A method for quantitative evaluation of in-situ pyrolysis gas and ex-situ pyrolysis gas

Abstract

The present application relates to a kind of source pyrolysis gas and source outside pyrolysis gas quantitative evaluation method, comprising: first, respectively establish the mathematical model describing the change of two types of gas products with geological evolution;Second, based on the results of mathematical model, build the analysis chart of gas composition under different mixing ratio;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 source pyrolysis gas and source outside pyrolysis gas is completed.The present application constructs a dynamic evolution model reflecting geological history to replace the traditional static model, and generates a gas source contribution ratio identification chart based on the model.Through the measured data point projection, quantitative analysis can be completed, which overcomes the limitations of traditional methods and improves the accuracy and reliability of identification.

Description

Technical Field

[0001] This invention relates to the fields of natural gas geochemistry and petroleum exploration technology, specifically to a quantitative characterization method for the origin of natural gas in deep to ultra-deep complex gas reservoirs. This method aims to quantitatively distinguish between two main thermogenic gases: source rock pyrolysis gas and secondary cracking gas of crude oil in the reservoir. It takes into account the dynamic geological evolution process and is particularly suitable for resource evaluation and favorable zone prediction in oil and gas exploration and development. Background Technology

[0002] Deep to ultra-deep natural gas reservoirs represent a crucial frontier and strategic successor area in current oil and gas exploration and development. A significant geological characteristic of these reservoirs is their complex and multi-stage formation history, encompassing long-term deep burial, multiple tectonic movements, and complex thermal evolution processes. This complex geological background leads to diverse natural gas sources. For example, a single reservoir may contain natural gas generated from the continuous cracking of kerogen within source rocks, as well as natural gas generated from the secondary cracking of early-accumulated crude oil due to intensified later thermal evolution; the mixing of multiple natural gas sources is widespread. Therefore, accurately identifying the origins and contribution proportions of various genetic source gases in the mixed gas has become a core technical challenge in the exploration and evaluation of deep to ultra-deep gas reservoirs, directly impacting the accurate assessment of resource potential, the effective reduction of exploration risks, and the scientific formulation of development plans. For deep gas reservoirs that have undergone multiple tectonic phases and complex thermal histories, the geochemical characteristics of the source gas itself are the result of dynamic accumulation throughout geological history. Therefore, to further improve the accuracy of quantitative characterization under complex geological backgrounds, it is still necessary to develop a technical solution that better reflects the finer segmentation of endmembers and the dynamic nature of geological processes. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for quantitative characterization of deep and ultra-deep natural gas from multiple sources, which solves the problem of difficulty in determining the contribution ratio of two types of gas sources (one from source rock gas and the other from crude oil cracking gas) in gas reservoirs during high-temperature evolution stages.

[0004] The technical solution of the present invention is as follows:

[0005] A method for quantitatively evaluating in-source pyrolysis gas and out-of-source pyrolysis gas includes:

[0006] First, mathematical models describing the changes of the two types of gaseous products with geological evolution are established respectively;

[0007] Secondly, analytical charts of gas composition under different mixing ratios were constructed based on the results of the mathematical model.

[0008] 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.

[0009] According to a preferred embodiment of the present invention, mathematical models describing the changes of two types of gaseous products with geological evolution are established respectively; including:

[0010] 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.

[0011] 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 ;

[0012] 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.

[0013] 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:

[0014] (1);

[0015] (2);

[0016] 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 Ci 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 generated from source rocks; I Let t be the isotope value of the gas generated instantaneously at time t.

[0017] The fourth step is to construct a dynamic geochemical model of secondary cracked gas in reservoirs coupled with geological events;

[0018] 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 ).

[0019] In a further preferred embodiment, the second step of staged heating refers to: 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;

[0020] 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.

[0021] In a further preferred 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:

[0022] (3);

[0023] (4);

[0024] 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 Ci The generation rate at that moment.

