Calculation method for obtaining nuclear magnetic porosity based on dynamic T2 cutoff value

Abstract

The invention provides a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cut-off value, and belongs to the field of petroleum and natural gas geology and exploration and development engineering, and the method comprises the steps: S1, carrying out the continuous difference operation of nuclear magnetic logging data, and obtaining two groups of dynamic T2 cut-off times; and S2, performing nuclear magnetic porosity calculation on the dynamic T2 deadline to obtain a nuclear magnetic total porosity, a nuclear magnetic effective porosity and a nuclear magnetic movable porosity, and realizing continuous characterization of the surface nuclear magnetic porosity. The method comprises the following steps: performing continuous differential operation on nuclear magnetic logging data by utilizing the Chlog software to obtain two groups of continuously changing dynamic T2 cutoff values T21 and T22, and calculating the nuclear magnetic effective porosity and the nuclear magnetic movable porosity under the dynamic cutoff values through an NMR (nuclear magnetic resonance) legacy module, so as to realize the continuous characterization of the nuclear magnetic porosity on the logging. And compared with the nuclear magnetic porosity calculated by a regional experience fixed cut-off value, the explanation precision is improved.

Description

Technical Field

[0001] The invention belongs to the field of petroleum and natural gas geology and exploration and development engineering, and in particular relates to a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value. Background Art

[0002] Complex clastic reservoirs are the main target of oil and gas exploration in oil fields. Complex clastic reservoirs are widely distributed, with an exploration area of ​​thousands of square kilometers. The oil and gas reservoirs are large in scale and rich in reserves. The sedimentary characteristics are mainly mixed deposition of multiple sources and rapid accumulation. They have the characteristics of complex and changeable mineral composition, weak diagenesis, strong heterogeneity and complex pore structure, making it difficult to evaluate the reservoir effectiveness.

[0003] Among them, the accurate calculation of nuclear magnetic logging plays an important role in the evaluation of pore structure and reservoir effectiveness. However, the traditional method of calculating nuclear magnetic tri-porosity by fixing the T2 cutoff value has low accuracy and certain limitations.

[0004] Chinese invention patent application CN 105240001 A provides a method and device for correction of NMR logging porosity. The method includes: obtaining the borehole electrical imaging logging image and NMR logging porosity corresponding to the target rock; establishing a correction model for NMR logging porosity based on the target rock size, gravel component size, non-gravel component size and the definition of porosity; obtaining the proportion of gravel components in the target rock based on the borehole electrical imaging logging image; calculating the NMR corrected porosity based on the proportion of gravel components in the target rock and the correction model, and the NMR corrected porosity is the correction value of the NMR logging porosity. The porosity calculation method constructed in this patent application has certain limitations and is more suitable for water-wet tight sandstone reservoirs. However, for oil-wet shale oil (gas) reservoirs, the NMR T2 spectrum reflects the fluid properties and does not reflect the pore structure. There will be certain differences in the morphology of the NMR T2 spectrum, which leads to low calculation accuracy of the dynamic cutoff value and inaccurate porosity calculation. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a calculation method for obtaining nuclear magnetic resonance porosity based on a dynamic T2 cutoff value. The technical problem to be solved by the present invention is how to achieve accurate characterization of nuclear magnetic resonance total porosity, nuclear magnetic resonance effective porosity and nuclear magnetic resonance movable porosity.

[0006] In order to solve the above technical problems, the present invention provides a method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value, comprising the following steps:

[0007] Step S1: Perform continuous differential operation on the nuclear magnetic logging data to obtain two sets of dynamic T2 cut-off times;

[0008] Step S2: Calculate the nuclear magnetic porosity of the dynamic T2 cutoff time to obtain the nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity, so as to realize the continuous characterization of the nuclear magnetic porosity on the well.

[0009] Furthermore, in step S1, Techlog software is used to perform continuous differential operations on the nuclear magnetic logging data.

[0010] Furthermore, in step S1, the nuclear magnetic logging data includes nuclear magnetic T2 spectrum:

[0011] F(x)=[x1,x2,x3,…,x n-1 ,x n ]

[0012] Where: F(x) is the nuclear magnetic T2 spectrum under saturation state; x n is the porosity component corresponding to a certain relaxation time; n is an integer.

