A method for quantitatively describing pressure plane distribution of source rock in a few-well area
By setting up virtual wells in areas with few wells and utilizing hydrocarbon generation pressurization and undercompactment pressurization models, combined with Kriging interpolation, the accuracy problem of formation pressure plane characterization in areas with few wells was solved, and high-precision pressure distribution of source rock formations was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA UNIV OF PETROLEUM (EAST CHINA)
- Filing Date
- 2026-03-05
- Publication Date
- 2026-06-02
AI Technical Summary
In areas with few wells, existing technologies struggle to accurately characterize formation pressure planes using well and seismic data, especially when exploration levels are low or seismic signal resolution is low. Traditional methods are highly dependent on these methods and prone to large errors.
By setting up virtual wells, the overpressure is calculated using hydrocarbon generation pressurization models and under-pressurization models. Combined with Kriging interpolation, the planar distribution of pressure in the source rock formation is quantitatively characterized, reducing the reliance on the number of actual drilled wells and seismic data.
This method improves the accuracy of the planar distribution of pressure in hydrocarbon source rock formations in areas with few wells, reduces reliance on actual drilling and seismic data, and enhances the operability and accuracy of the method.
Smart Images
Figure CN121787134B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of formation overpressure analysis technology, and in particular to a method for quantitatively characterizing the planar distribution of pressure in hydrocarbon source rock formations in areas with few wells. Background Technology
[0002] Formation overpressure, as a hydrocarbon accumulation factor, influences various aspects of hydrocarbon generation, migration, and accumulation. Accurate characterization of formation pressure plays a crucial role in advancing oil and gas exploration. Currently, conventional methods for predicting planar formation pressure are mostly based on well data. These methods often establish a correlation between actual well logging data, such as sonic transit time, and geological attributes like effective stress and formation pressure. Prediction parameters are adjusted based on measured pressure data to obtain the target formation pressure for each individual well, which is then interpolated to obtain the planar overpressure distribution. Common methods include the Eaton method and the Bowers method.
[0003] However, in some areas with few wells, due to the limited number of actual drilled wells, traditional methods relying on a large amount of well data are insufficient to meet the needs of depicting formation pressure planes. In such cases, it is often necessary to turn to methods relying on seismic data, such as the Fillippone method and seismic inversion methods. However, these methods also face serious challenges: on the one hand, for preliminary exploration areas with low exploration levels, there is often a lack of high-quality 3D seismic data covering the entire area; on the other hand, even if seismic data is available, when the target source rock strata are buried too deep, the seismic signal resolution is low and the quality is poor, resulting in large errors in the inversion and prediction results, making it difficult to meet the accuracy requirements.
[0004] Therefore, in areas with few wells, neither traditional methods relying on well data nor alternative methods relying on seismic data can reliably characterize formation pressure. How to provide a planar formation pressure characterization method with low dependence on well-seismic data and high accuracy is a technical problem that urgently needs to be solved. Summary of the Invention
[0005] This application addresses, to at least some extent, one of the technical problems in the related art.
[0006] Therefore, this application aims to provide a method for quantitatively characterizing the plane distribution of source rock pressure in areas with few wells. The method calculates the overpressure of virtual wells using a hydrocarbon generation and pressurization model, thereby calculating the predicted formation pressure value of virtual wells. For actual drilled wells, the method calculates the formation pressure benchmark value using the Eaton method, and combines the method of Kriging interpolation to obtain the plane distribution of source rock pressure in areas with few wells.
[0007] To achieve the above objectives, in a first aspect, this application provides a method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in areas with few wells, comprising:
[0008] Virtual wells were set up in the study area to obtain the predicted parameters of hydrocarbon source rock formation pressure for each virtual well and the parameters of hydrocarbon source rock formation pressure for actual drilled wells.
[0009] Calculate the overpressure of the source rock formation in each virtual well based on the predicted pressure parameters of the source rock formation in the virtual well.
[0010] Calculate the predicted formation pressure of the virtual well based on the overpressure of the source rock layer of the virtual well;
[0011] Calculate the formation pressure benchmark value of the actual drilled well based on the pressure parameters of the source rock formation in the actual drilled well;
[0012] Kriging interpolation was performed based on the formation pressure baseline values from actual drilled wells and the formation pressure prediction values from virtual wells to obtain the planar distribution of source rock pressure in the study area.
[0013] In this embodiment, formation pressure is decomposed into overpressure generated by hydrocarbon generation and overpressure generated by undercompaction. Hydrocarbon generation pressure enhancement model and undercompaction statistical model are constructed and calculated separately to ensure prediction accuracy. Virtual wells are introduced to enable prediction under the condition of sparse actual drilling wells. This significantly reduces the requirements of traditional methods that rely on the number of actual drilling wells and the quality of seismic data, making it more operable and solving the problem that existing technologies rely too much on the density of actual drilling wells and seismic data for calculation.
[0014] In conjunction with the first aspect, in certain implementations of the first aspect, methods for calculating the overpressure of a virtual well source rock formation based on predicted parameters of the virtual well source rock formation include:
[0015] The overpressure generated by hydrocarbon generation is calculated using a hydrocarbon generation and pressurization model based on the predicted parameters of the source rock layer in the virtual well.
[0016] The overpressure generated by undercompaction is calculated using the undercompaction boosting model based on the predicted parameters of the source rock layer in the virtual well.
