Radius cutoff value prediction method based on double eigenvalues

Abstract

The invention relates to a radius cut-off value prediction method based on double characteristic values, which comprises the following steps: on the basis of basic principles of a nuclear magnetic resonance core experiment and a high-pressure mercury injection core experiment, taking a high-pressure mercury injection maximum pore throat radius and a high-pressure mercury injection minimum pore throat radius as double characteristic values, and finding corresponding transverse relaxation time to predict the radius cut-off value of the core through the double characteristic values. The conversion coefficient is solved in a volume weighting mode, and then a calculation method of the radius cutoff value is established in combination with the T2 cutoff value. The invention provides a key technical means for accurately distinguishing the bound fluid and the free fluid in the rock core sample.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and specifically relates to a method for predicting a radius cut-off value based on double eigenvalues. Background Art

[0002] When the core sample is saturated with water, the nuclear magnetic resonance core experiment can reflect the almost complete pore-throat distribution inside the rock. Then, the core sample is dehydrated by means of centrifugation or displacement. By comparing the nuclear magnetic resonance core experiment after dehydration with the nuclear magnetic resonance core experiment of the saturated water, a T 2 cut-off value can be found on the nuclear magnetic resonance pore-throat distribution curve of the saturated water, which divides the nuclear magnetic resonance pore-throat distribution curve of the saturated water into two parts. The fluid located T on the left side of the 2 cut-off value is regarded as the bound fluid, and the fluid located T on the right side of the 2 cut-off value is regarded as the movable fluid.

[0003] In practical applications, it is found that when the same centrifugal force or displacement pressure is applied to different core samples, the obtained T 2 cut-off values are not the same, indicating that the fluid distribution characteristics of different core samples cannot be directly compared only based on T the 2 cut-off value. Therefore, if a method for converting the T 2 cut-off value into a radius cut-off value can be established, it will be possible to use the radius cut-off value to conduct a more reliable comparative analysis of different core samples, thereby significantly improving the accuracy and credibility of the analysis results. Summary of the Invention

[0004] The present invention aims at the above problems and proposes a method for predicting a radius cut-off value based on double eigenvalues.

[0005] The technical solution of the present invention lies in: According to the basic principle of nuclear magnetic resonance, the transverse relaxation process of the fluid in the pore-throat is affected by the combined action of three mechanisms: free relaxation, diffusion relaxation, and surface relaxation. Its transverse relaxation time is expressed as: 1 / T 2 = 1 / T 2B + 1 / T 2D + 1 / T 2S (1) In the formula: T 2 is the transverse relaxation time, ms; T 2B is the transverse free relaxation time, ms; T 2D is the transverse diffusion relaxation time, ms; T 2Sis the transverse surface relaxation time, in ms.

[0006] When the fluid in the pore throat is the wetting phase, its transverse free relaxation time T 2B is much greater than the transverse relaxation time T 2, the 1 / T 2B term in Equation (1) can be neglected; when the magnetic field gradient is small and the echo spacing is short enough, the transverse diffusion relaxation time T 2D is usually long, and the 1 / T 2D term in Equation (1) can be neglected. For nuclear magnetic resonance experiments, the fluid used in the experiment is usually simulated formation water, the magnetic field is weak and the echo spacing is short, so Equation (1) can be approximately written as: 1 / T 2≈1 / T 2S = ρ 2 S / V (2) In the formula: ρ 2 is the transverse surface relaxation intensity, in μm / ms; S is the surface area of the pore throat, in μm 2 ; V is the volume of the pore throat, in μm 3 ; Let S / V = F S / r , substituting into Equation (2), we get: r ≈ ρ 2 F S T 2 (3) In the formula: F S is the pore throat shape factor, dimensionless; r is the pore throat radius, in μm.

[0007] Since the influence of 1 / T 2B and 1 / T 2D on 1 / T 2 is neglected, so both Equation (2) and Equation (3) are approximate equations. For the convenience of solution, assume that the equation relationship between the pore throat radius r and the transverse relaxation time T 2 is: r= ( ρ 2 FS + δ ) T 2 (4) In the formula: δ is the correction coefficient of the transverse free relaxation time and the transverse diffusion relaxation time, μm / ms; Introduce δ in Equation (4) to make Equation (3) an equation.

[0008] Since ρ 2 F S and δ both have unknown variation laws and are difficult to accurately obtain, resulting in the correlation between the pore throat radius r and the transverse relaxation time T 2 being unknown.