[0013] Furthermore, in step S1, a second-order difference function is used to perform continuous difference operation on the nuclear magnetic logging data, and the second-order difference function is as follows:

[0014] Δ(Δy)=x n -2x n-1 +x n-2

[0015] Where Δ(Δy) is the rate of change of the porosity component after differentiation.

[0016] Furthermore, in the step S2, the dynamic T2 cutoff time is subjected to NMR porosity calculation by means of an NMR legacy module.

[0017] Furthermore, the dynamic T2 cutoff time includes a cutoff value T 21 and the cutoff value T 22 .

[0018] At present, the measurement of total porosity, effective porosity and movable porosity of complex clastic rocks is mainly calculated through nuclear magnetic resonance experiments and nuclear magnetic logging data. When measuring through nuclear magnetic resonance experiments, the centrifugation process is complicated, difficult to control, and expensive. The cost of batch experiments is high, and the pore structure cannot be accurately calibrated in the well section without coring. Nuclear magnetic logging data usually calculates total porosity, effective porosity and movable porosity with a fixed T2 cutoff value based on regional experience. The calculation accuracy is low and there is a lack of effective technical means.

[0019] The present invention provides a method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value. Techlog software is used to perform continuous differential operation on multiple segments of nuclear magnetic T2 spectra in nuclear magnetic logging data to obtain two sets of continuously changing dynamic T2 cutoff values ​​T 21and T 22 , the NMR legacy module is used to calculate the nuclear magnetic effective porosity and nuclear magnetic movable porosity under the dynamic cutoff value, realizing the continuous characterization of nuclear magnetic porosity on well logging, and the nuclear magnetic porosity calculated by the regional experience fixed cutoff value is compared and analyzed, the interpretation accuracy is improved, and the accurate characterization of nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity is realized; this method realizes the continuous dynamic calculation of nuclear magnetic porosity, and the calculation results are accurate and reliable with high precision, breaking the traditional fixed T2 cutoff value to calculate the nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity. The limitations of porosity, and the correction method of the present invention starts from the study of nuclear magnetic resonance mechanism, uses mathematical methods to analyze the changing law of nuclear magnetic signals, has a reliable theoretical basis, and innovates the quantitative calculation method of nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity in nuclear magnetic logging data, and provides a reliable and reasonable technical means for the calculation of nuclear magnetic porosity of wells with nuclear magnetic logging data but without corresponding nuclear magnetic resonance experiments, reduces the experimental cost of calibration through a large number of systematic coring, has obvious economic and social benefits, and has a good prospect for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of a method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value.

[0021] Figure 2 The invention discloses a nuclear magnetic resonance T2 spectrum distribution diagram of a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value.

[0022] Figure 3 It is a schematic diagram of the differential calculation results of a core sample of a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value of the present invention, Figure 3 Yes Figure 1 The distribution map of nuclear magnetic resonance T2 spectrum is obtained by differential calculation.

[0023] Figure 4 It is a comparison chart of the difference operation results of a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value of the present invention and the measurement results of a nuclear magnetic fixed cutoff value. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0027] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] In order to better understand the purpose, structure and function of the present invention, a calculation method for obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0029] Embodiment 1:

[0030] like Figure 1 As shown, the present invention provides a method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value, comprising the following steps:

[0031] Step S1: Perform continuous differential operation on the nuclear magnetic logging data to obtain two sets of dynamic T2 cut-off times;

[0032] Step S2: Calculate the nuclear magnetic porosity for the dynamic T2 cutoff time to obtain the total porosity, effective porosity and movable porosity, and realize the continuous characterization of the nuclear magnetic porosity on the well.

[0033] Embodiment 2:

[0034] like Figure 1 As shown, the present invention provides a method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value, comprising the following steps:

[0035] Step S1: Perform continuous differential operation on the nuclear magnetic logging data to obtain two sets of dynamic T2 cut-off times;

[0036] Step S2: Calculate the NMR porosity for the dynamic T2 cutoff time to obtain the NMR total porosity, NMR effective porosity and NMR movable porosity, so as to achieve continuous characterization of the NMR porosity on the well.

