Quantitative evaluation method for in-source pyrolysis gas and out-of-source pyrolysis gas

Abstract

The invention relates to a quantitative evaluation method for in-source pyrolysis gas and out-of-source pyrolysis gas, which comprises the following steps: firstly, respectively establishing mathematical models for describing changes of two gas products along with geological evolution; secondly, an analysis chart of gas composition under different mixing ratios is constructed based on the mathematical model result; and finally, projecting actually measured gas sample data onto the analysis chart, namely determining the proportion of the two types of source gases, and completing quantitative evaluation of the in-source pyrolysis gas and the out-source pyrolysis gas. According to the method, a dynamic evolution model reflecting geological history is constructed to replace a traditional static model, and a gas source contribution proportion identification chart is generated based on the model. Quantitative analysis can be completed through actual measurement data plumbing, the limitation of a traditional method is overcome, and the accuracy and reliability of identification are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of natural gas geochemistry and oil exploration, and particularly relates to a method for quantitatively characterizing the origin of natural gas, which is used for deep-ultra deep complex gas reservoirs, aims to quantitatively distinguish two main thermogenic gases, i.e., source rock pyrolysis gas and secondary cracking gas of crude oil in the reservoir, and considers the geological dynamic evolution process, and is particularly suitable for resource evaluation and favorable zone prediction in oil and gas exploration and development. BACKGROUND

[0002] Deep-ultra deep gas reservoirs are an important frontier field and strategic replacement direction of current oil and gas exploration and development. A significant geological feature of this type of gas reservoir is that it has experienced a complex and multi-stage accumulation history, including long-term deep burial, multi-stage tectonic movement and complex thermal evolution process. This complex geological background leads to diversification of natural gas sources, for example, the same gas reservoir may contain both natural gas generated by continuous cracking of kerogen in source rocks and natural gas generated by secondary cracking of early accumulated crude oil due to intensified thermal evolution, and the mixing of multi-source natural gas is very common. Therefore, accurately identifying the source and contribution ratio of each type of source gas in the mixed gas has become a core technical problem in the exploration and evaluation of deep-ultra deep gas reservoirs, and is directly related to the accurate assessment of resource potential, the effective reduction of exploration risk and the scientific formulation of development plan. For deep gas reservoirs that have experienced multi-stage tectonics and complex thermal history, the geochemical characteristics of source gas itself are the result of dynamic accumulation in the geological history. Therefore, in order to further improve the accuracy of quantitative characterization under complex geological background, a technical scheme that can better reflect the fine division of end members and the dynamic nature of geological processes still needs to be developed. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a deep-ultra deep natural gas multi-source quantitative characterization method, which is used to solve the problem that the contribution ratio of two types of gases (one from source rock gas and the other from oil cracking gas) is difficult to determine in high thermal evolution stage gas reservoirs.

[0004] The technical scheme of the present application is as follows: A method for quantitative evaluation of source pyrolysis gas and external cracking gas, comprising: First, a mathematical model describing the change of two types of gas products with geological evolution is established respectively; Second, an analysis chart of gas composition under different mixing ratios is constructed based on the results of the mathematical model; Finally, the measured gas sample data is projected onto the analysis chart to determine the proportion of the two types of source gas, and the quantitative evaluation of source pyrolysis gas and external cracking gas is completed.

[0005] According to the preferred embodiment of the present application, the mathematical model describing the change of two types of gas products with geological evolution is established respectively, which comprises: The first step is to obtain the geological process constraint conditions and starting materials, i.e., to obtain the boundary conditions and initial inputs required for constructing the model. The boundary conditions refer to defining a key time node as the starting point of dynamic geochemical model calculation, which defines the calculation starting point of the source of oil cracking gas. At the same time, obtain material samples representing the starting state of the two gas production processes, including rock core samples representing the source rock parent material without sufficient thermal evolution and oil or paleo-reservoir asphalt samples representing the composition of early charging oil; The second step is to obtain the gas production process data through heating experiments. The two kinds of material samples obtained in the first step are respectively placed in inert and closed reaction systems, and are subjected to staged heating to simulate the gas production process of the two kinds of material samples continuously heated underground, to obtain the component content and isotope characteristic values of the generated gas including CH4 and C2H6 in multiple different heating stages, and to calculate the dynamic coefficients including the reaction frequency coefficient k i and the temperature sensitivity index Ω i ; The third step is to construct a dynamic geochemical model of source rock pyrolysis gas. The generation process of source rock pyrolysis gas is dynamically simulated by combining the continuous burial-thermal evolution history restored in the first step and the kinetic parameters fitted in the second step. The dynamic geochemical model describes the process of natural gas components and isotopes accumulated in the continuous burial and heating process of source rock; The cumulative yield C i,s of source rock pyrolysis gas f is based on the first-order reaction kinetic model, and the generation rate from t0 to the final accumulation t f is integrated to calculate: (1); (2); In equations (1)-(2), is the reaction frequency coefficient of C i ; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of the convertible precursor in the source rock; is the isotope value of the instantaneously generated gas; is the generation rate of C i at this moment; C i i is the number of gas components; t is the geological time; exp() is the natural exponential function, i.e., the exponential function with the real number e as the base; is the cumulative molar fraction or yield of component i generated from the source rock at the final time t f ; I is the isotopic value of the gas generated at time t.

