Method for acquiring conversion coefficient interval of nuclear magnetic resonance linear correlation expression

Abstract

The invention relates to the technical field of oil and gas field development, in particular to a method for acquiring a conversion coefficient interval of a nuclear magnetic resonance linear correlation formula. According to the method, starting from a linear correlation between transverse relaxation time and pore throat radiuses, a transverse relaxation time lower limit corresponding to the high-pressure mercury injection minimum pore throat radius and a transverse relaxation time upper limit corresponding to the high-pressure mercury injection maximum pore throat radius are established by using the high-pressure mercury injection minimum pore throat radius and the high-pressure mercury injection maximum pore throat radius; the method for obtaining the conversion coefficient interval of the nuclear magnetic resonance linear correlation is formed, and the practicability and accuracy of the nuclear magnetic resonance technology in oil and gas reservoir evaluation are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and particularly relates to a method for obtaining the conversion coefficient interval of a nuclear magnetic resonance linear correlation formula. Background Art

[0002] Due to its advantages of non-destructiveness, rapidity, and accuracy, nuclear magnetic resonance technology shows great potential in pore-throat structure analysis. By measuring the transverse relaxation time of formation fluids in rock pore-throats, nuclear magnetic resonance technology can indirectly reflect the size and distribution characteristics of pore-throat radii. However, to accurately convert the transverse relaxation time into the pore-throat radius, a conversion coefficient needs to be obtained. For this purpose, a large number of studies have been carried out at home and abroad, and a linear correlation formula between the transverse relaxation time and the pore-throat radius has been derived. By combining nuclear magnetic resonance technology with high-pressure mercury injection experiments, various methods for obtaining the conversion coefficient have been proposed.

[0003] The accuracy of the conversion coefficient determines the reliability of reservoir evaluation results. However, there are few related studies. If the similarity between the nuclear magnetic resonance transverse relaxation time distribution and the high-pressure mercury injection pore-throat radius can be utilized to obtain the conversion coefficient of the nuclear magnetic resonance linear correlation formula, it has important theoretical value and practical significance for reservoir evaluation. Summary of the Invention

[0004] The present invention aims to address the above problems and proposes a method for obtaining the conversion coefficient interval of a nuclear magnetic resonance linear correlation formula.

[0005] The technical solution of the present invention is as follows: According to the basic principle of nuclear magnetic resonance, the transverse relaxation process of fluids in pore-throats is affected by the combined action of three mechanisms: free relaxation, diffusion relaxation, and surface relaxation. Its transverse relaxation time is expressed as: 1 / T2 = 1 / T 2B + 1 / T 2D + 1 / T 2S (1) In the formula: T2 is the transverse relaxation time, in ms; T 2B is the transverse free relaxation time, in ms; T 2D is the transverse diffusion relaxation time, in ms; T 2S is the transverse surface relaxation time, in ms.

[0006] When the fluid in the pore-throat is a wetting phase, its transverse free relaxation time T 2B is much greater than the transverse relaxation time T2, and the 1 / T 2B term in formula (1) can be ignored; when the magnetic field gradient is small and the echo interval is short enough, the transverse diffusion relaxation time T 2D is usually long, and the 1 / T 2DThe item can be ignored. For nuclear magnetic resonance experiments, the fluid used in the experiment is usually simulated formation water. The magnetic field is weak and the echo interval is short. Therefore, Equation (1) can be approximately written as: 1 / T2 ≈ 1 / T 2S = ρ2S / V (2) Where: ρ2 is the transverse surface relaxation intensity, μm / ms; S is the pore throat surface area, μm 2 ; V is the pore throat volume, μm 3 ; Let S / V = F S / r, substitute it into Equation (2), and we get: r ≈ ρ2F S T2 (3) Where: F S is the pore throat shape factor, dimensionless; r is the pore throat radius, μm.

[0007] Since the influence of 1 / T 2B and 1 / T 2D on 1 / T2 is ignored, both Equation (2) and Equation (3) are approximate equalities. For the convenience of solution, assume the equality relationship between the pore throat radius r and the transverse relaxation time T2 is: r = (ρ2F S + δ)T2 (4) Where: δ is the correction coefficient of the transverse free relaxation time and the transverse diffusion relaxation time, μm / ms; Introducing δ into Equation (4) makes Equation (3) an equality.

