A method for evaluating the wettability of shale mixture

Abstract

The present invention provides a method for evaluating the wettability of mixed shale, which belongs to the technical field of shale testing, and includes preparing samples, respectively immersing the samples saturated with water in oil, and filling the samples saturated with oil with water, and constructing a corresponding T2 spectrum signal change curve to evaluate the wettability of mixed shale. The present invention provides a method for evaluating the wettability of mixed shale, which quantifies the oil-water replacement efficiency of the pore space of the entire shale, and evaluates and analyzes the wettability of the pores inside the shale by comparing the equivalent oil-water replacement efficiency inside the shale, thereby evaluating the wettability of the mixed shale. The evaluation method is easy to operate and has accurate evaluation results. It analyzes and studies the wettability characteristics of the pore space with oil-water replacement capacity that accounts for a relatively large proportion inside the shale, deepens the study of the pore wettability inside the shale, and fills the gap in the evaluation method for accurately evaluating the mixed wettability of the pores inside the shale.

Description

Technical Field

[0001] The invention belongs to the technical field of shale testing, and more specifically, relates to a method for evaluating shale mixed wettability. Background Art

[0002] In the prior art, the contact angle method, spontaneous imbibition method and other methods are usually used to analyze the wettability of shale. Shale has a unique mixed "dalmatian" type wettability. The true reservoir wettability must be determined in a system where oil and water exist. It cannot be determined by comparing the water and oil wetting angles measured on the surface of dry rock. When organic matter is enriched in shale, the surface wettability of the shale will change because the surface wettability of the organic pores is oil-wet. The influence of organic matter in organic-rich shale changes the single wettability of the shale, causing mixed wettability in the shale pores, with both hydrophilic and oil-wet pores, resulting in the characteristic that shale wettability is not easy to evaluate. At present, the differences in shale wettability evaluation results are increasing, and the accuracy standard cannot meet the evaluation needs in actual production. Summary of the invention

[0003] The main purpose of the present invention is to provide a high-precision shale pore mixed wettability evaluation method and experimental process, using low-field nuclear magnetic resonance technology to compare the shale's replacement capacity for oil-water media, analyze and evaluate the wettability characteristics of pores in the shale with oil-water replacement capacity, and the evaluation results are accurate and have strong guidance for actual production.

[0004] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for evaluating the wettability of shale mixture, comprising the following steps:

[0005] S1: Prepare samples and mark sample A and sample B, test the sample base signal after drying them respectively, test the T2 spectrum signal change curve l1 after vacuuming sample A and saturating it with water, test the T2 spectrum signal change curve l2 after vacuuming sample B and saturating it with oil, immerse the saturated sample A in n-dodecane until the weight of sample A no longer changes and the T2 spectrum characteristics no longer fluctuate, immerse the saturated sample B in distilled water until the weight of sample B no longer changes and the T2 spectrum characteristics no longer fluctuate; place samples A and B in saturated manganese chloride solution respectively, let them stand and measure the T2 spectrum signal change curves of samples A and B, and the curves of the two samples are the same, which are l3;

[0006] S2: Establish a chart to compare the proportions of various pore spaces, normalize the relationship between curves l1, l2 and l3, and plot them together in the same coordinate system. The X-axis value of the coordinate system is the pore size, and the Y-axis value is the signal intensity. The curves l1, l2 and l3 and the horizontal axis are set to form three areas, and the area values ​​are recorded as s1, s2 and s3 respectively;

[0007] S3: Establish the oil-water conversion relationship chart of samples A and B, subtract the corresponding base signals from the T2 spectrum signals of sample A immersed in n-dodecane and sample B immersed in distilled water, and mark the first curve where the sample signal amplitude changes significantly and the first curve where the sample signal tends to be stable, and record the time records corresponding to the four curves as Ta1, Ta2, Tb1 and Tb2, and record t1=Ta2-Ta1, t2=Tb2-Tb1;

[0008] S4: Evaluation of shale wettability:

[0009] When s1-s2>s3, the sample is hydrophilic, when t1>t2, the sample is strongly hydrophilic, and when t1<t2, the sample is weakly hydrophilic;

[0010] When s1-s2<s3, the sample is lipophilic, when t1>t2, the sample is weakly lipophilic, and when t1<t2, the sample is strongly lipophilic.

[0011] In a possible implementation, in step S1, the prepared A and B samples are cylindrical, 20 cm long and 25 mm in diameter.

[0012] In a possible implementation, in step S1, samples A and B are dried in a drying oven at 100° C. for 48 hours.

[0013] In a possible implementation, in step S1, when sample A is evacuated and saturated with water, sample A is immersed in distilled water for 24 hours; when sample B is evacuated and saturated with oil, sample B is immersed in n-dodecane for 24 hours and continuously pressurized to 10 MP.