[0006] Fourthly, a dynamic geochemical model of the secondary cracking gas of the crude oil in the reservoir coupled with the geological event is constructed. The dynamic geochemical model describes the dynamic process of the cracking of the crude oil starting at a specific geological period, and the specific geological period starts at the key time node t event ; the cumulative yield C i,o (t f ) and the cumulative isotopic composition Iso C i,o (t f ) are calculated.

[0007] Further preferably, in the second step, the heating by the staged temperature rising refers to: the temperature is raised from low temperature to high temperature at a specific rate by the programmed temperature rising, and the constant temperature is maintained at multiple preset temperature points. The gases generated in the multiple different heating stages include methane, ethane, propane, isobutane, n-butane, isopentane and n-pentane; the component content is obtained by the gas chromatograph; and the isotopic characteristic value is obtained by the stable isotope mass spectrometer.

[0008] Further preferably, in the fourth step, the cumulative yield C i,o (t f ) and the cumulative isotopic composition Iso C i,o (t f ) are calculated by the formula (3) and (4); and the details are as follows: (3) and (4). In the formula, k i is the reaction frequency coefficient of C i ; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of the convertible precursor in the hydrocarbon source rock; is the isotopic value of the gas generated at time t; is the generation rate of C i at the time.

[0009] According to the present application, preferably, the analysis chart of the gas composition under different mixing ratios is constructed based on the results of the mathematical model; and the analysis chart includes: Fifthly, the CH4, C2H6 content and Iso C i , i=1, 2 of the pyrolysis gas of the hydrocarbon source rock and the secondary cracking gas of the crude oil are calculated respectively. The sixth step is to establish and apply a gas source mixing chart for a specific gas field, which is used to describe the final geochemical composition characteristics of the mixed gas of different proportions of parent gas; The contribution proportion X2 of the secondary cracking gas of the crude oil is 1-X1 when the contribution proportion X1 of the hydrocarbon source rock pyrolysis gas is changed from 0 to 1. Based on the final characteristic values of the two pure source gases, i.e., the cumulative yield and isotope value of the hydrocarbon source rock pyrolysis gas and the crude oil cracking gas calculated in the third step and the fourth step, the theoretical geochemical parameter values of the mixed gas at a series of different mixing proportions X1 are calculated by weighting.

[0010] Further preferably, in the sixth step, the theoretical geochemical parameter values of the mixed gas at a series of different mixing proportions X1 are calculated by weighting; the calculation formula is as follows: (5); In formula (5), i is a gas component, i=1 is methane, and i=2 is ethane; k is the number of the parent gas; X k is the contribution proportion of the parent gas k; w k (t) is a weighting function of the geological time scale; m i,k (t) is a function of the molar fraction of component i in the parent gas k with respect to the geological time scale; Iso C i,k (t) is a function of the isotope composition of component i in the parent gas k with respect to the geological time scale; t0, t f is the initial time and the final time; IsoC i,mix is the isotope composition of component i in the final mixed gas.

[0011] According to the present application, the measured gas sample data is projected onto the analysis chart, i.e., the proportions of the two types of source gases are determined; including: An analysis chart in a grid shape is established, the final geochemical composition of the pure hydrocarbon source rock pyrolysis gas is taken as a fixed endpoint, and the geochemical compositions of the secondary cracking gas of the crude oil at different thermal maturity stages are taken as a series of dynamic endpoints; For each dynamic endpoint, the fixed endpoint is mixed with different mixing proportions to obtain a series of theoretical mixing points; the theoretical mixing points at the same crude oil maturity are connected to form an isomaturity mixing line, and the points with the same mixing proportion on all the isomaturity mixing lines are connected to form an isoproportion mixing line, so as to finally form a quantitative identification chart in a grid shape; After establishing the quantitative identification chart, natural gas samples from the target gas well are collected to obtain measured data. These measured parameter values ​​are used as data points and located in the coordinate system of the grid-like quantitative identification chart. Based on the position of the data point in the grid of the grid-like quantitative identification chart, the contribution ratio of the two source gases is simultaneously read and determined.

