Method for identifying overpressure fluid migration direction by using pressure gradient evolution rate

Abstract

The present invention provides a method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient, which includes: Step 1, calculating the duration of each key event according to the key geological event stage; Step 2, predicting the current formation pressure by using the Eaton method; Step 3, restoring the paleo-pressure; Step 4, dividing the pressure structure of each key geological event stage according to the paleo-pressure restoration result; Step 5, calculating the pressure gradient of the overpressure top seal layer and the pressure gradient of the overpressure bottom seal layer; Step 6, calculating the evolution rate of each pressure gradient; Step 7: Comparing the magnitudes of the evolution rates of each pressure gradient, and the direction with the maximum evolution rate of the pressure gradient is the pressure migration direction. The method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient can more intuitively and quantitatively characterize the strength change of the oil and gas migration force during the oil and gas migration process, thereby effectively judging the direction of the strong oil and gas migration force, and can more effectively predict the oil and gas enrichment law in overpressure oil and gas basins.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and particularly to a method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient. Background Art

[0002] Overpressure develops in oil and gas bearing basins worldwide. As one of the main driving forces for oil and gas migration, the evolution rate of overpressure over time can directly characterize the strength of the driving force for oil and gas migration, thus indicating the direction of oil and gas migration. Currently, the commonly used overpressure characterization parameters are the current pressure coefficient, residual pressure, paleo-pressure, and current pressure gradient. However, these three parameters can only represent the strength of a point relative to hydrostatic pressure at a certain time point, and the current pressure gradient can only characterize the change in the strength of the driving force for oil and gas migration in a certain direction under the current burial state. There are certain limitations in the study of the dynamic evolution during the oil and gas migration process.

[0003] In the Chinese patent application with the application number: CN201810623559.8, a method for indicating the preferential migration direction of oil and gas by using pressure structure is involved. The specific steps are as follows: S1. Collect and sort out the geological data, logging data, mud logging data, and testing data of the study area; S2. Combine the mud logging and logging data of the study area, select a pressure prediction method to predict the formation pressure, and establish the vertical pressure distribution characteristics of a single well; S3. Divide the pressure structure morphology types through the morphological characteristics of the pressure structure, the overpressure amplitude of the pressure structure, and the change characteristics of the top and bottom boundaries of the pressure structure; S4. Calculate the top interface pressure gradient and the bottom interface pressure gradient; S5. Determine the morphology type of the pressure structure, and combine the pressure gradient calculation and the oil and gas distribution characteristics to clarify the preferential migration direction of oil and gas and the minimum pressure gradient for oil and gas preservation. This method is based on the current single-well pressure structure and can only indicate the vertical migration and enrichment of oil and gas in a single well. After the generation of overpressure oil and gas in the actual geological body, there is not only vertical migration, but also migration in all directions through connected sand bodies, transfer faults, and unconformities. Therefore, this patent has certain limitations in predicting the spatial migration direction and enrichment law of oil and gas.

[0004] In the Chinese patent application with the application number: CN201810622505.X, a method for calculating the pressure decay gradient is involved. The specific steps are as follows: S1. Collect and sort out the geological data, mud logging data, logging data, and well testing data of the study area; S2. Predict the mudstone pressure in the study area by using the Eaton method and the equivalent depth method, and correct it with the measured pressure; S3. Draw the pressure coefficient isolines according to the predicted formation pressure value, combined with the geological structure, sedimentary facies distribution characteristics, and fault development situation in the study area; S4. Establish different pressure decay gradient calculation models, and calculate the pressure decay gradient according to different pressure decay gradient calculation models.

[0005] In the Chinese patent application with the application number CN201410261645.0, a method and device for predicting the range of oil and gas migration and accumulation are involved. The method includes: obtaining the data of the bottom surface morphology of the cap rock, the distribution data of reservoir sand bodies, and the hydrodynamic data of the study area based on geological stratification, geological logging, and formation pressure test data; normalizing the data of the bottom surface morphology of the cap rock, the distribution data of reservoir sand bodies, and the hydrodynamic data; determining the weight coefficients of the normalized data of the bottom surface morphology of the cap rock, the distribution data of reservoir sand bodies, and the hydrodynamic data according to the degree of influence on the oil and gas migration in the study area; determining the normalized fluid potential of the study area according to the normalized data of the bottom surface morphology of the cap rock, the distribution data of reservoir sand bodies, and the hydrodynamic data and the weight coefficients; and predicting the range of oil and gas migration and accumulation in the study area based on the normalized fluid potential.

