Method for characterizing pore size of full pore diameter of shale based on combined measurement of gravimetric method and NMR (nuclear magnetic resonance)

Abstract

The invention discloses a method for characterizing the pore size of the full pore diameter of shale based on combined measurement of a gravimetric method and NMR. The method comprises the following steps: drawing a curve that the pore distribution frequency of a rock sample changes along with the pore diameter; calculating the saturated water porosity of the rock sample based on the weight of the dried rock sample and the weight of the saturated rock sample; based on the saturated water porosity of the rock sample, converting the nuclear magnetic semaphore of the nuclear magnetic resonance T2 spectrum after saturation treatment of the rock sample into a porosity component; based on the porosity component, drawing a change curve of the porosity component and the porosity accumulated value along with the relaxation time T2 after saturation treatment of the rock sample; calculating a space-time conversion coefficient between the nuclear magnetic resonance relaxation time T2 value and the pore size; and based on the space-time conversion coefficient, drawing a full-aperture pore size result graph after saturation treatment of the rock sample on the basis of the change curve of the porosity component and the porosity accumulated value along with the relaxation time T2 after saturation treatment of the rock sample. The phenomenon that the measurement ranges of the pore sizes are overlapped does not exist through multiple simultaneous measurement means, and the obtained full-aperture pore size result is higher in precision.

Description

Technical Field

[0001] The present invention relates to the field of unconventional shale oil and gas reservoir exploration, and in particular to a method for characterizing the full-aperture pore size of shale based on a gravimetric method and NMR combined measurement. Background Art

[0002] As oil and gas exploration and development technologies become more mature, unconventional oil and gas resources such as shale oil and gas have shown great development potential. The characterization of pore size in shale oil and gas reservoirs plays an important role and significance in shale oil exploration and development and reserve submission. Micro-nano pores are widely developed in shale oil and gas reservoirs, and traditional methods cannot accurately characterize their multi-scale pore structure characteristics.

[0003] At present, the commonly used methods for characterizing the pore size of shale reservoirs include core observation, gas adsorption, micro-nano CT, field emission electron microscopy, mercury injection and nuclear magnetic resonance. Due to the limitations of test instruments and measurement accuracy, it is impossible to accurately give the full-aperture pore size distribution of shale using a single method. The measurement range of pore size measurement in existing joint measurement technical methods overlaps, resulting in low accuracy of pore size characterization results given by joint measurement. Based on this, it is necessary to improve the joint measurement method for characterizing shale pore size. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for characterizing the full-aperture pore size of shale based on the combined measurement of gravimetric method and NMR, which can solve the technical problem that the measurement range of pore size measured in the existing combined measurement technical means overlaps, resulting in low accuracy of the pore size characterization results given by the combined measurement.

[0005] In a first aspect, an embodiment of the present invention discloses a method for characterizing the full-aperture pore size of shale based on a gravimetric method and NMR combined measurement, comprising the following steps:

[0006] Conduct high-pressure mercury injection testing on rock samples and draw a curve showing the variation of pore distribution frequency with pore diameter;

[0007] The rock samples were dried, weighed and tested for NMR T 2 spectrum;

[0008] Distilled water was injected into the rock sample for saturation treatment, and then the rock sample was weighed and tested for nuclear magnetic resonance T after saturation treatment. 2 spectrum;

[0009] The water-saturated porosity of the rock sample is calculated based on the weight of the rock sample after drying and the weight after saturation treatment;

[0010] Based on the water-saturated porosity of the rock sample, the rock sample was saturated with NMR T 2 The NMR signal of the spectrum is converted into porosity component;

[0011] Based on the porosity components, the porosity components and the cumulative porosity values ​​after saturation treatment of the rock sample are plotted along with the relaxation time T. 2 Change curve;

[0012] Based on the curve of the pore distribution frequency of the rock sample changing with the pore diameter and the nuclear magnetic resonance T 2 Spectra, calculate the NMR relaxation time T 2 The spatiotemporal conversion coefficient between values ​​and pore sizes;

[0013] Based on the time-space conversion coefficient, the porosity component and the porosity cumulative value after the rock sample saturation treatment change with the relaxation time T 2 Based on the change curve, the full-aperture pore size result diagram of the rock sample after saturation treatment is drawn.

[0014] According to one embodiment of the present invention, the calculation formula of the water-saturated porosity of the rock sample is as follows:

[0015]

[0016] Among them, φ iw is the water-saturated porosity of the rock sample, %; m iw is the weight of the rock sample after saturation treatment, g; m i0 is the weight of the rock sample after drying, g; ρ w is the water density, g / cm 3 ;d i is the diameter of the rock sample, cm; L i is the length of the rock sample, cm.

[0017] According to one embodiment of the present invention, based on the water-saturated porosity of the rock sample, the nuclear magnetic resonance T 2 The signal of the spectrum is converted into the porosity component, and the conversion formula is as follows:

[0018]

[0019] in, is the porosity component of the rock sample after saturation treatment, %; S iw The nuclear magnetic resonance T of the rock sample after saturation treatment 2 Spectral NMR signal quantity, PU; φ iw is the water-saturated porosity of the rock sample, %; S ac,iw T is the rock sample after saturation treatment 2 Spectral NMR signal accumulation, PU; S ac,id T is the rock sample after saturation treatment 2 The accumulated NMR signal corresponding to the first peak of the spectrum, PU.

