Volcanic rock natural gas reservoir overpressure cause contribution evaluation method based on logging identification

Abstract

The invention discloses a volcanic rock natural gas reservoir overpressure cause contribution evaluation method based on logging identification, and relates to the technical field of petroleum and natural gas exploration and development, and the method comprises the following steps: 1, utilizing geological data to distinguish overpressure and normal pressure volcanic rock depth sections, and determining an overpressure development scale; 2, using logging information to identify overpressure development causes; and 3, calculating the contribution of different causes of overpressure by using a rock resistivity-density relationship. According to the method, the contribution proportion of different causes to overpressure formation can be quantitatively calculated according to the variable quantity of the volume attribute and the conduction attribute of the rock in the overpressure section, the influence of manual intervention is reduced, manual errors or mistakes are avoided, and the prediction method has high quantitative prediction precision.

Description

Technical Field

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

[0002] During the formation and evolution of oil and gas basins, changes in the physical and chemical conditions inside the formations can easily lead to increased formation pressure, thus forming overpressure formations. According to the development mechanism, overpressure types in oil and gas basins can be divided into three categories: ① Overpressure caused by undercompaction of the formation; ② Overpressure caused by fluid expansion in the pores, such as dehydration of clay minerals, hydrothermal pressurization, hydrocarbon generation from source rocks, and gas generation from cracking of organic matter; 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 drive is an important driving force for oil and gas migration and large-scale accumulation. Therefore, in the process of overpressure research, the formation mechanism and quantitative analysis of overpressure can help the study of the advantageous migration and accumulation direction of oil and gas and the favorable oil and gas enrichment zones.

[0003] At present, scholars at home and abroad generally believe that the main reasons for the large-scale overpressure in my country's oil and gas basins are undercompaction and fluid expansion, and the distribution of overpressure due to these two causes accounts for as much as 86%. Among them, undercompaction mainly develops in clastic rock formations, while for volcanic rocks with strong anti-compaction ability, tectonic compression and fluid expansion may be the main reasons for the formation of large-scale overpressure in volcanic rock formations. At present, the evaluation methods for these two causes of overpressure mainly include: using mudstone acoustic time difference, cable formation testing and drill pipe testing data to identify the characteristics of overpressure development; using organic matter maturity to identify fluid expansion and pressurization caused by organic matter cracking; using tectonic stress numerical simulation technology is the main method to study formation pressure under compression. The quantitative characterization of overpressure of different causes is a difficult point in overpressure research. According to the elastic theory of sedimentary rocks, predecessors simulated the contribution of tectonic stress to formation pressure; Guo Xiaowen and others simulated the pressurization model of different stages of hydrocarbon generation and expulsion through physical experiments to calculate the hydrocarbon generation pressurization. Liu Hua et al., Wang Xin et al. used basin simulation methods to restore the pressure evolution of single wells (one-dimensional) and connected wells (two-dimensional), and quantitatively characterized the overpressure of different genetic types in sedimentary rock layers. Bowers found through experimental analysis that igneous rocks have weaker elasticity than sedimentary rocks due to the lack of connected pores.

[0004] A Chinese patent document with publication number CN106127343A and publication date November 16, 2016 discloses a method for analyzing the formation mechanism of formation overpressure. The method combines the formation pressure prediction method with the analysis of the formation mechanism of formation overpressure by using the measured formation pressure of a single well. The formation mechanism of formation overpressure is analyzed by comparing the differences between multiple pressure prediction curves and the differences between the predicted curves and the measured curves. Three formation pressure prediction methods are used: the Eaton method based on undercompaction formation, the equivalent depth method, and the Bowers method based on fluid expansion formation. The invention analyzes the formation mechanism of formation overpressure by comparing the differences between multiple pressure prediction curves and the differences between the prediction curves and the measured curves. If the differences between the three prediction curves are small and the differences between the three prediction curves and the measured curves are small, it means that the overpressure may be caused by undercompaction; if the differences between the three prediction curves are small but the differences between the three prediction curves and the measured curves are large, it means that the overpressure may be caused by tectonic compression; if the differences between the prediction results of the three methods are large, the prediction results are compared with the measured results respectively. If the error of the Eaton method or the equivalent depth method is small, it means that the overpressure may be caused by undercompaction; if the error of the Bowers method prediction result is small, it means that the overpressure may be caused by fluid expansion; if the prediction errors of the three methods are all large, it means that the overpressure may be caused by tectonic compression, which makes the analysis process of the formation mechanism of formation overpressure simple.

