A method for predicting formation pressure based on seismic data

Abstract

The present invention discloses a method for predicting formation pressure based on seismic data, and relates to the field of petroleum geological exploration and seismic data inversion technology. The method comprises the following steps: S1, determining a prediction formula for formation pressure; S2, preprocessing of seismic velocity data bodies; S3, calculation and normalization of various parameter data bodies; S4, optimization and adjustment of core parameters; S5, verification and improvement of prediction results. The present invention provides a method for predicting formation pressure based on seismic data. The method can be used efficiently over a large area with only seismic velocity data, is suitable for estimating the pressure of dense layers, is simple and efficient, can obtain the trend of pressure changes, and is conducive to the exploration and development of oil and gas resources.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geological exploration and seismic data inversion, and in particular to a method for predicting formation pressure based on seismic data. Background Art

[0002] The Triassic Xujiahe Formation in the Xinchang tectonic belt of the western Sichuan Depression is an important exploration area in the Sichuan Basin. It has a history of exploration and development for decades. The natural gas reservoirs in this area are rich, and there are high-yield wells such as Xinchang 2 well. However, the current exploration and development level is not high enough, and it still has huge exploration potential. With the continuous deepening of the exploration process, the Xujiahe Formation has a relatively concentrated phenomenon of high-yield oil and gas areas. Through research, it is found that the driving force of oil and gas migration can explain the cause of the high-yield concentrated area, and new oil and gas enrichment areas can be explored according to relevant laws. Formation pressure is an important driving force for oil and gas migration, and its distribution characteristics have an important influence on the direction and trend of oil and gas migration.

[0003] In order to understand the distribution law of the formation pressure plane of the Xujiahe Formation in the Xinye structural belt and guide the current well site development and subsequent well site deployment, scholars have carried out relevant research. The research results show that the formation pressure of the Xujiahe Formation generally has the problem of overpressure, among which the pressure coefficient of the Xujiahe Formation 3 is the highest, which can reach more than 2.0. The plane distribution characteristics of the pressure distribution are still unclear, and there is a lack of macroscopic pressure distribution laws, which is not conducive to the oil and gas exploration and development in the study area. Therefore, it is urgent to understand the pressure distribution law of the Xujiahe Formation. At present, the research on the distribution law of the formation pressure of the Xujiahe Formation focuses on geological mapping using measured points or pressure calculation based on single well logging data. The previous study preliminarily concluded the development characteristics of the overall overpressure of the Xujiahe Formation. The degree of overpressure development varies between different layers. However, due to the strong heterogeneity of the tight layer of the Xujiahe Formation, there is no completely unified development law for the overpressure characteristics of a single well. If the pressure characteristics of the study area can be analyzed as a whole through large-scale pressure prediction, it is crucial to understand the pressure distribution law of the Xujiahe Formation and the relationship between overpressure and oil and gas accumulation.

[0004] At present, there are two main methods for predicting formation pressure: the equivalent depth method and the empirical formula method. The equivalent depth method is the theoretical basis for predicting abnormal formation pore pressure. The imbalance between compaction and formation pore drainage is the main cause of abnormal overpressure. The abnormal formation pore pressure is not only affected by the compaction degree of sediments such as mudstone, but also closely related to the formation porosity. Common Eaton method, Bowers method, etc. are based on the equivalent depth method. This type of method requires the establishment of a normal compaction curve to predict formation pressure. It mainly uses logging data for calculation. It is often applicable to the calculation of a single well and has a high accuracy on a single well in conventional reservoirs. In tight reservoirs, due to heterogeneity, the screening of mud sediments becomes difficult, and the reference significance of a single well to the entire formation is reduced. The empirical formula method is often derived through an empirical model. Common empirical formula methods include the Fillippone method and the Eberhart-Phillips method. The empirical statistical model involves many parameters, which easily leads to the superposition of errors in each parameter, resulting in a decrease in the accuracy of formation pore pressure prediction. However, the empirical statistical model is not affected by the lithology and abnormal pressure genesis mechanism. It has greater advantages than other formation pore pressure prediction methods for complex lithology profiles and pressure genesis areas; some empirical statistical models directly calculate the formation pore pressure, avoiding the use of logging data to calculate intermediate parameters and causing error transmission. In tight reservoirs, due to the lithology differences caused by extremely strong heterogeneity, the causes of overpressure are also relatively complex, making it difficult for the empirical formula prediction method to guarantee a high degree of accuracy. In response to the above problems, the present invention provides a method for predicting formation pressure based on seismic data. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting formation pressure based on seismic data. The method can be used efficiently over a large area with only seismic velocity data, is suitable for estimating the pressure of dense layers, is simple and efficient, can obtain the trend of pressure changes, and is beneficial to the exploration and development of oil and gas resources.