[0006] All of the above prior arts are quite different from the present invention and fail to solve the technical problems we want to solve. Therefore, we have invented a new method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient. Summary of the Invention

[0007] The object of the present invention is to provide a method for identifying the preferential migration direction and enrichment position of overpressure fluids during the hydrocarbon accumulation process, which is beneficial to the oil and gas exploration research in overpressure hydrocarbon-bearing basins, by using the evolution rate of pressure gradient to identify the migration direction of overpressure fluids.

[0008] The object of the present invention can be achieved by the following technical measures: A method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient, which includes:

[0009] Step 1: Calculate the duration of each key event according to the key geological event stage.

[0010] Step 2: Predict the current formation pressure by using the Eaton method.

[0011] Step 3: Restore the paleo-pressure.

[0012] Step 4: Divide the pressure structure of each key geological event stage according to the paleo-pressure restoration result.

[0013] Step 5: Calculate the pressure gradient of the overpressure top seal layer and the pressure gradient of the overpressure bottom seal layer.

[0014] Step 6: Calculate the evolution rate of each pressure gradient.

[0015] Step 7: Compare the magnitudes of the evolution rates of each pressure gradient, and the direction with the maximum evolution rate of pressure gradient is the pressure migration direction.

[0016] The object of the present invention can also be achieved by the following technical measures:

[0017] In Step 1, collect the data of paleogeotemperature, paleoheat flow value, developed strata and their sedimentation time in the study area, divide the key geological event stages such as the formation uplift period, subsidence period and hydrocarbon generation period according to the burial history, and calculate the duration of each key event.

[0018] In Step 2, collect the data of well logging, borehole diameter, acoustic time difference, formation layering, repeated formation test pressure RFT, drillstem test pressure DST in the study area. Fit the normal compaction trend lines of acoustic time difference and formation density according to the acoustic time difference data of shallow normally compacted formations; remove the abnormal acoustic time difference data affected by hole enlargement according to the borehole diameter data, and then screen out the acoustic time difference data of mudstones with a thickness exceeding 5m according to the well logging data. Substitute the data into the Eaton formula to predict the current pressure of the entire well section of a single well, and use the measured pressure data of repeated formation test pressure RFT or drillstem test pressure DST for correction.

[0019] In Step 2, the Eaton formula is:

[0020]

[0021] In the formula, P ---- current pressure, Ma

[0022] σ 上覆 ----- overburden pressure, MPa;

[0023] P 静水 ----- hydrostatic pressure, MPa;

[0024] Δt ---- acoustic time difference, μs / ft; C ---- Eaton coefficient;

[0025] Δt o --- is the acoustic time difference of surface mudstone, μs / ft;

[0026] D ------ is the compaction coefficient;

[0027] H ------ is the burial depth, m.

[0028] In Step 3, combine the burial history, thermal history and the current predicted pressure value in Step 2 to restore the paleopressure.

[0029] In Step 5, according to the pressure structure in Step 4, divide the pressure structures of each key geological history event period and identify the overpressure top seal layer and overpressure bottom seal layer. Read the top seal layer thickness H T , unit m, and the corresponding pressure difference ΔP T , unit MPa, bottom seal layer thickness H B , unit m, and the corresponding pressure difference ΔP B , unit MPa, calculate the overpressure top seal layer GPT , in units of MPa·m -1 and the overpressure bottom seal layer pressure gradient GP B , in units of MPa·m -1 .

[0030] In step 5, calculate the overpressure top seal layer GP T and the overpressure bottom seal layer pressure gradient GP B using the formula:

[0031]

[0032]

[0033] In step 6, calculate the evolution rate of the overpressure top seal layer pressure gradient of a single well, the evolution rate of the overpressure bottom seal layer pressure gradient, and the evolution rate of the overpressure top and bottom seal layer pressure gradients between adjacent wells near key geological historical events respectively.

