A shale oil reservoir rock different scale pore throat wettability quantitative evaluation method

Abstract

This application relates to a method for quantitatively evaluating the wettability of pore throats at different scales in shale oil reservoirs, comprising the following steps: (1) cutting the core into two equal-length standard plunger core samples, C1 and C2, drying the core samples C1 and C2, and measuring the nuclear magnetic resonance T2 spectrum of the dry sample C1; (2) saturating the core samples C1 and C2 with oil and heavy water respectively, and measuring their nuclear magnetic resonance T2 spectra; (3) self-absorbing the core samples C1 and C2 with heavy water and oil respectively, and measuring their nuclear magnetic resonance T2 spectra; (4) drying the core sample C2, saturating the core sample C2 with oil, and measuring its nuclear magnetic resonance T2 spectrum; (5) drying the core sample C1 and conducting high-pressure mercury intrusion testing on it; (6) quantitatively evaluating the wettability of the core as a whole and at different scales of pore throats. This method can quantitatively characterize the proportion of water-wetted, oil-wetted, and neutral-wetted pore throats at different scales and in the whole pore throat for oil-saturable pore throats in the core, thereby achieving wettability evaluation.

Description

Technical Field

[0001] This invention relates to the field of rock wettability research in shale oil reservoirs during oil and gas production, specifically to a quantitative evaluation method for the pore throat wettability of shale oil reservoir rocks at different scales. Background Technology

[0002] Shale oil reservoirs possess multi-scale pore structures, rich in nanoscale pore throats and micron-scale bedding fractures, exhibiting strong microscopic heterogeneity. This makes conventional displacement recovery methods ineffective in utilizing the crude oil within the matrix. Both laboratory and field tests have demonstrated that percolation-displacement is one of the effective means of utilizing crude oil in the shale matrix. Percolation-displacement refers to the physical phenomenon where wetting fluids spontaneously enter rock pores and displace non-wetting fluids. Reservoir rock wettability is a decisive factor influencing the effectiveness and intensity of percolation-displacement. Therefore, accurately evaluating the wettability of shale oil reservoirs is of paramount importance for formulating rational development strategies for shale oil reservoirs.

[0003] Currently, the most commonly used methods for evaluating rock wettability include contact angle measurement, spontaneous adsorption experiments, Amott's method, USBM method, relative permeability method, and core experiments combined with nuclear magnetic resonance (NMR) measurements. Due to the extremely low permeability of shale oil reservoir cores, effective oil-water displacement is difficult to achieve. Therefore, the Amott method, USBM method, and relative permeability method, based on oil-water displacement experiments, are not suitable for evaluating the wettability of shale oil reservoir cores. Contact angle measurement can only evaluate the wettability of the core end face and cannot reflect the overall wettability of the core. Spontaneous adsorption experiments evaluate the overall wettability of the core by comparing the amount or rate of oil and water adsorption. However, shale oil reservoirs simultaneously possess clay pores, organic matter pores, and inorganic mineral pores, exhibiting a non-uniform mixed wettability characteristic. Spontaneous adsorption experiments are insufficient to characterize the wettability of different pore types in shale. Core experiments combined with nuclear magnetic resonance (NMR) measurements can simultaneously evaluate the overall wettability of cores and the wettability of pore throats at different scales. However, current methods often fail to consider the non-uniform mixing and wetting characteristics of pore throats at different scales. Furthermore, shale oil reservoirs are rich in nanoscale pores with varying wettability, and the oil- and water-saturated pores are not identical. Calculating the wetting volume ratio or wetting index based on the average oil- and water-saturated porosity is inaccurate, and the wettability of oil-bearing pores of development interest is difficult to evaluate effectively. Additionally, because shale oil reservoir cores are rich in clay minerals, saturated water during experiments can cause cracks in the core, altering the pore structure and affecting the shale wettability evaluation results. Therefore, current core experiment and NMR wettability evaluation methods are difficult to apply to shale oil reservoir cores and require further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a quantitative evaluation method for the wettability of pore throats at different scales in shale oil reservoirs. This method addresses the shortcomings of existing wettability evaluation methods that combine core experiments and nuclear magnetic resonance (NMR) measurements. These shortcomings include: failure to consider the non-uniform mixing and wetting characteristics of pore throats at different scales in shale oil reservoir cores; inaccurate calculation of wettability evaluation indicators due to differences in oil-water saturated pores; difficulty in effectively evaluating the wettability of oil-bearing pores; and the impact of saturated water on shale's pore structure, which affects the wettability evaluation results. Consequently, these methods cannot be applied to the wettability evaluation of shale oil reservoir cores.