[0008] If we let C = ρ2F S + δ, substitute it into Equation (4), and we get the linear correlation equation between the pore throat radius r and the transverse relaxation time T2: C = r / T2 (5) Where: C is the conversion coefficient, μm / ms.

[0009] To obtain the conversion coefficient C, usually a combination of nuclear magnetic resonance and high-pressure mercury injection, constant-rate mercury injection, nitrogen adsorption, etc. is adopted. Compared with constant-rate mercury injection and nitrogen adsorption, high-pressure mercury injection can measure a wider range of pore throat radius distributions and has lower experimental costs. Therefore, the combination of nuclear magnetic resonance and high-pressure mercury injection is more commonly used.

[0010] It can be seen from Equation (5) that the essence of obtaining the conversion coefficient C is to find the transverse relaxation time T2 corresponding to the high-pressure mercury injection pore throat radius r (pc) . According to the different values of the high-pressure mercury injection pore throat radius r (pc) and the transverse relaxation time T2 values selected, methods such as the cumulative saturation method, similarity coefficient method, maximum eigenvalue method, peak eigenvalue method, T2 cut-off value method, etc. are generated. However, whether the conversion coefficient C obtained by these methods is correct remains to be demonstrated.

[0011] The high-pressure mercury intrusion pore throat radius r measured by high-pressure mercury intrusion experiment (pc) The distribution cannot represent the complete pore throat radius r distribution. The nuclear magnetic resonance pore throat radius r converted from the transverse relaxation time T2 T2 The distribution represents an almost complete pore throat radius r distribution. Therefore, there is the objective fact of "the nuclear magnetic resonance pore throat radius r T2 distribution contains the high-pressure mercury intrusion pore throat radius r (pc) distribution".

[0012] Based on this objective fact, combined with the measurement results of high-pressure mercury intrusion and nuclear magnetic resonance being discrete data points, 6 constraint conditions can be derived: ① The minimum pore throat radius of nuclear magnetic resonance < the minimum pore throat radius of high-pressure mercury intrusion; ② The volume proportion of the minimum pore throat radius of high-pressure mercury intrusion ≤ the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury intrusion; ③ The cumulative volume proportion from the minimum pore throat radius of high-pressure mercury intrusion to any high-pressure mercury intrusion pore throat radius ≤ the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius; ④ The maximum pore throat radius of nuclear magnetic resonance ≥ the maximum pore throat radius of high-pressure mercury intrusion; ⑤ The volume proportion of the maximum pore throat radius of high-pressure mercury intrusion ≤ the cumulative volume proportion from the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion to the maximum transverse relaxation time; ⑥ The cumulative volume proportion from any high-pressure mercury intrusion pore throat radius to the maximum pore throat radius of high-pressure mercury intrusion ≤ the cumulative volume proportion from the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius to the maximum transverse relaxation time.

[0013] Constraint condition ①: The minimum pore throat radius of nuclear magnetic resonance < the minimum pore throat radius of high-pressure mercury intrusion, and its mathematical expression is: r(T 2min ) < r min (pc) (6) In the formula: r(T 2min ) is the minimum pore throat radius of nuclear magnetic resonance, μm; T 2min is the minimum transverse relaxation time, ms; r min (pc) is the minimum pore throat radius of high-pressure mercury intrusion, μm; Since r min (pc) = CT2(r min (pc) ), r(T 2min ) = CT 2min , so another mathematical expression of constraint condition ① is: T 2min <T2(r min (pc) ) (7)。

[0014] The constraint condition ② is: the volume proportion of the minimum pore throat radius in high-pressure mercury intrusion ≤ the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion; its mathematical expression is: (8) In the formula: γ(r min (pc) ) is the volume proportion of the minimum pore throat radius in high-pressure mercury intrusion, dimensionless; r min (pc) is the minimum pore throat radius in high-pressure mercury intrusion, μm; γ(T 2min ) is the volume proportion of T 2min , dimensionless; T 2min is the minimum transverse relaxation time, ms; is the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion, dimensionless; γ(T2(r min (pc) )) is the volume proportion of T2(r min (pc) ), dimensionless; T2(r min (pc) ) is the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion, ms; γ(T2 (M1) ) is the volume proportion of T2 (M1) , dimensionless; T2 (M1) is the intermediate parameter for calculating the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion, ms.

