Evaluation method for overpressure contribution of volcanic gas reservoir based on well logging identification

Abstract

The application discloses a kind of overpressure genesis contribution evaluation methods of volcanic gas reservoir based on well logging identification, it is related to the technical field of oil and gas exploration and development, its steps are as follows: first step: using geological data, distinguish overpressure and normal pressure volcanic rock depth section, clear overpressure development scale;Second step: using well logging data, identify overpressure development genesis;Third step: using rock resistivity-density relationship, the contribution of different genesis overpressure is obtained.The method can quantitatively calculate the contribution ratio of different genesis to overpressure formation according to the change amount of the volume properties and the conduction properties of the rock in the overpressure section, reducing the influence of manual intervention, avoiding artificial error or error, so that the prediction method has high quantitative prediction accuracy.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development technology, and more specifically to a method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification. Background Technology

[0002] During the formation and evolution of oil and gas basins, changes in the internal physical and chemical conditions of the strata can easily lead to increased formation pressure, resulting in overpressured strata. Based on their development mechanisms, overpressure in oil and gas basins can be classified into three types: ① overpressure caused by undercompaction of the strata; ② overpressure caused by fluid expansion within pores, such as clay mineral dehydration, hydrothermal pressurization, hydrocarbon generation from source rocks, and organic matter cracking and gas generation; ③ overpressure formed by tectonic compression. In my country's oil and gas basins, the formation of overpressure is generally controlled by multiple factors, and pressure is a crucial driving force for oil and gas migration and large-scale accumulation. Therefore, in the study of overpressure, understanding its formation mechanism and quantitative analysis can help in the research of advantageous oil and gas migration and accumulation directions and favorable oil and gas enrichment zones.

[0003] Currently, scholars both domestically and internationally generally believe that the main causes of large-scale overpressure in my country's oil and gas basins are undercompaction and fluid expansion, with these two factors accounting for as much as 86% of overpressure formations. Undercompaction primarily develops in clastic rock formations, while for volcanic rocks with strong compaction resistance, tectonic compression and fluid expansion are likely the main reasons for large-scale overpressure formations. Current evaluation methods for these two types of overpressure mainly include: using data such as sonic transit time of mudstone, cable strata testing, and drill pipe testing to identify overpressure development characteristics; using organic matter maturity to identify fluid expansion and pressurization caused by organic matter decomposition; and using tectonic stress numerical simulation technology as the main method for studying formation pressure under compression. Quantitative characterization of overpressure from different causes is a challenge in overpressure research. Previous researchers have simulated the contribution of tectonic stress to formation pressure based on the elasticity theory of sedimentary rocks; Guo Xiaowen et al. used physical experiments to simulate pressurization models at different stages of hydrocarbon generation and expulsion to calculate the amount of hydrocarbon generation pressurization. Liu Hua et al. and Wang Xin et al. used basin simulation methods to reconstruct the pressure evolution of single wells (one-dimensional) and interconnected wells (two-dimensional), and quantitatively characterized the overpressure of different genetic types in sedimentary strata. Bowers found through experimental analysis that igneous rocks have weaker elasticity than sedimentary rocks due to the lack of interconnected pores.

[0004] Chinese patent document CN106127343A, published on November 16, 2016, discloses an analytical method for the formation overpressure mechanism. It combines formation pressure prediction methods with formation overpressure formation mechanism analysis by using single-well measured formation pressure. By comparing the differences between various pressure prediction curves and the differences between the predicted curves and the measured curves, the formation overpressure formation mechanism is analyzed. Three formation pressure prediction methods are used: the Eaton method based on undercompaction, the equivalent depth method, and the Bowers method based on fluid expansion. This invention analyzes the formation overpressure mechanism by comparing the differences between various pressure prediction curves and the differences between the predicted curves and the measured curves. Small differences between the three predicted curves and the measured curves indicate that the overpressure may be caused by undercompaction. Small differences between the three predicted curves but large differences between the predicted curves and the measured curves indicate that the overpressure may be caused by tectonic compression. Large differences between the prediction results of the three methods are then compared with the measured results. If the Eaton method or the equivalent depth method has a small error, it indicates that the overpressure may be caused by undercompaction. If the Bowers method has a small error, it indicates that the overpressure may be caused by fluid expansion. Large errors in all three methods indicate that the overpressure may be caused by tectonic compression. This simplifies the analysis of the formation overpressure formation mechanism.