[0020] According to one embodiment of the present invention, it also includes: using CT to scan rock samples with a diameter of 25 mm and a diameter of 2 mm to obtain structural characteristics of pores with a diameter greater than 1 μm, extracting data from the data body according to different pore sizes, and drawing a bar graph of porosities of different pore sizes for calibrating the porosities of pores of different pore sizes with a diameter greater than 1 μm in the full-aperture pore size result graph after saturation treatment of the rock sample.

[0021] According to one embodiment of the present invention, the step of calibrating the porosity of pores with a diameter greater than 1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample includes: calculating the relative error between the porosity of different pore sizes of pores with a diameter greater than 1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample and the porosity of different pore sizes of pores with a diameter greater than 1 μm identified by CT scanning.

[0022] According to one embodiment of the present invention, the NMR relaxation time T is calculated. 2 The temporal and spatial conversion coefficient between the value and the pore size includes: the curve of the pore distribution frequency of the rock sample with the pore diameter and the nuclear magnetic resonance T after the rock sample is saturated 2 The spectrum curves are integrated in the same coordinate system to establish the NMR relaxation time T after saturation treatment. 2 The time-space conversion curve between the value and the pore size is shown in Figure 1. When the peak value of the NMR signal after saturation treatment corresponds to the peak value of the high-pressure mercury injection pore distribution frequency, the NMR relaxation time T is recorded at this time. 2 and the pore diameter d value to calculate the space-time conversion coefficient.

[0023] According to one embodiment of the present invention, the space-time conversion coefficient is determined by the nuclear magnetic resonance relaxation time T 2 The ratio between the value and the pore diameter d value is obtained.

[0024] According to one embodiment of the present invention, injecting distilled water into the rock sample for saturation treatment includes: injecting the distilled water in the piston container into the rock sample using an ISCO pump.

[0025] According to one embodiment of the present invention, before injecting distilled water into the rock sample for saturation treatment, the rock sample is placed in a core holder and a confining pressure is applied using a hand pump.

[0026] According to one embodiment of the present invention, a hand pump is used to load a confining pressure within a predetermined range, and then a vacuum pretreatment system is used to perform vacuum treatment on the rock sample for a first predetermined time.

[0027] According to an embodiment of the present invention, the predetermined range of confining pressure is 1 to 3 MPa.

[0028] According to an embodiment of the present invention, the first predetermined time for the vacuum treatment is 46 to 50 hours.

[0029] According to one embodiment of the present invention, the distilled water injection pressure and the confining pressure increase in a step-by-step manner in two adjacent time periods, and in each time period the confining pressure and the injection pressure are respectively constant and the difference between the confining pressure and the injection pressure remains constant, and when the injection pressure reaches the formation pressure of the study block, the saturation process is stopped.

[0030] According to one embodiment of the present invention, the difference between the confining pressure and the injection pressure is 2 MPa.

[0031] According to one embodiment of the present invention, the saturation process is also completed in a constant temperature box, and the temperature in the constant temperature box is consistent with the formation temperature.

[0032] According to one embodiment of the present invention, the total saturation time after adding up each time period is ≥48 hours.

[0033] According to one embodiment of the present invention, the rock sample drying process includes: placing the rock sample in a vacuum oven with controllable dryness and humidity, controlling the relative humidity during drying to 40%, and drying the rock sample until constant weight.

[0034] According to one embodiment of the present invention, the drying process of the rock sample includes: the total drying time is ≤ 4 hours.

[0035] In a second aspect, an embodiment of the present invention discloses a computer-readable storage medium, including instructions, which, when executed on a computer, enable the computer to execute the method for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR combined measurement as described in any one of the above embodiments to calculate the water-saturated porosity of the rock sample;

[0036] And / or, the instructions enable the computer to execute the calculation of the porosity component in the method described in any one of the above embodiments,

[0037] And / or, the instructions enable the computer to execute the method of any one of the above embodiments to plot the porosity component and the porosity cumulative value of the rock sample after saturation treatment with the relaxation time T 2 Change curve,

[0038] And / or, the instructions enable the computer to execute the method for calculating the nuclear magnetic resonance relaxation time T in any one of the above embodiments. 2 The spatiotemporal conversion coefficient between the value and the pore size,

[0039] And / or, the instructions enable the computer to execute the method described in any one of the above embodiments to draw a full-aperture pore size result diagram after the rock sample is saturated.

[0040] In a third aspect, an embodiment of the present invention discloses a system for characterizing the full-aperture pore size of shale based on a gravimetric method and NMR combined measurement, characterized in that the system comprises:

[0041] A first calculation module, which calculates the water-saturated porosity of the rock sample based on the weight of the rock sample after drying and the weight of the rock sample after saturation treatment;

[0042] The second calculation module calculates the nuclear magnetic resonance T of the rock sample after saturation treatment based on the saturated water porosity of the rock sample. 2 The NMR signal of the spectrum is converted into porosity component;

[0043] The first building module is based on the porosity component to plot the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T 2 Change curve;

[0044] The third calculation module is based on the curve of the pore distribution frequency of the rock sample changing with the pore diameter and the nuclear magnetic resonance T of the rock sample after saturation treatment. 2 spectrum to calculate the NMR relaxation time T 2 The spatiotemporal conversion coefficient between values ​​and pore sizes;

[0045] The second building module, the first building module is based on the time-space conversion coefficient, after the rock sample is saturated, the porosity component and the porosity cumulative value change with the relaxation time T 2 A building module for drawing the full-aperture pore size result diagram of the rock sample after saturation treatment based on the change curve.

