Method for evaluating light hydrocarbon component content in low permeability reservoirs

Abstract

The present application relates to oil and gas resource exploration and development technical field, and is a kind of low-permeability reservoir light hydrocarbon component content evaluation method, the method is carried out according to the following steps: first, drilling coring obtains fresh core sample, the T2 spectrum of fresh core sample is measured by carrying out nuclear magnetic resonance scanning to fresh core sample;Second, the fresh core sample is kept under the same pressure, temperature and humidity conditions, and nuclear magnetic resonance scanning is carried out every interval time, and the T2 spectrum at different time stages is obtained, when the T2 spectrum data is stable, the core sample after light component dispersion is obtained;Third, the effective porosity of fresh core sample and the core sample after light component dispersion is calculated, and then the content of light hydrocarbon component in effective pore is calculated.The present application uses nuclear magnetic resonance scanning test, calculates the difference of nuclear magnetic porosity before and after oil and gas dispersion, obtains the content of light hydrocarbon component, and the method has good applicability and can provide important basis for oil testing and layer selection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas resource exploration and development, and is a method for evaluating light hydrocarbon component content in low-permeability reservoirs. BACKGROUND

[0002] In the process of oil and gas exploration and development, oil and gas reservoirs are discovered and evaluated mainly through coring, logging, well logging and other data. However, with the deepening of exploration and development, complex lithology and low-resistivity reservoirs, high-viscosity oil and subtle oil reservoirs have become the objects of exploration and development. Due to strong reservoir heterogeneity, it is difficult to identify oil and gas shows, resulting in difficulties in selecting layers for testing and low oil and gas production rates, and there are also missed oil and gas layers, which affect the discovery of oil and gas reservoirs. The content of light hydrocarbon components in reservoir pores can reflect the quality of the reservoir. The more light components, the easier the oil and gas flows, and the greater the probability of oil and gas production. Reservoirs with less light components and more heavy components can be abandoned for testing, or in the process of testing and fracturing, the production capacity can be improved by reducing the viscosity of crude oil (such as pre-fracturing carbon dioxide).

[0003] Currently, oil and gas shows are mainly analyzed by using drilling cuttings, coring and gas logging data: oil abundance is analyzed by the fluorescence content of cuttings; reservoir oil and gas content is explained by the content of total hydrocarbons and C1 to C5 through gas logging; and core oil content levels (fluorescence, oil spots, oil traces, etc.) are described by visual observation. For the evaluation of light hydrocarbon components in reservoir pores, the amount of light components can be reflected by observing whether bubbles come out when the core is soaked in water and describing the amount of bubbles, but the qualitative description has large errors; the content of light components can be calculated by collecting light volatile components in a sealed tank after sealed pressure coring and releasing pressure in the sealed tank, but the sealed pressure coring has high cost and long cycle.

[0004] NMR technology is an important method for measuring reservoir porosity. Its principle is to detect the amount of hydrogen nuclei, and hydrogen nuclei are mainly contained in oil, gas and water media in pores. Through NMR T2 spectrum, the bound water porosity, movable fluid porosity and total porosity in the mudstone skeleton can be calculated. After the core is taken out of the barrel, the light hydrocarbon components will be lost (the amount of hydrogen nuclei will decrease). In order to improve the calculation accuracy of porosity, the core is generally saturated with brine, manganese or centrifuged and dried when the core NMR experiment is performed. The Chinese patent document with publication number CN112858364A discloses a method for measuring core properties by NMR. The core obtained on site is quickly sampled as a fresh sample, NMR fresh sample measurement is performed, then water saturation treatment is performed, and NMR water-saturated sample measurement is performed. The sample is mixed with excess saturated manganese chloride solution and sealed, and then placed in an NMR device for NMR manganese-saturated sample measurement; NMR water calibration and oil calibration are performed respectively; the test results are processed to obtain the core properties. The present invention can ensure that the amount of core fluid loss is minimized after the core is taken out of the barrel, but the invention needs to be saturated with water at a later stage. During the water saturation process, residual pressure exists in the core just taken out of the barrel, and light components will continue to overflow, resulting in deviation of the test results. Lu Feng et al. (Laser scanning confocal microscopic analysis technology for characterization of oil-bearing property in submicron pores of shale: A case study of Lucaogou shale in Junggar Basin[J]. Petroleum Geology & Experiment, 2023, 45(1): 193-202) modified the pre-filter configuration of the main spectrometer and detector of the laser scanning confocal microscope, so that it can better perform combined scanning of reflected light and fluorescence, eliminate the interference of mineral fluorescence, and achieve accurate observation of submicron pores and their oil-bearing properties, achieving the purpose of distinguishing between light and heavy components. However, in the experimental process of this method, rock thin sections need to be prepared, and volatile light components have already been lost during the grinding of rock thin sections, resulting in an observation of a smaller amount of light components. SUMMARY