[0014] In one possible implementation, in step S1, when the water-saturated A sample is immersed in n-dodecane, the T2 spectrum signal is measured every 20 minutes until the mass of the A sample no longer changes and the T2 spectrum characteristics no longer fluctuate; when the oil-saturated B sample is immersed in distilled water, the T2 spectrum signal is measured every 20 minutes until the mass of the B sample no longer changes and the T2 spectrum characteristics no longer fluctuate.

[0015] In a possible implementation, in step S1, samples A and B are placed in a saturated manganese chloride solution and need to be left to stand for 72 hours, and a T2 spectrum signal change curve l3 is measured during the standing stage.

[0016] In a possible implementation, in step S2, the area values ​​s1, s2 and s3 are constructed in the same chart in the form of a bar graph, and the percentages of oil-water pores are compared respectively.

[0017] In a possible implementation, in step S3, sample A immersed in n-dodecane and sample B immersed in distilled water are respectively detected every 20 minutes, and multiple T2 spectrum signal curves are constructed after subtracting the corresponding background signals, and the curve with the largest amplitude and the curve with the smallest amplitude are selected from the multiple curves.

[0018] The beneficial effect of a shale mixed wettability evaluation method provided by the present invention is that: compared with the prior art, the hydrogen ion nuclear magnetic resonance signal response characteristics that change with time under different shale oil-water states are measured, the displacement trend of the pore space of the shale reservoir for the oil-water medium is determined, and the T2 spectrum signal curves of different stages are converted into curves related to the liquid volume inside the shale sample by normalization, and the wettability characteristics of the shale reservoir are evaluated according to the oil-water displacement efficiency. The present invention quantifies the oil-water displacement efficiency of the pore space of the entire shale, and by comparing the equivalent oil-water displacement efficiency inside the shale, the wettability of the pores inside the shale is evaluated and analyzed, and then the mixed wettability of the shale is evaluated. This evaluation method is easy to operate and has accurate evaluation results. It analyzes and studies the wettability characteristics of the pore space with oil-water displacement capacity that accounts for a large proportion of the shale, deepens the study of the pore wettability inside the shale, and fills the gap in the evaluation method for accurately evaluating the mixed wettability of the pores inside the shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A flow chart of a shale mixed wettability evaluation method provided in an embodiment of the present invention;

[0021] Figure 2 A coordinate system diagram in which the l1, l2 and l3 curves provided in an embodiment of the present invention are plotted together in the same coordinate system;

[0022] Figure 3 A histogram formed by s1, s2 and s3 provided in an embodiment of the present invention;

[0023] Figure 4 The oil-water displacement relationship diagram of sample A provided in an embodiment of the present invention;

[0024] Figure 5 This is a diagram of the oil-water displacement relationship of sample B provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] See also Figure 1 , a shale mixed wettability evaluation method provided by the present invention is now described. The present invention uses low-field nuclear magnetic resonance technology to compare the replacement capacity of shale for oil-water media, analyze and evaluate the wettability characteristics of pores in shale with oil-water replacement capacity, and the evaluation results are accurate and have strong guidance for actual production. To achieve the above purpose, the present invention adopts the following technical solutions:

[0027] As a method for evaluating the mixed wettability of shale pores, the hydrogen ion nuclear magnetic resonance signal response characteristics under different shale oil-water states are determined, and the hydrogen ion nuclear magnetic resonance signal response characteristics that change with time under different shale oil-water states are determined to determine the replacement trend of the pore space of the shale reservoir for oil-water media. The T2 spectrum signal curves at different stages are converted into curves related to the liquid volume inside the shale sample by normalization, and the wettability characteristics of the shale reservoir are evaluated according to the oil-water replacement efficiency.

[0028] The evaluation method provided by the present invention needs to be carried out based on the preliminary experimental stage, wherein the experimental stage specifically includes:

[0029] (1) Sample preparation:

[0030] Two cylinders with a length of 20 cm and a diameter of 25 mm, named sample A and sample B;

[0031] (2) Sample drying:

[0032] Place samples A and B in a drying oven at 100°C for 48 hours to remove moisture from the samples, measure dry weights a1 and b1, and test sample base signals;

[0033] (3) Sample A is evacuated and saturated with water, and sample B is evacuated and saturated with oil:

[0034] Place sample A in a vacuum saturation device, evacuate the vacuum, and then immerse the sample in distilled water for 24 hours to absorb water. Measure the sample weight m 饱和水 , test the sample T2 spectrum signal; put the B sample into the vacuum saturation device, evacuate, and then immerse the sample in saturated n-dodecane under vacuum environment for 10MP pressure saturated oil absorption for 24 hours, and measure the sample weight m 饱和油 , test sample T2 spectrum signal;

[0035] The purpose of measuring the sample dry weight a1 and b1 is to calculate the original mass of the sample in order to calculate the mass of different fluids entering the sample in each stage. It is one of the data required for sample normalization. The basic principle is that the total intensity of the nuclear magnetic signal corresponding to the same liquid in the T2 spectrum measurement is in a linear relationship, that is, the nuclear magnetic signal intensity of 2 volumes of water is twice the nuclear magnetic signal intensity of 1 volume of water.

