storage rate of the CO2, the proportion of the structural storage form and the dissolution storage form of the CO2, and the proportion of the adsorption storage form and the free storage form in the structural storage form. According to the method, experimental mechanism evaluation can be carried out on the shale oil reservoir CO2 diffusion mechanism and the storage state under pressure driving, the diffusion characteristics and the storage state of CO2 in the shale development process are determined, and reliable technical support and theoretical basis are provided for efficient development of shale oil and geological storage of CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and specifically relates to a method for simultaneously evaluating CO 2 Methods and experimental setup for diffusion characteristics and storage status. Background Art

[0002] As an unconventional oil and gas resource, shale oil has played an increasingly important role in the global energy landscape in recent years. The rich reserves and wide distribution of shale oil have provided new guarantees for global energy supply. 2 As a potential oil displacement agent, CO plays an important role in the development of shale oil. 2 Flooding technology can not only effectively increase crude oil production, but also 2 Geological storage provides a pathway to reduce greenhouse gas emissions.

[0003] CO 2 Pre-fracture, CO 2 Huff and puff is a commonly used production-increasing technology in shale oil development, but in the process of implementation, CO 2 The diffusion behavior in shale reservoirs is complex and is affected by many factors such as reservoir pore structure, temperature, and pressure. 2 Diffusion characteristics in shale reservoirs help optimize CO 2 injection schemes, enhanced oil recovery, and CO 2 Geological storage provides a scientific basis. 2 In shale reservoirs, adsorption storage and capillary capture are the main methods, with low leakage risk and multiple environmental and economic benefits. 2 The storage status of CO in shale reservoirs can be better understood. 2 Behavior and stability under different conditions are important for optimizing CO 2 Storage methods to improve CO 2 In addition, these evaluations can also promote the development of relevant scientific research and promote the innovation of new technologies and methods, thereby improving the efficiency and safety of CO storage. 2 Overall sealing effect.

[0004] The core scale is a research scale that includes sandstone, siltstone, volcanic rock, carbonate rock and shale. Shale reservoir is a special type of rock. In addition to low porosity and low permeability, it also has nanopores, and the fluid in the shale reservoir can be divided into free state and adsorbed state. However, the current research on CO2 in shale reservoir is still unclear. 2 There are few studies on diffusion behavior of shale CO. 2 Research on oil recovery technology mainly focuses on CO 2The production increase effect is lacking in CO 2 Evaluation of storage effect. 2 There is still a lack of research on different storage states (structural storage, dissolution storage and mineralization storage, etc.) in shale reservoirs. Summary of the invention

[0005] The present invention aims at the lack of pressure-driven shale oil CO 2 The diffusion characteristics and storage status evaluation of shale reservoir CO2 are studied in this paper. 2 The method can be used to study the diffusion characteristics and storage state of CO in shale reservoirs under pressure-driven 2 The experimental mechanism evaluation of the diffusion mechanism and storage state was carried out to clarify the CO 2 The diffusion characteristics and storage status during shale development provide important references for the efficient development of shale oil and CO 2 It provides reliable technical support and theoretical basis for geological storage.

[0006] The specific technical solutions are as follows:

[0007] A method for simultaneously evaluating CO in shale reservoirs 2 A method for diffusion characterization and containment state, comprising the steps of:

[0008] (1) First, artificial fractures are created in the sampled shale cores. Then the basic physical properties of the shale cores are measured, including core dry weight, length, diameter, permeability and porosity, and the core pore volume is calculated.

[0009] Artificial fractures are created to simulate the fracturing process during actual exploitation of shale oil reservoirs.

[0010] The permeability and porosity were measured by the helium method and pulse decay method in the national standard GB / T 34533-2023, respectively.

[0011] Core pore volume Where V c is the core pore volume, cm 3 ; d is the core diameter, cm; L is the core length, cm; is the core porosity.

[0012] (2) Place the shale core in a container, evacuate the container, and pressurize it to saturate it with formation water. After the core is saturated with formation water, record the wet weight of the core.

[0013] (3) Degassed oil is prepared for experimental simulation based on the formation crude oil viscosity data.

[0014] (4) Under formation pressure, the degassed oil prepared in step (3) is used to displace the saturated formation water shale core to construct a shale core at irreducible water saturation; and the water output is recorded.

[0015] (5) Using nuclear magnetic resonance equipment to measure the T of the oil-saturated shale core obtained in step (4) 1 and T 2 Atlas.

[0016] (6) Establish the corresponding relationship between the NMR signal value and the actual saturated oil and water volume; calibrate the distribution characteristics of adsorbed oil, free oil, adsorbed water and free water in the shale core.

[0017] The saturated oil-water volume of the shale core is calculated by the following formula:

[0018]

[0019] In formula (1), V o is the volume of shale core saturated with crude oil, mL; V w is the saturated formation water volume of shale core, mL; V s is the total volume of shale core saturated with oil and water, mL; W 1 is the core dry weight, g; W 2 is the wet weight of the core, g; V 1 is the water output at the end, mL; ρ w is the formation water density, g / cm 3 .

