Method for evaluating content of light hydrocarbon component in low-permeability reservoir

Abstract

The invention relates to the technical field of oil and gas resource exploration and development, in particular to a low-permeability reservoir light hydrocarbon component content evaluation method which comprises the following steps: 1, drilling and coring to obtain a fresh rock core sample, performing nuclear magnetic resonance scanning on the fresh rock core sample, and measuring a T2 spectrogram of the fresh rock core sample; 2, standing the fresh rock core sample under the same pressure, temperature and humidity conditions, carrying out nuclear magnetic resonance scanning once at intervals to obtain T2 spectrograms at different time stages, and when the T2 spectrogram data is stable, obtaining the rock core sample with lost light components; and 3, calculating the effective porosity of the fresh rock core sample and the rock core sample with the dispersed light hydrocarbon component, and then calculating to obtain the content of the light hydrocarbon component in the effective porosity. According to the method, the nuclear magnetic resonance scanning test is utilized to calculate the difference of the nuclear magnetic porosity before and after oil gas loss, the content of the light hydrocarbon component is obtained, the method is good in applicability, and an important basis can be provided for oil testing and layer selection.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas resource exploration and development, and is a method for evaluating the content of light hydrocarbon components in low-permeability reservoirs. Background Art

[0002] In the process of oil and gas exploration and development, oil and gas reservoirs are mainly discovered and evaluated through coring, logging, and other data. However, with the continuous deepening of exploration and development, complex lithology and low-resistance reservoirs, high-viscosity oil and concealed reservoirs have become the objects of exploration and development. Due to the strong heterogeneity of the reservoir, oil and gas displays are difficult to identify, resulting in difficulty in selecting layers for oil testing, low oil and gas yields, and the presence of missed oil and gas layers, which affects the discovery of oil and gas reservoirs. The content of light hydrocarbon components in the reservoir pores can reflect the quality of the reservoir. The more light components, the easier it is for oil and gas to flow, and the greater the probability of obtaining oil and gas; while for reservoirs with fewer light components and more heavy components, oil testing can be abandoned, or during oil testing and fracturing, the viscosity of crude oil can be reduced (such as pre-fracturing carbon dioxide) to increase production capacity.

[0003] At present, the analysis of oil and gas shows mainly uses drilling cuttings, coring and gas logging data: the oil abundance is analyzed through the fluorescence content of the cuttings; the oil and gas content of the reservoir is interpreted through the total hydrocarbon and C1 to C5 content of gas logging; the oil content level of the core is described by visual observation (fluorescence, oil spots, oil traces, etc.). For the evaluation of light hydrocarbon components in the reservoir pores, the core can be immersed in water to observe whether there are bubbles, and the amount of bubbles can be described to reflect the amount of light components, but the qualitative description has a large error; coring is carried out by closed pressure maintenance, and then the pressure is released in a closed box to collect light volatile components and calculate the content of light components, but the cost of closed pressure maintenance coring is high and the cycle is long. There is an urgent need for a low-cost and high-accuracy method to evaluate the content of light hydrocarbon components in the pores of low-permeability reservoirs.

[0004] Nuclear magnetic resonance technology is an important method for measuring reservoir porosity. Its principle is to detect the amount of hydrogen nuclei, which are mainly contained in the oil, gas and water media in the pores. The bound water porosity, movable fluid porosity and total porosity in the mudstone skeleton can be calculated through the nuclear magnetic resonance T2 spectrum. After the core is taken out of the barrel, the light hydrocarbon components will be lost (the hydrogen nuclei are reduced). When doing the core nuclear magnetic experiment, in order to improve the accuracy of porosity calculation, the core is generally saturated with salt water, manganese or centrifuged and dried. The Chinese patent document with publication number CN112858364A discloses a method for measuring the physical properties of cores using nuclear magnetic resonance. It quickly samples the cores obtained on site, performs nuclear magnetic resonance fresh sample measurement, and then saturates them with water and performs nuclear magnetic resonance saturated sample measurement. The sample is mixed with an excess of saturated manganese chloride solution and sealed, and then placed in a nuclear magnetic resonance device for nuclear magnetic resonance saturated manganese sample measurement; nuclear magnetic resonance water calibration and oil calibration are performed respectively; the test results are processed to obtain the core physical properties. The invention proposes rapid sampling after the core is out of the barrel, which can ensure the minimum loss of core fluid, but the invention requires saturated water treatment in the later stage. During the saturated water process, due to the residual pressure in the core that has just been out of the barrel, the light component will continue to overflow, resulting in deviation in the test results. Lu Feng et al. (Characterization of Oil Content in Submicron Pores of Shale by Laser Scanning Confocal Microscopy Analysis Technology - Taking the Shale of Lucaogou Formation in Junggar Basin as an Example [J]. Experimental Petroleum Geology, 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 reflected light and fluorescence combined scanning, eliminate the interference of fluorescence emitted by minerals, and realize the accurate observation of submicron pores and their oil content, so as to achieve the purpose of distinguishing light and heavy components. However, during the experiment of this method, thin rock slices need to be made. The volatile light components are lost when the rock slices are ground, and the observed content of light components is relatively small. Summary of the invention

[0005] The present invention provides a method for evaluating the content of light hydrocarbon components in low permeability reservoirs, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problems of inaccurate methods for qualitatively observing and describing light components in low permeability reservoirs and high cost of closed pressure coring.

