Evaluation method for proportions of different types of wetting holes in rock

Abstract

The invention discloses a method for evaluating the proportion of different types of wetting holes in rock, and belongs to the technical field of oil-gas exploration and development, and the method comprises the following steps: drilling two parallel rock samples with similar holes and seepage, carrying out an oil (water) self-absorption and water (oil) drainage experiment after water (oil) saturation, obtaining nuclear magnetic resonance T1-T2 spectrums before and after the self-absorption experiment, and calculating the proportion of different types of wetting holes in the rock. And extracting nuclear magnetic resonance spectrums of an oil phase and a water phase. The self-absorption water amount and the self-absorption oil amount are calculated according to the change conditions of an oil peak and a water peak in the nuclear magnetic resonance spectrum before and after self-absorption, and finally the proportions of different types of wetted pores are calculated in combination with a substance balance principle, so that the evaluation method of the reservoir rock wettability is enriched.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas exploration and development, and particularly relates to a method for evaluating the proportion of different types of wetting pores in rocks. Background Art

[0002] Wettability is one of the important characteristic parameters of reservoir rocks in oil and gas reservoirs. It determines the occurrence characteristics of oil and water phases in the microscopic pores of rocks. At the same time, wettability also has a great impact on the irreducible water saturation, residual oil saturation, and oil-water ratio after water breakthrough in the reservoir. Therefore, accurately characterizing the wettability of reservoir rocks is of great significance in studying the occurrence characteristics of oil and water, oil-water seepage characteristics, and improving oil recovery.

[0003] Traditional wettability measurement methods include the contact angle method, the USBM method, and the Amott method. These methods can accurately measure the wettability of reservoir rocks when applied in conventional reservoirs. However, when applied in unconventional reservoir rocks, due to the characteristics of low porosity and low permeability in unconventional reservoirs, there are large errors in their application. With the application and development of nuclear magnetic resonance technology, due to its characteristics of rapid, accurate, and non-destructive measurement of rock physical properties, nuclear magnetic resonance technology has gradually become one of the main means to explore wettability. Currently, the methods for evaluating the wettability of reservoir rocks based on nuclear magnetic resonance technology mainly include: (1) the Amott method combined with nuclear magnetic resonance technology (a new method for determining the wettability of tight rocks, patent number CN109030292). This method uses nuclear magnetic resonance technology to quantitatively calculate the changes in fluid saturation in processes such as spontaneous imbibition and displacement, calculates the hydrophilic index and lipophilic index of the rock, and then calculates the Amott index to judge the wettability of the reservoir rock; (2) the nuclear magnetic resonance T2 spectrum method (Johannesen et al., 2006, 2007). The basic principle of this method is that the relaxation time of the non-wetting phase fluid is the same as that in the free state because it does not contact the pore wall, while the relaxation time of the wetting phase fluid is smaller than that in the free state due to surface relaxation. By analyzing the relaxation spectrum shift of pore media and rocks with different wettabilities and wetting intensities, the wetting characteristics can be qualitatively discriminated; (3) the nuclear magnetic resonance T1-T2 spectrum method (Valori et al., 2017). The basic principle of this method is that the two-dimensional nuclear magnetic resonance relaxation spectrum has a certain correlation with the contact relationship between pore fluid and the surface of the skeleton particles. Therefore, the wettability of pore media can be discriminated by the T1 / T2 ratio method; (4) the nuclear magnetic resonance D-T2 spectrum method (Cao Minh et al., 2015). This method mainly relies on the different diffusion coefficients of oil and water in the rock sample, and uses the different positions of the oil peak and water peak on the D-T2 curve to effectively distinguish the oil and water signals, thereby accurately judging the wettability of the rock sample.

[0004] However, the current testing methods have the following deficiencies:

[0005] (1) The Amott method combined with nuclear magnetic resonance technology is more used to evaluate the macroscopic wettability of rock samples. That is, when the rock samples show oil-wet, water-wet or neutral wettability, it is impossible to evaluate the wettability of different pore-throat spaces at the pore scale.

[0006] (2) When evaluating wettability by nuclear magnetic resonance T2 spectrum method, it is usually necessary to shield the nuclear magnetic resonance signal of a certain phase in the experiment, which results in the inability to use actual underground fluids, and further causes errors between the evaluation results and the actual underground situation.

[0007] (3) Although the nuclear magnetic resonance D-T2 two-dimensional spectrum method can effectively distinguish oil and water signals, it is difficult to apply this method to unconventional reservoir rocks such as shale oil with extremely short relaxation component information.