[0046] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0047] The method for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR joint measurement provided by the present invention is based on the high-pressure mercury injection test rock sample pore distribution frequency versus pore diameter change curve, based on the gravimetric method and NMR joint measurement to obtain the porosity component and porosity cumulative value of the rock sample after saturation treatment with relaxation time T 2 Change curve, and finally based on the shale NMR relaxation time T 2 The temporal and spatial conversion coefficient between the value and the pore size, the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T 2 Based on the change curve, the full-aperture pore size result diagram of the rock sample after saturation treatment is drawn, which realizes the characterization of the full-aperture pore size of shale. In addition, there is no overlap in the pore size measurement range of multiple joint measurement methods, and the full-aperture pore size result obtained is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 An overall schematic diagram of a rock sample used in an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of an original grayscale image and a three-dimensional reconstructed image obtained by CT scanning of a rock sample disclosed in an embodiment of the present invention;

[0051] Figure 3 A distribution histogram of porosity of rock samples with different pore sizes disclosed in an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of a curve showing a change between the mercury injection pore diameter and the pore distribution frequency of a rock sample disclosed in an embodiment of the present invention;

[0053] Figure 5 The porosity component and the cumulative value of the porosity component after the rock sample saturation treatment disclosed in one embodiment of the present invention are as T 2 Schematic diagram of the relaxation time variation relationship curve;

[0054] Figure 6 is the nuclear magnetic resonance relaxation time T of the rock sample after saturation treatment disclosed in one embodiment of the present invention 2 Schematic diagram of the integration of the change curve of the nuclear magnetic signal and the change curve of the pore distribution frequency with the pore diameter in the same coordinate system;

[0055] Figure 7 A schematic diagram of the full-aperture pore size results after shale saturation treatment disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0057] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0058] According to a first aspect of the present invention, an embodiment of the present invention discloses a method for characterizing the full-aperture pore size of shale based on a gravimetric method and NMR combined measurement, comprising the following steps:

[0059] Conduct high-pressure mercury injection testing on rock samples and draw a curve showing the variation of pore distribution frequency with pore diameter;

[0060] The rock samples were dried, weighed and tested for NMR T 2 spectrum;

[0061] Distilled water was injected into the rock sample for saturation treatment, and then the rock sample was weighed and tested for nuclear magnetic resonance T after saturation treatment. 2 spectrum;

[0062] The water-saturated porosity of the rock sample is calculated based on the weight of the rock sample after drying and the weight after saturation treatment;

[0063] Based on the water-saturated porosity of the rock sample, the rock sample was saturated with NMR T 2 The NMR signal of the spectrum is converted into porosity component;

[0064] Based on the porosity components, the porosity components and the cumulative porosity values ​​after saturation treatment of the rock samples are plotted along with the relaxation time T. 2 Change curve;

[0065] Based on the curve of the pore distribution frequency of the rock sample changing with the pore diameter and the nuclear magnetic resonance T 2 Spectra, calculate the NMR relaxation time T 2 The spatiotemporal conversion coefficient between values ​​and pore sizes;

[0066] Based on the time-space conversion coefficient, the porosity component and the porosity cumulative value after the rock sample saturation treatment change with the relaxation time T 2 Based on the change curve, the full-aperture pore size result diagram of the rock sample after saturation treatment is drawn.

[0067] In an embodiment of the present invention, the nuclear magnetic resonance T 2 The spectrum is the NMR signal intensity versus relaxation time T 2 By measuring the nuclear magnetic resonance T of the rock sample after drying 2 The spectrum can be compared with the NMR T 2 The NMR T of the rock samples in these two cases was compared. 2 The first peak in the spectrum represents the organic signal peak, so the NMR relaxation time T is calculated later. 2 The relaxation time T corresponding to the first peak is discarded when the spatiotemporal conversion coefficient between the value and the pore size is calculated. 2 Instead of using the relaxation time corresponding to the second peak, the calculation of the spatiotemporal conversion coefficient is performed starting from the relaxation time corresponding to the second peak.

[0068] In some embodiments, the water-saturated porosity of a rock sample is calculated as follows:

[0069]

[0070] Among them, φ iw is the water-saturated porosity of the rock sample, %; m iw is the weight of the rock sample after saturation treatment, g; m i0 is the weight of the rock sample after drying, g; ρ w is the water density, g / cm 3 ;d i is the diameter of the rock sample, cm; L i is the length of the rock sample, cm.

[0071] In some embodiments, based on the water-saturated porosity of the rock sample, the rock sample is saturated with water and the NMR T 2 The signal of the spectrum is converted into the porosity component, and the conversion formula is as follows:

[0072]

[0073] in, is the porosity component of the rock sample after saturation treatment, %; S iw The nuclear magnetic resonance T of the rock sample after saturation treatment 2 Spectral NMR signal quantity, PU; φ iw is the water-saturated porosity of the rock sample, %; S ac,iw T is the rock sample after saturation treatment 2 Spectral NMR signal accumulation, PU; S ac,id T is the rock sample after saturation treatment 2 The accumulated NMR signal corresponding to the first peak of the spectrum, PU.

