Method for identifying natural gas reservoir type, method for identifying non-mixed natural gas reservoir type and method for constructing identification chart

Abstract

The present application relates to a kind of natural gas reservoir type identification method, the construction method of non-mixed natural gas reservoir type identification method and its identification chart, belong to oil and gas exploration and development technical field.The identification method of the present application includes the following steps: judging whether the target natural gas reservoir is mixed gas reservoir, if the target natural gas reservoir is not mixed gas reservoir, then the ethane and methane carbon isotope difference of target natural gas reservoir natural gas sample, methane isotopic value is plotted in the identification chart of non-mixed natural gas type, according to the position of the demarcation line of coal-formed gas reservoir and oil-type gas reservoir, the type of target gas reservoir is judged.The natural gas reservoir type identification method of the present application can determine the genesis of different types of natural gas in complex oil and gas basin, not only can identify mixed gas reservoir, coal-formed gas reservoir and oil-type gas reservoir, but also can realize the rapid identification of different types of oil-type gas, coal-formed gas in low maturity-high maturity all-weather.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for identifying a natural gas reservoir type, a method for identifying a non-mixed natural gas reservoir type and a method for constructing an identification chart thereof, and belongs to the technical field of oil and gas exploration and development. BACKGROUND

[0002] In recent years, with the deepening of oil and gas exploration, the difficulty of exploration is gradually increasing, and the transition from shallow to deep exploration has become inevitable. With the gradual deepening of the burial depth and the gradual increase of the thermal evolution degree of different types of kerogen source rocks, the crude oil is affected by high heat and unstable cracking, and the deep layer oil and gas mainly exists in the form of condensate oil and gas reservoir and dry gas reservoir, and the oil and gas reservoir in the form of crude oil is less and less.

[0003] The identification of the source of gas in the gas reservoir is of great significance to the exploration and development of natural gas. If the gas in the gas reservoir is mainly derived from coal measures (coal-derived gas), exploration along the periphery of the coal measures source rock will greatly increase the success rate of exploration; similarly, if the gas in the gas reservoir is mainly derived from lacustrine source rock (oil-type gas), exploration along the periphery of the lacustrine source rock will also greatly increase the success rate of exploration. If a basin has the above two sets of source rocks, the above conclusions are reversed, which will lead to a major misjudgment in the exploration of natural gas, resulting in a large number of dry wells, and ultimately leading to a large loss of manpower and material resources.

[0004] Traditional methods for identifying different types of natural gas include ethane carbon isotope method (i.e., ethane carbon isotope greater than -27.5 ‰ is coal-derived gas, and less than -27.5 ‰ is oil-type gas), methane carbon isotope and rare gas 40 Ar / 36 Ar method, methane carbon isotope and component C1 / (C1+C2) ratio method, etc. Although these methods are widely used, they also have their limitations. For example, the ethane carbon isotope method, due to the small influence of heat on ethane carbon isotope, the carbon isotope is relatively stable, mainly reflecting the difference in parent material source, and its advantage is that it can quickly judge the general cause of natural gas, but it is too absolute, and some examples in the Dongpu Sag Qiaokou area do not meet the above characteristics. The methane carbon isotope and rare gas 40 Ar / 36Ar method and methane carbon isotope and component C1 / (C1+C2) method, there are many problems, these methods are considered that the methane carbon isotope of coal-derived gas is relatively heavy, and the methane carbon isotope of oil-type gas is relatively light, because these charts were established in China at the beginning, mainly based on the data of Wen 23 coal-derived gas field in Dongpu depression of Bohai Bay (Wen 23 gas field is the first large coal-derived gas field discovered in China). In recent years, with the gradual expansion of oil and gas exploration, Ordos Basin has become the largest gas field in China, and a large number of coal-derived gas fields have been discovered in Changqing oilfield. Through testing and analysis, it is found that the methane carbon isotope in a considerable number of coal-derived gas fields is not heavy, even relatively light, for example, the methane carbon isotope in Shenmu coal-derived gas field can be as light as-40‰, and the methane isotope is between-40‰ and-32‰, and the methane carbon isotope in Longnvsi coal-derived gas field in Sichuan can be as low as-42‰, which leads to a large uncertainty in the identification of a large number of previous charts. More and more data show that the methane isotope of coal-derived gas also has a lighter characteristic at a low thermal evolution stage. And no matter what the cause of natural gas is, the carbon isotope of methane gas is seriously affected by the thermal evolution degree of source rock, which has become a consensus in the academic circle, when the thermal evolution degree of coal measure source rock is low, the methane carbon isotope will also be light, and when the thermal evolution degree of lacustrine source rock is high, the methane carbon isotope will also be heavy, thus there will be a large error in the identification of natural gas genesis by single methane carbon isotope or ethane carbon isotope determination.

