Method for determining shell source helium mother source rock type in natural gas reservoir

Abstract

The invention discloses a method for determining a shell source helium mother source rock type in a natural gas reservoir, and belongs to the technical field of oil and gas associated helium exploration. The invention discloses a method for determining a shell source helium mother source rock type in a natural gas reservoir. The method comprises the following steps: S1, adopting 132Xe / 36Ar and 84Kr / 36Ar values as identification parameters of the shell source helium mother source rock type; s2, drawing 132Xe / 36Ar-84Kr / 36Ar correlation diagrams of different types of rocks, and counting distribution ranges of 132Xe / 36Ar and 84Kr / 36Ar of a basin substrate and a basin deposition cover layer; s3, judging whether helium in the natural gas sample is a crustal source or not; s4, on the premise of determining helium in the natural gas reservoir as a shell source, calculating 132Xe / 36Ar and 84Kr / 36Ar values of the sample, counting the distribution range of the values, and projecting the values to the correlation graph established in S2; and S5, determining the maternal source rock type of the sample helium according to the plumbing position of the sample to be detected on the graph in the step S4 or the comparison result of the distribution range of the sample to be detected and the distribution range of different types of rocks, so that whether the helium is from the substrate or the sedimentary cover rock can be quickly judged, and the judgment result is reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas associated helium exploration, and in particular relates to a method for determining the parent rock type of crust-derived helium in a natural gas reservoir. Background Art

[0002] Helium is widely used in high-tech fields and is an irreplaceable strategic scarce resource. Currently, extracting helium from natural gas is the only industrial means of producing helium. Helium in natural gas mainly comes from three sources: atmosphere, crust and mantle. Industrially exploitable helium resources mainly come from the radioactive decay of uranium and thorium in the earth's crust. Uranium and thorium are distributed in the three major types of rocks that make up the earth's crust (sedimentary rocks, igneous rocks and metamorphic rocks). Therefore, in the sedimentary basins where natural gas reservoirs are located, how to accurately identify whether the crust-derived helium in the natural gas reservoirs comes from the basin basement rocks (mainly igneous rocks and metamorphic rocks) or the basin overlying sedimentary rocks has become a bottleneck restricting the evaluation and exploration of helium resources.

[0003] Helium can be divided into three sources: atmospheric source, crust source and mantle source. 3 He mainly comes from mantle degassing, while 4 He mainly comes from the decay of radioactive elements. 3 He / 4 What is the order of magnitude of the He ratio, or the sample's 3 He / 4 He (R) and atmospheric 3 He / 4 The ratio of He to Ra (R / Ra) is used to determine whether the helium comes from the crust or the mantle. However, there is no publicly reported result on which source rock (igneous rock, metamorphic rock or sedimentary rock) the crust-derived helium comes from.

[0004] Regarding the specific source of crustal helium, the following technologies are also proposed in existing methods: For example, the document with publication number CN115356463A discloses a method for judging whether basement granite supplies helium to helium-rich natural gas reservoirs, including: collecting representative reservoir rock, underlying sedimentary layer and helium-rich natural gas samples in the study area basin; measuring the helium generation of reservoir rock and underlying sedimentary layer; measuring the average concentration of helium in the helium-rich natural gas sample to obtain the helium content in the helium-rich natural gas reservoir; comparing the helium generation of reservoir rock and underlying sedimentary layer with the helium content in the helium-rich natural gas reservoir, that is, whether the basement granite contributes to the helium source of the helium-rich natural gas reservoir: 1) If 4 He 生 ≥ 4 He 藏 , indicating that the basement granite has limited contribution to the helium source of helium-rich natural gas reservoirs; 2) if 4 He 生 <4 He 藏 When the helium source of the basement granite is significantly contributed to the helium source of the helium-rich natural gas reservoir. For example, the document with the publication number CN116071191A discloses a quantitative characterization method for the contribution of helium source rocks in a stable craton basin helium-rich gas field, including: obtaining a stable craton basin helium-rich gas field to be quantitatively characterized as the first natural gas field, collecting natural gas samples, obtaining the helium content and the average helium content in the natural gas samples of different zones; calculating the geological reserves of helium in 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; calculating the helium release yield of each sub-layer; and obtaining the helium share contributed by the sedimentary helium source rock layer and the basement granite in the first natural gas field.

[0005] Both of the above-mentioned documents judge the contribution of the basement and sedimentary cover to the source of the accumulated helium from the perspective of the helium generation and release of each set of helium source rocks. However, both of them ignore the fact that not all the helium released by the helium source rocks will be accumulated. Therefore, the calculation method itself is flawed and the results are ambiguous. Summary of the invention

[0006] To solve the aforementioned problems, the present invention provides a method for determining the source rock type of crust-derived helium in natural gas reservoirs, which can quickly determine whether the helium comes from the basement or the sedimentary cover rock, and does not have the multi-solution problem in the aforementioned background technology.

