A method for determining the type of source rock for crustal helium in a natural gas reservoir

Abstract

The present invention discloses a method for determining the source rock type of crust-derived helium in natural gas reservoirs, which belongs to the technical field of oil and gas associated helium exploration. A method for determining the source rock type of crust-derived helium in natural gas reservoirs comprises the following steps: S1, using 132 Xe / 36 Ar and 84 Kr / 36 Ar value is used as the identification parameter of the source rock type of crustal helium; S2, draw different types of rocks 132 Xe / 36 Ar~ 84 Kr / 36 Ar correlation diagram, statistics of basin basement and basin sedimentary cover 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar; S3, determine whether the helium in the natural gas sample is of crustal origin; S4, under the premise of determining that the helium in the natural gas reservoir is of crustal origin, calculate the sample 132 Xe / 36 Ar and 84 Kr / 36 Ar value, statistics its distribution range, and project it onto the correlation diagram established in S2; S5, based on the projected position of the sample to be tested on the diagram in S4, or the comparison results of its distribution range with the distribution range of different types of rocks, determine the parent rock type of the sample helium, which can quickly determine whether the helium comes from the basement or sedimentary cover rock, and the judgment result is reliable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas associated helium exploration, and particularly relates to a method for determining the type of source rock of crustal helium in a natural gas reservoir. BACKGROUND

[0002] Helium is widely used in high-tech fields and is a strategic scarce resource that cannot be replaced. Currently, extracting helium from natural gas is the only means of industrial helium production. The helium in natural gas mainly has three sources: atmospheric source, crustal source and mantle source. The industrially exploitable helium resources mainly come from the radioactive decay of uranium and thorium in the earth's crust. Uranium and thorium elements are distributed in the three types of rocks that make up the earth's crust (sedimentary rocks, magmatic rocks and metamorphic rocks). Therefore, in the sedimentary basin where the natural gas reservoir is hosted, how to accurately identify whether the crustal helium in the natural gas reservoir comes from the basin basement rock (mainly magmatic rock and metamorphic rock) or the overlying sedimentary rock becomes a bottleneck restricting helium resource evaluation and exploration deployment.

[0003] Helium can be divided into three sources: atmospheric source, crustal source and mantle source. 3 He mainly comes from the degassing of the mantle, while 4 He mainly comes from the decay of radioactive elements. Currently, the method of 3 He / 4 He ratio is commonly used to determine whether the helium comes from the earth's crust or the mantle. However, for crustal helium, it is still unclear which type of source rock it comes from (igneous rock, metamorphic rock or sedimentary rock). 3 He / 4 He (R) and the ratio of 3 He / 4 He (Ra) in the atmosphere to determine whether the helium comes from the earth's crust or the mantle. However, for crustal helium, it is still unclear which type of source rock it comes from (igneous rock, metamorphic rock or sedimentary rock).

[0004] Regarding the specific source of crustal helium, the following techniques have been proposed in existing methods: a method for determining whether basement granite contributes to the helium source of a helium-rich natural gas reservoir is disclosed in document CN115356463A, which includes: collecting representative reservoir rocks, underlying sedimentary layers and helium-rich natural gas samples in the study area; determining the helium production of the reservoir rocks and underlying sedimentary layers; determining the average concentration of helium in the helium-rich natural gas sample to obtain the content of helium in the helium-rich natural gas reservoir; comparing the helium production of the reservoir rocks and underlying sedimentary layers with the content of helium in the helium-rich natural gas reservoir to determine whether the basement granite contributes to the helium source of the helium-rich natural gas reservoir: 1) if 4 He 生 ≥ 4 He 藏 , it indicates that the basement granite has limited contribution to the helium source of the helium-rich natural gas reservoir; 2) if 4 He 生 , it indicates that the basement granite has a certain contribution to the helium source of the helium-rich natural gas reservoir.4 He 藏 , indicating that the basement granite contributes significantly to the helium source of the helium-rich natural gas reservoir. For example, the document with publication number CN116071191A discloses a method for quantitatively characterizing the contribution of helium source rocks in stable cratonic basin helium-rich gas fields, which comprises: obtaining a stable cratonic basin helium-rich gas field to be quantitatively characterized for contribution, as a first natural gas field, collecting natural gas samples, obtaining helium content and average helium content in different zone natural gas samples; calculating the helium geological reserves of each zone to obtain the total helium resources of the first natural gas field; obtaining the uranium and thorium element concentrations of the rocks in the sedimentary helium source rock layer section; calculating the helium release yield of each sub-layer section; obtaining the helium contribution of the sedimentary helium source rock layer section and the basement granite in the first natural gas field.