[0025] According to a preferred embodiment of the present invention, an analytical chart of gas composition under different mixing ratios is constructed based on mathematical model results; comprising:

[0026] 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;

[0027] 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.

[0028] 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.

[0029] 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.

[0030] In a further preferred step, the sixth step involves calculating the theoretical geochemical parameters of the mixture under a series of different mixing ratios X1 using a weighted average method; the calculation formula is as follows:

[0031] (5);

[0032] 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.

[0033] According to a preferred embodiment of the present invention, the measured gas sample data is projected onto an analytical chart to determine the ratio of the two types of source gases; including:

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The beneficial effects of this invention are as follows:

[0041] 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

[0042] 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.

[0043] Figure 2This 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

[0044] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0045] Example 1

[0046] 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:

[0047] First, mathematical models describing the changes of the two types of gaseous products with geological evolution are established respectively;

[0048] Secondly, analytical charts of gas composition under different mixing ratios were constructed based on the results of the mathematical model.

[0049] 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.

[0050] Example 2

[0051] The difference between the quantitative evaluation method for in-source pyrolysis gas and out-of-source pyrolysis gas described in Example 1 is as follows:

[0052] Mathematical models describing the changes of the two types of gaseous products with geological evolution were established, including:

[0053] 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 construct the model. Boundary conditions refer to defining a key time point as the starting point for the dynamic geochemical model calculation. This key time point is defined based on basin simulation and tectonic history analysis, and typically corresponds to the critical tectonic movement period that led to rapid deep burial or heating of the reservoir (t...). event This key time point defines the starting point for calculating the source of crude oil cracked gas (second source gas); at the same time, material samples representing the starting state of the two gas production processes are obtained, including core samples representing the source rock parent material that have not undergone sufficient thermal evolution (representing the first source gas) and crude oil or ancient reservoir bitumen samples representing the early charging crude oil components (representing the second source gas).

[0054] 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 ;

[0055] The third step is to construct a dynamic geochemical model of source rock pyrolysis gas (first source gas). The core of this dynamic geochemical model is a complete calculation process, which is specifically implemented by the following formulas (1) and (2). The function of this model is to simulate how source rocks continuously generate natural gas throughout a long geological history. That is, the model will use the gas production reaction rate coefficient (k) calculated in the second step experiment. i and Ω i Using 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.

[0056] 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:

[0057] (1);

[0058] (2);

[0059] In equations (1)-(2), Ci 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.

[0060] 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.

[0061] The fourth step is to construct a model related to geological events (t). event The dynamic geochemical model of crude oil secondary cracking gas (secondary source gas) coupled in the reservoir; namely, formulas (3) and (4) below.

[0062] 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 ).

[0063] In the second step, the staged heating refers to: using programmed heating to raise the temperature from a low temperature to a high temperature at a specific rate (20°C / h or 2°C / h), and maintaining the temperature at multiple preset temperature points;

[0064] The gases generated in the various heating stages include methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane; the component contents were obtained by gas chromatography (GC); and the isotope characteristics were obtained by stable isotope mass spectrometry (IRMS).

[0065] Calculate the dynamic coefficients used to describe the reaction rates of the two gas-producing processes, including the reaction frequency coefficient k. i and temperature sensitivity index Ω i ; refers to:

[0066] The calculation was performed by summing up the experimental data from all stages and fitting the data to a parallel first-order reaction kinetic model. Specifically, it was assumed that the formation of each gaseous component (such as methane) followed a first-order reaction equation governed by the Arrhenius equation. The goal of the calculation was to find a set of dynamic coefficients that best described the reaction process, i.e., the reaction frequency coefficients (k... i ) and temperature sensitivity index (Ω) i The specific method to achieve this goal is: by continuously adjusting k i and Ω i A theoretical yield curve is calculated numerically. Then, this theoretical curve is compared with all experimentally measured data points, and the sum of squared residuals (SSR) is calculated between the two. The iterative process continues until a set of k that minimizes the SSR is found. i and Ω i This set of parameters represents the final best-fit result. This calculation process is usually accomplished using existing dynamic analysis software (other people's software, Kinetics, the software by Professors Xia Xinyu and Tang Yongchun) or by using optimization programs programmed in Python or MATLAB.