[0005] The technical solution provided by this invention is: a method for quantitatively evaluating the pore-throat wettability of shale oil reservoir rocks at different scales, specifically including the following steps:

[0006] (1) Cut the core into two equal-length standard plunger cores C1 and C2, dry the cores C1 and C2, and measure the nuclear magnetic resonance T2 spectrum of the dry core C1: Select standard plunger cores with a length of 6-7 cm, cut them into two equal-length standard plunger cores C1 and C2, number the two cores, and dry the two cores C1 and C2 at 110℃ to constant weight. Perform nuclear magnetic resonance T2 spectrum test on the dried core C1 to determine the P of the dry core C1 nuclear magnetic resonance T2 spectrum. g1 ;

[0007] (2) Core C1 saturated with oil, core C2 saturated with heavy water, and the nuclear magnetic resonance T2 spectra of cores C1 and C2 after saturation: Nuclear magnetic resonance T2 spectra were measured for cores C1 and C2 saturated with oil and heavy water, respectively, and for cores C1 saturated with oil and C2 saturated with heavy water, to determine the nuclear magnetic resonance T2 spectrum P of core C1 in the oil-saturated state. o1 and the nuclear magnetic resonance T2 spectrum of core C2 under saturated heavy water conditions. zw2 ;

[0008] (3) Self-absorption of heavy water from core C1 and self-absorption of oil from core C2, and determination of the nuclear magnetic resonance T2 spectra of cores C1 and C2 after self-absorption: Experiments were conducted on self-absorption of heavy water from core C1 and self-absorption of oil from core C2. Nuclear magnetic resonance T2 spectra were measured on core C1 after self-absorption of heavy water and core C2 after self-absorption of oil to determine the P-value of the nuclear magnetic resonance T2 spectrum of core C1 under the condition of self-absorption of heavy water. ozw1 and the nuclear magnetic resonance T2 spectrum P of the core under self-absorption oil state in C2. zwo2 ;

[0009] (4) Drying core C2 and saturating it with oil, and measuring the nuclear magnetic resonance T2 spectrum of core C2 after saturation: Drying core C2, saturating core C2 with oil, and performing nuclear magnetic resonance T2 spectrum tests on core C2 after oil saturation to determine the nuclear magnetic resonance T2 spectrum P of core C2 in the oil-saturated state. o2 ;

[0010] (5) Drying core C1 and conducting high-pressure mercury intrusion testing: Core C1 was dried to constant weight at 110℃, and high-pressure mercury intrusion testing was conducted to determine the pore throat distribution S of the core. g ;

[0011] (6) Quantitative evaluation of the wettability of the core as a whole and different pore throats: Based on the experimental data, calculate the proportion of water-wetted, oil-wetted and neutral-wetted pore throats of the saturable oil in the core as a whole and in different pore size ranges, and evaluate the wettability of the saturable oil pore throats in the core as a whole and in different pore size ranges.

[0012] The specific method in step (2) above is as follows: wrap the annular surfaces of core C1 and core C2 with a thermoplastic film, place core C1 and core C2 in two pressure piston containers respectively, place the pressure piston containers in a constant temperature chamber set to the reservoir temperature, evacuate the pressure piston containers for 48 hours, and then inject representative single-component alkanes and heavy water from the formation crude oil into the pressure piston containers containing core C1 and core C2 respectively to ensure that the liquid submerges the cores. Use an ISCO pump to inject the liquid into the lower part of the pressure piston containers at a constant reservoir pressure. Distilled water was introduced to push the piston until the pressure inside the pressure piston container also rose to the reservoir pressure. The initial volume of distilled water injected by the two ISCO pumps was recorded. Subsequently, the volume of distilled water injected by the ISCO pumps was recorded every 24 hours. When the volume of injected distilled water was constant, saturation was stopped and the core was removed. The thermoplastic film on the core was removed, and excess liquid was removed from the surface of the two cores. Nuclear magnetic resonance (NMR) T2 spectra were performed on core C1 after it was saturated with oil and core C2 after it was saturated with heavy water, respectively, to determine the NMR T2 spectrum P of core C1 under oil saturation. o1 and the nuclear magnetic resonance T2 spectrum of core C2 under saturated heavy water conditions. zw2 .

[0013] The specific method in step (3) above is as follows: wrap the annulus of core C1 and core C2 with thermoplastic film, place core C1 and core C2 in two beakers respectively, inject heavy water into the beaker containing core C1, and inject representative single-component alkanes from the formation crude oil into the beaker containing core C2. Stop injecting when the liquid level rises to 0.5 cm above the upper end of the core, seal the mouth of the beaker with plastic wrap, place the beaker in a normal temperature and pressure environment, and carry out the core self-absorption experiment. If the liquid level drops during the experiment, replenish the liquid in time. After standing for 20 days, take out the core, remove the thermoplastic film from the core, and remove the excess liquid from the surface of the core. Conduct nuclear magnetic resonance T2 spectrum tests on core C1 after self-absorption of heavy water and core C2 after self-absorption of oil to determine the nuclear magnetic resonance T2 spectrum P of core C1 under the state of self-absorption of heavy water. ozw1 and the nuclear magnetic resonance T2 spectrum P of the core under self-absorption oil state in C2. zwo2 ;

