A method for evaluating the relative contribution of helium heat source under the influence of deep fluids based on the heat balance equation

Abstract

The present invention provides a method for evaluating the relative contribution of the heat source of helium under the influence of deep fluids based on the heat balance equation, which belongs to the technical field of helium source identification, migration mechanism, and reservoir formation process analysis. 3 The relative heat contribution of the mantle and crust to the basin geothermal system is calculated using He / enthalpy and heat balance equations, further improving the evaluation method for the relative contribution of helium to the heat source in the context of deep thermal fluid activity.

Description

Technical Field

[0001] The present invention relates to an evaluation method for the relative contribution of heat sources of helium under the background of deep thermal fluid activity, belonging to the technical field of helium genesis source identification, migration mechanism and reservoir formation process analysis. Background Art

[0002] Helium (He) is a unique and irreplaceable element. Its special physical and chemical properties make it have important application value in many fields such as military, industry, scientific research, etc. The special properties of helium, such as low reactivity, low boiling point and low density, make it an indispensable element in many fields.

[0003] The deep and large faults or diapir structures distributed in the oil and gas basins and the associated thermal fluid intrusion activities have opened up migration and accumulation channels for the migration and leakage of deep volatiles, which is conducive to the release and migration of helium. There is magmatic helium ( 3 He) component, 3 He / 4 He values ​​> 0.02Ra indicate that volatile substances come directly from the mantle or from degassed magma intruding into the crust. 3 He / 4 He distribution and R / Ra value (R=( 3 He / 4 He) sample; Ra=( 3 He / 4 He) air = 1.4 × 10 -6 ) as the basis for identifying the source of natural gas crust and mantle and their proportion. Since the mass transfer of helium from magma to fluid is geologically accompanied by heat transfer, it means that there is a direct transfer of heat and mass between the fluid and magma, so the relationship between helium and heat is often indirect. The continental geothermal system mainly has two types of heat sources: mantle and crust (radiogenic), each of which has specific 3 The He / enthalpy ratio can be used to analyze the relative contribution of helium heat sources. In a similar context, the driving heat mechanism and the relative contributions of magmatic heat and crustal heat to geothermal fields can also be predicted. There is currently no analysis method for the contribution of helium heat sources in China, and the heat sources in oil and gas basins will have an important impact on the formation of oil and natural gas in the basins, the geothermal background of the basins, and the restoration of burial history thermal history. In particular, in areas where there may be contributions from deep mantle heat, such as oil and gas basins with deep fault backgrounds, there is currently a lack of research on the thermal driving mechanism of helium in the context of deep thermal fluid activity, and the evaluation method has not been further improved. Summary of the invention

[0004] In view of the shortcomings of existing evaluation and analysis methods, in order to accurately identify the thermal contribution of mantle and crust to the geothermal system of a basin with a large fault background, the present invention provides an evaluation method for the relative contribution of mantle and crustal heat sources under the background of deep thermal fluid activity. Therefore, the present invention calculates the relative contribution of the two types of heat sources to the geothermal system of the basin based on the heat balance equation.

[0005] The technical solution of the present invention is as follows:

[0006] An evaluation method based on the relative contribution of mantle and crustal heat sources under the background of deep thermal fluid activity includes the following steps:

[0007] The first step is to conduct geological surveys to confirm the existence of deep channel communication generated by large faults in the study area, the development and evolution of mud diapirs, and the intrusion of thermal fluids;

[0008] The second step is to sample the reservoirs of typical wells in the study area and separate and purify them;

[0009] The third step is to test and analyze the obtained CO2, 3 He, 4 He content;

[0010] Step 4: Use formula (1) and the CO2 obtained from the test. 3 He concentration was calculated to obtain the samples at different depths. 3 He / enthalpy ratio, when expressed in dimensionless form, formula (1), i.e., φ = f / (RT), is divided into two parts, the ideal gas part φ° and the residual part φ r , so φ:

[0011]

[0012] In the formula, δ = ρ / ρ c , τ = T c / T; δ is the reduced density, τ is the reverse reduced temperature; ρ is the density under formation reservoir conditions, T is the temperature under formation reservoir conditions;

[0013] Step 5: The reference constants required by formula (1) are as follows:

[0014]

[0015] Where, T c is the critical temperature, ρ c is the critical density; the value of the specific gas constant R is given by the molar gas constant R m and the value of the molar mass M is derived;

[0016] Step 6. The equation for the dimensionless Helmholtz free energy φ° is obtained from the ideal gas state The specific isobaric heat capacity equation is obtained as follows:

[0017]