[0074] In some embodiments, the method for characterizing the full-aperture pore size of shale based on the gravimetric method and the NMR joint measurement further includes: using CT to scan rock samples with a diameter of 25 mm and a diameter of 2 mm to obtain the structural characteristics of pores with a diameter greater than 1 μm, extracting data from the data body according to different pore sizes, and drawing a bar graph of the porosity of different pore sizes for calibrating the porosity of pores with a diameter greater than 1 μm in the full-aperture pore size result graph after the rock sample is saturated. In this embodiment, for a rock sample with a diameter of 25 mm, the accuracy of the CT scan is set to the micron level; for a rock sample with a diameter of 2 mm, the accuracy of the CT scan is set to the nanometer level.

[0075] In some embodiments, the step of calibrating the porosity of pores with a diameter of >1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample includes: calculating the relative error between the porosity of different pore sizes of pores with a diameter of >1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample and the porosity of different pore sizes of pores with a diameter of >1 μm identified by CT scanning. In this embodiment, if the relative error is less than 10%, it indicates that the method for characterizing the full-aperture pore size of shale based on the combined measurement of gravimetric method and NMR disclosed in the embodiment of the present invention is highly reliable.

[0076] In the above embodiment, when performing high-pressure mercury injection testing, since the initial point of mercury injection is difficult to determine, the error of the macropore data obtained by the high-pressure mercury injection test is large, so the porosity of different pore sizes of macropores (diameter>1μm) in the full-aperture pore size result diagram after the rock sample is saturated can be corrected in combination with the CT scanning test results. Compared with the NMR technology, the pore size range of the CT scanning test is limited. By using the porosity distribution data of pores of different sizes obtained by CT scanning to calibrate the porosity of different pore sizes of macropores (diameter>1μm) in the full-aperture pore size result diagram after the rock sample is saturated, the method for characterizing the full-aperture pore size of shale based on the weight method and NMR joint measurement disclosed in the embodiment of the present invention has a self-correction function, so it can ensure that the result of the full-aperture pore size of shale obtained after the joint measurement is more accurate.

[0077] In some embodiments, the NMR relaxation time T is calculated 2 The time-space conversion coefficient of the pore size and the pore distribution frequency of the rock sample is included in the pore diameter change curve and the nuclear magnetic resonance T 2 The spectrum curves are integrated in the same coordinate system to establish the NMR relaxation time T after saturation treatment. 2 The time-space conversion curve between the value and the pore size is shown in Figure 1. When the peak value of the NMR signal after saturation treatment corresponds to the peak value of the high-pressure mercury injection pore distribution frequency, the NMR relaxation time T is recorded at this time. 2 and the pore diameter d value to calculate the space-time conversion coefficient.

[0078] In some embodiments, the spatiotemporal conversion coefficient is determined by the NMR relaxation time T 2 The ratio between the value and the pore diameter d value is obtained.

[0079] In some embodiments, injecting distilled water into the rock sample for saturation treatment includes: injecting distilled water in the piston container into the rock sample using an ISCO pump. This embodiment is conducive to better injecting distilled water into the pores of the rock sample.

[0080] In some embodiments, before injecting distilled water into the rock sample for saturation treatment, the rock sample is placed in a core holder and a confining pressure is applied using a hand pump. In this embodiment, applying confining pressure is helpful to avoid the problem of unsatisfactory saturation treatment effect caused by the injected distilled water escaping from the surrounding of the rock sample instead of entering the rock sample.

[0081] In some embodiments, a hand pump is used to load a confining pressure within a predetermined range, and then a vacuum pretreatment system is used to vacuum the rock sample for a first predetermined time. In this embodiment, vacuuming the rock sample can achieve a better effect of rock sample saturation treatment, and can allow distilled water to enter the rock sample better and more fully, thereby facilitating the accuracy of subsequent measurement data and obtaining a more accurate full-aperture pore size result.

[0082] In some embodiments, the predetermined range of confining pressure is 1-3 MPa. In other embodiments, the predetermined range of confining pressure is preferably 2 MPa. This can improve the effect of saturation treatment of the rock sample.

[0083] In some embodiments, the first predetermined time of the vacuum treatment is 46 to 50 hours, which can improve the effect of the rock sample saturation treatment and allow the distilled water to enter the rock sample better and more fully, thereby facilitating the acquisition of a more accurate full-aperture pore size result.

[0084] In some embodiments, the injection pressure of distilled water and the confining pressure increase in a step-wise manner in two adjacent time periods, and the confining pressure and the injection pressure are respectively constant in each time period and the difference between the confining pressure and the injection pressure is kept constant. When the injection pressure reaches the formation pressure of the study block, the saturation process is stopped. In this embodiment, the confining pressure and the injection pressure are respectively constant in a time period (for example, 30 minutes) and the difference between the confining pressure and the injection pressure is kept constant for a period of time for saturation treatment, followed by a certain amount of increase in the next time period and the difference between the confining pressure and the injection pressure in the time period is also kept constant (the same as the difference in the previous time period), until the injection pressure reaches the formation pressure of the study block, the saturation process is stopped. The above method allows distilled water to enter the rock sample better and more fully, which is beneficial to the accuracy of subsequent measurement data and to obtain more accurate full-aperture pore size results.

[0085] In some embodiments, the difference between the confining pressure and the injection pressure is 2 MPa. In this embodiment, the difference between the confining pressure and the injection pressure is 2 MPa, which can make the distilled water enter the rock sample better and more fully, thereby facilitating the accuracy of subsequent measurement data and facilitating obtaining a more accurate full-aperture pore size result.