[0037] The difference between this embodiment and the first embodiment is that:

[0038] In step S1, Techlog software is used to perform continuous differential operations on the nuclear magnetic logging data, and the nuclear magnetic logging data includes the nuclear magnetic T2 spectrum under saturation state:

[0039] F(x)=[x1,x2,x3,...,x n-1 ,x n ]

[0040] Where: F(x) is the nuclear magnetic T2 spectrum under saturation state; x n is the porosity component corresponding to a certain relaxation time; n is an integer.

[0041] In step S1, a second-order difference function is used to perform continuous difference operation on the nuclear magnetic logging data. The second-order difference function is as follows:

[0042] Δ(Δy)=x n -2x n-1 +x n-2

[0043] Where Δ(Δy) is the rate of change of the porosity component after differentiation.

[0044] In step S2, the NMR total porosity, NMR effective porosity and NMR movable porosity under the dynamic T2 cutoff time are calculated by the NMR legacy module, thereby realizing the continuous characterization of the NMR porosity on well logging.

[0045] Embodiment 3:

[0046] like Figure 1 As shown, the present invention provides a method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value, comprising the following steps:

[0047] Step S1: Perform continuous differential operation on the nuclear magnetic logging data to obtain two sets of dynamic T2 cut-off times;

[0048] Step S2: Calculate the NMR porosity for the dynamic T2 cutoff time to obtain the NMR total porosity, NMR effective porosity and NMR movable porosity, so as to achieve continuous characterization of the NMR porosity on the well.

[0049] In step S1, Techlog software is used to perform continuous differential operations on the nuclear magnetic logging data, and the nuclear magnetic logging data includes the nuclear magnetic T2 spectrum:

[0050] F(x)=[x1,x2,x3,…,x n-1 ,x n ]

[0051] Where: F(x) is the nuclear magnetic T2 spectrum under saturation state; x n is the porosity component corresponding to a certain relaxation time.

[0052] In step S1, a second-order difference function is used to perform continuous difference operation on the nuclear magnetic logging data. The second-order difference function is as follows:

[0053] Δ(Δy)=x n -2x n-1 +x n-2

[0054] Where Δ(Δy) is the rate of change of the porosity component after differentiation.

[0055] In step S2, the NMR total porosity, NMR effective porosity and NMR movable porosity under the dynamic T2 cutoff time are calculated by the NMR legacy module, thereby realizing the continuous characterization of the NMR porosity on well logging.

[0056] For the calibration method described in the above embodiment, the following method is used to verify the accuracy:

[0057] Step H1: sampling and testing the core to determine the nuclear magnetic effective porosity and nuclear magnetic movable porosity;

[0058] Step H2: using the core nuclear magnetic resonance effective porosity and nuclear magnetic resonance movable porosity obtained experimentally, determine the T2 cutoff time on the nuclear magnetic resonance T2 spectrum;

[0059] Step H3: using a second-order difference function to perform a differential operation on the nuclear magnetic T2 spectrum of the sample to obtain differential spectrum data corresponding to the sample, analyzing the differential spectrum data to determine two T2 cutoff times, and comparing them with the T2 cutoff time obtained in step H2 to verify the accuracy of the T2 cutoff time obtained by the differential operation;

[0060] In the step H1, the core is sampled, and a porosity test and a nuclear magnetic saturation and centrifugation test are performed. The effective porosity of the sample is determined according to the porosity test, and the total porosity and movable porosity of the sample are determined according to the nuclear magnetic saturation and centrifugation tests. The core sample is prepared by selecting a sandstone core sample of a reservoir section in the study area, and the core sample is a standard plunger sample.