[0020] When calibrating the distribution characteristics of various fluids inside the shale core, firstly, the NMR T 2 -T 1 The spectrum is used to divide the boundaries of each fluid occurrence state:

[0021] ①Oil adsorption: 0.2ms <T 2 <1ms, T 1 / T 2 >10; ② Free oil: 1ms <T 2 , T 1 / T 2 >10; ③ Adsorbed water: T 2 <0.2ms, T 1 / T 2 ≤100; ④ Free water: 0.2ms <T 2 , T 1 / T 2 ≤10; ⑤ Kerogen: T 2 <0.2ms, T 1 / T 2 >100.

[0022] Then calculate the proportion of each fluid based on the boundary division:

[0023] The occurrence states of different fluids in the calibrated shale cores are determined based on the NMR T 2 -T 1 The spectrum is combined with drying, pyrolysis and solvent extraction methods. For details, please refer to Adsorbed and free hydrocarbons in unconventional shale reservoir: A new insight from NMR T 1 -T 2 maps[J].Marine and Petroleum Geology, 2020, 116(2020):104311.

[0024] (7) CO injection 2 Carry out displacement diffusion experiments and record the oil output, gas output and CO 2 The pressure decay degree of CO 2 The pressure was pressurized to the specified pressure and then injected to carry out displacement diffusion experiment.

[0025] (8) Measuring CO 2 T of shale core after flooding diffusion 1 and T 2 Spectrum, clear CO 2 Oil and water distribution characteristics inside the shale core after displacement and diffusion.

[0026] (9) Calculation of CO 2 Effective diffusion coefficient D e , and calculate the CO 2 The proportion of different storage forms and the total storage rate.

[0027] ①CO 2 Effective diffusion coefficient D e Calculated by the following formula:

[0028]

[0029] In formula (2), P(t) is the pressure change function related to time, MPa; P 0 is the initial pressure, MPa; D e For CO 2 Effective diffusion coefficient; A is the core cross-sectional area, cm 2 ; t is time, s; V g For CO 2 Gas volume, mL; L is the core length, cm.

[0030] The calculation formula of core cross-sectional area A is as follows: d is the core diameter, cm.

[0031] Taking the logarithm of both sides of equation (2), we can get:

[0032] According to the different recorded CO 2 The pressure decay degree is obtained to obtain the value of ln(P(t)) in formula (3), and then the slope m of ln(P(t))-t is obtained by linear fitting, and D can be obtained according to the calculation formula (4) e The value of; the calculation formula is as follows:

[0033]

[0034] In formula (4), V g For CO 2 Gas volume, mL; L is the core length, cm; m is the slope of ln(P(t))-t obtained by linear fitting; A is the core cross-sectional area, cm 2 .

[0035] ②CO 2 The storage rate is calculated according to formula (5):

[0036]

[0037] In formula (5), η c For CO 2 Storage rate; V in For CO 2 Injection volume, mL; V out is the end outlet volume, mL.

[0038] Since gas is highly compressible, the CO collected at each pressure 2 The volume data needs to be converted to the volume at the initial pressure through the state equation, V in and V out First, convert the gas volume to the same pressure according to calculation formula (6), and then substitute it into formula (5) for calculation.

[0039]

[0040] In formula (6), P 1 is the final decay pressure, MPa; Z 0 is the initial pressure of CO 2 Compression factor; Z 1 To decay the final pressure of CO 2 Compression factor; P b is atmospheric pressure, 0.101MPa; Zb CO at atmospheric pressure 2 Compression factor; V gb CO collected at the end 2 Volume, mL.

[0041] ③CO 2 The storage forms in underground reservoirs mainly include structural storage and dissolution storage. 2 The proportion of structural storage and dissolved storage is calculated according to formula (7):

[0042]

[0043] In formula (7), R c For CO 2 The proportion of structural storage forms; R d For CO 2 The proportion of dissolved sealed forms; C s1 is the initial state core T 2 and T 1 The cumulative signal amplitude of the kerogen removal area; C s2 T is the core after diffusion is completed 2 and T 1 Accumulated signal amplitude in the kerogen-removed region of the map.

[0044] ④ For structural sealing, it is divided into two forms in shale core: adsorption sealing and free sealing. The proportion of adsorption sealing and free sealing in structural sealing is calculated by formula (8):

[0045]

[0046] In formula (8), R a For CO 2 The proportion of adsorption storage to structural storage; R f For CO 2 The proportion of free storage to structural storage; S a1 is the initial state core T 2 -T 1 Spectrum adsorption state oil and water cumulative signal amplitude; S a2 T is the core after diffusion is completed 2 -T 1 Spectrum adsorption state oil and water cumulative signal amplitude; S f1 is the initial state core T 2 -T 1 Spectrum free oil and water accumulation signal amplitude; S f2 T is the core after diffusion is completed 2 -T 1 Spectrum free oil and water accumulation signal amplitude; Cs1 is the initial state core T 2 and T 1 The cumulative signal amplitude of the kerogen removal area; C s2 T is the core after diffusion is completed 2 and T 1 Accumulated signal amplitude in the kerogen-removed region of the map.

