A method for determining the maximum burial temperature of a formation using carbonate rock cluster isotopes

Abstract

The present invention discloses a method for determining the maximum burial temperature of a formation by using carbonate clumped isotopes. The method provided by the present invention comprises the following steps: collecting formation samples and petrological analysis; testing the carbonate clumped isotope Δ47 of the samples; calculating the clumped isotope temperature T of the samples Δ47 ; preliminarily estimating the range of the maximum burial temperature of the formation where the samples are located; and according to the preliminary estimation result, selecting a solid-state reset model to determine the maximum burial temperature of the formation. The present invention solves the problem that it is difficult to accurately determine the maximum burial temperature for ancient marine carbonate rock formations due to the lack of vitrinite or zircon, reduces the result error, clarifies the applicable scope of the method, improves the feasibility, and has very important significance for the evolution of the organic matter maturity of source rocks and the evaluation of oil and gas resources in this formation series.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum geological exploration, and in particular relates to a method for determining the maximum burial temperature of a formation by utilizing carbonate rock cluster isotopes. Background Art

[0002] The maximum burial temperature refers to the highest temperature reached by a stratum during its geological history. The maximum burial temperature is of great significance to geological research and resource development. It not only helps to understand the thermal history of the stratum, but also has a direct impact on resource utilization such as oil and gas development.

[0003] At present, the commonly used methods for determining the maximum burial temperature of strata include the organic paleotherm method and the mineral paleotherm method. The organic paleotherm method characterizes the degree of thermal evolution of organic matter through vitrinite reflectance, and uses a specific organic matter evolution model (such as the Easy%Ro model) to determine the maximum burial temperature based on the current vitrinite reflectance. However, this method can only determine the maximum burial temperature range and cannot obtain the specific temperature value; for ancient marine strata where vitrinite is not developed, the equivalent vitrinite reflectance can be calculated through the asphalt reflectance and the graptolite reflectance, and then the maximum burial temperature range can be obtained, but the two methods are very different and have different applicable ranges, and the accuracy is low.

[0004] The mineral paleotherm method mainly relies on the fission track of minerals and (U-Th) / He thermochronology to determine the temperature evolution. The annealing kinetic model of apatite fission track is only applicable to low-temperature strata below 125°C, while for strata above 150°C, only zircon fission track can be used, but a unified annealing kinetic model has not yet been established. The (U-Th) / He method of zircon can determine the corresponding temperature and time, but in ancient marine strata, detrital zircons are usually difficult to obtain, which limits the application of this method and makes it less feasible. It can be seen that both the organic matter paleotherm method and the mineral paleotherm method have certain limitations in determining the maximum burial temperature of ancient marine strata.

[0005] For basins that have been subsiding, the maximum burial temperature of the strata is the current stratum temperature; while for basins that subsided early and were uplifted late, the maximum burial temperature of the ancient strata is often difficult to determine. Taking the Sichuan Basin as an example, Li Pingping et al. studied whether Δ47 can be used to reconstruct the maximum burial temperature (MBT) of ancient carbonate strata that lack vitrinite and detrital zircon data; they also proposed that different types of carbonate samples should be used to reconstruct the MBT of strata that have experienced different temperature histories, and that micrite limestone and micrite dolomite can be used to reconstruct the MBT of strata that have experienced <150-200℃ and >200-250℃, respectively. However, this method still has problems such as unclear scope of application, poor applicability of the method due to unclear scope of application of calcite and dolomite, and relatively large errors in the results of the maximum burial temperature determined.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for determining the maximum burial temperature of a formation using carbonate rock cluster isotopes, which can solve the above-mentioned problems existing in the current methods for determining the maximum burial temperature of ancient formations.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a method for determining the maximum burial temperature of a formation using carbonate rock cluster isotopes, comprising the following steps:

[0010] S1. Collection of stratigraphic samples and petrological analysis;

[0011] S2. Testing the carbonate cluster isotope Δ47 of the sample;

[0012] S3. Calculate the cluster isotope temperature T of the sample Δ47 ;

[0013] S4. Preliminarily estimate the maximum burial temperature range of the stratum where the sample is located;

[0014] S5. Based on the preliminary estimation results, a solid state reset model is selected to determine the maximum burial temperature of the formation.

[0015] Based on the cluster isotope temperature of carbonate rocks, the present invention proposes a method for determining the maximum burial temperature of ancient strata by preliminarily estimating the maximum burial temperature range of ancient strata and then selecting a suitable solid-state reset model. Compared with the prior art, the present invention clarifies the scope of application of this method for determining the maximum burial temperature of ancient strata based on cluster isotopes of carbonate rocks, which is more feasible and has correspondingly improved accuracy.