[0061] Specifically, firstly, the core sample is measured by helium porosity experiment according to the "Core Analysis Method (SY / T5336-2006)" to obtain the effective porosity, and then the "Rock Sample Nuclear Magnetic Resonance Parameter Laboratory Measurement Specification (SY / T6490-2014)" standard is referred to, and the appropriate waiting time (Tw), echo interval (Te), number of echoes (Ne) and inversion points are selected for the nuclear magnetic resonance experiment, and then the core is centrifuged and the nuclear magnetic resonance experiment is performed again to obtain the bound water saturation of tight sandstone and centrifugal nuclear magnetic T2 spectrum data. The formula for calculating nuclear magnetic porosity is as follows:

[0062] NMR porosity under water saturation

[0063] NMR porosity after centrifugation

[0064] Where, T 2min is the minimum relaxation time measured by the NMR experimental instrument, ms; T 2max The maximum relaxation time measured by the NMR experimental instrument, ms; They are total NMR porosity and NMR porosity after centrifugation, %; S(T2) is the measured NMR logging T2 spectrum;

[0065] The NMR movable porosity can be calculated using the NMR total porosity and the NMR porosity after centrifugation.

[0066] In the step H2, the accumulation lines of the nuclear magnetic T2 spectra before and after centrifugation are drawn respectively, and a line parallel to the X-axis is drawn from the maximum value of the T2 spectrum accumulation line after centrifugation, intersecting with the T2 spectrum accumulation line before centrifugation, and a vertical line is drawn from the intersection to the X-axis, and the corresponding cutoff value is T 22 The effective porosity value obtained from the experiment can be used to determine the effective pore T2 spectrum. 21 Deadline.

[0067] In step H3, the difference can reflect the trend and speed of data change. The difference between two adjacent data of the nuclear magnetic T2 spectrum is obtained, and the value obtained is the transition speed of the two data, which can reflect the law of signal change in different pore structures. Therefore, the second-order difference function is used to perform a difference operation on the nuclear magnetic saturation T2 spectrum of the rock sample to obtain a set of differential spectrum data. The different change trends of the differential spectrum will intersect with the X-axis, and the first intersection after 0.3ms is T' 21 Cut-off time, the second intersection is T' 22 The cut-off time is T obtained in step H2. 21 and T 22 The cut-off time was compared to verify the accuracy of the NMR porosity obtained by differential calculation.

[0068] In step H3, the nuclear magnetic T2 spectrum:

[0069] F(x)=[x1,x2,x3,…,x n-1 ,x n ]

[0070] Where: F(x) is the nuclear magnetic T2 spectrum under saturation state; x n is the porosity component corresponding to a certain relaxation time; n is an integer.

[0071] The second-order difference function is used to perform continuous difference operation on the nuclear magnetic T2 spectrum. The second-order difference function is as follows:

[0072] Δ(Δy)=x n -2x n-1 +x n-2

[0073] Where Δ(Δy) is the rate of change of the porosity component after differentiation.

[0074] At present, the measurement of total porosity, effective porosity and movable porosity of complex clastic rocks is mainly calculated through nuclear magnetic resonance experiments and nuclear magnetic logging data. When measuring through nuclear magnetic resonance experiments, the centrifugation process is complicated, difficult to control, and expensive. The cost of batch experiments is high, and the pore structure cannot be accurately calibrated in the well section without coring. Nuclear magnetic logging data usually calculates total porosity, effective porosity and movable porosity with a fixed T2 cutoff value based on regional experience. The calculation accuracy is low and there is a lack of effective technical means.

[0075] The present invention provides a method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value. Techlog software is used to perform continuous differential operation on nuclear magnetic logging data to obtain two sets of continuously changing dynamic T2 cutoff values ​​T 21 and T 22 , the NMR effective porosity and NMR movable porosity under the dynamic cutoff value are calculated by the NMRlegacy module, and the continuous characterization of the NMR porosity on logging is realized. The NMR porosity calculated by the fixed cutoff value based on regional experience is compared and analyzed, and the interpretation accuracy is improved; this method realizes the continuous dynamic calculation of NMR porosity, and the calculation results are accurate and reliable with high precision, breaking the limitations of the traditional fixed T2 cutoff value to calculate the total NMR porosity, NMR effective porosity and NMR movable porosity. In addition, the correction method of the present invention starts from the research on the mechanism of NMR, uses mathematical methods to analyze the changing law of NMR signals, has a reliable theoretical basis, and innovates the quantitative calculation method of the three porosities in NMR logging data. It provides a reliable and reasonable technical means for the calculation of NMR porosity of wells with NMR logging data but no corresponding NMR experiments, reduces the experimental cost of calibration through a large number of systematic coring, has obvious economic and social benefits, and has a good prospect for promotion and application.