[0005] The present application provides a method for evaluating the content of light hydrocarbon components in low permeability reservoirs, which overcomes the shortcomings of the prior art. It effectively solves the problem of inaccurate qualitative observation and description of light components in low permeability reservoirs, and the high cost of sealed pressure core sampling.

[0006] The technical solution of the present application is achieved by the following measures: a method for evaluating the content of light hydrocarbon components in low permeability reservoirs, which is performed according to the following steps:

[0007] First, drill cores to obtain fresh core samples, and perform NMR scanning on the fresh core samples to measure the T2 spectrum of the fresh core samples;

[0008] Secondly, the fresh core sample is kept under the same pressure, temperature and humidity conditions, and a nuclear magnetic resonance scanning is performed every interval time to obtain T2 spectrum at different time stages, and when the T2 spectrum data is stable, the core sample after the light component is dispersed is obtained;

[0009] Thirdly, the effective porosity of the fresh core sample and the effective porosity of the core sample after the light component is dispersed are calculated, and then the content of the light hydrocarbon component in the effective pore is calculated.

[0010] The following is a further optimization or / and improvement of the above technical solutions:

[0011] In the second step, the pressure is 0.09-0.11 MPa.

[0012] In the second step, the temperature is 15-40℃.

[0013] In the second step, the humidity is 40-70%.

[0014] In the second step, the interval time is 1.5-3h.

[0015] In the third step, the effective porosity of the fresh core sample and the core sample after the light component is dispersed is calculated according to the following formula:

[0016]

[0017] In the formula, T is the longest measurement time of T2 spectrum, T is the clay bound water relaxation time cutoff value of T2 spectrum, and S(T2)dT2 is the spectrum peak area of T2 spectrum per unit time. 2MAX 2CBW

[0018] In the third step, the content of the light hydrocarbon component in the effective pore is calculated according to the following formula:

[0019]

[0020] In the formula, φ is the effective porosity of the fresh core sample, φ' is the effective porosity of the core sample after the light component is dispersed, and υ is the content of the light hydrocarbon component in the effective pore. 有效 有效 有效

[0021] In the second step, the judgment basis for the stability of the T2 spectrum data is that the difference of the effective porosity calculated from the T2 spectrum of the adjacent two nuclear magnetic resonance scanning is ≤10%.

[0022] ​​​​​To address the challenges of poor pore-permeability conditions and slow dispersion of light hydrocarbon components in low-permeability reservoirs, this invention provides a method for evaluating the content of light hydrocarbon components in low-permeability reservoirs. By utilizing nuclear magnetic resonance (NMR) scanning experiments, the difference in NMR porosity before and after oil and gas loss is calculated to obtain the content of light hydrocarbon components. This effectively solves the problems of inaccurate qualitative observation methods for describing light components and high costs associated with closed-pressure coring. This invention has good applicability and can provide important basis for oil testing and reservoir selection. Attached Figure Description

[0023] Appendix Figure 1 This is the T2 spectrum of a fresh core sample from Example 8 of the present invention.

[0024] Appendix Figure 2 The T2 spectrum of a fresh core sample after standing for 2 hours in Example 8 of this invention.

[0025] Appendix Figure 3 The T2 spectrum of a fresh core sample after standing for 4 hours in Example 8 of this invention.

[0026] Appendix Figure 4 The T2 spectrum of a fresh core sample after standing for 6 hours in Example 8 of this invention.

