CN117494395B - Fluid migration calculation method and system based on one-dimensional steady flow model - Google Patents

Abstract

The invention discloses a fluid migration calculation method and a fluid migration calculation system based on a one-dimensional steady-state flow model, wherein the method comprises the following steps: collecting geothermal gas and performing air pollution correction treatment to obtain corrected geothermal gas; considering the permeability and density of the crust rock, constructing a one-dimensional steady-state flow model; and estimating the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas. According to the invention, the migration speed of the geothermic fluid curtain source helium is estimated by constructing a one-dimensional steady-state flow model by considering the permeability and density of the crust rock, so that the real migration condition of the curtain source fluid can be truly reflected. The fluid migration calculation method and the fluid migration calculation system based on the one-dimensional steady-state flow model can be widely applied to the technical field of fluid migration calculation.

Description

Fluid migration calculation method and system based on one-dimensional steady flow model

Technical Field

The present invention relates to the field of fluid migration calculation technology, and in particular to a fluid migration calculation method and system based on a one-dimensional steady-state flow model.

Background technique

Mantle-derived fluid components (such as He, CO ₂ , N ₂ ) are important means to understand the evolution of mass and energy between the Earth's surface and interior, and play an important role in volcanic eruptions, earthquake monitoring, and identifying potential geothermal resources. In Cenozoic volcanic areas, such as mid-ocean ridges, volcanic arcs in subduction zones, and hotspots, magma is the carrier of mantle-derived helium rising to the surface and released. However, in continental areas lacking modern volcanic activity, the source and release mechanism of mantle-derived helium remain unclear. Quantitative evaluation of the migration rate of mantle-derived fluids and the time scale of their passage through the crust is crucial to understanding the timing and activity of tectonic occurrence, and also provides theoretical guidance for earthquake monitoring and the exploration of favorable areas for geothermal resource development. At present, the method for quantitatively evaluating the migration rate of mantle-derived fluids is to calculate the average flow rate of mantle-derived helium, which is used to calculate the fluid ascent rate in the San Andreas fault system in California or is used to calculate the migration rate of fluid released from the Peruvian plate. However, the existing methods do not take into account the porosity of the crust and treat the fluid as a pipe flow. Ignoring the porosity of the crust will cause the estimated flow rate to be 1-2 orders of magnitude lower than the actual flow rate, or ignoring the difference between rock density and fluid density, that is, ignoring geological parameters. Therefore, the existing methods cannot truly reflect the actual migration conditions of mantle-derived fluids.

Summary of the invention

In order to solve the above technical problems, the purpose of the present invention is to provide a fluid migration calculation method and system based on a one-dimensional steady-state flow model. By considering the permeability and density of crustal rocks to construct a one-dimensional steady-state flow model to estimate the migration velocity of mantle-derived helium in geothermal fluid, it can truly reflect the actual migration conditions of mantle-derived fluids.

The first technical solution adopted by the present invention is: a fluid migration calculation method based on a one-dimensional steady-state flow model, comprising the following steps:

Collecting geothermal gas and performing air pollution correction processing to obtain corrected geothermal gas;

Considering the permeability and density of crustal rocks, a one-dimensional steady flow model is constructed;

The corrected geothermal gas is estimated according to the one-dimensional steady-state flow model to obtain the corrected geothermal gas migration rate.

Furthermore, the step of collecting geothermal gas and performing air pollution correction processing to obtain corrected geothermal gas specifically includes:

The geothermal fluid is collected and processed by the drainage gas collection method to obtain geothermal gas;

Performing component analysis on the geothermal gas by means of a mass spectrometer to obtain the components of the gas;

The components of the gas are measured and processed by an inert gas mass spectrometer to determine the ratio of ³ He/ ⁴ He of the geothermal gas and the ratio of ⁴ He/ ²⁰ Ne of the geothermal gas;

Based on the ratio of ⁴ He/ ²⁰ Ne of the geothermal gas, the ratio of ³ He/ ⁴ He of the geothermal gas is subjected to air pollution correction processing to obtain the corrected ratio of ³ He/ ⁴ He of the geothermal gas.