[0076] Embodiment 3:

[0077] This example takes the dense sandy conglomerate in a certain area as the research object, and describes in detail a calculation method of obtaining nuclear magnetic porosity based on a dynamic T2 cutoff value of the present invention:

[0078] Step S101: Select the dense sandy conglomerate in a certain area as the research object, collect the core and logging data of the target layer section, select the sandy conglomerate core sample in the reservoir section of the target layer for rock sample preparation, and the prepared rock sample is a standard plunger sample and is numbered as X0, X1, X2...etc.

[0079] Step S102: According to the "Core Analysis Method (SY / T5336-2006)", the core sample is measured for helium porosity to obtain the effective porosity, and then referring to the "Rock Sample Nuclear Magnetic Resonance Parameter Laboratory Measurement Specification (SY / T6490-2014)" standard, for the denser sandstone, we select the waiting time (Tw=5000ms), echo interval (Te=0.2), number of echoes (Ne=5000) and 200 inversion points and other experimental parameters for nuclear magnetic resonance experiments, and then select the centrifugal force of 450psi to centrifuge the core and conduct nuclear magnetic resonance experiments to obtain the nuclear magnetic T2 spectrum of the rock before and after centrifugation, that is, the relaxation signals of the saturated state and the bound water state are gradually accumulated according to the relaxation time from small to large, and the cumulative distribution curves of the saturated state and the bound water state spectrum are obtained. Using the total nuclear magnetic porosity and the nuclear magnetic porosity after centrifugation, the nuclear magnetic movable porosity can be calculated. Figure 2 As shown in the figure, a point is determined on the saturation state accumulation curve of sample X1, so that the NMR accumulation signal corresponding to this point is equal to the total NMR signal of bound water. Then the relaxation time corresponding to this point is the movable fluid cutoff value T of the core. 22 =12.43ms. Similarly, the effective pore cutoff value T can be obtained using the effective porosity value. 21 =1.59ms. The porosity calculation formula of NMR experiment is as follows:

[0080] Water-saturated nuclear magnetic porosity

[0081] NMR porosity after centrifugation

[0082] Where, T 2min and T 2max are the minimum and maximum relaxation time measured by the nuclear magnetic resonance experimental instrument, ms; φt and φwi are the total nuclear magnetic porosity and the nuclear magnetic porosity after centrifugation, %; S(T2) is the measured nuclear magnetic resonance logging T2 spectrum signal component;

[0083] Step S103: The relaxation time of the nuclear magnetic logging T2 spectrum corresponds to different pore spaces. The pore component corresponding to the short relaxation time is the bound pore, and the pore component corresponding to the long relaxation time is the movable pore. The movable pore is generally the large pore part, and the bound pore is the small pore part. Different pore types have different corresponding pore increments, that is, different pore types have different tangent slopes of the nuclear magnetic cumulative curve. The differential function can reflect the trend and speed of data changes, and the second-order difference can reflect the rate of change of three adjacent signal data, which is more accurate. Therefore, the second-order difference operation is performed on the nuclear magnetic T2 spectrum of sample X1 in the saturated state to obtain a set of differential spectrum data corresponding to the sample, such as Figure 3 As shown, the first intersection cut-off time T after 0.3ms with the X-axis is obtained. 21 =1.82ms, the second intersection cut-off time is T 22 =11.89ms. Combined with the core NMR experimental analysis and comparison, as shown in Table 1, the T2 cutoff time in the study area is basically less than 33ms, the original fixed cutoff value NMR hole calculation is too small, the difference between the second-order difference operation and the NMR double cutoff time is small, and the NMR double cutoff time can basically represent the real T2 cutoff time.

