Method for establishing a plot for evaluating properties of formation fluids based on nuclear magnetic resonance

Abstract

The present application relates to the technical field of interpretation chart establishment method, and is a method for establishing a formation fluid property evaluation chart based on nuclear magnetic resonance. The method analyzes three states of a rock sample, i.e., a direct state, a water-soaked state and a manganese-soaked state, through nuclear magnetic resonance. Correlation is calculated by using the analysis data, and a formation fluid property evaluation method and chart are established. The method can effectively distinguish an oil layer area, an oil-water mixed layer area and a water layer area, finely evaluate a reservoir, and improve the comprehensive interpretation coincidence rate of oil and gas.

Description

Technical Field

[0001] This invention relates to the technical field of chart creation methods, specifically a chart creation method for evaluating formation fluid properties based on nuclear magnetic resonance. Background Technology

[0002] Nuclear magnetic resonance (NMR) technology is widely used in oilfield logging. By measuring the T2 spectrum in the pores of rock samples and the interaction between fluids and the solid surface of rock pores, it can quickly obtain evaluation parameters such as reservoir porosity, permeability, oil-water saturation, mobile fluid saturation, and mobile water saturation. It plays an important role in reservoir delineation, pore structure research, and fluid property identification.

[0003] As drilling exploration and development become increasingly challenging, conventional methods of using nuclear magnetic resonance (NMR) to identify formation fluids have significant limitations. In practical NMR analysis, only two steps are typically performed: obtaining pore signals and oil phase signals. However, in large pores, there are usually significant differences between pore signals and oil phase signals. Summary of the Invention

[0004] This invention provides a method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance, which overcomes the shortcomings of the prior art and can effectively solve the problem that the existing nuclear magnetic resonance technology has great limitations in identifying formation fluids; the map established by it can provide a detailed evaluation of the reservoir.

[0005] The technical solution of this invention is achieved through the following measures: a method for establishing a map for evaluating formation fluid properties based on nuclear magnetic resonance, comprising the following steps:

[0006] Step 1:

[0007] a) Rock sample analysis

[0008] Direct NMR analysis: This involves directly performing NMR analysis on the rock sample to obtain information about the fluid content within the sample.

[0009] Water immersion analysis of rock samples: The rock samples were immersed in clean water for 6 hours until the water filled the internal pores of the rock samples. Then, nuclear magnetic resonance analysis was performed to collect the porosity data of the rock samples.

[0010] Manganese saturation analysis: The rock sample saturated with water was soaked again with manganese chloride solution for 6 hours to allow the manganese chloride solution to replace the water in the rock sample. Then, nuclear magnetic resonance analysis was performed to collect the oil saturation inside the rock sample.

[0011] b) Identification of confined fluids and movable fluids

[0012] Nuclear magnetic resonance (NMR) analysis was performed on the rock sample to obtain the NMR T2 spectrum. The T2 cutoff value was identified based on the morphology of the NMR T2 spectrum. The T2 cutoff value is the relaxation time limit that distinguishes between mobile fluids and bound fluids. The identification of bound fluids and mobile fluids is based on the T2 cutoff value. In the T2 spectrum, the fluid located to the left of the T2 cutoff value is the bound fluid, and the fluid located to the right of the T2 cutoff value is the mobile fluid.

[0013] Step 2: Calculate the fluid escape index using the fluid content of the rock sample obtained from direct NMR analysis and the size of the movable fluid pores in the rock sample; calculate the residual oil index using the oil content in the rock sample and the fluid content obtained from direct NMR analysis.

[0014] Step 3: Establish a three-terminal graph for evaluating fluid properties using the movable fluid component. The three-terminal graph is constructed from the residual oil index, fluid dissipation index, and oil saturation. Based on the established three-terminal graph, the fluid properties of the rock sample are identified.

[0015] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0016] For the above-mentioned rock sample soaking analysis, it is best to soak the rock sample in clean water for 6 hours.

[0017] For the above-mentioned manganese analysis, it is best to soak the rock sample saturated with water again for 6 hours with manganese chloride solution.

[0018] The formula for calculating the fluid dissipation index is as follows:

[0019] R fd =G / P

[0020] In the formula R fd Representative: Fluid dissipation index; G represents: Pore size of movable fluid; P represents: Fluid content obtained from direct NMR analysis.

[0021] The formula for calculating the above-mentioned remaining oil index is as follows:

[0022] Remaining oil = P / M

[0023] In the formula, R represents the remaining oil index; P represents the fluid content obtained from direct NMR analysis; and M represents the oil content in the rock sample.