[0015] The constraint condition ③ is: the cumulative volume proportion from the minimum pore throat radius in high-pressure mercury intrusion to any high-pressure mercury intrusion pore throat radius ≤ the cumulative volume proportion from the minimum transverse relaxation time to the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius, and its mathematical expression is: (9) In the formula: is the cumulative volume proportion from the minimum pore throat radius in high-pressure mercury intrusion to any high-pressure mercury intrusion pore throat radius, dimensionless; γ(r min (pc) ) is the volume proportion of the minimum pore throat radius in high-pressure mercury intrusion, dimensionless; r min (pc) is the minimum pore throat radius in high-pressure mercury intrusion, μm; γ(r (pc) ) is the volume proportion of the high-pressure mercury intrusion pore throat radius, dimensionless; r (pc)is the high-pressure mercury intrusion pore throat radius, μm; γ(r (M4) ) is the volume fraction of r (M4) , dimensionless; r (M4) is an intermediate parameter for calculating the cumulative volume fraction from the minimum pore throat radius of high-pressure mercury intrusion to any high-pressure mercury intrusion pore throat radius, μm; is the cumulative volume fraction from the minimum transverse relaxation time to the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius, dimensionless; γ(T 2min ) is the volume fraction of T 2min , dimensionless; T 2min is the minimum transverse relaxation time, ms; γ(T2(r (pc) )) is the volume fraction of T2(r (pc) ), dimensionless; T2(r (pc) ) is the transverse relaxation time corresponding to r (pc) , ms; γ(T2 (M2) ) is the volume fraction of T2 (M2) , dimensionless; T2 (M2) is an intermediate parameter for calculating the cumulative volume fraction from the minimum transverse relaxation time to the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius, ms; It can be seen that in equation (9), when r (pc) = r min (pc) , T2(r (pc) ) = T2(r min (pc) ), and equation (9) becomes equation (8). Therefore, equation (9) includes equation (8), that is, constraint condition ③ includes constraint condition ②.

[0016] Constraint condition ④ is: the maximum pore throat radius of nuclear magnetic resonance ≥ the maximum pore throat radius of high-pressure mercury intrusion; its mathematical expression is: r(T 2max ) ≥ r max (pc) (10) In the formula: r(T 2max ) is the maximum pore throat radius of nuclear magnetic resonance, μm; T 2max is the maximum transverse relaxation time, ms; r max (pc) is the maximum pore throat radius of high-pressure mercury intrusion, μm; Since r max (pc) = CT2(r max (pc) ), r(T 2max ) = CT 2max , so another mathematical expression of constraint condition ④ is: T2max ≥ T2(r max (pc) ) (11) In the formula: T 2max is the maximum transverse relaxation time, ms; T2(r max (pc) ) is the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion, ms; r max (pc) is the maximum pore throat radius of high-pressure mercury intrusion, μm.

[0017] Constraint condition ⑤ is: the volume proportion of the maximum pore throat radius of high-pressure mercury intrusion ≤ the cumulative volume proportion from the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion to the maximum transverse relaxation time of nuclear magnetic resonance; the mathematical expression of constraint condition ⑤ is: (12) In the formula: γ(r max (pc) ) is the volume proportion of the maximum pore throat radius of high-pressure mercury intrusion, dimensionless; r max (pc) is the maximum pore throat radius of high-pressure mercury intrusion, μm; is the cumulative volume proportion from the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion to the maximum transverse relaxation time, dimensionless; γ(T2(r max (pc) )) is the volume proportion of T2(r max (pc) ), dimensionless; T2(r max (pc) ) is the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion, ms; r max (pc) is the maximum pore throat radius of high-pressure mercury intrusion, μm; γ(T 2max ) is the volume proportion of T 2max , dimensionless; T 2max is the maximum transverse relaxation time, ms; γ(T2 (M3) ) is the volume proportion of T2 (M3) , dimensionless; T2 (M3) is an intermediate parameter for calculating the cumulative volume proportion from the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion to the maximum transverse relaxation time, ms; Constraint condition ⑥ is: the cumulative volume proportion from any high-pressure mercury intrusion pore throat radius to the maximum pore throat radius of high-pressure mercury intrusion ≤ the cumulative volume proportion from the transverse relaxation time corresponding to any high-pressure mercury intrusion pore throat radius to the maximum transverse relaxation time, and its mathematical expression is: (13) In the formula: is the cumulative volume fraction from any high-pressure mercury injection pore throat radius to the maximum high-pressure mercury injection pore throat radius, dimensionless; γ(r (pc) ) is the volume fraction of any high-pressure mercury injection pore throat radius, dimensionless; r (pc) is the high-pressure mercury injection pore throat radius, μm; γ(r max (pc) ) is the volume fraction of the maximum high-pressure mercury injection pore throat radius, dimensionless; r max (pc) is the maximum high-pressure mercury injection pore throat radius, μm; γ(r (M5) ) is the volume fraction of r (M5) , dimensionless; r (M5) is an intermediate parameter for calculating the cumulative volume fraction from any high-pressure mercury injection pore throat radius to the maximum high-pressure mercury injection pore throat radius, μm; is the cumulative volume fraction from the transverse relaxation time corresponding to any high-pressure mercury injection pore throat radius to the maximum transverse relaxation time, dimensionless; γ(T2(r (pc) )) is the volume fraction of T2(r (pc) ), dimensionless; T2(r (pc) ) is the transverse relaxation time corresponding to r (pc) , ms; r (pc) is the high-pressure mercury injection pore throat radius, μm; γ(T 2max ) is the volume fraction of T 2max , dimensionless; T 2max is the maximum transverse relaxation time, ms; γ(T2 (M6) ) is the volume fraction of T2 (M6) , dimensionless; T2 (M6) is an intermediate parameter for calculating the cumulative volume fraction from the transverse relaxation time corresponding to any high-pressure mercury injection pore throat radius to the maximum transverse relaxation time, ms.