[0006] The technical solution of the present invention is achieved by the following measures: A method for evaluating the content of light hydrocarbon components in a low permeability reservoir is carried out according to the following steps:

[0007] The first step is to obtain a fresh core sample by drilling and coring, and to perform nuclear magnetic resonance scanning on the fresh core sample to measure the T2 spectrum of the fresh core sample;

[0008] The second step is to place the fresh core sample at the same pressure, temperature and humidity conditions, and perform a nuclear magnetic resonance scan at regular intervals to obtain T2 spectra at different time stages. When the T2 spectrum data is stable, the core sample after the light component is lost is obtained.

[0009] The third step is to calculate the effective porosity of the fresh core sample and the effective porosity of the core sample after the light component is lost, and then calculate the content of the light hydrocarbon component in the effective pores.

[0010] The following are further optimizations and / or improvements to the above technical solutions:

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

[0012] In the above second step, the temperature is 15°C to 40°C.

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

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

[0015] In the third step above, the effective porosity of the fresh core sample and the core sample after the light component loss is calculated as follows:

[0016]

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

[0018] In the third step above, the content of light hydrocarbon components in the effective pores is calculated as follows:

[0019]

[0020] 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 lost, υ 有效 It is the content of light hydrocarbon components in the effective pores.

[0021] In the second step, the stability of the T2 spectrum data is determined based on the difference in effective porosity calculated from the T2 spectra of two adjacent nuclear magnetic resonance scans being ≤10%.

[0022] In view of the current situation that the porosity and permeability conditions of low permeability reservoirs are poor and the loss rate of light hydrocarbon components is slower than that of high permeability layers, the present invention provides a method for evaluating the content of light hydrocarbon components in low permeability reservoirs. By using nuclear magnetic resonance scanning tests, the difference in nuclear magnetic resonance porosity before and after oil and gas loss is calculated to obtain the content of light hydrocarbon components, which effectively solves the problems of inaccurate methods for qualitative observation and description of light components and high cost of closed pressure coring. The present invention has good applicability and can provide an important basis for oil testing and layer selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attached Figure 1 This is the T2 spectrum of the fresh core sample in Example 8 of the present invention.

[0024] Attached Figure 2 This is the T2 spectrum of the fresh core sample in Example 8 of the present invention after standing for 2 hours.

[0025] Attached Figure 3 This is the T2 spectrum of the fresh core sample in Example 8 of the present invention after standing for 4 hours.

[0026] Attached Figure 4 This is the T2 spectrum of the fresh core sample in Example 8 of the present invention after standing for 6 hours.

[0027] Attached Figure 5 This is the T2 spectrum of the fresh core sample after standing for 8 hours in Example 8 of the present invention (core sample after the light component is lost). DETAILED DESCRIPTION

[0028] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0029] The present invention will be further described below in conjunction with embodiments:

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

[0031] The first step is to obtain a fresh core sample by drilling and coring, and to perform nuclear magnetic resonance scanning on the fresh core sample to measure the T2 spectrum of the fresh core sample;

[0032] The second step is to place the fresh core sample at the same pressure, temperature and humidity conditions, and perform a nuclear magnetic resonance scan at regular intervals to obtain T2 spectra at different time stages. When the T2 spectrum data is stable, the core sample after the light component is lost is obtained.

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

[0034] In the present invention, in order to ensure the accuracy and reliability of the nuclear magnetic resonance scanning data of the fresh core sample, it is necessary to perform nuclear magnetic resonance scanning as soon as the core is unearthed. To meet this requirement, it is necessary to equip the drilling site with a nuclear magnetic resonance experimental device.

[0035] Embodiment 2: As an optimization of the above embodiment, in the second step, the pressure is 0.09 MPa to 0.11 MPa.

[0036] Embodiment 3: As an optimization of the above embodiment, in the second step, the temperature is 15°C to 40°C.

[0037] Embodiment 4: As an optimization of the above embodiment, in the second step, the humidity is 40% to 70%.

[0038] Embodiment 5: As an optimization of the above embodiment, in the second step, the interval time is 1.5h to 3h.

[0039] Example 6: As an optimization of the above example, in the third step, the effective porosity of the fresh core sample and the core sample after the light component is lost is calculated as follows:

[0040]

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

[0042] In the third step above, the content of light hydrocarbon components in the effective pores is calculated as follows:

[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 lost, υ 有效 It is the content of light hydrocarbon components in the effective pores.

[0045] Embodiment 7: As an optimization of the above embodiment, in the second step, the stability of the T2 spectrum data is determined based on the effective porosity difference calculated from the T2 spectra of two adjacent nuclear magnetic resonance scans being ≤ 10%. The effective porosity can be calculated according to the above formula 1.