[0017] The overpressure of the source rock layer in the virtual well is calculated based on the overpressure generated by hydrocarbon generation and the overpressure generated by undercompaction.
[0018] In this embodiment, the overpressure generation mechanism is analyzed and divided into two main controlling factors: hydrocarbon generation-induced pressure increase and under-pressure compaction-induced pressure increase. This allows for the establishment of different models for calculation, ensuring the scientific rigor of the calculation process. Furthermore, starting from the geological formation of overpressure rather than relying on data from traditional drilled wells, the overpressure generation of hydrocarbons in virtual wells is predicted and calculated, overcoming the limitation of the number of drilled wells.
[0019] In conjunction with the first aspect, in certain implementations of the first aspect, methods for calculating the overpressure generated by hydrocarbon generation in virtual wells include:
[0020] The overpressure generated by oil production is calculated using an oil production and pressurization calculation model based on the predicted parameters of the source rock formation in the virtual well.
[0021] The overpressure generated by gas is calculated using a gas pressurization calculation model based on the predicted parameters of the source rock formation in the virtual well.
[0022] The overpressure generated by hydrocarbon generation is calculated based on the overpressure generated by oil generation and the overpressure generated by gas generation.
[0023] In this embodiment, the overpressure of hydrocarbon generation is divided into two parts: overpressure of oil generation and overpressure of gas generation. Based on the characteristics of each part, calculation models for oil generation pressurization and gas generation pressurization are established respectively. This ensures the integrity and continuity of hydrocarbon generation pressurization throughout the thermal evolution simulation and reduces the errors that may occur in the model calculation.
[0024] In conjunction with the first aspect, in some implementations of the first aspect, the calculation model for oil-fueled booster is as follows: ;
[0025] Wherein, ΔP o The pressure generated by source rock oil production is expressed in MPa; I is the hydrogen index of the source rock, expressed in mg / g; F is the kerogen oil conversion rate, expressed in %; P h C represents the hydrostatic pressure at the depth of the source rock, expressed in MPa. o The compressibility coefficient of crude oil, expressed in MPa. -1 V w1 The original volume fraction of pore water, expressed in %; C w The compressibility coefficient of pore water is expressed in MPa. -1 α is the petroleum residue coefficient, in %; ρ k This refers to the density of kerogen, expressed in g / cm³. 3 ;ρ o This refers to the density of crude oil, expressed in g / cm³. 3 M k1 The original mass fraction of kerogen is expressed as %; C k The compressibility coefficient of kerogen is expressed in MPa. -1 .
[0026] In this embodiment of the application, by establishing a calculation model for oil generation and pressurization suitable for this study area based on the product characteristics of the oil generation and pressurization stage, the pressurization process of the oil generation stage can be described more accurately, thereby improving the accuracy of predicting the overpressure amount of hydrocarbon generation.
[0027] In conjunction with the first aspect, in some implementations of the first aspect, the calculation model for boosting air pressure is as follows:
[0028] ;
[0029] Wherein, ΔP gF' represents the pressure generated by gas production from the source rock, in MPa; F' represents the conversion rate of kerogen gas, in %; M k2 β represents the original mass fraction of residual kerogen after oil generation, in %; β represents the natural gas residue coefficient, in %; P1 represents the initial formation pressure during gas generation, in MPa; C g The compressibility coefficient of natural gas, measured in MPa. -1 V w2 This represents the original volume fraction of pore water, expressed in %.
[0030] In the embodiments of this application, by establishing a gas generation pressurization calculation model applicable to this study area based on the product characteristics of the gas generation pressurization stage, the pressurization process of the gas generation stage can be described more accurately, thereby improving the accuracy of predicting the overpressure amount of hydrocarbon generation.
[0031] In conjunction with the first aspect, in certain implementations of the first aspect, the kerogen hydrocarbon conversion rate includes the kerogen oil conversion rate F and the kerogen gas conversion rate F', and the methods for calculating the kerogen hydrocarbon conversion rate include:
[0032] Set up the central virtual well and obtain its basic parameters;
[0033] The evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance were simulated and calculated based on the basic parameters and thermal evolution history of the central virtual well.
[0034] Based on the evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance and the vitrinite reflectance values of each virtual well, the kerogen hydrocarbon generation conversion rate can be read from the evolution curves.
[0035] In this embodiment of the application, by selecting a central virtual well and using its basic parameters to simulate its thermal evolution history, the evolution curves of hydrocarbon generation conversion rate and vitrinite reflectance are generated. This eliminates the need for complex simulations of each virtual well in the study area. By obtaining its relatively easy vitrinite reflectance value, the accurate hydrocarbon generation conversion rate can be read, thus solving the problem of obtaining key parameters in areas with few wells.
[0036] In conjunction with the first aspect, in some implementations of the first aspect, the undercompaction boosting model is a multiple regression model fitted with the undercompaction boosting amount as the dependent variable and the mud-soil ratio, sedimentation rate, and depth as independent variables, in the following form: ;
[0037] Wherein, ΔP 欠 The unit is undercompaction pressure increase, in MPa; Q is the mud-to-soil ratio; V is the formation deposition rate, in m / Ma; and H is the depth, in m.
[0038] In this embodiment of the application, by utilizing limited actual drilling data in the study area, and taking mud-soil ratio, sedimentation rate and depth as inputs, a, b, c and d fixed coefficients are fitted by multiple linear regression to form an under-pressure compaction model suitable for this study area. The model is then used to calculate virtual wells, thereby applying it to areas with limited actual drilling data and enhancing its practicality.