[0005] Because of the small thermal evolution degree of ethane carbon isotope, when the thermal evolution degree of source rock is low, the methane carbon isotope will be light, and the difference between ethane and methane isotope will be large; when the thermal evolution degree of source rock is high, the methane carbon isotope will be heavy, and the difference between ethane and methane isotope will be small; domestic scholars try to establish a linear relationship between the two, so as to distinguish different types of natural gas genesis. For example, Renhuai Qiang et al. in “Review on geochemical identification method of coal-derived gas and oil-type gas” (Western Exploration Engineering, 2005 (09): 64-66.) mentioned that Δ(δ 13 C2-δ 13 C1) and δ 13 C1 are negatively correlated, that is, Δ(δ 13 C2-δ 13 C1) decreases with the increase of δ 13 C1. Δ(δ 13 C2-δ 13 C1) is a good indicator of gas reservoir maturity. Using the relationship between this value and methane carbon isotope, the genesis of natural gas can be determined. The regression equation of Δ(δ 13 C2-δ 13 C1)-δ 13 C1) of coal-derived gas and oil-type gas in China is:

[0006] Coal-derived gas: y = -0.8865x - 20.756 R = 0.78 (1)

[0007] Oil-type gas: y = -0.833x - 26.524 R = 0.77 (2)

[0008] In the formula: y = Δ (δ 13 C2- δ 13 C1) ; x = δ 13 C1; R = correlation coefficient.

[0009] (1) (2) Two regression curves divide the space into three areas, that is, the indexes can be substituted into the chart for analysis and discrimination. However, when the isotopes of the typical coal-derived gas reservoir in Ordos Basin and the typical oil-type gas reservoir in Dongpu Sag of Bohaiwan Basin, which are recognized by the academic circle, are projected on the above chart (see Figure 1 ), it is found that many typical coal-derived gas reservoirs in Ordos Basin fall in the mixed gas reservoir, even in the oil-type gas area. According to the analysis of the data, the chart is first proposed by MA Rooney in 1995, which is mainly based on the analysis of the thermal simulation experiment of type II kerogen, and lacks the thermal simulation experiment samples of type I and type III kerogen, while the coal-derived gas is mainly generated by type III kerogen. When the above chart is used to identify and verify the typical coal-derived gas reservoir in Ordos, the above application premise is not considered, resulting in misjudgment. Limited by the application premise condition of the application chart, the above chart cannot be used for the rapid identification of the type of natural gas reservoir. SUMMARY

[0010] The purpose of the present application is to provide a method for identifying the type of natural gas reservoir, which can realize the rapid identification of the type of natural gas reservoir with high identification certainty.

[0011] The present application also provides a method for identifying the type of non-mixed gas reservoir and a method for constructing the identification chart thereof.

[0012] In order to achieve the above purpose, the technical scheme adopted by the method for identifying the type of natural gas reservoir of the present application is as follows:

[0013] The method for identifying the type of natural gas reservoir comprises the following steps: judging whether the target natural gas reservoir is a mixed gas reservoir, and if the target natural gas reservoir is not a mixed gas reservoir, then:

[0014] The difference between the ethane and methane carbon isotopes and the methane isotope value of the target natural gas reservoir are projected in a rectangular coordinate system with the difference between the ethane and methane carbon isotopes as the vertical coordinate and the methane isotope value as the horizontal coordinate. If the projection point is located on the left side of the straight line y = ax + b, the target natural gas reservoir is an oil-type gas reservoir, and if the projection point is located on the right side of the straight line y = ax + b, the target natural gas reservoir is a coal-type gas reservoir. In the straight line y = ax + b, -1.10 ≤ a ≤ -0.90, and -31.0 ≤ b ≤ -30.0.