[0009] If we let C = ρ 2 F S + δ and substitute it into Equation (4), we get: r = CT 2 (5) In the formula: C is the conversion coefficient, μm / ms; Equation (5) is the linear correlation equation between the pore throat radius r and the transverse relaxation time T 2.

[0010] For nuclear magnetic resonance core experiments, the transverse relaxation time is a known parameter, and the nuclear magnetic resonance pore throat radius and the conversion coefficient are unknown parameters. For high-pressure mercury injection core experiments, the high-pressure mercury injection pore throat radius is a known parameter, and the transverse relaxation time and the conversion coefficient are unknown parameters. The pore throat radius r includes the nuclear magnetic resonance pore throat radius and the high-pressure mercury injection pore throat radius. To distinguish between the nuclear magnetic resonance pore throat radius and the high-pressure mercury injection pore throat radius, let r T2 represent the nuclear magnetic resonance pore throat radius, r (pc) represent the high-pressure mercury injection pore throat radius. Then the above representation becomes: For nuclear magnetic resonance experiments, T 2 is a known parameter, r T2 and C are unknown parameters; for high-pressure mercury injection experiments, r (pc) is a known parameter, T 2 and C are unknown parameters.

[0011] Therefore, the conversion coefficient can be obtained by combining nuclear magnetic resonance and high-pressure mercury injectionC , thereby realizing the conversion between the pore throat radius r and the transverse relaxation time T 2. Due to the differences in the experimental principles and procedures, the transverse relaxation time T 2 and the high-pressure mercury injection pore throat radius r (pc) There is a certain correlation, but it is not a one-to-one correspondence. Therefore, it is necessary to find the transverse relaxation time corresponding to the high-pressure mercury injection pore throat radius in order to obtain the conversion coefficient C .

[0012] The nuclear magnetic resonance pore throat radius converted according to the nuclear magnetic resonance core experiment r T2 distribution represents an almost complete pore throat radius r distribution. The high-pressure mercury injection pore throat radius measured according to the high-pressure mercury injection core experiment r (pc) distribution represents a partial pore throat radius r distribution. Therefore, there is an objective fact between nuclear magnetic resonance and high-pressure mercury injection: the nuclear magnetic resonance pore throat radius r T2 distribution contains the high-pressure mercury injection pore throat radius r (pc) distribution.

[0013] The high-pressure mercury injection core experiment measures the high-pressure mercury injection pore throat radius r (pc) distribution must have the minimum high-pressure mercury injection pore throat radius r min (pc) and the maximum high-pressure mercury injection pore throat radius r max (pc) , so r min (pc) and r max (pc) can be used as two characteristic values, using the objective fact that "the nuclear magnetic resonance pore throat radius r T2 distribution contains the high-pressure mercury injection pore throat radius r (pc) distribution" to find the transverse relaxation time corresponding to the maximum high-pressure mercury injection pore throat radius T 2max # , and the transverse relaxation time corresponding to the minimum high-pressure mercury injection pore throat radius T 2min # . The specific method is as follows: (1) On the 2 distribution curve of nuclear magnetic resonance saturated water, with T 2 distribution curve of nuclear magnetic resonance saturated water, withT 2max M is the first intermediate parameter, starting from T 2max M equal to the maximum transverse relaxation time of nuclear magnetic resonance T 2max and using r T2 =( r max (pc) / T 2max M )× T 2 to convert the T 2 distribution of nuclear magnetic resonance saturated water into the nuclear magnetic resonance pore throat radius r T2 distribution, and then plot the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 and the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) on the same graph to determine whether it satisfies "the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) is completely on the left side of the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 ": If it is satisfied, then use the T 2max M at this time as T 2max # ; If it is not satisfied, then gradually decrease the T 2max M value, and re-use r T2 =( r max (pc) / T 2max M )× T 2 to convert the T 2 distribution of nuclear magnetic resonance saturated water into the nuclear magnetic resonance pore throat radius r T2 distribution, and then plot the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 and the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) on the same graph to determine whether it satisfies "the high-pressure mercury injection pore throat radiusr (pc) The cumulative volume percentage curve of r T2 is completely on the left side of the cumulative volume percentage curve of the nuclear magnetic resonance pore throat radius T 2max M Take T 2max # ; (2)On the T 2 distribution curve of nuclear magnetic resonance saturated water, take T 2min M as the second intermediate parameter, starting from T 2min M equal to T 2max # Start calculating r min (pc) / T 2min M and the cumulative volume percentage from T 2min M to T 2max # Judge whether both r max (pc) / T 2max # ≤ r min (pc) / T 2min M and the cumulative volume percentage from T 2min M to T 2max # ≥ the cumulative volume percentage from r min (pc) to r max (pc) ; If satisfied, take the T 2min M at this time as T 2min # ; If not satisfied, gradually reduceT 2min M Take values and recalculate r min (pc) / T 2min M and from T 2min M to T 2max # The cumulative volume ratio from... to..., and determine whether both are satisfied r max (pc) / T 2max # ≤ r min (pc) / T 2min M and from T 2min M to T 2max # The cumulative volume ratio from... to... ≥ the cumulative volume ratio from... to..., and take the one that just meets the condition as r min (pc) to r max (pc) ; T 2min M as T 2min # ; Substitute r max (pc) and T 2max # into equation (5) to get C ( T 2max # ) = r max (pc) / T 2max # . Substitute r min (pc) and T 2min # into equation (5) to get C ( T2min # )= r min (pc) / T 2min # Since the measurement results of nuclear magnetic resonance and high-pressure mercury injection are both discrete data points, it leads to C ( T 2max # ) is not necessarily equal to C ( T 2min # ). C ( T 2max # ) and C ( T 2min # ) both represent the correct value of the conversion coefficient C , which means that the value of the conversion coefficient C is not necessarily a constant. However, in practical applications, the conversion coefficient C of a core is usually taken as a constant. Therefore, the volume ratio can be used for weighting to obtain a unique value of the conversion coefficient C .