[0047] Among them, the total NMR signal amplitude of adsorbed oil and water S a and the total NMR signal amplitude of free oil and water S f From formula (9), we get:

[0048]

[0049] In formula (9), S a is the total NMR signal amplitude of adsorbed oil and water; S ao is the total NMR signal amplitude of adsorbed oil; S aw is the total NMR signal amplitude of adsorbed water; S f is the total NMR signal amplitude of free oil and water; S fo is the total NMR signal amplitude of free oil; S fw is the total NMR signal amplitude of free water.

[0050] (10) Control the injection pressure to reduce it to atmospheric pressure and measure the discharged CO 2 Volume, verify the calculated storage results.

[0051] In the present invention, the simultaneous evaluation of shale oil reservoir CO 2 The method for determining diffusion characteristics and sealing status comprises the following steps: (1) artificially creating fractures in shale cores by using wire cutting technology.

[0052] In the present invention, the simultaneous evaluation of shale oil reservoir CO 2 The method for diffusion characteristics and sealing status, wherein the pressure of pressurized saturated formation water in step (2) is 25 MPa and the saturation time is 7 days.

[0053] In the present invention, the simultaneous evaluation of shale oil reservoir CO 2 The method for diffusion characteristics and sealing state, wherein in step (3), the degassed oil is selected from one or more of dodecane, kerosene, n-heptane and on-site degassed crude oil.

[0054] In the present invention, the simultaneous evaluation of shale oil reservoir CO 2The method for diffusion characteristics and sealing state, in which in step (4), during the process of constructing a shale core with bound water saturation by saturating oil, due to the presence of artificial fractures in the shale core, when the end of the shale core begins to produce oil continuously, the degassed oil displacement is first stopped, and the displacement is continued after being stationary for 24 hours under the formation pressure, and the cycle is repeated until no water flows out from the end of the shale core, thereby obtaining a saturated oil shale core. This saturation method can give full play to the oil-water replacement effect, so that the shale core is completely saturated with active oil.

[0055] The present invention also provides an experimental device for the above evaluation method. The specific technical solution is as follows:

[0056] An experimental device used in the above method, comprising a CO 2 containers, water containers, oil containers and core holders.

[0057] The CO 2 The top part of the container is provided with two pipelines, each of which is provided with a two-way valve, namely two-way valve I and two-way valve II; the two-way valve I is connected to the booster pump through a pipeline, and the booster pump is connected to the CO through the two-way valve III and the pipeline. 2 Gas cylinder connected, CO 2 A pressure gauge I is provided on the pipeline between the gas cylinder and the booster pump.

[0058] The CO 2 A two-way valve IV is provided at the bottom of the container.

[0059] The top and bottom of the water container are respectively provided with a two-way valve V and a two-way valve VI.

[0060] The top and bottom of the oil container are respectively provided with a two-way valve VII and a two-way valve VIII.

[0061] The two-way valve IV, the two-way valve VI and the two-way valve VIII are all connected to the four-way valve I through pipelines, and the four-way valve I is connected to the injection pump through a pipeline.

[0062] The two-way valve II, two-way valve V and two-way valve VII are all connected to the four-way valve II through a pipeline, and the four-way valve II is connected to the inlet end of the core clamp through a pipeline; a pressure gauge II, an injection valve and a four-way valve III are arranged on the pipeline between the inlet end of the core clamp and the four-way valve II; the four-way valve III is also connected to a vent valve and a two-way valve IX, and the two-way valve IX is connected to a gas volume meter I.

[0063] The core holder is located in the provided nuclear magnetic resonance measuring instrument.

[0064] The middle part of the core holder is connected to a hand pump I through a pipeline, and a pressure gauge III and a two-way valve X are arranged on the pipeline. The hand pump I provides confining pressure for the core holder.

[0065] The outlet end of the core holder is connected to the back pressure valve through a pipeline, and a pressure gauge IV and a two-way valve XI are arranged on the pipeline.

[0066] One end of the back pressure valve is connected to a liquid micrometer through a pipeline, and the liquid micrometer is connected to a gas volume meter II.

[0067] The other end of the back pressure valve is connected to a hand pump II through a pipeline, and a pressure gauge V and a two-way valve XII are arranged on the pipeline. The hand pump II provides back pressure for it.