[0027] Appendix Figure 5 This is the T2 spectrum of a fresh core sample after standing for 8 hours (core sample after loss of light components) in Example 8 of the present invention. Detailed Implementation

[0028] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0029] The present invention will be further described below with reference to embodiments:

[0030] Example 1: The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs is carried out according to the following steps:

[0031] The first step is to drill and obtain fresh core samples, and then perform nuclear magnetic resonance scanning on the fresh core samples to obtain the T2 spectrum of the fresh core samples.

[0032] The second step is to let the fresh core sample stand under the same pressure, temperature and humidity conditions, and perform nuclear magnetic resonance scanning at intervals to obtain T2 spectra at different time stages. When the T2 spectrum data is stable, the core sample after the loss of light components is obtained.

[0033] The third step is to calculate the effective porosity of fresh core samples and the effective porosity of core samples after the loss of light hydrocarbon components, and then calculate the content of light hydrocarbon components in the effective pores.

[0034] In the present application, in order to ensure the accuracy and reliability of the fresh core sample nuclear magnetic resonance scanning data, the nuclear magnetic resonance scanning needs to be performed at the first time when the core is unearthed. In order to meet this requirement, the nuclear magnetic resonance experimental device needs to be equipped at the drilling site.

[0035] Example 2: As an optimization of the above-mentioned example, in the second step, the pressure is 0.09 MPa to 0.11 MPa.

[0036] Example 3: As an optimization of the above-mentioned example, in the second step, the temperature is 15℃ to 40℃.

[0037] Example 4: As an optimization of the above-mentioned example, in the second step, the humidity is 40% to 70%.

[0038] Example 5: As an optimization of the above-mentioned example, in the second step, the interval time is 1.5h to 3h.

[0039] Example 6: As an optimization of the above-mentioned example, in the third step, the effective porosity of the fresh core sample and the core sample after the light component is dispersed is calculated according to the following formula:

[0040]

[0041] In the formula, T 2MAX is the longest measurement time of the T2 spectrum, T 2CBW is the clay bound water relaxation time cutoff value of the T2 spectrum, and S(T2)dT2 is the spectral peak area of the T2 spectrum per unit time.

[0042] In the above-mentioned third step, the content of the light hydrocarbon component in the effective pore is calculated according to the following formula:

[0043]

[0044] In the formula, φ 有效 is the effective porosity of the fresh core sample, φ′ 有效 is the effective porosity of the core sample after the light component is dispersed, and υ 有效 is the content of the light hydrocarbon component in the effective pore.

[0045] Example 7: As an optimization of the above-mentioned example, in the second step, the judgment basis for the stability of the T2 spectrum data is that the difference of the effective porosity calculated from the T2 spectrum of the adjacent two nuclear magnetic resonance scans is ≤10%. Wherein, the effective porosity can be calculated according to the above-mentioned formula 1.

[0046] Example 8: The low-permeability reservoir light hydrocarbon component content evaluation method is applied in a certain well area of Xinjiang Oilfield, and the nuclear magnetic resonance experimental device is equipped on site. After the core is taken out of the Ma23 well, the following steps are performed:

[0047] The first step, immediately after the core is out of the barrel, a fresh core sample (Ma23 well at 3300.5 meters) is taken, and the fresh core sample is measured by nuclear magnetic resonance scanning to obtain the T2 spectrum of the fresh core sample (i.e. 0 hour T2 spectrum), as shown in Figure 1. Figure 1 .