[0036] The weight of all samples measured during this experimental operation is m 饱和油 The technical units all contain the technical idea of ​​calculating the mass difference of the sample entering the internal fluid of the sample during this stage, which serves the "normalization" of the inversion of the sample NMR T2 curve.

[0037] (4) Oil-water coexistence simulation of samples A and B:

[0038] After saturating with water for 24 hours, sample A was immersed in saturated n-dodecane. From the time sample A was immersed, the sample T2 spectrum signal was measured every 20 minutes and the sample weight change was measured. When the sample mass no longer changed and the T2 spectrum characteristics no longer fluctuated, the measurement interval could be appropriately extended, and the total immersion time was 24 hours. After saturating with oil for 24 hours, sample B was immersed in distilled water. From the time sample A was immersed, the sample T2 spectrum signal was measured every 20 minutes and the sample weight change was measured. When the sample mass no longer changed and the T2 spectrum characteristics no longer fluctuated, the measurement interval could be appropriately extended, and the total immersion time was 24 hours.

[0039] (5) Manganese bubble eliminates water signal

[0040] Samples A and B were placed in two beakers of saturated manganese chloride solution respectively, left to stand for 72 hours, and the T2 spectrum signals of samples A and B were measured.

[0041] After the experimental stage, the relevant data were obtained:

[0042] The T2 spectrum signal change curve l1 of sample A after being vacuumed and saturated with water; the T2 spectrum signal change curve l2 of sample B after being vacuumed and saturated with oil; and the T2 spectrum signal change curve l3 of samples A and B after being immersed in oil and water and then passed through a saturated manganese chloride solution.

[0043] Afterwards, the data from the experimental phase were evaluated as follows:

[0044] Reference Figure 2 The normalized relationship among curves l1, l2 and l3 are plotted together in the same coordinate system. The X-axis value of the coordinate system is the pore size, the Y-axis value is the signal intensity, and the curves l1, l2 and l3 and the horizontal axis are set to form three areas, and the area values ​​are recorded as s1, s2 and s3 respectively.

[0045] Reference Figure 3, s1, s2, and s3 are constructed in the same graph in the form of a bar graph, comparing the percentages of oil and water pores, respectively.

[0046] (2) Establish the oil-water displacement relationship chart of samples A and B

[0047] The T2 spectrum (nuclear magnetic resonance reaction) signals of sample A immersed in n-dodecane and sample B immersed in distilled water were subtracted from the corresponding background signals, and two curves with temporal continuity were marked respectively: the first curve with an obvious change in the amplitude of the sample signal change and the first curve with a stable signal amount.

[0048] Reference Figure 4 and Figure 5 , record the time records corresponding to the four curves as Ta1, Ta2, Tb1 and Tb2 respectively, record t1=Ta2-Ta1, t2=Tb2-Tb1; at the same time, delete the redundant curves to beautify the plate and make the plate clearer.

[0049] During the simulation of oil-water coexistence, when the characteristic curve of the T2 spectrum (nuclear magnetic resonance reaction) signal of sample A shows obvious changes, it is considered that the absorption capacity of the internal space of the sample for n-dodecane has changed significantly, that is, the oily pores in sample A have been fully saturated with n-dodecane, and the remaining pores that have not been filled with n-dodecane are filled and replaced by distilled water (these pores are "oil-water pores" and oil and water can be converted into each other); when the nuclear magnetic resonance reaction curve of the sample tends to be stable, it is considered that the oil-water state in the sample will no longer change, and the time corresponding to the first stable curve is the time used for the oil-water coexistence simulation of the sample; the same is true for sample B.

[0050] (3) Evaluation of shale wettability

[0051] According to the principle, when the proportion of strong water-wetting in the pore space of the three types of shales is greater than that of strong oil-wetting, the shale is considered to have good water wettability; otherwise, the shale is considered to have poor water wettability. Therefore, when S1-S2>S3, the sample is hydrophilic, when t1>t2, the sample is strongly hydrophilic, when t1<t2, the sample is weakly hydrophilic; when S1-S2<S3, the sample is oil-wetting, when t1>t2, the sample is weakly oil-wetting, and when t1<t2, the sample is strongly oil-wetting. Refer to the following table 1

[0052]

[0053]

[0054] Table 1

[0055] Compared with the prior art, the shale mixed wettability evaluation method provided by the present invention is

[0056] 1. The displacement capacity of the oil-water medium in the pores of the regressive shale of the present invention is not affected by external characteristics and human factors, and the evaluation result is more scientific and objective.