[0015] or the ethane and methane carbon isotope difference of the target natural gas reservoir, the methane isotope value is plotted on the identification chart of the non-mixed natural gas reservoir type, and the type of the target natural gas reservoir is judged;

[0016] The identification chart is established by the method comprising the following steps:

[0017] 1) providing a plurality of natural gas samples; the carbon isotope in each natural gas sample in the plurality of natural gas samples is characterized in that the methane carbon isotope value < the ethane carbon isotope value < the propane carbon isotope value;

[0018] 2) performing geological analysis on the collected gas reservoir of each natural gas sample, and identifying the type of the collected gas reservoir of each natural gas sample;

[0019] 3) based on the ethane and methane isotope difference and the methane isotope value of the natural gas sample, performing point analysis on the collected gas reservoir of each natural gas sample, determining the range of the coal-derived gas reservoir and the oil-type gas reservoir according to the type of the collected gas reservoir of each natural gas sample identified in step 2), and demarcating the boundary line of the coal-derived gas reservoir and the oil-type gas reservoir to establish the identification chart of the non-mixed natural gas reservoir type.

[0020] The isotopes of natural gas produced by different types of source rocks at different thermal evolution stages have great differences, which can cause the natural gas produced by coal-derived gas at a low thermal evolution stage to be misjudged as oil-type gas at a high maturity. The straight line y=ax+b and the identification chart used in the identification method of the type of the target natural gas reservoir of the mixed gas reservoir are established by point analysis of the ethane and methane isotope difference and the methane isotope value of the natural gas sample of the typical coal-derived gas reservoir and the oil-type gas reservoir identified by geological analysis, and have high identification certainty. The identification method of the type of the natural gas reservoir can determine the genesis of different types of natural gas in a complex oil and gas bearing basin, can not only identify the mixed gas reservoir, the coal-derived gas reservoir and the oil-type gas reservoir, but also can realize the all-weather rapid identification of different types of oil-type gas and coal-derived gas at low maturity and high maturity, and can provide technical support for the natural gas exploration and development of a complex oil and gas bearing basin.

[0021] It can be understood that for a specific natural gas reservoir, the methane isotope value and the ethane-methane isotope difference value can be obtained by determining the carbon isotope of the natural gas sample collected from the natural gas reservoir. Since the carbon isotope in multiple natural gas samples is characterized by the methane carbon isotope value < the ethane carbon isotope value < the propane carbon isotope value, in the geological analysis of the collection gas reservoir of each natural gas sample, it is determined that the collection gas reservoir type of each natural gas sample is either a coal-derived gas reservoir or an oil-type gas reservoir, and therefore for a single natural gas sample, based on the geological analysis result of the collection gas reservoir of the natural gas sample, one of the coal-derived gas reservoir and the oil-type gas reservoir is selected as the type of the collection gas reservoir of the corresponding natural gas sample. In the point analysis of the target natural gas reservoir, if the point falls into which interval, the target gas reservoir belongs to the corresponding type of gas reservoir.

[0022] Considering that natural gas may be affected by differences in formation burial depth, temperature, pressure and burial medium due to different hosting media, in order to improve the reliability of the identification chart, further, multiple natural gas samples are collected from natural gas reservoirs in a rift basin, a craton basin and a foreland basin, and the collection gas reservoirs of the multiple natural gas samples are hosted in carbonate strata and clastic rock strata. The collected natural gas samples cover a wide area, and the identification of the origin of natural gas is more comprehensive.

[0023] Further, the straight line y=ax+b is y=-1.08x-30.5.

[0024] Further, the method for identifying the type of the collection gas reservoir of the natural gas sample comprises the following steps:

[0025] determining the number of sets of source rocks and the types of the source rocks in the basin where the collection gas reservoir of the natural gas sample is located;

[0026] When there is only one set of source rocks in the basin where the collection gas reservoir of the natural gas sample is located, if this set of source rocks is lacustrine mudstone, the collection gas reservoir of the natural gas sample is identified as an oil-type gas reservoir; if this set of source rocks is coal measure source rock, the collection gas reservoir of the natural gas sample is identified as a coal-derived gas reservoir;

[0027] When there are more than two sets of source rocks in the basin where the collection gas reservoir of the natural gas sample is located and at least one set of coal measure source rock and at least one set of lacustrine source rock are included, the geological background is analyzed, if the collection gas reservoir of the natural gas sample is hosted in a lacustrine mudstone development layer section and there is no fault communication in the vertical direction, the collection gas reservoir of the natural gas sample is identified as an oil-type gas reservoir, if the collection gas reservoir of the natural gas sample is hosted in a coal measure source rock development layer section and there is no fault communication in the vertical direction, the collection gas reservoir of the natural gas sample is identified as a coal-type gas reservoir;

[0028] When there are two sets of hydrocarbon source rocks in the basin where the natural gas sample is collected, and each set of hydrocarbon source rock is coal source rock or lacustrine mudstone, if each set of hydrocarbon source rock is coal source rock, the natural gas reservoir is identified as a coal-derived gas reservoir, and if each set of hydrocarbon source rock is lacustrine mudstone, the natural gas reservoir is identified as an oil-type gas reservoir.