[0008] (4) The evaluation of wettability by nuclear magnetic resonance T1-T2 two-dimensional spectrum method still remains at the qualitative stage, and the evaluation of wettability is not precise enough, making it difficult to quantitatively characterize the wettability of reservoir rocks.

[0009] In summary, wettability is one of the important characteristic parameters of reservoir rocks, which can reflect the occurrence state of fluids in reservoir pores. At present, the indoor evaluation methods of wettability have large errors when applied to unconventional reservoirs with low porosity and low permeability, mostly remaining at the qualitative stage of wettability evaluation, and it is difficult to achieve quantitative evaluation by some means. Summary of the Invention

[0010] The present invention provides a method for evaluating the proportion of different types of wetting pores in rocks, which conducts quantitative evaluation of reservoir wettability through imbibition experiments and nuclear magnetic resonance technology, and realizes the identification and measurement of different types of wetting pores at the pore scale.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for evaluating the proportion of different types of wetting pores in rocks, comprising the following steps:

[0013] Step S1: Divide the plug rock sample into two sections to make parallel rock samples: the first section of rock sample and the second section of rock sample;

[0014] Step S2: Conduct an experiment on the first section of rock sample to vacuumize and pressurize to saturate it with manganese chloride solution. After the first section of rock sample is completely saturated, measure the mass of the first section of rock sample, and at the same time obtain the nuclear magnetic resonance T1-T2 spectrum curve of the first section of rock sample saturated with manganese chloride solution; conduct an imbibition oil and drainage experiment on the first section of rock sample after saturation. When the imbibition oil and drainage volume remains stable for a continuous set time, end the imbibition oil and drainage experiment, record the imbibition oil and drainage volume at this time, dry and weigh the first section of rock sample, and at the same time obtain the nuclear magnetic resonance T1-T2 spectrum curve after imbibition oil and drainage;

[0015] Perform a vacuum pressurization experiment on the second rock sample to saturate it with formation crude oil. After complete saturation, measure the mass of the second rock sample, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve of the second rock sample saturated with crude oil. Conduct a self-water imbibition oil displacement experiment on the second rock sample after saturation is completed. End the self-water imbibition oil displacement experiment when the amount of oil displaced by self-water imbibition remains unchanged for a continuous set time. Record the amount of oil displaced by self-water imbibition at this time, dry the rock sample and weigh it, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve after self-water imbibition oil displacement.

[0016] S3. Calculate the proportion of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample based on the nuclear magnetic resonance T1-T2 spectrum curves of the first rock sample saturated with manganese chloride solution, the nuclear magnetic resonance T1-T2 spectrum curves after self-oil imbibition and water drainage, the nuclear magnetic resonance T1-T2 spectrum curves of the second rock sample saturated with crude oil, and the nuclear magnetic resonance T1-T2 spectrum curves after self-water imbibition oil displacement.

[0017] Further, in step S1, the determination requirements for parallel rock samples are as follows:

[0018] |φ1 - φ2| ≤ 0.2% (1)

[0019]

[0020] where φ1 is the porosity of the first rock sample, φ2 is the porosity of the second rock sample, K1 is the permeability of the first rock sample, and K2 is the permeability of the second rock sample;

[0021] For two rock samples that simultaneously satisfy equations (1) and (2), it is determined that the two rock samples meet the requirements for parallel rock samples; otherwise, it is determined that the two rock samples do not meet the requirements for parallel rock samples.

[0022] Further, in step S2, the determination requirements for whether the rock sample is completely saturated are as follows:

[0023]

[0024]

[0025]

[0026] In the formula: m1 - the mass of the rock sample after saturation is completed; m0 - the mass of the rock sample before saturation is completed; ρ - the density of the fluid used for saturation; V peff —— the effective pore volume of the rock sample; V - the total volume of the rock sample; φ p —— the effective porosity of the rock sample; φ He — the helium-measured porosity of the rock sample (φ He = φ1 ≈ φ2);

[0027] When the effective porosity φ of the rock sample pand the helium-measured porosity φ of the rock sample He When the requirement of Equation (5) is satisfied, the evacuation and saturation of the rock sample reach the requirement; otherwise, it is determined that the evacuation and saturation of the rock sample do not meet the requirement, and the rock sample is resaturated until Equation (5) is satisfied.

[0028] Furthermore, in step S2, the method for determining the concentration of the manganese chloride solution used is as follows: Prepare manganese chloride solutions with various different concentrations, and select the concentration that can separate the oil peak and water peak in the nuclear magnetic resonance T1-T2 spectrum.