Further, the correction process step specifically includes:

The correction determination coefficient is determined based on the ⁴ He/ ²⁰ Ne ratio in the atmosphere and the ⁴ He/ ²⁰ Ne ratio in the geothermal gas;

Construct the threshold of the corrected determination coefficient;

The geothermal gas corresponding to the correction determination coefficient being greater than the correction determination coefficient threshold is selected as the corrected geothermal gas. Further, the expression of the correction processing is specifically as follows:

R _c / _Ra = [(R _yp / _Ra )X-1]/(X-1)

X＝( ⁴ He/ ²⁰ Ne) _yp /( ⁴ He/ ²⁰ Ne) _air

In the above formula, R _c represents the corrected ³ He/ ⁴ He ratio, _Ra represents the ³ He/ ⁴ He ratio in the atmosphere, ( ⁴ He/ ²⁰ Ne) _air represents the ⁴ He/ ²⁰ Ne ratio in the atmosphere, ( ⁴ He/ ²⁰ Ne) _yp represents the geothermal gas ⁴ He/ ²⁰ Ne ratio, R _yp represents the geothermal gas ³ He/ ⁴ He ratio, and X represents the correction determination coefficient.

Furthermore, the expression of the one-dimensional steady-state flow model is specifically as follows:

In the above formula, q represents the migration rate of mantle-derived fluid, t represents the migration time of mantle-derived fluid, _Hc represents the thickness of the crust through which geothermal fluid passes, P( ^4He ) represents the generation rate of ^4He in crustal rocks, _ρs represents the density of crustal rocks, represents porosity, [ ⁴ He] _i,mantle represents the initial ⁴ He concentration in mantle-derived fluid, ρ _f represents the density of crustal fluid, R _s represents the ³ He/ ⁴ He ratio of geothermal gas sample, R _c represents the ³ He/ ⁴ He ratio in crustal rock, and R _i,mantle represents the initial ³ He/ ⁴ He ratio of mantle-derived fluid.

Furthermore, the step of estimating the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the corrected geothermal gas migration rate specifically includes:

Determine the generation rate of ³ He and the generation rate of ⁴ He in crustal rocks;

Considering the density of crustal rocks, the density of crustal fluids and the porosity of crustal rocks, and combining the generation rate of ³ He and the generation rate of ⁴ He in crustal rocks, the accumulation rate of ³ He and ⁴ He generated from crustal rocks in crustal fluids is obtained;

Determine the He concentration in the geothermal water and combine it with the corrected ³ He/ ⁴ He ratio to obtain the initial ⁴ He concentration in the mantle fluid;

Determine the corrected migration time of geothermal gas according to the accumulation rate of ³ He and ⁴ He generated by the crustal rocks in the crustal fluid and the initial concentration of ⁴ He in the mantle fluid;

Combined with the thickness of the crustal rocks, the corrected geothermal gas migration rate is determined.

Furthermore, the expression for obtaining the accumulation rate of ³ He and ⁴ He generated by crustal rocks in crustal fluids is specifically as follows:

In the above formula, A( ^3,4 He) represents the accumulation rate of ³ He and ⁴ He generated by crustal rocks in crustal fluids, P( ^3,4 He) represents the generation rate of ³ He and ⁴ He in crustal rocks, _ρs represents the density of crustal rocks, _ρf represents the density of crustal fluids, Represents the porosity of crustal rocks.

Furthermore, the expression for obtaining the initial concentration of ⁴ He in the mantle fluid is specifically as follows:

[ ⁴ He] _i,mantle ＝[ ⁴ He] _s ×F( ⁴ He)

In the above formula, [ ^4He ] _i,mantle represents the initial concentration of ^4He in the mantle fluid, [ ^4He ] _s represents the He concentration in geothermal water, and F( ^4He ) represents the proportion of mantle-derived ^4He .

Furthermore, the expression for determining the corrected migration time of geothermal gas is specifically as follows:

In the above formula, t represents the corrected migration time of geothermal gas.