[0012] Further preferred, two key geochemical parameters are selected in a two-dimensional coordinate system to determine the theoretical mixing isotopic composition IsoC. 2,mix The x-axis is IsoC 1,mix The vertical axis is used as the ordinate, and the final composition of the calculated pure hydrocarbon source rock pyrolysis gas is used as a fixed endpoint.

[0013] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the above-described method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas.

[0014] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas.

[0015] The beneficial effects of this invention are as follows: This invention constructs a dynamic mathematical model that reflects the geological evolution history and combines it with thermal simulation experimental data to obtain the final composition of two pure source gases (hydrocarbon source rock pyrolysis gas and crude oil cracking gas) under deep gas reservoir conditions. It improves the quantitative characterization method of mixed gas sources that relies on static "standard samples" and is conducive to more accurate evaluation and analysis of the genesis of deep natural gas in the context of multi-stage tectonic and complex thermal history. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to the present invention. Figure 2 This is a schematic diagram of a graph for quantitatively identifying the gas source ratio of gas fields C and D based on a dynamic evolution model. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0018] Example 1 A method for quantitatively evaluating in-source pyrolysis gas and out-of-source cracking gas. The core of this invention lies in constructing a dynamic evolutionary geochemical model and establishing a gas source ratio identification chart based on this model; such as... Figure 1 As shown; including: First, mathematical models describing the changes of the two types of gaseous products with geological evolution are established respectively; Secondly, based on the results of mathematical model, the analysis chart of gas composition under different mixing ratio is constructed; Finally, the measured gas sample data is projected on the analysis chart, i.e. the proportion of two types of source gas is determined, and the quantitative evaluation of in-source pyrolysis gas and extra-source cracking gas is completed.

[0019] Example 2 The quantitative evaluation method of in-source pyrolysis gas and extra-source cracking gas according to example 1, the difference is: Respectively, a mathematical model describing the change of two types of gas products with geological evolution is established; including: First, obtain the geological process constraints and starting materials, i.e. obtain the boundary conditions and initial input required for model construction; the boundary conditions are: define a key time node as the starting point of dynamic geochemical model calculation, the key time node is defined according to basin simulation and tectonic history analysis, usually corresponding to the key tectonic movement period (t event ) that leads to rapid deep burial or heating of the reservoir; the key time node defines the calculation starting point of the source cracking gas (second parent gas); at the same time, obtain the material samples representing the starting state of two types of gas production processes, including core samples representing the source rock parent material (representing the first parent gas) and oil or paleo-reservoir asphalt samples representing the composition of early charging oil (representing the second parent gas) which have not been fully thermally evolved; Second, obtain the gas production process data through heating experiment; place the two types of material samples obtained in the first step in an inert and closed reaction system respectively, and heat them in stages to simulate the gas production process of the two types of material samples under continuous heating underground, obtain the component content and isotope characteristic values of the generated gas including CH4 and C2H6 in multiple different heating stages, and calculate the dynamic coefficients including reaction frequency coefficient k i and temperature sensitivity index Ω i ; Third, construct a dynamic geochemical model of source rock pyrolysis gas (first parent gas); the core of the dynamic geochemical model is a complete calculation process, which is realized by the following formula (1) and formula (2). The function of this model is to simulate how the source rock continuously generates natural gas in the long geological history. That is, the model calculates the gas production reaction rate coefficients (k i and Ω iUsing these parameters and conditions as basic parameters, the function T(t) representing the change of formation temperature over time, determined by basin simulation and tectonic history, is used as input. By substituting these parameters and conditions into formulas (1) and (2) for calculation, the model can trace and accumulate the amount and characteristics of natural gas generated at every point in time from the past to the present, ultimately obtaining the complete chemical composition and isotopic information of pure natural gas generated from source rocks at the present moment. Combined with the continuous burial-thermal evolution history restored in the first step, i.e., the temperature history function T(t) and t(t) obtained from basin simulation and tectonic history in the first step, the model can achieve the same results. event , t0, t f The kinetic parameters fitted in the second step include the reaction frequency coefficient (k i ) and temperature sensitivity index (Ω) i The dynamic geochemical model simulates the generation process of gas from the pyrolysis of source rocks. It describes the process of natural gas components and isotopes accumulating and being generated during the continuous burial and heating of source rocks.