[0018] In the formula, the nonlinear least squares method is used to fit The coefficients b0 and b i and exponential β i ;make i is an integer from 1 to 5. The formula can be simplified; is the simplified coefficient, is the simplified exponent, which can be rearranged to get Formula 5;

[0019] Step 7: The residual part of the dimensionless Helmholtz free energy φ r The general form is as follows:

[0020]

[0021] In formula (6), d i ,t i , α i , β i , γ i and∈ i Parameters belonging to the 45 Gaussian bell-shaped terms; ψ is a special heat function, Δ is an arbitrary quantity difference function, and θ is an adjustable parameter function;

[0022] Step 8: Calculate the values ​​of the functions Δ, θ, and ψ of the relevant non-analytical terms:

[0023]

[0024] In formulas (7)-(9), A i , B i , C i , D i , a i , b i , β i are the introduced “internal” parameters, i.e. the parameters of non-analytical terms, which are included in the nonlinear fitting of the whole equation;

[0025] Step 9. Calculation formula of enthalpy:

[0026] h=u+pv (10)

[0027] Right now,

[0028] in,

[0029] h is the enthalpy value, u is the internal energy of the system, p is the external pressure, and v is the volume of the system. Yes ° Taking the first-order derivative with respect to τ, Yes r Taking the first-order derivative with respect to τ, Yes r Take the first derivative of δ;

[0030] Step 10: Assume that the mantle and crust are hot 3 The He / enthalpy ratios are 0.5×10 -12 cm 3 STp / J and 1×10 - 15 cm 3 STp / J, estimates of the thermal contributions of the mantle and crust to the basin geothermal system based on the heat balance equation;

[0031] ( 3 He / enthalpy) calculated =X M ( 3 He / enthalpy) mantle +(1-X M )( 3 He / enthalpy) crust (13)

[0032] Where, X M is the mantle heat fraction in the sample, ( 3 He / enthalpy) calculated It is calculated by formula (1) 3 He / enthalpy ratio, ( 3 He / enthalpy) mantle 、( 3 He / enthalpy) crust Represent the hot end elements of the mantle and crust, respectively 3 He / enthalpy ratio;

[0033] In the eleventh step, the calculated mantle heat fraction is the relative thermal contribution of the mantle to the basin geothermal system, and the remaining contribution of the basin geothermal system comes from the crust; the sum of the contributions of the two sources is 100%, and the calculated mantle heat fraction can refer to the mantle source contribution ratio, and the remaining percentage value refers to the crust source contribution ratio.

[0034] There are two major heat sources in oil and gas basins, namely the mantle source and the crust source. By analyzing the relative contribution of helium heat sources, it can assist in analyzing the thermal driving mechanism of helium in the presence of deep thermal fluid activities, which is conducive to finding helium-enriched areas.

[0035] The beneficial effects of the present invention are:

[0036] The present invention is obtained by combining the formula 1 3He / enthalpy and heat balance equations are used to estimate the relative thermal contributions of the mantle and crust to the basin geothermal system. 3 He / 4 The evaluation and analysis method of using He distribution and R / Ra value to determine the sources of natural gas in the crust and mantle and their proportions is more accurate, and further improves the evaluation method of the relative contribution of helium heat sources in the context of deep thermal fluid activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the histogram of mantle heat fraction for each sample;

[0038] Figure 2 This is the correlation diagram between the mantle heat fraction and the earth's heat flow value;

[0039] Figure 3 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0041] Embodiment 1:

[0042] An evaluation method based on the relative contribution of mantle and crustal heat sources under the background of deep thermal fluid activity includes the following steps:

[0043] The first step is to conduct geological surveys to confirm the existence of deep channel communication generated by large faults in the study area, the development and evolution of mud diapirs, and the intrusion of thermal fluids;

[0044] The second step is to sample the reservoirs of typical wells in the study area and separate and purify them;

[0045] The third step is to test and analyze the obtained CO2, 3 He, 4 He content;

[0046] Step 4: Use formula (1) and the CO2 obtained from the test. 3 He concentration was calculated to obtain the samples at different depths. 3 He / enthalpy ratio, when expressed in dimensionless form, formula (1), i.e., φ = f / (RT), is divided into two parts, the ideal gas part φ° and the residual part φ r , so φ:

[0047]

[0048] In the formula, δ = ρ / ρ c , τ = T c / T; δ is the reduced density, τ is the reverse reduced temperature; ρ is the density under formation reservoir conditions, T is the temperature under formation reservoir conditions;

[0049] Step 5: The reference constants required by formula (1) are as follows:

[0050]