The second technical solution adopted by the present invention is: a fluid migration calculation system based on a one-dimensional steady-state flow model, comprising:

A correction module, used for collecting geothermal gas and performing air pollution correction processing to obtain corrected geothermal gas;

A building block for constructing a one-dimensional steady-state flow model taking into account the permeability and density of crustal rocks;

An estimation module is used to estimate the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas.

The beneficial effects of the method and system of the present invention are as follows: the present invention avoids air pollution that may be caused during sampling and testing by collecting geothermal gas and performing correction processing, further considers the permeability and density of crustal rocks, and constructs a one-dimensional steady-state flow model, which can better reveal the migration law of fluids under natural conditions at the lithospheric scale. By constructing a one-dimensional steady-state flow model, the migration speed and migration time of mantle-derived helium in geothermal fluids are estimated, geochemical constraints on the lithospheric structure are provided, and the fluid rising position of the geothermal field is determined, which can truly reflect the actual migration status of the mantle-derived fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the steps of a fluid migration calculation method based on a one-dimensional steady-state flow model according to an embodiment of the present invention;

2 is a structural block diagram of a fluid migration calculation system based on a one-dimensional steady-state flow model according to an embodiment of the present invention;

FIG3 is a schematic diagram of a device for collecting geothermal gas by a drainage gas collection method according to a specific embodiment of the present invention;

4 is a schematic diagram showing a comparison of the fluid migration rate calculated by the calculation method of the present invention and the existing calculation method under the condition of a porosity of 10% in a specific embodiment of the present invention;

FIG5 is a schematic diagram showing a comparison of the fluid migration rate calculated by the calculation method of the present invention and the existing calculation method under the condition of 1% porosity in a specific embodiment of the present invention.

Detailed ways

The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

Mantle-derived fluid components (such as He, CO ₂ , and N ₂ ) are important means of understanding the evolution of mass and energy between the Earth's surface and interior, and play an important role in volcanic eruptions, earthquake monitoring, and identifying potential geothermal resources. Hot springs and geothermal wells release a large amount of hydrothermal fluids (such as He, CO ₂ , and N ₂ ). Mantle-derived helium contains more original gas and is enriched in ³ He ( ³ He/ ⁴ He = 8±1Ra, where Ra is the ³ He/ ⁴ He ratio of the atmosphere, which is 1.39×10 ^-6 ); crust-derived helium is enriched in ⁴ He, which is produced by U ( ^235,238 U) and Th ( ²³² Th) through α radioactive decay, and has a lower ³ He/ ⁴ He value (~ _0.02RA ). Therefore, based on the difference in the ³ He/ ⁴ He ratio between crust-derived helium and mantle-derived helium, the area of mantle gas degassing can be effectively identified. In Cenozoic volcanic areas, such as mid-ocean ridges, volcanic arcs in subduction zones, and hotspots, magma is the carrier of mantle-derived helium rising to the surface and being released. However, in continental areas lacking modern volcanic activity, the source and release mechanism of mantle-derived helium remain unclear. Existing studies have shown that in areas lacking modern volcanism, potential factors causing mantle-derived helium release include: extensional tectonic zones where mantle melts intrude into the shallow crust, enhanced permeability at the lithospheric scale caused by increased right-lateral shear strain, and activation of helium in the continental lithospheric mantle by lithospheric strike-slip faults or plate-derived fluids. Quantitative evaluation of these processes, such as the migration rate of mantle-derived fluids and the time scale of their passage through the crust, is crucial to understanding the timing and activity of tectonic occurrence, and also provides theoretical guidance for seismic monitoring and the exploration of favorable areas for geothermal resource development. Hot springs and geothermal wells release large amounts of hydrothermal fluids (such as He, CO ₂ , and N ₂ ). Currently, there are two main methods for quantitatively evaluating the migration rate of mantle-derived helium based on gases collected from hot springs and geothermal wells:

Method 1: The average flow rate can be calculated by the following formula

This method is widely used to calculate fluid rise rates in the San Andreas fault system in California.

Method 2:

The method was applied to the migration rates of fluids released from the Peruvian slab.