[0046] Example 8: This method for evaluating the content of light hydrocarbon components in low-permeability reservoirs was applied in a well area in Xinjiang Oilfield, and a nuclear magnetic resonance experimental device was equipped on site. After the core was taken out of the barrel from the Ma23 well, the following steps were followed:

[0047] The first step is to take fresh core samples immediately after the core is taken out of the barrel (Ma23 well is cored at 3300.5 meters), perform nuclear magnetic resonance scanning measurement on the fresh core samples, and measure the T2 spectrum of the fresh core samples (i.e., the T2 spectrum at 0 hours), see Figure 1 .

[0048] In the second step, the fresh core sample was placed in a constant temperature and humidity chamber at the drilling site, and allowed to stand for 2 hours under the conditions of 0.101 MPa (normal pressure), temperature 20°C, and humidity 60%. A nuclear magnetic resonance scanning experiment was performed, and the T2 spectrum after standing for 2 hours was measured (see Figure 2 ), and compared with the T2 spectrum of the fresh core sample, it was found that the two T2 spectra were different, reflecting that the light hydrocarbon components were constantly dissipating. The NMR scanning experiment was carried out every 2 hours to obtain the T2 spectra of different time periods ( Figures 3 to 5 ), and compared the T2 spectra of the last two times. According to the T2 spectrum after standing for 6 hours ( Figure 4 ) and T2 spectra after standing for 8 hours ( Figure 5 ) The calculated effective porosity difference is 5.6%, and the core sample after standing for 8 hours is the core sample after the light component has been lost.

[0049] The third step is to calculate the effective porosity of the fresh core sample to be 8.45% and the effective porosity of the core sample after the light component is lost to be 7.65% according to the above formula 1 based on the T2 spectrum of the NMR scan. According to the above formula 2, the content of the light hydrocarbon component in the NMR effective pores of the low permeability reservoir is 9.47%.

[0050] By comparing and analyzing the data of the tested 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 pores calculated by the method of the present invention, it is found that the gas-oil ratio, crude oil density and the content of light hydrocarbon components in the effective pores have a good correlation. The corresponding wells with high light hydrocarbon component content obtained in multiple blocks of Xinjiang Oilfield also have high production. For wells that have just been drilled, the evaluation of the light hydrocarbon component content in low-permeability reservoirs based on nuclear magnetic resonance scanning can be used as an important reference indicator for the optimization of test oil layers and fracturing optimization. The present invention has been applied and verified in multiple blocks of Xinjiang Oilfield, providing important guidance for oil testing and fracturing layer selection.

[0051] In summary, the present invention realizes the quantitative evaluation of the content of light hydrocarbon components in low permeability reservoirs. Its advantage lies in the principle of calculating porosity by using nuclear magnetic resonance to detect the amount of hydrogen nuclei. Nuclear magnetic resonance detection is performed before and after the light hydrocarbon components in the core are dispersed and lost. By comparing the difference in nuclear magnetic porosity, the content of the lost light hydrocarbon components is calculated, which solves the problems of inaccurate qualitative description of light hydrocarbon components and high cost of analyzing the content of light hydrocarbon components by closed pressure coring. By evaluating the content of light hydrocarbon components, an important basis is provided for oil testing and layer selection.

[0052] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements 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 obtain a fresh core sample by drilling and coring, and to perform nuclear magnetic resonance scanning on the fresh core sample to measure the T2 spectrum of the fresh core sample; The second step is to place the fresh core sample at the same pressure, temperature and humidity conditions, and perform a nuclear magnetic resonance scan at regular intervals to obtain T2 spectra at different time stages. When the T2 spectrum data is stable, the core sample after the light component is lost is obtained. The third step is to calculate the effective porosity of the fresh core sample and the effective porosity of the core sample after the light component is lost, and then calculate the content of the light hydrocarbon component 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 15°C to 40°C.

4. The method for evaluating the content of light hydrocarbon components in a low permeability reservoir according to any one of claims 1 to 3, 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 a low permeability reservoir according to any one of claims 1 to 4, characterized in that In the second step, the interval time is 1.5h to 3h.

6. The method for evaluating the content of light hydrocarbon components in a low permeability reservoir according to any one of claims 1 to 5, characterized in that In the third step, the effective porosity of the fresh core sample and the core sample after the light component loss is calculated as follows: Where, T 2MAX is the longest measurement time of the T2 spectrum, T 2CBW is the clay bound water relaxation time cutoff value of T2 spectrum, and S(T2)dT2 is the peak area of ​​T2 spectrum per unit time.

7. The method for evaluating the content of light hydrocarbon components in a low permeability reservoir according to any one of claims 1 to 6, characterized in that In the third step, the content of light hydrocarbon components in the effective pores is calculated as follows: 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 lost, υ 有效 It is the content of light hydrocarbon components in the effective pores.

8. The method for evaluating the content of light hydrocarbon components in a low permeability reservoir according to any one of claims 1 to 7, characterized in that In the second step, the stability of the T2 spectrum data is determined based on the difference in effective porosity calculated from the T2 spectra of two adjacent nuclear magnetic resonance scans being ≤10%.

Images