[0068] The beneficial effects of the present invention are as follows: the present invention innovatively designs a method that can simultaneously evaluate the CO 2 Diffusion characteristics and storage state methods, based on nuclear magnetic resonance measurement technology, simultaneous CO 2 The diffusion characteristics and storage effects in shale oil reservoirs were comprehensively evaluated. The method can not only accurately measure CO 2 The diffusion behavior under different shale conditions can also identify the specific form and mechanism of its storage, which is helpful for optimizing injection strategy and improving CO 2 The storage efficiency in shale oil reservoirs is of great significance. It also helps to predict CO 2 The stability of long-term underground storage reduces the risk of leakage and ensures the environmental safety of the storage process.

[0069] The invention is simple to operate, has rigorous theoretical calculation and is easy to understand. 2 The diffusion and storage of CO in shale reservoirs provides a new perspective on the 2 The oil displacement and storage experimental technology has certain reference value. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 Schematic diagram of the experimental device for evaluating the method described in the present invention.

[0071] Among them, 1 is CO 2 Gas cylinder, 2 is pressure gauge I, 3 is two-way valve III, 4 is booster pump, 5 is injection pump, 6 is two-way valve I, 7 is two-way valve II, 8 is two-way valve V, 9 is two-way valve VII, 10 is four-way valve II, 11 is CO 2Container, 12 is a water container, 13 is an oil container, 14 is a two-way valve IV, 15 is a two-way valve VI, 16 is a two-way valve VIII, 17 is a four-way valve I, 18 is a four-way valve III, 19 is a two-way valve IX, 20 is a vent valve, 21 is an injection valve, 22 is a pressure gauge II, 23 is a gas volume meter I, 24 is a core holder, 25 is a nuclear magnetic resonance measuring instrument, 26 is a pressure gauge III, 27 is a two-way valve X, 28 is a hand pump I, 29 is a pressure gauge IV, 30 is a two-way valve XI, 31 is a back pressure valve, 32 is a liquid micrometer, 33 is a gas volume meter II, 34 is a pressure gauge V, 35 is a two-way valve XII, and 36 is a hand pump II.

[0072] Figure 2 is the T of the shale core in the initial state 1 -T 2 Atlas.

[0073] Figure 3 For CO 2 T of shale core after diffusion 1 -T 2 Atlas.

[0074] Figure 4 It is the pressure decay curve. DETAILED DESCRIPTION

[0075] The present invention will be further described below in conjunction with specific embodiments.

[0076] Example 1

[0077] A method for simultaneously evaluating shale reservoir CO 2 The experimental setup in the diffusion characterization and storage state approach includes CO 2 Container 11 , water container 12 , oil container 13 and core holder 24 .

[0078] The CO 2 The top part of the container 11 is provided with two pipelines, each of which is provided with a two-way valve, namely, a two-way valve I6 and a two-way valve II7; the two-way valve I6 is connected to the booster pump 4 through a pipeline, and the booster pump 4 is connected to the CO through a two-way valve III3 and a pipeline. 2 Gas cylinder 1 connected, CO 2 A pressure gauge I2 is provided on the pipeline between the gas cylinder 1 and the booster pump 4.

[0079] The CO 2 A two-way valve IV14 is provided at the bottom of the container 11 .

[0080] The top and bottom of the water container 12 are respectively provided with a two-way valve V8 and a two-way valve VI15.

[0081] The top and bottom of the oil container 13 are provided with a two-way valve VII9 and a two-way valve VIII16 respectively.

[0082] The two-way valve IV14, the two-way valve VI15 and the two-way valve VIII16 are all connected to the four-way valve I17 through pipelines, and the four-way valve I17 is connected to the injection pump 5 through pipelines.

[0083] The two-way valve II7, the two-way valve V8 and the two-way valve VII9 are all connected to the four-way valve II10 through pipelines, and the four-way valve II10 is connected to the inlet end of the core clamp 24 through a pipeline; a pressure gauge II22, an injection valve 21 and a four-way valve III18 are provided on the pipeline between the inlet end of the core clamp 24 and the four-way valve II10; the four-way valve III18 is also connected to the vent valve 20 and the two-way valve IX19, and the two-way valve IX19 is connected to the gas volume meter I23.

[0084] The core holder 24 is located in the provided nuclear magnetic resonance measuring instrument 25 .

[0085] The middle part of the core holder 24 is connected to a hand pump I28 through a pipeline, and a pressure gauge III26 and a two-way valve X27 are arranged on the pipeline. The hand pump I28 provides confining pressure for the core holder 24.

[0086] The outlet end of the core holder 24 is connected to a back pressure valve 31 through a pipeline, and a pressure gauge IV29 and a two-way valve XI30 are provided on the pipeline.

[0087] One end of the back pressure valve 31 is connected to a liquid micrometer 32 through a pipeline, and the liquid micrometer 32 is connected to a gas volume meter II33.

[0088] The other end of the back pressure valve 31 is connected to a hand pump II36 through a pipeline, and a pressure gauge V34 and a two-way valve XII35 are provided on the pipeline.