[0016] In the present invention, in step S1, the sample collection standard is: select samples with uniform lithology and no obvious calcite cement or other veins.

[0017] In the present invention, in step S1, the petrological analysis is performed according to the following operations: the sample is made into a common rock thin section and a cathode luminescence thin section, and a microscope and a cathode ray luminometer are used to screen out qualified samples;

[0018] The screening criteria for qualified samples are: particle size less than 50 μm, no obvious luminescence under a cathode luminescence microscope. Generally, samples that meet this condition are considered to have not undergone significant diagenetic alteration.

[0019] In the present invention, in step S2, the test is performed according to the following operations:

[0020] (1) crushing the sample to obtain sample powder;

[0021] (2) extracting the sample powder with dichloromethane, and then adding hydrogen peroxide to remove impurities;

[0022] (3) reacting the sample obtained by removing impurities in step (2) with phosphoric acid in an acid bath to generate CO2, and then proceeding to the next step immediately;

[0023] (4) The abundance of CO2 molecules was measured using a MAT253 gas source isotope mass spectrometer, and the carbonate cluster isotope Δ47 of the sample was calculated.

[0024] In the present invention, in step (1), the particle size of the powder is 100 μm.

[0025] In the present invention, the extraction time is 24 hours; the mass fraction of the hydrogen peroxide is 3%.

[0026] In the present invention, in step (3), the mass fraction of the phosphoric acid is 103%; and the temperature of the acid bath reaction is 90°C.

[0027] In step S2 of the present invention, impurities in the sample are removed by dichloromethane extraction and hydrogen peroxide, and then the sample is reacted with phosphoric acid in an acid bath, and the generated CO2 should be immediately tested for abundance.

[0028] In the present invention, by optimizing the screening conditions and pre-processing operations of the above samples, the result error can be reduced and the accuracy of the method can be improved.

[0029] In the present invention, in step S3, the cluster isotope temperature T of the sample Δ47 The calculation formula is as follows:

[0030] Δ47 (I-CDES90℃) =0.0391±0.0004×10 6 ×T Δ47 -2 +0.154±0.004(r 2 =0.97);

[0031] Among them, Δ47 I-CDES90℃ International standard reference system representing Δ47, T Δ47 Delegates cluster isotope temperature.

[0032] In the present invention, in step S4, the preliminary estimation is performed according to the following operations:

[0033] If shale is developed in the same layer system of the stratum, the vitrinite reflectance Ro value of the shale stratum sample of the same layer system of the stratum is measured, and the maximum burial temperature range of the stratum is preliminarily estimated according to the Ro value;

[0034] If shale is not developed in the same layer of the formation, the cluster isotope temperature T of calcite or dolomite is used. Δ47 Preliminary estimate of the maximum burial temperature range of the formation.

[0035] For the case where shale is not developed in the same stratum of the formation: if the cluster isotope temperature of calcite T Δ47 The maximum burial temperature of the stratum is preliminarily estimated to be between 40 and 140 °C, and between 100 and 175 °C. Δ47 Between 80-200°C, a preliminary estimate of the maximum burial temperature range of the formation is 175-250°C.

[0036] In the present invention, in step S5, based on the preliminary estimated maximum burial temperature range, for the strata with an estimated temperature range of 100-250°C, combined with the cluster isotope temperature T Δ47 and a solid-state reset model to determine the maximum burial temperature of the formation.

[0037] Specifically, the solid-state reset model is selected according to the following situations:

[0038] The selection of the solid state reset model is performed as follows:

[0039] 1) It is estimated that the maximum burial temperature of the formation is between 100° C. and 175° C., and calcite or dolomite undergoes partial solid-state reset, and the solid-state reset model is a calcite solid-state reset model or a dolomite solid-state reset model;

[0040] 2) It is estimated that the maximum burial temperature of the formation is in the range of 175-250°C, and the calcite undergoes complete solid-state reset, and the solid-state reset model selects the dolomite solid-state reset model.

[0041] It should be noted that if the preliminary estimated temperature range is <100°C, it means that calcite and dolomite have not undergone solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention; if the preliminary estimated temperature range exceeds 250-300°C, calcite and dolomite have undergone complete solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention.

