A hydrocarbon accumulation analysis system based on multi-isotope simultaneous monitoring

Abstract

The present invention discloses an oil and gas accumulation analysis system based on multi-isotope synchronous monitoring, belonging to the field of oil and gas accumulation technology. The system comprises a signal acquisition module, a signal processing module, and a main control module connected in sequence. The main control module is respectively connected to a DAC and a DDS, which are jointly connected to a drive module, and the drive module and a temperature control module are jointly connected to the signal acquisition module. The signal acquisition module comprises an EC-QCL, a converging lens group, an As2S3 optical fiber, an off-axis integrating cavity, a converging lens, and a photodetector. The main control module obtains isotope values by data analysis of the second harmonic signal, and then calculates the isotope abundances of C, H, and O. The system then uses a multi-isotope joint analysis oil and gas accumulation mechanism analysis model to analyze the oil and gas source, maturity, migration, and accumulation process. This system improves the shortcomings of the current single-isotope or dual-isotope analysis of the accumulation mechanism, which is not comprehensive, and fills the gap in multi-isotope joint analysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas accumulation, and in particular relates to an oil and gas accumulation analysis system based on multi-isotope synchronous monitoring. Background Art

[0002] During the oil and gas exploration process, shale gas seeping out of the rock formation contains a variety of isotopes, among which C, H, and O isotopes are the most common. With the continuous deepening of oil and gas geochemical research, the detection of isotope abundance provides an effective basis for the traceability, migration, maturity and accumulation process of chemical substances in oil and gas resources. Therefore, the simultaneous monitoring of the C, H, and O isotope abundance (δ 13 C、δD、δ 18 O), analyzing the mechanism of oil and gas accumulation can provide key geochemical basis for the detailed evaluation of complex oil and gas reservoirs.

[0003] In spectral logging, δ 13 C、δD、δ 18 O is an important geochemical indicator, providing key information about the origin, maturity, migration, and accumulation of oil and gas. Existing research, however, has focused on single or dual isotope analysis. Huang Shipeng and others from the China National Petroleum Exploration and Development Research Institute explored the application of H isotopes in alkane gases to natural gas genesis, maturity identification, and the water environment of source rock sedimentation. Ni Yunyan and others from the China University of Petroleum conducted a comprehensive analysis of the carbon and hydrogen isotopic characteristics of natural gas and explored the application of C and H isotopes in natural gas genesis. Yang Yang from the School of Exploration and Surveying Engineering at Changchun Institute of Technology explored the genesis of dolomite using geochemical methods such as C and O isotope analysis. Research has not yet identified a clear application of the combined C, H, and O isotope ratios to analyze oil and gas accumulation mechanisms.

[0004] Currently, gas isotope analysis techniques, both domestically and internationally, are primarily categorized into mass spectrometry and spectral analysis. Mass spectrometry, which detects isotope abundances through differences in the mass-to-charge ratio of isotopes, offers high accuracy and precision, making it a key tool for laboratory isotope detection. However, for shale gas component analysis, mass spectrometry must be coupled with gas chromatography, which is limited by chromatographic separation efficiency. This results in long detection cycles, poor real-time performance, and bulky equipment, making in situ detection difficult. Furthermore, the complex operation makes it difficult to obtain continuous geochemical data, limiting subsequent mechanistic analysis. In recent years, spectral analysis has become an emerging isotope detection method due to its rapidity, convenience, low cost, and non-destructive nature. Currently, spectral techniques commonly used for gas isotope detection can be divided into photoacoustic spectroscopy and absorption spectroscopy. However, most spectral techniques utilize light sources that can only emit lasers with a narrow tunable range. Therefore, a single laser cannot detect multiple gas components with widely separated absorption lines. Multiple lasers consume significant resources and hinder system integration. Lasers with a wide tuning range can meet the requirements of simultaneous multi-component gas monitoring and integration. Currently, quantum cascade laser frequency combs (QCL-FCs) and external cavity quantum cascade lasers (EC-QCLs) offer wide tuning ranges. However, the bulk of QCL-FCs makes them unsuitable for downhole measurements. EC-QCLs, on the other hand, offer wide tuning, narrow linewidth, long lifetime, and fast tuning, while also providing optical output power up to 70 mW. Based on these advantages, EC-QCLs were ultimately chosen as the light source for monitoring the isotopic abundances of C, H, and O. Summary of the Invention

[0005] In response to the above problems existing in the prior art, the present invention proposes an oil and gas reservoir analysis system based on multi-isotope synchronous monitoring, which has a reasonable design, solves the shortcomings of the prior art, and has good effects.