[0086] In some embodiments, the method for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR combined measurement further includes: the saturation process is completed in a constant temperature box, and the temperature in the constant temperature box is consistent with the formation temperature. The formation environment where the rock sample is located is simulated, which is conducive to improving the effect of the rock sample saturation treatment and obtaining a more accurate full-aperture pore size result.

[0087] In some embodiments, the total saturation time after adding up each time period is ≥ 48 hours, so that the distilled water can enter the rock sample better and more fully, which is beneficial to the accuracy of subsequent measurement data and to obtaining a more accurate full-aperture pore size result.

[0088] In some embodiments, the rock sample drying process includes: placing the rock sample in a vacuum oven with controllable humidity, controlling the relative humidity during drying to 40%, and drying the rock sample until the rock sample has a constant weight. This embodiment is conducive to sufficient drying of the rock sample.

[0089] In some embodiments, the drying process of the rock sample includes: total drying time ≤ 4 hours.

[0090] According to a second aspect of the present invention, an embodiment of the present invention discloses a computer-readable storage medium, which includes instructions. When the instructions are executed on a computer, the instructions cause the computer to execute the method for characterizing the full-aperture pore size of shale based on the weight method and NMR joint measurement as described in the above embodiment to calculate the water-saturated porosity of the rock sample;

[0091] and / or, the instructions enable the computer to perform the calculation of the porosity component in any of the methods of the above embodiments,

[0092] And / or, the instructions enable the computer to execute the method of any one of the above embodiments to draw the curve of the porosity component and the porosity cumulative value after the rock sample is saturated and the change curve of the relaxation time T2,

[0093] And / or, the instructions enable the computer to execute the method of calculating the nuclear magnetic resonance relaxation time T in any one of the above embodiments. 2 The spatiotemporal conversion coefficient between the value and the pore size,

[0094] And / or, the instructions enable the computer to execute the method of any one of the above embodiments to draw a full-aperture pore size result diagram after the rock sample is saturated.

[0095] According to a third aspect of the present invention, an embodiment of the present invention discloses a method for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR combined measurement as described in the above embodiment, and a system for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR combined measurement, the system comprising:

[0096] A first calculation module, the first calculation module calculates the water-saturated porosity of the rock sample based on the weight of the rock sample after drying and the weight of the rock sample after saturation treatment;

[0097] The second calculation module calculates the nuclear magnetic resonance T of the rock sample after saturation treatment based on the saturated water porosity of the rock sample. 2 The NMR signal of the spectrum is converted into porosity component;

[0098] The first building module is based on the porosity component to plot the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T 2 Change curve;

[0099] The third calculation module is based on the curve of the pore distribution frequency of the rock sample changing with the pore diameter and the nuclear magnetic resonance T 2 spectrum to calculate the NMR relaxation time T 2 The spatiotemporal conversion coefficient between values ​​and pore sizes;

[0100] The second building module is based on the time-space conversion coefficient, and the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T 2 A building module for drawing the full-aperture pore size result diagram of the rock sample after saturation treatment based on the change curve.

[0101] The present invention is described below with reference to specific embodiments. It should be noted that the embodiments are merely illustrative and do not limit the present invention in any way.

[0102] 1. Rock sample preparation

[0103] Two standard plunger shale samples from the same coring layer section in the study block were selected and numbered 1# and 2#. The core length was 6 cm, and the 2# sample was used as a control sample to carry out the same experiment as the 1# sample. The 1# sample was cut into three cores with lengths of 1 cm, 1.5 cm and 3.5 cm by wire cutting, and they were numbered 1-1, 1-2 and 1-3 for standby use. A 2mm diameter rock sample was drilled from the 1-1 sample for CT scanning test, the 1-2 sample was used for high-pressure mercury injection test, and the 1-3 sample was used for CT scanning test and nuclear magnetic resonance test. The processing process of the 2# sample was the same as that of the 1# sample, wherein a 2mm diameter rock sample was drilled from the 2-1 sample for CT scanning test, the 2-2 sample was used for high-pressure mercury injection test, and the 2-3 sample was used for CT scanning test and nuclear magnetic resonance test. The whole rock sample for the experiment is attached. Figure 1 Under the conditions of the present invention, the test results of the 1# and 2# rock samples are highly consistent, so the subsequent implementation process of the embodiment is described based on the results of the 1# rock sample.

[0104] 2. CT scan test

[0105] The prepared 1-3 and 2-3 shale plug samples with a diameter of 25 mm and the 1-1 and 2-1 shale plug samples with a diameter of 2 mm were dried according to GB / T 29172-2012 "Core Analysis Methods", and then CT scanning of the 25 mm and 2 mm diameter samples was used to characterize the structural characteristics of pores with a diameter greater than 1 μm in the core cores of the study area. Figure 2 The original grayscale image and three-dimensional reconstruction image obtained by CT scanning of rock samples 1-3 with a diameter of 25 mm are shown. Data is extracted from the data body according to different pore sizes, and the distribution bar graph of porosity of different pore sizes is drawn (such as Figure 3 Table 1 below is a statistical table of pore size distribution of rock samples 1-1 (2 mm plunger rock sample) and 1-3 (25 mm plunger rock sample) in three-dimensional CT scanning.