[0005] The existing technology, represented by the aforementioned patent document CN106127343A, can only determine the type of formation overpressure. It cannot quantitatively identify overpressure formed by multiple factors. Overall, the quantitative characterization of overpressure of different formation types in volcanic rock formations with strong compaction resistance and weak elastic rebound response is still relatively weak. Most methods are based on simple sedimentary rock pore elasticity models, which still have shortcomings in the study of volcanic rock overpressure with complex fluid, structure and pore throat relationships. Summary of the Invention

[0006] This invention aims to address the deficiencies and shortcomings of the existing technologies by providing a method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification. This method can quantitatively calculate the contribution ratio of different genesis to overpressure formation based on the changes in the volumetric and conductive properties of rocks in the overpressure zone, reducing the influence of human intervention, avoiding human errors or mistakes, and enabling the prediction method to have high quantitative prediction accuracy.

[0007] This invention is achieved by adopting the following technical solution:

[0008] A method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification, characterized by the following steps:

[0009] Step 1: Using geological data, distinguish between overpressured and normal-pressured volcanic rock depths to determine the scale of overpressure development;

[0010] Step 2: Use well logging data to identify the causes of overpressure development;

[0011] Step 3: Utilize the rock resistivity-density relationship to determine the contribution of overpressure from different origins.

[0012] The first step, more specifically:

[0013] For permeable rock formations, formation pressure is obtained using cable formation testing, drill pipe testing, and mud density analysis. For non-permeable rock formations, formation pressure is calculated using the fitting relationship between measured formation pressure of adjacent permeable formations and sonic transit time logging data. Based on formation pressure characteristics, overpressure and normal pressure volcanic rock depths are distinguished, and resistivity and density logging data corresponding to different formation depths are extracted.

[0014] The permeable rock layers include pyroclastic rocks and fractured volcanic rocks.

[0015] The aforementioned non-permeable rock strata include basalt and diabase porphyry.

[0016] The second step, more specifically:

[0017] Based on the rock resistivity and density data of the normal pressure volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the normal pressure volcanic rock section was fitted.

[0018] Based on the rock resistivity and density data of the overpressured volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the overpressured volcanic rock section was fitted.

[0019] The rock resistivity-density cross plots under normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship under normal pressure and overpressure are compared.

[0020] If the rock resistivity-density cross plots and the trend lines of the rock resistivity-density relationship match under normal and overpressure conditions, then the overpressure is mainly caused by tectonic compression.

[0021] If the trend line of the rock resistivity-density relationship in the overpressured volcanic rock section deviates from the trend line of the rock resistivity-density relationship in the normal pressure strata in the direction of decreasing resistivity, then the development of overpressure is affected by the combined effects of fluid expansion within the pores and tectonic compression.

[0022] The third step, more specifically:

[0023] The deviation of the resistivity-density variation trend line of volcanic rock in the overpressure section from that in the normal pressure section is calculated. Combined with the effective vertical stress in the normal pressure section and the overpressure section of volcanic rock, the relationship between the rock resistivity deviation and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation and the vertical stress variation is obtained.

[0024] The fluid expansion overpressure is equal to the change in vertical stress, so the fluid expansion overpressure ΔP1 is obtained; the fluid expansion overpressure is subtracted from the formation residual pressure to obtain the overpressure value ΔP2 caused by tectonic compression.

[0025] The ratios of fluid expansion overpressure ΔP1 and tectonic compression overpressure ΔP2 to the formation residual pressure were calculated respectively, thereby obtaining the contribution ratios of fluid expansion overpressure and tectonic compression overpressure to formation overpressure.

[0026] The first step also includes: using formula P 静 =ρ w Calculate hydrostatic pressure (ρ) using gH w Density of formation water, kg / m³ 3 g is the acceleration due to gravity, m / s² 2 (H is the burial depth of the stratum, m). By comparing the measured stratum pressure and hydrostatic pressure at the same depth, the stratum pressure coefficient and residual pressure are obtained.

[0027] In the second step, a rock resistivity-density cross-plot is established using a Cartesian coordinate system. Based on the rock resistivity and density of the normal or overpressure volcanic rock sections, the fitting formula for the rock resistivity-density function relationship under normal or overpressure conditions is derived as follows:

[0028] R=0.0002ρ 10.141 ;

[0029] Where R is the rock resistivity and ρ is the rock density.

