Low-permeability reservoir test layer selection evaluation method

Abstract

The present application relates to low permeability oil and gas reservoir oil testing layer selection method technical field, it is a kind of low permeability reservoir oil testing layer selection evaluation method, including fresh rock sample every 1 hour is carried out once nuclear magnetic resonance experiment, according to the total porosity of core just when out of cylinder and the total porosity of last nuclear magnetic resonance experiment, the content of light hydrocarbon component in total pore is calculated, light hydrocarbon component dispersion coefficient X is calculated again, with the oil testing result of oil well that has been tested and light hydrocarbon component dispersion coefficient X establish low permeability reservoir oil testing layer selection chart.The present application is advantageous in that using nuclear magnetic resonance full diameter core experiment, light hydrocarbon component dispersion coefficient is calculated, the permeability and oil-gas-bearing property of core are dynamically reflected, avoid the problem of big difference in artificial rock sample test result.Light hydrocarbon component dispersion coefficient is compared and analyzed with the oil testing result that has been tested, and low permeability reservoir oil testing layer selection chart is established, low permeability reservoir oil testing layer is guided, and oil and gas rate of oil testing is improved.

Description

TECHNICAL FIELD

[0001] The application relates to a low-permeability oil and gas reservoir oil testing and layer selection method. BACKGROUND

[0002] Exploration well oil testing is an important link in exploration and production, and oil testing scheme discussion is the primary work of exploration well oil testing. At present, an important task in oil testing scheme discussion is to analyze and predict the oil testing conclusion of a well to be tested, and to select an oil testing layer according to the expected oil testing result. In general, only an oil and gas layer with industrial exploitation value is subjected to oil testing and fracturing. In order to improve the oil and gas recovery rate of oil testing and avoid cost waste caused by no oil and gas flow, layer selection before oil testing is particularly important. With the deepening of exploration and development, complex lithology low-porosity low-permeability reservoirs become the main objects of exploration and development. Due to the complexity and concealment of the reservoirs, it is more and more difficult to judge the oil testing result.

[0003] A reservoir gas production prediction method and device based on pore analysis are disclosed in Chinese patent application document No. 201310088247.9. The method selects at least one full-diameter core in a target layer, obtains CT test data (including the total number of core slices and the total area of each core slice) of each full-diameter core, calculates the porosity of each full-diameter core according to the CT test data, predicts the production of the target layer according to the average value of all target porosities, and further judges the gas production grade. The method uses the porosity reflecting the characteristics of the reservoir to predict the production, excludes the influence factors of engineering, does not consider the influence of other parameters such as permeability and gas saturation on the production capacity, and has insufficient accuracy of the calculation result and certain limitations in application.

[0004] A reservoir productivity prediction model establishment method and system are disclosed in Chinese patent application document No. 201510142449.6. The method is to analyze the existing core productivity simulation data, use the related properties of the reservoir characteristics to determine the reservoir characteristic parameters with the best correlation with the production to participate in fitting modeling, classify and establish a model relationship, and then combine the logging gas detection data to select a model relationship meeting the actual situation of the target reservoir as the reservoir productivity prediction model. The method needs to collect core porosity, permeability and other data. Due to the strong heterogeneity of low-permeability reservoirs, the sampling on the full-diameter core is greatly affected by human factors. The obtained porosity and permeability data are greatly different due to different sampling positions, which may cause large prediction error of the productivity prediction model.

[0005] At present, the core parameters used for the capacity prediction test oil selected layer mainly include porosity, permeability, pore ratio, average capillary radius and other parameters, which need to be artificially sampled and then obtained by experiments. However, the full-diameter core experiment is not easy to obtain the dynamic parameters such as permeability and saturation under the undisturbed formation condition, and a low-permeability reservoir test oil selected layer method which can reflect the dynamic parameters of the reservoir and is not affected by artificial sampling is urgently needed. SUMMARY

[0006] The present application provides a low-permeability reservoir test oil selected layer evaluation method, which overcomes the shortcomings of the prior art and effectively solves the problems that the existing test oil selected layer evaluation method cannot dynamically reflect the permeability and oil-gas content of the core and the experimental results of artificial rock sampling are greatly different.

[0007] The technical scheme of the present application is realized by the following measures: a low-permeability reservoir test oil selected layer evaluation method, comprising the following steps:

[0008] Firstly, after the core is taken out of the barrel, a fresh core sample is immediately taken for a full-diameter rock sample experiment by nuclear magnetic resonance to measure the T2 spectrum of the fresh rock sample (fresh core sample);

[0009] Secondly, the fresh rock sample is placed under the conditions of normal pressure, constant temperature and same humidity, and a nuclear magnetic resonance experiment is performed every 1 hour to obtain the T2 spectrum at different time stages. When the change amplitude of the T2 spectrum is not large, the nuclear magnetic resonance experiment is stopped, and the total standing time t of the rock sample is recorded.