[0067] 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:

[0068] (3);

[0069] (4);

[0070] 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.

[0071] Based on the results of the mathematical model, analytical charts of gas composition under different mixing ratios were constructed, including:

[0072] 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. Ci i=1,2;

[0073] The fifth step summarizes the final calculation results of the complex modeling described above, making them the initial input data for subsequent hybrid calculations and map creation. The fifth step involves calculating the final output results using the dynamic geochemical model established in steps three and four.

[0074] The sixth step is to establish and apply a gas source mixing map for a specific gas field. This gas source mixing map is used to describe the final geochemical composition characteristics after mixing of different proportions of source gas. The isotopic values ​​after mixing are calculated by formula (5).

[0075] If the contribution ratio X1 of the source rock pyrolysis gas (first source gas) changes from 0 to 1 (i.e. 0% to 100%), then the contribution ratio X2 of the crude oil secondary cracking gas (second source gas) is 1-X1.

[0076] 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 (first source gas) and crude oil cracking gas (second source 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.

[0077] 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:

[0078] (5);

[0079] In equation (5), i represents the gas component, i=1 for methane and i=2 for ethane; k is the source gas number (k=1, 2, 3...N); 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.

[0080] N represents the total number of source gases, N=2; four key parameters are selected, including component parameter m. i,1 (t), component parameter m i,2 (t), isotopic parameter IsoC i,1 (t) and isotopic parameter C i,2(t);

[0081] The aforementioned key parameters refer to the four sets of basic data required for mixed calculations when two source gases (pyrolysis gas from hydrocarbon source rocks and cracked crude oil, N=2) are present, and methane and ethane are selected for analysis. These data are all calculated by the dynamic model in steps three and four, and specifically include:

[0082] Composition and isotopic evolution data of the first source gas (pyrolysis gas from source rocks) (Step 3, Equations (1) and (2)):

[0083] m 1,1 (t) and IsoC 1,1 (t): That is, the first source gas at t f The mole fraction of methane at time (derived from the cumulative yield C) 1,k (t f (It can be obtained) and isotopic composition, unique value.

[0084] m 2,1 (t) and IsoC 2,1 (t): That is, the first source gas at t f The mole fraction of ethane at time (derived from the cumulative yield C) 2,k (t f (It can be obtained) and isotopic composition, unique value.

[0085] Composition and isotopic evolution data of the second source gas (crude oil cracking gas) (step four, formulas (3) and (4)):

[0086] m 1,2 (t) and IsoC 1,2 (t): the mole fraction of methane from the second source gas (derived from the cumulative yield C). 1,o (t f (It can be obtained that) and isotopic composition with time t (t event To t f A function that changes, a set of discrete values.

[0087] m 2,2 (t) and IsoC 2,2 (t): the mole fraction of ethane in the source gas (derived from the cumulative yield C). 2,o (t f (It can be obtained that) and isotopic composition with time tt(t) event To t f A function that changes, a set of discrete values.

[0088] In this invention example, when the number of source gases is 2, the calculation formula is as follows:

[0089] ;

[0090] IsoC i,mix This represents the isotopic composition of component i in the final gas mixture, where i=1 represents methane and i=2 represents ethane. It's important to note that this value is not a fixed constant, but rather varies with the contribution ratio X2 of the selected second source gas (ranging from 0 to 1) and the discrete data points of the second source gas (crude oil cracking gas). The calculated result represents the coordinates of a point on the chart. i,1 and IsoC i,1 These represent the fixed component mole fractions and isotopic composition of the pyrolysis gas from the source rock (first source gas) at the final time tƒ; m i,2 (t) and IsoC i,2 (t) represents the mole fraction and isotopic composition of crude oil cracked gas (second source gas) at a specific discrete time point t.