[0018] It can be seen that in equation (13), when r (pc) =r max (pc) , T2(r (pc) )=T2(r max (pc) ), and equation (13) becomes equation (12). Therefore, equation (13) includes equation (12), that is, constraint condition ⑥ includes constraint condition ⑤.

[0019] From equation (6) to equation (13), the known parameters and unknown parameters are as follows: r min (pc) , T 2min , γ(r min (pc) ), T 2max , r max (pc), γ(r max (pc) ), γ(T 2max ) are known parameters, and r(T 2min ), T2(r min (pc) ), γ(T2(r min (pc) ), r(T 2max ), T2(r max (pc) ), γ(T2(r max (pc) ) are unknown parameters.

[0020] Both high-pressure mercury intrusion and nuclear magnetic resonance measure discrete data points, making it difficult to find the exact value of T2(r min (pc) ). Since T2(r min (pc) ) needs to satisfy equations (6), (7), (8), and (9) simultaneously, that is, T2(r min (pc) ) needs to satisfy both the transverse relaxation time and the cumulative volume fraction. Therefore, there is a lower limit T min (pc) for the value of T2(r 2min * ), that is: T2(r min (pc) ) ≥ T 2min * (14) In the formula: T 2min * is the lower limit of the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion.

[0021] Since T2(r min (pc) ) = r min (pc) / C, substituting it into equation (14), the upper limit of the conversion coefficient C is obtained: C ≤ r min (pc) / T 2min * (15) Similarly, it is difficult to find the exact value of T2(r max (pc) ). Since T2(r max (pc) ) needs to satisfy equations (10), (11), (12), and (13) simultaneously, that is, T2(r max (pc) ) needs to satisfy both the transverse relaxation time and the cumulative volume fraction. Therefore, T2(rmax (pc) ) The value has an upper limit T 2max * , that is: T2(r max (pc) ) ≤ T 2max * (16) Where: T 2max * is the upper limit of the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury intrusion.