However, method 1 does not consider the porosity of the crust and treats the fluid as a pipe flow. According to actual conditions, the upper limit of the porosity of the lower crust is 1%, while the porosity of the middle and upper crust is usually 10%. Therefore, ignoring the porosity of the crust will cause the estimated flow rate to be 1-2 orders of magnitude lower than the actual flow rate. Method 2 ignores the difference between rock density and fluid density. Usually, the average density of the crust is 2.8g cm ^-3 , and the fluid density is 1.0g cm ^-3 . It can be seen that the two methods ignore geological parameters to varying degrees and cannot truly reflect the actual migration of mantle-derived fluids.

Based on this, referring to FIG. 1 , the present invention provides a fluid migration calculation method based on a one-dimensional steady-state flow model, the method comprising the following steps:

S1. Collect geothermal gas and perform air pollution correction processing to obtain corrected geothermal gas;

S11, collecting and processing geothermal fluid by drainage and gas collection method to obtain geothermal gas;

Specifically, geothermal gas (such as He, CO ₂ , N ₂ ) is collected from hot springs or geothermal wells. The gas is collected by the drainage gas collection method. The funnel connected to the silicone tube is inverted and immersed in the hot spring mouth. Initially, the salt water glass bottle (50 mL) is filled with geothermal water and immersed in the geothermal water. After the local hot water and gas rinse the silicone tube and the funnel for 30 minutes, the silicon tube is inserted into the glass bottle, and the gas is collected by the gas collection and drainage method, as shown in Figure 3, until a small amount of geothermal water remains in the bottle (sealed), and the glass bottle is sealed with a rubber stopper. During the whole process, the mouth of the glass bottle is always immersed below the surface of the geothermal water; then the glass bottle is taken out and further sealed with an aluminum cap, and placed in a 500 ml polyethylene bottle filled with the corresponding geothermal water to ensure that there is no bubble residue, and sealed with sealing glue to avoid atmospheric pollution during transportation.

S12, performing component analysis on the geothermal gas by means of a mass spectrometer to obtain components of the gas;

S13, measuring and processing the components of the gas by an inert gas mass spectrometer to determine the ratio of ³ He/ ⁴ He of the geothermal gas and the ratio of ⁴ He/ ²⁰ Ne of the geothermal gas;

Specifically, gas composition and isotope analysis were performed in the Stable Isotope Composition Analysis Laboratory and the Rare Gas Isotope Analysis Laboratory of Lanzhou Oil and Gas Center, Institute of Geology and Geophysics, Chinese Academy of Sciences. The gas composition was determined using a MAT271 mass spectrometer with a detection limit of 0.0001% and a relative standard error of <5%. The ³ He/ ⁴ He and ⁴ He/ ²⁰ Ne ratios were determined by a Noblesse inert gas mass spectrometer (Nu Instruments, UK).

S14. Correcting the ratio of ³ He/ ⁴ He of the geothermal gas based on the ratio of ⁴ He/ ²⁰ Ne of the geothermal gas to obtain corrected geothermal gas.

S141. Determine the correction determination coefficient based on the ⁴ He/ ²⁰ Ne ratio in the atmosphere and the ⁴ He/ ²⁰ Ne ratio in the geothermal gas;

S142, constructing a correction determination coefficient threshold;

S143, selecting the geothermal gas corresponding to the correction determination coefficient being greater than the correction determination coefficient threshold as the corrected geothermal gas.

Specifically, in order to eliminate possible air pollution during sampling and testing, it is assumed that all Ne in the sample comes from the atmosphere, and the ³ He/ ⁴ He ratio in the sample is corrected based on the ⁴ He/ ²⁰ Ne ratio in the sample, as shown below:

R _c / _Ra = [(R _yp / _Ra )X-1]/(X-1)

X＝( ⁴ He/ ²⁰ Ne) _yp /( ⁴ He/ ²⁰ Ne) _air

In the above formula, R _c represents the corrected ³ He/ ⁴ He ratio, _Ra represents the ³ He/ ⁴ He ratio in the atmosphere, ( ⁴ He/ ²⁰ Ne) _air represents the ⁴ He/ ²⁰ Ne ratio in the atmosphere, ( ⁴ He/ ²⁰ Ne) _yp represents the geothermal gas ⁴ He/ ²⁰ Ne ratio, R _yp represents the geothermal gas ³ He/ ⁴ He ratio, and X represents the correction determination coefficient;

When the X value of the sample is greater than 10, it indicates that the helium isotope composition is less affected by atmospheric helium. When the X value is less than 10, it indicates that the sample is seriously contaminated and the data cannot be used.