[0034] In step 6, calculate the evolution rate of the overpressure top seal layer pressure gradient GP Ti , in units of (MPa·m -1 ) / Ma, the evolution rate of the overpressure bottom seal layer pressure gradient GP Ti , in units of (MPa·m -1 ) / Ma, and the evolution rate of the top seal layer pressure gradient GP NTi , in units of (MPa·m -1 ) / Ma and the evolution rate of the overpressure bottom seal layer pressure gradient GP NBi , in units of (MPa·m -1 ) / Ma between the adjacent A and B wells on the left and right sides;

[0035]

[0036]

[0037]

[0038]

[0039] In the formula, GP T is the overpressure top seal layer, in units of MPa·m -1 ,

[0040] GP B is the overpressure bottom seal layer pressure gradient, in units of MPa·m -1 ; Ti is the difference in adjacent geological historical events, in units of Ma,

[0041] P AT,The pressure value of the top seal layer of Well A, unit: MPa,

[0042] P BT ,The pressure value of the top seal layer between Well Bs, unit: MPa,

[0043] P AB ,The pressure value of the bottom seal layer of Well A, unit: MPa,

[0044] P BB ,The pressure value of the bottom seal layer between Well Bs, unit: MPa.

[0045] In step 6, compare GP Ti 、GP Ti 、GP NTi and GP NBi in terms of size. The direction with the largest pressure decay gradient is the pressure migration direction.

[0046] The method for identifying the overpressure fluid migration direction by using the pressure gradient evolution rate in the present invention not only considers the current pressure gradients of the top and bottom interfaces of a single well, but also compares the magnitudes of the top and bottom interfaces of a single well at different geological burial times and the magnitudes of the pressure gradient evolution rates among multiple wells within the spatial range. It can more intuitively and effectively quantitatively characterize the strength change of the oil and gas migration force in the space-time range, thereby effectively judging the direction of the strong oil and gas migration force and more effectively predicting the oil and gas enrichment law in the overpressure hydrocarbon-bearing basin.

[0047] The present invention can more intuitively quantitatively characterize the strength change of the oil and gas migration force during the oil and gas migration process, thereby effectively judging the direction of the strong oil and gas migration force and more effectively predicting the oil and gas enrichment law in the overpressure hydrocarbon-bearing basin. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a flowchart of a specific embodiment of the method for identifying the overpressure fluid migration direction by using the pressure gradient evolution rate of the present invention;

[0049] Figure 2 is a schematic diagram of the key geological event stage division in a specific embodiment of the present invention;

[0050] Figure 3 is a schematic diagram of the key geological event pressure structure division in a specific embodiment of the present invention;

[0051] Figure 4 is a schematic diagram of the identification of the top and bottom of the overpressure seal box in a key geological event in a specific embodiment of the present invention;

[0052] Figure 5 is a schematic diagram of the overpressure fluid migration direction in the key period 1 in a specific embodiment of the present invention;

[0053] Figure 6 Schematic diagram of the overpressure fluid migration direction in the key period 2 in a specific embodiment of the present invention;

[0054] Figure 7 Schematic diagram of the overpressure fluid migration direction in the key period 3 in a specific embodiment of the present invention;

[0055] Figure 8 Schematic diagram of the overpressure fluid migration direction in the key period 4 in a specific embodiment of the present invention;

[0056] Figure 9 Schematic diagram of the overpressure fluid migration direction in the key period 5 in a specific embodiment of the present invention. Specific embodiments

[0057] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0058] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0059] The method for identifying the overpressure fluid migration direction by using the pressure gradient evolution rate of the present invention includes the following steps:

[0060] Step 1: Divide the key geological event stages such as the formation uplift period, subsidence period, and hydrocarbon generation period according to the burial history, and calculate the duration of each key event;

[0061] Step 2: Collect data such as well logging, well diameter, acoustic travel time, formation stratification, RFT (Repeat Formation Tester), DST (Drill Stem Test) in the study area, and predict the current formation pressure by using the Eaton method;

[0062] Step 3: Combine the burial history, thermal history and the current predicted pressure value in Step 2 to perform paleopressure restoration;

[0063] Step 4: Divide the pressure structure of each key geological event stage according to the paleopressure restoration result in Step 3;