[0091] Projecting measured gas sample data onto an analytical chart determines the ratio of the two source gases; this includes:

[0092] Establish a grid-like analysis chart, using the final geochemical composition (IsoC1, IsoC2) of the calculated pure source rock pyrolysis gas (first source gas) as a fixed endpoint, and the geochemical composition of crude oil secondary cracking gas (second source gas) at different thermal maturity stages as a series of dynamic endpoints.

[0093] For each dynamic endpoint, mixing calculations are performed with the fixed endpoint at different mixing ratios (e.g., the contribution ratio of crude oil cracking gas ranges from 0% to 100%) (calculation basis is shown in formula (5)), resulting in 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, and 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; relevant examples can be found Figure 1 .

[0094] After establishing the quantitative identification chart, natural gas samples from the target gas well are collected to obtain measured data (i.e., IsoC1 and IsoC2). These measured parameter values ​​are used as a data point (X coordinate: IsoC2, Y coordinate: IsoC1) 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.

[0095] 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,mixThe vertical axis is used as the coordinate axis, and the final composition of the calculated pure hydrocarbon source rock pyrolysis gas (first source gas) is used as a fixed endpoint.

[0096] Example 3

[0097] The difference between the quantitative evaluation method for in-source pyrolysis gas and out-of-source pyrolysis gas described in Example 2 is as follows:

[0098] Taking the C and D gas fields in a large superimposed basin in western my country as examples, the specific application process of this invention is illustrated. The deep reservoirs of these two gas fields are platform marginal facies dolomite of the P2 layer, and their main natural gas source is believed to be related to the underlying P1 layer source rocks and possible ancient oil reservoirs.

[0099] Through in-depth basin simulation studies of this region, its detailed burial and thermal evolution history was reconstructed. The study shows that the source rocks of the P1 strata entered the oil-generating window from the late T1 (Early Triassic), reaching their peak in the late J1 (Early Jurassic). Subsequently, due to the continuous increase in burial depth and temperature, the early-generated crude oil began to crack and generate gas in large quantities, entering a wet gas stage. After J3-K1 (Late Jurassic-Early Cretaceous), both the source rocks and the generated crude oil entered a high-to-overmature stage, primarily generating dry gas. This evolutionary history clearly reveals the existence of two gas generation mechanisms in this region: "source rock pyrolysis" and "secondary cracking of crude oil." To ensure the representativeness of the simulation, this invention selects two key samples: one is a low-mature source rock sample that is highly matched with the parent material type of the P1 layer in the region by geochemical index comparison, used to simulate "source rock pyrolysis gas"; the other is a typical marine low-mature crude oil sample obtained from the adjacent area, which has been confirmed to be genetically homologous with the residual bitumen in the P2 reservoir of this region, used to simulate "secondary cracking gas of crude oil".

[0100] The aforementioned low-maturity source rock samples and marine low-maturity crude oil samples were subjected to hydrocarbon generation simulation experiments in a semi-open system. The experiments covered the complete evolutionary sequence from low maturity to high-over-maturity, and included simulations at several key maturity points (such as...). R o The composition and isotopic composition of gaseous products (e.g., 0.7%, 1.0%, 1.3%, 2.0%) were collected and analyzed, yielding detailed geochemical evolution data. Using this data, kinetic parameters representing the gas generation processes of source rock pyrolysis (first source gas) and crude oil cracking (second source gas) were fitted.

[0101] The fitted kinetic parameters were substituted into the geological-thermal evolutionary history framework reconstructed in the first step, and dynamic geochemical models of two source gases were constructed using formulas (1) and (2) of this invention. Through model calculations, the final geochemical composition characteristics of pure source rock pyrolysis gas (first source gas) and pure crude oil secondary cracking gas (second source gas) at the final hydrocarbon accumulation moment were obtained.