[0022] Since T2(r max (pc) ) = r max (pc) / C, substituting into equation (16), the lower limit of the conversion coefficient C is obtained: C ≥ r max (pc) / T 2max * (17) According to equations (15) and (17), the value range of the conversion coefficient for establishing the linear correlation equation is: r max (pc) / T 2max * ≤ C ≤ r min (pc) / T 2min * (18) According to equation (18), constraint condition ⑦ can be derived: r max (pc) / T 2max * ≤ r min (pc) / T 2min * ; r max (pc) and r min (pc) can be directly read from the high-pressure mercury intrusion pore throat radius distribution curve, while T 2max * and T 2min * need to satisfy constraint conditions ① to ⑦, so the acquisition methods of T 2max * and T 2min * can be established: (1) Define the first intermediate parameter T 2max M and the second intermediate parameter T 2min M; (2) Using T 2max M = T 2max ; Using r T2 = (r max (pc) / T 2max M ) × T2 to convert T2 into nuclear magnetic resonance pore throat radius r T2 ; Plot the cumulative volume fraction distribution curve of r T2 ; Construct the first judgment condition: whether the cumulative volume fraction distribution curve of r T2 is entirely on the right side of the cumulative volume fraction distribution curve of r (pc) ; If the first judgment condition is satisfied, use the current T 2max M as T 2max * ; Otherwise, decrease the value of T 2max M and restart until the first judgment condition is satisfied; (3) Starting with T 2min M = T 2min , construct the second judgment condition: r max (pc) / T 2max * ≤ r min (pc) / T 2min M ; If the second judgment condition is satisfied, calculate ; If the second judgment condition is not satisfied, increase the value of T 2min M and restart until the second judgment condition is satisfied; Construct the third judgment condition: ; If the third judgment condition is satisfied, use the current T 2min M as T 2min * ; If the third judgment condition is not satisfied, increase the value of T 2min M and rejudge whether the second judgment condition is satisfied until T 2min M simultaneously satisfies the second judgment condition and the third judgment condition; In the formula: T 2max M is the first intermediate parameter, ms; T 2min M is the second intermediate parameter, ms; γ(T 2minM ) is the volume fraction of T, dimensionless; 2min M The volume fraction of, dimensionless; r T2 is the nuclear magnetic resonance pore throat radius, μm; is the cumulative volume fraction from the minimum transverse relaxation time to the second intermediate parameter, dimensionless; γ(T2 (M7) ) is the volume fraction of T2, dimensionless; T2 (M7) The volume fraction of, dimensionless; T2 (M7) is the intermediate parameter for calculating the cumulative volume fraction from the minimum transverse relaxation time to the second intermediate parameter, and the value ranges from T 2min to T2(r min (pc) ), ms.

[0023] The technical effect of the present invention is as follows: Starting from the linear correlation between the transverse relaxation time and the pore throat radius, the present invention uses the minimum pore throat radius and the maximum pore throat radius of high-pressure mercury injection to establish a method for obtaining the lower limit of the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection and the upper limit of the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection, forming a method for obtaining the conversion coefficient interval of the nuclear magnetic resonance linear correlation, and improving the practicability and accuracy of the nuclear magnetic resonance technology in oil and gas reservoir evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the cumulative volume fraction distribution curve of the high-pressure mercury injection pore throat radius.

[0025] Figure 2 is the cumulative volume fraction distribution curve of the transverse relaxation time.

[0026] Figure 3 is T 2max M = 1445.10 ms, the judgment curve of the first judgment condition.

[0027] Figure 4 is T 2max M = 649.53 ms, the judgment curve of the first judgment condition. DETAILED DESCRIPTION OF THE INVENTION

[0028] A method for obtaining the conversion coefficient interval of the nuclear magnetic resonance linear correlation is as follows: Step 1: Determine the distribution data of the high-pressure mercury injection pore throat radius r (pc) through high-pressure mercury injection experiments, including the minimum pore throat radius r of high-pressure mercury injection min (pc) , the maximum pore throat radius r of high-pressure mercury injection max(pc) and the volume fraction γ(r min (pc) ) of the minimum pore throat radius in high-pressure mercury intrusion; and then obtain the cumulative volume fraction distribution curve of the pore throat radius in high-pressure mercury intrusion; Step 2: Measure the distribution data of the transverse relaxation time T2 through high-pressure mercury intrusion experiments, including the maximum transverse relaxation time T 2max and the minimum transverse relaxation time T 2min ; and then obtain the cumulative volume fraction distribution curve of the transverse relaxation time; Step 3: Obtain the upper limit T 2max * of the transverse relaxation time corresponding to the maximum pore throat radius in high-pressure mercury intrusion and the lower limit T 2min * of the transverse relaxation time corresponding to the minimum pore throat radius in high-pressure mercury intrusion; the specific process is as follows: (1) Define T 2max M and T 2min M ; (2) Let T 2max M = T 2max ; use r T2 = (r max (pc) / T 2max M ) × T2 to convert T2 into the nuclear magnetic resonance pore throat radius r T2 ; draw the cumulative volume fraction distribution curve of r T2 ; construct the first judgment condition: whether the cumulative volume fraction distribution curve of r T2 is entirely on the right side of the cumulative volume fraction distribution curve of r (pc) ; if the first judgment condition is satisfied, then use the current T 2max M as T 2max * ; otherwise, reduce the value of T 2max M and start over until the first judgment condition is satisfied; (3) Start with T 2min M = T 2min and construct the second judgment condition: r max (pc) / T 2max * ≤ r min (pc) / T 2min M ; if the second judgment condition is satisfied, then calculate ; if the second judgment condition is not satisfied, then increase T2min M The value-taking restarts until the second judgment condition is satisfied; construct a third judgment condition: ; if the third judgment condition is satisfied, use the current T 2min M as T 2min * ; if the third judgment condition is not satisfied, increase T 2min M and re-judge whether the second judgment condition is satisfied until T 2min M simultaneously satisfies the second judgment condition and the third judgment condition; Step 4: Construct the value range of the conversion coefficient C: Calculate r max (pc) / T 2max * and r min (pc) / T 2min * , and then obtain the range of the conversion coefficient C.