[0042] In the present invention, the solid-state reset model is a relationship model between the final equilibrium temperature and the maximum burial temperature; wherein the calcite solid-state reset model is the calcite solid-state reset model proposed by Stolper and Eiler in 2015; the dolomite solid-state reset model is the dolomite solid-state reset model proposed by Lloyd et al. in 2018.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention determines the maximum burial temperature of ancient marine carbonate strata based on cluster isotopes of carbonate rocks, reduces result errors and improves accuracy by screening and preprocessing samples, and clarifies the scope of application of the method and improves the feasibility of the method by estimating the maximum burial temperature range of the strata and selecting a solid-state reset model. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention provides a flow chart of the method for determining the maximum burial temperature.

[0046] Figure 2 is the cluster isotope temperature of dolomite and calcite in gas field B (T Δ47 ) evolution process, in which it is assumed that its maximum burial temperature is 220℃, which then drops to 110℃, and FAT = final equilibrium temperature.

[0047] Figure 3 Figure 3 is the relationship between the final equilibrium temperature (FAT) and the maximum burial temperature of the limestone in area A, assuming that calcite crystallizes at 20°C.

[0048] Figure 4 Figure 2 shows the relationship between the final equilibrium temperature (FAT) and the maximum burial temperature of dolomite in gas fields B and C, where it is assumed that dolomite crystallizes at 30°C. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0050] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0051] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0052] The phosphoric acid used in the following examples is super-concentrated phosphoric acid with a mass fraction of 103%. The reference source for the preparation method of the super-concentrated phosphoric acid is: Wacker et al., 2013, Clumped isotope analysis of carbonates: comparison of two different acid digestion technique.

[0053] Example: Determination of the maximum burial temperature of ancient marine carbonate rock formations

[0054] like Figure 1 The specific steps are as follows:

[0055] S1. Collect carbonate rock samples from carbonate rock formations and shale formation samples from the same formation, conduct petrological analysis, and screen out qualified samples;

[0056] Collect limestone samples from area A, dolomite samples from gas field B, and dolomite samples from gas field C, select samples with relatively uniform lithology and no obvious calcite cement or other veins, prepare ordinary rock thin sections and cathode luminescence thin sections from them, observe them using a microscope and a cathode luminescence instrument, and screen out rock samples that have not undergone significant rock alteration (generally, if the particle size is less than 50μm and there is no obvious luminescence under a cathode luminescence microscope, it is considered that no significant diagenetic alteration has occurred);

[0057] Screening results: The micritic limestone sample L1 from area A, the micritic dolomite sample D1 from gas field B, and the micritic dolomite sample D2 from gas field C were used as carbonate rock samples, and their shale samples from the same strata for subsequent experiments.

[0058] S2. Performing carbonate cluster isotope (Δ47) testing on the carbonate rock sample screened in step S1. The specific steps are as follows:

[0059] (1) grinding the screened carbonate rock sample into powder in a crucible to 100 μm to obtain carbonate rock sample powder;

[0060] (2) extracting the carbonate rock sample powder obtained in step (1) with dichloromethane for 24 hours, and then reacting the carbonate rock sample with 3% hydrogen peroxide (H2O2) to remove organic matter in the carbonate rock sample;

[0061] (3) taking 10 mg of the carbonate rock sample treated in step (2), and conducting an acid bath reaction with 103% super-concentrated phosphoric acid in an automatic acid bath device at a reaction temperature of 90° C. to generate CO2;

[0062] (4) Using the MAT253 gas-source isotope mass spectrometer, the abundance of CO2 molecules was measured, and then the carbonate cluster isotope Δ47 of the carbonate rock samples was calculated; each carbonate rock sample was tested more than twice, and the error of Δ47 obtained from a single test was within 0.02‰;

[0063] S3. Calculate the cluster isotope temperature T of carbonate rock samples using the temperature calibration equation Δ47 ;

[0064] The temperature calibration equation is as follows:

[0065] Δ47 (I-CDES90℃) =0.0391±0.0004×10 6 ×T Δ47 -2 +0.154±0.004(r2 =0.97):

[0066] Among them, Δ47 I-CDES90℃ International standard reference system representing Δ47, T Δ47 Delegates cluster isotope temperature.

[0067] The calculation results are shown in Table 1.