[0006] A system for analyzing oil and gas accumulation based on multi-isotope synchronous monitoring, comprising a signal acquisition module, a signal processing module, and a main control module connected in sequence, wherein the main control module is further connected to a DAC and a DDS, respectively; the DAC and the DDS are connected to a drive module, and the drive module and the temperature control module are connected to the signal acquisition module.

[0007] The signal acquisition module includes an EC-QCL, a converging lens group, an As2S3 optical fiber, an off-axis integrating cavity, a converging lens and a photodetector, and is used to collect optical signals containing gas absorption information and convert the optical signals into electrical signals that are easy to process;

[0008] The signal processing module includes a preamplifier circuit, a filter circuit, a lock-in amplifier and an AD acquisition circuit, which are used to filter and demodulate the electrical signal to obtain a second harmonic signal that can reflect the gas concentration;

[0009] The main control module is used to control the DAC and DDS to generate driving voltage signals. On the other hand, it analyzes the second harmonic signal to obtain isotope values, and then calculates the abundance of three isotopes: C, H, and O. It also uses a multi-isotope joint analysis model to analyze the source, maturity, migration, and accumulation process of oil and gas, predict oil and gas sweet spots, and assist in resource estimation.

[0010] The driving module and temperature control module are used to realize current driving and temperature control of the EC-QCL, so that the EC-QCL output wavelength covers the three isotope absorption lines of C, H and O.

[0011] Furthermore, in the signal acquisition module, the EC-QCL output wavelength used is 3.26μm~3.55μm, and the laser output by the EC-QCL is converged to the mid-infrared fiber head through a converging lens group and coupled to the off-axis integrating cavity by an As2S3 fiber;

[0012] The off-axis integrating cavity uses a highly reflective mirror and a sapphire window with a reflectivity of 99.98% in the target wavelength band. The off-axis integrating cavity is connected to a gas sampling device, which includes an air pump and a filter. The air pump draws filtered shale gas into the cavity for absorption by the laser.

[0013] The optical signal output by the off-axis integrating cavity is converged by a converging lens to the photosensitive surface of the photodetector and is converted into an electrical signal by the photodetector.

[0014] Furthermore, in the main control module, the abundance of the three isotopes of C, H and O 、 、 They are:

[0015] ;

[0016] ;

[0017] ;

[0018] in, To contain 13 The second harmonic signal amplitude of CH4 concentration information, for 12 The absorption cross section of CH4 at the center of the absorption line, for 12 The incident light intensity corresponding to the CH4 absorption line is To contain12 The second harmonic signal amplitude of CH4 concentration information, for 13 The absorption cross section of CH4 at the center of the absorption line, for 13 The incident light intensity corresponding to the CH4 absorption line;

[0019] is the amplitude of the second harmonic signal containing CH3D concentration information, is the absorption cross section of CH4 at the center of the absorption line, is the incident light intensity corresponding to the CH4 absorption line, is the amplitude of the second harmonic signal containing CH4 concentration information, is the absorption cross section of CH3D at the center of the absorption line, is the incident light intensity corresponding to the CH3D absorption line;

[0020] Contains OC 18 The second harmonic signal amplitude of O concentration information, For OC 16 The absorption cross section of O at the center of the absorption line, For OC 16 The incident light intensity corresponding to the O absorption line is Contains OC 16 The second harmonic signal amplitude of O concentration information, For OC 18 The absorption cross section of O at the center of the absorption line, For OC 18 The incident light intensity corresponding to the O absorption line.

[0021] Furthermore, the multi-isotope joint analysis oil and gas accumulation mechanism analysis model includes a four-layer structure of data input layer, data processing layer, isotope analysis layer, and prediction and evaluation layer;

[0022] The data input layer inputs the standard abundance values of each isotope and the detection geographical location information;

[0023] The data processing layer filters and fuses abnormal data based on The guidelines are:

[0024] ;

[0025] in, Representative Sample data, is the sample mean, is the standard deviation of the sample; the error is located in Extraneous data were removed to ensure the validity of the data;

[0026] The isotope analysis layer analyzes the oil and gas sources, maturity, migration and accumulation process respectively;

[0027] The prediction and assessment layer predicts exploration targets and estimates resource quantities.

[0028] Furthermore, in the isotope analysis layer, the oil and gas source analysis is specifically as follows: The value can distinguish the origin of coal-generated gas. If the value distribution range is between -94‰ and -55‰, it is caused by microbial chemical action; The value distribution range is between -55‰ and -29‰, which is caused by pyrolysis maturity; The value is between -260‰~-150‰, and the oil-type gas Values above -180‰;

[0029] The specific analysis of oil and gas maturity is as follows: For oil-type gas, there is the following formula:

[0030] ;

[0031] For coal-derived gas, there is the following formula:

[0032] ;

[0033] Where, is the reflectance of organic matter vitrinite in source rocks, which is used to judge the maturity of oil and gas. When it is lower than 0.5%, it is in the immature stage; when it is between 0.5% and 1.3%, it is in the low-maturity to mature stage; when it is between 1.3% and 2.0%, it is in the high-maturity stage; when it is higher than 2.0%, it is in the over-mature stage.