[0010] Thirdly, the total porosity φ of the core just after being taken out of the barrel is calculated by the nuclear magnetic resonance experiment (i.e. the full-diameter rock sample experiment by nuclear magnetic resonance), then the total porosity φ' of the last nuclear magnetic resonance experiment after the loss of the light hydrocarbon component is calculated, and the content of the light hydrocarbon component in the total porosity is calculated according to the total porosity φ of the core just after being taken out of the barrel and the total porosity φ' of the last nuclear magnetic resonance experiment. 总 总 总 总

[0011] Fourthly, the loss coefficient X of the light hydrocarbon component is calculated according to the predicted value of the formation pressure P at the downhole coring position, the content of the light hydrocarbon component in the total porosity and the total standing time t of the rock sample.

[0012] Fifthly, in the same exploration area and the same layer, the test oil results of the tested wells are collected and compared with the loss coefficient X of the light hydrocarbon component to establish a low-permeability reservoir test oil selected layer chart.

[0013] The following is a further optimization or / and improvement of the above-mentioned technical scheme of the application:

[0014] ​​​​For the Permian low-permeability reservoirs in the Xiayan area, when 0 ≤ X ≤ 4, the reservoir is a water layer or a dry layer; when 4 < X ≤ 6, the reservoir is an oil-bearing layer or a gas-bearing layer; when 6 < X ≤ 10, the reservoir is an oil and gas layer; and when 10 < X ​​≤ 12, the reservoir is a gas layer.

[0015] In the second step above, the T2 spectrum variation is small, specifically meaning that the error of the T2 spectrum data in the last two experiments is ≤10%.

[0016] The formula for calculating the content of the above-mentioned light hydrocarbon components in the total porosity is as follows:

[0017]

[0018] In the formula, v 总 This represents the content of light hydrocarbon components in the total porosity.

[0019] The formula for calculating the dispersion loss coefficient of the above light hydrocarbon group is as follows:

[0020]

[0021] In the formula, X represents the dispersion loss coefficient of the light hydrocarbon group, v 总 This represents the content of light hydrocarbon components in the total porosity, P represents the predicted formation pressure at the downhole coring location, and t represents the total settling time of the rock sample during the nuclear magnetic resonance experiment. It reflects the amount of oil and gas lost per unit pressure difference (the difference between the pressure at the downhole coring location and the atmospheric pressure) per unit time. The larger the loss coefficient X, the more and faster the light hydrocarbon components are lost.

[0022] The advantage of this invention lies in utilizing full-diameter nuclear magnetic resonance core experiments to calculate the dispersion coefficient of light hydrocarbon components, dynamically reflecting the permeability and hydrocarbon-bearing properties of the core, thus avoiding the problem of large discrepancies in results from manual sample selection experiments. By comparing and analyzing the dispersion coefficient of light hydrocarbon components with the results of oil testing, a chart for selecting oil testing layers in low-permeability reservoirs is established to guide the selection of oil testing layers in low-permeability reservoirs and improve the oil and gas yield of oil testing. Attached Figure Description

[0023] Appendix Figure 1 T2 spectrum of fresh rock sample (0 hours).

[0024] Appendix Figure 2 T2 spectra of fresh rock samples (1 hour).

[0025] Appendix Figure 3 T2 spectrum of fresh rock sample (2 hours).

[0026] Appendix Figure 4 T2 spectrum of fresh rock sample (3 hours).

[0027] Appendix Figure 5 T2 spectrum of fresh rock sample (4 hours).

[0028] attached Figure 6 The application provides a method for selecting layers for oil testing of a low-permeability reservoir in a Permian salt area. DETAILED DESCRIPTION

[0029] The application is not limited by the following examples, and the specific implementation can be determined according to the technical scheme of the application and the actual situation.

[0030] In the application, the nuclear magnetic resonance experiment refers to a nuclear magnetic resonance full-diameter rock sample experiment.