[0039] In conjunction with the first aspect, some implementations of the first aspect also include methods for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in areas with few wells, such as determining whether the hydrocarbon generation and pressurization model is applicable to the study area.
[0040] In this embodiment of the application, by determining whether the hydrocarbon generation pressurization model is applicable to the study area before large-scale calculations, the matching between the hydrocarbon generation pressurization model and the study area is ensured, and the accuracy of the hydrocarbon generation overpressure calculated by the hydrocarbon generation pressurization model in the study area is guaranteed.
[0041] In conjunction with the first aspect, among certain implementations of the first aspect, methods for determining whether the hydrocarbon generation and pressurization model is applicable to the study area include:
[0042] Based on the pressure parameters of the source rock formation in the actual drilled well, the predicted value of the overpressure generated by hydrocarbon generation in the actual drilled well is calculated using a hydrocarbon generation and pressurization model.
[0043] Calculate the benchmark value of overpressure generated by hydrocarbon generation in actual drilling based on the pressure parameters of the source rock formation in the actual drilling well.
[0044] The error between the baseline value of hydrocarbon overpressure in actual drilled wells and the predicted value of hydrocarbon overpressure in actual drilled wells is calculated.
[0045] Determine whether the error is less than a preset threshold;
[0046] If yes, then the hydrocarbon generation and pressurization model is applicable to the study area; otherwise, the hydrocarbon generation and pressurization model or its parameters are not applicable to the study area.
[0047] In this embodiment, a reliable pressure value is calculated using the effective stress method and compared with the hydrocarbon generation pressure increase calculated by the hydrocarbon generation pressure increase model, thereby ensuring the accuracy and reliability of the subsequent virtual well data verification.
[0048] In conjunction with the first aspect, in certain implementations of the first aspect, methods for calculating the predicted formation pressure of a virtual well based on the overpressure of the source rock formation include:
[0049] The hydrostatic pressure of the virtual well is calculated based on the predicted parameters of the source rock pressure of the virtual well.
[0050] The predicted formation pressure of the virtual well is calculated based on the hydrostatic pressure of the virtual well and the overpressure of the source rock layer of the virtual well.
[0051] In this embodiment of the application, the hydrostatic pressure and overpressure are calculated separately. When calculating the overpressure, the overpressure is further divided into the overpressure generated by hydrocarbon generation and the overpressure generated by undercompaction. The accuracy of the final result is ensured by calculating in blocks.
[0052] Compared with the prior art, the advantages and positive effects of this application include at least the following:
[0053] The method provided in this application for quantitatively characterizing the planar distribution of source rock pressure in low-well areas calculates predicted and baseline values of formation pressure using pressure parameters from different sources. The planar distribution of source rock pressure in low-well areas is then obtained by combining the predicted and baseline values with Kriging interpolation. This method provides a highly accurate quantitative characterization of the planar distribution of source rock pressure in low-well areas. Attached Figure Description
[0054] Figure 1 This is a flowchart illustrating a method for quantitatively characterizing the plane distribution of pressure in hydrocarbon source rock formations in areas with few wells, according to an embodiment of this application.
[0055] Figure 2 This is a flowchart illustrating the method for calculating the overpressure of a virtual well source rock layer based on predicted parameters of the virtual well source rock layer according to an embodiment of this application.
[0056] Figure 3 This is a flowchart illustrating a method for calculating the overpressure generated by hydrocarbon generation in a virtual well according to an embodiment of this application.
[0057] Figure 4 This is a flowchart illustrating the method for calculating the hydrocarbon conversion rate of kerogen according to the embodiments of this application;
[0058] Figure 5 This is a flowchart illustrating a method for determining whether a hydrocarbon generation booster model is applicable based on embodiments of this application.
[0059] Figure 6 This is a flowchart illustrating a method for calculating the predicted formation pressure of a virtual well based on the overpressure of the source rock layer of the virtual well, according to an embodiment of this application.
[0060] Figure 7 The curves showing the hydrocarbon conversion rate of kerogen from source rock and the reflectance of vitrinite are based on embodiments of this application.
[0061] Figure 8 This is a comparison chart of the results of the actual drilling hydrocarbon generation and pressurization model and the effective stress method in the study area of this application embodiment;
[0062] Figure 9 This is a graph showing the relative error between the actual drilling hydrocarbon generation and pressurization model and the calculation results using the effective stress method in the study area of this application's embodiments;
[0063] Figure 10This is a diagram showing the relationship between the undercompaction boost amount and depth of the source rock in the study area of this application's embodiments;
[0064] Figure 11 This is a graph showing the relationship between the amount of undercompaction and the mud-soil ratio in the study area of the hydrocarbon source rock in the embodiment of this application. Detailed Implementation
[0065] The present application will now be described in detail through exemplary embodiments.
[0066] In existing technologies, accurate characterization of formation pressure is crucial for various aspects of oil and gas generation, migration, accumulation, and preservation in oil and gas exploration. Current methods for predicting planar formation pressure face two main problems: First, traditional methods such as the Eaton method and Bowers method heavily rely on well data for calculations, requiring extensive actual well logging data and measured pressures for calibration. This makes them difficult to apply in newly explored areas with few actual wells or complex structural zones due to insufficient data support, or results in significant calculation errors.