[0029] Further, the method for determining whether the target natural gas reservoir is a mixed gas reservoir comprises the following steps: determining the isotope values of methane, ethane and propane in the natural gas sample of the natural gas reservoir to be identified, if the methane carbon isotope value < ethane carbon isotope value > propane carbon isotope value or the methane carbon isotope value > ethane carbon isotope value < propane carbon isotope value, the target natural gas reservoir is a mixed natural gas reservoir, otherwise the target natural gas reservoir is not a mixed gas reservoir. The identification method of whether it is a mixed gas reservoir is different from the identification of coal-derived gas reservoir and oil-type gas reservoir. Before determining whether the target natural gas reservoir is a mixed gas reservoir, the carbon isotope sequence of the sample of the target natural gas reservoir is analyzed first, if it is a mixed carbon isotope sequence, it is determined to be a mixed gas reservoir. The basis for judging by using the carbon isotope sequence relationship is that the mixed gas reservoir shows a mixed sequence, mainly in two forms, either δ 13 C1>δ 13 C2<δ 13 C3, or δ 13 C1<δ 13 C2>δ 13 C3(δ 13 C1, δ 13 C2, δ 13 C3 are the methane carbon isotope value, ethane carbon isotope value and propane carbon isotope value respectively); and a single coal-derived gas reservoir or oil-type gas reservoir shows a positive sequence, i.e. δ 13 C1<δ 13 C2<δ 13 C3.

[0030] The technical scheme adopted by the identification method of the non-mixed natural gas reservoir type of the present application is:

[0031] A method for identifying a non-mixed natural gas reservoir type, comprising the following steps: projecting an ethane-methane carbon isotope difference and a methane isotope value of a target non-mixed natural gas reservoir on a Cartesian coordinate system with the ethane-methane carbon isotope difference as the ordinate and the methane isotope value as the abscissa, if the point is located on the left side of a straight line y=ax+b, the target natural gas reservoir is an oil-type gas reservoir, if the point is located on the right side of the straight line y=ax+b, the target natural gas reservoir is a coal-type gas reservoir; in the straight line y=ax+b, -1.10<=a<=-0.90, -31.0<=b<=-30.0; or projecting the ethane-methane carbon isotope difference and the methane isotope value of the target non-mixed natural gas reservoir on an identification chart of the non-mixed natural gas reservoir to identify the type of the natural gas reservoir; the identification chart is established by the following method: 1) providing a plurality of natural gas samples; the carbon isotope in each natural gas sample in the plurality of natural gas samples is characterized by a methane carbon isotope value < an ethane carbon isotope value < a propane carbon isotope value; 2) performing geological analysis on the collected gas reservoirs of the natural gas samples to identify the types of the collected gas reservoirs of the natural gas samples; 3) based on the natural gas samples, the ethane-methane carbon isotope difference and the methane isotope value, performing point projection analysis on the collected gas reservoirs of the natural gas samples, determining the ranges of coal-type gas reservoirs and oil-type gas reservoirs according to the types of the collected gas reservoirs of the natural gas samples identified in step 2), and demarcating the boundary lines of the coal-type gas reservoirs and the oil-type gas reservoirs to establish the identification chart of the non-mixed natural gas reservoir type.

[0032] The method for identifying a non-mixed natural gas reservoir type can realize all-weather rapid identification of different types of oil-type gas and coal-type gas with low maturity and high maturity, and has high identification certainty.

[0033] Further, the plurality of natural gas samples are collected from natural gas reservoirs in a faulted basin, a craton basin and a foreland basin, and the collected gas reservoirs of the plurality of natural gas samples are hosted in carbonate strata and clastic rock strata.

[0034] Further, the straight line y=ax+b is y=-1.08x-30.5.