[0007] The objective of the present invention is achieved through the following technical solutions: A method for determining the source rock type of crust-derived helium in a natural gas reservoir comprises the following steps: S1. Adoption 132 Xe / 36 Ar and 84 Kr / 36 Ar value is used as a parameter for identifying the type of rock source of crustal helium; S2. Test the abundance and isotope data of rare gases in gases released from different types of rocks at high temperatures, and draw the data of different types of rocks. 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation diagram, and statistics of basin basement and basin sedimentary cover 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar; S3. Detect the abundance and isotopic composition of the rare gas in the natural gas sample to be tested. 3 He / 4 He determines whether the helium is of crustal origin; S4, under the premise of determining that the helium in the natural gas reservoir is the shell source, calculate the helium of the natural gas sample to be tested obtained in step S3 132 Xe / 36 Ar and 84 Kr / 36 The value of Ar, its distribution range, and the point projection to the different rock types established in step S2 132 Xe / 36 Ar ~ 84 Kr / 36 On the Ar correlation graph; S5, according to the natural gas sample to be tested 132 Xe / 36 Ar and 84 Kr / 36 The location of the projection 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.

[0008] Further, in step S1, using 132 Xe / 36 Ar and 84 Kr / 36 The basis for using Ar value as a parameter for identifying the source rock type of crustal helium is: 20 Ne, 36 Ar, 84 Kr and 132 The characteristics of Xe's air-derived noble gases are not affected by crust-derived radiogenic or mantle-derived noble gases, and the helium in natural gas reservoirs has a similar migration and aggregation process as the air-derived noble gases.

[0009] Furthermore, in step S2, the different types of rocks include igneous rocks, metamorphic rocks and sedimentary rocks.

[0010] Furthermore, in step S2, the basin basement is a crystalline basement or a folded basement with igneous rocks and metamorphic rocks as the main rock types.

[0011] Furthermore, in step S2, the basin sedimentary cover is a sedimentary stratum with sedimentary rock as the main rock type.

[0012] Furthermore, in step S2, the basin basement and the sedimentary cover 132 Xe / 36 Ar~ 84 Kr / 36 Ar correlation diagram and two major rock types 132 Xe / 36 Ar and 84 Kr / 36The distribution range of Ar becomes more accurate as the number of measured samples increases.

[0013] Further, in step S3, when 3 He / 4 The ratio of He is n *10 -9 ~ n *10 -8 At this order of magnitude, it is believed that the source of the helium is the earth's crust.

[0014] Further, in step S5, the method for determining the parent rock type of the shell-derived helium in the natural gas reservoir is: a. 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 basin basement obtained by statistics, it indicates that the crust-derived helium in the natural gas comes from basin basement granite and / or metamorphic rocks; b. If the natural gas sample falls within the variation range of sedimentary rocks in the figure, or within the numerical distribution range of the sedimentary cover of the basin obtained statistically, it indicates that the crust-derived helium in the natural gas comes from the sedimentary rocks overlying the basement.

[0015] The beneficial effects of this technical solution are as follows: 1. In the present invention, in view of the lack of a method for directly identifying the precise source of crust-derived helium in natural gas reservoirs, a method for determining the parent rock type of crust-derived helium in natural gas reservoirs is proposed, which provides a helium source rock basis for helium exploration and resource exploration in my country's oil and gas basins.

[0016] Second, the present invention proposes a method of directly utilizing the noble gas isotopes in natural gas 132 Xe / 36 Ar, 84 Kr / 36 The new method of using Ar to determine whether the helium comes from the basin basement or the sedimentary cover is more direct, easier to operate and more reliable than the existing geological analysis methods.

[0017] 3. In the present invention, the identification method is used to determine that the helium in the Weiyuan gas field in the Sichuan Basin comes from the basin basement granite. This conclusion is consistent with the conclusions drawn by predecessors based on geochemical and geological analysis. It can be seen that this method can be mutually corroborated with the understanding of the geological elements of natural gas accumulation in the study area, and provide a basis for the identification of the source of helium in oil and gas basins. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the present invention.

[0019] 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

[0020] 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 protection scope of the present invention.