[0029] Furthermore, in step S2, the set time is 24 hours.

[0030] Furthermore, step S3 includes the following steps:

[0031] S3.1. According to the nuclear magnetic resonance T1-T2 spectrum curves of the first-section rock sample saturated with the saturated manganese chloride solution, the nuclear magnetic resonance T1-T2 spectrum curve after self-aspirating oil and draining water, the nuclear magnetic resonance T1-T2 spectrum curve of the second-section rock sample saturated with crude oil, and the nuclear magnetic resonance T1-T2 spectrum curve after self-aspirating water and draining oil, extract the oil spectrum and water spectrum of the rock sample after the end of self-aspirating oil and draining water and self-aspirating water and draining oil, and calculate the self-aspirating oil drainage volume and self-aspirating water drainage volume of the rock sample, the ratio of the pore volume occupied by the oil phase to the rock volume after the end of self-aspirating oil and draining water, and the ratio of the pore volume occupied by the water phase to the rock volume after the end of self-aspirating water and draining oil;

[0032] S3.2. According to the principle of material balance, construct a material balance equation after the end of self-aspirating oil and draining water and self-aspirating water and draining oil, and substitute the self-aspirating oil drainage volume and self-aspirating water drainage volume of the rock sample, the ratio of the pore volume occupied by the oil phase to the rock volume after the end of self-aspirating oil and draining water, and the ratio of the pore volume occupied by the water phase to the rock volume after the end of self-aspirating water and draining oil into the material balance equation to construct a ternary linear equation about the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity;

[0033] S3.3. Solve the ternary linear equation to obtain the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity of the rock sample.

[0034] Furthermore, in step S3.1, the self-aspirating oil drainage volume ratio p of the rock sample is calculated according to the following formula o , the self-aspirating water drainage volume ratio p w , the ratio φ of the pore volume occupied by the oil phase to the rock volume after the end of self-aspirating oil and draining water o and the ratio φ of the pore volume occupied by the water phase to the rock volume after the end of self-aspirating water and draining oil w :

[0035]

[0036]

[0037] φ o = p o × φ1(8)

[0038] φ w = p w × φ2(9)

[0039] Wherein:

[0040] A o —— The nuclear magnetic resonance signal amplitude of the oil phase after the self - suction oil and water drainage ends;

[0041] A o-w-o —— The total nuclear magnetic resonance signal amplitude of the oil phase and the water phase after the self - suction oil and water drainage ends;

[0042] A w —— The nuclear magnetic resonance signal amplitude of the water phase after the self - suction water and oil drainage ends;

[0043] A w-w-o —— The total nuclear magnetic resonance signal amplitude of the oil phase and the water phase after the self - suction water and oil drainage ends.

[0044] Furthermore, the system of linear equations in step S3.2 is:

[0045]

[0046] Wherein: φ o-wet —— The oil - wet pore porosity in the rock sample; φ w-wet —— The water - wet pore porosity in the rock sample; φ mix-wet —— The mixed - wet pore porosity in the rock sample.

[0047] Furthermore, in step 3.3, according to equations (11) - (13), calculate the proportion of water - wet pores, oil - wet pores, and mixed - wet pores in the rock sample;

[0048]

[0049]

[0050] I mix = 1 - I w - I o (13)

[0051] Wherein: I w , I o , I mix —— The proportions of water - wet pores, oil - wet pores, and mixed - wet pores.

[0052] Furthermore, in step 1, before dividing the plunger rock sample into two sections, wash and dry the plunger rock sample.

[0053] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0054] The present invention utilizes the characteristics of nuclear magnetic resonance technology to quickly, accurately and non-destructively measure the fluids in rock samples. Drill two parallel rock samples with similar pore and permeability. After saturating them with water (oil), conduct the spontaneous imbibition of oil (water) and drainage of water (oil) experiments, obtain the nuclear magnetic resonance T1-T2 spectra before and after the spontaneous imbibition experiment, and extract the nuclear magnetic resonance spectra of the oil phase and the water phase from them. Calculate the imbibed water volume and the imbibed oil volume according to the changes in the oil peaks and water peaks in the nuclear magnetic resonance spectra before and after the spontaneous imbibition, and finally calculate the proportion of different types of wetting pores by combining the material balance principle. This method determines the proportion of different types of wetting pores in reservoir rocks at the pore scale, enriching the evaluation methods of reservoir rock wettability. At the same time, the introduction of the nuclear magnetic resonance two-dimensional spectrum technology makes the present invention also have the characteristics of simple process, more objective and accurate evaluation results.