[0067] Secondly, while methods such as the Fillippone method and seismic inversion can compensate for the insufficient number of actual drilled wells, their accuracy is severely limited by the resolution and signal-to-noise ratio of seismic data, especially when the data quality is poor for deep targets or preliminary exploration areas, significantly reducing the reliability of their prediction results. In summary, in exploration scenarios with few wells and insufficient seismic data, existing technologies lack a plane pressure prediction method that is both low-dependent on well and seismic data and can guarantee accuracy.
[0068] Based on this, this application proposes a method for quantitatively characterizing the planar distribution of pressure in source rock formations in areas with few wells.
[0069] Figure 1 This is a schematic flowchart of a method for quantitatively characterizing the plane distribution of pressure in hydrocarbon source rock formations in a low-well area, provided by the first aspect of this application. The method includes the following steps.
[0070] S1. Set up virtual wells in the study area and obtain the predicted parameters of the source rock pressure of each virtual well and the pressure parameters of the source rock pressure of the actual drilled well.
[0071] Specifically, a virtual well is not a real borehole, but a computational node assigned precise spatial coordinates and complete geological property parameters. The depth, total organic carbon (TOC), and vitrinite reflectance (R) of the virtual well can be inferred through geological methods. o Key attributes such as mud-to-soil ratio are considered. The parameters for predicting source rock pressure in virtual wells are typically derived from a comprehensive interpretation and spatial interpolation of regional geological maps, geophysical data, and known research findings. The parameters for source rock pressure in actual drilled wells are derived from measured data during the drilling process and a comprehensive analysis of geological data from the study area and adjacent wells.
[0072] It should be noted that virtual wells can be set up using a regular grid layout within the study area. A regular planar coordinate grid is established within the planar boundary of the study area, with one virtual well placed at the intersection of each grid, thus ensuring uniform distribution of virtual wells. The number of virtual wells should be determined based on the area of the study area to ensure a sufficient number of virtual wells. The density of virtual wells should be dynamically adjusted according to the exploration and research stage and the geological complexity.
[0073] S2. Calculate the overpressure of the source rock layer in each virtual well based on the predicted pressure parameters of the source rock layer in the virtual well.
[0074] like Figure 2 As shown, the method for calculating the overpressure of the source rock layer in a virtual well based on the predicted parameters of the source rock layer is as follows.
[0075] S21. Calculate the overpressure generated by hydrocarbon generation using the hydrocarbon generation and pressurization model based on the predicted parameters of the source rock layer in the virtual well.
[0076] Specifically, the hydrocarbon generation pressurization model includes an oil generation pressurization calculation model and a gas generation pressurization calculation model. The oil generation pressurization calculation model and the gas generation pressurization calculation model used in this application are the quantitative hydrocarbon generation pressurization models established by Guo Xiaowen et al. based on the laws of conservation of mass and volume. In the embodiments of this application, the model is divided into an oil generation pressurization calculation model and a gas generation pressurization calculation model to be used for different maturity stages of source rock evolution.
[0077] like Figure 3 As shown, the method for calculating the overpressure generated by hydrocarbon generation in a virtual well is as follows.
[0078] S211. Calculate the overpressure generated by oil production using the oil production and pressurization calculation model based on the predicted parameters of the source rock formation in the virtual well.
[0079] Specifically, the calculation model for oil-fueled turbocharging is as follows:
[0080] ;
[0081] Wherein, ΔP o The pressure generated by source rock oil production is expressed in MPa; I is the hydrogen index of the source rock, expressed in mg / g; F is the kerogen oil conversion rate, expressed in %; P h C represents the hydrostatic pressure at the depth of the source rock, expressed in MPa. o The compressibility coefficient of crude oil, expressed in MPa. -1 V w1 The original volume fraction of pore water, expressed in %; C w The compressibility coefficient of pore water is expressed in MPa. -1 α is the petroleum residue coefficient, in %; ρk This refers to the density of kerogen, expressed in g / cm³. 3 ;ρ o This refers to the density of crude oil, expressed in g / cm³. 3 M k1 The original mass fraction of kerogen is expressed as %; C k The compressibility coefficient of kerogen is expressed in MPa. -1 .
[0082] It should be noted that the kerogen hydrocarbon conversion rate includes the kerogen oil conversion rate F, which represents the proportion of kerogen that has been converted into oil. This parameter is related to the hydrostatic pressure P at the depth of the source rock. h None of them can be obtained directly by measurement.
[0083] Crude oil compressibility coefficient C o The compressibility coefficient C of pore water w The compressibility coefficient C of kerogen k Density ρ of kerogen k The density ρ of crude oil o These are physical property parameters, which adopt accepted values in this field for this type of source rock (such as Type II kerogen) or empirical values obtained through experimental tests in this and adjacent areas. Petroleum residue coefficient α, original volume fraction of pore water V w1 These are geological and geochemical parameters, typically derived from geochemical analysis data of drill cores and well logging interpretation results within the study area.
[0084] Hydrogen index I of source rocks can be assigned a typical range of values for that type based on measured geochemical data or on its kerogen type (Type I, II, III).
[0085] The original mass fraction M of kerogen k1 Kerogen mass fraction refers to the percentage of kerogen content in the source rock before hydrocarbon generation, relative to the total rock mass. Kerogen mass fraction = rock density × total organic carbon content × conversion factor. Total organic carbon content (TOC) can be obtained from measured geochemical data or a planar distribution map. The conversion factor depends on the kerogen type; for example, the conversion factor for type II kerogen can be taken as 1.2.