[0034] Furthermore, in the isotope analysis layer, the oil and gas migration path analysis is specifically as follows:

[0035] Calculate the migration direction gradient, Gradient = / Distance, if If the gradient is greater than 1‰ / km, it indicates a short-distance rapid migration, which is a fault channel; If the gradient is less than 0.5‰ / km, it indicates long-distance diffusion and a homogeneous reservoir. In the vertical direction, if If the value changes from high value in deep part to low value in shallow part, it indicates that there is a vertical migration channel; in horizontal direction, if If the value decreases with the increase of exploration distance, it means that there is horizontal migration; during the migration process, if If the value is close to that of the surrounding rock, that is, the difference with the background value of the surrounding rock is within ±1%, it indicates that the migration path passes through a specific lithologic interval and water-rock interaction occurs;

[0036] The specific analysis of the reservoir-forming environment is as follows:

[0037] when When the value is higher than -0.8‰, CO2 comes from carbonate dissolution, and its oxygen isotope fractionation is related to temperature. The paleotemperature can be calculated according to the carbonate-water oxygen isotope balance formula:

[0038] ;

[0039] In the formula The value needs to be input from outside the model. If it is marine sediment, ;

[0040] Combine and The paleo-salinity during the reservoir formation period can be inferred collaboratively. The value is higher than -160‰, and If the value is higher than -0.8‰, it is a marine hypersaline environment; The value is lower than -160‰, and If the value is negative, it is a terrestrial low-salinity environment;

[0041] The sealing of the reservoir environment is indirectly reflected by isotope fractionation dynamics and gas adsorption behavior. The value change range does not exceed ±3% and the CO2 content is higher than 50%. The value change range is less than 10‰, indicating that the gas has not diffused significantly and has high sealing. High sealing means that the fractionation range is less than 10‰. On the contrary, if Higher than -0.8‰ and CO2 content is lower than 20%, and The value change range is higher than 20‰, indicating that the gas diffuses significantly, and it is considered to be an open system. The open system has a fractionation range higher than 20‰; when When it is negative, it indicates that the sealing is poor, causing CO2 to escape preferentially or react with groundwater.

[0042] Furthermore, the prediction and assessment layer first integrates the isotope data and geological parameters based on the results of the isotope analysis layer, combines the data with visual graphics, updates the data on the topographic map, and calculates the potential migration path. Gradient: Steep gradient areas indicate the main migration channel, and the steep gradient area is higher than 0.5‰ / km. Next, the exploration target is delineated, and the area that meets the comprehensive indicators is considered the sweet spot:

[0043] ;

[0044] In the formula, the calculation formula for hydrocarbon generation intensity is:

[0045] ;

[0046] Where, is the total organic carbon content, is the thickness of the source rock, is the hydrogen index, for maturity;

[0047] The calculation formula for oil and gas resources Q is:

[0048] ;

[0049] Where, Q is the amount of oil and gas resources, A is the effective reservoir area, h is the effective thickness of the reservoir, is the porosity, is the hydrocarbon saturation, is the density of crude oil, is the volume coefficient of crude oil.

[0050] Beneficial technical effects brought about by the present invention:

[0051] The present invention uses a single external cavity quantum cascade laser combined with off-axis integrating cavity output spectroscopy technology to complete in-situ synchronous monitoring of the abundance of three isotopes of carbon, hydrogen and oxygen in shale gas, and based on this, constructs a multi-isotope joint analysis model for oil and gas accumulation mechanism analysis, which makes up for the shortcomings of the current use of single isotope or dual isotope analysis of the accumulation mechanism that is not comprehensive enough, and fills the gap in multi-isotope joint analysis.

[0052] 1. Using a single EC-QCL as the light source, based on its wide tuning range and narrow linewidth, it can simultaneously scan multiple isotope absorption peaks for simultaneous multi-isotope monitoring, rather than using multiple lasers for multi-gas detection as in traditional spectroscopy. This reduces the instrument size and greatly improves system integration.

[0053] 2. To adapt to the high temperature and vibration environment during drilling, the laser beam is coupled into the cavity using a high-temperature resistant mid-infrared optical fiber, and the off-axis integrating cavity window is made of sapphire. This adapts to high-temperature environments and solves the problem that traditional reflector groups are difficult to adapt to bumpy environments, thereby ensuring the smooth operation of the detection device.

