Nuclear magnetic resonance characterization method and apparatus for rock wettability considering the influence of saturation history

Abstract

This application provides a method and apparatus for characterizing rock wettability using nuclear magnetic resonance (NMR) considering the influence of saturation history, relating to the field of rock NMR wettability characterization technology. It acquires bulk NMR references for the aqueous and oil phases, saturated water core references, and saturated oil core references, as well as two-dimensional NMR spectra of the two saturation history final states. Water-oil signals are separated, and the saturation of the aqueous phase, oil phase, and the transverse relaxation rates of the aqueous and oil phases are determined. After bulk subtraction and normalization using the saturated core references, the effective pore wall contact fractions of the aqueous and oil phases are obtained. After closure determination and normalization, the normalized pore wall contact fractions of the two final states are obtained, based on which the NMR wettability index and the saturation history influence index are determined. This application can characterize the pore wall contact state of the oil and water phases and distinguish between rock wettability and the influence of saturation history.

Description

Technical Field

[0001] This application relates to the field of petrophysical and nuclear magnetic resonance (NMR) testing technology for oil and gas reservoirs, specifically to a method based on... Two-dimensional nuclear magnetic resonance (NMR) data is a technique for characterizing the contact state and wettability of the pore walls of oil-water two-phase rocks. Background Technology

[0002] Rock wettability is an important parameter characterizing the interaction between fluids such as oil and water and the pore walls of rocks, and it has a significant impact on the distribution and migration characteristics of fluids in oil and gas reservoirs. Existing methods for evaluating rock wettability include the contact angle method, the Amott-Harvey method, and the United States Bureau of Mines (USBM) method. Among them, the contact angle method mainly reflects the wetting characteristics of local visible surfaces, while the Amott-Harvey method and the USBM method mainly evaluate based on fluid displacement or self-absorption behavior at the core scale, and are difficult to directly reflect the contact state of oil and water phases on the pore walls inside the rock.

[0003] Low-field nuclear magnetic resonance (NMR) technology can non-destructively detect the fluid state inside rocks based on the relaxation response of pore fluids, and therefore can be used for rock wettability evaluation. However, in cores containing both oil and water phases, the NMR signals of the water and oil phases may overlap. It is difficult to accurately distinguish the relaxation responses of different fluids based solely on the peak positions of the one-dimensional transverse relaxation time spectrum or changes in overall relaxation parameters. Furthermore, fluid saturation characterizes the proportion of pore volume occupied by the corresponding fluid, while rock wettability is related to the contact state of different fluids on the pore wall. These two concepts have different physical meanings, making it difficult to directly use fluid saturation to characterize the pore wall contact state.

[0004] Furthermore, even after a core sample reaches a stable state following different initial saturation states and fluid ingress processes, the internal oil-water distribution may still be affected by its saturation history. If wettability is directly characterized based on a single final state or the difference between final states with different saturation histories, the final state differences caused by the saturation history may be confused with the wettability characteristics of the rock itself, thus affecting the wettability evaluation results.

[0005] Therefore, how to distinguish the nuclear magnetic resonance responses of the aqueous and oil phases, obtain characterization parameters that can reflect the contact state of the pore walls of the oil and water phases, and further distinguish the rock wettability characterization from the influence of saturation history are problems that need to be solved in the existing nuclear magnetic resonance rock wettability evaluation. Summary of the Invention

[0006] This application provides a method and apparatus for characterizing rock wettability using nuclear magnetic resonance (NMR) considering the influence of saturation history, in order to solve the problems in existing NMR rock wettability evaluations, such as the difficulty in effectively distinguishing the NMR responses of the aqueous and oil phases, the difficulty in quantitatively characterizing the contact state of the pore walls of the oil and water phases, and the difficulty in distinguishing rock wettability characterization from the influence of saturation history.

[0007] In a first aspect, this application provides a method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history, comprising: Obtain bulk NMR references for the aqueous and oil phases, as well as references for saturated water and saturated oil cores, and references for the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; Based on the aforementioned bulk NMR reference, saturated water core reference, and saturated oil core reference, the final states were analyzed. Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state. The transverse relaxation rates of the aqueous phase and the transverse relaxation rates of the oil phase in each final state are respectively subtracted from the corresponding transverse relaxation rates of the bulk phase, and based on the water phase saturation and oil phase saturation in each final state, they are normalized using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state. The effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state are judged by closure deviation. The effective pore wall contact fractions of the two final states that pass the closure deviation judgment are normalized by closure to obtain the corresponding normalized aqueous phase pore wall contact fraction. The difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 is determined as the NMR wetting index, and the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state is determined as the saturation history influence index.

[0008] A second aspect of this application provides a nuclear magnetic resonance rock wettability characterization device that takes into account the influence of saturation history, comprising: The data acquisition module is used to acquire bulk NMR references for the aqueous and oil phases, saturated water core references, and saturated oil core references, as well as the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; The signal separation module is used to separate the signals at each final state based on the bulk nuclear magnetic resonance reference, saturated water core reference, and saturated oil core reference. Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state. The pore wall contact fraction determination module is used to subtract the corresponding bulk phase lateral relaxation rate from the water phase lateral relaxation rate and the oil phase lateral relaxation rate of each final state, and to normalize them based on the water phase saturation and oil phase saturation of each final state using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the water phase and the effective pore wall contact fraction of the oil phase of each final state. The closure processing module is used to determine the closure deviation between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state, and to perform closure normalization on the effective pore wall contact fractions of the two final states that pass the closure deviation determination, so as to obtain the corresponding normalized aqueous phase pore wall contact fraction. The index determination module is used to determine the difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 as the NMR wetting index, and to determine the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state as the saturation history influence index.

[0009] Compared with existing technologies, this application obtains bulk NMR references for the aqueous and oil phases, as well as saturated water core references and saturated oil core references, and then uses these references to analyze the first and second final states. Two-dimensional nuclear magnetic resonance spectroscopy is used to separate water and oil signals, enabling... In two-dimensional nuclear magnetic resonance (NMR) spectra, the originally mixed aqueous and oil phase responses can be attributed to their respective fluid phases, thereby determining the final states of aqueous and oil phase saturation, as well as the transverse relaxation rates of both phases. This reduces the interference caused by the overlap of aqueous and oil phase NMR signals on the determination of the relaxation responses of each phase, and helps to distinguish between the aqueous and oil phase NMR responses.