[0014] For nuclear magnetic resonance core experiments and high-pressure mercury injection core experiments, the volume ratio of any measurement data point essentially represents the cumulative volume ratio in the interval from this data point to its adjacent data point. Since the number of measurement data points of high-pressure mercury injection is much less than that of nuclear magnetic resonance, compared with r max (pc) 's volume ratio γ ( r max (pc) ) and r min (pc) 's volume ratio γ ( r min (pc) ), T 2max # 's volume ratio γ ( T 2max # ) and T 2min # 's volume ratio γ ( T 2min #)Closer to the true volume fraction of pore throats.

[0015] Therefore, it can be utilized γ ( T 2max # ) and γ ( T 2min # ) to construct the weighting coefficient of r max (pc) / T 2max # as γ ( T 2max # ) / γ ( T 2max # ) + γ ( T 2min # )], and then construct the weighting coefficient of r min (pc) / T 2min # as γ ( T 2min # ) / γ ( T 2max # ) + γ ( T 2min # )]; thus, the calculation formula for the conversion coefficient C is established as follows: (6) In the formula: γ ( T 2max # ) is the volume fraction of T 2max # , dimensionless; T 2max # is the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection, ms; r max (pc) is the maximum pore throat radius of high-pressure mercury injection, μm; γ ( T 2min # ) is T 2min # the volume fraction, dimensionless; T 2min # is the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection, ms; r min (pc) is the minimum pore throat radius of high-pressure mercury injection, μm.

[0016] An important application of nuclear magnetic resonance core experiments is to obtain T 2 cut-off value T 2cutoff , for distinguishing the bound fluid and free fluid in core samples. According to the industry standard "SY / T 6490-2014", the method for obtaining T 2cutoff is: carry out centrifugation or displacement experiments for dehydration, calculate the cumulative volume fraction according to the T 2 distribution after dehydration, and then find a point on the T 2 distribution saturated with water, so that the cumulative volume fraction on the left side of this point is equal to the total cumulative volume fraction after dehydration. The T 2 value corresponding to this point is T 2 cut-off value T 2cutoff .

[0017] It is found in practical applications that when centrifugation experiments are carried out on different core samples with the same centrifugal force to obtain T 2cutoff , or when displacement experiments are carried out on different core samples with the same displacement pressure to obtain T 2cutoff , the T 2cutoff of different cores are not necessarily equal or even have large differences; at the same time, the T 2cutoff under different centrifugal forces or displacement pressures are not the same. If the T 2 cut-off value T 2cutoff is converted into a radius cut-off value r cutoff , and r cutoff is used for comparative analysis of different core samples, and the analysis results will be more reliable. Therefore, equation (6) and T 2cutoffSubstitute into Equation (5) to obtain the calculation formula for the radius cut-off value: (7) In the formula: r cutoff is the radius cut-off value, μm; T 2cutoff is T the 2 cut-off value, ms.