[0020] Cumulative yield C of source rock pyrolysis gas i,s (t f Based on a first-order reaction kinetic model, by analyzing the entire geological timeframe from t0 to the final hydrocarbon accumulation t... f The generation rate is calculated by integral: (1); (2); In equations (1)-(2), C i The reaction frequency coefficient; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of convertible precursors in the source rock; It is the isotopic value of the gas generated instantaneously; It is C i The generation rate at that moment; C i In this context, i represents the number of the gas component (i=1, C1 is methane, i=2, C2 is ethane); t represents the geological time; exp() is the natural exponential function, which is an exponential function with the real number e (e≈2.71828) as its base. For component i at the final time t f The cumulative mole fraction or yield generated from source rock (S); I The isotope value (‰) of the gas generated instantaneously at time t.

[0021] Formula (1) is the cumulative yield integral formula based on the Arrhenius equation, and Formula (2) is the weighted average integral formula of the cumulative isotope composition.

[0022] Fourthly, build a dynamic geochemical model of secondary cracking gas (second mother-source gas) in reservoirs coupled with geological events (t event ) in the following formula (3) and (4).

[0023] This dynamic geochemical model describes the dynamic process of oil cracking starting at a specific geological period, which starts at the key time node t event ; calculate the cumulative yield C i,o (t f ) and the cumulative isotopic composition Iso C i,o (t f ).

[0024] In the second step, the heating is divided into stages, which means that the temperature is raised in stages from low to high at a certain rate (20°C / h or 2°C / h), and the temperature is kept constant at multiple preset temperature points. The gases generated in multiple different heating stages include methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane. The component content is tested by a gas chromatograph (GC), and the isotopic characteristic value is tested by an isotope ratio mass spectrometer (IRMS).

[0025] Calculate the dynamic coefficients used to describe the reaction rate of the two gas production processes, including the reaction frequency coefficient k i and the temperature sensitivity index Ω i ; that is: This calculation process is obtained by fitting the data using a parallel first-order reaction kinetic model after summarizing all the experimental data of the stages. Specifically, it is assumed that the generation of each gas component (such as methane) follows a first-order reaction equation controlled by the Arrhenius equation. The goal of the calculation is to find a set of dynamic coefficients that best describe the reaction process, i.e., the reaction frequency coefficient (k i ) and the temperature sensitivity index (Ω i ). The specific method to achieve this goal is to calculate a theoretical yield curve by continuously adjusting the values of k i and Ω i . Then, compare the theoretical curve with all the experimental data points, and calculate the sum of squared residuals (SSR) between them. The iteration process will continue until a set of k i and Ω i is found that makes the sum of squared residuals reach a minimum value, which is the final best fitting result. This calculation process is usually completed with existing kinetic analysis software (other people's software, Kinetics, software by Xinxu Xia and Professor Yongchun Tang) or self-programmed optimization programs using Python or MATLAB.

[0026] In the fourth step, the cumulative yield C is calculated by formula (3) and (4) i,o (t f ) and the cumulative isotopic composition Iso C i,o (t f ) are calculated as follows: (3) and (4) (3) and (4) where k i is the reaction frequency coefficient of C i ; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of the convertible precursor in the source rock; is the instantaneous generation gas isotope value; is the generation rate of C i at this moment.

[0027] Based on the results of the mathematical model, an analysis chart of gas composition under different mixing ratios is constructed, including: In the fifth step, the CH4, C2H6 content and Iso C i , i = 1, 2 The fifth step summarizes the final calculation results of the above complex modeling, making it the initial input data for subsequent mixing calculation and chart establishment. The fifth step is the final output result obtained by calculating the dynamic geochemical model established in the third and fourth steps.

[0028] In the sixth step, a gas source mixing chart for a specific gas field is established and applied, which is used to describe the final geochemical composition characteristics of the mixed parent gas under different proportions. The isotope value of the mixed gas is calculated by formula (5).