[0086] The formula for calculating hydrostatic pressure is: .
[0087] Among them, P h ρ is the hydrostatic pressure, expressed in MPa. w This refers to the density of formation water, expressed in g / cm³. 3 g is the acceleration due to gravity, with units of m / s². 2 H represents the depth of the stratum, in meters (m).
[0088] like Figure 4As shown, the kerogen hydrocarbon conversion rate includes the kerogen oil conversion rate F and the kerogen gas conversion rate F'. The methods for calculating the kerogen hydrocarbon conversion rate include:
[0089] S2111. Set the central virtual well and obtain the basic parameters of the central virtual well.
[0090] Specifically, a geologically representative virtual well, whose location represents the main thermal evolution history of the source rocks in the study area, is selected as the central virtual well. The basic parameters of the central virtual well are obtained in the same way as those of ordinary virtual wells.
[0091] S2112. Based on the basic parameters and thermal evolution history of the central virtual well, simulate and calculate the evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectivity.
[0092] Specifically, the basic parameters of the central virtual well are input into specialized basin simulation software (such as PetroMod) to perform numerical simulation calculations. PetroMod software simulates the thermal evolution history, calculating the temperature experienced by each stratum at each geological period from deposition to the present, based on the aforementioned parameters and by solving heat conduction equations. After the simulation is complete, the temperature history is input into a kerogen hydrocarbon generation kinetic model (such as the LLNL model), and the simulation outputs the evolution curves of kerogen hydrocarbon conversion rate and vitrinite reflectance.
[0093] S2113. Based on the evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance and the vitrinite reflectance values of each virtual well, read the kerogen hydrocarbon generation conversion rate from the evolution curves.
[0094] Specifically, what the software generates are the evolution curves of kerogen oil conversion rate and vitrinite reflectance, and the evolution curves of kerogen gas conversion rate and vitrinite reflectance. The two curves share the same coordinate system. By selecting a vitrinite reflectance value, the kerogen oil conversion rate F and the kerogen gas conversion rate F' can be read from the two evolution curves.
[0095] S212. Calculate the overpressure generated by gas through the gas pressurization calculation model based on the predicted parameters of the source rock layer in the virtual well.
[0096] Specifically, the calculation model for boosting air pressure is as follows:
[0097] ;
[0098] Wherein, ΔP g F' represents the pressure generated by gas production from the source rock, in MPa; F' represents the conversion rate of kerogen gas, in %; M k2β represents the original mass fraction of residual kerogen after oil generation, in %; β represents the natural gas residue coefficient, in %; P1 represents the initial formation pressure during gas generation, in MPa; C g The compressibility coefficient of natural gas, measured in MPa. -1 V w2 This represents the original volume fraction of pore water, expressed in %.
[0099] It should be noted that the kerogen-to-gas conversion rate F' is obtained according to the method for calculating the kerogen-to-hydrogen conversion rate. The original mass fraction M of residual kerogen after oil generation... k2 The compressibility coefficient C of natural gas is obtained by progressively extrapolating from the previous calculations of oil consumption. g These are physical property parameters, obtained using regional experimental data or generally accepted values. The natural gas residual coefficient β and the original volume fraction of pore water V... w2 These are geological and geochemical parameters, typically derived from geochemical analysis data of drill cores and well logging interpretation results within the study area.
[0100] In this embodiment, the core basis for establishing the hydrocarbon generation and pressurization model is to obtain the unified kerogen oil generation conversion rate F and kerogen gas generation conversion rate F' curves for the entire study area through thermal evolution simulation of the central virtual well. Based on the current vitrinite reflectance, the corresponding kerogen oil generation conversion rate F and kerogen gas generation conversion rate F' can be obtained, and then the determined oil generation and pressurization calculation models and gas generation and pressurization calculation models can be obtained. By inputting different parameters (such as depth, mud-soil ratio, etc.) into the model, the pressurization amount at that point can be calculated.
[0101] In some embodiments of this application, because the geological conditions of the study area may not conform to the default assumptions of the model—for example, the study area may have multiple phases of hydrocarbon generation or an exceptionally complex thermal evolution history—the basic theory of the model may fail, and the hydrocarbon generation model may not be applicable to this study area. Therefore, as... Figure 5 As shown, the method for quantitatively characterizing the plane distribution of hydrocarbon source rock pressure in areas with few wells also includes a method for determining whether the hydrocarbon generation and pressurization model is applicable to the study area, as shown below.
[0102] S2121. Based on the pressure parameters of the source rock formation in the actual well, calculate the predicted value of the overpressure generated by hydrocarbon generation in the actual well using the hydrocarbon generation and pressurization model.
[0103] Specifically, by substituting the measured data from actual drilling wells into the oil generation and gas generation pressure calculation models established in steps S211 and S212, the predicted value of the overpressure generated by hydrocarbon generation in actual drilling wells is calculated.
[0104] S2122. Calculate the benchmark value of overpressure generated by hydrocarbon generation in actual drilling based on the pressure parameters of the source rock formation in the actual drilling well.