[0068] Table 1 Δ47 and T of carbonate rock samples in area A and gas fields B and C Δ47

[0069] area Carbonate rock sample name Δ47CDES.‰ <![CDATA[T Δ47 ,℃]]> Region A L1 0.499±0.004 63.5 B Gas Field D1 0.449±：0.009 90.9 C gas field D2 0.382±0.007 141.0

[0070] Figure 2 This is the relationship between the formation temperature of gas field B and the isotopic temperature of calcite and dolomite clusters over time, and also shows the difference in the applicable temperatures of calcite and dolomite.

[0071] S4. Preliminary estimate of the range of maximum burial temperature of carbonate formations;

[0072] If shale is developed in the same layer system of the stratum, the vitrinite reflectance Ro value of the shale stratum sample of the same layer system of the stratum is measured, and the maximum burial temperature range of the stratum is preliminarily estimated according to the Ro value;

[0073] If shale is not developed in the same layer of the formation, the cluster isotope temperature T of calcite or dolomite is used. Δ47 Preliminary estimate of the maximum burial temperature range of the stratum; if the calcite cluster isotope temperature T Δ47 The maximum burial temperature of the stratum is estimated to be between 40 and 140 °C, and the maximum burial temperature of the stratum is estimated to be between 100 and 175 °C. Δ47 Between 80-200°C, the maximum burial temperature range of the formation is estimated to be 175-250°C.

[0074] The specific estimation results are as follows:

[0075] Samples from region A: Cluster isotope temperature T of limestone (L1) in this region Δ47 It is 63.5℃, and the vitrinite reflectance Ro value of the shale formation samples in the same layer is calculated to be 0.92-0.96%. According to the Ro value, it is calculated that the maximum burial temperature of the carbonate rock formation in area A is in the range of 132-140℃.

[0076] B gas field sample: Cluster isotope temperature T of the micrite dolomite (D1) in the area Δ47The vitrinite reflectance Ro value of the shale formation samples in the same layer is calculated to be 2.39-3.11%. According to the Ro value, the maximum burial temperature range of the carbonate formation in the B gas field is calculated to be 207-232°C.

[0077] C gas field sample: Shale is not developed in the same layer in this area. The cluster isotope temperature of dolomite (D2) is T Δ47 It is 141.0℃. According to the solid-state reset model of dolomite, it can be directly estimated that the maximum burial temperature of the C gas field formation ranges from 175-250℃.

[0078] S5. According to the preliminary estimated maximum burial temperature range, for the strata with an estimated temperature range between 100-250°C, determine the maximum burial temperature of the strata; the specific operations are:

[0079] (1) If the preliminary estimated temperature range is <100°C, it means that calcite and dolomite have not undergone solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention;

[0080] (2) It is preliminarily estimated that the temperature range is between 100-175° C., and calcite or dolomite undergoes partial solid-state reset, and the solid-state reset model selects a calcite solid-state reset model or a dolomite solid-state reset model;

[0081] (3) It is preliminarily estimated that within the temperature range of 175-250° C., calcite undergoes complete solid-state reset and dolomite undergoes partial solid-state reset. The solid-state reset model is the dolomite solid-state reset model.

[0082] (4) It is preliminarily estimated that the temperature range exceeds 250-300°C, and the calcite and dolomite have undergone complete solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention.

[0083] The results are as follows:

[0084] Samples from area A: The maximum burial temperature of carbonate formations in area A ranges from 132 to 140°C, indicating that the calcite and dolomite in this area have undergone partial solid-state reset. The solid-state reset model of calcite or dolomite can be used to determine the maximum burial temperature of carbonate formations. Specifically, the cluster isotope temperature T of limestone (L1) in this area is Δ47 The temperature of the seawater during its deposition period was 20°C, so its initial formation temperature is 20°C. Based on the relationship model between the final equilibrium temperature of calcite and the maximum burial temperature, it can be determined that the maximum burial temperature of the limestone (L1) in area A is 148°C. Figure 3 shown.

[0085] B gas field samples: The maximum burial temperature of the carbonate formation in the B gas field ranges from 207 to 232 °C, indicating that the calcite in this area undergoes complete solid-state reset and the dolomite undergoes partial solid-state reset. Therefore, the maximum burial temperature of the carbonate formation can only be determined using the solid-state reset model of dolomite. Specifically, the cluster isotope temperature T of the micrite dolomite (D1) is Δ47 The temperature of seawater during its deposition period was 30°C, so its initial formation temperature was 30°C. Based on the relationship model between the final equilibrium temperature of dolomite and the maximum burial temperature, it can be determined that the maximum burial temperature of the micrite dolomite (D1) is 202°C. Figure 4 shown.