[0035] The technical scheme adopted by the method for establishing the identification chart of the non-mixed natural gas reservoir type is as follows:

[0036] A method for establishing an identification chart of a non-mixed natural gas reservoir type, comprising the following steps:

[0037] 1) providing a plurality of natural gas samples; the carbon isotope in each natural gas sample in the plurality of natural gas samples is characterized by a methane carbon isotope value < an ethane carbon isotope value < a propane carbon isotope value;

[0038] 2) performing geological analysis on the collected gas reservoirs of the natural gas samples to identify the types of the collected gas reservoirs of the natural gas samples;

[0039] 3) Based on the ethane and methane isotopic difference and the methane isotopic value of the natural gas sample, the collection gas reservoir of each natural gas sample is analyzed by point projection, the type of each natural gas sample collection gas reservoir is identified according to step 2), the range of coal-derived gas reservoir and oil-type gas reservoir is determined, the boundary line of coal-derived gas reservoir and oil-type gas reservoir is drawn, and the identification chart of non-mixed natural gas reservoir type is established.

[0040] The construction method of the identification chart of non-mixed natural gas reservoir type of the present application can realize the all-weather rapid identification of different types of oil-type gas and coal-derived gas with low maturity-high maturity, and has high identification certainty.

[0041] Further, the plurality of natural gas samples are collected from natural gas reservoirs in a faulted basin, a craton basin and a foreland basin, and the collection gas reservoirs of the plurality of natural gas samples are hosted in carbonate strata and clastic rock strata.

[0042] The present application adopts PDB standard when determining the methane, ethane and propane isotopic values of the natural gas sample to be identified. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The ethane and methane carbon isotopic difference and the methane isotopic value of the typical coal-derived gas reservoir in Ordos and the typical oil-type gas reservoir in Dongpu Sag of Bohaiwan Basin are projected in the identification chart determined by the two regression curves in the background technology (1) (2) to obtain a point projection schematic diagram;

[0044] Figure 2 The coal-derived gas reservoir distribution map obtained by point projection in Example 1;

[0045] Figure 3 The oil-type gas reservoir distribution map obtained by point projection in Example 1;

[0046] Figure 4 The identification chart of non-mixed natural gas reservoir type constructed in Example 1. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be further described in combination with the specific embodiments.

[0048] The following Example 1 is the construction method of the identification chart of non-mixed natural gas reservoir type, Example 2 is an embodiment of the identification method of natural gas reservoir type, and Example 3 is an embodiment of the identification method of non-mixed natural gas reservoir type.

[0049] Example 1

[0050] The construction method of the identification chart of non-mixed natural gas reservoir type of the present application, comprising the following steps:

[0051] 1) Collection of natural gas samples from different types of oil and gas bearing basins

[0052] In order to avoid non-representativeness, the natural gas samples collected in this collection cover natural gas reservoirs in three main types of oil and gas bearing basins, i.e. rift basin, craton basin and foreland basin; and the hosting strata of all the natural gas samples collected cover carbonate strata and clastic rock strata.

[0053] 2) Determination of carbon isotopes of methane, ethane and propane in natural gas samples

[0054] The carbon isotopes of methane, ethane and propane in all the natural gas samples collected in step 1 were determined by using stable isotope mass spectrometer, with PDB standard, and the instrument error of the determination was 0±0.2‰, and the determination results are shown in Table 1.

[0055] 3) Identification of the type of the gas reservoir from which each natural gas sample was collected

[0056] i) According to the determination results of step 2), all the natural gas samples were analyzed, and the natural gas samples with mixed carbon isotope sequence (i.e. δ 13 C1>δ 13 C2<δ 13 C3or δ 13 C1<δ 13 C2>δ 13 C3) were identified as mixed gas reservoirs (results are shown in Table 1);

[0057] ii) The natural gas samples identified as mixed gas reservoirs in step i) were excluded, and the remaining natural gas samples all had normal carbon isotope sequence (i.e. δ 13 C1<δ 13 C2<δ 13 C3) and the hosting strata of all the remaining natural gas samples also covered natural gas reservoirs in three main types of oil and gas bearing basins, i.e. rift basin, craton basin and foreland basin, and covered carbonate strata and clastic rock strata, and the hosting gas reservoirs of the remaining natural gas samples were analyzed geologically to identify the type of each natural gas reservoir; when judging the type of the gas reservoir from which a single natural gas sample was collected, firstly, the number of sets of source rocks and the types of each set of source rocks in the basin in which the gas reservoir was located were determined;