[0102] Select carbon isotopes (Iso) from the products C 1 and Iso C 2 (Iso) is used as the key identification parameter. C 2 Iso is the x-axis. C 1 Using the vertical axis as the ordinate, the calculated final compositions of source gas A and source gas B are used as the two endpoints. Then, according to different mixing ratios (the proportion of the second source gas ranging from 0% to 100%), a series of theoretical mixing points are calculated using Iso. C 1 and Iso C 2 Values ​​were used to connect these points, forming a theoretical mixing line. A scale was then marked on the line, thus establishing a gas source identification chart applicable to the P2 layer gas reservoirs in this region (see...). Figure 2 ).

[0103] Natural gas samples were collected from multiple production wells in gas fields C and D, and systematic geochemical tests were conducted. The measured isotopes of these samples were then analyzed. C 1 and Iso C 2 The data, as data points, is projected onto the established identification chart.

[0104] The plotting results show that all sample points from gas fields C and D fall near the theoretical mixing line formed by pure endmembers A and B, clearly indicating that both gas fields are typical binary mixing-genetic gas reservoirs. Quantitative conclusions were drawn by reading the positions of each data point on the plot:

[0105] (1) Due to the relatively stable structure in the later stage, the sample points of the C gas field are concentrated. The calculation results show that the contribution ratio of crude oil secondary cracking gas in its natural gas is highly concentrated between 70% and 85%, indicating that the gas field is a natural gas reservoir with ancient oil reservoir cracking as the absolute mainstay and good preservation conditions.

[0106] (2) The sample point distribution range of the D gas field is wider, and the calculation results show that the contribution ratio of secondary cracked crude oil gas in its natural gas is between 60% and 85%. This wider range of proportions is highly consistent with the tectonic modification events experienced by the gas field in the later period. The tectonic tilting and natural gas adjustment and dissipation caused by the formation of the K mountain anticline may have caused a certain degree of fractionation of the gas components in some well areas, or secondary mixing with trace amounts of source rock pyrolysis gas in the later period, thus complicating the gas source ratio.

[0107] This conclusion is highly consistent with the phenomenon observed in regional exploration practice where cracked bitumen is prevalent in gas field C, while oil and gas shows show slight differences in some areas of gas field D. This demonstrates the accuracy and reliability of the method of this invention and provides crucial quantitative basis for subsequent rolling exploration and development adjustments in this region.

[0108] The calculation results are shown in Table 1:

[0109] Table 1. Application examples and results of the method of the present invention in gas fields C and D;

[0110]

[0111] Example 3

[0112] 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 quantitative evaluation method for source-internal pyrolysis gas and source-external pyrolysis gas described in Embodiment 1 or 2.

[0113] Example 4

[0114] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a method for quantitative evaluation of source-internal pyrolysis gas and source-external pyrolysis gas as described in Embodiment 1 or 2.

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 and complete the quantitative evaluation of in-source pyrolysis gas and external-source cracking gas. 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 that represent the initial state of two gas production processes, including core samples that have not undergone sufficient thermal evolution and represent the source rock parent material, and crude oil or paleo-oil reservoir bitumen samples that represent 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 R is the temperature sensitivity index; R is the gas constant; T(t) is the temperature under the geological function. is an abundance function of convertible precursors in source rocks; It is the isotopic value of the gas generated instantaneously; It is C i The generation rate at time t; 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 The cumulative mole fraction or yield generated from source rocks; 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 IsoC and its accumulated isotopes form IsoC i,o (t f ).

2. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 1, 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.

3. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 1, characterized in that, In the fourth step, the cumulative yield C is calculated using formulas (3) and (4). i,o (t f IsoC and its accumulated isotopes form IsoC 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.

4. 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 IsoC content of the source rock pyrolysis gas and the crude oil secondary cracking gas, respectively. 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.

5. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 4, 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; IsoC 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.

6. 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.

7. The method for quantitative evaluation of in-source pyrolysis gas and out-of-source pyrolysis gas according to claim 6, 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.

8. 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 1-7.

9. 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 1-7.

Images