[0030] In the second step, the rock resistivity-density cross plots of normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship of normal pressure and overpressure are compared. Specifically, the rock resistivity and density data of the extracted overpressure volcanic rock depth segment are plotted on the rock resistivity-density cross plot of the normal pressure volcanic rock depth segment, and then the trend lines of the rock resistivity-density relationship of the overpressure volcanic rock depth segment and the normal pressure volcanic rock depth segment are compared.

[0031] In the second step, when the overpressure is mainly caused by tectonic compression, the effect of tectonic compression on formation pressure is equal to the residual pressure.

[0032] In the third step, the formula for calculating the change in rock resistivity ΔR is as follows:

[0033] ΔR=0.0002ρ 10.141 +2.372-R 实测 ;

[0034] Among them, R 实测 ρ is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressured volcanic rock depth section, where ρ is the rock density.

[0035] The formula for calculating the vertical stress change Δδ is as follows:

[0036] Δδ = 1.138·ΔR + 1.125;

[0037] Wherein, ΔR is the change in rock resistivity;

[0038] The formula for calculating the overpressure ΔP1 caused by fluid expansion within the overpressure volcanic rock depth range is as follows:

[0039] ΔP1 = Δδ = 1.138 · ΔR + 1.125;

[0040] Where Δδ is the change in vertical stress and ΔR is the change in rock resistivity;

[0041] Subtracting the fluid expansion overpressure from the residual formation pressure, the formula for calculating the overpressure value ΔP2 caused by tectonic compression is as follows:

[0042] ΔP2 = ΔP - ΔP1;

[0043] Where ΔP is the formation residual pressure and ΔP1 is the fluid expansion overpressure;

[0044] The ratios of fluid expansion overpressure ΔP1, tectonic compression overpressure ΔP2, and formation residual pressure were calculated separately to determine the contribution ratios of fluid expansion-type overpressure and tectonic compression-type overpressure to formation overpressure.

[0045] The contribution ratio of fluid expansion to overpressure, G1:

[0046] G1 = ΔP1 / ΔP·100%;

[0047] The contribution ratio of structural extrusion to overpressure, G2:

[0048] G2 = ΔP2 / ΔP·100%.

[0049] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0050] 1. In this invention, geological data is used to distinguish between overpressure and normal pressure volcanic rock depths and to clarify the scale of overpressure development. The calculation is based on the fitting relationship between measured formation pressure and sonic transit time logging data, which simplifies the calculation of the scale of overpressure development in volcanic rock formations and the analysis of overpressure depths in volcanic rocks.

[0051] 2. In this invention, well logging data is used to identify the causes of overpressure development, reducing the impact of human intervention, simplifying the process of analyzing the formation overpressure mechanism, and reducing the impact of human intervention.

[0052] 3. In this invention, the contribution of overpressure of different origins is obtained by utilizing the rock resistivity-density relationship, and an evaluation method for the contribution of overpressure of different origin mechanisms is established. The calculation method is based on the changes in the volume properties (density) and conductivity properties (resistivity) of the rock in the overpressure range, which reduces the influence of human intervention and makes the prediction method have high quantitative prediction accuracy.

[0053] 4. In summary, compared with the prior art represented by the patent document with publication number CN106127343A, this method, based on the accurate characterization of overpressure development characteristics and accurate identification of overpressure formation mechanisms in volcanic rock formations, utilizes well logging data to establish a quantitative evaluation method for the contribution of overpressure from different formation mechanisms. The analysis method is mainly based on the changes in the volumetric properties (density) and conductive properties (resistivity) of rocks in the overpressure zone. The method is simple and reduces the influence of human intervention, avoiding human error or mistakes. Furthermore, it is the first time that a quantitative calculation method for predicting the contribution of overpressure from different formation mechanisms has been proposed in volcanic rock formations.