[0005] The prior art represented by the above-mentioned CN106127343A patent document can only determine the genesis type of formation overpressure, but cannot quantitatively identify the overpressure formed by a combination of multiple genesis. In general, the current research on quantitative characterization of overpressure of different genesis types of volcanic rock formations with strong anti-compaction ability and weak elastic rebound response is still relatively weak. Most methods are based on simple sedimentary rock pore elasticity models, and there are still defects in the research on overpressure of volcanic rocks with complex fluid, structure and pore throat relationships. Summary of the invention

[0006] The present invention aims to address the defects and shortcomings of the above-mentioned prior art and provide a method for evaluating the contribution of the causes of overpressure in volcanic natural gas reservoirs based on well logging identification. The method can quantitatively calculate the contribution ratio of different causes to the overpressure formation according to the changes in the volume properties and conductivity properties of the rock in the overpressure section, thereby reducing the impact of human intervention, avoiding human errors or mistakes, and making the prediction method have a higher quantitative prediction accuracy.

[0007] The present invention is achieved by adopting the following technical solutions: A method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification, characterized by the following steps: Step 1: Use geological data to distinguish the depth sections of overpressure and normal-pressure volcanic rocks and clarify the scale of overpressure development; Step 2: Use logging data to identify the causes of overpressure development; Step 3: Use the rock resistivity-density relationship to calculate the contribution of overpressure of different origins.

[0008] The first step, more specifically, is: For permeable rock formations, cable formation testing, drill pipe testing and mud density analysis are used to obtain formation pressure. For impermeable rock formations, the formation pressure of impermeable rock formations is calculated using the fitting relationship between the measured formation pressure of adjacent permeable formations and the acoustic time difference logging data. Based on the formation pressure characteristics, the depth sections of overpressured and normal-pressure volcanic rocks are distinguished, and the resistivity logging and density logging data corresponding to formations at different depths are extracted.

[0009] The permeable rock layer includes pyroclastic rock and fractured volcanic rock.

[0010] The impermeable rock formations include basalt and diabase porphyry.

[0011] The second step is more specifically: According to the rock resistivity and density data of the normal-pressure volcanic rock section, the rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the normal-pressure volcanic rock section is fitted; Based on the rock resistivity and density data of the overpressure volcanic rock section, a rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the overpressure volcanic rock section is fitted; The resistivity-density cross plots of rock under normal pressure and overpressure are compared, and the resistivity-density relationship trend lines of rock under normal pressure and overpressure are compared; If the rock resistivity-density cross-plots and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are consistent, the overpressure is mainly caused by tectonic compression; If the rock resistivity-density relationship variation trend line of the overpressure volcanic rock section deviates from the rock resistivity-density relationship variation trend line of the normal pressure formation in the direction of resistivity decrease, the development of overpressure is affected by the joint influence of fluid expansion in the pores and tectonic compression.

[0012] The third step is more specifically: The deviation amplitude of the rock resistivity-density variation trend line of the volcanic rock overpressure section and the rock resistivity-density variation trend line of the volcanic rock normal pressure section is calculated. Combined with the vertical effective stress of the volcanic rock normal pressure section and the volcanic rock overpressure section, the relationship between the rock resistivity deviation amplitude and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation amplitude and the vertical stress variation is obtained. The fluid expansion overpressure is equal to the change in vertical stress, and the fluid expansion overpressure ΔP1 is obtained; the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the formation residual pressure are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure.