[0029] Specific application case 1 Method for obtaining the conversion coefficient range of the nuclear magnetic resonance linear correlation formula, the method is as follows: The distribution data of the high-pressure mercury intrusion pore throat radius r (pc) measured by the high-pressure mercury intrusion experiment is shown in Table 1; the distribution data of the transverse relaxation time T2 measured by the nuclear magnetic resonance experiment is shown in Table 2; Table 1 Distribution data of the high-pressure mercury intrusion pore throat radius r (pc)

[0030] Table 2 Distribution data of the transverse relaxation time T2

[0031] Step 1: According to the data in Table 1, draw the cumulative volume fraction distribution curve of the high-pressure mercury intrusion pore throat radius r (pc) (); read the maximum pore throat radius r Figure 1 of the high-pressure mercury intrusion max (pc) = 0.4003μm, the minimum pore throat radius r min (pc) of the high-pressure mercury intrusion = 0.0036μm, and the volume fraction γ(r min (pc) ) of the minimum pore throat radius of the high-pressure mercury intrusion = 1.04%.

[0032] ​Step 2: According to the data in Table 2, plot the cumulative volume fraction distribution curve of the transverse relaxation time T2 ( Figure 2 ); Read the maximum transverse relaxation time T 2max = 1445.10 ms and the minimum transverse relaxation time T 2min = 0.08 ms.

[0033] Step 3: Obtain the upper limit T 2max * of the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection and the lower limit T 2min * of the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection; The specific process is as follows: (1) Define the first intermediate parameter T 2max M and the second intermediate parameter T 2min M ; (2) With T 2max M = T 2max = 1445.10 ms, use r T2 = (r max (pc) / T 2max M ) × T2 = 0.000277T2 to convert T2 into the nuclear magnetic resonance pore throat radius r T2 ; In the cumulative volume fraction distribution curve graph of the high-pressure mercury injection pore throat radius r (pc) , plot the cumulative volume fraction distribution curve of r T2 , as Figure 3 shown; At this time, the cumulative volume fraction distribution curve of r T2 does not entirely lie on the right side of the cumulative volume fraction distribution curve of r (pc) ; Then when T 2max M = 1445.10 ms, the first judgment condition is not satisfied; Then let T 2max M = 1289.09 ms, repeat the above steps, and it still does not satisfy the first judgment condition; Until T 2max M = 649.53 ms, the cumulative volume fraction distribution curve of r T2 entirely lies on the right side of the cumulative volume fraction distribution curve of r (pc) , as Figure 4 shown; Then when T 2max M = 649.53 ms, the first judgment condition is satisfied; Then T 2max * = T2max M = 649.53 ms; (3)Starting from T 2min M = T 2min = 0.08 ms, construct the second judgment condition: r max (pc) = 0.4003 μm, T 2max * = 649.53 ms, so r max (pc) / T 2max * = 0.000616 μm / ms; r min (pc) = 0.0036 μm, at this time, T 2min M = 0.08 ms, so r min (pc) / T 2min M = 0.045 μm / ms; the second judgment condition is satisfied; Calculate the cumulative volume ratio from T 2min = 0.08 ms to T 2min M = 0.08 ms = 0.002%; construct the third judgment condition: γ(r min (pc) ) = 1.04%, = 0.002%, the third judgment condition is not satisfied; then increase T 2min M and re-judge whether the second judgment condition is satisfied; Let T 2min M = 0.09 ms, and judge the second judgment condition and the third judgment condition in turn. The result shows that when T 2min M = 0.09 ms, the third judgment condition is still not satisfied; Continue to increase T 2min M , until T 2min M = 1.08 ms, = 1.116%, since γ(r min (pc) ) = 1.04%, so the third judgment condition is satisfied, then T 2min * = T 2min M = 1.08 ms.