S2. Considering the permeability and density of crustal rocks, a one-dimensional steady-state flow model is constructed;

Specifically, the expression of the one-dimensional steady flow model is as follows:

In the above formula, q represents the migration rate of mantle-derived fluid, t represents the migration time of mantle-derived fluid, _Hc represents the thickness of the crust through which geothermal fluid passes, P( ^4He ) represents the generation rate of ^4He in crustal rocks, _ρs represents the density of crustal rocks, represents porosity, [ ⁴ He] _i,mantle represents the initial ⁴ He concentration in mantle-derived fluid, ρ _f represents the density of crustal fluid, R _s represents the ³ He/ ⁴ He ratio of geothermal gas sample, R _c represents the ³ He/ ⁴ He ratio in crustal rock, and R _i,mantle represents the initial ³ He/ ⁴ He ratio of mantle-derived fluid.

S3. Estimate the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas.

S31. Determine the generation rate of ³ He and the generation rate of ⁴ He in crustal rocks;

Specifically, the generation rate of ³ He (P( ³ He)) and the generation rate of ⁴ He (P( ⁴ He)) in the crust (cm ³ STP g ^-1 rock year ^-1 ) are calculated based on the concentrations of Li, U and Th in the crustal rocks (in ppm). The expressions are:

P( ^3He )＝(2.64× ^10-4 [U]+6.40× ^10-5 [Th])×[Li]× ^10-23 ×22414

P( ⁴ He)＝1.19634×10 ^-13 [U]+2.89665×10 ^-14 [Th]

In the above formula, P( ³ He) represents the generation rate of ³ He in rocks in the earth's crust, P( ⁴ He) represents the generation rate of ⁴ He in rocks in the earth's crust, and Li, U and Th represent the concentrations of Li, U and Th in crustal rocks.

S32. Considering the density of crustal rocks, the density of crustal fluids and the porosity of crustal rocks, and combining the generation rate of ³ He and the generation rate of ⁴ He in crustal rocks, the accumulation rate of ³ He and ⁴ He generated from crustal rocks in crustal fluids is obtained;

Specifically, according to the crust density (ρ _s ), fluid density (ρ _f ), is the porosity, the generation rate of ³ He and ⁴ He in the crust (cm ³ STP g ^-1 rock year ^-1 ), the accumulation rate of ³ He and ⁴ He in the crust (cm ³ STPg ^-1 H ₂ O year ^-1 ) is calculated, and the expression is:

In the above formula, A( ^3,4 He) represents the accumulation rate of ³ He and ⁴ He generated by crustal rocks in crustal fluids, P( ^3,4 He) represents the generation rate of ³ He and ⁴ He in crustal rocks, _ρs represents the density of crustal rocks, _ρf represents the density of crustal fluids, Represents the porosity of crustal rocks.

S33, determining the He concentration in the geothermal water and combining the corrected ³ He/ ⁴ He ratio to obtain the initial ⁴ He concentration in the mantle-derived fluid;

Specifically, the initial ⁴ He concentration in the mantle-derived fluid ([ ⁴ He] _i,mantle , cm ³ g ^-1 H ₂ O) is calculated based on the measured He concentration in the geothermal water and the ³ He/ ⁴ He ratio of the sampled fluid after air correction, and its expression is:

[ ⁴ He] _i,mdntle ＝[ ⁴ He] _s ×F( ⁴ He)

In the above formula, [ ^4He ] _i,mantle represents the initial concentration of ^4He in mantle-derived fluid, [ ^4He ] _s represents the He concentration in geothermal water, F( ^4He ) represents the proportion of mantle-derived ^4He , _Rs represents the ^3He / ^4He ratio of geothermal gas samples, _Rc represents the ^3He / ^4He ratio in crustal rocks, and _Rm represents the ^3He / ^4He ratio in the mantle.