[0089] The experimental device was used to investigate the CO 2 When evaluating the diffusion characteristics and sealing state method, first put the shale core saturated with water into the core holder 24, open the two-way valve X27, and use the hand pump I28 to apply confining pressure to the core holder 24, where the confining pressure value can be read from the pressure gauge III26.

[0090] Open two-way valve VII9, two-way valve VIII16, injection valve 21, two-way valve XI30 and two-way valve XII35, apply back pressure to back pressure valve 31 through hand pump II36, the back pressure value can be read through pressure gauge V34, and then use injection pump 5 to drive the crude oil in oil container 13 into core clamp 24 at constant pressure, and use liquid micrometer 32 to measure the water and oil output.

[0091] When oil is continuously discharged from the end, the injection valve 21 and the two-way valve XI30 are closed. After standing still for 24 hours under the displacement pressure, the injection valve 21 and the two-way valve XI30 are opened to continue the constant pressure displacement until no water flows out from the end.

[0092] The T of the shale core at this time is measured using a nuclear magnetic resonance measuring instrument 25. 1 and T 2 Atlas.

[0093] Adjust the back pressure value of the back pressure valve 31 by hand pump II36, close the two-way valve VII9, two-way valve VIII16 and injection valve 21. Open the two-way valve III3, two-way valve I6 and vent valve 20, and use CO 2 The gas in cylinder 1 empties the residual oil in the pipeline.

[0094] Then close the vent valve 20, open the two-way valve II7, and use the booster pump 4 to pump CO 2 The gas pressure in the container 11 is pressurized to the diffusion pressure. The injection pump 5 can also be used to inject CO through the two-way valve IV14. 2 Gas pressurization.

[0095] The injection valve 21 is opened to conduct a displacement diffusion experiment. During this process, the pressures at the inlet and outlet of the core holder 24 are recorded by pressure gauge II 22 and pressure gauge IV 29, respectively. At the same time, the liquid micrometer 32 is used to measure the oil output, and the gas volume meter II 33 is used to record the gas output at the outlet.

[0096] Then, the T of the shale core at the end of the displacement diffusion experiment was measured using a nuclear magnetic resonance instrument25 1 and T 2 After the displacement diffusion experiment, the inlet pressure was reduced to atmospheric pressure through the two-way valve IX19, and the discharged CO was measured by the gas volume meter I23. 2 Volume, the calculation results are verified by converting the gas volume.

[0097] If the core is saturated with water using the displacement method, the two-way valve V8 can control the water container 12 to be connected to the core clamp 24 system, and the two-way valve VI15 can control the water container 12 to be connected to the injection pump 5.

[0098] Example 2

[0099] The core used in this example is an actual core from a shale block in Shengli, and the device used to carry out the experiment is the experimental device described in Example 1.

[0100] The specific experimental steps are as follows:

[0101] (1) Based on the on-site shale core, the core was artificially fractured using wire cutting technology and saturated with formation water. The basic physical properties of the shale core were finally measured as shown in Table 1.

[0102] Table 1 Core basic properties

[0103] Core number Length / cm Diameter / cm Dry weight / g Permeability / mD Matrix porosity / % Wet weight / g 1 4.73 2.52 61.81 1.79 1.27 62.31

[0104] (2) In order to make the shale core more fully saturated with hydrocarbons, this example uses dodecane instead of formation crude oil for operation.

[0105] (3) The shale core saturated with formation water is placed in the core holder 24, and the experimental temperature is set to the formation temperature of 50° C. The two-way valve X27 is opened, and a confining pressure of 20 MPa is applied to the core holder 24 using a hand pump I28.

[0106] Open two-way valve VIII16, two-way valve VII9, two-way valve XI30 and injection valve 21, and use injection pump 5 to displace dodecane in oil container 13 into shale core at a pressure of 15MPa. When the outlet of core holder 24 starts to produce oil continuously, close two-way valve XI30 and continue displacing after standing for 24 hours until no water flows out of the end. Use liquid micrometer 32 to record the water output. Finally, it is calculated that the volume of saturated dodecane is 0.3mL, the mass of saturated dodecane is 0.225g, and the volume of remaining formation water in the core is 0.2mL.

[0107] (4) Using a nuclear magnetic resonance instrument 25 to measure the T of the shale core after oil saturation 1 and T 2 Spectrum. Figure 2 shown.

[0108] (5) Based on the measured NMR signal values, the signal values ​​and proportions of kerogen, adsorbed oil, free oil, adsorbed water and free water were statistically calculated and shown in Table 2.

[0109] According to the volume of saturated dodecane in the core (0.3 mL) and the volume of the remaining formation water (0.2 mL), it can be calculated that the volumes of adsorbed oil, free oil, adsorbed water and free water in the core are 0.18 mL, 0.12 mL, 0.006 mL and 0.194 mL, respectively.