[0064] Step 5: On the basis of the pressure structure division in Step 4, identify the overpressure top seal layer and overpressure bottom seal layer in each key geological history event period, and calculate the pressure gradient of the overpressure top seal layer and the pressure gradient of the overpressure bottom seal layer;

[0065] Step 6: Calculate the evolution rate of the pressure gradient of the top seal layer of abnormal pressure, the evolution rate of the pressure gradient of the bottom seal layer of abnormal pressure, and the evolution rate of the pressure gradient of the top and bottom seal layers of abnormal pressure between adjacent wells for each key geological historical event respectively;

[0066] Step 7: Compare the magnitudes of the evolution rates of the pressure gradients. The direction with the maximum evolution rate of the pressure gradient is the direction of pressure migration.

[0067] The following are several specific embodiments of applying the present invention.

[0068] Embodiment 1:

[0069] As shown in the Figure 1 flow chart, the specific implementation of the method for identifying the migration direction of abnormal pressure fluids using the pressure gradient includes the following steps:

[0070] Step 101: Collect and organize the subsidence history, lithology, paleocurrent, and paleogeothermal data of the study area, restore the burial history of the study area, divide the key geological historical events, and calculate the time difference Ti between the key geological historical events;

[0071] Step 102:

[0072] Collect and organize the logging data, mud logging data, and measured pressure data of the study area, predict the single-well pressure in the study area using the Eaton pressure prediction model and the equivalent depth pressure prediction model, and correct it using the measured pressure;

[0073] In the embodiment of the present invention, the mud logging data, logging data, and measured pressure data mainly include: formation stratification data, lithology change data, formation water density data, rock density data, acoustic time difference logging data, density logging data, and measured pressure data. In this step, the lithology change data, acoustic time difference data, and density data are used in combination with the Eaton pressure prediction model and the equivalent depth pressure prediction model to predict the pressure of different layers in the study area, and the measured pressure is used for correction.

[0074] Specifically, the Eaton pressure prediction model is used for calculating the abnormal pressure in the hydrocarbon generation area. The pore pressure PE is obtained through the following formula:

[0075] PE = σv - (σv - Ph)(Δtnorm / Δt)x (1)

[0076] In the formula, x is the exponent, σv is the vertical pressure, Ph is the hydrostatic pressure, Δtnorm is the normal compaction acoustic time difference, and Δt is the acoustic time difference in the acoustic time difference logging data.

[0077] Step 103:

[0078] According to the burial history of the study area, taking the current pressure as the standard, the paleo-pressure in the key geological historical periods is restored, and the paleo-pressure structure in each period is divided.

[0079] Step 104:

[0080] According to the paleo-pressure restoration results in the key geological historical periods in Step 103, the pressure structure is divided.

[0081] Step 105. According to the pressure structure in Step 104, identify the overpressure top seal layer and the overpressure bottom seal layer in each key geological historical event period. Read the top seal layer thickness HT, unit m, and the corresponding pressure difference ΔPT, unit MPa, the bottom seal layer thickness HB, unit m, and the corresponding pressure difference ΔPB, unit MPa( Figure 4 ), and calculate the overpressure top seal layer GPT, unit MPa·m-1 and the overpressure bottom seal layer pressure gradient GPB, unit MPa·m-1 according to Formula 2 and Formula 3;

[0082]

[0083]

[0084] Step 106: Calculate the evolution rate GP of the overpressure top seal layer pressure gradient with time according to Formulas 4 - 7 respectively Ti , unit (MPa·m -1 ), / Ma, the evolution rate GP of the overpressure bottom seal layer pressure gradient with time Bi , unit (MPa·m -1 ), / Ma and the evolution rate GP of the top seal layer pressure gradient with time between the adjacent A well and B well on the left and right sides NTi , unit (MPa·m -1 ), / Ma and the evolution rate GP of the overpressure bottom seal layer pressure gradient with time NBi , unit (MPa·m -1 ), / Ma;

[0085]

[0086]

[0087]

[0088]

[0089] Example 2:

[0090] In a specific Example 1 of applying the present invention, Figure 1The figure is a flow chart of the method for identifying the migration direction of overpressure fluids using the evolution rate of pressure gradient in the present invention. The Bonan area in the Zhanhua Sag of the Bohai Bay Basin is selected as the study area, and the overpressure interval in the Niuzhuang Sub-sag of the Dongying Sag in the Bohai Bay Basin is selected as the research object. The overpressure interval in the Niuzhuang Sub-sag of the Dongying Sag in the Bohai Bay Basin is used as the study area, including the following steps:

[0091] Step 101: Collect the data of paleogeotemperature, paleoheat flow value, developed strata and their sedimentation time in the study area, input them into the Petromod-1D module of basin simulation software to simulate the burial history map of the study area, divide the key geological event periods such as the formation subsidence period, formation uplift period, hydrocarbon generation and expulsion period, etc. into i key geological event periods according to the burial evolution history map, and calculate the duration Ti of each key geological period ( Figure 2 ).

[0092] Step 102: Collect the data of well logging, well diameter, acoustic time difference, formation layering, RFT, DST, etc. in the study area, fit the normal compaction trend lines of acoustic time difference and formation density according to the acoustic time difference data of shallow normal compaction strata; remove the abnormal acoustic time difference data affected by hole enlargement according to the well diameter data, and then screen out the acoustic time difference data of mudstones with a thickness exceeding 5m according to the well logging data, substitute the data into the Eaton formula (Formula 1) to predict the current pressure of the entire well section of a single well, and use the measured pressure data of RFT or DST for correction;

[0093]

[0094] In the formula, σ 上覆 ----- Overburden pressure, MPa;

[0095] P 静水 ----- Hydrostatic pressure, MPa;

[0096] Δt----- Acoustic time difference, μs / ft;

[0097] Δt 正常 ---- Acoustic time difference on the normal compaction trend line at the same depth, μs / ft;

[0098] C----- Eaton coefficient;

[0099] Δt o --- Acoustic time difference of surface mudstone, μs / ft;

[0100] D------ Compaction coefficient;

[0101] H------ Burial depth, m.

[0102] Step 103: Based on the burial history, thermal history of the study area, the current predicted pressure values in Step 102, DST and RFT data, use the 1D module of the software Petromod to recover the paleo-pressure evolution.

[0103] Step 104: According to the pressure recovery results output by Petromod 1D in Step 103, divide the pressure structure according to the vertical pressure change law in each key geological event stage in Step 101 ( Figure 3 );

[0104] Step 105: According to the pressure structure in Step 104, identify the overpressure top seal layer and overpressure bottom seal layer in each key geological history event period. Read the top seal layer thickness H T , in m, and the corresponding pressure difference ΔP T , in MPa, the bottom seal layer thickness H B , in m, and the corresponding pressure difference ΔP B , in MPa ( Figure 4 ), and calculate the overpressure top seal layer GP T , in MPa·m -1 and the overpressure bottom seal layer pressure gradient GP B , in MPa·m -1 ;

[0105]

[0106]

[0107] Step 106: Calculate the evolution rate of the overpressure top seal layer pressure gradient with time GP Ti , in units of (MPa·m -1 ) / Ma, the evolution rate of the overpressure bottom seal layer pressure gradient with time GP Ti , in units of (MPa·m -1 ) / Ma, and the evolution rate of the top seal layer pressure gradient with time GP NTi , in units of (MPa·m -1 ) / Ma and the evolution rate of the overpressure bottom seal layer pressure gradient with time GP NBi , in units of (MPa·m -1 ) / Ma between the adjacent A well and B well on the left and right sides according to Formulas 4 - 7 respectively;

[0108]

[0109]

[0110]

[0111]

[0112] Step 107: Compare GP Ti , GP Ti , GP NTi and GP NBi to find the size differences among them. The direction with the maximum pressure decay gradient is the pressure migration direction ( Figures 5 - 9 ).

[0113] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0114] Except for the technical features described in the specification, the rest are well-known technologies to those skilled in the art.

Claims

1. A method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient, characterized in that, The method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient includes the following steps: Step 1: Calculate the duration of each key event according to the key geological event stage. Step 2: Predict the current formation pressure by using the Eaton method. Step 3: Conduct paleo-pressure restoration. Step 4: Divide the pressure structure of each key geological event stage according to the results of paleo-pressure restoration. Step 5: Calculate the pressure gradient of the overpressure top seal layer and the pressure gradient of the overpressure bottom seal layer. Step 6: Calculate the evolution rate of each pressure gradient. Step 7: Compare the magnitudes of the evolution rates of each pressure gradient. The direction with the maximum evolution rate of the pressure gradient is the pressure migration direction.