[0021] Example 1 This embodiment proposes a method for determining the parent rock type of crust-derived helium in a natural gas reservoir, which belongs to the technical field of oil and gas associated helium exploration. This method fills the gap in the direct identification method of the fine source of crust-derived helium in a natural gas reservoir. Figure 1 , the method specifically comprises the following steps: (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 aggregation 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 type of rock source of crustal helium; (2) Test the abundance and isotope data of the noble gases released by different types of rocks (igneous rocks, metamorphic rocks and sedimentary rocks) at high temperatures, and draw the data of the abundance and isotope of the noble gases released by different types of rocks. 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation diagram, and statistical analysis of the basin basement (magmatic rock and metamorphic rock as the main rock types) and the basin sedimentary cover (mainly sedimentary rock) 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar; (3) Detect the abundance and isotopic composition of the rare gas in the natural gas sample to be tested. 3 He / 4 He determines whether the helium is from the crust. 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 earth's crust; (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 point projection to the different rock types established in step (2) 132 Xe / 36 Ar ~ 84 Kr / 36 On the Ar correlation graph; (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: 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 basin basement obtained by statistics, it indicates that the crust-derived helium in the natural gas comes from basin basement granite and / or metamorphic rocks; 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.

[0022] The method for determining the source rock type of crust-derived helium in natural gas reservoirs in the present invention avoids judging the source contribution of the basement and sedimentary cover to the accumulated helium from the perspective of the helium generation and release of the helium source rock. Therefore, there will be no ambiguity caused by the problem that the helium released from the helium source rock is not fully accumulated. This scheme combines the use of specific rare gas isotope indicators to directly judge whether the helium comes from the basement or the sedimentary cover rock. The method is simple, easy to judge and the results are reliable.

[0023] With the development of oil and gas exploration technology in my country, it is necessary to identify the crustal helium in natural gas reservoirs more precisely and accurately. The method proposed in the present invention fills the gap in the direct identification method of the fine source of crustal helium in natural gas reservoirs, and provides a helium source rock basis for helium exploration and resource evaluation in oil and gas basins in my country.

[0024] Taking the Weiyuan gas field in the Sichuan Basin as an example, the method of determining the source rock type of crustal helium in natural gas reservoirs of the present invention is further explained. A total of 7 natural gas samples from the Sinian Dengying Formation, the Cambrian Longwangmiao Formation and the Xixiangchi Formation, and the Ordovician in the Weiyuan gas field were selected to identify the source rock type of helium.

[0025] The identification results show that all 7 samples fall into the range of granite and metamorphic rocks, see Figure 2 .Depend on Figure 2 This shows that the helium in the natural gas of Weiyuan gas field comes from the basin basement. This is consistent with the previous understanding. While proving that this method is feasible, it also further proves that the helium in the natural gas of Weiyuan gas field comes from the basin basement.

Claims

1. A method for determining the source rock type of crustal helium in a natural gas reservoir, characterized in that: The following steps are involved: S1. Adoption 132 Xe / 36 Ar and 84 Kr / 36 Ar value is used as a parameter for identifying the type of rock source of crustal helium; S2. Test the abundance and isotope data of rare gases in gases released from different types of rocks at high temperatures, and draw the data of different types of rocks. 132 Xe / 36 Ar ~ 84 Kr / 36 Ar correlation diagram, and statistics of basin basement and basin sedimentary cover 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar; S3. Detect the abundance and isotopic composition of the rare gas in the natural gas sample to be tested. 3 He / 4 He determines whether the helium is of crustal origin; S4, under the premise of determining that the helium in the natural gas reservoir is the shell source, calculate the helium of the natural gas sample to be tested obtained in step S3 132 Xe / 36 Ar and 84 Kr / 36 The value of Ar, its distribution range, and the point projection to the different rock types established in step S2 132 Xe / 36 Ar ~ 84 Kr / 36 On the Ar correlation graph; S5, according to the natural gas sample to be tested 132 Xe / 36 Ar and 84 Kr / 36 The location of the projection 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.

2. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S1, 132 Xe / 36 Ar and 84 Kr / 36 The basis for using Ar value as a parameter for identifying the source rock type of crustal helium is: 20 Ne, 36 Ar, 84 Kr and 132 The characteristics of Xe's air-derived noble gases are not affected by crust-derived radiogenic or mantle-derived noble gases, and the helium in natural gas reservoirs has a similar migration and aggregation process as the air-derived noble gases.

3. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S2, the different types of rocks include igneous rocks, metamorphic rocks and sedimentary rocks.

4. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S2, the basin basement is a crystalline basement or a folded basement with igneous rocks and metamorphic rocks as the main rock types.

5. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S2, the basin sedimentary cover is a sedimentary stratum with sedimentary rock as the main rock type.

6. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S2, the basin basement and sedimentary cover 132 Xe / 36 Ar~ 84 Kr / 36 Ar correlation diagram and two major rock types 132 Xe / 36 Ar and 84 Kr / 36 The distribution range of Ar becomes more accurate as the number of measured samples increases.

7. The method for determining the source rock type of crust-derived helium in a natural gas reservoir according to claim 1, characterized in that: In step S3, when 3 He / 4 The ratio of He is n *10 -9 ~ n *10 -8 At this order of magnitude, it is believed that the source of the helium is the earth's crust.

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

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