[0006] To achieve the above object, the present invention provides a method for predicting formation pressure based on seismic data, which specifically comprises the following steps:

[0007] S1. Determine the prediction formula for formation pressure;

[0008] S2, preprocessing of seismic velocity data volume;

[0009] S3. Calculation and normalization of various parameter data bodies;

[0010] S4, optimization and adjustment of core parameters;

[0011] S5. Verification and improvement of prediction results.

[0012] Preferably, the step S1 specifically includes: selecting the Fillippone method, and proposing an empirical formula according to the equilibrium relationship between the drilling fluid and the formation pressure, which is specifically as follows:

[0013]

[0014] Among them, P p is the formation pressure, MPa; P ov is the overlying formation pressure, MPa; V i is the layer velocity, m / s; V max is the matrix velocity, m / s; V min is the pore fluid velocity, m / s.

[0015] Preferably, the step S2 specifically includes: estimating the stacking velocity according to the time difference information, converting the stacking velocity into the root mean square velocity, and finally calculating the main velocity parameter V using the Dix formula. i , the Dix formula is as follows:

[0016]

[0017] Among them, v R,i and v R,i-1 are the root mean square velocity of the top and bottom interfaces of the formation, m / s; t 0,i and t 0,i-1 are the travel time of the reflected wave at the top and bottom interfaces of the formation, s; v i is the layer velocity, m / s.

[0018] Preferably, the step S3 specifically comprises: calculating and normalizing the data body of the secondary parameters of overlying formation pressure and overlying sediment density;

[0019] Overlying formation pressure P ov is the pressure generated by the total gravity of the formation rock skeleton and pore fluid, expressed as:

[0020]

[0021] Where H is the vertical depth of the overlying formation pressure calculation point, m; g is the gravity acceleration, which is 9.8 m / s 2 ρ s is the density of the overlying sediment, g / cm 3 ;

[0022] ρ s The expression is:

[0023]

[0024] Among them, ρ sis the density of the overlying sediment, g / cm 3 ; V i is the layer velocity, m / s.

[0025] Preferably, the step S4 is specifically as follows: the root mean square speed change causes V max and V min The specific relationship is as follows:

[0026] V max =1.4V R0 +3kt

[0027] V min =0.7V R0 +0.5kt (6)

[0028] Where t is the round trip travel time of the reflected wave, s; V R0 is the intercept of the RMS velocity changing with t; k is the slope; due to the differences in lithology and compaction degree of the strata in different study areas, V needs to be adjusted based on the actual geological conditions. R0 Make adjustments.

[0029] Preferably, the step S5 specifically includes: using the pressure coefficient as a quantitative indicator, the pressure coefficient is the ratio of the formation pressure to the hydrostatic pressure, and the pressure coefficient α p The calculation formula is:

[0030]

[0031] Among them, α p is the pressure coefficient, P h is the hydrostatic pressure, MPa; ρ is the formation water density, which is taken as 1.02 g / cm 3 ; h is the height of the still water column;

[0032] The above parameters are input to calculate the data body of pressure coefficient, and the accuracy of the prediction result is confirmed by comparing the predicted value and the measured value in each layer.

[0033] Therefore, the present invention provides a method for predicting formation pressure based on seismic data, which has the following beneficial effects:

[0034] (1) This method can be used efficiently over a large area with only seismic velocity data;

[0035] (2) Based on the formation pressure prediction formula, this method preprocesses the seismic velocity data body to obtain reliable calculation data; then calculates and normalizes various parameter data bodies so that various parameters can be calculated in the form of data bodies; then optimizes and adjusts the core parameters to ensure the accuracy of the prediction; finally, the prediction results are verified and improved.