[0005] Both of the above-mentioned documents judge the contribution of the basement and the sedimentary cover to the source of the formed helium gas from the perspective of the helium generation amount and release amount of each set of helium source rocks, but both of them ignore the fact that the helium released by the helium source rocks may not all be stored, so the calculation method itself has defects, and the results have multiple solutions. SUMMARY

[0006] To solve the foregoing problems, the present application provides a method for determining the type of crustal helium source rock in a natural gas reservoir, which can quickly determine whether the helium is derived from the basement or the sedimentary cover rock, and does not have the multiple solution problem in the foregoing background art.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A method for determining the type of crustal helium source rock in a natural gas reservoir, comprising the following steps:

[0009] S1, using 132 Xe / 36 Ar and 84 Kr / 36 Ar values as identification parameters for the type of crustal helium source rock;

[0010] S2, testing the abundance of rare gases and isotope data of the released gas at high temperature of different types of rocks, drawing a correlation diagram of different types of rocks 132 Xe / 36 Ar ~ 84 Kr / 36 Ar, and counting the distribution range of 132 Xe / 36 Ar and 84 Kr / 36 Ar of the basin basement and the basin sedimentary cover;

[0011] S3, detecting the noble gas abundance and isotopic composition of the natural gas sample to be tested, and determining whether the helium in the natural gas sample to be tested is crustal helium according to the 3 He / 4 He value.

[0012] S4, under the premise that the helium in the natural gas reservoir is crustal helium, calculating the values of 132 Xe / 36 Ar and 84 Kr / 36 Ar of the natural gas sample to be tested obtained in step S3, and determining the distribution range thereof, and then plotting the values on the correlation diagram of different rock types 132 Xe / 36 Ar ~ 84 Kr / 36 Ar established in step S2.

[0013] S5, determining the rock type of the crustal helium source in the natural gas reservoir according to the plotting position of the natural gas sample to be tested on the 132 Xe / 36 Ar and 84 Kr / 36 Ar diagram, or the comparison result of the distribution range thereof with the distribution range of different types of rocks.

[0014] Further, in step S1, the values of 132 Xe / 36 Ar and 84 Kr / 36 Ar are used as the basis for identifying the rock type of the crustal helium source because the air-derived noble gases including 20 Ne, 36 Ar, 84 Kr and 132 Xe are not affected by the crustal radiogenic or mantle-derived noble gases, and the helium in the natural gas reservoir has similar migration and accumulation processes with the air-derived noble gases.

[0015] Further, in step S2, the different types of rocks include magmatic rocks, metamorphic rocks and sedimentary rocks.

[0016] Further, in step S2, the basin basement is a crystalline basement or a folded basement with magmatic rocks and metamorphic rocks as the main rock types.

[0017] Further, in step S2, the basin sedimentary cover is a sedimentary formation with sedimentary rocks as the main rock type.

[0018] Further, in step S2, the 132 Xe / 36 Ar ~ 84 Kr / 36Ar correlation diagram, and two types of rock 132 Xe 36 Ar and 84 Kr 36 The distribution range of Ar is gradually accurate with the increase of measured samples.

[0019] Further, in step S3, when 3 He 4 The ratio of He is n *10 -9 ~ n *10 -8 When the ratio of He is of the order of magnitude, the helium is considered to be of crustal origin.

[0020] Further, in step S5, the method for determining the parent rock type of crustal helium in a natural gas reservoir is:

[0021] a. If the natural gas sample falls within the range of basin basement granite and metamorphic rock in the diagram, or within the numerical distribution range of the statistically obtained basin basement, it indicates that the crustal helium in the natural gas comes from the basin basement granite and / or metamorphic rock;

[0022] b. If the natural gas sample falls within the range of sedimentary rock in the diagram, or within the numerical distribution range of the statistically obtained basin sedimentary cover, it indicates that the crustal helium in the natural gas comes from the overlying sedimentary rock of the basement.