[0031] The application will be further described below in combination with examples:

[0032] Example 1: The method for selecting layers for oil testing of a low-permeability reservoir, comprising the following steps:

[0033] Step 1: Immediately after the core is taken out of the barrel, a fresh core sample is taken, and a nuclear magnetic resonance full-diameter rock sample experiment is performed to measure the T2 spectrum of the fresh rock sample (fresh core sample);

[0034] Step 2: The fresh rock sample is placed under the conditions of normal pressure, constant temperature and the same humidity, and a nuclear magnetic resonance experiment is performed every 1 hour, to obtain the T2 spectrum at different time stages. When the change in the T2 spectrum is not large, the nuclear magnetic resonance experiment is stopped, and the total standing time t of the rock sample is recorded;

[0035] Step 3: The total porosity of the nuclear magnetic resonance experiment (i.e. the nuclear magnetic resonance full-diameter rock sample experiment) when the core is just taken out of the barrel is calculated as φ 总 , then the total porosity of the last nuclear magnetic resonance experiment after the light hydrocarbon component is lost is calculated as φ' 总 , and the content of the light hydrocarbon component in the total porosity is calculated according to the total porosity of the core when it is just taken out of the barrel φ 总 and the total porosity of the last nuclear magnetic resonance experiment φ' 总 ;

[0036] Step 4: The light hydrocarbon component loss coefficient X is calculated according to the predicted value of the formation pressure P at the downhole coring position, the content of the light hydrocarbon component in the total porosity and the total standing time t of the rock sample;

[0037] Step 5: In the same exploration area and the same layer, the oil testing results of the wells that have been tested are collected, and are compared with the light hydrocarbon component loss coefficient X, to establish a low-permeability reservoir oil testing layer selection chart.

[0038] Subsequently, the light hydrocarbon component loss coefficient X can be calculated according to the nuclear magnetic resonance full-diameter rock sample experiment, and the reservoir property is determined according to X in the low-permeability reservoir oil testing layer selection chart, i.e. the reservoir is determined to be a water layer, a dry layer, an oil-bearing layer, a gas-bearing layer, an oil-gas layer or a gas layer.

[0039] Example 2: As the optimization of the above-mentioned example, in the second step, the T2 spectrum changes little, specifically, the T2 spectrum data error of the last two experiments is less than or equal to 10%.

[0040] Example 3: As the optimization of the above-mentioned example, the content of the light hydrocarbon component in the total pore is calculated according to the following formula:

[0041]

[0042] In the formula, v 总 represents the content of the light hydrocarbon component in the total pore.

[0043] Example 4: As the optimization of the above-mentioned example, the light hydrocarbon component loss coefficient is calculated according to the following formula:

[0044]

[0045] In the formula, X represents the light hydrocarbon component loss coefficient, v 总 represents the content of the light hydrocarbon component in the total pore, P represents the predicted value of the formation pressure at the downhole coring position, and t represents the total standing time of the rock sample in the nuclear magnetic resonance experiment.

[0046] After the core is taken out, the light oil and gas component will volatilize under normal pressure, and the amount and speed of volatilization of the light component are related to the permeability of the core and the content of the light component. The better the permeability of the core, the higher the content of the light component in the core, and the faster and more the light component volatilizes. At the same time, the better the permeability of the core, the higher the content of the light component, and the greater the probability of obtaining industrial oil and gas flow in oil testing. By evaluating the content and volatilization speed of the light component of the core, the relationship between the well and the industrial oil and gas flow is established, and the oil testing layer selection of the low-permeability reservoir is realized.

[0047] In the present application, after the fresh core is taken out, a nuclear magnetic resonance full-diameter core experiment is performed, the core is allowed to stand for a period of time, the light hydrocarbon component is allowed to volatilize, and then a nuclear magnetic resonance full-diameter core experiment is performed again. The light hydrocarbon component loss coefficient is calculated through the nuclear magnetic resonance experiment data, the dynamic evaluation parameter is compared with the tested oil well, and the low-permeability reservoir oil testing layer selection chart is established.

[0048] Example

[0049] In the first step, the Permian in the Xiayan area on the northwest margin of the Junggar Basin, X36 well is drilled at 4200 meters, and a fresh core sample is immediately taken out for a nuclear magnetic resonance full-diameter rock sample experiment, and the T2 spectrum of the fresh rock sample is measured. Figure 1

[0050] In the second step, the fresh rock sample is placed in the laboratory at the drilling site, and is allowed to stand for 1 hour under normal pressure (atmospheric pressure), constant temperature (20°C), and humidity of 60%, and a nuclear magnetic resonance experiment is performed to measure the T2 spectrum​Figure 2 ), and Figure 1 (0 hours) T2 spectrum contrast, found that the two T2 spectrum difference, reflecting the light hydrocarbon components in the loss. Again 1 hours of NMR experiment, comparison of the last two T2 spectrum ( Figures 4-5 ), the third hour and the fourth hour, T2 spectrum change amplitude change little (≤10%), stop NMR experiment, record the total static time t rock sample is 4 hours.