[0058] When there was only one set of source rocks in the basin in which the gas reservoir was located, if this set of source rocks was lacustrine mudstone, then the gas reservoir belonged to oil-type gas reservoir; if this set of source rocks was coal measure source rock, then the gas reservoir belonged to coal-derived gas reservoir;

[0059] When there are two or more sets of hydrocarbon source rocks in the basin where the gas reservoir is located, and at least one set of coal measures and at least one set of lacustrine source rocks, analyze the geological background. If the gas reservoir is present in the lacustrine mudstone development section, and there is no fault communication in the vertical direction, even if the coal measures source rock is developed above and / or below, the gas reservoir will be determined as an oil-type gas reservoir; if the gas reservoir is present in the coal measures source rock development section, and there is no fault communication in the vertical direction, even if the lacustrine source rock is developed above and / or below, the gas reservoir will be determined as a coal-type gas reservoir (see Table 1).

[0060] When there are two or more sets of hydrocarbon source rocks in the basin where the gas reservoir is located, and each set of hydrocarbon source rock is coal measures or lacustrine mudstone, then if each set of hydrocarbon source rock is coal measures, the gas reservoir will be determined as a coal-derived gas reservoir, and if each set of hydrocarbon source rock is lacustrine mudstone, the gas reservoir will be determined as an oil-type gas reservoir.

[0061] Table 1 Classification of typical gas reservoirs in different types of oil and gas basins

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070] 4) The ethane and methane isotope difference and methane isotope value of the typical oil-type gas reservoir and coal-derived gas reservoir determined in step 3) are analyzed by point projection, and a discrimination chart is established:

[0071] i) Based on the ethane and methane isotope difference and methane isotope value of the natural gas samples of the coal-derived gas reservoir determined in step 3), the coal-derived gas reservoir is projected (the vertical coordinate is the ethane and methane isotope difference, and the horizontal coordinate is the methane isotope value), see Figure 2 ; then based on the ethane and methane isotope difference and methane isotope value of the natural gas samples of the oil-type gas reservoir determined in step 3), the oil-type gas reservoir is projected (the vertical coordinate is the ethane and methane isotope difference, and the horizontal coordinate is the methane isotope value), see Figure 3 .

[0072] From Figure 2 and Figure 3It can be seen that oil-type gas and coal-derived gas are not in the same interval, and have a certain linear demarcation line (vertical coordinate is the difference between ethane and methane isotopes, and horizontal coordinate is the value of methane isotope).

[0073] ii) Based on the difference between ethane and methane isotopes and the value of methane isotope of the remaining natural gas sample in step 3), the gas reservoirs of each remaining natural gas sample are plotted (vertical coordinate is the difference between ethane and methane isotopes, and horizontal coordinate is the value of methane isotope), see Figure 4 According to the identification type of each remaining natural gas reservoir sample in step 3), the interval range of coal-derived gas reservoir and oil-type gas reservoir is determined, the linear demarcation line (y=-1.08x-30.5) of coal-derived gas reservoir and oil-type gas reservoir is drawn, and the identification chart of non-mixed natural gas reservoir is established.

[0074] Through Figure 4 It can be seen that the demarcation line of coal-derived gas reservoir and oil-type gas reservoir is approximately a straight line, and the straight line is y=Ax+B. When the horizontal coordinate x is about -29.3, the vertical coordinate can be read from the graph as 0, that is, there is a relationship of 0=-29.3A+B. When the horizontal coordinate x is about -47.7, the vertical coordinate y is about 20, that is, there is a relationship of 20=-47.7A+B. By adding and subtracting the two relationships, A=-1.08 and B=-30.5 can be determined. Figure 4 The uppermost point in the figure is about -47.7 when y=20, that is, there is a relationship of 20=-47.7A+B. By adding and subtracting the two relationships, A=-1.08 and B=-30.5 can be determined.

[0075] Example 2

[0076] The identification method of the natural gas reservoir type of the present embodiment comprises the following steps:

[0077] 1) Carbon isotope determination is performed on natural gas samples 1-4 collected from different natural gas reservoirs, and the results are shown in Table 2.