[0055] Furthermore, by preparing multiple manganese chloride solutions with different concentrations in advance, selecting the concentration that can separate the oil peaks and water peaks in the nuclear magnetic resonance T1-T2 spectrum, and using the manganese chloride solution with this concentration in the subsequent experimental water, within the permeability range of shale oil (<0.2 mD), after experiments with multiple concentrations and rock samples with different permeabilities, a 5% manganese chloride solution is applicable, that is, for the same type of rock, it is not necessary to optimize the concentration each time before the experiment, which can improve the efficiency and operability of the entire evaluation process. Description of the Drawings

[0056] Figure 1 is the specific implementation process of the method of the present invention;

[0057] Figure 2 is the nuclear magnetic resonance T1-T2 two-dimensional spectral curve for the separation of oil peaks and water peaks. Detailed Embodiments

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0059] Refer to Figure 1 , a method for evaluating the proportion of different types of wetting pores in a rock, comprising the following steps:

[0060] Step S1: Select a cylindrical plunger rock sample. After washing the oil and drying the cylindrical plunger rock sample, cut the plunger rock sample into two sections to make parallel rock samples, divided into the first section of rock sample and the second section of rock sample. Measure the dry weight, length, diameter, porosity and permeability of the two sections of rock samples, and record them as m 01 (m02 )、L1 (L2), D1 (D2), φ1 (φ2) and K1 (K2);

[0061] Step S2. Conduct an experiment on the first - stage rock sample by evacuating and pressurizing it to saturate it with a manganese chloride solution with a concentration of 5%. After complete saturation, measure the mass m1 of the first - stage rock sample. At the same time, use a high - temperature and high - pressure nuclear magnetic resonance on - line monitor to obtain the nuclear magnetic resonance T1 - T2 spectral curve of the first - stage rock sample saturated with the manganese chloride solution. The determination process of the concentration of the 5% manganese chloride solution is as follows: Prepare manganese chloride solutions with various different concentrations, and preferably select the concentration that can separate the oil peak and water peak in the nuclear magnetic resonance T1 - T2 spectrum.

[0062] Step S3. Put the saturated first - stage rock sample into a self - suction bottle filled with formation crude oil to carry out a self - suction oil - drainage experiment. During the experiment, record the self - suction oil - drainage volume multiple times. When the self - suction oil - drainage volume remains stable for 24 consecutive hours, end the self - suction oil - drainage experiment, and record the self - suction oil - drainage volume at this time as V o1 , take out the first - stage rock sample from the self - suction bottle, dry the oil on its surface, and weigh it. Record its mass as m2. At the same time, use a high - temperature and high - pressure nuclear magnetic resonance on - line monitor to obtain the nuclear magnetic resonance T1 - T2 spectral curve after self - suction oil - drainage.

[0063] Step S4. Conduct an experiment on the second - stage rock sample by evacuating and pressurizing it to saturate it with formation crude oil. After complete saturation, measure the mass m3 of the second - stage rock sample. At the same time, use a high - temperature and high - pressure nuclear magnetic resonance on - line monitor to obtain the nuclear magnetic resonance T1 - T2 spectral curve of the second - stage rock sample saturated with crude oil.

[0064] Step S5. Put the saturated second - stage rock sample into a self - suction bottle filled with a manganese chloride solution with a concentration of 5% to carry out a self - suction water - oil - drainage experiment. During the experiment, record the self - suction water - oil - drainage volume multiple times. When the self - suction water - oil - drainage volume remains stable for 24 consecutive hours, end the self - suction water - oil - drainage experiment, and record the self - suction water - oil - drainage volume at this time as V o2 , take out the rock sample from the self - suction bottle, dry the water on its surface, and weigh it. Record its mass as m4. At the same time, use a high - temperature and high - pressure nuclear magnetic resonance on - line monitor to obtain the nuclear magnetic resonance T1 - T2 spectral curve after self - suction water - oil - drainage.

[0065] S6. Combine the changes in the nuclear magnetic resonance T1 - T2 spectra after self - suction oil - drainage and self - suction water - oil - drainage and the material balance principle to calculate and obtain the proportions of water - wet pores, oil - wet pores, and mixed - wet pores in the rock sample.

[0066] A further technical solution is that the basic physical property parameters such as the porosity and permeability of the rock sample in Step S1 are based on the national standard "GB / T 29172 - 2012 Core Analysis Method".