[0036] (3) This method is suitable for estimating the pressure of dense layers. It is simple and efficient and can obtain the trend of pressure changes, which is beneficial to the exploration and development of oil and gas resources.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a cross-sectional diagram of the root mean square velocity in an embodiment of the present invention;

[0039] Figure 2 is a cross-sectional diagram of the layer velocity in an embodiment of the present invention;

[0040] Figure 3 is a density profile diagram in an embodiment of the present invention;

[0041] Figure 4 is a comparison chart of predicted values ​​and measured values ​​in an embodiment of the present invention;

[0042] Figure 5 is a cross-sectional diagram of pressure coefficient in an embodiment of the present invention;

[0043] Figure 6 It is a plane diagram of pressure coefficient in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example

[0046] The present invention provides a method for predicting formation pressure based on seismic data, comprising the following steps:

[0047] S1. Determine the prediction formula for formation pressure;

[0048] The Xujiahe Formation is a tight reservoir with complex causes of pressure. It is difficult to ensure high accuracy by establishing a prediction method based on a normal compaction trend. The empirical formula method does not require the establishment of a normal compaction trend and is suitable for pressure estimation in large work areas. It has obvious advantages in pressure prediction of tight reservoirs.

[0049] The Fillippone method is selected in the empirical formula method. This method is based on the comprehensive research of scholars on seismic, logging, drilling and other data of oil fields in the Gulf of Mexico and other regions. It is found that the decrease in seismic wave velocity coincides with the occurrence of overpressure. Based on the equilibrium relationship between drilling fluid and formation pressure, an empirical formula is proposed, which is as follows:

[0050]

[0051] Among them, P p is the formation pressure, MPa; P ov is the overlying formation pressure, MPa; V i is the layer velocity, m / s; V max is the matrix velocity, which is the velocity when the porosity approaches zero, and is close to the upper limit of rock velocity, m / s; V min is the pore fluid velocity, the velocity when the rock rigidity approaches zero, which is approximately the lower limit of rock velocity, m / s.

[0052] The core of this type of empirical formula prediction is the setting and adjustment of key parameters. Selecting the most appropriate parameters can maximize the accuracy of the prediction.

[0053] S2, preprocessing of seismic velocity data volume;

[0054] Velocity parameter is an important parameter for pressure prediction. Its changing trend is closely related to the pressure changing trend. It is very important to accurately determine the formation velocity. In the Fillippone formula, the main parameters are all velocity-related parameters. The connection between various parameters can be established by using the seismic layer velocity data body.

[0055] Since the seismic layer velocity cannot be directly obtained in actual seismic data acquisition, it is necessary to estimate the stacking velocity based on the normal time difference information, and then convert the stacking velocity into the root mean square velocity based on the assumption that the formation medium is horizontal or has little fluctuation, and then use the Dix formula to calculate the formation layer velocity.

[0056]

[0057] Among them, v R,i and v R,i-1 are the root mean square velocity of the top and bottom interfaces of the formation, m / s; t 0,i and t 0,i-1 are the travel time of the reflected wave at the top and bottom interfaces of the formation, s; v i is the layer velocity, m / s.

[0058] In the Xujiahe Formation, the interbedded sandstone and mudstone are obvious. Figure 1 and Figure 2As shown in the figure, the root mean square velocity shows an increasing trend from shallow to deep, and the overall velocity is low, which cannot reflect the real velocity of the formation; the change trend of the layer velocity is irregular, and the velocity value is greater than the root mean square velocity, and the velocity range is also wider; the thicker shale layer in the third section corresponds to the velocity decrease, and the increase in the velocity of the second section also corresponds to its lithological characteristics. The data body of the layer velocity can better reflect the real velocity of the formation.

[0059] S3. Calculation and normalization of various parameter data bodies;

[0060] In the Fillippone method, the secondary parameters are the overlying formation pressure, the overlying sediment density, etc. The data volume calculation and normalization processing of the secondary parameters of the overlying formation pressure and the overlying sediment density can ensure the accuracy of the prediction.

[0061] Overlying formation pressure P ov It is the pressure generated by the total gravity of the formation rock skeleton and pore fluid, and its expression is:

[0062]

[0063] Where H is the vertical depth of the overlying formation pressure calculation point, m; g is the gravity acceleration, which is 9.8 m / s 2 ρ s is the density of the overlying sediment, g / cm 3 .