[0051] Where, T c is the critical temperature, ρ c is the critical density; the value of the specific gas constant R is given by the molar gas constant R m and the value of the molar mass M is derived;

[0052] Step 6. The equation for the dimensionless Helmholtz free energy φ° is obtained from the ideal gas state The specific isobaric heat capacity equation is obtained as follows:

[0053]

[0054] In the formula, the nonlinear least squares method is used to fit The coefficients b0 and b i and exponential β i ;make i is an integer from 1 to 5. The formula can be simplified; is the simplified coefficient, is the simplified exponent, which can be rearranged to get Formula 5;

[0055] Step 7: The residual part of the dimensionless Helmholtz free energy φ r The general form is as follows:

[0056]

[0057] In formula (6), d i ,t i , α i , β i , γ i and∈ i Parameters belonging to the 45 Gaussian bell-shaped terms; ψ is a special heat function, Δ is an arbitrary quantity difference function, and θ is an adjustable parameter function;

[0058] Step 8: Calculate the values ​​of the functions Δ, θ, and ψ of the relevant non-analytical terms:

[0059]

[0060] In formulas (7)-(9), A i , B i , C i , D i , a i , b i , βi are the introduced “internal” parameters, i.e. the parameters of non-analytical terms, which are included in the nonlinear fitting of the whole equation;

[0061] Step 9. Calculation formula of enthalpy:

[0062] h=u+pv (10)

[0063] Right now,

[0064] in,

[0065] h is the enthalpy value, u is the internal energy of the system, p is the external pressure, and v is the volume of the system. is the first-order derivative of φ° with respect to τ, Yes r Taking the first-order derivative with respect to τ, Yes r Take the first derivative of δ;

[0066] Step 10: Assume that the mantle and crust are hot 3 The He / enthalpy ratios are 0.5×10 -12 cm 3 STp / J and 1×10 - 15 cm 3 STp / J, estimates of the thermal contributions of the mantle and crust to the basin geothermal system based on the heat balance equation;

[0067] ( 3 He / enthalpy) calculated =X M ( 3 He / enthalpy) mantle +(1-X M )( 3 He / enthalpy) crust (13)

[0068] Where, X M is the mantle heat fraction in the sample, ( 3 He / enthalpy) calculated It is calculated by formula (1) 3 He / enthalpy ratio, ( 3 He / enthalpy) mantle 、( 3 He / enthalpy) crust Represent the hot end elements of the mantle and crust, respectively 3 He / enthalpy ratio;

[0069] In the eleventh step, the calculated mantle heat fraction is the relative thermal contribution of the mantle to the basin geothermal system, and the remaining contribution of the basin geothermal system comes from the crust; the sum of the contributions of the two sources is 100%, and the calculated mantle heat fraction can refer to the mantle source contribution ratio, and the remaining percentage value refers to the crust source contribution ratio.

[0070] Experimental example

[0071] According to the steps and methods of Example 1, a typical well in gas field A with deep thermal fluid influence and deep and large fault development was selected for verification.

[0072] According to the first to third steps, gas samples are collected in the well and tested to obtain the main components CO2, 3 He, 4 He content.

[0073] The formula (1) in steps 4 to 9 is used to calculate the 3 He / enthalpy ratio.

[0074] The mantle heat fraction X is calculated by the tenth step heat balance equation M .

[0075] In order to further verify the feasibility of the present invention, we use the correlation between the terrestrial heat flow value and the mantle heat fraction to analyze from the side. 3 He / 4 The formula of He value is:

[0076]

[0077] In formula (14), R C / R A After atmospheric correction 3 He / 4 He value, q is the earth's heat flow value, unit is mW / m 2 .

[0078] The calculation results are shown in Table 1:

[0079] Table 1 Calculation results of relative heat contribution of mantle and crust of A gas field to geothermal system

[0080]

[0081] Where: Column a is the CO2 concentration under reservoir conditions, mol / kg. Column b is the CO2 concentration under reservoir conditions, mol / kg. 3 He concentration, 10 -12 mol / kg. Column c is the reservoir condition 3 He concentration (mol / kg) multiplied by 22414cm 3, to obtain the molar volume at STP (1 atm, 0 °C), 10 -8 cm 3 STP / kg. Column d is the enthalpy calculated by equation (1), kj / kg. Column e is the molar volume 3 He concentration to enthalpy ratio, 10 -12 cm 3 STP / J. Column f is the number of atoms converted to moles 3 He concentration and enthalpy ratio, atoms 3 mxD -1 s -1 Column g is the mantle heat fraction, %. Column h is the earth's heat flow, mW / m 2 .