[0067] A further technical solution is that the determination requirements for the parallel rock samples in Step S1 are as follows:

[0068] |φ1 - φ2| ≤ 0.2% (1)

[0069]

[0070] For two rock samples that simultaneously satisfy Equation (1) and Equation (2), it is determined that the two rock samples meet the requirements of parallel rock samples; if either Equation (1) or Equation (2) is not satisfied, it is determined that the two rock samples do not meet the requirements of parallel rock samples, and rock samples need to be reselected until the requirements of parallel rock samples are met.

[0071] A further technical solution is that the determination requirements for the saturation degree of the rock samples in steps S2 and S4 are as shown in Formula (5):

[0072]

[0073]

[0074]

[0075] In the formula: m1——the mass of the rock sample after saturation completion, g;

[0076] m0——the mass of the rock sample before saturation completion, g;

[0077] V peff ——the effective pore volume of the rock sample, cm 3 ;

[0078] ρ——the density of the fluid used for saturation, g / cm 3 ;

[0079] φ p ——the effective porosity of the rock sample, decimal;

[0080] φ He —the helium-measured porosity of the rock sample, φ He = φ1 ≈ φ2;

[0081] V——the total volume of the rock sample, cm 3 .

[0082] When the relationship between the effective porosity φ p of the rock sample and the porosity φ He of the rock sample obtained according to the industry standard satisfies Equation (5), it is determined that the evacuation saturation of the rock sample meets the requirements; if Equation (5) is not satisfied, it is determined that the evacuation saturation of the rock sample does not meet the requirements, and the rock sample needs to be resaturated until Equation (5) is satisfied. Obtaining the rock sample according to the industry standard refers to the porosity determined by experimental measurement in the national standard "GB / T 29172 - 2012 Core Analysis Method".

[0083] A further technical solution is that the method for calculating the proportions of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample in step S6 is as follows:

[0084] S61. According to the NMR T1-T2 map distributions after the end of spontaneous imbibition of oil and drainage of water and spontaneous imbibition of water and drainage of oil, extract the oil spectrum and water spectrum of the rock sample after the end of spontaneous imbibition of oil and drainage of water and spontaneous imbibition of water and drainage of oil, and calculate the proportion p of the amount of oil drained by spontaneous imbibition of the rock sample using formulas (6) to (9). o The proportion p of the amount of water drained by spontaneous imbibition of water and the amount of oil drained. w The ratio φ of the pore volume occupied by the oil phase to the rock volume after the end of spontaneous imbibition of oil and drainage of water. o And the ratio φ of the pore volume occupied by the water phase to the rock volume after the end of spontaneous imbibition of water and drainage of oil. w .

[0085]

[0086]

[0087] φ o = p o × φ1 (8)

[0088] φ w = p w × φ2 (9)

[0089] In the formula:

[0090] A o —— The NMR signal amplitude of the oil phase after the end of spontaneous imbibition of oil and drainage of water, which can be read from the high-temperature and high-pressure NMR on-line monitor;

[0091] A o-w-o —— The total NMR signal amplitude of the oil phase and the water phase after the end of spontaneous imbibition of oil and drainage of water, which can be read from the high-temperature and high-pressure NMR on-line monitor;

[0092] A w —— The NMR signal amplitude of the water phase after the end of spontaneous imbibition of water and drainage of oil, which can be read from the high-temperature and high-pressure NMR on-line monitor;

[0093] A w-w-o —— The total NMR signal amplitude of the oil phase and the water phase after the end of spontaneous imbibition of water and drainage of oil, which can be read from the high-temperature and high-pressure NMR on-line monitor;

[0094] φ o —— The ratio of the pore volume occupied by the oil phase to the rock volume after the end of spontaneous imbibition of oil and drainage of water, %;

[0095] φ w —— The ratio of the pore volume occupied by the water phase to the rock volume after the end of spontaneous imbibition of water and drainage of oil, %;

[0096] S62. According to the principle of material balance, a material balance equation (10) is constructed after the self-aspirating oil drainage and self-aspirating water drainage are completed. Substituting the calculation results in equations (6) to (9) into equation (10) can construct a ternary linear equation about the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity:

[0097]

[0098] In the formula: φ o-wet ——The oil-wet pore porosity in the rock sample, %;

[0099] φ w-wet ——The water-wet pore porosity in the rock sample, %;

[0100] φ mix-wet ——The mixed-wet pore porosity in the rock sample, %;

[0101] S63. By solving the above ternary linear equation, the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity in the rock sample are obtained respectively, and the proportions of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample are calculated according to equations (11) to (13).