[0064] Early scholars statistically analyzed the relationship between the layer velocity of different rock formations and the density of overlying sediments, and established an empirical relationship:

[0065]

[0066] Among them, ρ s is the density of the overlying sediment, g / cm 3 ; V i is the layer velocity, m / s.

[0067] With the improvement of geophysical technology and processing accuracy, many scholars have improved formula (4) by using high-resolution wave velocity and deep well electron density measurements. The new improved formula was used in the prediction of formation pressure based on seismic data and achieved good results. The new formula is:

[0068] ρ s =0.357+1.114V i -0.182V i 2 +0.010V i 3 (5)

[0069] like Figure 3 As shown in the density profile of the Xujiahe Formation, the main range is 2.5-2.62 g / cm 3 The density changes slightly, which is consistent with the logging density and can reflect the more realistic density characteristics.

[0070] S4, optimization and adjustment of core parameters;

[0071] In the Fillippone method, V max and V min The velocity characteristics of the formations in the Gulf of Mexico and other regions were statistically analyzed, indicating that the change of the root mean square velocity will lead to V max and V min The following relationship is established:

[0072] V max =1.4V R0 +3kt

[0073] V min =0.7V R0 +0.5kt (6)

[0074] Where t is the round trip travel time of the reflected wave, s; V R0 is the intercept of the root mean square velocity changing with t; k is the slope. Due to the differences in lithology and compaction degree of the strata in different study areas, it is necessary to combine the actual geological conditions to calculate V R0 Make adjustments.

[0075] In the Xujiahe Formation, due to the differences in lithology and sand-mud ratio between layers, it is necessary to set parameters for each layer. The most suitable root mean square velocity for each layer is screened out based on the lithology characteristics of each layer, and then the rock skeleton velocity and pore fluid velocity of each layer are determined. The selection and configuration of key parameters are shown in Table 1 below.

[0076] Table 1

[0077] Formation <![CDATA[V max (m / s)]]> <![CDATA[V min (m / s)]]> <![CDATA[V R0 (m / s)]]> <![CDATA[T3x 5 ]]> 6846 3107 4196 <![CDATA[T3x 4 ]]> 7428 3244 4305 <![CDATA[T3x 3 ]]> 8872 3989 4398 <![CDATA[T3x 2 ]]> 8073 3446 4507

[0078] pass Figure 1 In the RMS velocity data, select each layer V R0 Parameters. Since V R0 The value is not fixed. The key to improving accuracy is to use V in each layer. R0 Select the most suitable set of parameters within the range, which can make the error in each part of the layer smaller. R0 4196m / s, three sections of V are required R0 is 4398m / s. These two layers are affected by the large proportion of mudstone. Finally, V R0 Select the V R0The mudstones in the fourth and second members of Xuzhou account for a small proportion, and their V R0 They are the higher values ​​in their respective layers, which are 4305m / s and 4507m / s respectively.

[0079] S5. Verification and improvement of prediction results;

[0080] In order to intuitively reflect the strength of overpressure development in different areas of the study area, the pressure coefficient is used as a quantitative indicator in this study. The pressure coefficient is the ratio of formation pressure to hydrostatic pressure and is a common parameter for determining the strength of overpressure in sedimentary basins. p The calculation formula is

[0081]

[0082] Among them, α p is the pressure coefficient, P h is the hydrostatic pressure, MPa; ρ is the formation water density, which is taken as 1.02 g / cm 3 ; h is the height of the still water column.

[0083] By inputting the above parameters to calculate the data body of the pressure coefficient, the accuracy of the prediction result can be confirmed by comparing the predicted value and the measured value in each layer.

[0084] like Figure 4 As shown in the figure, in the Xujiahe Formation, the prediction results of the Xu2, Xu4 and Xu5 sections are good, and the relative errors are generally within 10%. The prediction results of the Xu3 section are slightly worse. Its strong heterogeneity makes it difficult to select a set of parameters that meet the requirements of the entire layer. By comparing the predicted values ​​with the measured values, the parameters can be adjusted and optimized in reverse. If the overall error is too high or too low, the V R0 Reselection is used to optimize and repeated adjustments are made to obtain a relatively good set of prediction results.