[0105] Specifically, the effective stress method is used to calculate the baseline value of overpressure generated by hydrocarbon generation in actual drilled wells. The effective stress method refers to a type of method that quantitatively calculates formation overpressure based on rock physical responses (mainly well logging data). Specifically, based on the pressure parameters of the source rock formation in the actual drilled well, the effective stress method is used to calculate the baseline value of overpressure resulting from hydrocarbon generation in the actual drilled well. Since the effective stress method relies on well logging data from the actual drilled well, this baseline value represents the actual overpressure generated in the actual drilled well.
[0106] S2123. Calculate the error between the baseline value of hydrocarbon overpressure in actual drilled wells and the predicted value of hydrocarbon overpressure in actual drilled wells.
[0107] Specifically, the error calculation formula is: (actual baseline value - model predicted value) / model predicted value × 100%. Substituting the calculated value into the calculation formula yields the error between the model predicted value and the actual baseline value.
[0108] S2124. Determine whether the error is less than the preset threshold.
[0109] Specifically, the preset threshold is 15%, and the system determines whether the calculated error is less than 15%.
[0110] S2125. If yes, then the hydrocarbon generation pressurization model is applicable to the study area; if no, then the hydrocarbon generation pressurization model or the parameters of the hydrocarbon generation pressurization model are not applicable to the study area.
[0111] S213. Calculate the overpressure generated by hydrocarbon generation based on the overpressure generated by oil generation and the overpressure generated by gas generation.
[0112] Specifically, the formula for calculating the overpressure generated by hydrocarbon generation is as follows: The total overpressure of hydrocarbon generation is obtained by calculating the sum of the overpressure generated by the oil and the overpressure generated by the gas.
[0113] S22. Calculate the overpressure generated by undercompaction using the undercompaction pressurization model based on the predicted parameters of the source rock layer in the virtual well.
[0114] Specifically, the undercompaction boosting model is a multiple regression model fitted with the undercompaction boosting amount as the dependent variable and the mud-soil ratio, sedimentation rate, and depth as independent variables, as follows: ;
[0115] Wherein, ΔP 欠 The unit is undercompaction pressure increase, in MPa; Q is the mud-to-soil ratio; V is the formation deposition rate, in m / Ma; and H is the depth, in m.
[0116] It should be noted that the mud-to-soil ratio, formation deposition rate, and depth can be obtained from well logging data and geological analysis of actual drilled wells. The above data are input into the software for multiple linear regression analysis. By fitting the data, the regression coefficients a, b, c, and d of this study area can be obtained, thereby determining the final form of the model and obtaining an empirical statistical model for this study area using actual drilled well data.
[0117] For any virtual well, parameters such as mud-soil ratio, formation deposition rate, and depth can be obtained or inferred from the geological map corresponding to its coordinates, thereby calculating the overpressure generated by the undercompaction of the virtual well.
[0118] S23. Calculate the overpressure of the source rock layer in the virtual well based on the overpressure generated by hydrocarbon generation and the overpressure generated by undercompaction.
[0119] Specifically, the formula for calculating the overpressure of the source rock formation is as follows: The total overpressure is obtained by summing the overpressure generated by hydrocarbon generation and the overpressure generated by undercompaction.
[0120] Where: ΔP is the total formation overpressure, ΔP 欠 For undercompaction overpressure, ΔP 生 ΔP represents the hydrocarbon generation and pressurization rate from the source rock. o The overpressure generated by oil production, ΔP g The excess pressure generated by anger.
[0121] S3. Calculate the predicted formation pressure of the virtual well based on the overpressure of the source rock layer of the virtual well.
[0122] like Figure 6 As shown, the method for calculating the predicted formation pressure of a virtual well based on the overpressure of the source rock formation includes:
[0123] S31. Calculate the hydrostatic pressure of the virtual well based on the predicted parameters of the source rock pressure of the virtual well.
[0124] S32. Calculate the predicted formation pressure of the virtual well based on the hydrostatic pressure of the virtual well and the overpressure of the source rock layer of the virtual well.
[0125] Specifically, the formula for calculating hydrostatic pressure is the same as in step 211. Formation pressure is the sum of hydrostatic pressure and overpressure of the source rock layer. Therefore, based on the overpressure of the virtual well calculated in step S2 and the hydrostatic pressure calculated in step S31, the predicted value of formation pressure of the virtual well can be obtained.
[0126] S4. Calculate the formation pressure benchmark value of the actual drilled well based on the pressure parameters of the source rock formation of the actual drilled well.
[0127] Specifically, the traditional Eaton method or Bowers method uses existing, pressure-sensitive raw logging data and applies mature rock physics models or empirical formulas based on the effective stress principle to directly calculate the formation pressure of the actual drilled well.
[0128] Since the source rock pressure parameters of the actual drilled wells in this application fully meet the input requirements of the Eaton method or the Bowers method, the formation pressure benchmark value of the actual drilled wells can be directly calculated using the source rock pressure parameters of the actual drilled wells.
[0129] S5. Perform Kriging interpolation based on the formation pressure benchmark value of the actual drilled well and the formation pressure prediction value of the virtual well to obtain the planar distribution of the source rock pressure in the study area.
[0130] It should be noted that Kriging interpolation can be performed using geological analysis software such as DoubleFox.
[0131] In some embodiments, the predicted pressure of the source rock in the virtual well can be compared and corrected with that of nearby actual drilled wells to avoid large errors.