[0013] The first step also includes: by formula P 静 =ρ w gH Calculate the hydrostatic pressure (ρ w is the formation water density, kg / m 3 , g is the acceleration due to gravity, m / s 2 , H is the burial depth of the formation, m), and the measured formation pressure and hydrostatic pressure at the same depth are compared to obtain the formation pressure coefficient and residual pressure.

[0014] In the second step, a rock resistivity-density cross plot is established using a plane rectangular coordinate system, and the rock resistivity-density function relationship of normal pressure or overpressure is fitted according to the rock resistivity and rock density of the normal pressure or overpressure volcanic rock section: R=0.0002ρ 10.141 ; Where R is the rock resistivity and ρ is the rock density.

[0015] In the second step, the rock resistivity-density cross plots of normal pressure and overpressure are compared, and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are compared. Specifically, the rock resistivity and density data of the overpressure volcanic rock depth segment are projected onto the rock resistivity-density cross plot of the normal pressure volcanic rock depth segment, and then the rock resistivity-density relationship change trend lines of the overpressure volcanic rock depth segment and the normal pressure volcanic rock depth segment are compared.

[0016] In the second step, when the overpressure is mainly caused by tectonic compression, the effect of tectonic compression on the formation pressure is equal to the residual pressure.

[0017] In the third step, the calculation formula of the rock resistivity change ΔR is as follows: ΔR=0.0002ρ 10.141 +2.372-R 实测 ; Among them, R 实测 is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressure volcanic rock depth section, ρ is the rock density; The calculation formula of vertical stress change Δδ is as follows: Δδ=1.138·ΔR+1.125; Among them, ΔR is the change in rock resistivity; The calculation formula for the overpressure ΔP1 caused by fluid expansion in the overpressure volcanic rock depth section is: ΔP1=Δδ=1.138·ΔR+1.125; Among them, Δδ is the change in vertical stress, and ΔR is the change in rock resistivity; The calculation formula for the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure: ΔP2=ΔP-ΔP1; Among them, ΔP is the residual pressure of the formation, and ΔP1 is the fluid expansion overpressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the residual pressure of the formation are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure, that is: The contribution ratio of fluid expansion to overpressure G1: G1=ΔP1 / ΔP·100%; The contribution ratio of tectonic compression to overpressure G2: G2=ΔP2 / ΔP·100%.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: 1. In the present invention, geological data is used to distinguish the depth sections of overpressured and normal-pressured volcanic rocks, and the scale of overpressure development is clarified. The calculation is based on the fitting relationship between the measured formation pressure and the acoustic time difference logging data, so that the calculation of the scale of overpressure development in volcanic rock formations and the process of analyzing the overpressure depth section of volcanic rocks are simpler.

[0019] 2. In the present invention, the logging data is used to identify the causes of overpressure development, which reduces the impact of human intervention, simplifies the process of analyzing the formation overpressure mechanism, and reduces the impact of human intervention.

[0020] 3. In the present invention, the contribution of overpressure of different causes is obtained by utilizing the rock resistivity-density relationship, and an evaluation method for the contribution of overpressure of different causes is established. The calculation method is based on the change in the volume properties (density) and conductivity properties (resistivity) of the rock in the overpressure section, which reduces the influence of human intervention and makes the prediction method have a higher quantitative prediction accuracy.

[0021] 4. In summary, compared with the prior art represented by the patent document with publication number CN106127343A, the present method, based on the precise characterization of the overpressure development characteristics of volcanic rock formations and the accurate identification of the overpressure genesis mechanism, uses logging data to establish a quantitative evaluation method for the overpressure contribution of different genesis mechanisms. The analysis method is mainly based on the changes in the volume properties (density) and conductivity properties (resistivity) of rocks in the overpressure section. The method is simple and reduces the influence of human intervention, avoiding human errors or mistakes. In addition, a calculation method for quantitatively predicting the overpressure contribution of different genesis mechanisms is proposed for the first time in volcanic rock formations.