[0084] Table 1 Comparison analysis of sample difference calculation results and experimental results

[0085] method <![CDATA[T 21 ]]> <![CDATA[T 22 ]]> Experimental analysis 1.59 12.43 Second-order difference operation 1.82 11.89

[0086] Step S104: Use Techlog software to perform differential calculations on the nuclear magnetic logging data one by one, and obtain continuously changing differential spectrum data corresponding to the nuclear magnetic T2 spectrum. Through the continuous differential spectrum, the continuously changing dynamic T2 cut-off time T can be obtained. 21 and T 22 The NMR legacy module is used to calculate the dual dynamic cutoff value nuclear magnetic porosity calculation, and then the continuous nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity on the well can be obtained, realizing the continuous characterization of nuclear magnetic porosity on well logging. The error comparison analysis is carried out with the calculation results of regional fixed cutoff values ​​of 3ms and 33ms, as shown in Tables 2 and 3. The calculation error of nuclear magnetic porosity based on dynamic dual cutoff values ​​is reduced by 20%.

[0087] Table 2. Data and error analysis of effective NMR porosity calculated by two methods

[0088]

[0089] Table 3. Data and error analysis of NMR movable porosity calculated by two methods

[0090]

[0091] like Figure 4As shown in the figure, the dynamic NMR porosity obtained by differential calculation method and the original NMR logging porosity are compared. Figure 4 From left to right, the first track is the stratigraphic unit track, the second track is the depth track, the third track is the lithology profile, the fourth track is the drilling coring track, the fifth track is the NMR T2 spectrum with a fixed cutoff value, the sixth track is the NMR tri-porosity track calculated with 3ms and 33ms, the seventh track is the NMR T2 spectrum with a dynamic double cutoff value, the eighth track is the NMR tri-porosity track calculated with a dynamic double cutoff value, the ninth track is the comparison track between the porosity calculated with 3ms and the porosity analyzed by core analysis, and the tenth track is the T 21 The calculated porosity is compared with the porosity of the core analysis. The eleventh track is the comparison of the porosity calculated by 33ms and the movable pore of the NMR analysis. The twelfth track is T 22 The calculated porosity is compared with the movable pores of NMR analysis. The circles in the curve are the experimental porosity scale points. The comparison and analysis of the porosity calculated by the experimental data and the dynamic cutoff value of NMR show a high degree of agreement, and the calculation accuracy has been effectively improved. It can accurately characterize the true three-porosity components of complex clastic rocks, breaking the limitations of the traditional use of fixed T2 cutoff value to calculate the three-porosity of NMR.

[0092] This study takes the tight sandstone in a certain area as the research object, uses core analysis data to calibrate the algorithm, verifies the accuracy of differential nuclear magnetic porosity, realizes the continuous characterization of the on-well nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity, improves the calculation accuracy of nuclear magnetic, and provides technical support for the later oil and gas exploration and development of complex clastic rocks.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for calculating nuclear magnetic porosity based on a dynamic T2 cutoff value, characterized in that: The following steps are involved: Step S1: Perform continuous differential operation on the nuclear magnetic logging data to obtain two sets of dynamic T2 cut-off times; Step S2: Calculate the nuclear magnetic porosity of the dynamic T2 cutoff time to obtain the nuclear magnetic total porosity, nuclear magnetic effective porosity and nuclear magnetic movable porosity, so as to realize the continuous characterization of the nuclear magnetic porosity on the well.

2. The method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value according to claim 1, characterized in that: In step S1, Techlog software is used to perform continuous differential operations on the nuclear magnetic logging data.

3. The method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value according to claim 1, characterized in that: In step S1, the nuclear magnetic logging data includes the nuclear magnetic T2 spectrum: F(x)=[x1,x2,x3,…,x n-1 ,x n ] Where: F(x) is the nuclear magnetic T2 spectrum under saturation state; x n is the porosity component corresponding to a certain relaxation time; n is an integer.

4. The method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value according to claim 1, characterized in that: In step S1, a second-order difference function is used to perform continuous difference operation on the nuclear magnetic logging data. The second-order difference function is as follows: Δ(Δy)=x n -2x n-1 +x n-2 Where Δ(Δy) is the rate of change of the porosity component after differentiation.

5. The method for calculating nuclear magnetic porosity based on dynamic T2 cutoff value according to claim 1, characterized in that: In the step S2, the dynamic T2 cutoff time is subjected to NMR porosity calculation by the NMR legacy module.

6. According to the calculation method for obtaining nuclear magnetic porosity based on dynamic T2 cutoff value in claim 1, the dynamic T2 cutoff time includes the cutoff value T 21 and the cutoff value T 22 .

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