[0014] The specific method in step (4) above is as follows: the core C2 is dried to constant weight at 110℃, the annular surface of the dried core C2 is wrapped with a thermoplastic film and the core C2 is placed in a pressure piston container. The pressure piston container is placed in a constant temperature chamber set to the reservoir temperature and the pressure piston container is evacuated for 48 hours. Then, representative single-component alkanes from the formation crude oil are injected into the pressure piston container to ensure that the liquid submerges the core. Distilled water is injected into the lower part of the pressure piston container at a constant reservoir pressure using an ISCO pump to push the piston until the pressure inside the pressure piston container also rises to the reservoir pressure. The initial volume of distilled water injected by the ISCO pump is recorded. Then, the volume of distilled water injected by the ISCO pump is recorded every 24 hours. When the volume of injected distilled water is constant, saturation is stopped and the core is taken out. The thermoplastic film of the core is removed and the excess liquid on the surface of the core is removed. Nuclear magnetic resonance T2 spectrum test is carried out on the core C2 after oil saturation to determine the nuclear magnetic resonance T2 spectrum P of the core C2 in the oil saturation state. o2 ;

[0015] The specific method in step (6) above is as follows:

[0016] (1) P o1 Subtract P g1 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in core C1. or1 According to P or1 and S g To complete the benchmarking of T2-r, T2=Cr is selected. n The conversion relationship is given by R, where C and n are constants related to core properties, pore structure, and fluid properties. The values ​​of C and n are determined based on the T2-r benchmark results, and the conversion relationship R of T2-r is obtained.

[0017] (2) P o1 Subtract P ozw1 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected, and T2 was converted to r according to R. The corresponding cumulative curve was calculated to obtain the cumulative curve S of the water-wet pore throat distribution. w , will P or1 T2 is converted to r based on R, and the corresponding cumulative curve is calculated to obtain the cumulative curve S of saturated oil distribution in core C1. s1 Select the pore throat classification criteria, determine the number of pore throat types n, and the boundary values ​​r of the pore throat radii of different types. L (j) (j=0,1,2...n) (r should be made) L (j) <r L (j+1), r L (0)=r min r L (n)=r max r min For Ss1 Minimum throat radius, r max For S s1 The maximum throat radius value in S is respectively from S s1 and S w Read r L (j) corresponds to the cumulative porosity s s1 (j) and s w (j) (j=0,1,2...n), respectively, the total porosity component f1(i)=s of the throat at different scales is calculated. s1 (i)-s s1 (i-1) (i=1,2...n) and the porosity component f of the water-wetting throat. w (i)=s w (i)-s w (i-1) (i=1,2...n), calculate the proportion B of water-wet pores in pores of different sizes. w (i)=f w (i) / f1(i) (i=1,2...n) and the proportion of water-wet pores and throats in the core as a whole B wa =s w (n) / s s1 (n);

[0018] (3) P zwo2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected, and T2 was converted to r according to R. The corresponding cumulative curve was calculated to obtain the cumulative curve S of the oil wet pore throat distribution. o , will P o2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in core C2. or2 , will P or2 T2 is converted to r based on R, and the corresponding cumulative curve is calculated to obtain the cumulative curve S of saturated oil distribution in core C2. s2 From S respectively s2 and S o Read r from L (j) corresponds to the cumulative porosity s s2 (j) and s o (j) (j=0,1,2...n), respectively, the total porosity component f2(i)=s of pore throats of different scales is calculated. s2 (i)-s s2 (i-1) (i=1,2...n) and the porosity component f of the oil-wet pore throat. o (i)=s o (i)-s o(i-1) (i=1,2...n), calculate the proportion B of oil-wet pore throats in pore throats of different scales. o (i)=f o (i) / f2(i) (i=1,2...n) and the proportion of oil-wet pore throats in the core as a whole B oa =s o (n) / s s2 (n);

[0019] (4) Calculate the proportion B of neutrally wetted pore throats in pore throats of different sizes. m (i)=1-B o (i)-B w (i) (i=1,2...n), calculate the proportion B of neutral wetting pore throats in the overall core. ma =1-B oa -B wa According to B respectively w (i), B o (i), B m (i) (i=1,2...n) and B wa B oa B ma The pore throats and overall wettability of the core at different scales were evaluated. The evaluation method was as follows: If B w If (i) > 0.6, then the radius is r. L (i-1)~r L (i) The wettability of the pore throat is water-wet, if B o If (i) > 0.6, then the radius is r. L (i-1)~r L (i) has an oily wettability in its throat, if B m If (i) > 0.6, then the radius is r. L (i-1)~r L (i) The pore throat wettability is neutral wettability; otherwise, the radius r L (i-1)~r L (i) The throat is mixed-wetting (i=1,2...n); if B wa If B > 0.6, the overall wettability of the core is water-wet. oa If B > 0.6, the overall wettability of the core is oily. ma If the wettability is greater than 0.6, the overall wettability of the core is neutral wettability; otherwise, the overall wettability of the core is mixed wettability.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This application is based on the principle that the initial state of oil discharged after self-absorption of water from saturated oil cores is stored in water-wet but oil-saturable pore throats, and the oil absorbed after self-absorption of oil from water-saturated cores is stored in oil-wet saturable oil pore throats. Furthermore, resaturating the dried core sample after self-absorption of oil from water-saturated cores and measuring the T2 NMR spectrum can characterize the core pore structure after the water saturation process. This invention establishes a quantitative evaluation method for the wettability of pore throats at different scales in shale oil reservoir rocks. This method can quantitatively characterize the water-wetness of pore throats at different scales and the overall pore throat within the oil-saturable pore throat of the core. The wettability evaluation is achieved by determining the proportion of oil-wetted and neutral-wetted pore throats. Furthermore, the influence of saturated water processes on the pore structure of shale is considered. This addresses the problems of existing wettability evaluation methods that combine core experiments and nuclear magnetic resonance (NMR) measurements, which fail to consider the non-uniform mixing and wetting characteristics of pore throats at different scales in shale oil reservoir cores, the inaccurate calculation of wettability evaluation indicators due to varying oil- and water-saturated pore sizes, the difficulty in effectively evaluating the wettability of saturated oil pores, and the impact of saturated water on the pore structure of shale, thus affecting the wettability evaluation results and preventing their application to shale oil reservoir core wettability evaluation. Attached Figure Description