[0024] Identification of the T2 cutoff value in the above T2 spectrum:

[0025] a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, if the peak is before 10ms, the cutoff point is the half-arc point of the peak; if the peak is within 10ms, the cutoff point is the center of the peak; if the peak is after 10ms, the cutoff point is the half-arc point of the peak.

[0026] b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins.

[0027] c) For a three-peak T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

[0028] This invention analyzes rock samples in three states—direct, water-soaked, and manganese-soaked—using nuclear magnetic resonance. By utilizing the analytical data, correlations are calculated, and a method and chart for evaluating formation fluid properties are established. This effectively distinguishes oil-bearing zones, oil-water mixed zones, and water-bearing zones, enabling refined reservoir evaluation and improving the overall accuracy of oil and gas interpretation. Attached Figure Description

[0029] Appendix Figure 1 This is a nuclear magnetic resonance (NMR) analysis image of a non-igneous rock sample.

[0030] Appendix Figure 2 Nuclear magnetic resonance (NMR) analysis of crude oils of different densities.

[0031] Appendix Figure 3 Nuclear magnetic resonance (NMR) analysis of crude oils of different densities.

[0032] Appendix Figure 4 A method for identifying T2 values ​​in T2 spectra of non-igneous rock samples with different peak shapes.

[0033] Appendix Figure 5 A method for identifying T2 values ​​in T2 spectra of non-igneous rock samples with different peak shapes.

[0034] Appendix Figure 6 This is a chart for evaluating the residual oil index and fluid dissipation index of mobile fluids in non-igneous rock samples.

[0035] Appendix Figure 7 This is a chart for evaluating the residual oil index and fluid dissipation index of mobile fluids in non-igneous rock samples.

[0036] Appendix Figure 8 This is a three-terminal plate depicting movable fluids in a non-igneous rock sample. Detailed Implementation

[0037] The present invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of the present invention.

[0038] The present invention will be further described below with reference to embodiments:

[0039] The research process of the method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance described in this invention:

[0040] Rock sample analysis:

[0041] a) Select a rock sample of igneous rock, seal it with plastic wrap, and perform nuclear magnetic resonance analysis within 24 hours (24 hours is the optimal time);

[0042] b) Perform NMR analysis directly on the rock samples to collect the fluid content inside the samples (mainly analyzing the fluid content preserved in the rock samples), see [link to NMR analysis]. Figure 1 The dried sample signal;

[0043] c) Soak the rock sample in clean water for 6 hours (6 hours is optimal) to fill the internal pores of the rock sample with water, then perform nuclear magnetic resonance analysis and collect the porosity data. See [link to data]. Figure 1 Gap signal;

[0044] d) Immerse the water-saturated rock sample again with manganese chloride solution for 6 hours (6 hours is optimal) to allow the manganese chloride solution to replace the water in the rock sample. Perform nuclear magnetic resonance analysis and collect the oil saturation data inside the rock sample. See [link to data]. Figure 1 oil signal;

[0045] NMR spectroscopy of crude oils of different densities:

[0046] a) Select standard light oil (0.79 g / cm³) respectively 3 ), medium quality oil (0.85g / cm) 3 ), heavy oil (0.89g / cm³) 3 Three oil samples; NMR analysis of the three oil samples is shown in [link to NMR analysis]. Figure 2 and Figure 3 ;

[0047] b) Inject oil samples of different concentrations into a standard core column (a core sample that does not contain any fluid);

[0048] c) Perform NMR analysis on a standard core column with an oil saturation of 50%;

[0049] d) Conclusion:

[0050] ① The dry sweeping signal and the oil signal have good agreement within 24 hours, which can accurately reflect the fluid properties and eliminate the influence of external water in the pore signal;

[0051] ② Different types of oils have different relaxation times. Lighter oils have relatively longer relaxation times and their main peak is located later in the relaxation process; heavier oils have relatively shorter relaxation times and their main peak is located earlier in the relaxation process. This can be used as an indirect indicator of oil quality.

[0052] Identification of T2 spectra morphology of different non-igneous rock samples, see [link to T2 spectra]. Figure 4 and Figure 5 :

[0053] a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, if the peak is before 10ms, the cutoff point is the half-arc point of the peak; if the peak is within 10ms, the cutoff point is the center of the peak; if the peak is after 10ms, the cutoff point is the half-arc point of the peak.

[0054] b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins.

[0055] c) For a three-peaked T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

[0056] Parameter definition:

[0057] a) T2 cutoff value: The relaxation time boundary that distinguishes between movable fluid and bound fluid. The left side of the T2 cutoff value is bound fluid, and the right side is movable fluid.

[0058] b) Direct analysis of rock samples: The residual fluid content in the core obtained by direct measurement of the rock sample (reflecting the fluid present in the rock sample at that time);

[0059] c) Water saturation analysis of rock samples: After soaking the rock sample in water to completely fill the pores, the pore signal is measured and used to calculate the porosity.