[0082] Depend on Figure 1 It can be seen that according to geological surveys, samples 1 and 2 are located in the center of gas field A, and the areas corresponding to samples 1 and 2 are affected by deep heat sources; samples 3-5 are located far away from the center of the gas field and are not greatly affected by deep heat sources. Figure 1 As shown in the figure, the mantle source heat fraction corresponding to sample 1 is the highest, followed by sample 2, and samples 3 to 5 are relatively low. This shows that the closer to the center and the more affected by the deep heat source, the higher the relative heat contribution of the mantle will be.

[0083] Depend on Figure 2 As shown in the figure, the mantle heat fraction between samples 1 to 5 is positively correlated with the terrestrial heat flow value, which is consistent with the deep thermal fluid 3 The thermal driving effect of He further verifies the feasibility of the present invention.

Claims

1. A method for evaluating the relative contribution of the heat source of helium under the influence of deep fluid based on the heat balance equation, characterized in that: The steps include: The first step is to conduct geological surveys to confirm the existence of deep channel communication generated by large faults in the study area, the development and evolution of mud diapirs, and the intrusion of thermal fluids; The second step is to sample the reservoirs of typical wells in the study area and separate and purify them; The third step is to test and analyze the obtained CO2, 3 He, 4 He content; Step 4: Use formula (1) and the CO2 obtained from the test. 3 He concentration was calculated to obtain the samples at different depths. 3 He / enthalpy ratio, when expressed in dimensionless form, formula (1), i.e., φ = f / (RT), is divided into two parts, the ideal gas part φ° and the residual part φ r , so φ: In the formula, δ = ρ / ρ c , τ = T c / T; δ is the reduced density, τ is the reverse reduced temperature; ρ is the density under formation reservoir conditions, T is the temperature under formation reservoir conditions; Step 5: The reference constants required by formula (1) are as follows: Where, T c is the critical temperature, ρ c is the critical density; Step 6. The equation for the ideal gas part φ° is obtained from the ideal gas state The specific isobaric heat capacity equation is obtained as follows: In the formula, the nonlinear least squares method is used to fit The coefficients b0 and b i and exponential β i ;make i is an integer from 1 to 5. That is, simplify the formula; is the simplified coefficient, is the simplified exponent, that is, formula (5) is obtained after sorting; Step 7: Residual φ r The form is as follows: In formula (6), d i ,t i , α i , β i , γ i and∈ i Parameters belonging to the 45 Gaussian bell-shaped terms; ψ is a special heat function, Δ is an arbitrary quantity difference function, and b i is the internal parameter introduced, that is, the parameter of the non-analytical term, c i Determined by the exponent of the Gaussian bell term, it is a parameter among the 45 Gaussian bell terms; Step 8: Calculate the values ​​of the functions Δ, θ, and ψ of the relevant non-analytical terms: In formulas (7)-(9), A i , B i , C i , D i , a i , β i are the internal parameters introduced, i.e. the parameters of non-analytical terms, which are included in the nonlinear fitting of the whole equation, and θ is an adjustable parameter function; Step 9. Calculation formula of enthalpy: h=u+pv (10) Right now, in, h is the enthalpy value, u is the internal energy of the system, p is the external pressure, and v is the volume of the system. is the first-order derivative of φ° with respect to τ, Yes r Taking the first-order derivative with respect to τ, Yes r Take the first derivative of δ; Step 10: Assume that the mantle and crust are hot 3 He / enthalpy ratios, estimating the thermal contributions of the mantle and crust to the basin geothermal system based on the heat balance equation; ( 3 He / Enthalpy) calculated = X M ( 3 He / Enthalpy) mantle +(1 - X M )( 3 He / Enthalpy) crust (13) Where, X M is the mantle heat fraction in the sample, ( 3 He / enthalpy) calculated It is calculated by formula (1) 3 He / enthalpy ratio, ( 3 He / enthalpy) mantle 、( 3 He / enthalpy) crust Represent the hot end elements of the mantle and crust, respectively 3 He / enthalpy ratio; In the eleventh step, the calculated mantle heat fraction is the relative thermal contribution of the mantle to the basin geothermal system, and the remaining contribution of the basin geothermal system comes from the crust; the sum of the contributions of the two sources is 100%, and the calculated mantle heat fraction can refer to the mantle source contribution ratio, and the remaining percentage value refers to the crust source contribution ratio.

2. The method for evaluating the relative contribution of the heat source of helium under the influence of deep fluid based on the heat balance equation according to claim 1, characterized in that: Assuming that the mantle and crust are hot 3 The He / enthalpy ratios are 0.5×10 -12 cm 3 STp / J and 1×10 - 15 cm 3 STp / J.

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