[0102]

[0103]

[0104] I mix = 1 - I w -I o (13)

[0105] In the formula: I w 、I o 、I mix ——The proportions of water-wet pores, oil-wet pores, and mixed-wet pores.

[0106] Example

[0107] Next, the technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0108] As Figure 1 shown, a method for evaluating the proportion of different types of wet pores in a rock includes the following steps:

[0109] Step S1: Select a cylindrical plunger rock sample. After washing and drying the cylindrical plunger rock sample, cut the plunger rock sample into two sections to make parallel rock samples, which are divided into the first-section rock sample and the second-section rock sample. According to the regulations in the national standard GB / T29172-2012 "Rock Sample Analysis Method", measure the dry weight, length, diameter, porosity and permeability of the two-section rock samples, and record them as m 01 (m 02 ), L1 (L2), D1 (D2), φ1 (φ2) and K1 (K2). When the two-section rock samples simultaneously satisfy Equation (1) and Equation (2), it is determined that the two-section rock samples meet the requirements of parallel rock samples; if they do not satisfy any one of Equation (1) and Equation (2), it is determined that the two-section rock samples do not meet the requirements of parallel rock samples, and the rock samples need to be reselected.

[0110] |φ1 - φ2| ≤ 0.2% (1)

[0111]

[0112] Step S2: Conduct an experiment on the first-section rock sample to vacuumize and pressurize it to saturate it with a manganese chloride solution with a mass concentration of 5%. First, put the first-section rock sample into an intermediate container and vacuumize it to 133 Pa, and then pressurize and saturate it with formation water solution at a pressure of 25 MPa for 48 hours. Then measure the mass of the first-section rock sample and record it as m1, and calculate the effective pore volume V peff and the effective porosity φ p . When the effective porosity φ p of the rock sample and the helium-measured porosity φ He of the rock sample satisfy Equation (5), the saturation of the rock sample is completed; otherwise, resaturate it according to the above steps. At the same time, turn on the nuclear magnetic resonance instrument, set the parameters of the nuclear magnetic resonance instrument, and test to obtain the nuclear magnetic resonance T1-T2 spectral curve of the first-section rock sample saturated with the manganese chloride solution;

[0113]

[0114]

[0115]

[0116] In the formula: m1——the mass of the rock sample after saturation is completed, g;

[0117] m0——the mass of the rock sample before saturation is completed, g;

[0118] V peff ——the effective pore volume of the rock sample, cm 3 ;

[0119] ρ——the density of the fluid used for saturation, g / cm 3 ;

[0120] φ p —— The effective porosity of the rock sample, in decimals;

[0121] φ He — The helium-measured porosity of the rock sample;

[0122] V — The total volume of the rock sample, in cm 3 。

[0123] Step S3: Place the first section of the rock sample after saturation into a self-aspiration bottle filled with formation crude oil to conduct a self-aspiration oil and water drainage experiment. During the experiment, record the self-aspiration oil and water drainage volume multiple times. When the self-aspiration oil and water drainage volume remains stable for 24 consecutive hours, end the self-aspiration oil and water drainage experiment, and record the self-aspiration oil and water drainage volume at this time as V o1 . Take out the first section of the rock sample from the self-aspiration bottle, dry the oil on its surface, and weigh it. Record its mass as m2. At the same time, obtain the nuclear magnetic resonance T1-T2 spectral curve after self-aspiration oil and water drainage;

[0124] Step S4: Conduct a vacuum pumping and pressure saturation experiment on the second section of the rock sample according to the requirements of Step S3. After the rock sample is saturated, test and obtain the nuclear magnetic resonance T1-T2 two-dimensional spectrum of the second section of the rock sample completely saturated with crude oil;

[0125] Step S5: Place the second section of the rock sample after saturation into a self-aspiration bottle filled with a 5% manganese chloride solution to conduct a self-aspiration water and oil drainage experiment. During the experiment, record the self-aspiration water and oil drainage volume multiple times. When the self-aspiration water and oil drainage volume remains stable for 24 consecutive hours, end the self-aspiration water and oil drainage experiment, and record the self-aspiration water and oil drainage volume at this time as V o2 . Take out the rock sample from the self-aspiration bottle, dry the water on its surface, and weigh it. Record its mass as m4. At the same time, obtain the nuclear magnetic resonance T1-T2 spectral curve after self-aspiration water and oil drainage;

[0126] S6: Calculate and obtain the proportions of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample by combining the changes in the nuclear magnetic resonance T1-T2 spectra after self-aspiration oil and water drainage and self-aspiration water and oil drainage and the material balance principle.