[0029] The contribution ratio X1 of the source rock pyrolysis gas (the first parent gas) is set to change from 0 to 1 (i.e. 0% to 100%), and the contribution ratio X2 of the oil secondary cracking gas (the second parent gas) is 1-X1. Based on the final characteristic values of the two pure source gases, i.e. the cumulative yield and isotope value of the source rock pyrolysis gas (the first parent gas) and the oil cracking gas (the second parent gas) calculated in the third and fourth steps, the theoretical geochemical parameter values of the mixed gas under a series of different mixing ratios X1 are calculated by weighting.

[0030] In the sixth step, the theoretical geochemical parameter values of the mixed gas under a series of different mixing ratios X1 are calculated by weighting. The calculation formula is as follows: (5); In formula (5), i is a gas component, i = 1 is methane, and i = 2 is ethane; k is a parent gas number (k = 1, 2, 3,..., N); X k is a contribution ratio of the parent gas k; w k (t) is a weighted function of a geological time scale; m i,k (t) is a function of a mole fraction of component i in the parent gas k with respect to a geological time scale; Iso C i,k (t) is a function of an isotopic composition (‰) of component i in the parent gas k with respect to a geological time scale; t0, t f are a starting time and a final time; IsoC i,mix is an isotopic composition (‰) of component i in a final mixed gas.

[0031] N is a total number of parent gases, N = 2; four key parameters are selected and include a component parameter m i,1 (t), a component parameter m i,2 (t), an isotopic parameter IsoC i,1 (t), and an isotopic parameter C i,2 (t). The above key parameters respectively refer to four groups of basic data required for mixing calculation when there are two source gases (hydrocarbon source rock pyrolysis gas and oil cracking gas, N = 2) and two components (methane and ethane) are selected for analysis. These data are calculated by the dynamic model of the third step and the fourth step, and specifically include:

[0032] Component and isotopic evolution data of the first parent gas (hydrocarbon source rock pyrolysis gas) (third step, formulas (1) and (2)): m 1,1 (t) and IsoC 1,1 (t): that is, a mole fraction (obtained from the cumulative yield C f (t 1,k )) and an isotopic composition of methane of the first parent gas at t f , unique values.

[0033] m 2,1 (t) and IsoC 2,1 (t): that is, a mole fraction (obtained from the cumulative yield C f (t 2,k )) and an isotopic composition of ethane of the first parent gas at t f , unique values.

[0034] Component and isotopic evolution data of the second parent gas (oil cracking gas) (fourth step, formulas (3) and (4)): m 1,2 (t) and IsoC1,2 (t): the mole fraction of the second parent gas methane (obtained from the cumulative yield C 1,o (t f ) and the isotopic composition as a function of time t (t event to t f ), a set of discrete values.

[0035] m 2,2 (t) and IsoC 2,2 (t): the mole fraction of the second parent gas methane (obtained from the cumulative yield C 2,o (t f ) and the isotopic composition as a function of time t (t event to t f ), a set of discrete values.

[0036] In the present example with two parent gases, the formula is as follows: ; IsoC i,mix is the isotopic composition of component i in the final mixture gas, i = 1 for methane and i = 2 for ethane; it is noted that this value is not a constant, but varies with the selected contribution ratio X2 of the second parent gas (ranging from 0 to 1) and the discrete data points of the second parent gas (crude oil cracking gas), and its calculation result represents the coordinate value of a point on the chart; m i,1 and IsoC i,1 are the fixed component mole fraction and isotopic composition of the source rock pyrolysis gas (first parent gas) at the final time tƒ; m i,2 (t) and IsoC i,2 (t) are the component mole fraction and isotopic composition of the crude oil cracking gas (second parent gas) at a certain specific discrete time point t.

[0037] Projecting the measured gas sample data onto the analysis chart determines the proportion of the two types of source gases; including: Establishing a grid-like analysis chart, taking the calculated final geochemical composition (IsoC1, IsoC2) of the pure source rock pyrolysis gas (first parent gas) as a fixed endpoint, and taking the geochemical composition of the secondary cracking gas of crude oil (second parent gas) at different thermal maturity stages as a series of dynamic endpoints; For each dynamic endpoint, respectively mixed with fixed endpoint according to different mixing ratio (for example, the contribution ratio of crude oil cracking gas from 0% to 100%), a series of theoretical mixing points are obtained (the calculation is shown according to formula (5)); the theoretical mixing points under the same crude oil maturity are connected into the equal maturity mixing line, at the same time, the points with the same mixing ratio on all the equal maturity mixing lines are connected into the equal ratio mixing line, finally forming a grid-shaped quantitative identification chart; the related examples can be seen in Figure 1 .