[0110] Table 2 Initial core T 1 and T 2 Signal value and ratio of each area of ​​the spectrum

[0111] Region Name Signal value Proportion / % Kerogen 1.83 0.65 Absorbing oil 63.15 22.43 Free oil 44.61 15.84 Adsorption of water 5.64 2.00 Free water 166.36 59.08 Total effective signal 281.59 100

[0112] (6) Open the two-way valve XII35 and use the hand pump II36 to pressurize the back pressure valve 31 to 15 MPa. Open the two-way valve III3 and the two-way valve I6 and use the booster pump 4 to pump CO 2 The gas in cylinder 1 is pressurized to CO 2 In the container 11, the two-way valve III3 and the two-way valve I6 are then closed.

[0113] Open the two-way valve II7 and the two-way valve IV14, and use the injection pump 5 to inject CO 2 The container 11 and the system pressure are pressurized to 22 MPa, and the volume pumped in by the injection pump 5 is recorded.

[0114] Then close the two-way valve IV14, open the injection valve 21 and the two-way valve XI30 to start the diffusion experiment. During this process, the pressure gauge II22 and the pressure gauge IV29 monitor the pressure at both ends of the core holder 24 in real time. The liquid micrometer 32 and the gas volume meter II33 are used to record the oil output and gas output at the outlet of the core holder 24 respectively.

[0115] (7) After the diffusion experiment pressure stabilizes, the core T is measured using a nuclear magnetic resonance measuring instrument 25. 1 and T 2 The signal values ​​and proportions of each area of ​​the spectrum are shown in Table 3.

[0116] Table 3 Core T after diffusion 1 and T 2 Signal value and ratio of each area of ​​the spectrum

[0117]

[0118]

[0119] (8) The pressure decay curve recorded in the experiment is as follows Figure 4 As shown, it can be clearly seen that the pressure decay curve can be divided into three linear segments, where the fitting formula of each linear segment, the slope m of ln(P(t))-t and the effective diffusion coefficient are shown in Table 4.

[0120] The analysis shows that there are three linear characteristics and CO 2 The displacement diffusion behavior is related to the linear segment 1, which can be considered as CO 2 The linear segment 2 is the dissolution start-up stage, the linear segment 2 is the displacement flow stage, and the linear segment 3 is the dissolution diffusion stage.

[0121] Table 4 Segmental fitting results of pressure failure curve and CO 2 Effective diffusion coefficient

[0122] Linear segment area Fitting formula m <![CDATA[D e / (cm 2 / s)]]> Linear segment 1 ln(P(t))=-0.0002t+3.1054 -0.0002 <![CDATA[2.0810×10 -2 ]]> Linear segment 2 ln(P(t))=-0.0006t+3.2158 -0.0006 <![CDATA[5.2660×10 -2 ]]> Linear segment 3 ln(P(t))=-0.00003t+2.7830 -0.00003 <![CDATA[3.4389×10 -3 ]]>

[0123] (9) The experimental record shows that the gas output at 0.101 MPa (50°C) is 1470 mL.

[0124] Using formula (6) This converts to a volume of 3.04 mL at 22 MPa.

[0125] At the inlet end of the core holder 24, CO 2 The gas pressure dropped from 22MPa to 15MPa, CO 2 The gas volume is converted into 12.34 mL at 22 MPa. Therefore, the CO buried in the core 2 The volume at 22 MPa is 9.3 mL.

[0126] Using formula (5) CO can be calculated 2 The sealing rate is 75.36%.

[0127] (10) Statistical analysis of the initial T of shale core 2 and T 1 The total effective signal value of the spectrum is 281.59, and the total signal value after removing the kerogen area is 279.76.

[0128] After diffusion, shale core T 2 and T 1 The total effective signal value of the spectrum is 208.11, and the total signal value of the kerogen area is 206.28. The difference between the two signals is 73.48. The total volume of oil and water saturated in this core is 0.5mL.

[0129] According to formula (7) CO can be calculated 2 Tectonic storage accounts for 1.4%, CO 2 The proportion of dissolved sealing is 98.60%.

[0130] (11) Based on T 2 and T 1 Spectrum measurement data, according to formula (9) It can be calculated that the total NMR signal amplitude of the adsorbed oil and water in the core in the initial state is 68.79, and the total NMR signal amplitude of the free oil and water is 210.97. After the diffusion is completed, the total NMR signal amplitude of the adsorbed oil and water in the core is 59.53, and the total NMR signal amplitude of the free oil and water is 146.75.

[0131] Therefore, the difference in the amplitude of the adsorbed oil-water NMR signals before and after diffusion is 9.26, and the difference in the amplitude of the free oil-water NMR signals is 64.22.

[0132] According to formula (8) CO can be calculated 2The adsorption storage ratio is 12.60%, CO 2 The free burial ratio is 87.40%.