[0022] 5. This method characterizes the characteristics of overpressure development and identifies the causes of overpressure development under the constraints of fully considering the actual geological conditions of volcanic rock formations and the selection of reasonable logging response parameters. By constructing a rock resistivity-density relationship cross-plot, it can effectively evaluate the size of fluid expansion-type overpressure and structural 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 formation pressure based on the fitting relationship between logging resources and adjacent permeable rock formation pressure makes the characterization of non-permeable rock formation overpressure more accurate; 2) Based on rock resistivity-density, the identification of the causes of overpressure in the rock formation is realized; 3) By comparing the differences in rock resistivity and density between the normal pressure section and the overpressure section of volcanic rocks, the contribution rate of overpressure of different genesis types is accurately quantified. The whole set of calculation methods solves the key problems of inaccurate characterization of volcanic rock formation pressure, unclear identification of overpressure types, and unclear contribution rates of different types of overpressure, and realizes the identification and quantitative evaluation of the overpressure formation mechanism of volcanic rock formations, which has a more obvious guiding effect on the exploration and development of volcanic rock oil and gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 is a flow chart of the present invention; Figure 2 This is a rock density-resistivity cross-plot according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] Example 1 See also Figure 1 As a preferred embodiment of the present invention, a method for evaluating the contribution of overpressure genesis of volcanic gas reservoirs based on well logging identification is disclosed, and the steps are as follows: Step 1: Use geological data to distinguish the depth sections of overpressure and normal-pressure volcanic rocks and clarify the scale of overpressure development; Step 2: Use logging data to identify the causes of overpressure development; Step 3: Use the rock resistivity-density relationship to calculate the contribution of overpressure of different origins.

[0025] The first step, more specifically, is: For permeable rock formations, formation pressure is obtained by cable formation testing, drill pipe testing and mud density analysis; for impermeable rock formations, formation pressure of impermeable rock formations is calculated by using the fitting relationship between the measured formation pressure of adjacent permeable formations and the acoustic time difference logging data; according to the formation pressure characteristics, the depth sections of overpressure and normal pressure volcanic rocks are distinguished, and the resistivity logging and density logging data corresponding to formations at different depths are extracted. The permeable rock formations include pyroclastic rocks and fractured volcanic rocks. The impermeable rock formations include basalt and diabase porphyry.

[0026] This embodiment is based on the calculation based on the measured formation pressure and the fitting relationship of the acoustic time difference logging data, which makes the calculation of the development scale of volcanic rock formation overpressure and the analysis of volcanic rock overpressure depth section simpler.

[0027] Example 2 See also Figure 1 As another preferred embodiment of the present invention, based on Example 1, the second step is more specifically: According to the rock resistivity and density data of the normal-pressure volcanic rock section, the rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the normal-pressure volcanic rock section is fitted; Based on the rock resistivity and density data of the overpressure volcanic rock section, a rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the overpressure volcanic rock section is fitted; The resistivity-density cross plots of rock under normal pressure and overpressure are compared, and the resistivity-density relationship trend lines of rock under normal pressure and overpressure are compared; If the rock resistivity-density cross-plots and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are consistent, the overpressure is mainly caused by tectonic compression; If the rock resistivity-density relationship variation trend line of the overpressure volcanic rock section deviates from the rock resistivity-density relationship variation trend line of the normal pressure formation in the direction of resistivity decrease, the development of overpressure is affected by the joint influence of fluid expansion in the pores and tectonic compression.

[0028] This embodiment uses logging data to identify the cause of overpressure development, reduces the impact of human intervention, simplifies the process of analyzing the mechanism of formation overpressure, and reduces the impact of human intervention.

[0029] Example 3 See also Figure 1 As the best embodiment of the present invention, a method for evaluating the contribution of overpressure genesis of volcanic gas reservoirs based on well logging identification is disclosed, and the steps are as follows: Step 1: Use geological data to distinguish the depth sections of overpressure and normal pressure volcanic rocks and clarify the scale of overpressure development: For permeable rock formations, formation pressure is obtained by cable formation testing, drill pipe testing and mud density analysis; for impermeable rock formations, the formation pressure of impermeable rock formations is calculated by using the fitting relationship between the measured formation pressure of adjacent permeable formations and the acoustic time difference logging data; according to the formation pressure characteristics, the depth sections of overpressure and normal pressure volcanic rocks are distinguished, and the resistivity logging and density logging data corresponding to formations at different depths are extracted. Permeable rock formations include pyroclastic rocks and fractured volcanic rocks. Impermeable rock formations include basalt and diabase porphyry.