[0106] Table 1 Statistical table of pore size distribution of rock samples by three-dimensional CT scanning

[0107]

[0108] 3. High-pressure mercury injection test

[0109] The prepared 1-2 and 2-2 shale samples were dried according to GB / T 29172-2012 "Core Analysis Methods", and the dried samples were subjected to high-pressure mercury injection testing. The pore distribution frequency versus pore diameter curve was plotted under semi-logarithmic coordinate conditions to determine the pore distribution characteristics of the shale samples. The mercury injection pore distribution frequency of sample 1-2 is shown in the attached figure. Figure 4 shown.

[0110] 4. Gravimetric method + nuclear magnetic resonance test

[0111] 1) Dry and weigh the 1-3 and 2-3 shale samples with a diameter of 25 mm according to GB / T 29172-2012 "Core Analysis Method";

[0112] 2) Test the NMR T of the dried shale sample 2 spectrum;

[0113] 3) placing the 1-3 and 2-3 standard rock samples after step 2) in the core holder respectively, applying a 2MPa confining pressure using a hand pump, and then vacuuming the standard rock samples using a vacuum pretreatment system for 48 hours;

[0114] 4) Place the distilled water for the experiment in a piston container, and use an ISCO pump to inject the distilled water in the piston container into the core holder rock sample containing 1-3 and 2-3 rock samples. During the saturation process, the injection pressure of the distilled water and the confining pressure increase in a step-by-step manner in two adjacent time periods. In each time period, the confining pressure and the injection pressure are respectively constant, and the difference between the confining pressure and the injection pressure is 2MPa. When the injection pressure reaches the formation pressure of the study block, the saturation process is stopped; the rock sample saturation process is completed in a thermostatic box, the temperature of the thermostatic box is consistent with the formation temperature, and the total saturation time is not less than 48 hours;

[0115] 5) Take out the saturated samples 1-3 and 2-3 from the core holder and record their mass. Test the nuclear magnetic resonance T of the saturated samples. 2 spectrum;

[0116] 6) Experimental data processing and analysis.

[0117] (1) Nuclear magnetic resonance T 2 Establishment of calibration relationship between spectral nuclear magnetic resonance signal and shale water-saturated porosity

[0118] ① Calculate the water-saturated porosity of shale samples 1-3 and 2-3 based on the weight method. The calculation formula is as follows:

[0119]

[0120] Among them, φ iw is the water-saturated porosity of the i# rock sample, %; m iw is the weight of the i# rock sample after saturation treatment, g; m i0 is the weight of the i#th rock sample after drying, g; ρ w is the water density, g / cm 3 ;d i is the diameter of the i# rock sample, cm; L i is the length of the i#th rock sample, cm.

[0121] Taking rock sample 1# as an example, the saturated water porosity is calculated by formula 1 to be 10.89%.

[0122] ② Based on the nuclear magnetic resonance T after rock sample saturation treatment 2 The nuclear magnetic signal of the spectrum is calculated by using formula (1) to calculate the shale saturation T 2 The NMR signal of the spectrum is converted into the porosity component, and the conversion formula is as follows:

[0123]

[0124] in, is the porosity component of the i#th rock sample after saturation treatment, %; S iw is the NMR T of the i#th rock sample after saturation treatment 2Spectral NMR signal quantity, PU; φ iw is the water-saturated porosity of the i# rock sample, %; S ac,iw T is the i#th rock sample after saturation treatment 2 Spectral NMR signal accumulation, PU; S ac,id T is the i#th rock sample after saturation treatment 2 The accumulated NMR signal corresponding to the first peak of the spectrum, PU.

[0125] Taking rock sample 1# as an example, the signal quantity-porosity conversion coefficient is 0.005634 obtained by formula 2.

[0126] ③ Based on the porosity component obtained in step ②, plot the porosity component after shale saturation treatment and the cumulative value of the porosity component with T 2 Relaxation time variation curve, see attached Figure 5 .

[0127] (2) NMR relaxation time T 2 Calculation of the value and the spatial-temporal conversion coefficient of pore size

[0128] ① Extract the NMR relaxation time T of 1-3 and 2-3 rock samples after saturation treatment 2 The NMR signal data were plotted against the relaxation time T under semi-logarithmic coordinate conditions. 2 Change curve, see attached Figure 6 .

[0129] ② Extract the pore diameter and pore distribution frequency data from the high-pressure mercury injection test results of rock samples 1-2 and 2-2, and draw a curve of pore distribution frequency versus pore diameter under semi-logarithmic coordinate conditions. See the attached Figure 6 .

[0130] ③Integrate the curve data of steps ① and ② in the same coordinate system to establish the time-space conversion curve between NMR and high-pressure mercury injection pore distribution frequency, where the bottom coordinate of the X-axis is the pore diameter, the main coordinate of the Y-axis is the pore distribution frequency; the top coordinate of the X-axis is the relaxation time T 2 , the Y-axis sub-coordinate is the nuclear magnetic signal, see attached Figure 6 .

[0131] ④ NMR T of shale samples after saturation treatment 2 The first peak of the spectrum represents the organic matter signal display, so the time-space conversion coefficient calculation starts with the relaxation time corresponding to the second peak. When the peak value of the NMR signal corresponds to the peak value of the high-pressure mercury injection pore distribution frequency, the NMR relaxation time T at this time is recorded. 2 and pore diameter d, and then calculate the NMR relaxation time T 2 The spatiotemporal conversion coefficient between the value and the pore size.

[0132] Taking rock sample 1# as an example, the time-space conversion coefficient (i.e., the NMR relaxation time T 2 The spatiotemporal conversion coefficient between the value and the pore size) is 18.97 nm / ms.