[0022] Figure 1 This is a picture of a shale core sample.

[0023] Figure 2 It is the T2 NMR spectrum of the dry core sample 1-1#.

[0024] Figure 3 It is the nuclear magnetic resonance T2 spectrum of core 1-1# in saturated oil state.

[0025] Figure 4 It is the nuclear magnetic resonance T2 spectrum of cores 1-2 in a saturated heavy water state.

[0026] Figure 5 It is the nuclear magnetic resonance T2 spectrum of core 1-1# under the condition of self-absorption of heavy water.

[0027] Figure 6 It is the nuclear magnetic resonance T2 spectrum of core 1-2 under self-absorption oil conditions.

[0028] Figure 7 These are the nuclear magnetic resonance T2 spectra of cores #1-2 in a saturated oil state.

[0029] Figure 8 This is a map showing the distribution of pore throats in the rock core.

[0030] Figure 9 It is the nuclear magnetic resonance T2 spectrum corresponding to the distribution of saturated oil in core 1-1#.

[0031] Figure 10 This is a graph showing the comparison results of T2-r.

[0032] Figure 11This is a cumulative curve of water-wet pore throat distribution.

[0033] Figure 12 This is a cumulative curve of saturated oil distribution in core 1-1#.

[0034] Figure 13 This is a cumulative curve of oil-wet pore throat distribution.

[0035] Figure 14 The T2 NMR spectrum corresponds to the distribution of saturated oil in cores 1-2.

[0036] Figure 15 This is a cumulative curve of saturated oil distribution in cores 1-2. Detailed Implementation

[0037] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0038] The specific embodiments of the present invention will be further described in detail below with reference to examples. A method for quantitatively evaluating the wettability of pore throats at different scales in shale oil reservoir rocks specifically includes the following steps:

[0039] Example: A shale sample from a certain location was selected. The sample was 7.04 cm in length and 2.48 cm in diameter. Quantitative evaluation of its pore-throat wettability at different scales was conducted. See Appendix for the experimental shale sample. Figure 1 .

[0040] (1) The core was cut into two standard plunger cores of equal length and numbered 1-1# and 1-2# respectively. The cores 1-1# and 1-2# were dried at 110℃. The core mass was measured every 24 hours. When the core mass was constant for 48 consecutive hours, the drying was stopped and the core was removed. The nuclear magnetic resonance T2 spectrum of the dried core 1-1# was tested according to the standard "SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples" to determine the P of the dried core 1-1#. g1 (See attached) Figure 2 );

[0041] (2) Wrap the annular surfaces of cores 1-1# and 1-2# with thermoplastic film. Place cores 1-1# and 1-2# in two pressure piston containers respectively. Place the pressure piston containers in a constant temperature chamber at 110℃ (the reservoir temperature in this example) and evacuate the pressure piston containers for 48 hours. Then, inject hexadecane (a representative single-component alkane of the formation crude oil in this example) and heavy water into the pressure piston containers containing cores 1-1# and 1-2# respectively to ensure that the cores are submerged in liquid. Use an ISCO pump to inject distilled water into the lower part of the pressure piston container at a constant pressure of 30MPa (the reservoir pressure in this example) to push the piston until the pressure inside the pressure piston container also rises to 30MPa. Record the initial volume of distilled water injected by the two ISCO pumps respectively. Then, record the volume of distilled water injected by the ISCO pumps every 24 hours. When the volume of distilled water injected is constant for 48 consecutive hours, stop saturation and remove the cores. Remove the thermoplastic film from the cores and follow the standard GB / T 29172-2012. The excess liquid on the surface of the two core samples was removed according to the "Core Analysis Method". Following the standard "SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples", nuclear magnetic resonance (NMR) T2 spectral analysis was performed on core sample 1-1# after it was saturated with oil and core sample 1-2# after it was saturated with heavy water. The NMR T2 spectrum P of core sample 1-1# under oil saturation was determined. o1 (See attached) Figure 3 ) and the nuclear magnetic resonance T2 spectra of cores 1-2 under saturated heavy water conditions zw2 (See attached) Figure 4 );