[0133] (12) Close two-way valve II7 and two-way valve XI30, open two-way valve IX19, vent the gas inside the core, and use gas volume meter I23 to record the CO discharged. 2 , compared with the amount of buried gas calculated above, to verify the reliability of the experimental results.

[0134] The gas volume recorded in this example at 0.101 MPa (50° C.) is 4585 mL, with an error of 1.8% from the calculation.

Claims

1. A method for simultaneously evaluating the CO2 diffusion characteristics and storage status of shale oil reservoirs, characterized in that: It includes the following steps: (1) First, artificially create fractures in the sampled shale core, and then measure the basic physical properties of the shale core, including core dry weight, length, diameter, permeability, and porosity, and calculate the core pore volume; (2) Place the shale core in a container, evacuate it, and then pressurize it to saturate it with formation water. After saturation with formation water, record the core wet weight; (3) Prepare degassed oil for experimental simulation according to the formation crude oil viscosity data; (4) Under formation pressure, use the degassed oil prepared in step (3) to displace the shale core saturated with formation water to construct a shale core under irreducible water saturation; and record the water production; (5) Use nuclear magnetic resonance equipment to measure the T1 and T2 spectra of the shale core saturated with oil obtained in step (4); (6) Establish the corresponding relationship between the nuclear magnetic signal value and the actual saturated oil and water volume; calibrate the distribution characteristics of each fluid of adsorbed oil, free oil, adsorbed water, and free water inside the shale core; Among them, the saturated oil and water volume of the shale core is calculated by the following formula: In formula (1), V o is the volume of shale core saturated with crude oil, mL; V w is the saturated formation water volume of shale core, mL; V s is the total volume of shale core saturated with oil and water, mL; W1 is the dry weight of the core, g; W2 is the wet weight of the core, g; V1 is the terminal water output, mL; ρ w is the formation water density, g / cm 3 ; When calibrating the distribution characteristics of each fluid inside the shale core, first divide the boundaries of the occurrence states of each fluid in the nuclear magnetic T2-T1 spectrum according to the following criteria: ① Adsorbed oil: 0.2 ms < T2 < 1 ms, T1 / T2 > 10; ② Free oil: 1 ms < T2, T1 / T2 > 10; ③ Adsorbed water: T2 < 0.2 ms, T1 / T2 ≤ 100; ④ Free water: 0.2 ms < T2, T1 / T2 ≤ 10; ⑤ Kerogen: T2 < 0.2 ms, T1 / T2 > 100; Then calculate the proportion of each fluid based on the boundary division: (7) Inject CO2 for displacement and diffusion experiments, and record the oil production, gas production, and the pressure decay degree of CO2 at different times; (8) Measure the T1 and T2 spectra of the shale core after CO2 displacement and diffusion to clarify the oil and water distribution characteristics inside the shale core after CO2 displacement and diffusion; (9) Calculate the CO2 effective diffusion coefficient D e , and calculate the proportion of different CO2 storage forms and the total storage rate during the diffusion process; ①CO2 effective diffusion coefficient D e Calculated by the following formula: In formula (2), P(t) is the pressure change function related to time, MPa; P0 is the initial pressure, MPa; D e is the effective diffusion coefficient of CO2; A is the cross-sectional area of ​​the core, cm 2 ; t is time, s; V g is the volume of CO2 gas, mL; L is the core length, cm; Taking the logarithm of both sides of equation (2), we can get: According to the pressure decay degree of CO2 recorded at different times, the value of ln(P(t)) in formula (3) is obtained, and then the slope m of ln(P(t))-t is obtained by linear fitting, and D can be obtained according to calculation formula (4): e The value of; the calculation formula is as follows: In formula (4), V g is the volume of CO2 gas, mL; L is the core length, cm; m is the slope of ln(P(t))-t obtained by linear fitting; A is the cross-sectional area of ​​the core, cm 2 ; ② The CO2 sequestration rate is obtained according to the calculation formula (5): In formula (5), η c is the CO2 storage rate; V in V is the volume of CO2 injected, mL; out is the end outlet volume, mL; Among them, V in and V out First, convert the gas volume to the same pressure according to calculation formula (6), and then substitute it into formula (5) for calculation; In formula (6), P1 is the final pressure of decay, MPa; Z0 is the CO2 compression factor at the initial pressure; Z1 is the CO2 compression factor at the final pressure of decay; P b is atmospheric pressure, 0.101MPa; Z b V is the CO2 compression factor under atmospheric pressure; gb is the volume of CO2 collected at the end, mL; ③ The proportions of the structural sequestration form and the dissolution sequestration form are calculated according to formula (7): In formula (7), R c R is the proportion of CO2 structural storage; d is the proportion of CO2 dissolved storage; C s1 The cumulative signal amplitude of the T2 and T1 maps of the initial core after removing the kerogen area; C s2 The cumulative signal amplitude of the core T2 and T1 maps after the diffusion is completed, removing the kerogen area; ④ For the structural sequestration form, it is divided into two forms in the shale core: adsorbed sequestration and free sequestration; the proportions of adsorbed sequestration and free sequestration in the structural sequestration are calculated by formula (8): In formula (8), R a R is the proportion of CO2 adsorption storage to structural storage; f is the proportion of free CO2 storage to structural storage; S a1 S is the cumulative signal amplitude of adsorbed oil and water in the T2-T1 spectrum of the initial core; a2 S is the cumulative signal amplitude of adsorbed oil and water in the core T2-T1 spectrum after the diffusion is completed; f1 S is the cumulative signal amplitude of free oil and water in the T2-T1 spectrum of the core in the initial state; f2 C is the cumulative signal amplitude of free oil and water in the core T2-T1 spectrum after the diffusion is completed; s1 The cumulative signal amplitude of the T2 and T1 maps of the initial core after removing the kerogen area; C s2 The cumulative signal amplitude of the core T2 and T1 maps after the diffusion is completed, removing the kerogen area; Among them, the total NMR signal amplitude of adsorbed oil and water S a and the total NMR signal amplitude of free oil and water S f From formula (9), we get: In formula (9), S a is the total NMR signal amplitude of adsorbed oil and water; S ao is the total NMR signal amplitude of adsorbed oil; S aw is the total NMR signal amplitude of adsorbed water; S f is the total NMR signal amplitude of free oil and water; S fo is the total NMR signal amplitude of free oil; S fw is the total NMR signal amplitude of free water; (10) Control the injection end pressure to reduce it to atmospheric pressure, measure the volume of CO2 discharged, and verify the calculated storage result.