[0010] Furthermore, this application subtracts the corresponding bulk phase lateral relaxation rate from the water phase lateral relaxation rate and the oil phase lateral relaxation rate at each final state to reduce the influence of the fluid's own bulk relaxation on the characterization of the pore wall contact state. Based on this, the water phase saturation and oil phase saturation at each final state are combined and normalized using saturated water core references and saturated oil core references, respectively, so that the water phase and oil phase can respectively use the corresponding saturated core state as the reference endpoint to obtain the effective pore wall contact fraction of the water phase and the effective pore wall contact fraction of the oil phase at each final state. Thus, by combining the water phase saturation and oil phase saturation, which only reflect the proportion of fluid pore volume, with the corresponding fluid's lateral relaxation response, a characterization parameter that can reflect the degree of pore wall contact between the oil and water phases is formed, thereby helping to quantitatively characterize the pore wall contact state of the oil and water phases inside the rock.

[0011] Furthermore, this application determines the closure deviation of the effective pore wall contact fractions of the aqueous phase and the oil phase in the first and second final states, respectively, and performs closure normalization on the two final states that pass the closure deviation determination. Based on a physical consistency check of the pore wall contact results of the two phases, the normalized aqueous phase pore wall contact fractions for each of the two opposite saturation history final states are obtained. The normalized aqueous phase pore wall contact fractions of the two final states are then used to jointly determine the NMR wettability index, and the difference between the two is used to determine the saturation history influence index. Thus, the NMR wettability index is used to characterize the overall rock wettability reflected by the two opposite saturation history final states, while the saturation history influence index is used to characterize the final state differences caused by different saturation histories. This allows for separate characterization of rock wettability and the influence of saturation history, reducing the possibility of directly evaluating the final state differences caused by saturation history as differences in rock wettability. Attached Figure Description

[0012] Figure 1 This is a flowchart of a nuclear magnetic resonance rock wettability characterization method considering the influence of saturation history, provided in an embodiment of this application. Figure 2 This is a schematic diagram of the reference state and the final state of the saturation history provided in the embodiments of this application; Figure 3 This is a schematic diagram of data processing and variable transfer relationships for nuclear magnetic resonance characterization of rock wettability provided in an embodiment of this application; Figure 4 These are different test states in the embodiments of this application. Two-dimensional nuclear magnetic resonance spectrum; Figure 5 These are ultrashort circuits under different test conditions in the embodiments of this application. Weak signal verification result diagram; Figure 6 This is a structural block diagram of a nuclear magnetic resonance rock wettability characterization device that takes into account the influence of saturation history, as provided in the embodiments of this application. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate this application and are not intended to limit the scope of protection of this application.

[0014] like Figure 1 As shown in the embodiments of this application, a method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history is provided.

[0015] Step S101: Obtain bulk NMR references for the aqueous and oil phases, saturated water core references, and saturated oil core references, as well as the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; This step is used to obtain reference data and two saturation history final state data required for subsequent water-oil signal separation and orifice wall contact state characterization.

[0016] In this application, Indicates the longitudinal relaxation time. Indicates the lateral relaxation time. Two-dimensional nuclear magnetic resonance (NMR) spectrum represents NMR spectrum with longitudinal relaxation time and transverse relaxation time as the two relaxation dimensions.

[0017] like Figure 2 As shown, the reference states include bulk water, bulk oil, saturated water core reference, and saturated oil core reference. Specifically, the bulk water refers to the water phase from the same batch without rock, and the bulk oil refers to the oil phase from the same batch without rock; these two serve as bulk NMR references for the water and oil phases, respectively. The saturated water core reference is the reference state formed when water fills all accessible pore spaces in the core, and the saturated oil core reference is the reference state formed when oil fills all accessible pore spaces in the core; these two serve as saturated reference endpoints for the water and oil phases, respectively.

[0018] The first final state is the final state of water entering the final state, obtained from an initial saturated oil core after self-absorption of water to stability; the second final state is the final state of oil entering the final state, obtained from an initial saturated water core after self-absorption of oil to stability. Both the saturated oil core reference and the initial saturated oil core before the formation of the first final state correspond to the oil phase saturation state, but they serve different functions in this embodiment. The saturated oil core reference provides a saturation reference endpoint for the oil phase, while the initial saturated oil core is used to form the first final state. Correspondingly, the saturated water core reference provides a saturation reference endpoint for the water phase, while the initial saturated water core is used to form the second final state.

[0019] In one embodiment, the first and second final states are obtained sequentially from the same core sample. After testing one final state, the core sample can be cleaned, saturated, aged, and its wettability restored to form the other final state. In another embodiment, the first and second final states can be obtained from paired core samples with matched pore structures, the paired core samples being determined based on porosity, permeability, mineral composition, and baseline. Spectra were matched to reduce the influence of differences in the pore structure of different core samples on the comparison results of the two saturation history final states.

[0020] Subsequently, nuclear magnetic resonance (NMR) tests were performed on the aforementioned reference state, as well as the first and second final states. The first and second final states... Two-dimensional nuclear magnetic resonance (NMR) spectra can be obtained by inversion from NMR data acquired using a saturation recovery-carry-purcell-Meiboom-Gill (SR-CPMG) sequence. The SR-CPMG sequence is obtained by setting multiple recovery time pairs. The direction is encoded, and the echo train is acquired at each recovery time to obtain... and Response information in two relaxation dimensions.

[0021] In an alternative implementation, a Carr-Purcell-Meiboom-Gill (CPMG) sequence can also be used to obtain a one-dimensional representation of the same test state. Spectrum, used for the one-dimensional aspect discussed later. Spectrum and Two-dimensional nuclear magnetic resonance spectroscopy Consistency check between projections.

[0022] In one implementation, the recovery time range of the SR-CPMG sequence covers the maximum extent of the tested state. At least 5 times.

[0023] The hydrogen index (HI) is used to characterize the relative ability of a unit volume of fluid to generate a nuclear magnetic resonance (NMR) signal. The hydrogen index and NMR signal per unit volume of the aqueous and oil phases can be calibrated using bulk water and bulk oil, respectively, to correct for differences in NMR signals generated per unit volume by different fluids. Bulk water and bulk oil are also used to determine the corresponding bulk transverse relaxation rates for subsequent bulk subtraction in step S103.

[0024] To ensure the comparability of reference endpoints and data from different test states, the validity of endpoints for saturated water cores and saturated oil cores can be checked by combining the effective pore volume of the core, the mass increment before and after saturation, and the total nuclear magnetic resonance signal. If the reference state does not reach the expected saturation level, the reference state can be prepared and tested again. Different reference states, as well as the first and second final states, are preferably tested under the same or uniformly calibrated conditions of temperature, echo interval, receiver gain, number of scans, and inversion grid.