[0018] The technical effect of the present invention lies in: Based on the basic principles of nuclear magnetic resonance core experiments and high-pressure mercury injection core experiments, the present invention takes the maximum pore throat radius and the minimum pore throat radius of high-pressure mercury injection as double characteristic values, finds their corresponding transverse relaxation times, solves the conversion coefficient by volume weighting, and then combines T the 2 cut-off value to establish a calculation method for the radius cut-off value, providing a key technical means for accurately distinguishing between bound fluid and free fluid in core samples. Description of the Drawings

[0019] Figure 1 is the cumulative volume fraction curve of the pore throat radius of high-pressure mercury injection r (pc) of.

[0020] Figure 2 is the cumulative volume fraction curve of the nuclear magnetic resonance transverse relaxation time of saturated water.

[0021] Figure 3 is T 2max M = 649.53 ms, the judgment curve of the first judgment condition.

[0022] Figure 4 is T 2max M == 147.10 ms, the judgment curve of the first judgment condition. Detailed Embodiment

[0023] A method for predicting the radius cut-off value based on double characteristic values is as follows: Step 1: Obtain the parameters of the high-pressure mercury injection core experiment; According to the results of the high-pressure mercury injection core experiment, read the maximum pore throat radius of high-pressure mercury injection r max (pc) , the minimum pore throat radius of high-pressure mercury injection r min (pc) , and draw the cumulative volume fraction curve of the pore throat radius of high-pressure mercury injection r (pc) of.

[0024] Step 2: Obtain the nuclear magnetic resonance core experiment parameters; According to the nuclear magnetic resonance core experiment results of saturated water, read the maximum transverse relaxation time T 2max and the minimum transverse relaxation time T 2min , and plot the cumulative volume fraction curve of the transverse relaxation time of nuclear magnetic resonance for saturated water; According to the nuclear magnetic resonance core experiment results after dehydration, use the method in the industry standard "SY / T 6490-2014" to obtain T 2 cut-off values T 2cutoff .

[0025] Step 3: Obtain the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection T 2max # ; (1) Define the first intermediate parameter T 2max M ; (2) Construct the first judgment condition: The cumulative volume fraction curve of the pore throat radius of high-pressure mercury injection r (pc) is completely located on the left side of the cumulative volume fraction curve of the pore throat radius of nuclear magnetic resonance r T2 ; (3) Start with T 2max M being equal to the nuclear magnetic resonance maximum transverse relaxation time T 2max , and use r T2 = ( r max (pc) / T 2max M ) × T 2 Convert the T 2 distribution of nuclear magnetic resonance saturated water into the pore throat radius of nuclear magnetic resonance r T2 distribution, and then, according to the cumulative volume fraction curve of the pore throat radius of nuclear magnetic resonance r T2 and the cumulative volume fraction curve of the pore throat radius of high-pressure mercury injection r (pc) , judge the first judgment condition; If it is satisfied, then use the current T 2max M asT 2max # ; If not satisfied, gradually decrease T 2max M the value, and reconstruct the cumulative volume fraction curve of nuclear magnetic resonance pore throat radius r T2 and the cumulative volume fraction curve of high-pressure mercury injection pore throat radius r (pc) until the first judgment condition is satisfied, then take the T 2max M that satisfies the first judgment condition as T 2max # .

[0026] Step 4: Obtain the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection T 2min # ; (1) Define the second intermediate parameter T 2min M ; (2) Construct the second judgment condition: r max (pc) / T 2max # ≤ r min (pc) / T 2min M and from T 2min M to T 2max # the cumulative volume fraction ≥ from r min (pc) to r max (pc) the cumulative volume fraction; (3) Starting with T 2min M equal to T 2max # calculate r min (pc) / T 2min M and fromT 2min M to T 2max # Judge the second judgment condition based on the cumulative volume ratio from to . If it is satisfied, then at this time T 2min M is used as T 2min # ; If it is not satisfied, then gradually decrease T 2min M the value until a T 2min M that satisfies the second judgment condition is found. Then, the T 2min M that satisfies the second judgment condition is used as T 2min # .

[0027] Step 5: According to the nuclear magnetic resonance core experiment results of saturated water, obtain T 2max # volume ratio γ ( T 2max # ) and T 2min # volume ratio γ ( T 2min # ).

[0028] Step 6: Calculate the radius cut-off value r cutoff .