[0127] S61: According to the distribution of the nuclear magnetic resonance T1-T2 spectra after self-aspiration oil and water drainage and self-aspiration water and oil drainage (as Figure 2 shown), extract the oil spectrum and water spectrum of the rock sample after self-aspiration oil and water drainage and self-aspiration water and oil drainage, and calculate the self-aspiration oil and water drainage volume of the rock sample using formulas (6) to (9).

[0128]

[0129]

[0130] φ o =p o ×φ1 (8)

[0131] φ w = p w ×φ2 (9)

[0132] Where: A o ——The amplitude of the nuclear magnetic resonance signal of the oil phase after the end of self - absorbing oil and draining water;

[0133] A o-w-o ——The total amplitude of the nuclear magnetic resonance signals of the oil phase and the water phase after the end of self - absorbing oil and draining water;

[0134] A w ——The amplitude of the nuclear magnetic resonance signal of the water phase after the end of self - absorbing water and draining oil;

[0135] A w-w-o ——The total amplitude of the nuclear magnetic resonance signals of the oil phase and the water phase after the end of self - absorbing water and draining oil;

[0136] φ o ——The ratio of the pore volume occupied by the oil phase to the rock volume after the end of self - absorbing oil and draining water, %;

[0137] φ w ——The ratio of the pore volume occupied by the water phase to the rock volume after the end of self - absorbing water and draining oil, %;

[0138] S62. According to the principle of material balance, construct the material balance equations (Equation 10) after the end of self - absorbing oil and draining water and self - absorbing water and draining oil, and substitute the calculation results in Equations (6) - (9) into Equation (10) to construct a ternary linear equation about the porosities of water - wet pores, oil - wet pores and mixed - wet pores:

[0139]

[0140] Where: φ o-wet ——The porosity of oil - wet pores in the rock sample, %;

[0141] φ w-wet ——The porosity of water - wet pores in the rock sample, %;

[0142] φ mix-wet ——The porosity of mixed - wet pores in the rock sample, %;

[0143] S63. Obtain the porosities of water - wet pores, oil - wet pores and mixed - wet pores in the rock sample by solving the above ternary linear equation, and calculate the proportions of water - wet pores, oil - wet pores and mixed - wet pores in the rock sample according to Equations (11) - (13).

[0144]

[0145]

[0146] Imix = 1 - I w -I o (13)

[0147] where: I w 、I o 、I mix —— the proportions occupied by water-wet pores, oil-wet pores, and mixed-wet pores.

[0148] As described above, it is not any form of limitation to the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make changes or modifications using the disclosed technical content within the scope of the technical solution of the present invention as equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the proportion of different types of wetting pores in a rock, characterized in that, It includes the following steps: Step S1: Divide the plunger rock sample into two sections to make parallel rock samples: the first-section rock sample and the second-section rock sample; Step S2: Conduct an experiment of vacuumizing and pressurizing to saturate the first-section rock sample with manganese chloride solution. After the first-section rock sample is completely saturated, measure the mass of the first-section rock sample, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve of the first-section rock sample saturated with manganese chloride solution. Conduct a self-absorbing oil and draining water experiment on the first-section rock sample after saturation. End the self-absorbing oil and draining water experiment when the self-absorbing oil and draining water volume remains stable for a continuously set time. Record the self-absorbing oil and draining water volume at this time. Dry and weigh the first-section rock sample, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing oil and draining water; Conduct an experiment of vacuumizing and pressurizing to saturate the second-section rock sample with formation crude oil. After complete saturation, measure the mass of the second-section rock sample, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve of the second-section rock sample saturated with crude oil. Conduct a self-absorbing water and draining oil experiment on the second-section rock sample after saturation. End the self-absorbing water and draining oil experiment when the self-absorbing water and draining oil volume remains unchanged for a continuously set time. Record the self-absorbing water and draining oil volume at this time. Dry and weigh the rock sample, and simultaneously obtain the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing water and draining oil; S3: Calculate the proportion of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample according to the nuclear magnetic resonance T1-T2 spectrum curve of the first-section rock sample saturated with manganese chloride solution, the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing oil and draining water, the nuclear magnetic resonance T1-T2 spectrum curve of the second-section rock sample saturated with crude oil, and the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing water and draining oil.

2. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, characterized in that In the above step S1, the determination requirements for parallel rock samples are as follows: |φ1 - φ2| ≤ 0.2% (1) where φ1 is the porosity of the first-section rock sample, φ2 is the porosity of the second-section rock sample, K1 is the permeability of the first-section rock sample, and K2 is the permeability of the second-section rock sample; For two sections of rock samples that simultaneously meet formula (1) and formula (2), it is determined that the two sections of rock samples meet the requirements for parallel rock samples; otherwise, it is determined that the two sections of rock samples do not meet the requirements for parallel rock samples.

3. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, wherein In the above step S2, the determination requirements for whether the rock sample is completely saturated are as follows: Where: m1—the mass of the rock sample after saturation is completed; m0—the mass of the rock sample before saturation is completed; ρ—the density of the fluid used for saturation; V peff —the effective pore volume of the rock sample; V—the total volume of the rock sample; φ p —the effective porosity of the rock sample; φ He —the helium porosity of the rock sample; When the effective porosity φ of the rock sample p and the porosity φ of the rock sample He meet the formula (5), the evacuation saturation of the rock sample reaches the requirement; otherwise, it is determined that the evacuation saturation of the rock sample does not meet the requirement, and the rock sample is resaturated until the formula (5) is satisfied.

4. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, wherein In the above step S2, the method for determining the concentration of the manganese chloride solution used is: prepare manganese chloride solutions with various different concentrations, and select the concentration that can separate the oil peak and water peak in the nuclear magnetic resonance T1-T2 spectrum.

5. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, characterized in that In the above step S2, the set time is 24 hours.

6. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, characterized in that, The above step S3 includes the following steps: S3.1: According to the nuclear magnetic resonance T1-T2 spectrum curve of the first-section rock sample saturated with manganese chloride solution, the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing oil and draining water, the nuclear magnetic resonance T1-T2 spectrum curve of the second-section rock sample saturated with crude oil, and the nuclear magnetic resonance T1-T2 spectrum curve after self-absorbing water and draining oil, extract the oil spectrum and water spectrum of the rock sample after the end of self-absorbing oil and draining water and self-absorbing water and draining oil, and calculate the self-absorbing oil and draining water volume and self-absorbing water and draining oil volume of the rock sample, the ratio of the pore volume occupied by the oil phase to the rock volume after the end of self-absorbing oil and draining water, and the ratio of the pore volume occupied by the water phase to the rock volume after the end of self-absorbing water and draining oil; S3.

2. According to the principle of material balance, establish the material balance equations after the self-aspirated oil drainage and self-aspirated water oil drainage are completed, and substitute the self-aspirated oil drainage volume and self-aspirated water oil drainage volume of the rock sample, the ratio of the pore volume occupied by the oil phase to the rock volume after the self-aspirated oil drainage is completed, and the ratio of the pore volume occupied by the water phase to the rock volume after the self-aspirated water oil drainage is completed into the material balance equation to establish a ternary linear equation about the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity; S3.

3. Solve the ternary linear equation to obtain the water-wet pore porosity, oil-wet pore porosity, and mixed-wet pore porosity of the rock sample.

7. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 6, wherein In the step S3.1, the self-aspirated oil drainage ratio p of the rock sample is calculated according to the following formula o , the self-aspirated water oil drainage ratio p w , the ratio φ of the pore volume occupied by the oil phase to the rock volume after the self-aspirated oil drainage ends o and the ratio φ of the pore volume occupied by the water phase to the rock volume after the self-aspirated water oil drainage ends w : φ o = p o × φ1(8) φ w = p w × φ2 (9) Where: A o —— NMR signal amplitude of the oil phase after the self-priming oil drainage ends; A o-w-o —— the total nuclear magnetic resonance signal amplitude of the oil phase and the water phase after the self-priming oil drainage ends; A w —— the NMR signal amplitude of the aqueous phase after the self-absorbing oil drainage ends; A w-w-o —— The total nuclear magnetic resonance signal amplitude of the oil phase and the water phase after the self - absorbing oil drainage ends.

8. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 6, characterized in that, The ternary linear equation in step S3.2 is: Where: φ o-wet —— Oil-wet pore porosity in the rock sample; φ w-wet —— Water-wet pore porosity in the rock sample; φ mix-wet —— Mixed-wet pore porosity in the rock sample.

9. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 6, characterized in that, In step 3.3, calculate the proportion of water-wet pores, oil-wet pores, and mixed-wet pores in the rock sample according to formulas (11) to (13); I mix = 1 - I w -I o (13) Where: I w 、I o 、I mix —— Proportions occupied by water-wet pores, oil-wet pores, and mixed-wet pores.

10. The evaluation method for the proportion of different types of wetting pores in a rock according to claim 1, characterized in that, In step 1, before dividing the plug rock sample into two sections, wash the oil and dry the plug rock sample.

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