[0023] The beneficial effects of the technical solution are as follows:

[0024] First, in the present application, a method for determining the parent rock type of crustal helium in a natural gas reservoir is proposed to fill the blank of direct identification method for fine source of crustal helium in a natural gas reservoir, which provides the basis for helium source rock for helium exploration and resource exploration in oil and gas basins in China.

[0025] Secondly, in the present application, a new method is proposed for directly using rare gas isotopes 132 Xe 36 Ar, 84 Kr 36 Ar in natural gas to determine whether the helium comes from the basin basement or the sedimentary cover, which is more direct, more convenient to operate and more reliable than the existing geological analysis method.

[0026] Thirdly, in the present application, the helium in the Weiyuan gas field in Sichuan Basin is determined to come from the basin basement granite by using the identification method, which is consistent with the conclusion obtained by predecessors based on geochemistry and geological analysis, and it can be seen that the method can be mutually corroborated with the understanding of geological elements of natural gas accumulation in the research area, and provides the basis for identification of helium source in oil and gas basins. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Flowchart of the present invention.

[0028] Figure 2 This is the identification diagram of the helium source rock type in the Weiyuan gas field in the Sichuan Basin in Example 1. DETAILED DESCRIPTION

[0029] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment proposes a method for determining the source rock type of crust-derived helium in natural gas reservoirs, which belongs to the field of oil and gas associated helium exploration technology. This method fills the gap in the direct identification method of the fine source of crust-derived helium in natural gas reservoirs. Figure 1 , the method specifically comprises the following steps:

[0032] (1) Based on the rare gases from air ( 20 Ne, 36 Ar, 84 Kr and 132 The characteristics of Xe) that are not affected by crustal radiogenic or mantle-derived noble gases, and the similar migration and accumulation processes of helium in natural gas reservoirs and air-derived noble gases, determine 132 Xe / 36 Ar and 84 Kr / 36 The Ar value can be used as a parameter to identify the source rock type of crustal helium;

[0033] (2) Test the abundance and isotope data of rare gases released by different types of rocks (igneous rocks, metamorphic rocks and sedimentary rocks) at high temperatures, and draw the 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation diagram, and statistical analysis of the basin basement (mainly igneous rocks and metamorphic rocks) and the basin sedimentary cover (mainly sedimentary rocks) 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar;

[0034] (3) Detect the abundance and isotopic composition of the rare gas in the natural gas sample to be tested, based on 3 He / 4He determines whether the helium is of crustal origin. 3 He / 4 The ratio of He is n *10 -9 ~ n *10 -8 When the order of magnitude is , it is believed that the source of the helium is the crust;

[0035] (4) Under the premise that the helium in the natural gas reservoir is of shell origin, calculate the helium of the natural gas sample obtained in step (3). 132 Xe / 36 Ar and 84 Kr / 36 The value of Ar, its distribution range, and the projection points to the different rock types established by step (2) 132 Xe / 36 Ar ~ 84 Kr / 36 On the Ar correlation graph;

[0036] (5) According to the natural gas sample to be tested 132 Xe / 36 Ar and 84 Kr / 36 The location of the point on the Ar map, or the comparison of its distribution range with the distribution range of different types of rocks, can determine the parent rock type of the crust-derived helium in the natural gas reservoir:

[0037] ① If the natural gas sample falls within the range of basin basement granite and metamorphic rocks in the figure, or within the numerical distribution range of the basin basement obtained statistically, it indicates that the crust-derived helium in the natural gas comes from the basin basement granite and / or metamorphic rocks;

[0038] ② If the natural gas sample falls within the variation range of sedimentary rocks in the figure, or within the numerical distribution range of the basin sedimentary cover obtained statistically, it indicates that the crust-derived helium in the natural gas comes from the sedimentary rocks overlying the basement.

[0039] The method of determining the source rock type of crustal helium in natural gas reservoirs in the present invention avoids judging the contribution of the basement and sedimentary cover to the accumulated helium from the perspective of the helium generation and release of the source rock. Therefore, the ambiguity caused by the problem that not all the helium released by the source rock is accumulated will not occur. This scheme combines the use of specific rare gas isotope indicators to directly determine whether the helium comes from the basement or the sedimentary cover rock. The method is simple, easy to judge, and the results are reliable.

[0040] With the development of oil and gas exploration technology in China, it is necessary to distinguish the crustal helium in natural gas reservoir more accurately. The method provided by the application fills the blank of the direct identification method for the fine source of the crustal helium in natural gas reservoir, and provides the basis of helium source rock for the helium exploration and resource evaluation work of the oil and gas bearing basin in China.