[0132] For example, in this embodiment of the application, the source rock W of the oil and gas basin Z with few wells is selected as the study area. Within the study area of 300,000 square kilometers, 300 virtual wells are set up, with an average spacing of one virtual well every 32 kilometers, so that the density of virtual wells meets the needs of geological survey.
[0133] According to geochemical analysis, the source rock strata in this study area are mainly of type II kerogen, which have good hydrocarbon generation potential. They exhibit undercompaction due to rapid burial and hydrocarbon generation caused by the volume expansion and pressurization of large amounts of hydrocarbons generated by the kerogen.
[0134] Based on the actual geological conditions of the study area, the crude oil compressibility coefficient C was selected. o 22×10 -4 MPa -1 Natural gas compressibility coefficient C g 90×10 -4 MPa -1 kerogen compressibility coefficient C k 14×10 -4 MPa -1 pore water compressibility coefficient C w 4.4×10 - 4 MPa -1 Simultaneously, take the crude oil density ρ o 0.85 g / cm 3 Natural gas density ρ g It is 6.73×10 -4 g / cm 3 kerogen density ρk 1.55 g / cm 3 Formation water density ρ w It is 1.03 g / cm³ 3 In addition, the density ρ of the source rock was taken. r 2.6 g / cm 3 The crude oil residual coefficient α is 0.8; the natural gas residual coefficient β is 0.8; and the initial porosity of the source rock W is set to 20%. The overpressure calculation parameters and results of each actual drilled well in the study area are shown in Table 1.
[0135] Table 1 shows the overpressure calculation parameters and results for each actual drilled well in the study area.
[0136]
[0137] Since porosity decreases with depth, in this example, the initial surface porosity is 20%, and the porosity is calculated using a reciprocal compaction model, with a compressibility factor of 2.4 × 10⁻⁶. -3 m -1 To control the compaction rate, the model uses the actual porosity corresponding to the current burial depth at the time of hydrocarbon generation, making the calculation more consistent with actual geological conditions.
[0138] Based on the hydrostatic pressure calculation formula, the formation water density ρ is... w The hydrostatic pressure is calculated by substituting the formation depth into the formula.
[0139] Original mass fraction of kerogen M k1 The typical value of hydrocarbon source rocks in this study area, calculated using the formula, is 2.6 g / cm³. 3 The conversion factor is taken as 1.2 based on type II kerogen, then M k1 =2.6×1.2×TOC.
[0140] The thermal evolution of the source rock W in the central virtual well of the study area was simulated using the LLNL kerogen hydrocarbon generation kinetic model in the basin simulation software PetroMod. The evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance were obtained, as shown below. Figure 7 As shown, the corresponding kerogen oil conversion rate F and kerogen gas conversion rate F' are read from the current vitrinite reflectance.
[0141] With vitrinite reflectivity R o As the boundary parameter, when R o When the hydrocarbon content is less than 1.3%, the source rock is mainly in the oil generation stage. The overpressure ΔP is calculated using the oil generation and pressurization model. o When R o ≥1.3%, the source rock enters the stage of abundant gas generation, and the pressure ΔP is calculated using the gas generation pressurization model. g .
[0142] To avoid discrepancies between the geological conditions of the study area and the default conditions of the hydrocarbon generation and pressurization model, which could lead to significant errors in calculations using the model, the effective stress method was used to calculate the overpressure generated by actual drilling in the study area before applying the hydrocarbon generation and pressurization model. This calculation was then compared with the overpressure calculated using the hydrocarbon generation and pressurization model. Figure 8 , Figure 9 As shown, the errors are all less than 10%. Since 10% < 15%, the hydrocarbon generation and pressurization model is applicable to this study area and can be extended for calculation within this study area.
[0143] After successful verification, a positive correlation was found between the depth of source rock W and the mud-to-soil ratio in the study area and the calculated undercompaction intensification amount, such as... Figure 10 , Figure 11 As shown, therefore, with mud-to-soil ratio and sedimentation rate as independent variables, a binary linear regression model of undercompaction overpressure amount with depth and mud-to-soil ratio is established to calculate the undercompaction overpressure amount of each virtual well.
[0144] By adding the hydrostatic pressure to the overpressure generated by undercompaction and the overpressure generated by hydrocarbon generation, the predicted formation pressure of the source rock layer in each virtual well can be obtained. Then, by using the gridding function of the Shuanghu software to perform kriging interpolation on the predicted formation pressure of the source rock layer in each virtual well and the formation pressure benchmark value of the actual drilled well, the planar distribution of the source rock layer pressure in the study area can be obtained.
[0145] In this embodiment, formation pressure is decomposed into overpressure generated by hydrocarbon generation and overpressure generated by undercompaction. Hydrocarbon generation pressure enhancement model and undercompaction statistical model are constructed respectively for quantitative calculation, ensuring prediction accuracy. Virtual wells are introduced to enable prediction under the condition of sparse actual drilling wells. This significantly reduces the requirements of traditional methods that rely on the number of actual drilling wells and the quality of seismic data, making it more operable and solving the problem that existing technologies rely too much on the density of actual drilling wells and seismic data for calculation.
[0146] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.