[0060] d) Manganese chloride replacement analysis: Rock samples are soaked in manganese chloride to measure the oil content, which is used to calculate data such as oil saturation.

[0061] Based on the data obtained from the above "rock sample analysis", a chart was created:

[0062] a) The degree of fluid loss in the sample; the higher the ratio, the more fluid is lost, and vice versa. Calculation formula:

[0063] R fd =G / P

[0064] In the formula R fd Representative: Fluid dissipation index; G represents: Pore size of movable fluid; P represents: Fluid content for direct analysis;

[0065] b) Properties of residual fluid in the sample: The lower the ratio, the higher the residual oil content; the higher the ratio, the lower the residual oil content, and the greater the probability of water content in the reservoir fluid. Calculation formula:

[0066] Remaining oil R = P / M

[0067] In the formula, R represents the residual oil index; P represents the content of the fluid being directly analyzed; and M represents the oil content in the sample.

[0068] c) Construct an evaluation chart of the residual oil index and fluid escape index of nuclear magnetic resonance mobile fluid with the fluid escape index as the x-axis and the residual oil index as the y-axis, see [link to chart]. Figure 6 ;

[0069] d) Based on Figure 6 The figure shown establishes the evaluation criteria for the nuclear magnetic resonance mobile fluid index (see Table 1), which can effectively distinguish between oil-bearing and oil-water mixed-layer zones and has a significant effect on identifying formation fluid properties. Under the current conditions, it can accurately identify fluid properties, but it cannot identify water-bearing zones.

[0070] e) based on the above Figure 6 Based on the original chart, and without defining the T2 cutoff value, to minimize interference, the fluid escape index and residual oil index were calculated using the three analytical methods (direct rock sample analysis, water saturation analysis, and manganese chloride replacement analysis) originally measured in the sample (the same rock sample used in the "Rock Sample Analysis" section above). A chart for evaluating the original residual oil index and fluid escape index based on nuclear magnetic resonance was established. (See attached chart.) Figure 7 ;

[0071] f) Based on Figure 7 The diagram shows the establishment of a nuclear magnetic resonance (NMR) primitive index fluid property evaluation standard (see Table 2); it can effectively distinguish between oil-bearing and oil-water mixed-layer zones, and has a significant effect on formation fluid identification. It can effectively distinguish between oil-bearing and oil-water mixed-layer zones, and has a significant effect on formation fluid property identification. Under current conditions, it can accurately identify fluid properties, but it cannot identify water-bearing zones.

[0072] g) Based on the two types of diagrams mentioned above ( Figure 6 and Figure 7 None of the above methods could precisely classify the reservoir fluid properties. Therefore, all data were summarized, and a correlation was established between oil saturation data and oil testing conclusions. The oil saturation parameter was introduced into the above parameters, combining the abundance of oil and gas in the formation with the degree of fluid escape and remaining oil. A three-terminal element model for nuclear magnetic resonance fluid property evaluation was established. (See attached diagram). Figure 8 ;

[0073] h) Based on Figure 8 The figure shown establishes a three-terminal evaluation standard for fluid properties based on nuclear magnetic resonance (NMR) (see Table 3), which effectively distinguishes between oil-bearing, oil-water mixed, and water-bearing zones. It has a good effect on the evaluation of reservoir fluid properties and uses NMR analysis to accurately identify the fluid properties of rock samples, thereby improving the consistency rate of oil and gas interpretation.

[0074] The method for establishing a formation fluid property evaluation chart based on nuclear magnetic resonance described in this invention is also applicable to the identification of fluid properties in carbonate formations.

[0075] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0076] Table 1

[0077] parameter Remaining oil index Fluid Dispersion Index oil layer region ≤3 ≤4 Oil-water mixed zone ＞3 ＞4

[0078] Table 2

[0079] parameter Remaining oil index Fluid Dispersion Index oil layer region ≤5 ≤2 Oil-water mixed zone ＞2 ＞2

[0080] Table 3

[0081] Evaluation criteria oil saturation Remaining oil index Fluid Dispersion Index oil layer region 0.28-1.00 0-1.00 0-0.72 Oil-water mixed zone 0-0.28 0-0.50 0.72-1.00 water layer zone 0-0.28 0.50-1.00 0.72-1.00