S34, determining the corrected migration time of geothermal gas according to the accumulation rate of ³ He and ⁴ He generated by the crustal rocks in the crustal fluid and the initial concentration of ⁴ He in the mantle-derived fluid;

Specifically, the initial mantle-derived fluid will be further diluted by ^{the 3} He produced by the reaction of ⁴ He of radioactive origin and neutrons in the crust during its ascent from the mantle to the surface. Therefore, the ³ He/ ⁴ He ratio of the mantle-derived fluid reaching the surface is related to the migration time and can be expressed by the following equation:

_Rs = (R _i,mantle × [ ⁴ He] _i,mantle + A( ³ He) × t) / ([ ⁴ He] _i,mantle + A( ⁴ He) × t)

In the above formula, _Rs represents the ³ He/ ⁴ He value of the sample after air contamination correction, t represents the fluid migration time, R _i,mantle and [ ⁴ He] _i,mantle represent the initial ³ He/ ⁴ He ratio (8±1Ra) and ⁴ He concentration (cm ³ g ^-1 H ₂ O) of the mantle-derived fluid, respectively, A( ³ He) and A( ⁴ He) represent the accumulation rates of ³ He and ⁴ He produced in the crust in the fluid;

It can be concluded that the migration time of mantle-derived fluid is:

In the above formula, t represents the corrected migration time of geothermal gas.

S35. Determine the corrected migration rate of geothermal gas based on the thickness of the earth's crust.

Referring to Figures 4 and 5, according to the existing methods 1 and 2, it can be seen from the comparison of the three methods that, compared with the present invention and method 2, method 1 does not consider the porosity of the crust and treats the fluid as a pipeline flow. According to actual conditions, the upper limit of the porosity of the lower crust is 1%, while the porosity of the middle and upper crust is usually 10%. Therefore, ignoring the porosity of the crust will cause the estimated flow rate to be 1-2 orders of magnitude lower than the actual flow rate. Compared with this study and method 1, method 2 ignores the differences in rock density and fluid density. Generally, the average density of the crust is 2.8g cm ^-3 , and the three-dimensional density is 1.0g cm ^-3 . Therefore, the formula for calculating the migration rate and time of the lithospheric scale fluid based on the one-dimensional steady-state flow model of the present invention fully considers the permeability of the crust, the differences in the density of rocks and fluids, and can more truly reflect the average rising speed of mantle-derived fluids under natural conditions.

Furthermore, the experiment of the present invention was carried out using the Qinghai-Tibet Plateau as the testing area;

Geothermal fluids from Yangbajing and Gariqiong in the Yadong Valley graben system of the Qinghai-Tibet Plateau were collected in the field. The helium content and ³ He/ ⁴ He ratio (R _m ) were analyzed and corrected for air pollution (R _c ). As shown in Tables 1 and 2, the porosity Taking the upper limit of 1% of the crust, based on the U content of 1.3ppm, Th content of 5.6ppm, Th/U of 4.3, the average yield of ⁴ He in the crust P( ⁴ He) is 3.17×10 ^-13 cm ³ STP g ^-1 rock year ^-1 , the crust density (ρ _s ) is 2.8g cm ^-3 , and the fluid density (ρ _f ) is 1g cm ^-3 ; the crust thickness (H _c ) is obtained according to geophysical data, which is 75.2km in Yangbajing and 74.3km in Gariqiong. The initial content of mantle-derived ⁴ He is obtained according to the calculation formula for the initial concentration of ⁴ He in mantle-derived fluid [ ⁴ He] _i,mantle ; Substituting the above parameters into the calculation formula for determining the corrected geothermal gas migration time and the calculation formula of the one-dimensional steady-state flow model, we can obtain that the average migration time of geothermal fluid in Yangbajing is 20.2ka, the upward migration rate is 3720mm/year, and the average migration time of Gariqiong is 37.8ka and the upward migration rate is 1960mm/year. It can be seen that Yangbajing has a better fluid upward channel than Gariqiong, and the conditions for geothermal resource exploitation are more favorable. It also shows that the deep dynamic evolution state revealed by the ³ He/ ⁴ He ratio of the Qinghai-Tibet Plateau is between the lithosphere structure state revealed by the Qinghai-Tibet Plateau petrology (>8Ma) and geophysical detection methods.