[0042] (3) Wrap the annular surfaces of cores 1-1# and 1-2# with thermoplastic film. Place cores 1-1# and 1-2# in two beakers respectively. Pour heavy water into the beaker containing core 1-1# and hexadecane (a representative single-component alkane of the formation crude oil in this example) into the beaker containing core 1-2#. Stop pouring when the liquid level rises to 0.5 cm above the upper end of the core. Seal the mouth of the beaker with plastic wrap and place the beaker in a normal temperature and pressure environment to carry out the core self-absorption experiment. If the liquid level drops during the experiment, replenish the liquid in time. After standing for 20 days, take out the core, remove the thermoplastic film, and remove the excess liquid on the surface of the core according to the standard "GB / T 29172-2012 Core Analysis Method". The "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples" (6490-2023) specifies the NMR T2 spectrum test for core 1-1# after self-absorption of heavy water and core 1-2# after self-absorption of oil, to determine the P-value of the NMR T2 spectrum of core 1-1# under the self-absorption of heavy water state. ozw1 (See attached) Figure 5 ) and the nuclear magnetic resonance T2 spectrum P of cores 1-2 under self-absorption oil conditions zwo2 (See attached) Figure 6 );

[0043] (4) Dry the 1-2# core at 110℃. Measure the core mass every 24 hours. When the core mass remains constant for 48 consecutive hours, stop drying and remove the core. Wrap the annular surface of the dried 1-2# core with a thermoplastic film and place the core in a pressure piston container. Place the pressure piston container in a constant temperature chamber at 110℃ (the reservoir temperature in this example) and evacuate the pressure piston container for 48 hours. Then, inject hexadecane (a representative single component of the formation crude oil in this example) into the pressure piston container. Alkane), ensuring the core is submerged in liquid, using an ISCO pump to inject distilled water into the lower part of the pressure piston container at a constant pressure of 30 MPa (reservoir pressure in this example), pushing the piston until the pressure inside the pressure piston container also rises to 30 MPa (reservoir pressure in this example), recording the initial volume of distilled water injected by the ISCO pump, and then recording the volume of distilled water injected by the ISCO pump every 24 hours. When the volume of distilled water injected is constant for 48 consecutive hours, saturation is stopped and the core is removed. The thermoplastic film on the core is removed, and excess liquid on the core surface is removed according to the standard GB / T 29172-2012 Core Analysis Methods. According to the standard SY / T 6490-2023 Laboratory Measurement Specification for Nuclear Magnetic Resonance Parameters of Rock Samples, nuclear magnetic resonance T2 spectrum tests are performed on cores 1-2 after oil saturation to determine the P-value of the nuclear magnetic resonance T2 spectrum of cores 1-2 in the oil-saturated state. o2 (See attached) Figure 7 );

[0044] (5) The 1-1# core was dried at 110℃. The core mass was measured every 24 hours. When the core mass remained constant for 48 consecutive hours, the drying was stopped and the core was removed. The core was subjected to high-pressure mercury intrusion testing according to the standard GB / T 21650.1 2008 Determination of pore size distribution and porosity of solid materials by mercury intrusion and gas adsorption method - Part 1: Mercury intrusion method, to determine the pore throat distribution S of the core. g (See attached) Figure 8 );

[0045] (6) Based on the experimental data, calculate the proportions of water-wetted, oil-wetted, and neutral-wetted pore throats in the core saturable oil, both overall and within different pore size ranges. Evaluate the overall wettability of the core saturable oil pore throats and their wettability within different pore size ranges. The specific method is as follows:

[0046] ① P o1 Subtract P g1 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in core 1-1#. or1 (See attached) Figure 9 According to P or1 and S g Complete the benchmarking of T2-r (see appendix) Figure 10), the T2-r calibration results are: 0.30ms-0.002μm, 39.81ms-3.33μm, 94.41ms-12.11μm, T2=Cr is selected n (where C and n are constants related to core properties, pore structure and fluid properties) is the conversion relational expression. According to the T2-r calibration results, it is determined that in the T2-r relational expression, C=17.75 and n=0.67, and then the conversion relational expression R of T2-r is obtained: T2=17.75r 0.67 ;