[0030] Step 2: Use logging data to identify the causes of overpressure development: According to the rock resistivity and density data of the normal-pressure volcanic rock section, the rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the normal-pressure volcanic rock section is fitted; Based on the rock resistivity and density data of the overpressure volcanic rock section, a rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the overpressure volcanic rock section is fitted; The resistivity-density cross plots of rock under normal pressure and overpressure are compared, and the resistivity-density relationship trend lines of rock under normal pressure and overpressure are compared; If the rock resistivity-density cross-plots and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are consistent, the overpressure is mainly caused by tectonic compression; If the rock resistivity-density relationship variation trend line of the overpressure volcanic rock section deviates from the rock resistivity-density relationship variation trend line of the normal pressure formation in the direction of resistivity decrease, the development of overpressure is affected by the joint influence of fluid expansion in the pores and tectonic compression.

[0031] Step 3: Using the rock resistivity-density relationship, calculate the contribution of overpressure of different origins: The deviation amplitude of the rock resistivity-density variation trend line of the volcanic rock overpressure section and the rock resistivity-density variation trend line of the volcanic rock normal pressure section is calculated. Combined with the vertical effective stress of the volcanic rock normal pressure section and the volcanic rock overpressure section, the relationship between the rock resistivity deviation amplitude and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation amplitude and the vertical stress variation is obtained. The fluid expansion overpressure is equal to the change in vertical stress, and the fluid expansion overpressure ΔP1 is obtained; the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the formation residual pressure are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure.

[0032] This embodiment, based on the precise characterization of overpressure development characteristics of volcanic rock formations and accurate identification of overpressure genesis mechanisms, uses logging data to establish a quantitative evaluation method for overpressure contributions of different genesis mechanisms. The analysis method is mainly based on the changes in the volume properties (density) and conductivity properties (resistivity) of rocks in the overpressure section. The method is simple and reduces the impact of human intervention, avoiding human errors or mistakes. For the first time, a calculation method for quantitatively predicting overpressure contributions of different genesis mechanisms is proposed in volcanic rock formations.

[0033] Example 4 See also Figure 1-Figure 2 Taking the Permian Emeishan volcanic rock group in a certain area of ​​the Southwest Oil and Gas Field as an example, the specific technical scheme of the invention is explained by quantitatively evaluating the fluid expansion type overpressure and the structural compression type overpressure: Step 1: Based on geological data, distinguish between normal pressure and overpressure volcanic rock layers, and extract the logging rock resistivity and density of the volcanic rock layers respectively. The specific steps include: (1) For permeable rock formations, the measured pressure data of a single well is statistically analyzed based on the 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 the adjacent permeable formation and the acoustic time difference logging data. 静 =ρ w gH Calculate the hydrostatic pressure (ρ w is the formation water density, kg / m 3 , g is the acceleration due to gravity, m / s 2 By comparing the measured pressure data with the hydrostatic pressure at the same depth, the formation pressure coefficient and residual pressure were obtained, and the depth section where the overpressure and normal pressure formations of the Permian Emeishan volcanic rock group developed was clarified (Table 1).

[0034] Table 1 (2) Based on the logging data, the logging rock resistivity R and logging rock density ρ data of the corresponding depths are extracted according to the overpressure and normal pressure depth sections.

[0035] Step 2: Use the plane rectangular coordinate system to establish the rock resistivity-density cross plot, and fit the normal-pressure rock resistivity-density function relationship fitting formula and trend line based on the rock resistivity and rock density of the normal-pressure volcanic rock section.