[0025] like Figure 4 As shown, in one specific embodiment, core references for bulk water, bulk oil, saturated water, saturated oil, the first final state, and the second final state are obtained respectively. Two-dimensional nuclear magnetic resonance spectrum. The horizontal axis represents... The vertical axis represents The color bars on the right indicate the corresponding The nuclear magnetic resonance (NMR) spectral amplitude at the grid location. The peak positions and shapes vary depending on the test conditions, resulting in different values. Two-dimensional nuclear magnetic resonance spectroscopy is used for water-oil signal separation in subsequent step S102, as well as for determining the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate.

[0026] Step S102, based on the aforementioned bulk nuclear magnetic resonance reference, saturated water core reference, and saturated oil core reference, perform analysis on each final state... Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state.

[0027] This step is used to switch between the first final state and the second final state. The aqueous phase signal and the oil phase signal were determined in the two-dimensional nuclear magnetic resonance spectrum, and the aqueous phase saturation, oil phase saturation, aqueous phase transverse relaxation rate and oil phase transverse relaxation rate were determined based on the separated phase signals.

[0028] Before performing water-oil signal separation, the final states can be analyzed. Two-dimensional nuclear magnetic resonance spectroscopy was used for dry core background subtraction and grid registration, and signal screening was performed based on signal-to-noise ratio thresholds. Physical domain selection for tolerance conditions and ultrashort Region identification, together with other methods, determines the effective main spectrum for subsequent water-oil signal separation and transverse relaxation rate determination. This is the tolerance coefficient. The above three types of processing are used together for effective signal selection, and there is no fixed order in which they are executed. Through grid registration, different reference states and final states are assigned corresponding values. A two-dimensional mesh is used to subsequently utilize the reference state to determine the final state. Assignment of grid signals in two-dimensional nuclear magnetic resonance spectra.

[0029] For ease of subsequent representation, the first and second final states will be collectively referred to as saturated history states. ,in, , Indicates the first final state. This represents the second final state. Any two-dimensional grid in a two-dimensional nuclear magnetic resonance spectrum is denoted as ,in, express Grid number of direction, express Grid number in the direction; Indicates the first indivual The longitudinal relaxation time corresponding to the grid. Indicates the first indivual The lateral relaxation time corresponding to the grid. State In the grid The two-dimensional spectral amplitude at the location is denoted as .

[0030] To meet the above signal-to-noise ratio conditions, physical domain tolerance conditions, and abnormal or ultra-short... Region co-identification plays a role in determining the effective signal, and can construct an effective signal mask:

[0031] in, Representing state In the grid Effective signal mask at the location; This represents an indicator function, which takes the value 1 if the condition within the parentheses is met, and 0 otherwise. This represents the amplitude threshold, which can be determined based on the results of blank tests and repeated measurements. express Tolerance factor for physical relationships; This indicates an exception or an extremely short message that requires separate handling. Region. Signals exceeding the tolerance range are not included in the effective main spectrum subsequently used to determine the transverse relaxation rate of the aqueous or oil phase.

[0032] for Ultrashort duration less than 0.1ms In response, when the source and phase of this signal have not yet been independently calibrated, it is identified separately and not included in the calculation of the transverse relaxation rate of the aqueous or oil phase, in order to avoid subsequent 1 / The weighted effect amplifies the impact of weak and ultrashort signals.

[0033] After completing the above preprocessing, water phase reference templates and oil phase reference templates are constructed using the bulk NMR references for the water phase and oil phase, the saturated water core reference, and the saturated oil core reference obtained in step S101. The fluid phases are denoted as... ,in, , Indicates the aqueous phase. Indicates the oil phase; Indicates phase In the grid The phase reference template value at the location. The phase reference template is used to characterize the corresponding... The grid signal is a relative reference information for the aqueous or oil phase.

[0034] In one specific implementation, saturated water core references and saturated oil core references can be subjected to the same background subtraction, grid registration, and effective signal filtering as in the final state, and then unified... Amplitude normalization is performed on the mesh, serving as the main body for the aqueous and oil phase reference templates; bulk water and bulk oil are used to further define the corresponding fluids. The response range is used to determine the corresponding bulk NMR reference parameters. A uniform normalized scale is used for both aqueous and oil phase reference templates to avoid the absolute signal amplitude differences between the two reference states directly affecting subsequent probability weights.

[0035] In one implementation, a priori saturation values ​​for each final state are obtained. These priori saturation values ​​characterize the estimated saturation ratio of the aqueous and oil phases in the corresponding final state and serve as constraint information for probabilistically weighted assignment of overlapping water-oil signal regions. The priori saturation values ​​can be determined based on at least one of the following: weighing results, volume balance results, or the total nuclear magnetic resonance signal corrected for hydrogen content index. These priori saturation values ​​are used for phase assignment constraints during the water-oil signal separation process; the aqueous and oil phase saturation values ​​are then determined based on the separated aqueous and oil phase signals. The priori saturation values ​​are only used for phase assignment constraints in overlapping water-oil signal regions and do not force the subsequent aqueous and oil phase saturation values ​​calculated from the phase-separated signals to be equal to the priori values; the deviation between the two can be used as a basis for checking the validity of the phase separation results.

[0036] Based on the aforementioned aqueous phase reference template and oil phase reference template, the final states can be determined. In two-dimensional nuclear magnetic resonance (NMR) spectra, grid signals are assigned to water and oil phases respectively. For grid signals that can be distinguished between water and oil phase spectral regions, they can be assigned to water or oil phase signals according to their corresponding spectral regions. For regions where water and oil phase signals overlap, probability-weighted assignment is further performed by combining the prior of final-state saturation.

[0037] Specifically, for overlapping regions of water and oil signals, the grid signals in the overlapping region are probabilistically weighted and assigned based on the prior knowledge of the final state saturation. (State) Medium grid The signal belongs to the phase The probability weights can be expressed as:

[0038] in, Representing state Medium grid The signal belongs to the phase The probability weights; Representing state Middle phase The prior of final-state saturation; This indicates the fluid phase index used for summing the aqueous and oil phases; This is used to prevent small positive numbers from having a denominator of zero.

[0039] Therefore, for overlapping signals within the same grid, the corresponding spectral amplitudes can be assigned to the aqueous and oil phases respectively, based on their probability weights, instead of classifying the entire grid signal into one phase. When the aqueous and oil phases are in... When the spectral regions in a two-dimensional nuclear magnetic resonance spectrum can be completely separated, integration can be performed directly according to their respective spectral regions without the aforementioned probability weighting.