[0078] 2) Whether each natural gas sample is a mixed carbon isotope sequence is determined, and the collection gas reservoir of the natural gas sample with a mixed carbon isotope sequence is determined as a mixed gas reservoir.

[0079] As can be seen from Table 2, the carbon isotopes of each component of natural gas samples 2, 3, and 4 are reversed to a certain extent. Sample 2 belongs to the δ 13 C1<δ 13 C2>δ 13 C3 type, samples 3 and 4 belong to the δ 13 C1>δ 13 C2<δ 13 C3 type, and therefore the collection gas reservoirs of natural gas samples 2, 3, and 4 are mixed gas reservoirs. Natural gas sample 1 belongs to a normal carbon isotope sequence, and therefore the collection gas reservoir of natural gas sample 1 is not a mixed gas reservoir.

[0080] 3) According to the ethane and methane carbon isotope difference value and the methane isotope value of the natural gas sample 1, the gas collection reservoir of the natural gas sample 1 is analyzed by point projection (the vertical coordinate is the ethane and methane isotope difference value, and the horizontal coordinate is the methane isotope value), and is projected into the identification chart established in Example 1, and it is found that the gas collection reservoir of the natural gas sample 1 is located in the coal-derived gas reservoir interval, so it can be determined that the gas collection reservoir of the natural gas sample 1 belongs to the coal-derived gas reservoir. This is also consistent with the fact that a large number of coal seams and carbonaceous mudstone and other coal measures source rocks are found in the vicinity of the gas reservoir.

[0081] Table 2 Carbon isotope values in each natural gas sample

[0082]

[0083] Example 3

[0084] The identification method of the non-mixed natural gas reservoir type in this example is the same as step 3) in Example 2, which will not be repeated here.

[0085] Experimental example

[0086] In order to verify the certainty of the natural gas reservoir type identification method of the present application, 7 natural gas samples collected from different natural gas reservoirs are taken respectively, and the carbon isotope values in each natural gas sample are shown in Table 3.

[0087] Table 3 Carbon isotope values in each natural gas sample and the identified gas collection reservoir type

[0088]

[0089]

[0090] According to the natural gas reservoir type identification method of Example 2, the natural gas reservoir type is identified, 2 natural gas reservoirs are identified as mixed gas reservoirs, 3 natural gas reservoirs are identified as coal-derived gas reservoirs, and 2 natural gas reservoirs are identified as oil-type gas reservoirs. After exploration practice in the later period, it is confirmed that all the identifications are correct, and it can be seen that the natural gas reservoir type identification method of the present application has high identification certainty.

Claims

1. A method of identifying a natural gas reservoir type, characterized by: The method comprises the following steps: determining whether the target natural gas reservoir is a mixed gas reservoir, if the target natural gas reservoir is not a mixed gas reservoir, then: plotting the ethane-methane carbon isotope difference and the methane isotope value of the target natural gas reservoir in a rectangular coordinate system with the ethane-methane carbon isotope difference as the vertical coordinate and the methane isotope value as the horizontal coordinate, if the plot is located on the left side of the straight line y=ax+b, the target natural gas reservoir is an oil-type gas reservoir, if the plot is located on the right side of the straight line y=ax+b, the target natural gas reservoir is a coal-type gas reservoir; in the straight line y=ax+b, -1.10≤a≤-0.90, -31.0≤b≤-30.0; or plotting the ethane-methane carbon isotope difference and the methane isotope value of the target natural gas reservoir on a discrimination chart of non-mixed natural gas reservoir types to determine the type of the target natural gas reservoir; The discrimination chart is established by the following method: 1) providing a plurality of natural gas samples; the carbon isotopes in each natural gas sample in the plurality of natural gas samples all show that the methane carbon isotope value is less than the ethane carbon isotope value which is less than the propane carbon isotope value; 2) performing geological analysis on the collected gas reservoirs of each natural gas sample to determine the types of the collected gas reservoirs of each natural gas sample; 3) based on the ethane-methane carbon isotope difference and the methane isotope value of the natural gas samples, plotting analysis is performed on the collected gas reservoirs of each natural gas sample, the ranges of coal-type gas reservoirs and oil-type gas reservoirs are determined according to the types of the collected gas reservoirs of each natural gas sample determined in step 2), the boundary line between the coal-type gas reservoirs and the oil-type gas reservoirs is drawn, and the discrimination chart of non-mixed natural gas reservoir types is established.