[0054] 3. Compared with single-isotope or dual-isotope analysis, this method provides a more comprehensive analysis of key information such as oil and gas sources, maturity, migration pathways, and accumulation processes based on the collected in-situ carbon, hydrogen, and oxygen isotope abundance information. It also establishes an oil and gas accumulation mechanism analysis model based on multi-isotope joint analysis, reveals the isotopic response of the entire chain of oil and gas generation, migration, and accumulation, predicts the distribution of oil and gas resources, and thus guides oil and gas development. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The diagram is a structural diagram of an oil and gas reservoir analysis system based on multi-isotope synchronous monitoring in the present invention.

[0056] Figure 2 For the present invention 12 CH4, 13 Graph showing changes in infrared absorption intensity of CH4 molecules.

[0057] Figure 3 This is a graph showing changes in the infrared absorption intensity of CH4 and CH3D molecules in the present invention.

[0058] Figure 4 OC in the present invention 16 O, OC 18 Graph showing changes in infrared absorption intensity of O molecules.

[0059] Figure 5 Schematic diagram of the multi-isotope combined analysis model for oil and gas accumulation mechanism analysis in the present invention.

[0060] Among them, 1-main control module; 2-digital-to-analog converter; 3-digital frequency synthesizer; 4-drive module; 5-temperature control module; 6-external cavity quantum cascade laser; 7-converging lens group; 8-As2S3 optical fiber; 9-off-axis integrating cavity; 10-air pump; 11-filter device; 12-converging lens; 13-photodetector; 14-signal processing module. DETAILED DESCRIPTION

[0061] The specific implementation of the present invention will be further described below with reference to specific embodiments:

[0062] A hydrocarbon accumulation analysis system based on multi-isotope simultaneous monitoring, such as Figure 1 As shown, it includes a signal acquisition module, a signal processing module and a main control module 1 connected in sequence. The main control module 1 is connected to a digital-to-analog converter 2 (DAC) and a digital frequency synthesizer 3 (DDS) respectively. The DAC and the DDS are connected to a driving module 4. The driving module 4 and the temperature control module 5 are connected to the signal acquisition module.

[0063] The signal acquisition module includes an external cavity quantum cascade laser 6 (EC-QCL), a converging lens group 7, an As2S3 optical fiber 8, an off-axis integrating cavity 9, a converging lens 12, and a photodetector 13, and is used to collect optical signals containing gas absorption information and convert the optical signals into electrical signals that are easy to process;

[0064] The EC-QCL output wavelength used is 3.26 μm~3.55 μm, which completely covers the absorption lines of C, H, and O isotopes (3.39 μm, 3.31 μm, and 3.34 μm). The absorption line positions of the three isotopes are as follows: Figure 2 、 Figure 3 、 Figure 4 As shown; the converging lens group consists of a convex lens and a concave lens, which are fixed at the laser output port of the EC-QCL to couple the laser beam into the optical fiber; the As2S3 optical fiber is a mid-infrared optical fiber that can transmit the laser emitted by the EC-QCL, and the other end is connected to the off-axis integrating cavity to couple it into the cavity; the off-axis integrating cavity is the place where the laser and the gas absorb each other, and a high-reflectivity mirror with a reflectivity of 99.98% in the target band is used. Its optical path can reach the kilometer level. In order to adapt to the high-temperature environment downhole, a sapphire window is used; the off-axis integrating cavity is connected to a gas sampling device, which includes an air pump 10 and a filtering device 11. Due to the complex downhole environment and the fact that the gas is often mixed with fine particles and other substances, a filtering device is required to prevent contamination of the lens in the cavity. The air pump draws the filtered shale gas into the cavity to absorb the laser;

[0065] The signal processing module 14 includes a preamplifier circuit, a filter circuit, a lock-in amplifier and an AD acquisition circuit, which is used to filter and demodulate the electrical signal to obtain a second harmonic signal that can reflect the gas concentration;

[0066] The main control module 1 is embedded with digital noise reduction, concentration inversion, and oil and gas accumulation mechanism analysis algorithms, and communicates with other modules. It is the core unit of the entire system. On the one hand, it is used to control the DAC and DDS to generate driving voltage signals. On the other hand, it analyzes the second harmonic signal through noise reduction, inversion and other data analysis to obtain isotope values, and then calculates the abundance of three isotopes: C, H, and O. It uses the multi-isotope joint analysis oil and gas accumulation mechanism analysis model to analyze the source, maturity, migration and accumulation process of oil and gas, predict oil and gas sweet spots, and assist in resource estimation.