[0085] like Figure 5 As shown in the figure, the pressure changes on the Xujiahe Formation section are clearly presented, which can effectively show the strength of pressure between layers, especially the strong overpressure in the Xujiahe Formation 3 and the weak overpressure in the Xujiahe Formation 2. Figure 6 As shown, the plane distribution of the obtained pressure is clearly presented with clear details, which is conducive to the analysis of the action mechanism of macroscopic pressure. In the predicted pressure plane and profile, the pressure distribution trend of the Xujiahe Formation can be clearly identified, among which the pressure coefficient of the Xujiahe Formation 3 is the highest, and the pressure coefficient in the middle area of ​​the plane is relatively low. The pressure distribution prediction results are of great significance to the oil and gas migration, development and drilling in the region.

[0086] Therefore, the present invention provides a method for predicting formation pressure based on seismic data. The method pre-processes the seismic velocity data body on the basis of determining the formation pressure prediction formula to obtain reliable calculation data; then calculates and normalizes various parameter data bodies so that various parameters can be calculated in the form of data bodies; then optimizes and adjusts the core parameters to ensure the accuracy of the prediction; finally, the prediction results are verified and improved. The method can be used efficiently over a large area with only seismic velocity data, and is suitable for estimating the pressure of dense layers. The method is simple and efficient, and can obtain the trend of pressure changes, which is conducive to the exploration and development of oil and gas resources.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for predicting formation pressure based on seismic data, characterized in that: The specific steps include: S1. Determine the prediction formula for formation pressure; The step S1 specifically includes: selecting the Fillippone method, and proposing an empirical formula according to the equilibrium relationship between the drilling fluid and the formation pressure, which is as follows: Among them, P p is the formation pressure, MPa; P ov is the overlying formation pressure, MPa; V i is the layer velocity, m / s; V max is the matrix velocity, m / s; V min is the pore fluid velocity, m / s; S2, preprocessing of seismic velocity data volume; S3. Calculation and normalization of various parameter data bodies; The step S3 specifically includes: calculating and normalizing the data body of the secondary parameters of overlying formation pressure and overlying sediment density; Overlying formation pressure P ov is the pressure generated by the total gravity of the formation rock skeleton and pore fluid, expressed as: Where H is the vertical depth of the overlying formation pressure calculation point, m; g is the gravity acceleration, which is 9.8 m / s 2 ρ s is the density of the overlying sediment, g / cm 3 ; ρ s The expression is: r s =0.357+1.114V i -0.182V i 2 +0.010V i 3 (5) Among them, ρ s is the density of the overlying sediment, g / cm 3 ; V i is the layer velocity, m / s; S4, core parameter optimization and adjustment; The step S4 is specifically as follows: the root mean square speed change causes V max and V min The specific relationship is as follows: V max =1.4V R0 +3kt V min =0.7V R0 +0.5kt (6) Where t is the round trip travel time of the reflected wave, s; V R0 is the intercept of the RMS velocity changing with t; k is the slope; due to the differences in lithology and compaction degree of the strata in different study areas, V needs to be adjusted based on the actual geological conditions. R0 Make adjustments; S5. Verification and improvement of prediction results; The pressure coefficient is used as a quantitative indicator. The pressure coefficient is the ratio of formation pressure to hydrostatic pressure. The pressure coefficient α p The calculation formula is: Among them, α p is the pressure coefficient, P h is the hydrostatic pressure, MPa; ρ is the formation water density, which is taken as 1.02 g / cm 3 ; h is the height of the still water column; The above parameters are input to calculate the data body of pressure coefficient, and the accuracy of the prediction result is confirmed by comparing the predicted value and the measured value in each layer.

2. The method for predicting formation pressure based on seismic data according to claim 1, characterized in that: The step S2 specifically includes: estimating the stacking velocity according to the time difference information, converting the stacking velocity into the root mean square velocity, and finally calculating the main velocity parameter V using the Dix formula. i , the Dix formula is as follows: Among them, v R,i and v R,i-1 are the root mean square velocity of the top and bottom interfaces of the formation, m / s; t 0,i and t 0,i-1 are the travel time of the reflected wave at the top and bottom interfaces of the formation, s; v i is the layer velocity, m / s.

Images