[0038] After establishing the quantitative identification chart, the natural gas samples of the target gas well are collected to obtain the measured data (i.e.IsoC1 and IsoC2), the measured parameter values are taken as a data point (X coordinate: IsoC2, Y coordinate: IsoC1), and the data point is positioned in the coordinate system of the grid-shaped quantitative identification chart, according to the position of the data point in the grid-shaped quantitative identification chart, the contribution ratio of the two source gases is determined.

[0039] In the two-dimensional coordinate system, two key geochemical parameters are selected, the theoretical mixed isotopic composition IsoC 2,mix is taken as the horizontal coordinate, and IsoC 1,mix is taken as the vertical coordinate, and the final composition of the pure hydrocarbon source rock pyrolysis gas (the first mother source gas) is taken as a fixed endpoint.

[0040] Example 3 According to the quantitative evaluation method of the intra-source pyrolysis gas and the extra-source cracking gas according to the embodiment 2, the difference lies in that: Taking C gas field and D gas field in a large superimposed basin in the west of China as examples, the specific application process of the present application is illustrated. The deep reservoirs of the two gas fields are both P2 layer system platform margin facies dolomite, and the main natural gas source is considered to be related to the underlying P1 layer system hydrocarbon source rock and the possible ancient oil reservoir in the reservoir.

[0041] Through the in-depth basin simulation research on the area, the detailed burial history and thermal evolution history are reconstructed. The research shows that the hydrocarbon source rock of P1 layer system enters the oil window from T1 (early Triassic) late, reaches the oil generation peak in J1 (early Jurassic) late, and then due to the continuous increase of burial depth and the increase of temperature, the early generated crude oil begins to crack and generate gas, and enters the wet gas stage; after J3-K1 (late Jurassic-early Cretaceous), the hydrocarbon source rock and the generated crude oil enter the high-mature stage, and mainly generate dry gas. The evolution history clearly reveals that there are two gas generation mechanisms of "hydrocarbon source rock cracking" and "crude oil secondary cracking" in the area. In order to ensure the representativeness of simulation, two kinds of key samples are preferred: one is a low mature hydrocarbon source rock sample which is highly matched with the P1 layer system hydrocarbon source rock mother substance type through geochemical index comparison, and is used to simulate "hydrocarbon source rock cracking gas"; the other is a typical marine low mature crude oil sample which is obtained in the adjacent area and is proved to be the same origin as the residual asphalt in the P2 reservoir in the area, and is used to simulate "crude oil secondary cracking gas".

[0042] The above low mature hydrocarbon source rock sample and marine low mature crude oil sample are respectively subjected to oil and gas simulation experiment in a semi-open system. The experiment covers a complete evolution sequence from low maturity to high-mature, and at multiple key maturity points (such as 0.7%, 1.0%, 1.3%, 2.0% and the like), the component and isotopic composition of gaseous products are collected and analyzed, and detailed geochemical evolution data are obtained. By using the data, the kinetic parameters representing the gas generation processes of hydrocarbon source rock cracking (first parent gas) and crude oil cracking (second parent gas) are respectively fitted. R o

[0043] The fitted kinetic parameters are respectively substituted into the first step reconstructed geological-thermal evolution history framework, and the dynamic geochemical models of the two parent gases are constructed by using the formula (1) and (2) of the application. Through model calculation, the final geochemical composition characteristics of pure hydrocarbon source rock cracking gas (first parent gas) and pure crude oil secondary cracking gas (second parent gas) at the final reservoir forming moment are obtained.

[0044] The carbon isotopes (Iso C 1 and Iso C 2 ) in the products are selected as key identification parameters. Taking Iso C 2 as the horizontal coordinate and Iso C 1 as the vertical coordinate, the final compositions of the parent gas A and the parent gas B calculated are taken as two end points. Then, according to different mixing proportions (the proportion of the second parent gas from 0% to 100%), a series of Iso C 1 ​and Iso C 2 The points are connected to form a theoretical mixing line, and a scale is marked on the line, thereby establishing a gas source identification chart applicable to the P2 layer series gas reservoir in the region (see Figure 2 ).

[0045] Natural gas samples of multiple production wells in C gas field and D gas field are collected, and systematic geochemical tests are performed. The measured Iso C 1 and Iso C 2 data are taken as data points and projected onto the established identification chart.