[0040] Specifically, background subtraction of dry core samples can be performed according to the following formula. To distinguish the spectral amplitude values ​​before and after background subtraction, the state is defined here. The two-dimensional spectral amplitude before background subtraction is denoted as Dry cores in a grid The background spectral amplitude at that location is denoted as And the two-dimensional spectral amplitude after background subtraction is denoted as Then we have:

[0041] in, This means truncating results less than 0 to 0; Representing state Middle phase The integral nuclear magnetic resonance signal.

[0042] Using the unit volume calibration information and hydrogen content index obtained from bulk water and bulk oil, the integrated nuclear magnetic resonance signal after phase separation can be corrected, and the fluid volume and pore volume saturation of the water and oil phases can be obtained.

[0043] in, Representing state Middle phase The corresponding fluid volume; Indicates phase The corresponding unit volume nuclear magnetic resonance signal calibration coefficient; Indicates phase The corresponding hydrogen content index; Representing state Middle phase The pore volume saturation. Therefore, the water phase saturation and oil phase saturation of the first and second final states can be obtained respectively. This refers to the signal scale calibration coefficients established under uniform test conditions, which are not counted repeatedly in the definition. The differences in the hydrogen content index of the fluids being characterized; and Together they are used to convert the phase-integrated signal into the corresponding fluid volume.

[0044] After obtaining the effective signals of each phase from the water-oil signal separation, 1 / can be used in the effective signal regions corresponding to the water phase and the oil phase respectively. The weighted moments determine the corresponding transverse relaxation rates:

[0045] in, Representing state Middle phase lateral relaxation rate; Representing state Middle phase of Harmonic average value. From this, the transverse relaxation rates of the aqueous phase and the oil phase in the first and second final states can be obtained, respectively.

[0046] The above formula determines the transverse relaxation rate of each phase based on the effective main spectrum after the aforementioned screening.

[0047] In one alternative implementation, when testing is performed using no fewer than three different echo intervals (EchoTime, TE) for the same state, the method can also be adjusted according to different... The transverse relaxation rate obtained under the condition Extrapolate the transverse relaxation rate when it approaches 0 to reduce the additional attenuation effect caused by the coupling effect of the internal magnetic field gradient and molecular diffusion.

[0048]

[0049] in, Indicates the echo interval; Representing state Middle phase With echo interval of The transverse relaxation rate determined at time; Indicates will The phase obtained by extrapolation to 0 Lateral relaxation rate; This indicates the influence of internal magnetic field gradient, molecular diffusion coupling, and specific echo conditions. Correction factor.

[0050] When using the above multiple When extrapolating, the subsequent bulk phase subtraction and effective hole wall contact fraction calculation are preferably performed using... ; Not adopted multiple When extrapolating, the method determined based on the aforementioned effective main spectrum can be used. Proceed to subsequent processing. This will unify the output of this step into the corresponding final state water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate, and provide them for step S103 to perform bulk phase transverse relaxation rate subtraction and saturated core reference normalization.

[0051] like Figure 3 As shown, after the first and second final states are separated by water and oil signals, the water phase saturation, oil phase saturation, water phase transverse relaxation rate and oil phase transverse relaxation rate corresponding to each final state are obtained, and then enter the subsequent process of determining the effective hole wall contact fraction.

[0052] Step S103: Subtract the corresponding bulk phase lateral relaxation rate from the water phase lateral relaxation rate and the oil phase lateral relaxation rate of each final state, and normalize them based on the water phase saturation and oil phase saturation of each final state using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the water phase and the effective pore wall contact fraction of the oil phase of each final state.

[0053] This step is used to determine the effective pore wall contact fraction, which characterizes the degree of contact between the corresponding fluid and the pore wall, based on the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate obtained in step S102.

[0054] The transverse relaxation response of nuclear magnetic resonance is influenced not only by the interaction between the fluid and the pore wall, but also by the bulk relaxation contribution of the fluid itself. Therefore, for state... phase in First, the transverse relaxation rate determined in step S102 is subtracted from the corresponding fluid's bulk transverse relaxation rate to obtain the net transverse relaxation rate. For the corresponding saturated core reference, the same bulk subtraction method is used to obtain the corresponding saturated reference net transverse relaxation rate.

[0055] The net transverse relaxation rate after subtracting the bulk phase can be expressed as:

[0056] in, Represents the final state Middle phase Net transverse relaxation rate after deducting the corresponding volumetric transverse relaxation rate; Indicates phase The corresponding bulk transverse relaxation rate determined by the bulk NMR reference; Indicates phase The corresponding saturated core reference net transverse relaxation rate after deducting the bulk transverse relaxation rate. Indicates phase The corresponding transverse relaxation rate of the saturated core reference.

[0057] If step S102 adopts multiple Test and extrapolate to =0, then the final-state transverse relaxation rate, the bulk transverse relaxation rate, and the saturated core reference transverse relaxation rate can all be represented by the corresponding values. =0 extrapolation value, thereby reducing the influence of the internal magnetic field gradient and the additional attenuation caused by diffusion on the subsequent determination of the contact fraction of the hole wall.

[0058] To ensure consistency in the symbols used in subsequent formulas, the final state, bulk phase, and saturated core reference transverse relaxation rates used in step S103 and subsequent calculations should be consistent. Handling method: Perform multiple During testing, the corresponding values ​​were taken. =0 extrapolated value; no multiplication was performed. During testing, the same rules were applied to all cases. The transverse relaxation rate measured under the given conditions remains unchanged after subsequent volume subtraction and normalization formulas.

[0059] Under conditions of rapid diffusion and comparable fluid-surface systems, the net transverse relaxation rate after bulk subtraction satisfies the following relationship with the corresponding fluid pore wall contact area and fluid volume:

[0060] in, Indicates phase Transverse surface relaxation rate in the corresponding fluid-pore wall system; Representing state Middle phase The actual contact area of ​​the hole wall; This represents the final state determined in step S102. Middle phase The fluid volume; This represents the total accessible borehole wall area of ​​the core sample; This represents the effective pore volume of the core. The aforementioned "comparable same fluid-surface systems" requires at least that the final state and the corresponding saturated core reference use the same type of fluid and maintain the same or equivalent experimental conditions to make the transverse relaxation responses of the corresponding fluid phases comparable.