[0054] 5. This method, under the constraints of fully considering the actual geological conditions of volcanic rock formations and the selection of reasonable logging response parameters, characterizes overpressure development features and identifies the causes of overpressure development. By constructing a cross-plot of rock resistivity-density relationships, it can effectively evaluate the magnitude of fluid expansion-type and tectonic compression-type overpressure, and quantify the contribution ratio of different types of overpressure to formation overpressure. The following breakthroughs have been achieved: 1) The calculation of non-permeable rock pressure based on the fitting relationship between logging resources and the pressure of adjacent permeable rock formations makes the characterization of overpressure in non-permeable rock formations more accurate; 2) The identification of the causes of overpressure in rock formations is realized based on rock resistivity-density; 3) By comparing the differences in rock resistivity and density between the normal pressure and overpressure sections of volcanic rocks, the contribution rate of different types of overpressure is accurately quantified. The entire calculation method solves key problems such as inaccurate characterization of volcanic rock formation pressure, unclear identification of overpressure types, and unclear contribution rates of different types of overpressure, realizing the identification and quantitative evaluation of the formation mechanism of overpressure in volcanic rock formations. This has a more significant guiding effect on the exploration and development of oil and gas in volcanic rocks. Attached Figure Description

[0055] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein:

[0056] Figure 1 This is a flowchart of the present invention;

[0057] Figure 2 This is a rock density-resistivity cross plot of an embodiment of the present invention. Detailed Implementation

[0058] Example 1

[0059] See Figure 1 As a preferred embodiment of the present invention, it discloses a method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification, the steps of which are as follows:

[0060] Step 1: Using geological data, distinguish between overpressured and normal-pressured volcanic rock depths to determine the scale of overpressure development;

[0061] Step 2: Use well logging data to identify the causes of overpressure development;

[0062] Step 3: Utilize the rock resistivity-density relationship to determine the contribution of overpressure from different origins.

[0063] The first step, more specifically:

[0064] For permeable rock formations, formation pressure is obtained using cable formation testing, drill pipe testing, and mud gravity analysis. For impermeable rock formations, formation pressure is calculated using a fitting relationship between measured formation pressure from adjacent permeable formations and sonic transit time logging data. Based on formation pressure characteristics, overpressured and normal-pressured volcanic rock depths are distinguished, and resistivity and density logging data corresponding to different depths are extracted. The permeable rock formations include pyroclastic rocks and fractured volcanic rocks. The impermeable rock formations include basalt and diabase porphyry.

[0065] This embodiment is based on the fitting relationship between measured formation pressure and sonic transit time logging data, which simplifies the calculation of the scale of overpressure development in volcanic rock formations and the analysis of overpressure depths in volcanic rocks.

[0066] Example 2

[0067] See Figure 1 As another preferred embodiment of the present invention, based on embodiment 1, the second step is more specifically:

[0068] Based on the rock resistivity and density data of the normal pressure volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the normal pressure volcanic rock section was fitted.

[0069] Based on the rock resistivity and density data of the overpressured volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the overpressured volcanic rock section was fitted.

[0070] The rock resistivity-density cross plots under normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship under normal pressure and overpressure are compared.

[0071] If the rock resistivity-density cross plots and the trend lines of the rock resistivity-density relationship match under normal and overpressure conditions, then the overpressure is mainly caused by tectonic compression.

[0072] If the trend line of the rock resistivity-density relationship in the overpressured volcanic rock section deviates from the trend line of the rock resistivity-density relationship in the normal pressure strata in the direction of decreasing resistivity, then the development of overpressure is affected by the combined effects of fluid expansion within the pores and tectonic compression.

[0073] This embodiment utilizes well logging data to identify the causes of overpressure development, reducing the impact of human intervention, simplifying the process of analyzing the formation overpressure mechanism, and minimizing the influence of human intervention.

[0074] Example 3

[0075] See Figure 1 As the preferred embodiment of the present invention, it discloses a method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification, the steps of which are as follows:

[0076] Step 1: Using geological data, distinguish between overpressured and normal-pressured volcanic rock depths to determine the scale of overpressure development:

[0077] For permeable rock formations, formation pressure is obtained using cable formation testing, drill pipe testing, and mud gravity analysis. For impermeable rock formations, formation pressure is calculated using the fitting relationship between measured formation pressure from adjacent permeable formations and sonic transit time logging data. Based on formation pressure characteristics, overpressured and normal-pressured volcanic rock depths are distinguished, and resistivity and density logging data corresponding to different depths are extracted. Permeable rock formations include pyroclastic rocks and fractured volcanic rocks. Impermeable rock formations include basalt and diabase porphyry.

[0078] Step 2: Using well logging data, identify the causes of overpressure development:

[0079] Based on the rock resistivity and density data of the normal pressure volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the normal pressure volcanic rock section was fitted.

[0080] Based on the rock resistivity and density data of the overpressured volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the overpressured volcanic rock section was fitted.