[0046] The projection result shows that all sample points from C gas field and D gas field fall near the theoretical mixing line composed of pure end member A and pure end member B, clearly indicating that the two gas fields are typical binary mixed gas reservoirs. By reading the positions of each data point on the chart, the following quantitative conclusions are obtained:

[0047] (1) The sample points of C gas field are concentrated due to the relatively stable structure in the later period, and the calculation result shows that the contribution proportion of secondary cracking gas of crude oil in the natural gas is highly concentrated between 70% and 85%, indicating that the gas field is a natural gas reservoir dominated by cracking of ancient oil reservoirs and has good preservation conditions.

[0048] (2) The sample points of D gas field are more widely distributed, and the calculation result shows that the contribution proportion of secondary cracking gas of crude oil in the natural gas is between 60% and 85%. This wider proportion range is highly consistent with the structural reconstruction events experienced by the gas field in the later period. The structural tilting caused by the formation of K mountain anticline and the adjustment and escape of natural gas may cause a certain degree of fractionation of gas components in some well areas, or secondary mixing with a small amount of hydrocarbon source rock pyrolysis gas, thereby causing the complexity of gas source proportion.

[0049] This conclusion is highly consistent with the phenomenon that cracking bitumen is generally developed in C gas field, while oil and gas shows are slightly different in some regions of D gas field, proving the accuracy and reliability of the method, and providing a key quantitative basis for subsequent rolling exploration and development adjustment in the region.

[0050] The calculation result is shown in Table 1: Table 1 Application examples and results of the method in C and D gas fields

[0051] Example 3 A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the steps of a method for quantitative evaluation of in-situ pyrolysis gas and ex-situ pyrolysis gas according to embodiment 1 or 2 when executing the computer program.

[0052] Embodiment 4 A computer readable storage medium having stored thereon a computer program, the computer program implementing the steps of a method for quantitative evaluation of in-situ pyrolysis gas and ex-situ pyrolysis gas according to embodiment 1 or 2 when executed by a processor.

Claims

1. A method for quantitatively evaluating in-source pyrolysis gas and out-of-source pyrolysis gas, characterized in that, include: First, mathematical models describing the changes of the two types of gaseous products with geological evolution are established respectively; Secondly, analytical charts of gas composition under different mixing ratios were constructed based on the results of the mathematical model. Finally, the measured gas sample data are projected onto the analysis chart to determine the ratio of the two types of source gases, thus completing the quantitative evaluation of in-source pyrolysis gas and external-source cracking gas.

2. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 1, characterized in that, Mathematical models describing the changes of the two types of gaseous products with geological evolution were established, including: The first step is to obtain the geological process constraints and starting materials, that is, to obtain the boundary conditions and initial inputs required to build the model. The boundary conditions refer to: defining a key time node as the starting point for the calculation of the dynamic geochemical model, which defines the calculation starting point for the source of crude oil cracking gas; at the same time, obtaining material samples representing the initial state of two gas production processes, including core samples representing the source rock parent material that have not undergone sufficient thermal evolution and crude oil or paleo-oil reservoir bitumen samples representing the early charging crude oil components. The second step involves obtaining gas production process data through heating experiments. The two substance samples obtained in the first step were placed in inert and closed reaction systems, respectively, and subjected to staged heating to simulate the gas production process of the two substance samples under continuous underground heating. The composition and isotopic characteristics of the gases generated in multiple different heating stages, including CH4 and C2H6, were obtained, along with IsoC2 and IsoC2. Dynamic coefficients describing the reaction rates of the two gas production processes, including the reaction frequency coefficient k, were calculated. i and temperature sensitivity index Ω i ; The third step is to construct a dynamic geochemical model of source rock pyrolysis gas. Combining the continuous burial-thermal evolution history recovered in the first step and the kinetic parameters fitted in the second step, the generation process of source rock pyrolysis gas is dynamically simulated. This dynamic geochemical model describes the process of natural gas components and isotopes accumulating and being generated during the continuous burial and heating process of source rocks. Cumulative yield C of source rock pyrolysis gas i,s (t f Based on a first-order reaction kinetic model, by analyzing the entire geological timeframe from t0 to the final hydrocarbon accumulation t... f The generation rate is calculated by integral: (1)； (2)； In equations (1)-(2), C i The reaction frequency coefficient; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of convertible precursors in the source rock; It is the isotopic value of the gas generated instantaneously; It is C i The generation rate at that moment; C i In this context, i represents the number of the gas component; t represents the geological time; and exp() represents the natural exponential function, which is an exponential function with the real number e as the base. For component i at the final time t f Cumulative mole fraction or yield of hydrocarbons generated from source rocks; I The isotope values ​​of the gas generated instantaneously at time t; The fourth step is to construct a dynamic geochemical model of secondary cracked gas in reservoirs coupled with geological events; This dynamic geochemical model describes the dynamic process of crude oil cracking that begins at a specific geological time point t. event ; Calculate the cumulative yield C i,o (t f Iso and its accumulated isotopes constitute Iso C i,o (t f ).

3. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 2, characterized in that, In the second step, the staged heating means: using programmed heating to raise the temperature from a low temperature to a high temperature at a specific rate, and maintaining a constant temperature at multiple preset temperature points; The gases generated in multiple different heating stages include methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane; the component contents were obtained by gas chromatography; and the isotope characteristic values ​​were obtained by stable isotope mass spectrometry.

4. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 2, characterized in that, In the fourth step, the cumulative yield C is calculated using formulas (3) and (4). i,o (t f Iso and its accumulated isotopes constitute Iso C i,o (t f ); Specifically as follows: (3)； (4)； In the formula, k i C i The reaction frequency coefficient; Ω i is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function; Ps(t) is the abundance function of convertible precursors in the source rock; It is the isotopic value of the gas generated instantaneously; It is C i The generation rate at that moment.

5. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 1, characterized in that, Based on the results of the mathematical model, analytical charts of gas composition under different mixing ratios were constructed, including: The fifth step involves calculating the CH4 and C2H6 contents and Iso content of the source rock pyrolysis gas and the crude oil secondary cracking gas, respectively. C i i=1,2; The sixth step is to establish and apply a gas source mixing map for a specific gas field, which is used to describe the final geochemical composition characteristics after mixing of different proportions of source gas. If the contribution ratio X1 of the source rock pyrolysis gas changes from 0 to 1, then the contribution ratio X2 of the crude oil secondary cracking gas is 1-X1. Based on the final characteristic values ​​of the two pure source gases, namely the cumulative yield and isotopic values ​​of the source rock pyrolysis gas and crude oil cracking gas calculated in the third and fourth steps, the theoretical geochemical parameters of the mixed gas under a series of different mixing ratios X1 are calculated by weighting.

6. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 5, characterized in that, In step six, the theoretical geochemical parameters of the mixture are calculated using weighted averages for a series of different mixing ratios X1; the calculation formula is as follows: (5); In equation (5), i represents the gas component, i=1 for methane and i=2 for ethane; k is the source gas number; X k The contribution ratio of the parent gas k; w k (t) is a weighted function of geological timescales; m i,k (t) is a function of the mole fraction of component i in source gas k as a function of geological time scale; Iso C i,k (t) is a function of the isotopic composition of component i in source gas k as a function of geological time scale; t0, t f For start time and end time; IsoC i,mix The isotopic composition of component i in the final gas mixture.

7. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 1, characterized in that, Projecting measured gas sample data onto an analytical chart determines the ratio of the two source gases; this includes: Establish a grid-like analysis chart, using the final geochemical composition of the calculated pure hydrocarbon source rock pyrolysis gas as a fixed endpoint, and the geochemical composition of the secondary cracked gas of crude oil at different thermal maturity stages as a series of dynamic endpoints. For each dynamic endpoint, mixing calculations are performed with the fixed endpoint according to different mixing ratios to obtain a series of theoretical mixing points. The theoretical mixing points under the same crude oil maturity are connected to form an equal maturity mixing line. At the same time, points with the same mixing ratio on all equal maturity mixing lines are connected to form an equal proportion mixing line, ultimately forming a grid-like quantitative identification chart. After establishing the quantitative identification chart, natural gas samples from the target gas well are collected to obtain measured data. These measured parameter values ​​are used as data points and located in the coordinate system of the grid-like quantitative identification chart. Based on the position of the data point in the grid of the grid-like quantitative identification chart, the contribution ratio of the two source gases is simultaneously read and determined.

8. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 7, characterized in that, Two key geochemical parameters are selected in a two-dimensional coordinate system to determine the theoretical mixing isotopic composition IsoC. 2,mix The x-axis is IsoC 1,mix The vertical axis is used as the ordinate, and the final composition of the calculated pure hydrocarbon source rock pyrolysis gas is used as a fixed endpoint.

9. A computer device comprising a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the quantitative evaluation method for in-source pyrolysis gas and out-of-source pyrolysis gas according to any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor to implement the steps of the method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas as described in any one of claims 1-8.

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