[0034] Step 4: Construct the value range of the conversion coefficient C: r max (pc) / T 2max * = 0.000616 μm / ms, r min (pc) / T 2min * = 0.003333 μm / ms. Therefore, the specific value range of the conversion coefficient C is [0.000616, 0.003333].

Claims

1. A method for obtaining a conversion coefficient interval of a nuclear magnetic resonance linear correlation equation, characterized in that: The conversion coefficient range is [r max (pc) / T 2max * , r min (pc) / T 2min * ]; Among them, T 2max * and T 2min * The specific process of obtaining is: (1) Definition of T 2max M and T 2min M ; (2) T 2max M =T 2max ; Using r T2 =(r max (pc) / T 2max M )×T2 converts T2 into NMR pore throat radius r T2 ; draw r T2 The cumulative volume proportion distribution curve of ; construct the first judgment condition: r T2 Are all the cumulative volume proportion distribution curves located within r (pc) The right side of the cumulative volume proportion distribution curve of ; if the first judgment condition is met, the current T 2max M As T 2max * ; otherwise reduce T 2max M The value taking starts again until the first judgment condition is met; (3) T 2min M =T 2min Start by building the second judgment condition: r max (pc) / T 2max * ≤r min (pc) / T 2min M ; If the second judgment condition is met, calculate If the second judgment condition is not met, increase T 2min M The value is taken again until the second judgment condition is met; Construct the third judgment condition: ; If the third judgment condition is met, then the current T 2min M As T 2min * ; If the third judgment condition is not met, increase T 2min M The value is re-judged to determine whether the second judgment condition is met until T 2min M The second judgment condition and the third judgment condition are satisfied at the same time; in, r max (pc) r is the maximum pore throat radius of high-pressure mercury injection; min (pc) is the minimum pore throat radius of high-pressure mercury injection; T 2max * is the upper limit of the transverse relaxation time corresponding to the maximum pore throat radius of high-pressure mercury injection; T 2min * is the lower limit of the transverse relaxation time corresponding to the minimum pore throat radius of high-pressure mercury injection; T 2max M is the first intermediate parameter, ms; T 2min M is the second intermediate parameter, ms; T2 is the transverse relaxation time, ms; T 2max is the maximum transverse relaxation time, ms; T 2min is the minimum transverse relaxation time, ms; r T2 is the NMR pore throat radius, μm; r (pc) is the pore throat radius of high-pressure mercury injection, μm; r max (pc) r is the maximum pore throat radius of high-pressure mercury injection, μm; min (pc) is the minimum pore throat radius of high-pressure mercury injection, μm; γ(r min (pc) ) is the volume fraction of the minimum pore throat radius of high-pressure mercury injection, dimensionless; is the cumulative volume fraction from the minimum transverse relaxation time to the second intermediate parameter, dimensionless; γ(T 2min ) is T 2min Volume fraction, dimensionless; γ(T 2min M ) is T 2min M The volume percentage of , dimensionless; γ(T2 (M7) ) is T2 (M7) The volume percentage of , dimensionless; T2 (M7) To calculate the intermediate parameter of the cumulative volume fraction from the minimum transverse relaxation time to the second intermediate parameter, the value is taken from T 2min To T2(r min (pc) ), ms.

2. The method for obtaining the conversion coefficient interval of the nuclear magnetic resonance linear correlation equation according to claim 1, characterized in that: The r (pc) 、r max (pc) 、r min (pc) and γ(r min (pc) ) were obtained through high-pressure mercury injection experiments.

3. The method for obtaining the conversion coefficient interval of the nuclear magnetic resonance linear correlation equation according to claim 1, characterized in that: The T 2max and T 2min All were obtained through nuclear magnetic resonance experiments.

4. The method for obtaining conversion coefficient intervals of the nuclear magnetic resonance linear correlation equation according to claim 1, characterized in that: The reduction of T 2max M Value / increase T 2min M The value varies with the distribution data of the transverse relaxation time T2 obtained from the nuclear magnetic resonance experiment.

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