Claims

1. A method for establishing a map for evaluating formation fluid properties based on nuclear magnetic resonance, characterized in that... Includes the following steps: Step 1: a) Rock sample analysis Direct NMR analysis: This involves directly performing NMR analysis on the rock sample to obtain information about the fluid content within the sample. Rock sample immersion analysis: The rock sample is immersed in clean water until the water fills the internal pores of the rock sample, and then nuclear magnetic resonance analysis is performed to collect the porosity data of the rock sample. Manganese saturation analysis: The rock sample saturated with water was soaked again with manganese chloride solution to replace the water in the rock sample. Then, nuclear magnetic resonance analysis was performed to collect the oil saturation inside the rock sample. b) Identification of confined fluids and movable fluids Direct nuclear magnetic resonance (NMR) analysis was performed on the rock sample to obtain the NMR T2 spectrum. The T2 cutoff value was identified based on the morphology of the NMR T2 spectrum. The T2 cutoff value is the relaxation time limit that distinguishes between mobile fluids and bound fluids. The identification of bound fluids and mobile fluids is based on the T2 cutoff value. In the T2 spectrum, the fluid located to the left of the T2 cutoff value is the bound fluid, and the fluid located to the right of the T2 cutoff value is the mobile fluid. Step 2: Calculate the fluid escape index using the fluid content of the rock sample obtained from direct NMR analysis and the size of the movable fluid pores in the rock sample; calculate the residual oil index using the oil content in the rock sample and the fluid content obtained from direct NMR analysis. Step 3: Establish a three-terminal graph for evaluating fluid properties using the movable fluid component. The three-terminal graph is constructed from the residual oil index, fluid dissipation index, and oil saturation. Based on the established three-terminal graph, the fluid properties of the rock sample are identified.

2. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 1, characterized in that... When performing water analysis on rock samples, it is best to soak the rock samples in clean water for 6 hours.

3. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 1 or 2, characterized in that... For manganese analysis, it is best to soak the rock sample, which is saturated with water, in a manganese chloride solution for another 6 hours.

4. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 1 or 2, characterized in that... The formula for calculating the fluid dissipation index is as follows: R fd =G / P In the formula R fd Representative: Fluid dissipation index; G represents: Pore size of movable fluid; P represents: Fluid content obtained from direct NMR analysis.

5. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 3, characterized in that... The formula for calculating the fluid dissipation index is as follows: R fd =G / P In the formula R fd Representative: Fluid dissipation index; G represents: Pore size of movable fluid; P represents: Fluid content obtained from direct NMR analysis.

6. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 1, 2, or 5, characterized in that... The formula for calculating the residual oil index is as follows: Remaining oil = P / M In the formula, R represents the remaining oil index; P represents the fluid content obtained from direct NMR analysis; and M represents the oil content in the rock sample.

7. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 3, characterized in that... The formula for calculating the residual oil index is as follows: Remaining oil = P / M In the formula, R represents the remaining oil index; P represents the fluid content obtained from direct NMR analysis; and M represents the oil content in the rock sample.

8. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 4, characterized in that... The formula for calculating the residual oil index is as follows: Remaining oil = P / M In the formula, R represents the remaining oil index; P represents the fluid content obtained from direct NMR analysis; and M represents the oil content in the rock sample.

9. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 1, 2, 5, 7, or 8, characterized in that... Identification of T2 cutoff value in T2 spectrum: a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, when the peak is before 10ms, the half-arc point of the peak fall is used as the reference; when the peak is within 10ms, the center of the peak is used as the reference; when the peak is after 10ms, the half-arc point of the peak rise is used as the reference. b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins. c) For a three-peak T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

10. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 3, characterized in that... Identification of T2 cutoff value in T2 spectrum: a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, when the peak is before 10ms, the half-arc point of the peak fall is used as the reference; when the peak is within 10ms, the center of the peak is used as the reference; when the peak is after 10ms, the half-arc point of the peak rise is used as the reference. b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins. c) For a three-peak T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

11. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 4, characterized in that... Identification of T2 cutoff value in T2 spectrum: a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, when the peak is before 10ms, the half-arc point of the peak fall is used as the reference; when the peak is within 10ms, the center of the peak is used as the reference; when the peak is after 10ms, the half-arc point of the peak rise is used as the reference. b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins. c) For a three-peak T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

12. The method for establishing a formation fluid property evaluation map based on nuclear magnetic resonance according to claim 6, characterized in that... Identification of T2 cutoff value in T2 spectrum: a) For a single-peak T2 spectrum, the T2 cutoff value is: with a relaxation time of 10ms as the boundary, when the peak is before 10ms, the half-arc point of the peak fall is used as the reference; when the peak is within 10ms, the center of the peak is used as the reference; when the peak is after 10ms, the half-arc point of the peak rise is used as the reference. b) For bimodal T2 spectra, the T2 cutoff value is determined by the point where the first peak ends and the point where the second peak begins. c) For a three-peak T2 spectrum, the T2 cutoff value is based on the point where the first peak ends and the point where the second peak begins.

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