Claims
1. A method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in areas with few wells, characterized in that, include: Virtual wells were set up in the study area to obtain the predicted parameters of hydrocarbon source rock formation pressure for each virtual well and the parameters of hydrocarbon source rock formation pressure for actual drilled wells. Calculate the overpressure of the source rock formation in each virtual well based on the predicted pressure parameters of the source rock formation in the virtual well. Calculate the predicted formation pressure of the virtual well based on the overpressure of the source rock layer of the virtual well; Calculate the formation pressure benchmark value of the actual drilled well based on the pressure parameters of the source rock formation in the actual drilled well; Kriging interpolation was performed based on the formation pressure baseline value of the actual drilled well and the formation pressure prediction value of the virtual well to obtain the planar distribution of the source rock formation pressure in the study area. The methods for calculating the overpressure of the source rock layer in a virtual well based on the predicted parameters of the source rock layer in the virtual well include: calculating the overpressure of the source rock layer in the virtual well based on the overpressure generated by hydrocarbon generation and the overpressure generated by undercompaction; The methods for calculating the overpressure generated by hydrocarbon generation in a virtual well include: calculating the overpressure generated by oil generation using an oil generation and pressurization calculation model based on the predicted parameters of the source rock formation in the virtual well; calculating the overpressure generated by gas generation using a gas generation and pressurization calculation model based on the predicted parameters of the source rock formation in the virtual well; and calculating the overpressure generated by hydrocarbon generation based on the overpressure generated by oil generation and the overpressure generated by gas generation. The calculation model for oil-fueled turbocharging is as follows: ； Wherein, ΔP o The pressure generated by source rock oil production is expressed in MPa; I is the hydrogen index of the source rock, expressed in mg / g; F is the kerogen oil conversion rate, expressed in %; P h C represents the hydrostatic pressure at the depth of the source rock, expressed in MPa. o The compressibility coefficient of crude oil, expressed in MPa. -1 V w1 The original volume fraction of pore water, expressed in %; C w The compressibility coefficient of pore water is expressed in MPa. -1 α is the petroleum residue coefficient, in %; ρ k This refers to the density of kerogen, expressed in g / cm³. 3 ;ρ o This refers to the density of crude oil, expressed in g / cm³. 3 M k1 The original mass fraction of kerogen is expressed as %; C k The compressibility coefficient of kerogen is expressed in MPa. -1 ; The calculation model for boosting air pressure is as follows: ； Wherein, ΔP g F' represents the pressure generated by gas production from the source rock, in MPa; F' represents the conversion rate of kerogen gas, in %; M k2 β represents the original mass fraction of residual kerogen after oil generation, in %; β represents the natural gas residue coefficient, in %; P1 represents the initial formation pressure during gas generation, in MPa; C g The compressibility coefficient of natural gas, measured in MPa. -1 V w2 This represents the original volume fraction of pore water, expressed in %.
2. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 1, characterized in that, The overpressure generated by hydrocarbon generation is calculated using a hydrocarbon generation pressurization model based on the predicted parameters of the source rock formation in the virtual well; the overpressure generated by undercompaction is calculated using an undercompaction pressurization model based on the predicted parameters of the source rock formation in the virtual well.
3. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 1, characterized in that, The kerogen hydrocarbon conversion rate includes the kerogen oil conversion rate F and the kerogen gas conversion rate F'. Methods for calculating the kerogen hydrocarbon conversion rate include: Set up the central virtual well and obtain its basic parameters; The evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance were simulated and calculated based on the basic parameters and thermal evolution history of the central virtual well. Based on the evolution curves of kerogen hydrocarbon generation conversion rate and vitrinite reflectance and the vitrinite reflectance values of each virtual well, the kerogen hydrocarbon generation conversion rate can be read from the evolution curves.
4. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 1, characterized in that, The undercompaction boosting model is a multiple regression model fitted with undercompaction boosting amount as the dependent variable and mud-soil ratio, sedimentation rate, and depth as independent variables, as follows: ; Wherein, ΔP 欠 The unit is undercompaction pressure increase, in MPa; Q is the mud-to-soil ratio; V is the formation deposition rate, in m / Ma; and H is the depth, in m.
5. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 1, characterized in that, Methods for quantitatively characterizing the planar distribution of pressure in source rock formations in areas with few wells also include determining whether the hydrocarbon generation and pressurization model is applicable to the study area.
6. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 5, characterized in that, Methods for determining whether a hydrocarbon generation and pressurization model is applicable to the study area include: Based on the pressure parameters of the source rock formation in the actual drilled well, the predicted value of the overpressure generated by hydrocarbon generation in the actual drilled well is calculated using a hydrocarbon generation and pressurization model. Calculate the benchmark value of overpressure generated by hydrocarbon generation in actual drilling based on the pressure parameters of the source rock formation in the actual drilling well. The error between the baseline value of hydrocarbon overpressure in actual drilled wells and the predicted value of hydrocarbon overpressure in actual drilled wells is calculated. Determine whether the error is less than a preset threshold; If yes, then the hydrocarbon generation and pressurization model is suitable for the study area; otherwise, the hydrocarbon generation and pressurization model or its parameters are not suitable for the study area.
7. The method for quantitatively characterizing the planar distribution of hydrocarbon source rock pressure in a low-well area according to claim 1, characterized in that, Methods for calculating the predicted formation pressure of a virtual well based on the overpressure of the source rock layer include: The hydrostatic pressure of the virtual well is calculated based on the predicted parameters of the source rock pressure of the virtual well. The predicted formation pressure of the virtual well is calculated based on the hydrostatic pressure of the virtual well and the overpressure of the source rock layer of the virtual well.