[0048] The second step, the fresh core sample is placed in a constant temperature and humidity box at the drilling site, and is left to stand for 2 hours under the conditions of 0.101 MPa (normal pressure), 20℃ and 60% humidity, and a nuclear magnetic resonance scanning experiment is performed to obtain the T2 spectrum after standing for 2 hours (as shown in Figure 2), which is compared with the T2 spectrum of the fresh core sample, and it is found that there is a difference between the two T2 spectra, reflecting the continuous loss of light hydrocarbon components. A nuclear magnetic resonance scanning experiment is performed every 2 hours to obtain the T2 spectrum at different time intervals (as shown in Figures 3-5), and the T2 spectrum after standing for 6 hours (as shown in Figure 3) and the T2 spectrum after standing for 8 hours (as shown in Figure 4) are compared, and the difference in effective porosity calculated from the T2 spectrum after standing for 6 hours (as shown in Figure 3) and the T2 spectrum after standing for 8 hours (as shown in Figure 4) is 5.6%, and the standing is ended, and the core sample after standing for 8 hours is the core sample after the loss of light components. Figure 2 Figures 3 to 5 The third step, according to the T2 spectrum obtained by nuclear magnetic resonance scanning, the effective porosity of the fresh core sample is calculated to be 8.45% according to the above formula 1, and the effective porosity of the core sample after the loss of light components is 7.65% according to the above formula 2. According to the above formula 2, the content of light hydrocarbon components in the effective porosity of the low permeability reservoir is 9.47%. Figure 4 Figure 5 By comparing and analyzing the data of the tested oil wells in the exploration and development area (oil and gas production, gas-oil ratio, crude oil density, viscosity, etc.) with the content of light hydrocarbon components in the effective porosity calculated by the method, the gas-oil ratio and the content of light hydrocarbon components in the effective porosity have good correlation. The wells corresponding to the high content of light hydrocarbon components obtained by the application in multiple blocks of Xinjiang Oilfield also have high production. For a newly drilled well, the evaluation of the content of light hydrocarbon components in the low permeability reservoir based on nuclear magnetic resonance scanning can be used as an important reference index for the selection of tested layers and the optimization of fracturing, and the application and verification of the application in multiple blocks of Xinjiang Oilfield provide important guidance for the selection of tested layers and fracturing.

[0049]

[0050]

[0051] ​​​​In summary, the present application realizes quantitative evaluation of light hydrocarbon component content in low-permeability reservoirs, and has the advantages that the principle of calculating porosity by detecting hydrogen nuclear amount by nuclear magnetic resonance is used, nuclear magnetic resonance detection is carried out before and after the light hydrocarbon component of the core is lost, the difference in nuclear magnetic porosity is compared, the lost light hydrocarbon component content is calculated, the problem of inaccurate qualitative description of the light hydrocarbon component and high cost of analyzing the light hydrocarbon component content by sealed pressure-maintaining coring is solved, and important basis is provided for oil testing and layer selection through evaluation of the light hydrocarbon component content.

[0052] The above technical features constitute embodiments of the present application, have strong adaptability and implementation effects, and can be increased or decreased in unnecessary technical features according to actual needs to meet the needs of different situations.

Claims

1. A method for evaluating the content of light hydrocarbon components in low-permeability reservoirs, characterized in that... Follow these steps: The first step is to drill and obtain fresh core samples, and then perform nuclear magnetic resonance scanning on the fresh core samples to obtain the T2 spectrum of the fresh core samples. The second step is to let the fresh core sample stand under the same pressure, temperature and humidity conditions, and perform nuclear magnetic resonance scanning at intervals to obtain T2 spectra at different time stages. When the T2 spectrum data is stable, the core sample after the loss of light components is obtained. The third step is to calculate the effective porosity of fresh core samples and the effective porosity of core samples after the loss of light hydrocarbon components, and then calculate the content of light hydrocarbon components in the effective pores. The content of the light hydrocarbon component in the effective pores is calculated using the following formula: In the formula, The effective porosity of a fresh core sample. The effective porosity of the core sample after the loss of light fraction dispersion. This represents the content of light hydrocarbon components in the effective pores.

2. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1, characterized in that... In the second step, the pressure is 0.09 MPa to 0.11 MPa.

3. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1 or 2, characterized in that... In the second step, the temperature is between 15°C and 40°C.

4. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1, characterized in that... In the second step, the humidity is 40% to 70%.

5. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1 or 4, characterized in that... In the second step, the interval is 1.5 hours to 3 hours.

6. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1, characterized in that... In the third step, the effective porosity of fresh core samples and core samples after the loss of light components is calculated using the following formula: In the formula, T 2MAX The longest measurement time for the T2 spectrum, T 2CBW S(T2)dT2 is the cutoff value of the clay-bound water relaxation time of the T2 spectrum, and S(T2)dT2 is the peak area of ​​the T2 spectrum per unit time.

7. The method for evaluating the content of light hydrocarbon components in low-permeability reservoirs according to claim 1, characterized in that... In the second step, the criterion for judging the stability of T2 spectrum data is that the difference in effective porosity calculated from the T2 spectra of two adjacent nuclear magnetic resonance scans is ≤10%.

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