Table 1 Correction of ³ He/ ⁴ He values of geothermal gases in Yangbajing and Gariqiong in the Qinghai-Tibet Plateau

Table 2 Calculation of geothermal fluid rise rate and migration time in Yangbajing and Gariqiong in the Qinghai-Tibet Plateau

2, a fluid migration calculation system based on a one-dimensional steady-state flow model includes:

A correction module, used for collecting geothermal gas and performing air pollution correction processing to obtain corrected geothermal gas;

A building block for constructing a one-dimensional steady-state flow model taking into account the permeability and density of crustal rocks;

An estimation module is used to estimate the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas.

The contents of the above method embodiments are all applicable to the present system embodiments. The functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims (7)

1. The fluid migration calculation method based on the one-dimensional steady-state flow model is characterized by comprising the following steps of:

Collecting geothermal gas and performing air pollution correction treatment to obtain corrected geothermal gas, wherein the corrected geothermal gas represents corrected ³He/⁴ He ratio, and geothermal fluid comprises geothermal gas and geothermal water, and specifically comprises:

collecting and processing geothermal fluid by a drainage and gas collection method to obtain geothermal gas;

carrying out component analysis treatment on the geothermal gas by a mass spectrometer to obtain a component of the gas;

Determining the ratio of geothermal gas ³He/⁴ He and the ratio of geothermal gas ⁴He/²⁰ Ne by measuring the components of the gases by an inert gas mass spectrometer;

Performing air pollution correction treatment on the ratio of the geothermal gas ³He/⁴ He based on the ratio of the geothermal gas ⁴He/²⁰ Ne to obtain corrected geothermal gas;

Wherein the correction process includes the steps of:

Determining a correction determination coefficient according to a ratio of ⁴He/²⁰ Ne in the atmosphere to ⁴He/²⁰ Ne of the geothermal gas;

Constructing a correction judgment coefficient threshold value;

Selecting geothermal gas corresponding to the correction judgment coefficient larger than the correction judgment coefficient threshold as corrected geothermal gas;

Considering the permeability and density of the crust rock, constructing a one-dimensional steady-state flow model;

the expression of the one-dimensional steady-state flow model is specifically as follows:

Where q represents the veil source fluid migration rate, t represents the veil source fluid migration time, H _c represents the geothermal fluid through the crust thickness, P (⁴ He) represents the rate of formation of ⁴ He in the crust rock, ρ _s represents the crust rock density, Representing porosity, [ ⁴He]_i,mantle ] representing the initial concentration of ⁴ He in the veil source fluid, ρ _f representing crust fluid density, R _s representing the ³He/⁴ He ratio of geothermal gas sample, R _c representing the ³He/⁴ He ratio in crust rock, R _i,mantle representing the veil source fluid initial ³He/⁴ He ratio;

and estimating the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas.

2. The fluid migration calculation method based on the one-dimensional steady-state flow model according to claim 1, wherein the expression of the correction process is specifically as follows:

R_c/R_a＝[(R_yp/R_a)X-1]/(X-1)

X＝(⁴He/²⁰Ne)_yp/(⁴He/²⁰Ne)_air

In the above formula, R _c represents the corrected ³He/⁴ He ratio, R _a represents the ³He/⁴ He ratio in the atmosphere, (⁴He/²⁰Ne)_air represents the ⁴He/²⁰ Ne ratio in the atmosphere, (⁴He/²⁰Ne)_yp represents the ratio of geothermal gas ⁴He/²⁰ Ne, R _yp represents the ratio of geothermal gas ³He/⁴ He, and X represents the correction determination coefficient.