2. The method for identifying the type of natural gas reservoir according to claim 1, characterized in that: The plurality of natural gas samples are collected from natural gas reservoirs in a faulted basin, a cratonic basin and a foreland basin, and the collected gas reservoirs of the plurality of natural gas samples are hosted in carbonate strata and clastic rock strata.

3. The method for identifying the type of a natural gas deposit according to claim 1 or 2, characterized in that: The method for determining whether the target natural gas reservoir is a mixed gas reservoir comprises the following steps: determining the methane, ethane and propane isotope values in a natural gas sample of a natural gas reservoir to be determined, if the methane carbon isotope value is less than the ethane carbon isotope value which is greater than the propane carbon isotope value or the methane carbon isotope value is greater than the ethane carbon isotope value which is less than the propane carbon isotope value, the target natural gas reservoir is a mixed natural gas reservoir, otherwise, the target natural gas reservoir is not a mixed gas reservoir.

4. A method of identifying a non-mixed natural gas reservoir type, characterized by: The method comprises the following steps: plotting the ethane-methane carbon isotope difference and the methane isotope value of the target non-mixed natural gas reservoir in a rectangular coordinate system with the ethane-methane carbon isotope difference as the vertical coordinate and the methane isotope value as the horizontal coordinate, if the plot is located on the left side of the straight line y=ax+b, the target natural gas reservoir is an oil-type gas reservoir, if the plot is located on the right side of the straight line y=ax+b, the target natural gas reservoir is a coal-type gas reservoir; in the straight line y=ax+b, -1.10≤a≤-0.90, -31.0≤b≤-30.0; or plotting the ethane-methane carbon isotope difference and the methane isotope value of the target non-mixed natural gas reservoir on a discrimination chart of non-mixed natural gas reservoir types to determine the type of the natural gas reservoir; The discrimination chart is established by the following method: 1) providing a plurality of natural gas samples; the carbon isotopes in each natural gas sample in the plurality of natural gas samples all show that the methane carbon isotope value is less than the ethane carbon isotope value which is less than the propane carbon isotope value; 2) performing geological analysis on the collected gas reservoirs of each natural gas sample to determine the types of the collected gas reservoirs of each natural gas sample; 2) geological analysis of the gas reservoirs from which each natural gas sample was collected, to identify the type of gas reservoir from which each natural gas sample was collected; 3) based on the ethane-methane isotopic difference and the methane isotopic value of the natural gas samples, point analysis of the gas reservoirs from which each natural gas sample was collected, determination of the coal-derived gas reservoir and oil-type gas reservoir interval range according to the type of gas reservoir from which each natural gas sample was identified in step 2), demarcation of the boundary between the coal-derived gas reservoir and the oil-type gas reservoir, and establishment of a discrimination chart for non-mixed natural gas reservoirs.

5. The method of identifying non-mixed natural gas reservoirs as claimed in claim 4, wherein: The plurality of natural gas samples are collected from natural gas reservoirs in a rift basin, a cratonic basin and a foreland basin, and the occurrence strata of the gas reservoirs from which the plurality of natural gas samples were collected include carbonate strata and clastic rock strata.

6. A method of constructing a discrimination chart for non-mixed natural gas reservoir types, characterized by: The method comprises the following steps: 1) providing a plurality of natural gas samples; the carbon isotopes in each natural gas sample in the plurality of natural gas samples all exhibit a methane carbon isotope value < ethane carbon isotope value < propane carbon isotope value; 2) geological analysis of the gas reservoirs from which each natural gas sample was collected, to identify the type of gas reservoir from which each natural gas sample was collected; 3) based on the ethane-methane isotopic difference and the methane isotopic value of the natural gas samples, point analysis of the gas reservoirs from which each natural gas sample was collected, determination of the coal-derived gas reservoir and oil-type gas reservoir interval range according to the type of gas reservoir from which each natural gas sample was identified in step 2), demarcation of the boundary between the coal-derived gas reservoir and the oil-type gas reservoir, and establishment of a discrimination chart for non-mixed natural gas reservoirs.

7. The method for constructing a discrimination chart for non-mixed natural gas reservoir types according to claim 6, characterized in that: The plurality of natural gas samples are collected from natural gas reservoirs in a rift basin, a cratonic basin and a foreland basin, and the occurrence strata of the gas reservoirs from which the plurality of natural gas samples were collected include carbonate strata and clastic rock strata.

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