[0061] Under the condition that the final effective pore space is occupied only by the water phase and the oil phase in a two-phase configuration, the sum of the fluid volumes of the water phase and the oil phase equals the effective pore volume of the core. V p Combining the definitions of water phase saturation and oil phase saturation in step S102, the phase... The fluid volume satisfies: = V p Substituting the above relationships into the equation relating the net transverse relaxation rate after bulk subtraction to the corresponding fluid pore wall contact area and fluid volume, and then considering the state... By comparing the net transverse relaxation rate of the sample with the net transverse relaxation rate of the corresponding saturated core reference, the phase can be obtained. Effective hole wall contact fraction:

[0062] in, Representing state Middle phase The proportion of the effective hole wall area in contact to the total reachable hole wall area, i.e., phase The effective borehole wall contact fraction is normalized by the net transverse relaxation rate of the corresponding saturated core reference, so that the water phase and oil phase determine the corresponding borehole wall contact degree with their respective saturated reference endpoints.

[0063] When phase Corresponding saturated core reference net transverse relaxation rate If the value is not greater than 0, or its absolute value is not significantly higher than the uncertainty determined by repeated testing, the effective pore wall contact fraction of that phase should not be directly calculated. Priority should be given to checking the bulk phase reference, the saturated core reference endpoint, and... Processing results.

[0064] It should be noted that the effective pore wall contact fraction and the pore volume saturation of the corresponding fluid represent different physical quantities. Indicates phase The proportion of the effective pore volume, while Indicates phase The effective contact area with the pore wall is the proportion of the total accessible pore wall area. For example, when the wetting phase is distributed on the pore wall surface in the form of a continuous thin film, even if the volume saturation of this phase is low, its corresponding effective pore wall contact fraction may still be significantly higher than its volume saturation. Therefore, the water phase saturation or oil phase saturation cannot be directly used to replace the corresponding effective pore wall contact fraction.

[0065] For the first final state, let... =w and =o, and the effective pore wall contact fractions of the aqueous phase and oil phase in the first final state can be obtained; the same treatment is applied to the second final state to obtain the effective pore wall contact fractions of the aqueous phase and oil phase in the second final state. For example... Figure 3 As shown, the effective hole wall contact fractions obtained from the two final states are respectively entered into the subsequent step S104 for closure deviation determination and closure normalization processing.

[0066] Step S104: Determine the closure deviation between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state, and normalize the effective pore wall contact fraction of the two final states that pass the closure deviation determination to obtain the corresponding normalized aqueous phase pore wall contact fraction.

[0067] This step is used to check the physical consistency between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase obtained in step S103, and to obtain the normalized aqueous phase pore wall contact fraction for subsequent wettability characterization based on the consistency requirement.

[0068] Under ideal oil-water two-phase conditions, the water and oil phases in the same final state jointly occupy the accessible pore wall. Therefore, the sum of the effective pore wall contact fractions of the water phase and the oil phase in the same final state should be close to 1. Based on this relationship, the closure deviations are determined for the first and second final states respectively:

[0069] in, Representing state The closure deviation between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase; and The aforementioned states are respectively Effective pore wall contact fraction in the aqueous phase and effective pore wall contact fraction in the oil phase.

[0070] Closure deviation reflects the degree of deviation between the sum of the effective pore wall contact fractions of the two phases in the same final state and the ideal closure value of 1. For the first and second final states, the corresponding closure deviations are compared with a preset deviation threshold. When the closure deviation of the corresponding final state does not exceed the preset deviation threshold, the final state is determined to pass the closure deviation judgment. The preset deviation threshold can be determined based on repeated experiments, control samples, and suitability tests of the test method used.

[0071] When the closure deviation of any final state exceeds the preset deviation threshold, the data set is not directly used for final wettability classification. Further checks can be made on the overlap of the water-oil reference templates and ultra-short... The source of the signal, the hydrogen index calibration results, the reference endpoint of the saturated core, and the internal magnetic field gradient correction results are used to determine the source of the closure deviation anomaly. For data that fails the closure deviation judgment, the corresponding original NMR spectrum and the proportion of the anomalous signal can be retained for subsequent re-examination or testing.

[0072] After both the first and second final states passed the closure deviation determination, the effective pore wall contact fractions of the aqueous phase and the effective pore wall contact fractions of the oil phase in the two final states were subjected to closure normalization. The corresponding normalized aqueous phase pore wall contact fraction can be expressed as:

[0073] in, Representing state The contact fraction of the water phase pore wall obtained after closed-loop normalization.

[0074] By using closed-loop normalization, the sum of the effective pore wall contact fractions of the water phase and oil phase in the same final state is normalized to 1. This allows the water phase pore wall contact state in the final state to be represented by the relative proportion of the water phase in the total effective pore wall contact between the two phases. Correspondingly, the oil phase pore wall contact fraction in the same final state after closed-loop normalization can be expressed as 1 – Sure.

[0075] like Figure 3 As shown, the effective pore wall contact fractions of the aqueous phase and the effective pore wall contact fractions of the oil phase in the first final state are first subjected to closure deviation determination, and the normalized aqueous phase pore wall contact fraction of the first final state is obtained after passing the determination. The second final state is subjected to closure deviation determination and closure normalization independently in the same way to obtain the normalized aqueous phase pore wall contact fraction of the second final state. The normalized aqueous phase pore wall contact fractions of the two final states are used as inputs for step S105 to determine the NMR wetting index and the saturation history influence index, respectively.

[0076] Step S105: The difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 is determined as the NMR wetting index, and the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state is determined as the saturation history influence index.

[0077] This step is used to determine the NMR wettability index, reflecting the overall wettability of the rock, and the saturation history influence index, reflecting the difference between the two saturation history final states, based on the normalized aqueous pore wall contact fractions obtained in step S104. For example... Figure 3 As shown, after the first and second final states have completed the separation of water and oil signals, determination of effective orifice wall contact fraction, determination of closure deviation and closure normalization in the aforementioned steps, the normalized water phase orifice wall contact fraction of the two final states is used to jointly determine the above two output indicators in this step.

[0078] The difference between the sum of the normalized aqueous phase pore wall contact fractions of the first and second final states and 1 is determined as the NMR wetting index:

[0079] in, Indicates the NMR wetting index; superscript This indicates the first final state, that is, the water in the initially saturated oil core reaches a stable state after self-absorption; superscript This indicates the second final state, which is the final state of oil after the initial saturated water core has undergone self-absorption and stabilized. and These represent the normalized aqueous phase pore wall contact fractions for the first and second final states, respectively.

[0080] Since the normalized aqueous phase pore wall contact fractions in both final states are between 0 and 1, the NMR wetting index... The value range is [-1, 1]. When When the value is >0, it indicates a high degree of contact between the water phase pore walls and the two opposite saturated history final states, and the rock as a whole exhibits a slightly water-wet appearance; when When <0, the rock generally exhibits an oily and wet appearance; when A value close to 0 indicates a near-neutral or mixed wetting state. For further classification of the degree of water-wetting or oil-wetting, samples with known wettability can be used for calibration, without the need to pre-set a uniform fixed classification threshold in this method.