[0047] ② Subtract P o1 from P ozw1 , select the part with T2≥0.1ms in the obtained T2 spectrum, convert T2 into r according to R, calculate the corresponding cumulative curve, and obtain the cumulative curve S of water-wet pore throat distribution w (see appendix Figure 11 ), convert T2 in P or1 into r according to R, calculate the corresponding cumulative curve, and obtain the cumulative curve S of saturated oil distribution in 1-1# core s1 (see appendix Figure 12 ), read from S s1 the minimum pore throat radius r min =0.0004μm and the maximum pore throat radius r max =12662.23μm. The pores are divided into 3 types: micropores (r≤0.01μm), small pores (0.01μm<r≤0.1μm) and medium-large pores (r>0.1μm), that is, n=3, r L (0)=r min =0.0004μm, r L (1)=0.01μm, r L (2)=0.1μm, r L (3)=r max =12662.23μm, read from S s1 the cumulative porosities corresponding to r L (0), r L (1), r L (2) and r L (3) are s s1 (0)=0%, s s1 (1)=3.88%, s s1 (2)=7.72%, s s1 (3)=9.77%, read from S w the cumulative porosities corresponding to r L (0), r L (1), r L (2) and r L (3) are respectively sw (0)=0%, s w (1) = 2.09%, s w (2) = 2.84%, s w (3) = 2.88%, and the total porosity component of the micropores, f1(1) = s, was calculated respectively. s1 (1)-s s1 (0) = 3.88%, total porosity component of small pores f1(2) = s s1 (2)-s s1 (1) = 3.84%, the total porosity component of medium and large pores f1(3) = s s1 (3)-s s1 (2) = 2.05%, porosity component f of water-wet throat in micropores w (1)=s w (1)-s w (0) = 2.09%, porosity component f of water-wetted throat in small pores w (2)=s w (2)-s w (1) = 0.75%, porosity component f of water-wet pore throat in medium and large pores w (3)=s w (3)-s w (2) = 0.04%, the proportion B of water-wet throat in the micropores was calculated. w (1)=f w (1) / f1(1)=0.54, the proportion of water wetting the throat in the small hole B w (2)=f w (2) / f1(2)=0.20, the proportion of water-wet throat in medium and large pores B w (3)=f w (3) / f1(3)=0.02, the proportion of water-wet pores and throats in the core as a whole B wa =s w (3) / s s1 (3) = 0.29;

[0048] ③ P zwo2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms is selected, and T2 is converted to r according to R. The corresponding cumulative curve is calculated to obtain the cumulative curve S of the oil wet pore throat distribution. o (See attached) Figure 13 ), P o2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in cores 1-2#. or2 (See attached) Figure 14 ), P or2T2 is converted to r based on R, and the corresponding cumulative curve is calculated to obtain the cumulative curve S of saturated oil distribution in core #1-2. s2 (See attached) Figure 15 ), from S s2 Read r from L (0), r L (1) r L (2) r L (3) The corresponding cumulative porosities are s s2 (0)=0%, s s2 (1) = 3.05%, s s2 (2) = 6.62%, s s2 (3) = 9.71%, from S o Read r from L (0), r L (1) r L (2) r L (3) The corresponding cumulative porosities are s o (0)=0%, s o (1) = 0.88%, s o (2) = 1.77%, s o (3) = 3.94%, and the total porosity component of the micropores, f2(1) = s, was calculated respectively. s2 (1)-s s2 (0) = 3.05%, total porosity component of small pores f2(2) = s s2 (2)-s s2 (1) = 3.57%, the total porosity component of medium and large pores f2(3) = s s2 (3)-s s2 (2) = 3.09%, porosity component f of oil-wet throat in micropores o (1)=s o (1)-s o (0) = 0.88%, porosity component f of oil-wet throat in small holes o (2)=s o (2)-s o (1) = 0.89%, porosity component f of oil-wet pore throat in medium and large pores o (3)=s o (3)-s o (2) = 2.17%, the calculated percentage B of oil-wet throats in the micropores. o (1)=f o (1) / f2(1)=0.29, the proportion of oil-wet throat in the small hole B o (2)=f o (2) / f2(2)=0.25, the proportion of oil-wet throat in medium and large pores B o(3)=f o (3) / f2(3)=0.70, the proportion of oil-wet pore throats in the core as a whole B oa =s o (3) / s s2 (3) = 0.41;

[0049] ④ Calculate the proportion B of neutral wetting throats within the micropores. m (1) = 1 - B o (1)-B w (1) = 0.17, the proportion of neutral wetting of the pore throat in the small hole B m (2) = 1 - B o (2)-B w (2) = 0.55, the proportion of neutral wetting throat in medium and large pores B m (3) = 1 - B o (3)-B w (3) = 0.28, calculate the proportion B of neutral wetting pore throats in the overall core. ma =1-B oa -B wa =0.3, because B o (1) B w (1) B m (1) If none of them are greater than 0.6, then the radius is r. L (0)~r L (1) The pore throat, i.e., the micropore, is for mixed wetting, due to B o (2) B w (2) B m (2) If none of them are greater than 0.6, then the radius is r. L (1)~r L (2) The pore throat, i.e., the pore, is for mixed wetting, due to B o (3) > 0.6, then the radius is r L (2)~r L (3) The pore throat, i.e., the mesopore, has an oily wettability; due to B wa B oa B ma If none of them are greater than 0.6, then the overall wettability of the core is mixed wettability.