[0041] Taking the Weiyuan gas field in Sichuan Basin as an example, the method for determining the parent rock type of the crustal helium in natural gas reservoir is further illustrated. Seven natural gas samples of Sinian Dengying Formation, Cambrian Longwangmiao and Xixiangchi Formations and Ordovician in the Weiyuan gas field are selected to identify the parent rock type of the helium therein.

[0042] The identification result shows that the seven samples all fall within the range of granite and metamorphic rock, see Figure 2 It is shown from Figure 2 that the helium in the natural gas of the Weiyuan gas field is derived from the basin basement. This is consistent with the previous understanding, which proves that the method can be implemented, and further demonstrates that the helium in the natural gas of the Weiyuan gas field is derived from the basin basement.

Claims

1. A method of determining the type of source rock for crustal helium in a natural gas reservoir, characterized by, The method comprises the following steps: S1, adopt 132 Xe / 36 Ar and 84 Kr / 36 Ar values as a parameter for identifying the type of helium parent rock source S2, test the noble gas abundance and isotope data of different types of rocks in the outgassing of gas at high temperature, draw different types of rocks 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation diagram, and statistics of the distribution range of 132 Xe / 36 Ar and 84 Kr / 36 Ar of the basin basement and the basin sedimentary cover; S3, detecting the noble gas abundance and isotopic composition of the natural gas sample to be tested, according to 3 He / 4 He judging whether the helium is of crustal origin; S4、in the premise of determining that helium in the natural gas reservoir is crustal source, calculating the values of Xe / 4He, 40Ar / 36Ar and 130Xe / 4He of the natural gas sample to be measured obtained from step S3, counting the distribution range of the values, and projecting points to the correlation graph of different rock types established by step S2; 132 Xe / 36 Ar and 84 Kr / 36 Ar; counting the distribution range of the values, and projecting points to the correlation graph of different rock types established by step S2; 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation graph; S5、According to the position of the sample on the Ar-Kr 132 Xe / 36 Ar and 84 Kr / 36 The position of the sample on the Ar-Kr diagram, or the comparison of the distribution range of the sample with the distribution range of different types of rocks, determines the source rock type of the crust-derived helium in the natural gas reservoir.

2. The method of determining the type of source rock for helium in a natural gas reservoir according to claim 1, wherein: In step S1, the Ar value is used as a parameter for identifying the type of the crustal source helium parent rock 132 Xe 36 Ar and 84 Kr 36 The basis for using the Ar value as a parameter for identifying the type of the crustal source helium parent rock is that the air-derived rare gases, including 20 Ne, 36 Ar, 84 Kr and 132 Xe, are not affected by the crustal source radiogenic or mantle source rare gases, and the helium in natural gas reservoirs has similar migration and accumulation processes as the air-derived rare gases.

3. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein: In step S2, the different types of rocks include magmatic rocks, metamorphic rocks and sedimentary rocks.

4. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein: In step S2, the basin basement is a crystalline basement or a folded basement with magmatic rocks and metamorphic rocks as the main rock types.

5. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein: In step S2, the basin sedimentary cover is a sedimentary formation with sedimentary rocks as the main rock type.

6. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein, In step S2, the 132 Xe / 36 Ar 84 Kr / 36 Ar correlation diagram, and the distribution range of the two major rock types 132 Xe / 36 Ar and 84 Kr / 36 Ar gradually become more accurate with the increasing of measured samples.

7. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein, In step S3, when 3 He 4 He is in the ratio of n *10 -9 ~ n *10 -8 orders of magnitude, the helium is considered to be of crustal origin.

8. The method of determining the type of source rock for helium in a natural gas reservoir of claim 1, wherein, In step S5, the method for determining the parent rock type of the crustal helium in the natural gas reservoir is: a. If the natural gas sample falls within the range of the basin basement granite and metamorphic rock in the figure, or within the numerical distribution range of the statistically obtained basin basement, it indicates that the crustal helium in the natural gas comes from the basin basement granite and / or metamorphic rock; b. If the natural gas sample falls within the range of the sedimentary rock in the figure, or within the numerical distribution range of the statistically obtained basin sedimentary cover, it indicates that the crustal helium in the natural gas comes from the overlying sedimentary rock of the basement.

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