[0067] The driver module includes a constant current source circuit and an overcurrent protection circuit. The constant current source circuit converts the driving voltage signal into a current signal to complete the current drive of the laser. The overcurrent protection circuit is to prevent excessive current from damaging the laser. The temperature control module integrates a temperature control chip and uses a semiconductor cooler (TEC) controller to perform high-precision control of the TEC inside the EC-QCL to stabilize the laser temperature.

[0068] The device operates as follows: The main control module controls the DAC and DDS to generate a low-frequency sawtooth wave and a high-frequency sine wave, respectively. The superposition of these two signals serves as a driving voltage signal, which is converted into a current signal by the driver module. The temperature control module, in conjunction with the laser, drives the laser and controls its temperature, ensuring that the laser output wavelength covers the absorption lines of the three isotopes of C, H, and O. The laser output is focused by a converging lens assembly onto a mid-infrared fiber head, which is then coupled to an off-axis integrating cavity via an As2S3 fiber. Shale gas is pumped into the cavity, where it is fully absorbed by the laser. The optical signal from the off-axis integrating cavity is focused by a converging lens onto the photosensitive surface of a photodetector, where it is converted into a more easily processed electrical signal. The signal processing module filters and demodulates the detector signal to produce a second harmonic signal that directly reflects gas concentration. The main control module collects the signal, performs noise reduction, inversion, and other data analysis, and then obtains the isotope value. This is then used to calculate the isotope abundance. Integrated analytical algorithms are then used to analyze the source, maturity, migration, and accumulation of oil and gas.

[0069] When using laser absorption spectroscopy to measure gas concentration, according to the Beer-Lambert law, it is expressed as follows:

[0070] ;

[0071] in, is the laser input intensity when there is no gas absorption, is the intensity of the transmitted light of the laser through the absorbed gas; The wavelength is The absorption cross section of the medium per unit concentration per unit length, also known as the absorption coefficient, is the concentration of the gas being measured, It is the optical path of the laser through the gas being measured.

[0072] Assume that the initial light intensity entering the integrating cavity is I in The cavity length is L0. The integrating cavity consists of an input mirror and an output mirror, both with a reflectivity of R and a transmittance of T = 1-R. The total loss of light during a single propagation within the cavity (including gas absorption, scattering, and off-axis diffraction) is d. When light enters the cavity, a portion of it is transmitted outward with each reflection. The path length of each transmitted light and the ratio of the transmitted light intensity are shown in Table 1:

[0073] Table 1 Path length of each transmitted light and ratio of transmitted light intensity

[0074] ;

[0075] Total effective optical path L eff It is the weighted average of the path length of each transmitted light and its light intensity contribution. Since the light intensity decays with the number of reflections, the total optical path can be expressed as:

[0076] ;

[0077] The driving current of the laser is sinusoidally modulated, and the corresponding light intensity and frequency of the light source are also modulated and are proportional to the injection current.

[0078] ;

[0079] ;

[0080] in is the light intensity modulation coefficient, is the center frequency of the light source when it is not modulated, is the frequency modulation amplitude (usually on the same order of magnitude as the absorption half-width), is the sinusoidal modulation frequency, ;

[0081] The Beer-Lambert law can be expressed in frequency form as follows:

[0082] ;

[0083] The light intensity modulation coefficient and the gas absorption coefficient are both very small, that is, and , perform approximate calculations and obtain the following formula:

[0084] ;

[0085] Gas absorption line shape It can be described by the normalized Lorentz line shape, namely:

[0086] ;

[0087] in is the absorption cross section of pure gas at the center of the absorption line, is the center frequency of the absorption peak, is the half-width of the absorption line.

[0088] You can get:

[0089] ;

[0090] When the center frequency of the light source output is precisely locked on the gas absorption peak, that is, ,but:

[0091] ;

[0092] in, ;

[0093] Expand the above equation into a Fourier series. Since the amplitude of higher harmonics is small, they are not expanded here one by one. The coefficients of the first harmonic (f) and the second harmonic (2f) are as follows:

[0094] ;

[0095] ;

[0096] in , the size of k is related to w, ,Right now When the second harmonic reaches a maximum amplitude of 3.43, the first harmonic signal is mainly caused by light intensity modulation and its magnitude is proportional to the average power of the light source. The magnitude of the second harmonic signal is related to the initial light intensity and the concentration of the gas. Extracting the second harmonic signal can obtain gas concentration information. The concentration can be expressed as:

[0097] ;

[0098] The effective absorption path length of the off-axis integrating cavity Substituting the above formula, we can get the expression of concentration C:

[0099] ;

[0100] Isotope abundance Indicates the ratio of heavy isotope to light isotope content in the substance being tested The ratio of heavy isotope to light isotope content in the standard material The relative deviation between:

[0101] ;

[0102] The calculation method of isotope abundance can be obtained:

[0103] ;

[0104] When measuring isotope abundance, the standard substances selected are shown in Table 2:

[0105] Table 2 Standard substances

[0106] ;

[0107] Therefore, δ can be calculated 13 C, δ 2 D. δ 18 O:

[0108] ;

[0109] ;

[0110] ;

[0111] After obtaining the standard abundance values of the three isotopes, a multi-isotope joint analysis model for oil and gas accumulation mechanism was constructed, such as Figure 5 As shown in the figure, the system consists of four layers: data input layer, data processing layer, isotope analysis layer, and prediction and evaluation layer. First, the data input layer is established to input the standard abundance values of each isotope and the detection geographic location information. The data processing layer is established to filter abnormal data and fuse data to make the data more reliable. The isotope analysis layer uses isotope data to identify oil and gas sources, calculate maturity, reconstruct migration paths, and infer reservoir formation environments. Finally, the prediction and evaluation layer uses isotope analysis to predict exploration targets and assist in estimating resource quantities, guiding oil and gas development.

[0112] The specific construction steps are as follows:

[0113] The data input layer inputs the standard abundance values of each isotope and the detection geographical location information;

[0114] The data processing layer filters and fuses abnormal data based on The guidelines are:

[0115] ;

[0116] in, Representative Sample data, is the sample mean, is the standard deviation of the sample; the error is located in Extraneous data were removed to ensure the validity of the data;

[0117] Isotope analysis layer, first of all, the oil and gas source analysis is carried out using - Collaborative discrimination method. The value can distinguish the origin of coal-generated gas. If the value distribution range is between -94‰ and -55‰, it is a typical microbial chemical cause; If the value distribution range is between -55‰ and -29‰, it is caused by pyrolysis and maturity. It is difficult to distinguish between oil-type gas and coal-generated gas. Value-assisted identification, coal-derived gas The value is usually lighter, ranging from -260‰ to -150‰; oil-type gas The value is heavier, higher than -180‰.

[0118] The second step is oil and gas maturity analysis. The initial carbon isotope composition of different organic matter types varies significantly, so it is necessary to select an appropriate maturity calculation formula based on the parent material type. For oil-type gas (sapropelic natural gas), the following formula is used:

[0119] ;

[0120] For coal-derived gas (humic natural gas), there is the following formula:

[0121] ;

[0122] Next, the migration path is reconstructed using and Combined tracing method. There is diffusion fractionation in the migration process. The light isotope molecules diffuse faster. The methane at the far end of the migration path Lighter. So according to The value and the measurement location can determine the direction of the migration path. gradient( / distance), if If the gradient is greater than 1‰ / km, it indicates a short-distance rapid migration, which is a fault channel; If the gradient is less than 0.5‰ / km, it indicates long-distance diffusion and a homogeneous reservoir. The value transitions from high value in deep to low value in shallow, indicating the existence of vertical migration channel; in horizontal direction, if If the value decreases with the increase of exploration distance, it means that there is horizontal migration. The value is close to that of the surrounding rock, that is, the difference with the background value of the surrounding rock is within ±1%, indicating that the migration path passes through a specific lithologic interval and water-rock interaction occurs.

[0123] The next step is to speculate on the reservoir-forming environment. and Combined speculation method. High temperature will enhance the fractionation effect of hydrogen isotopes in methane molecules, resulting in It becomes more positive (heavier) as the temperature increases. When the value is higher than -0.8‰, CO2 comes from carbonate dissolution, and its oxygen isotope fractionation is related to temperature. The paleotemperature can be calculated according to the carbonate-water oxygen isotope balance formula:

[0124] ;

[0125] In the formula The value needs to be input from outside the model. If it is marine sediment, . Combined and The paleo-salinity during the reservoir formation period can be inferred collaboratively. The value is higher than -160‰, and If the value is higher than -0.8‰, it can be inferred that it is a marine hypersaline environment; The value is lower than -160‰, and If the value is negative, it can be inferred that it is a continental low-salinity environment. The closedness of the reservoir environment is indirectly reflected by the isotope fractionation dynamics and gas adsorption behavior. The value change range does not exceed ±3% and the CO2 content is higher than 50%. The value change range is less than 10‰, indicating that the gas has not diffused significantly and has high sealing (fractionation range is less than 10‰); on the contrary, if Higher than -0.8‰ and CO2 content is lower than 20%, and The value change range is higher than 20‰, indicating that the gas is obviously diffused, and it is considered to be an open system (fractionation range is higher than 20‰). When it is negative, it indicates that the sealing is poor, causing CO2 to escape preferentially or react with groundwater.