[0086] C gas field samples: The maximum burial temperature of the C gas field formation ranges from 175 to 250 °C, indicating that calcite undergoes complete solid-state reset and dolomite undergoes partial solid-state reset. Therefore, the maximum burial temperature of the carbonate formation can only be determined using the solid-state reset model of dolomite. Specifically, the cluster isotope temperature T of the micrite dolomite (D2) is Δ47 The temperature of seawater during its deposition period was 30°C, so its initial formation temperature was 30°C. Based on the relationship model between the final equilibrium temperature of dolomite and the maximum burial temperature, it can be determined that the maximum burial temperature of dolomite (D2) in the C gas field is 253°C. Figure 4 shown.

[0087] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for determining the maximum burial temperature of a formation using carbonate rock cluster isotopes, comprising the following steps: S1. Collection of stratigraphic samples and petrological analysis; S2. Testing the carbonate cluster isotope Δ47 of the sample; S3. Calculate the cluster isotope temperature T of the sample Δ47 ; S4. Preliminarily estimate the maximum burial temperature range of the stratum where the sample is located; S5. According to the preliminary estimation result, a solid state reset model is selected to determine the maximum burial temperature of the formation; Wherein, in step S4, the preliminary estimation is performed according to the following operations: If shale is developed in the same layer system of the stratum, the vitrinite reflectance Ro value of the shale stratum sample of the same layer system of the stratum is measured, and the maximum burial temperature range of the stratum is preliminarily estimated according to the Ro value; If shale is not developed in the same layer of the formation, the cluster isotope temperature T of calcite or dolomite is used. Δ47 Preliminary estimate of the maximum burial temperature range of the stratum; if the calcite cluster isotope temperature T Δ47 The maximum burial temperature of the stratum is estimated to be between 40 and 140 °C, and the maximum burial temperature of the stratum is estimated to be between 100 and 175 °C. Δ47 Between 80-200°C, the maximum burial temperature of the formation is estimated to be in the range of 175-250°C; Wherein, in step S5, the determination of the maximum burial temperature of the formation is performed according to the following operations: (1) If the preliminary estimated temperature range is <100°C, it means that calcite and dolomite have not undergone solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention; (2) It is preliminarily estimated that the temperature range is between 100-175°C, and calcite or dolomite undergoes partial solid-state reset, and the solid-state reset model is selected as the calcite solid-state reset model or the dolomite solid-state reset model; (3) It is preliminarily estimated that the temperature range is between 175-250°C, calcite undergoes complete solid-state reset, and dolomite undergoes partial solid-state reset. The solid-state reset model is the dolomite solid-state reset model; (4) It is preliminarily estimated that the temperature range exceeds 250-300°C, and calcite and dolomite have undergone complete solid-state reset, and the maximum burial temperature cannot be determined using the method described in the present invention.

2. The method according to claim 1, characterized in that In step S1, the sample collection standard is: select samples with uniform lithology and no obvious calcite cement or other veins; The petrological analysis is carried out according to the following operations: the samples are made into ordinary rock thin sections and cathode luminescence thin sections, and qualified samples are screened out using a microscope and a cathode ray luminometer; The screening criteria for the qualified samples are: particle size less than 50 μm and no obvious luminescence under a cathode luminescence microscope.

3. The method according to claim 1 or 2, characterized in that: In step S2, the test is performed according to the following operations: (1) crushing the sample to obtain sample powder; (2) extracting the sample powder with dichloromethane, and then adding hydrogen peroxide to remove impurities; (3) The sample obtained by removing impurities in step (2) is reacted with phosphoric acid in an acid bath to generate CO2, and the next step is immediately carried out; (4) The abundance of CO2 molecules was measured using the MAT253 gas source isotope mass spectrometer, and the carbonate cluster isotope Δ47 of the sample was calculated.

4. The method according to claim 3, characterized in that In step (1), the particle size of the powder is 100 μm; In step (2), the extraction time is 24 hours; the mass fraction of the hydrogen peroxide is 3%; In step (3), the mass fraction of the phosphoric acid is 103%; and the temperature of the acid bath reaction is 90°C.

5. The method according to claim 1, characterized in that In step S3, the cluster isotope temperature T Δ47 The calculation formula is as follows: Δ47 (I-CDES90℃) =0.0391±0.0004×10 6 ×T Δ47 -2 +0.154±0.004(r 2 =0.97); Among them, Δ47 (I-CDES90℃) International standard reference system representing Δ47, T Δ47 Delegates cluster isotope temperature.

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