[0081] Furthermore, the difference between the normalized aqueous phase pore wall contact fraction in the first final state and the normalized aqueous phase pore wall contact fraction in the second final state is determined as the saturation history influence index:

[0082] in, This indicates the saturation historical influence index.

[0083] The saturation history influence index is used to reflect the difference between two opposite saturation history final states. Its positive or negative sign indicates the relative magnitude of the normalized aqueous phase pore wall contact fraction between the first and second final states, and is not used to directly determine whether the rock is water-wet or oil-wet. Therefore, the saturation history influence index and the NMR wettability index represent different technical meanings: the former represents the difference in final states caused by the two saturation histories, while the latter is used to represent the overall wettability reflected by the two final states together.

[0084] In one implementation, the magnitude of the saturation historical impact can also be determined based on the absolute value of the saturation historical impact index:

[0085] in, This indicates the extent of historical saturation. The larger the value, the greater the difference in the normalized aqueous phase pore wall contact fraction corresponding to the two saturated history final states. The saturated history influence magnitude can be used as an auxiliary output of the saturated history influence index to represent the magnitude of the saturated history influence without changing the... The relative direction indicated.

[0086] Before outputting the NMR wetting index and saturation history influence index, the validity of the characterization results can be determined by combining the data validity check results from the aforementioned steps. The data validity check may include reference endpoint validity check, water-oil reference template overlap check, unspecified signal proportion check, saturation residual check based on phase-separated signal back-calculation check, and closure deviation check in step S104. When all the above check results meet the corresponding requirements, the NMR wetting index and saturation history influence index are output; when any check result does not meet the corresponding requirements, the original NMR spectrum and corresponding anomaly information can be retained, and the final wetting classification result is not directly output.

[0087] When the effective signal quantity of any fluid phase is lower than the detection limit determined by blank test and repeated test, the transverse relaxation rate of the phase and the two-phase closure result are not forcibly calculated; at this time, the state can be marked as a low signal or end state, and quantitative characterization can be performed after improving the signal-to-noise ratio, re-preparing the sample or supplementing the test.

[0088] In one alternative implementation, one-dimensional data can also be collected for the same test state. Data, and Two-dimensional nuclear magnetic resonance spectrum along Integrating along the direction yields the corresponding two-dimensional result. projection.

[0089]

[0090] in ， Indicates the corresponding test status Two-dimensional nuclear magnetic resonance spectrum amplitude function; Indicates The natural logarithm is the integral infinitesimal of the integral variable; express Two-dimensional nuclear magnetic resonance spectrum along Directional integral obtained projection.

[0091] By Compared with one-dimensional sequences obtained using CPMG sequences Chi Yu Pu By comparing them, the consistency of the main peak position, cumulative distribution and total signal volume can be checked.

[0092] When the same test state is one-dimensional Spectrum and Two-Dimensional When the projection is within the range allowed by repeated testing in terms of the main peak position, cumulative distribution, and total signal quantity, the one-dimensional... In the score Partition mapping to Two-dimensional nuclear magnetic resonance spectroscopy, and in different Subsequent characterization is performed within the interval or the corresponding aperture interval. The one-dimensional... Spectrum and Two-Dimensional The projections are in a projection correspondence relationship, rather than a one-to-one correspondence between different spectral peaks.

[0093] After completing one dimension Relaxation spectrum and two-dimensional After the consistency check of the projections, they can also be processed according to different... The process of separating water and oil signals, determining the transverse relaxation rate, determining the effective pore wall contact fraction, closure normalization, and determining indices is repeatedly performed within a range or the corresponding pore size range to obtain different results. The wettability characterization results and saturation history influence results for intervals or different pore size intervals.

[0094] like Figure 3 As shown, after obtaining the normalized aqueous phase pore wall contact fractions for the first and second final states, the normalized aqueous phase pore wall contact fractions from both final states are input into the index determination process to obtain the NMR wetting index and the saturation history influence index. Through the above steps S101 to S105, the NMR wetting index and the saturation history influence index are determined from different saturation history states. Two-dimensional nuclear magnetic resonance spectra, through water-oil signal separation, determination of water phase saturation, oil phase saturation and corresponding transverse relaxation rates, determination of effective pore wall contact fraction and closure normalization, yielded rock wettability characterization results and saturation history influence characterization results.

[0095] In one specific embodiment, nuclear magnetic resonance (NMR) data of bulk water, bulk oil, saturated water core reference, saturated oil core reference, first final state, and second final state were obtained from the core samples. The first final state refers to the water phase after the initial saturated oil core has undergone self-absorption to stabilize, and the second final state refers to the oil phase after the initial saturated water core has undergone self-absorption to stabilize.

[0096] In this embodiment, The two-dimensional nuclear magnetic resonance spectrum uses a 128×128 two-dimensional inversion grid. The range is 0.1ms to 10000ms. The range is 0.01ms to 10000ms; the test temperature is 25℃, and the echo interval is... The latency was 0.1 ms, and the echo count was 12000. The hydrogen index (HI) for the aqueous phase was 1.00, and the hydrogen index (HI) for the oil phase was 0.92. All test data for the above six states are actual measured NMR results.

[0097] The hydrogen content index, water phase saturation, oil phase saturation, and integral nuclear magnetic resonance signals corresponding to the six states are as follows:

[0098] Where au represents the arbitrary unit, used to represent the relative amplitude of the nuclear magnetic resonance integral signal.

[0099] In this embodiment, the dry core mass was 58.4200 g, the saturated water core mass was 61.0628 g, and the mass of water in the pores was 2.6428 g. The saturated oil core mass was 60.6334 g, and the oil phase density was calculated to be approximately 0.8375 g / mL based on the corresponding mass data. When the water phase saturation in the first final state was 0.44 and the water phase saturation in the second final state was 0.79, the corresponding predicted core masses were 60.8223 g and 60.9726 g, respectively, which are consistent with the measured data. This result can be used to check the consistency between the final state saturation and the mass data.

[0100] The hydrogen content index of the first and second final states can also be determined by weighting the volume fractions of the aqueous and oil phases, i.e.:

[0101] in, Representing state The equivalent hydrogen content index formed by the combined oil and water phases; and These represent the hydrogen content indices of the aqueous phase and the oil phase, respectively.