[0029] Specific application case A method for predicting the radius cut-off value based on double eigenvalues is as follows: Step 1: Obtain the high-pressure mercury injection core experiment parameters, and the results are shown in Table 1; Table 1 High-pressure mercury injection core experiment results ; According to the high-pressure mercury injection core experiment results, read the maximum pore throat radius r max (pc) = 0.5584μm, the minimum pore throat radius of high-pressure mercury injection rmin (pc) = 0.0036 μm, plot the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) whose cumulative volume fraction curve is shown in Figure 1 .

[0030] Step 2: Obtain the nuclear magnetic resonance core experiment parameters, and obtain the T T2 distribution of nuclear magnetic resonance saturated water as shown in Table 2; Table 2 T2 distribution of nuclear magnetic resonance saturated water T T2 distribution ; According to the nuclear magnetic resonance core experiment results of saturated water, read the maximum transverse relaxation time T 2max = 649.53 ms, the minimum transverse relaxation time T 2min = 0.03 ms, plot the cumulative volume fraction curve of the nuclear magnetic resonance transverse relaxation time of saturated water, as shown in Figure 2 ; For the nuclear magnetic resonance core experiment results after dehydration, obtain the T T2 distribution after nuclear magnetic resonance dehydration, as shown in Table 3; Obtain the T T2 cut-off value T 2cutoff = 0.98 ms; Table 3 T2 distribution after nuclear magnetic resonance dehydration T T2 distribution .

[0031] Step 3: Obtain the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection T 2max # ; (1) Define the first intermediate parameter T 2max M ; (2) Construct the first judgment condition: the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) is completely on the left side of the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 ; (3) Starting from T 2max M = T 2max = 649.53 ms, using r T2 = (r max (pc) / T 2max M )× T 2 = 0.00086 T 2 converts the T 2 distribution of nuclear magnetic resonance saturated water into the nuclear magnetic resonance pore throat radius r T2 distribution, and then plots the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 on the same graph as the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) ; make a judgment on the first judgment condition; as can be seen from Figure 3 ; when Figure 3 it can be seen that when T 2max M = 649.53 ms, the first judgment condition is not satisfied; Gradually decrease T 2max M the value of T 2max M until r T2 = ( r max (pc) / T 2max M )× T 2 = 0.0038 T 2 converts the T 2 distribution of nuclear magnetic resonance saturated water into the nuclear magnetic resonance pore throat radius r T2 distribution, and then plots the cumulative volume fraction curve of the nuclear magnetic resonance pore throat radius r T2 on the same graph as the cumulative volume fraction curve of the high-pressure mercury injection pore throat radius r (pc) ; according to Figure 4 ; it can be seen that the first judgment condition is satisfied; then Figure 4 it can be seen that the first judgment condition is satisfied; then T 2max # = T 2max M = 147.10 ms.

[0032] Step 4: Obtain the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection T2min # ; (1) Define the second intermediate parameter T 2min M ; (2) Construct the second judgment condition: r max (pc) / T 2max # ≤ r min (pc) / T 2min M and the cumulative volume ratio from T 2min M to T 2max # ≥ the cumulative volume ratio from r min (pc) to r max (pc) ; (3) Starting from T 2min M = T 2max # = 147.10 ms, calculate to get: r max (pc) / T 2max # = 0.0038 μm / ms, r min (pc) / T 2min M = 2.45×10 -05 μm / ms, T 2min M = 147.10 ms to T 2max # = 147.10 ms is 1.043%; r min (pc) to r max (pc) is 28.46%; judge that the second judgment condition is not satisfied; Then gradually decreaseT 2min M Take a value. When T 2min M = 3.39 ms, the calculation gives: r min (pc) / T 2min M = 0.001061947 μm / ms, T 2min M = 3.39 ms to T 2max # 147.10 ms, the cumulative volume ratio is 29.235%. It satisfies "from T 2min M to T 2max # the cumulative volume ratio ≥ from r min (pc) to r max (pc) the cumulative volume ratio", but does not satisfy " r max (pc) / T 2max # ≤ r min (pc) / T 2min M ", so the corresponding second judgment condition is still not satisfied; Until T 2min M = 0.86 ms, the calculation gives: r min (pc) / T 2min M = 0.0042 μm / ms, T 2min M = 0.86 ms to T 2max # = 147.10 ms, the cumulative volume ratio is 62.056%. r min (pc) to r max(pc) The cumulative volume fraction is 28.46%; the second judgment condition is satisfied; then T 2min # = T 2min M = 0.86 ms.