[0081] The rock resistivity-density cross plots under normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship under normal pressure and overpressure are compared.

[0082] If the rock resistivity-density cross plots and the trend lines of the rock resistivity-density relationship match under normal and overpressure conditions, then the overpressure is mainly caused by tectonic compression.

[0083] If the trend line of the rock resistivity-density relationship in the overpressured volcanic rock section deviates from the trend line of the rock resistivity-density relationship in the normal pressure strata in the direction of decreasing resistivity, then the development of overpressure is affected by the combined effects of fluid expansion within the pores and tectonic compression.

[0084] Step 3: Using the rock resistivity-density relationship, determine the contribution of overpressure from different origins:

[0085] The deviation of the resistivity-density variation trend line of volcanic rock in the overpressure section from that in the normal pressure section is calculated. Combined with the effective vertical stress in the normal pressure section and the overpressure section of volcanic rock, the relationship between the rock resistivity deviation and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation and the vertical stress variation is obtained.

[0086] The fluid expansion overpressure is equal to the change in vertical stress, so the fluid expansion overpressure ΔP1 is obtained; the fluid expansion overpressure is subtracted from the formation residual pressure to obtain the overpressure value ΔP2 caused by tectonic compression.

[0087] The ratios of fluid expansion overpressure ΔP1 and tectonic compression overpressure ΔP2 to the formation residual pressure were calculated respectively, thereby obtaining the contribution ratios of fluid expansion overpressure and tectonic compression overpressure to formation overpressure.

[0088] Based on the accurate characterization of overpressure development features and the accurate identification of overpressure formation mechanisms in volcanic rock formations, this embodiment establishes a quantitative evaluation method for the contribution of overpressure from different formation mechanisms using well logging data. The analysis method is mainly based on the changes in the volumetric properties (density) and conductive properties (resistivity) of rocks in the overpressure zone. The method is simple and reduces the influence of human intervention, avoiding human error or mistakes. For the first time, a quantitative calculation method for predicting the contribution of overpressure from different formation mechanisms in volcanic rock formations is proposed.

[0089] Example 4

[0090] See Figures 1-2Taking the Permian Emeishan volcanic rock group in a certain area of ​​the Southwest Oil and Gas Field as an example, this paper uses quantitative evaluation of fluid expansion type overpressure and tectonic compression type overpressure to illustrate the specific technical solution of the invention:

[0091] Step 1: Based on geological data, distinguish between normal-pressure and overpressure volcanic rock layers, and extract the resistivity and density of the volcanic rock layers from well logging. Specific steps include:

[0092] (1) For permeable formations, the measured pressure data of a single well are statistically analyzed based on drill pipe and cable formation tests; for non-permeable formations, the formation pressure of the permeable formation section is calculated using the fitting relationship between the measured formation pressure of adjacent permeable formations and sonic transit time logging data. The formula P... 静 =ρ w Calculate hydrostatic pressure (ρ) using gH w Density of formation water, kg / m³ 3 g is the acceleration due to gravity, m / s² 2 (H represents the burial depth, m). By comparing the measured pressure data and hydrostatic pressure at the same depth, the formation pressure coefficient and residual pressure were obtained, and the depth ranges of overpressure and normal pressure strata of the Permian Emeishan volcanic rock group were identified (Table 1).

[0093]

[0094] Table 1

[0095] (2) Based on the logging data, extract the logging rock resistivity R and logging rock density ρ data for the corresponding depths according to the overpressure and normal pressure depths.

[0096] Step 2: Establish a rock resistivity-density cross plot using a plane rectangular coordinate system, and fit the rock resistivity and rock density of the normal pressure volcanic rock section to derive the fitting formula and trend line of the normal pressure rock resistivity-density function relationship.

[0097] Plot a rock resistivity-density cross plot at normal pressure volcanic rock depth range, using rock resistivity as the x / y axis and rock density as the y / y axis. Figure 2 The fitting formula for the rock resistivity-density function relationship in the normal pressure volcanic rock depth range shown in the figure is:

[0098] R=0.0002ρ 10.141

[0099] The extracted rock resistivity and density data of the overpressured volcanic rock depth range were plotted onto the rock resistivity-density cross plot of the normal-pressured volcanic rock depth range. Then, the fitted lines of the rock resistivity-density relationship between the overpressured and normal-pressured volcanic rock depth ranges were compared.