2. The method for identifying the migration direction of overpressure fluids by using the evolution rate of pressure gradient according to claim 1, characterized in that, In Step 1, collect the data of paleo-geotemperature, paleo-heat flow value, developed strata and their sedimentation time in the study area. Divide the key geological event stages such as the formation uplift period, subsidence period and hydrocarbon generation period according to the burial history, and calculate the duration of each key event.

3. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 1, wherein In Step 2, collect the data of well logging, well diameter, acoustic time difference, formation stratification, repeated formation test pressure RFT, and drillstem test pressure DST in the study area. Fit the normal compaction trend line of acoustic time difference and formation density according to the acoustic time difference data of shallow normal compaction strata; Remove the abnormal acoustic time difference data affected by hole enlargement according to the well diameter data, and then select the acoustic time difference data of mudstone with a thickness exceeding 5m according to the well logging data. Substitute the data into the Eaton formula to predict the current pressure of the whole well section of a single well, and correct it by using the measured pressure data of repeated formation test pressure RFT or drillstem test pressure DST.

4. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 3, wherein In Step 2, the Eaton formula is as follows: Where P is the current formation pressure, MPa; σ 上覆 -----Overlying strata pressure, MPa; P 静水 -----Hydrostatic pressure, MPa; Δt is the acoustic time difference, μs / ft; C is the Eaton coefficient; Δt o --- is the acoustic travel time of surface mudstone, μs / ft; D is the compaction coefficient; H is the burial depth, m.

5. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 1, characterized in that In Step 3, combine the burial history, thermal history and the current predicted pressure value in Step 2 to conduct paleo-pressure restoration.

6. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 1, wherein In step 5, according to the pressure structure in step 4, identify the overpressure top seal layer and the overpressure bottom seal layer for each key geological history event period, and read the top seal layer thickness H T , in m, and the corresponding pressure difference ΔP T , in MPa, the bottom seal layer thickness H B , in m, and the corresponding pressure difference ΔP B , in MPa, calculate the overpressure top seal layer GP T , in MPa·m -1 and the overpressure bottom seal layer pressure gradient GP B , in MPa·m -1 .

7. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 6, wherein In step 5, calculate the overpressure top seal GP T and the overpressure bottom seal pressure gradient GP B The formula is as follows:

8. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 1, characterized in that In Step 6, calculate the evolution rate of the pressure gradient of the overpressure top seal layer of a single well, the evolution rate of the pressure gradient of the overpressure bottom seal layer, and the evolution rate of the pressure gradient of the overpressure top seal layer and the overpressure bottom seal layer between adjacent wells for adjacent key geological history events respectively.

9. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 8, characterized in that In step 6, calculate the evolution rate GP of the overpressure top seal layer pressure gradient with time according to Formulas 4 - 7 respectively Ti , unit (MPa·m -1 ) / Ma, the evolution rate GP of the overpressure bottom seal layer pressure gradient with time Bi , unit (MPa·m -1 ) / Ma, and the evolution rate GP of the top seal layer pressure gradient with time between the adjacent A well and B well on the left and right sides NTi , unit (MPa·m -1 ) / Ma, and the evolution rate GP of the overpressure bottom seal layer pressure gradient with time NBi , unit (MPa·m -1 ) / Ma; where, GP T is the overpressure top seal layer, in MPa·m -1 , GP B is the overpressure bottom seal layer pressure gradient, with the unit of MPa·m -1 ; Ti is the difference in adjacent geological history events, with the unit of Ma P AT ,The pressure value of the top seal layer of Well A, unit: MPa P BT , formation pressure value between Wells B, unit: MPa P AB , the bottom hole packer pressure value, unit: MPa P BB , bottom sealing layer pressure value between Well B, unit: MPa.

10. The method for identifying the migration direction of overpressure fluid by using the evolution rate of pressure gradient according to claim 9, characterized in that, In step 6, compare GP Ti , GP Ti , GP NTi and GP NBi in terms of size. The direction with the maximum pressure decay gradient is the pressure migration direction.

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