[0033] Step 5: According to the nuclear magnetic resonance core experiment results of saturated water, obtain T 2max # the volume fraction of γ ( T 2max # ) = 1.043%, T 2min # the volume fraction of γ ( T 2min # ) = 2.945%.

[0034] Step 6: Calculate the radius cut-off value through equation (7) r cutoff = 0.004 μm.

Claims

1. A radius cutoff value prediction method based on double eigenvalues, characterized in that: The method is as follows: obtain the parameters of high-pressure mercury injection core experiment and nuclear magnetic resonance core experiment, and then substitute them into the following formula (7) to solve the radius cutoff value: （7） Among them, the maximum pore throat radius of high-pressure mercury injection r max (pc) The corresponding transverse relaxation time T 2max # The specific process of obtaining is: (1) Define the first intermediate parameter T 2max M ; (2) Constructing the first judgment condition: high-pressure mercury injection pore throat radius r (pc) The cumulative volume fraction curve is completely located at the NMR pore throat radius r T2 The left side of the cumulative volume share curve; (3) T 2max M Equal to the maximum transverse relaxation time of NMR T 2max Start using r T2 =( r max (pc) / T 2max M )× T 2. NMR saturated water T 2 Distribution converted to NMR pore throat radius r T2 distribution, and then according to the NMR pore throat radius r T2 Cumulative volume fraction curve and high-pressure mercury injection pore throat radius r (pc) The cumulative volume proportion curve is used to determine the first judgment condition; If satisfied, then the current T 2max M As T 2max # ; If not satisfied, gradually reduce T 2max M Take the value and reconstruct the NMR pore throat radius r T2 Cumulative volume fraction curve and high-pressure mercury injection pore throat radius r (pc) The cumulative volume proportion curve of the first judgment condition is met, and the first judgment condition is met. T 2max M As T 2max # ; Among them, the minimum pore throat radius of high-pressure mercury injection r min (pc) The corresponding transverse relaxation time T 2min # The specific process of obtaining is: (1) Define the second intermediate parameter T 2min M ; (2) Construct the second judgment condition: r max (pc) / T 2max # ≤ r min (pc) / T 2min M and from T 2min M arrive T 2max # The cumulative volume share of ≥ r min (pc) arrive r max (pc) The cumulative volume share of (3) T 2min M equal T 2max # Start calculating r min (pc) / T 2min M and from T 2min M arrive T 2max # The second judgment condition is judged based on the cumulative volume proportion of If satisfied, then T 2min M As T 2min # ; If not satisfied, gradually reduce T 2min M Take values ​​until you find a value that satisfies the second judgment condition T 2min M , then the second judgment condition will be met T 2min M As T 2min # ; Where: r cutoff is the radius cutoff, μm; γ ( T 2max # )for T 2max # The volume percentage of , dimensionless; T 2max # is the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection, ms; r max (pc) is the maximum pore throat radius of high-pressure mercury injection, μm; γ ( T 2min # )for T 2min # The volume percentage of , dimensionless; T 2min # is the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection, ms; r min (pc) is the minimum pore throat radius of high-pressure mercury injection, μm; T 2cutoff for T 2 cutoff value, ms; T 2 is the transverse relaxation time, ms; T 2max is the maximum transverse relaxation time of NMR, ms; T 2max M is the first intermediate parameter, ms; T 2min M is the second intermediate parameter, ms; r (pc) is the pore throat radius of high-pressure mercury injection, μm; r T2 is the NMR pore throat radius, μm.

2. The radius cutoff value prediction method based on double eigenvalues ​​according to claim 1, characterized in that: The maximum pore throat radius of high pressure mercury injection r max (pc) and the minimum pore throat radius of high-pressure mercury injection r min (pc) Obtained through high-pressure mercury injection core experiments.

3. The radius cutoff value prediction method based on double eigenvalues ​​according to claim 1, characterized in that: The maximum transverse relaxation time T 2max , T 2max # Volume share γ ( T 2max # )and T 2min # Volume share γ ( T 2min # ) are obtained through water-saturated nuclear magnetic resonance core experiments. T 2 Cutoff value T 2cutoff Obtained through nuclear magnetic resonance core experiments after dehydration.

4. The radius cutoff value prediction method based on double eigenvalues ​​according to claim 1, characterized in that: The reduction T 2max M / Reduce T 2min M With the NMR saturated water T 2Distribution changes.

Images