[0057] 2. The wettability characteristics of the samples were quantitatively calculated and obtained, which has good guiding significance for actual mining.

[0058] 3. The quantitative characterization of shale mixed wettability is achieved. Combined with the oil-water change trend, the wettability characteristics of the pores with oil-water exchange capacity in the shale are clearly characterized, filling the gap in the evaluation of shale mixed wettability, which is of great significance for the in-depth study of shale wettability.

[0059] 4. Compared with the existing evaluation methods, the evaluation parameters of the method of the present invention are easier to obtain, the calculation process is relatively simple, and the evaluation range of shale mixed wettability is more comprehensive, and the evaluation results are more accurate and more instructive.

[0060] 5. The present invention is simple to operate, has clear principles, accurate results, is easy to implement, and can be promoted on a large scale.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating shale mixed wettability, characterized in that: The following steps are involved: S1: Prepare samples and mark sample A and sample B, test the sample base signal after drying them respectively, test the T2 spectrum signal change curve l1 after vacuuming sample A and saturating it with water, test the T2 spectrum signal change curve l2 after vacuuming sample B and saturating it with oil, immerse the saturated sample A in n-dodecane until the weight of sample A no longer changes and the T2 spectrum characteristics no longer fluctuate, immerse the saturated sample B in distilled water until the weight of sample B no longer changes and the T2 spectrum characteristics no longer fluctuate; place samples A and B in saturated manganese chloride solution respectively, let them stand and measure the T2 spectrum signal change curves of samples A and B, and the curves of the two samples are the same, which are l3; S2: Establish a chart to compare the proportions of various pore spaces, normalize the relationship between curves l1, l2 and l3, and plot them together in the same coordinate system. The X-axis value of the coordinate system is the pore size, and the Y-axis value is the signal intensity. The curves l1, l2 and l3 and the horizontal axis are set to form three areas, and the area values ​​are recorded as s1, s2 and s3 respectively; S3: Establish the oil-water conversion relationship chart of samples A and B, subtract the corresponding base signals from the T2 spectrum signals of sample A immersed in n-dodecane and sample B immersed in distilled water, and mark the first curve where the sample signal amplitude changes significantly and the first curve where the sample signal tends to be stable, and record the time records corresponding to the four curves as Ta1, Ta2, Tb1 and Tb2, and record t1=Ta2-Ta1, t2=Tb2-Tb1; S4: Evaluation of shale wettability: When s1-s2>s3, the sample is hydrophilic, when t1>t2, the sample is strongly hydrophilic, and when t1<t2, the sample is weakly hydrophilic; When s1-s2<s3, the sample is lipophilic, when t1>t2, the sample is weakly lipophilic, and when t1<t2, the sample is strongly lipophilic.

2. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S1, the prepared A and B samples are cylindrical, 20 cm long and 25 mm in diameter.

3. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S1, samples A and B are dried in a drying oven at 100°C for 48 hours.

4. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S1, when sample A is evacuated and saturated with water, sample A is immersed in distilled water for 24 hours; when sample B is evacuated and saturated with oil, sample B is immersed in n-dodecane for 24 hours and continuously pressurized to 10 MP.

5. The method for evaluating shale mixed wettability according to claim 1, characterized in that: In step S1, when the water-saturated A sample is immersed in n-dodecane, the T2 spectrum signal is measured every 20 minutes until the mass of the A sample no longer changes and the T2 spectrum characteristics no longer fluctuate. When the oil-saturated B sample is immersed in distilled water, the T2 spectrum signal is measured every 20 minutes until the mass of the B sample no longer changes and the T2 spectrum characteristics no longer fluctuate.

6. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S1, samples A and B are placed in a saturated manganese chloride solution and need to be left to stand for 72 hours. During the standing stage, a T2 spectrum signal change curve l3 is measured.

7. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S2, the area values ​​s1, s2 and s3 are constructed in the same graph in the form of a bar graph, respectively comparing the percentages of oil and water pores.

8. A shale mixed wettability evaluation method according to claim 1, characterized in that: In step S3, sample A immersed in n-dodecane and sample B immersed in distilled water are tested every 20 minutes, and multiple T2 spectrum signal curves are constructed after subtracting the corresponding background signals, and the curve with the largest amplitude and the curve with the smallest amplitude are selected from the multiple curves.

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