[0051] Third, according to the NMR experiment, calculate the core just out of the barrel (0 hours) nuclear magnetic total porosity φ 总 11.28%, core out of the barrel (4 hours) nuclear magnetic total porosity is 10.14%, light hydrocarbon components in the content of nuclear magnetic total porosity 10.11%.

[0052] Fourth, the calculation of light hydrocarbon components loss coefficient. X36 well at 4200 meters, the formation pressure is expected to 53.56 MPa, the calculation of loss coefficient X is 4.72.

[0053] Fifth, the collection of the northwest margin of Junggar Basin Xiayan area Permian 20 layer of oil test results, oil test results and the loss coefficient X comparison, establish Xiayan area Permian low permeability reservoir test layer chart ( Figure 6 ).

[0054] From Figure 6 can be seen, for Xiayan area Permian low permeability reservoir, when 0≤X≤4, the reservoir is water or dry layer; when 4X≤6, the reservoir is oil or gas layer; when 6X≤10, the reservoir is oil and gas layer; when 10X≤12, the reservoir is gas layer.

[0055] The above technical features constitute the embodiment of the present application, it has strong adaptability and implementation effect, can be added or subtracted unnecessary technical features according to actual needs, to meet the needs of different situations.

Claims

1. A method for evaluating oil testing and selection of low-permeability reservoirs, characterized in that... Includes the following steps: The first step is to take a fresh core sample immediately after the core is removed from the tube and perform a nuclear magnetic resonance full-diameter rock sample experiment to obtain the T2 spectrum of the fresh rock sample. The second step is to let the fresh rock sample stand under normal pressure, constant temperature and humidity conditions, and perform a nuclear magnetic resonance experiment every 1 hour to obtain T2 spectra at different time stages. When the T2 spectrum changes little, the nuclear magnetic resonance experiment is stopped and the total standing time t of the rock sample is recorded. The third step is to calculate the total porosity φ of the nuclear magnetic resonance experiment immediately after the core is removed from the tube. 总 Then, the total porosity φ′ of the last NMR experiment after the dispersion of light hydrocarbon groups was calculated. 总 Based on the total porosity φ of the core immediately after exiting the casing 总 The total porosity φ′ of the last nuclear magnetic resonance experiment 总 Calculate the content of light hydrocarbon components in the total porosity; The fourth step is to calculate the dispersion coefficient X of the light hydrocarbon component based on the predicted formation pressure P at the downhole coring location, the content of light hydrocarbon components in the total porosity, and the total settling time t of the rock sample. The fifth step is to collect the oil testing results of the tested wells in the same exploration area and the same stratigraphic layer, compare them with the light hydrocarbon group dispersion loss coefficient X, and establish a low-permeability reservoir oil testing layer selection chart. In the second step, the T2 spectrum changes are not significant, specifically meaning that the error in the T2 spectrum data of the last two experiments is ≤10%.

2. The method for evaluating low-permeability reservoirs by oil testing according to claim 1, characterized in that... For the Permian low-permeability reservoirs in the Xiayan area, when 0 ≤ X ≤ 4, the reservoir is a water layer or a dry layer; when 4 < X ≤ 6, the reservoir is an oil-bearing layer or a gas-bearing layer; when 6 < X ≤ 10, the reservoir is an oil and gas layer; and when 10 < X ​​≤ 12, the reservoir is a gas layer.

3. The method for evaluating low-permeability reservoirs by oil testing according to claim 1 or 2, characterized in that... The formula for calculating the content of light hydrocarbon components in total porosity is as follows: In the formula, v 总 This represents the content of light hydrocarbon components in the total porosity.

4. The method for evaluating low-permeability reservoirs by oil testing according to claim 1 or 2, characterized in that... The formula for calculating the dispersion loss coefficient of light hydrocarbons is as follows: In the formula, X represents the dispersion loss coefficient of the light hydrocarbon group, v 总 P represents the content of light hydrocarbon components in the total porosity, P represents the expected formation pressure at the downhole coring location, and t represents the total settling time of the rock sample in the nuclear magnetic resonance experiment.

5. The method for evaluating low-permeability reservoirs by oil testing according to claim 3, characterized in that... The formula for calculating the dispersion loss coefficient of light hydrocarbons is as follows: In the formula, X represents the dispersion loss coefficient of the light hydrocarbon group, v 总 P represents the content of light hydrocarbon components in the total porosity, P represents the expected formation pressure at the downhole coring location, and t represents the total settling time of the rock sample in the nuclear magnetic resonance experiment.

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