[0100] If the fitting lines of the overpressured volcanic rock depth segment and the normal pressured volcanic rock depth segment are similar, then the overpressure origin type is tectonic compression, and the effect of tectonic compression on formation pressure is equal to the residual pressure.

[0101] If the fitting line of the depth segment of overpressured volcanic rock deviates from the fitting line of the depth segment of normal pressured volcanic rock along the direction of decreasing resistivity, then the development of overpressure is affected by the combined effects of fluid expansion within the pores and tectonic compression.

[0102] Step 3: Determine the deviation of the rock resistivity-density trend line from the normal pressure volcanic rock depth range. Statistically analyze the resistivity and vertical effective stress values ​​of mudstone, tuffaceous mudstone, and tuff interlayers or adjacent mudstone, tuffaceous mudstone, and tuff. Analyze the relationship between the change in rock resistivity ΔR and the change in vertical effective stress Δδ, deriving a fitting formula for the change in resistivity and the change in vertical stress. Calculate the change in vertical effective stress based on the actual change in resistivity. Since fluid expansion overpressure is the main stress causing the change in vertical effective stress, calculate the fluid expansion overpressure ΔP1 based on the change in vertical effective stress. Subtract the fluid expansion overpressure ΔP1 from the residual pressure ΔP in the overpressure volcanic rock depth range to obtain the overpressure ΔP2 caused by tectonic compression.

[0103] Specifically, based on the fitting formula for the functional relationship between rock resistivity and density in the normal-pressure volcanic rock depth range, the change in rock resistivity in the overpressure volcanic rock depth range is determined according to the rock resistivity-density cross-plot of the overpressure volcanic rock depth range. The formula for calculating the change in rock resistivity ΔR is as follows:

[0104] ΔR=0.0002ρ 10.141 +2.372-R 实测 ;

[0105] Among them, R 实测 ρ is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressured volcanic rock depth section, where ρ is the rock density.

[0106] The formula for calculating the vertical stress change Δδ is as follows:

[0107] Δδ = 1.138·ΔR + 1.125;

[0108] Wherein, ΔR is the change in rock resistivity;

[0109] The formula for calculating the overpressure ΔP1 caused by fluid expansion within the overpressure volcanic rock depth range is as follows:

[0110] ΔP1 = Δδ = 1.138 · ΔR + 1.125;

[0111] Where Δδ is the change in vertical stress and ΔR is the change in rock resistivity;

[0112] Subtracting the fluid expansion overpressure from the residual formation pressure, the formula for calculating the overpressure value ΔP2 caused by tectonic compression is as follows:

[0113] ΔP2 = ΔP - ΔP1;

[0114] Where ΔP is the formation residual pressure and ΔP1 is the fluid expansion overpressure;

[0115] The ratios of fluid expansion overpressure ΔP1, tectonic compression overpressure ΔP2, and formation residual pressure were calculated separately to determine the contribution ratios of fluid expansion-type overpressure and tectonic compression-type overpressure to formation overpressure.

[0116] The contribution ratio of fluid expansion to overpressure, G1:

[0117] G1 = ΔP1 / ΔP·100%;

[0118] The contribution ratio of structural extrusion to overpressure, G2:

[0119] G2 = ΔP2 / ΔP·100%.

Claims

1. A method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification, characterized in that... The steps are as follows: Step 1: Using geological data, distinguish between overpressured and normal-pressured volcanic rock depths to determine the scale of overpressure development; Step 2: Use well logging data to identify the causes of overpressure development; Step 3: Utilize the rock resistivity-density relationship to determine the contribution of overpressure from different origins; The second step, more specifically: Based on the rock resistivity and density data of the normal pressure volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the normal pressure volcanic rock section was fitted. Based on the rock resistivity and density data of the overpressured volcanic rock section, a rock resistivity-density cross plot was drawn and a trend line of rock resistivity-density relationship variation of the overpressured volcanic rock section was fitted. The rock resistivity-density cross plots under normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship under normal pressure and overpressure are compared. If the rock resistivity-density cross plots and the trend lines of the rock resistivity-density relationship match under normal and overpressure conditions, then the overpressure is mainly caused by tectonic compression. If the trend line of the rock resistivity-density relationship in the overpressured volcanic rock section deviates from the trend line of the rock resistivity-density relationship in the normal pressure strata in the direction of decreasing resistivity, then the development of overpressure is affected by the combined effects of fluid expansion in the pores and tectonic compression. The third step, more specifically: The deviation of the resistivity-density variation trend line of volcanic rock in the overpressure section from that in the normal pressure section is calculated. Combined with the effective vertical stress in the normal pressure section and the overpressure section of volcanic rock, the relationship between the rock resistivity deviation and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation and the vertical stress variation is obtained. The fluid expansion overpressure is equal to the change in vertical stress, so the fluid expansion overpressure ΔP1 is obtained; the fluid expansion overpressure is subtracted from the formation residual pressure to obtain the overpressure value ΔP2 caused by tectonic compression. The ratios of fluid expansion overpressure ΔP1 and tectonic compression overpressure ΔP2 to the formation residual pressure were calculated respectively, thereby obtaining the contribution ratios of fluid expansion overpressure and tectonic compression overpressure to formation overpressure.

2. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 1, characterized in that: The first step, more specifically: For permeable rock formations, formation pressure is obtained using cable formation testing, drill pipe testing, and mud density analysis. For non-permeable rock formations, formation pressure is calculated using the fitting relationship between measured formation pressure of adjacent permeable formations and sonic transit time logging data. Based on formation pressure characteristics, overpressure and normal pressure volcanic rock depths are distinguished, and resistivity and density logging data corresponding to different formation depths are extracted.

3. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 2, characterized in that: The permeable rock layers include pyroclastic rocks and fractured volcanic rocks.

4. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 2, characterized in that: The aforementioned non-permeable rock strata include basalt and diabase porphyry.

5. A method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification, as described in claim 1 or 2, characterized in that: The first step also includes: using formula P 静 =ρ w gH is used to calculate the hydrostatic pressure, ρ w Density of formation water, kg / m³ 3 g is the acceleration due to gravity, m / s² 2 H represents the burial depth of the formation in meters. By comparing the measured formation pressure and hydrostatic pressure at the same depth, the formation pressure coefficient and residual pressure are obtained.

6. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 1, characterized in that: In the second step, a rock resistivity-density cross-plot is established using a Cartesian coordinate system. Based on the rock resistivity and density of the normal or overpressure volcanic rock sections, the fitting formula for the rock resistivity-density function relationship under normal or overpressure conditions is derived as follows: R=0.0002ρ 10.141 ; Where R is the rock resistivity and ρ is the rock density.

7. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 6, characterized in that: In the second step, the rock resistivity-density cross plots of normal pressure and overpressure are compared, and the trend lines of the rock resistivity-density relationship of normal pressure and overpressure are compared. Specifically, the rock resistivity and density data of the extracted overpressure volcanic rock depth segment are plotted on the rock resistivity-density cross plot of the normal pressure volcanic rock depth segment, and then the trend lines of the rock resistivity-density relationship of the overpressure volcanic rock depth segment and the normal pressure volcanic rock depth segment are compared.

8. The method for evaluating the contribution of overpressure genesis in volcanic natural gas reservoirs based on well logging identification according to claim 1, characterized in that: In the third step, the formula for calculating the change in rock resistivity ΔR is as follows: ΔR=0.0002ρ 10.141 +2.372-R 实测 ; Among them, R 实测 ρ is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressured volcanic rock depth section, where ρ is the rock density. The formula for calculating the vertical stress change Δδ is as follows: Δδ = 1.138·ΔR + 1.125; Wherein, ΔR is the change in rock resistivity; The formula for calculating the overpressure ΔP1 caused by fluid expansion within the overpressure volcanic rock depth range is as follows: ΔP1 = Δδ = 1.138 · ΔR + 1.125; Where Δδ is the change in vertical stress and ΔR is the change in rock resistivity; Subtracting the fluid expansion overpressure from the residual formation pressure, the formula for calculating the overpressure value ΔP2 caused by tectonic compression is as follows: ΔP2 = ΔP - ΔP1; Where ΔP is the formation residual pressure and ΔP1 is the fluid expansion overpressure; The ratios of fluid expansion overpressure ΔP1, tectonic compression overpressure ΔP2, and formation residual pressure were calculated separately to determine the contribution ratios of fluid expansion-type overpressure and tectonic compression-type overpressure to formation overpressure. The contribution ratio of fluid expansion to overpressure, G1: G1 = ΔP1 / ΔP·100%; The contribution ratio of structural extrusion to overpressure, G2: G2 = ΔP2 / ΔP·100%.

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