[0036] With the logging rock resistivity as the horizontal / vertical coordinate and the logging rock density as the vertical / horizontal coordinate, a rock resistivity-density cross-plot of the normal pressure volcanic rock depth section is drawn ( Figure 2 ), the functional relationship between rock resistivity and density in the depth section of normal pressure volcanic rock in the figure is fitted as follows: R=0.0002ρ10.141 The rock resistivity and density data of the extracted overpressure volcanic rock depth section are projected onto the rock resistivity-density cross-plot of the normal-pressure volcanic rock depth section, and then the rock resistivity-density relationship fitting lines of the overpressure volcanic rock depth section and the normal-pressure volcanic rock depth section are compared: If the fitting lines of the overpressure volcanic rock depth section and the normal pressure volcanic rock depth section are similar, the overpressure genesis type is tectonic compression, and the effect of tectonic compression on the formation pressure is equal to the residual pressure; If the fitting line of the overpressure volcanic rock depth section deviates from the fitting line of the normal pressure volcanic rock depth section in the direction of decreasing resistivity, the development of overpressure is affected by the expansion of fluid in the pores and tectonic compression.

[0037] Step 3: Determine the deviation amplitude of the rock resistivity-density relationship trend line from the normal pressure volcanic rock depth section. Statistical 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 rock resistivity change ΔR and the vertical effective stress change Δδ, and obtain the fitting relationship between the resistivity change and the vertical stress change. Calculate the change in vertical effective stress based on the actual resistivity change. Since fluid expansion overpressure is the main stress for the change in vertical effective stress, the fluid expansion overpressure ΔP1 is obtained based on the change in vertical effective stress, and then the residual pressure ΔP in the overpressure volcanic rock depth section is subtracted from the fluid expansion overpressure ΔP1 to obtain the overpressure ΔP2 caused by tectonic compression.

[0038] Among them, combined with the functional relationship fitting formula of rock resistivity-density in the normal pressure volcanic rock depth section, the rock resistivity change in the overpressure volcanic rock depth section is determined according to the rock resistivity-density cross-plot in the overpressure volcanic rock depth section. The calculation formula of the rock resistivity change ΔR is as follows: ΔR=0.0002ρ 10.141 +2.372-R 实测 ; Among them, R 实测 is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressure volcanic rock depth section, ρ is the rock density; The calculation formula of vertical stress change Δδ is as follows: Δδ=1.138·ΔR+1.125; Among them, ΔR is the change in rock resistivity; The calculation formula for the overpressure ΔP1 caused by fluid expansion in the overpressure volcanic rock depth section is: ΔP1=Δδ=1.138·ΔR+1.125; Among them, Δδ is the change in vertical stress, and ΔR is the change in rock resistivity; The calculation formula for the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure: ΔP2=ΔP-ΔP1; Among them, ΔP is the residual pressure of the formation, and ΔP1 is the fluid expansion overpressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the residual pressure of the formation are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure, that is: The contribution ratio of fluid expansion to overpressure G1: G1=ΔP1 / ΔP·100%; The contribution ratio of tectonic compression to overpressure G2: G2=ΔP2 / ΔP·100%.

Claims

1. A method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification, characterized in that Here are the steps: Step 1: Use geological data to distinguish the depth sections of overpressure and normal-pressure volcanic rocks and clarify the scale of overpressure development; Step 2: Use logging data to identify the causes of overpressure development; Step 3: Use the rock resistivity-density relationship to calculate the contribution of overpressure of different origins.

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

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

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

5. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 1, characterized in that: The second step is more specifically: According to the rock resistivity and density data of the normal-pressure volcanic rock section, the rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the normal-pressure volcanic rock section is fitted; Based on the rock resistivity and density data of the overpressure volcanic rock section, a rock resistivity-density cross-plot is drawn and the rock resistivity-density relationship trend line of the overpressure volcanic rock section is fitted; The resistivity-density cross plots of rock under normal pressure and overpressure are compared, and the resistivity-density relationship trend lines of rock under normal pressure and overpressure are compared; If the rock resistivity-density cross-plots and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are consistent, the overpressure is mainly caused by tectonic compression; If the rock resistivity-density relationship variation trend line of the overpressure volcanic rock section deviates from the rock resistivity-density relationship variation trend line of the normal pressure formation in the direction of resistivity decrease, the development of overpressure is affected by the joint influence of fluid expansion in the pores and tectonic compression.

6. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 1, characterized in that: The third step is more specifically: The deviation amplitude of the rock resistivity-density variation trend line of the volcanic rock overpressure section and the rock resistivity-density variation trend line of the volcanic rock normal pressure section is calculated. Combined with the vertical effective stress of the volcanic rock normal pressure section and the volcanic rock overpressure section, the relationship between the rock resistivity deviation amplitude and the vertical stress variation is analyzed, and the fitting relationship between the rock resistivity deviation amplitude and the vertical stress variation is obtained. The fluid expansion overpressure is equal to the change in vertical stress, and the fluid expansion overpressure ΔP1 is obtained; the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the formation residual pressure are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure.

7. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 1 or 2, characterized in that: The first step also includes: by formula P 静 =ρ w gH Calculate the hydrostatic pressure (ρ w is the formation water density, kg / m 3 , g is the acceleration due to gravity, m / s 2 , H is the burial depth of the formation, m), and the measured formation pressure and hydrostatic pressure at the same depth are compared to obtain the formation pressure coefficient and residual pressure.

8. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 1 or 5, characterized in that: In the second step, a rock resistivity-density cross plot is established using a plane rectangular coordinate system, and the rock resistivity-density function relationship of normal pressure or overpressure is fitted according to the rock resistivity and rock density of the normal pressure or overpressure volcanic rock section: R=0.0002ρ 10.141 ; Where R is the rock resistivity and ρ is the rock density.

9. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 8, characterized in that: In the second step, the rock resistivity-density cross plots of normal pressure and overpressure are compared, and the rock resistivity-density relationship change trend lines of normal pressure and overpressure are compared. Specifically, the rock resistivity and density data of the overpressure volcanic rock depth segment are projected onto the rock resistivity-density cross plot of the normal pressure volcanic rock depth segment, and then the rock resistivity-density relationship change trend lines of the overpressure volcanic rock depth segment and the normal pressure volcanic rock depth segment are compared.

10. The method for evaluating the contribution of overpressure genesis in volcanic gas reservoirs based on well logging identification according to claim 1, characterized in that: In the third step, the calculation formula of the rock resistivity change ΔR is as follows: ΔR=0.0002ρ 10.141 +2.372-R 实测 ; Among them, R 实测 is the measured rock resistivity of mudstone, tuffaceous mudstone and tuff interlayers or adjacent mudstone, tuffaceous mudstone and tuff in the overpressure volcanic rock depth section, ρ is the rock density; The calculation formula of vertical stress change Δδ is as follows: Δδ=1.138·ΔR+1.125; Among them, ΔR is the change in rock resistivity; The calculation formula for the overpressure ΔP1 caused by fluid expansion in the overpressure volcanic rock depth section is: ΔP1=Δδ=1.138·ΔR+1.125; Among them, Δδ is the change in vertical stress, and ΔR is the change in rock resistivity; The calculation formula for the overpressure value ΔP2 caused by structural compression is obtained by subtracting the fluid expansion overpressure from the formation residual pressure: ΔP2=ΔP-ΔP1; Among them, ΔP is the residual pressure of the formation, and ΔP1 is the fluid expansion overpressure; The ratios of the fluid expansion overpressure ΔP1, the overpressure value ΔP2 caused by structural compression and the residual pressure of the formation are calculated respectively, so as to obtain the contribution ratio of the fluid expansion overpressure and the structural compression overpressure to the formation overpressure, that is: The contribution ratio of fluid expansion to overpressure G1: G1=ΔP1 / ΔP·100%; The contribution ratio of tectonic compression to overpressure G2: G2=ΔP2 / ΔP·100%.

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