Claims

1. A method for quantitatively evaluating the pore-throat wettability of shale oil reservoir rocks at different scales, specifically including the following steps: (1) Cut the core into two equal-length standard plunger cores C1 and C2, dry the cores C1 and C2, and measure the nuclear magnetic resonance T2 spectrum of the dry core C1: Select standard plunger cores with a length of 6-7 cm, cut them into two equal-length standard plunger cores C1 and C2, number the two cores, and dry the two cores C1 and C2 at 110℃ to constant weight. Perform nuclear magnetic resonance T2 spectrum test on the dried core C1 to determine the P of the dry core C1 nuclear magnetic resonance T2 spectrum. g1 ; (2) Core C1 saturated with oil, core C2 saturated with heavy water, and the nuclear magnetic resonance T2 spectra of cores C1 and C2 after saturation: Nuclear magnetic resonance T2 spectra were measured for cores C1 and C2 saturated with oil and heavy water, respectively, and for cores C1 saturated with oil and C2 saturated with heavy water, to determine the nuclear magnetic resonance T2 spectrum P of core C1 in the oil-saturated state. o1 and the nuclear magnetic resonance T2 spectrum P of core C2 under saturated heavy water condition zw2 ; (3) Self-absorption of heavy water from core C1 and self-absorption of oil from core C2, and determination of the nuclear magnetic resonance T2 spectra of cores C1 and C2 after self-absorption: Experiments were conducted on self-absorption of heavy water from core C1 and self-absorption of oil from core C2. Nuclear magnetic resonance T2 spectra were measured on core C1 after self-absorption of heavy water and core C2 after self-absorption of oil to determine the P-value of the nuclear magnetic resonance T2 spectrum of core C1 under the condition of self-absorption of heavy water. ozw1 and the nuclear magnetic resonance T2 spectrum P of the core under self-absorption oil state in C2. zwo2 ; (4) Drying core C2 and saturating it with oil, and measuring the nuclear magnetic resonance T2 spectrum of core C2 after saturation: Drying core C2, saturating core C2 with oil, and performing nuclear magnetic resonance T2 spectrum tests on core C2 after oil saturation to determine the nuclear magnetic resonance T2 spectrum P of core C2 in the oil-saturated state. o2 ; (5) Drying core C1 and conducting high-pressure mercury intrusion testing: Core C1 was dried to constant weight at 110℃, and high-pressure mercury intrusion testing was conducted to determine the pore throat distribution S of the core. g ; (6) Quantitative evaluation of the wettability of the core as a whole and different pore throats: Based on the experimental data, calculate the proportion of water-wetted, oil-wetted and neutral-wetted pore throats of the saturable oil in the core as a whole and in different pore size ranges, and evaluate the wettability of the saturable oil in the core as a whole and in different pore size ranges. The specific method in step (6) above is as follows: (1) P o1 Subtract P g1 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in core C1. or1 According to P or1 and S g Complete the benchmarking of T2-r, and select T2=Cr n The conversion relationship is given by R, where C and n are constants related to core properties, pore structure, and fluid properties. The values ​​of C and n are determined based on the T2-r benchmark results, and the conversion relationship R of T2-r is obtained. (2) P o1 Subtract P ozw1 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected, and T2 was converted to r according to R. The corresponding cumulative curve was calculated to obtain the cumulative curve S of the water-wet pore throat distribution. w , will P or1 T2 is converted to r based on R, and the corresponding cumulative curve is calculated to obtain the cumulative curve S of saturated oil distribution in core C1. s1 Select the pore throat classification criteria, determine the number of pore throat types n, and the boundary values ​​r of the pore throat radii for different types. L (j) (j=0,1,2...n) (r should be made) L (j) <r L (j+1), r L (0)=r min r L (n)=r max r min For S s1 Minimum throat radius, r max For S s1 The maximum throat radius value in S is respectively from S s1 and S w Read r L (j) corresponds to the cumulative porosity s s1 (j) and s w (j) (j=0,1,2...n), respectively, the total porosity component f1(i)=s of the throat at different scales is calculated. s1 (i)-s s1 (i-1) (i=1,2...n) and the porosity component f of the water-wetting throat. w (i)=s w (i)-s w (i-1) (i=1,2...n), calculate the proportion B of water-wet pores in pores of different sizes. w (i)=f w (i) / f1(i) (i=1,2...n) and the proportion of water-wet pores and throats in the core as a whole B wa =s w (n) / s s1 (n); (3) P zwo2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected, and T2 was converted to r according to R. The corresponding cumulative curve was calculated to obtain the cumulative curve S of the oil wet pore throat distribution. o , will P o2 Subtract P zw2 The portion of the obtained T2 spectrum with T2 ≥ 0.1 ms was selected to obtain the nuclear magnetic resonance T2 spectrum P corresponding to the saturated oil distribution in core C2. or2 , will P or2 T2 is converted to r based on R, and the corresponding cumulative curve is calculated to obtain the cumulative curve S of saturated oil distribution in core C2. s2 From S respectively s2 and S o Read r L (j) corresponds to the cumulative porosity s s2 (j) and s o (j) (j=0,1,2...n), respectively, the total porosity component f2(i)=s of pore throats of different scales is calculated. s2 (i)-s s2 (i-1) (i=1,2...n) and the porosity component f of the oil-wet pore throat. o (i)=s o (i)-s o (i-1) (i=1,2...n), calculate the proportion B of oil-wet pore throats in pore throats of different scales. o (i)=f o (i) / f2(i) (i=1,2...n) and the proportion of oil-wet pore throats in the core as a whole B oa =s o (n) / s s2 (n); (4) Calculate the proportion B of neutrally wetted pore throats in pore throats of different sizes. m (i)=1-B o (i)-B w (i) (i=1,2...n), calculate the proportion B of neutral wetting pore throats in the overall core. ma =1-B oa -B wa Based on B respectively w (i), B o (i), B m (i) (i=1,2...n) and B wa B oa B ma The pore throats and overall wettability of the core at different scales were evaluated. The evaluation method was as follows: If B w If (i) > 0.6, then the radius is r. L (i-1)~r L (i) The wettability of the pore throat is water-wet, if B o If (i) > 0.6, then the radius is r. L (i-1)~r L (i) has an oily wettability in its throat, if B m If (i) > 0.6, then the radius is r. L (i-1)~r L (i) The pore throat wettability is neutral wettability; otherwise, the radius r L (i-1)~r L (i) The throat is mixed-wetting (i=1,2...n); if B wa If B > 0.6, the overall wettability of the core is water-wet. oa If B > 0.6, the overall wettability of the core is oily. ma If the wettability is greater than 0.6, the overall wettability of the core is neutral wettability; otherwise, the overall wettability of the core is mixed wettability.