[0126] The prediction and assessment layer first integrates the isotope data and geological parameters based on the results of the isotope analysis layer, combines the data with visual graphics, updates the data on the topographic map, and calculates along the potential migration path. Gradient: steep gradient areas (higher than 0.5‰ / km) indicate the main migration channels;

[0127] Next, we will identify exploration targets, and areas that meet comprehensive indicators will be considered sweet spots:

[0128] ;

[0129] In the formula, the calculation formula for hydrocarbon generation intensity is:

[0130] ;

[0131] Where, is the total organic carbon content, is the thickness of the source rock, is the hydrogen index, for maturity;

[0132] To assist in resource estimation, the calculation formula for oil and gas resource Q is:

[0133] ;

[0134] Where, Q is the amount of oil and gas resources, 10,000 tons; A is the effective reservoir area, km 2 ; h is the effective thickness of the reservoir, m; is the porosity; is the hydrocarbon saturation; is the density of crude oil g / cm 3 ; is the crude oil volume coefficient. Although the isotope abundance value is directly used as a factor in resource calculation, it plays an auxiliary role in parameter determination. Indicates high-mature source rock (R o >1.0%), indicating a large hydrocarbon generation potential; along the migration path The decay gradient can delineate the effective reservoir area (A); A change of less than 5‰ indicates good preservation conditions and increases hydrocarbon saturation ( ) reliability.

[0135] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A system for analyzing oil and gas accumulation based on multi-isotope synchronous monitoring, characterized in that: It includes a signal acquisition module, a signal processing module and a main control module connected in sequence, wherein the main control module is further connected to the DAC and the DDS respectively, the DAC and the DDS are connected to the driving module, and the driving module and the temperature control module are connected to the signal acquisition module; The signal acquisition module includes an EC-QCL, a converging lens group, an As2S3 optical fiber, an off-axis integrating cavity, a converging lens and a photodetector, and is used to collect optical signals containing gas absorption information and convert the optical signals into electrical signals that are easy to process; The signal processing module includes a preamplifier circuit, a filter circuit, a lock-in amplifier and an AD acquisition circuit, which are used to filter and demodulate the electrical signal to obtain a second harmonic signal that can reflect the gas concentration; The main control module is used to control the DAC and DDS to generate driving voltage signals. On the other hand, it analyzes the second harmonic signal to obtain isotope values, and then calculates the abundance of three isotopes: C, H, and O. It also uses a multi-isotope joint analysis model to analyze the source, maturity, migration, and accumulation process of oil and gas, predict oil and gas sweet spots, and assist in resource estimation. The driving module and temperature control module are used to realize the current driving and temperature control of the EC-QCL, so that the EC-QCL output wavelength covers the three isotope absorption lines of C, H and O; In the main control module, the abundance of the three isotopes of C, H and O 、 、 They are: ； ； ； in, To contain 13 The second harmonic signal amplitude of CH4 concentration information, for 12 The absorption cross section of CH4 at the center of the absorption line, for 12 The incident light intensity corresponding to the CH4 absorption line is To contain 12 The second harmonic signal amplitude of CH4 concentration information, for 13 The absorption cross section of CH4 at the center of the absorption line, for 13 The incident light intensity corresponding to the CH4 absorption line; is the amplitude of the second harmonic signal containing CH3D concentration information, is the absorption cross section of CH4 at the center of the absorption line, is the incident light intensity corresponding to the CH4 absorption line, is the amplitude of the second harmonic signal containing CH4 concentration information, is the absorption cross section of CH3D at the center of the absorption line, is the incident light intensity corresponding to the CH3D absorption line; Contains OC 18 The second harmonic signal amplitude of O concentration information, For OC 16 The absorption cross section of O at the center of the absorption line, For OC 16 The incident light intensity corresponding to the O absorption line is Contains OC 16 The second harmonic signal amplitude of O concentration information, For OC 18 The absorption cross section of O at the center of the absorption line, For OC 18 The incident light intensity corresponding to the O absorption line; The analysis of oil and gas sources is as follows: The value can distinguish the origin of coal-generated gas. If the value distribution range is between -94‰ and -55‰, it is caused by microbial chemical action; The value distribution range is between -55‰ and -29‰, which is caused by pyrolysis maturity; The value is between -260‰~-150‰, and the oil-type gas Values above -180‰; The specific analysis of oil and gas maturity is as follows: For oil-type gas, there is the following formula: ； For coal-derived gas, there is the following formula: ； Where, is the reflectance of organic matter vitrinite in source rocks, which is used to judge the maturity of oil and gas. When the content is lower than 0.5%, it is in the immature stage; when it is between 0.5% and 1.3%, it is in the low-maturity to mature stage; when it is between 1.3% and 2.0%, it is in the high-maturity stage; when it is higher than 2.0%, it is in the over-mature stage; The specific analysis of oil and gas migration pathways is as follows: Calculate the migration direction gradient, Gradient = / Distance, if If the gradient is greater than 1‰ / km, it indicates a short-distance rapid migration, which is a fault channel; If the gradient is less than 0.5‰ / km, it indicates long-distance diffusion and a homogeneous reservoir. In the vertical direction, if If the value changes from high value in deep part to low value in shallow part, it indicates that there is a vertical migration channel; in horizontal direction, if If the value decreases with the increase of exploration distance, it means that there is horizontal migration; during the migration process, if If the value is close to that of the surrounding rock, that is, the difference with the background value of the surrounding rock is within ±1%, it indicates that the migration path passes through a specific lithologic interval and water-rock interaction occurs; The specific analysis of the reservoir-forming environment is as follows: when When the value is higher than -0.8‰, CO2 comes from carbonate dissolution, and its oxygen isotope fractionation is related to temperature. The paleotemperature can be calculated according to the carbonate-water oxygen isotope balance formula: ； In the formula The value needs to be input from outside the model. If it is marine sediment, ; Combine and The paleo-salinity during the reservoir formation period can be inferred collaboratively. The value is higher than -160‰, and If the value is higher than -0.8‰, it is a marine hypersaline environment; The value is lower than -160‰, and If the value is negative, it is a terrestrial low-salinity environment; The sealing of the reservoir environment is indirectly reflected by isotope fractionation dynamics and gas adsorption behavior. The value change range does not exceed ±3% and the CO2 content is higher than 50%. The value change range is less than 10‰, indicating that the gas has not diffused significantly and has high sealing. High sealing means that the fractionation range is less than 10‰. On the contrary, if Higher than -0.8‰ and CO2 content is lower than 20%, and The value change range is higher than 20‰, indicating that the gas diffuses significantly, and it is considered to be an open system. The open system has a fractionation range higher than 20‰; when When it is negative, it indicates that the sealing is poor, causing CO2 to escape preferentially or react with groundwater.