2. The method for simultaneously evaluating the CO2 diffusion characteristics and storage status of shale oil reservoirs according to claim 1, characterized in that: In step (1), wire cutting technology is used to artificially create fractures in the shale core.

3. The method for simultaneously evaluating the CO2 diffusion characteristics and storage status of shale oil reservoirs according to claim 1, characterized in that: In step (2), the pressure for pressurized saturation with formation water is 25 MPa, and the saturation time is 7 days.

4. The method for simultaneously evaluating the CO2 diffusion characteristics and storage status of shale oil reservoirs according to claim 1, characterized in that: In step (3), the degassed oil is selected from one or more of dodecane, kerosene, n-heptane, and field degassed crude oil.

5. The method for simultaneously evaluating the CO2 diffusion characteristics and storage status of shale oil reservoirs according to claim 1, characterized in that: In step (4), during the process of constructing a shale core under irreducible water saturation by saturating it with oil, when continuous oil production starts at the end of the shale core, first stop the displacement of the degassed oil, keep it stationary for 24 h under formation pressure, and then continue the displacement. Repeat this cycle until no water flows out at the end of the shale core to obtain a shale core saturated with oil.

6. An experimental device used in the method according to any one of claims 1 to 5, characterized in that: It includes a CO2 container, a water container, an oil container, and a core holder; The top part of the CO2 container is provided with two pipelines, wherein each of the two pipelines is provided with a two-way valve, namely, a two-way valve I and a two-way valve II; the two-way valve I is connected to the booster pump through a pipeline, the booster pump is connected to the CO2 cylinder through a two-way valve III and a pipeline, and a pressure gauge I is provided on the pipeline between the CO2 cylinder and the booster pump; A two-way valve IV is provided at the bottom of the CO2 container; The top and bottom of the water container are respectively provided with a two-way valve V and a two-way valve VI; The top and bottom of the oil container are respectively provided with a two-way valve VII and a two-way valve VIII; The two-way valve IV, two-way valve VI and two-way valve VIII are all connected to the four-way valve I through pipelines, and the four-way valve I is connected to the injection pump through a pipeline; The two-way valve II, two-way valve V and two-way valve VII are all connected to the four-way valve II through a pipeline, and the four-way valve II is connected to the inlet end of the core holder through a pipeline; a pressure gauge II, an injection valve and a four-way valve III are provided on the pipeline between the inlet end of the core holder and the four-way valve II; the four-way valve III is also connected to a vent valve and a two-way valve IX, and the two-way valve IX is connected to a gas volume meter I; The core holder is located in the provided nuclear magnetic resonance measuring instrument; The middle part of the core holder is connected to a hand pump I through a pipeline, and a pressure gauge III and a two-way valve X are provided on the pipeline; The outlet end of the core holder is connected to a back pressure valve via a pipeline, on which a pressure gauge IV and a two-way valve XI are provided; One end of the back pressure valve is connected to a liquid micrometer through a pipeline, and the liquid micrometer is connected to a gas volume meter II; The other end of the back pressure valve is connected to a hand pump II through a pipeline, and a pressure gauge V and a two-way valve XII are arranged on the pipeline.

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