[0102] Substituting the water phase saturation (0.44), oil phase saturation (0.56), and hydrogen indices of the water and oil phases for the first final state into the above relationship, we obtain HI = 0.9552 for the first final state. Correspondingly, substituting the water phase saturation (0.79) and oil phase saturation (0.21) for the second final state, we obtain HI = 0.9832 for the second final state. These results are consistent with the HI values ​​used in the measured data, thus allowing for the verification of the data relationships between water phase saturation, oil phase saturation, hydrogen indices, and integrated nuclear magnetic resonance signals.

[0103] like Figure 4 As shown, bulk water, bulk oil, saturated water core reference, saturated oil core reference, first final state, and second final state each have corresponding... Two-dimensional nuclear magnetic resonance (NMR) spectra. After statistical analysis of the main peaks in each two-dimensional spectrum, the following results were obtained:

[0104] The main peak positions of bulk water and bulk oil differ significantly. After fluid enters the core pores, the reference values ​​of saturated water cores and saturated oil cores show differences. Both shorten relative to their corresponding bulk states, and both are in direction and / There are also differences in the ratios. Specifically, the main peak of the saturated water core reference is located at... Approximately 108ms The position is approximately 83.4 ms; the main peak of the saturated oil core reference is located at... Approximately 155ms The position is approximately 31.3 ms. The first and second final states exhibit short, medium, and long relaxation components under conditions of oil-water coexistence. These spectral characteristics provide a data basis for subsequent water-oil signal separation using a reference state.

[0105] Furthermore, for each test state Ultrashort duration less than 0.1ms The response should be independently verified. For example... Figure 5 As shown, "<0.1 ms integral percentage" indicates an ultra-short time. The proportion of the regional integral signal to the total integral signal of the corresponding test state; "ultra-short peak / main peak amplitude" indicates the ultra-short peak amplitude. The ratio of the peak amplitude to the corresponding main peak amplitude. In bulk water and bulk oil. The integral percentages less than 0.1 ms were 0.03% and 0.02%, respectively, and the integral percentages corresponding to saturated water core reference, saturated oil core reference, first final state and second final state were 0.80%, 0.25%, 0.65% and 0.45%, respectively.

[0106] In this embodiment, the ultrashort duration of each test state The proportion of responses was generally low. When determining the effective main spectrum, Ultrashort duration less than 0.1ms The response is identified separately; if its source and fluid phase are not independently determined, this portion of the signal is not included in the weighted calculation of the transverse relaxation rate of the aqueous or oil phase. This avoids ultra-short... Weak signal due to 1 / The weight is too large, which has a disproportionate effect on the transverse relaxation rate.

[0107] In this embodiment Physical domain filtering adopts The tolerance conditions, among which =0.8045. Signals located outside the tolerance domain do not enter the effective main spectrum used to determine the transverse relaxation rates of the aqueous and oil phases. It should be noted that 0.8045 is the specific tolerance coefficient used in this embodiment, and the aforementioned general implementation method is not limited to this. This value must be used.

[0108] After filtering the effective signals, reference templates for the water and oil phases were established using bulk water, bulk oil, saturated water cores, and saturated oil cores. The measured water and oil saturations of the first and second final states were used as priors for the final state saturation, and the overlapping regions of the water and oil signals were assigned probabilistically weighted. The separated water and oil phase signals were then used to determine the transverse relaxation rates of the water and oil phases at each final state, respectively. Weak signals less than 0.1 ms are not included in the weighted moment calculation of the transverse relaxation rate.

[0109] The main phase calculation results for the two saturated history final states are obtained as follows:

[0110] In this process, the bulk lateral relaxation rate of the corresponding fluid is subtracted from the first and second final states, and then normalized using the corresponding saturated core reference to obtain the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase for each final state. After meeting the closure deviation requirements, closure normalization is performed to obtain the normalized aqueous phase pore wall contact fraction of 0.520 for the first final state and 0.823 for the second final state.

[0111] Furthermore, based on the normalized aqueous phase pore wall contact fractions of the two final states, we obtain:

[0112] Therefore, the NMR wettability index in this embodiment is 0.343, which is greater than 0, indicating that the core is generally water-wet. This value is positive but not close to the water-wet endpoint, and this embodiment can be characterized as generally water-wet. For further classification of the degree of water-wetness, it can still be calibrated based on samples with known wettability, without setting a fixed classification boundary separately according to this embodiment.

[0113] Based on the normalized aqueous phase pore wall contact fraction of the two final states, the saturation history influence index is obtained:

[0114] The corresponding historical saturation impact range is:

[0115] in, A negative sign indicates that the normalized aqueous phase pore wall contact fraction of the second final state is higher than that of the first final state. This negative sign only indicates the relative direction between the two saturated history final states and does not indicate that the rock is oil-wet. The value is approximately 0.303, indicating a difference between the two saturation history final states in this embodiment. Combining the NMR wettability index and the saturation history influence index, the core samples tested in this embodiment generally exhibit a tendency towards water wettability, and their wettability characterization results are influenced by the saturation history.

[0116] Furthermore, in this embodiment, each test state, reference endpoint, two-dimensional spectrum, water-oil template, saturation back-calculation result, and closure deviation can all be checked according to the aforementioned data validity determination method. If any item fails to meet the corresponding requirements, the final wetting classification result will not be directly output; only after all checks meet the requirements will the NMR wetting index and saturation history influence index be output.

[0117] This application also provides a nuclear magnetic resonance (NMR) rock wettability characterization device that takes into account the influence of saturation history. See also Figure 6 The device includes a data acquisition module, a signal separation module, a hole wall contact fraction determination module, a closure processing module, and an index determination module.

[0118] The data acquisition module is used to acquire bulk NMR references for the aqueous and oil phases, saturated water core references, and saturated oil core references, as well as the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; The signal separation module is used to separate the signals at each final state based on the bulk nuclear magnetic resonance reference, saturated water core reference, and saturated oil core reference. Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state. The pore wall contact fraction determination module is used to subtract the corresponding bulk phase lateral relaxation rate from the water phase lateral relaxation rate and the oil phase lateral relaxation rate of each final state, and to normalize them based on the water phase saturation and oil phase saturation of each final state using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the water phase and the effective pore wall contact fraction of the oil phase of each final state. The closure processing module is used to determine the closure deviation between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state, and to perform closure normalization on the effective pore wall contact fractions of the two final states that pass the closure deviation determination, so as to obtain the corresponding normalized aqueous phase pore wall contact fraction. The index determination module is used to determine the difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 as the NMR wetting index, and to determine the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state as the saturation history influence index.