2. The oil and gas reservoir analysis system based on multi-isotope synchronous monitoring according to claim 1 is characterized in that: In the signal acquisition module, the EC-QCL output wavelength used is 3.26μm~3.55μm. The laser output by the EC-QCL is converged to the mid-infrared fiber head through a converging lens group and coupled to the off-axis integrating cavity by an As2S3 fiber. The off-axis integrating cavity uses a highly reflective mirror and a sapphire window with a reflectivity of 99.98% in the target wavelength band. The off-axis integrating cavity is connected to a gas sampling device, which includes an air pump and a filter. The air pump draws filtered shale gas into the cavity for absorption by the laser. The optical signal output by the off-axis integrating cavity is converged by a converging lens to the photosensitive surface of the photodetector and is converted into an electrical signal by the photodetector.

3. The oil and gas reservoir analysis system based on multi-isotope synchronous monitoring according to claim 2 is characterized in that: The multi-isotope joint analysis oil and gas accumulation mechanism analysis model includes a four-layer structure: data input layer, data processing layer, isotope analysis layer, and prediction and evaluation layer; The data input layer inputs the standard abundance values of each isotope and the detection geographical location information; The data processing layer filters and fuses abnormal data based on The guidelines are: ； in, Representative Sample data, is the sample mean, is the standard deviation of the sample; the error is located in Extraneous data were removed to ensure the validity of the data; The isotope analysis layer analyzes the oil and gas sources, maturity, migration and accumulation process respectively; The prediction and assessment layer predicts exploration targets and estimates resource quantities.

4. The oil and gas reservoir analysis system based on multi-isotope synchronous monitoring according to claim 3 is characterized in that: The prediction and assessment layer first integrates the isotope data and geological parameters based on the results of the isotope analysis layer, combines the data with visual graphics, updates the data on the topographic map, and calculates the potential migration path. Gradient: Steep gradient areas indicate the main migration channel, and the steep gradient area is higher than 0.5‰ / km. Next, the exploration target is delineated, and the area that meets the comprehensive indicators is considered the sweet spot: ； In the formula, the calculation formula for hydrocarbon generation intensity is: ； Where, is the total organic carbon content, is the thickness of the source rock, is the hydrogen index, for maturity; The calculation formula for oil and gas resources Q is: ； Where, Q is the amount of oil and gas resources, A is the effective reservoir area, h is the effective thickness of the reservoir, is the porosity, is the hydrocarbon saturation, is the density of crude oil, is the volume coefficient of crude oil.

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