3. The fluid migration calculation method based on the one-dimensional steady-state flow model according to claim 1, wherein the step of estimating the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas specifically comprises:

determining the generation rate of ³ He and the generation rate of ⁴ He in the crust rock;

Taking the density of the crust rock, the density of the crust fluid and the porosity of the crust rock into consideration, and combining the generation rate of ³ He and the generation rate of ⁴ He in the crust rock to obtain the accumulation rates of ³ He and ⁴ He generated by the crust rock in the crust fluid;

determining the concentration of He in geothermal water and combining the corrected ³He/⁴ He ratio to obtain the initial concentration of ⁴ He in the mantle fluid;

Determining corrected geothermal gas migration time based on the rate of accumulation of ³ He and ⁴ He in the crust fluid generated by the crust rock and the initial concentration of ⁴ He in the mantle fluid;

and determining the migration rate of the corrected geothermal gas by combining the thickness of the crust rock.

4. A fluid migration calculation method based on a one-dimensional steady-state flow model according to claim 3, wherein the expression for obtaining the accumulation rate of ³ He and ⁴ He generated by the crust rock in the crust fluid is specifically as follows:

In the above formula, A (^3,4 He) represents the accumulation rate of ³ He and ⁴ He generated by the crust rock in the crust fluid, P (^3,4 He) represents the generation rate of ³ He and ⁴ He in the crust rock, ρ _s represents the density of the crust rock, ρ _f represents the crust fluid density, Representing the porosity of the earth's crust rock.

5. The fluid migration calculation method based on the one-dimensional steady-state flow model according to claim 3, wherein the expression for obtaining the initial concentration of ⁴ He in the mantle fluid is specifically as follows:

[⁴He]_i,mantle＝[⁴He]_s×F(⁴He)

In the above formula, [ ⁴He]_i,mantle ] represents the initial concentration of ⁴ He in the mantle fluid, [ ⁴He]_s ] represents the concentration of He in geothermal water, and F (⁴ He) represents the proportion of mantle source ⁴ He.

6. A fluid migration calculation method based on a one-dimensional steady-state flow model according to claim 3, wherein the expression for determining the migration time of the corrected geothermal gas is specifically as follows:

in the above formula, t represents the corrected geothermal gas migration time.

7. A fluid migration computing system based on a one-dimensional steady-state flow model, comprising the following modules:

The correction module is used for collecting geothermal gas and performing air pollution correction treatment to obtain corrected geothermal gas, wherein the corrected geothermal gas represents corrected ³He/⁴ He ratio, and geothermal fluid comprises geothermal gas and geothermal water and specifically comprises the following components:

collecting and processing geothermal fluid by a drainage and gas collection method to obtain geothermal gas;

carrying out component analysis treatment on the geothermal gas by a mass spectrometer to obtain a component of the gas;

Determining the ratio of geothermal gas ³He/⁴ He and the ratio of geothermal gas ⁴He/²⁰ Ne by measuring the components of the gases by an inert gas mass spectrometer;

Performing air pollution correction treatment on the ratio of the geothermal gas ³He/⁴ He based on the ratio of the geothermal gas ⁴He/²⁰ Ne to obtain corrected geothermal gas;

Wherein the correction process includes the steps of:

Determining a correction determination coefficient according to a ratio of ⁴He/²⁰ Ne in the atmosphere to ⁴He/²⁰ Ne of the geothermal gas;

Constructing a correction judgment coefficient threshold value;

Selecting geothermal gas corresponding to the correction judgment coefficient larger than the correction judgment coefficient threshold as corrected geothermal gas;

the construction module is used for considering the permeability and density of the crust rock and constructing a one-dimensional steady-state flow model;

the expression of the one-dimensional steady-state flow model is specifically as follows:

Where q represents the veil source fluid migration rate, t represents the veil source fluid migration time, H _c represents the geothermal fluid through the crust thickness, P (⁴ He) represents the rate of formation of ⁴ He in the crust rock, ρ _s represents the crust rock density, Representing porosity, [ ⁴He]_i,mantle ] representing the initial concentration of ⁴ He in the veil source fluid, ρ _f representing crust fluid density, R _s representing the ³He/⁴ He ratio of geothermal gas sample, R _c representing the ³He/⁴ He ratio in crust rock, R _i,mantle representing the veil source fluid initial ³He/⁴ He ratio;

And the estimation module is used for estimating the corrected geothermal gas according to the one-dimensional steady-state flow model to obtain the migration rate of the corrected geothermal gas.