[0119] The specific processing procedures performed by each of the above modules can be referred to the relevant descriptions of steps S101 to S105 in the aforementioned method embodiments, and will not be repeated here.

[0120] In one implementation, the device may be implemented by a processor and a memory, the memory storing program instructions for executing the above-described nuclear magnetic resonance rock wettability characterization method, and when the processor executes the program instructions, it implements the nuclear magnetic resonance rock wettability characterization method described in any of the foregoing embodiments.

[0121] Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history, characterized in that, include: Obtain bulk NMR references for the aqueous and oil phases, as well as references for saturated water and saturated oil cores, and references for the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; Based on the aforementioned bulk NMR reference, saturated water core reference, and saturated oil core reference, the final states were analyzed. Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state. The transverse relaxation rates of the aqueous phase and the transverse relaxation rates of the oil phase in each final state are respectively subtracted from the corresponding transverse relaxation rates of the bulk phase, and based on the water phase saturation and oil phase saturation in each final state, they are normalized using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state. The effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state are judged by closure deviation. The effective pore wall contact fractions of the two final states that pass the closure deviation judgment are normalized by closure to obtain the corresponding normalized aqueous phase pore wall contact fraction. The difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 is determined as the NMR wetting index, and the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state is determined as the saturation history influence index.

2. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The effective pore wall contact fractions of the aqueous phase and the effective pore wall contact fractions of the oil phase in each final state are determined according to the following formula: in, Indicates the first or second final state. Indicates whether it is an aqueous phase or an oil phase. Represents the final state Middle phase saturation Represents the final state phase in Net transverse relaxation rate after deducting the corresponding volumetric transverse relaxation rate. Indicates phase The net transverse relaxation rate after subtracting the corresponding bulk phase transverse relaxation rate from the reference saturated core. Represents the final state phase in Effective hole wall contact fraction.

3. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The first final state and the second final state Two-dimensional nuclear magnetic resonance spectra were obtained by inversion of nuclear magnetic resonance data acquired using saturation recovery-echo train sequences.

4. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, In the context of each final state Before separating water and oil signals using two-dimensional nuclear magnetic resonance spectroscopy, the signal-to-noise ratio threshold is used. Tolerance conditions and ultra-short The region identification results, for the Two-dimensional nuclear magnetic resonance spectroscopy was used for joint effective signal screening to obtain effective main spectra for subsequent water-oil signal separation and transverse relaxation rate determination. This is the tolerance coefficient.

5. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The terms for each final state Two-dimensional nuclear magnetic resonance spectroscopy is used for water-oil signal separation, including: Based on the bulk nuclear magnetic resonance references of the aqueous and oil phases, the reference of the saturated water core, and the reference of the saturated oil core, an aqueous phase reference template and an oil phase reference template are established. Based on the aqueous phase reference template and the oil phase reference template, for each final state The grid signals in the two-dimensional nuclear magnetic resonance spectrum are used to assign phases of water and oil. Obtain the prior saturation of each final state; For the overlapping region of water and oil signals, based on the water phase reference template, the oil phase reference template, and the prior of final saturation, the probability weights of each grid signal in the overlapping region belonging to the water phase and the oil phase are determined, and the grid signals are respectively counted into the water phase signal and the oil phase signal according to the probability weights to obtain the separated water phase signal and oil phase signal.

6. The nuclear magnetic resonance rock wettability characterization method considering the influence of saturation history according to claim 5, characterized in that, The final state saturation prior is determined based on at least one of the following: weighing results, volume balance results, or total nuclear magnetic resonance signal corrected for hydrogen content index.

7. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The transverse relaxation rate of the aqueous phase is based on the separated aqueous phase signal. 1 / in dimension The weighted moment is determined based on the oil phase transverse relaxation rate according to the separated oil phase signal. 1 / in dimension The weighted moments are determined.

8. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The closure deviation is determined according to the following formula: When the closure deviation does not exceed a preset deviation threshold, the corresponding final state is determined to have passed the closure deviation determination; for the final state that has passed the closure deviation determination, the normalized aqueous phase pore wall contact fraction is determined according to the following formula: in, Indicates the first or second final state. and Representing the final state respectively Effective pore wall contact fraction of aqueous phase and effective pore wall contact fraction of oil phase Represents the final state Closure deviation, Represents the final state Normalized water phase pore wall contact fraction.

9. The method for characterizing rock wettability using nuclear magnetic resonance considering the influence of saturation history according to claim 1, characterized in that, The first and second final states are obtained sequentially from the same core sample after washing, saturation, aging, and wettability restoration; or, the first and second final states are obtained from paired core samples with matched pore structures, the matching of which is based on porosity, permeability, mineral composition, and baseline. The spectrum has been determined.

10. A nuclear magnetic resonance rock wettability characterization device considering the influence of saturation history, characterized in that, include: The data acquisition module is used to acquire bulk NMR references for the aqueous and oil phases, saturated water core references, and saturated oil core references, as well as the first and second final states. Two-dimensional nuclear magnetic resonance spectrum; wherein, the first final state is the state of the initial saturated oil core after self-absorption of water to a stable state, and the second final state is the state of the initial saturated water core after self-absorption of oil to a stable state; The signal separation module is used to separate the signals at each final state based on the bulk nuclear magnetic resonance reference, saturated water core reference, and saturated oil core reference. Two-dimensional nuclear magnetic resonance spectroscopy was used to separate water and oil signals, and the water phase saturation, oil phase saturation, water phase transverse relaxation rate, and oil phase transverse relaxation rate were determined for each final state. The pore wall contact fraction determination module is used to subtract the corresponding bulk phase lateral relaxation rate from the water phase lateral relaxation rate and the oil phase lateral relaxation rate of each final state, and to normalize them based on the water phase saturation and oil phase saturation of each final state using the saturated water core reference and the saturated oil core reference, respectively, to obtain the effective pore wall contact fraction of the water phase and the effective pore wall contact fraction of the oil phase of each final state. The closure processing module is used to determine the closure deviation between the effective pore wall contact fraction of the aqueous phase and the effective pore wall contact fraction of the oil phase in each final state, and to perform closure normalization on the effective pore wall contact fractions of the two final states that pass the closure deviation determination, so as to obtain the corresponding normalized aqueous phase pore wall contact fraction. The index determination module is used to determine the difference between the sum of the normalized aqueous phase pore wall contact fractions of the first final state and the second final state and 1 as the NMR wetting index, and to determine the difference between the normalized aqueous phase pore wall contact fractions of the first final state and the normalized aqueous phase pore wall contact fractions of the second final state as the saturation history influence index.

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