2. The method for quantitatively evaluating the pore-throat wettability of shale oil reservoir rocks at different scales according to claim 1, characterized in that: The specific method in step (2) is as follows: wrap the annular surfaces of core C1 and core C2 with a thermoplastic film, place core C1 and core C2 in two pressure piston containers respectively, place the pressure piston containers in a constant temperature chamber set to the reservoir temperature, evacuate the pressure piston containers for 48 hours, and then inject representative single-component alkanes and heavy water from the formation crude oil into the pressure piston containers containing core C1 and core C2 respectively to ensure that the cores are submerged in liquid. Use an ISCO pump to inject into the lower part of the pressure piston containers at a constant reservoir pressure. Distilled water pushes the piston until the pressure inside the pressure piston container rises to the reservoir pressure. The initial volume of distilled water injected by the two ISCO pumps is recorded. Then, the volume of distilled water injected by the ISCO pumps is recorded every 24 hours. When the injected distilled water volume is constant, saturation is stopped, and the core is removed. The thermoplastic film on the core is removed, and excess liquid is removed from the surface of both cores. Nuclear magnetic resonance (NMR) T2 spectra are then performed on core C1 after oil saturation and core C2 after heavy water saturation to determine the NMR T2 spectrum P of core C1 under oil saturation. o1 and the nuclear magnetic resonance T2 spectrum P of core C2 under saturated heavy water condition zw2 .

3. The method for quantitatively evaluating the pore-throat wettability of shale oil reservoir rocks at different scales according to claim 1, characterized in that: The specific method in step (3) is as follows: Wrap the annular surfaces of core C1 and core C2 with thermoplastic film, place core C1 and core C2 in two beakers respectively, inject heavy water into the beaker containing core C1, and inject representative single-component alkanes from the formation crude oil into the beaker containing core C2. Stop injecting when the liquid level rises to 0.5 cm above the upper end of the core, seal the mouth of the beaker with plastic wrap, place the beaker in a normal temperature and pressure environment, and carry out the core self-absorption experiment. If the liquid level drops during the experiment, replenish the liquid in time. After standing for 20 days, take out the core, remove the thermoplastic film from the core, and remove the excess liquid from the surface of the core. Conduct nuclear magnetic resonance T2 spectrum tests on core C1 after self-absorption of heavy water and core C2 after self-absorption of oil to determine the P of the nuclear magnetic resonance T2 spectrum of core C1 under the state of self-absorption of heavy water. ozw1 and the nuclear magnetic resonance T2 spectrum P of the core under self-absorption oil state in C2. zwo2 .

4. The method for quantitatively evaluating the pore-throat wettability of shale oil reservoir rocks at different scales according to claim 1, characterized in that: The specific method in step (4) is as follows: the core C2 is dried to constant weight at 110℃. The annular surface of the dried core C2 is wrapped with a thermoplastic film and the core C2 is placed in a pressure piston container. The pressure piston container is placed in a constant temperature chamber set to the reservoir temperature and the pressure piston container is evacuated for 48 hours. Then, representative single-component alkanes from the formation crude oil are injected into the pressure piston container to ensure that the core is submerged in liquid. Distilled water is injected into the lower part of the pressure piston container at a constant reservoir pressure using an ISCO pump to push the piston until the pressure inside the pressure piston container also rises to the reservoir pressure. The initial volume of distilled water injected by the ISCO pump is recorded. Then, the volume of distilled water injected by the ISCO pump is recorded every 24 hours. When the volume of injected distilled water is constant, saturation is stopped and the core is taken out. The thermoplastic film of the core is removed and the excess liquid on the surface of the core is removed. Nuclear magnetic resonance T2 spectrum test is carried out on the core C2 after oil saturation to determine the nuclear magnetic resonance T2 spectrum P of the core C2 in the oil saturation state. o2 .

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