[0133] ⑤ Based on the time-space conversion coefficient of 18.97nm / ms determined in step ④, the NMR porosity component curve + porosity cumulative curve (see attached Figure 5 ) based on which the full-aperture pore size results of the rock sample after saturation treatment were plotted (see Appendix Figure 7 ).

[0134] Based on the full-aperture pore size result diagram after the rock sample is saturated, the total porosity value of macropores (diameter>1μm) and the porosity values ​​of different pore sizes of macropores (diameter>1μm) can be determined (i.e., the porosity of different pore sizes of macropores (diameter>1μm) identified by nuclear magnetic resonance). By comparing the porosity results of different void sizes of macropores (diameter>1μm) identified by nuclear magnetic resonance with the porosity results of different pore sizes of macropores (diameter>1μm) identified by CT, the relative errors of the porosities of different pore sizes of macropores (diameter>1μm) determined by these two methods are calculated (as shown in Table 2 below). In the above embodiment, the relative error is about 9.10%, indicating that the method for characterizing the full-aperture pore size of shale based on the gravimetric method + NMR joint measurement established in the embodiment of the present invention is reliable.

[0135] Table 2 Statistical results of pore size distribution of rock samples identified by 3D CT scanning and NMR

[0136]

[0137]

[0138] In summary, the method for characterizing the full-aperture pore size of shale based on the gravimetric method and NMR joint measurement disclosed in the embodiment of the present invention is based on the high-pressure mercury injection test rock sample pore distribution frequency versus pore diameter change curve, based on the gravimetric method and NMR joint measurement to obtain the porosity component and porosity cumulative value of the rock sample after saturation treatment with relaxation time T 2 Change curve, and finally based on the shale NMR relaxation time T 2 The temporal and spatial conversion coefficient between the porosity value and the pore size, the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T 2 Based on the change curve, the full-aperture pore size result diagram of the rock sample after saturation treatment is drawn, which realizes the characterization of the full-aperture pore size of shale. In addition, there is no overlap in the pore size measurement range of multiple joint measurement methods, and the full-aperture pore size result obtained is more accurate.

[0139] It should be particularly pointed out that the various components or steps in the above-mentioned embodiments can be cross-linked, replaced, added, or deleted with each other. Therefore, the combinations formed by these reasonable arrangements and combinations should also fall within the scope of protection of the present invention, and the scope of protection of the present invention should not be limited to the embodiments.

[0140] The above are exemplary embodiments disclosed in the present invention. The order disclosed in the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. However, it should be noted that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope (including claims) disclosed in the embodiments of the present invention is limited to these examples. Various changes and modifications may be made without departing from the scope defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0141] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for characterizing the full-aperture pore size of shale based on gravimetric and NMR combined measurement, characterized in that: The steps include: Conduct high-pressure mercury injection testing on rock samples and draw a curve showing the variation of pore distribution frequency with pore diameter; The rock samples were dried, weighed and tested for nuclear magnetic resonance T2 spectrum; Distilled water was injected into the rock sample for saturation treatment, and then the rock sample was weighed and the nuclear magnetic resonance T2 spectrum after saturation treatment was tested; The water-saturated porosity of the rock sample is calculated based on the weight of the rock sample after drying and the weight after saturation treatment; Based on the water-saturated porosity of the rock sample, converting the nuclear magnetic signal of the nuclear magnetic resonance T2 spectrum after the rock sample is saturated into a porosity component; Based on the porosity components, a curve of the porosity components and the cumulative porosity value after saturation treatment of the rock sample versus relaxation time T2 is drawn; Based on the curve of the pore distribution frequency of the rock sample changing with the pore diameter and the nuclear magnetic resonance T2 spectrum of the rock sample after saturation treatment, the time-space conversion coefficient between the nuclear magnetic resonance relaxation time T2 value and the pore size is calculated; Based on the time-space conversion coefficient, a full-aperture pore size result diagram of the rock sample after saturation treatment is drawn on the basis of the curves of the porosity component and the porosity cumulative value after the rock sample is saturated with the relaxation time T2.

2. The method according to claim 1, characterized in that The calculation formula of the rock sample saturated water porosity is as follows: Among them, φ iw is the water-saturated porosity of the rock sample, %; m iw is the weight of the rock sample after saturation treatment, g; m i0 is the weight of the rock sample after drying, g; ρ w is the water density, g / cm 3 ;d i is the diameter of the rock sample, cm; L i is the length of the rock sample, cm.

3. The method according to claim 2, characterized in that Based on the water-saturated porosity of the rock sample, the signal amount of the nuclear magnetic resonance T2 spectrum after the rock sample saturation treatment is converted into a porosity component. The conversion formula is as follows: in, is the porosity component of the rock sample after saturation treatment, %; S iw is the nuclear magnetic resonance T2 spectrum nuclear magnetic signal after rock sample saturation treatment, PU; φ iw is the water-saturated porosity of the rock sample, %; S ac,iw PU is the cumulative amount of T2 spectrum nuclear magnetic signal after rock sample saturation treatment; S ac,id It is the accumulated amount of nuclear magnetic signal corresponding to the first peak of T2 spectrum after saturation treatment of rock sample, PU.

4. The method according to claim 1, characterized in that: Also includes: CT was used to scan rock samples with diameters of 25 mm and 2 mm to obtain the structural characteristics of pores with diameters greater than 1 μm. Data were extracted from the data body according to different pore sizes, and a bar graph of the porosity of different pore sizes was drawn to calibrate the porosity of pores with diameters greater than 1 μm in the full-aperture pore size result graph after saturation treatment of the rock samples.

5. The method according to claim 4, characterized in that The step of calibrating the porosity of pores with a diameter greater than 1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample includes: calculating the relative error between the porosity of pores of different pore sizes with a diameter greater than 1 μm in the full-aperture pore size result diagram after saturation treatment of the rock sample and the porosity of pores of different pore sizes with a diameter greater than 1 μm identified by CT scanning.

6. The method according to claim 1, characterized in that Calculating the time-space conversion coefficient between the nuclear magnetic resonance relaxation time T2 value and the pore size includes: integrating the rock sample pore distribution frequency versus pore diameter change curve and the nuclear magnetic resonance T2 spectrum curve after saturation treatment of the rock sample in the same coordinate system, establishing the time-space conversion curve between the nuclear magnetic resonance relaxation time T2 value and the pore size after saturation treatment, and when the peak value of the nuclear magnetic signal after saturation treatment corresponds one by one to the peak value of the high-pressure mercury injection pore distribution frequency, recording the nuclear magnetic resonance relaxation time T2 and the pore diameter d value at this time to calculate the time-space conversion coefficient.

7. The method according to claim 6, characterized in that The space-time conversion coefficient is obtained by the ratio between the nuclear magnetic resonance relaxation time T2 value and the pore diameter d value.

8. The method according to claim 1, characterized in that Injecting distilled water into the rock sample for saturation treatment includes: injecting the distilled water in the piston container into the rock sample using an ISCO pump.

9. The method according to claim 8, characterized in that Before injecting distilled water into the rock sample for saturation treatment, the rock sample was placed in a core holder and the confining pressure was applied using a hand pump.

10. The method according to claim 9, characterized in that A hand pump is used to load a predetermined range of confining pressure, and then a vacuum pretreatment system is used to vacuum the rock sample for a first predetermined time.

11. The method according to claim 10, characterized in that The predetermined range of confining pressure is 1 to 3 MPa.

12. The method according to claim 10, characterized in that The first predetermined time of the vacuum treatment is 46 to 50 hours.

13. The method according to claim 9, characterized in that The distilled water injection pressure and the confining pressure increase in a step-by-step manner in two adjacent time periods. In each time period, the confining pressure and the injection pressure are respectively constant and the difference between the confining pressure and the injection pressure remains constant. When the injection pressure reaches the formation pressure of the study block, the saturation process is stopped.

14. The method according to claim 13, characterized in that The difference between the confining pressure and the injection pressure is 2 MPa.

15. The method according to claim 13, characterized in that Also includes: The saturation process is completed in a constant temperature box, and the temperature in the constant temperature box is consistent with the formation temperature.

16. The method according to claim 13, characterized in that The total saturation time after adding up each time period is ≥48 hours.

17. The method according to claim 1, characterized in that The rock sample drying process includes: placing the rock sample in a vacuum oven with controllable dryness and humidity, controlling the relative humidity during drying to 40%, and drying the rock sample until constant weight.

18. The method according to claim 14, characterized in that The rock sample drying process includes: total drying time ≤ 4h.

19. A computer-readable storage medium, comprising instructions, which, when executed on a computer, enable the computer to perform the method for characterizing the full-aperture pore size of shale based on the combined measurement of gravimetric method and NMR as claimed in any one of claims 1 to 15, to calculate the water-saturated porosity of a rock sample; And / or, the instructions enable the computer to execute the calculation of the porosity component in the method according to any one of claims 1 to 15, And / or, the instructions enable the computer to execute the method according to any one of claims 1 to 15, which is to draw the curve of the porosity component and the cumulative porosity value of the rock sample after saturation treatment versus the relaxation time T2, And / or, the instructions enable the computer to execute the method of calculating the time-space conversion coefficient between the nuclear magnetic resonance relaxation time T2 value and the pore size in any one of claims 1 to 15, And / or, the instructions enable the computer to execute the method according to any one of claims 1 to 15, which comprises drawing a full-aperture pore size result graph after saturation treatment of the rock sample.

20. A system for characterizing the full-aperture pore size of shale based on gravimetric and NMR combined measurement, characterized in that: The system comprises: A first calculation module, which calculates the water-saturated porosity of the rock sample based on the weight of the rock sample after drying and the weight of the rock sample after saturation treatment; A second calculation module, which converts the nuclear magnetic resonance signal of the nuclear magnetic resonance T2 spectrum after the rock sample is saturated with water into a porosity component based on the porosity of the rock sample; A first construction module, wherein the first construction module is based on the porosity component to draw a curve of the porosity component and the porosity cumulative value after the rock sample is saturated and the change with the relaxation time T2; A third calculation module, wherein the third calculation module calculates the time-space conversion coefficient between the nuclear magnetic resonance relaxation time T2 value and the pore size based on the curve of the pore distribution frequency of the rock sample versus the pore diameter and the nuclear magnetic resonance T2 spectrum of the rock sample after saturation treatment; The second construction module is a construction module for drawing a full-aperture pore size result diagram of the rock sample after saturation treatment based on the time-space conversion coefficient and the curve of the porosity component and the cumulative porosity value after the rock sample is saturated with the relaxation time T2.

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