Method for judging gas-bearing property of carbonate reservoir by array sonic logging

Abstract

The present application belongs to the technical field of acoustic logging data processing and interpretation method, and specifically provides a method for judging gas content of carbonate reservoir by array acoustic logging, which first converts the longitudinal and transverse wave velocities measured by the carbonate saturated rock sample into the longitudinal and transverse wave time difference, then establishes a linear relationship between the longitudinal and transverse wave time difference and the core porosity based on the geostatistical method, determines the empirical formula for calculating the apparent porosity by using the longitudinal and transverse wave time difference, calculates the longitudinal and transverse wave apparent porosity by using the longitudinal and transverse wave time difference obtained by the carbonate reservoir logging based on the empirical formula, and finally constructs the velocity drop factor based on the calculated longitudinal and transverse wave apparent porosity; the present application solves the problem that the existing carbonate reservoir gas content is difficult to be simply, quickly and accurately quantitatively evaluated; the present application can quickly and accurately quantitatively evaluate the carbonate reservoir gas content, and increases the accuracy of the carbonate reservoir fluid property identification.

Description

Technical Field

[0001] This invention belongs to the technical field of acoustic logging data processing and interpretation methods, specifically relating to a method for determining the gas content of carbonate reservoirs using array acoustic logging. Background Technology

[0002] Carbonate reservoirs are characterized by diverse reservoir space types, complex combinations, and difficulties in effectively identifying gas-bearing properties. Based on well logging data, methods for identifying gas-bearing properties in carbonate reservoirs generally rely on resistivity logging and compensated neutron logging. However, these methods are highly dependent on the type of reservoir space and rock structure, resulting in relatively poor reliability.

[0003] Chinese patent document CN105988136B, published on November 24, 2020, discloses a method for analyzing reservoir gas-bearing capacity using P-wave and S-wave velocity data. The specific steps are as follows: The equivalent elastic modulus of the rock skeleton is calculated using the Voigt-Reuss-Hill average model; the porosity ratio is calculated using the Xu-White model and the rock shear modulus; the elastic modulus of dry rock is calculated using the Xu-White model; the measured elastic modulus minus the elastic modulus of dry rock is defined as the gas-bearing factor, and the formation gas-bearing capacity is analyzed. This document comprehensively considers the influence of minerals and porosity properties using P-wave and S-wave velocity information, providing a reservoir gas-bearing capacity evaluation factor. Compared with the traditional method of analyzing reservoir gas-bearing capacity using the P-wave and S-wave velocity ratio, this method considers more comprehensive factors and utilizes more integrated P-wave and S-wave velocity information. However, this document does not address the problem of how to quickly and accurately quantitatively evaluate the gas-bearing capacity of carbonate reservoirs using array acoustic logging. Summary of the Invention

[0004] The present invention provides a method for determining the gas content of carbonate reservoirs using array acoustic logging, aiming to overcome the problem that the gas content of carbonate reservoirs is difficult to quantitatively evaluate simply, quickly and accurately in the existing technology.

[0005] Therefore, the present invention provides a method for determining the gas content of carbonate reservoirs using array acoustic logging, comprising the following steps:

[0006] 1) Convert the measured P-wave velocity of the carbonate saturated rock sample into P-wave transit time, and convert the measured S-wave velocity of the carbonate saturated rock sample into S-wave transit time.

[0007] 2) Based on geostatistical methods, a linear relationship was established between P-wave transit time, S-wave transit time and core porosity, and an empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time was determined.

[0008] 3) Based on the empirical formula for apparent porosity, the apparent porosity of the P-wave and the apparent porosity of the S-wave are calculated using the P-wave transit time and S-wave transit time obtained from well logging of carbonate reservoirs.

[0009] 4) Based on the calculated apparent porosity of longitudinal waves and apparent porosity of transverse waves, construct reservoir gas-bearing characterization parameters, and quantitatively evaluate the gas-bearing capacity of carbonate reservoirs according to the reservoir gas-bearing characterization parameters.

[0010] Preferably, the formula for converting the measured P-wave velocity of the carbonate saturated rock sample into P-wave transit time in step 1) is as follows:

[0011] The formula for converting the measured shear wave velocity of a saturated carbonate rock sample into shear wave transit time is as follows:

[0012] Where: Δt p Longitudinal wave time difference, s / m; V p Longitudinal wave velocity, m / s; Δt s Transverse wave time difference, s / m; V s : Shear wave velocity, m / s.

[0013] Preferably, the specific steps of step 2) are as follows: First, convert the P-wave transit time units and S-wave transit time units of all carbonate rock saturated samples from s / m to μs / m; then, establish a linear relationship between all P-wave transit time units and S-wave transit time units in μs / m and the corresponding analytical porosity, thereby determining the empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time.

[0014] Preferably, in step 3), the P-wave transit time and S-wave transit time obtained from the carbonate reservoir logging are continuous data that vary with well depth, obtained from array sonic logging.

[0015] Preferably, the formula for constructing reservoir gas-bearing characterization parameters based on the calculated P-wave apparent porosity and S-wave apparent porosity in step 4) is as follows: Where, φ s Shear wave apparent porosity, %; φ c : Pending wave apparent porosity, %; Δφ: The difference between the Pending wave apparent porosity and the Transverse wave apparent porosity, Δφ = φ c -φ s ,%;S d : Parameters characterizing reservoir gas content.

[0016] Preferably, in step 4), the reservoir gas content characterization parameter is between 0 and 1, and the variation trend of the reservoir gas content characterization parameter is positively correlated with the water saturation of the carbonate reservoir.

[0017] The beneficial effects of this invention are:

[0018] This invention provides a method for determining the gas-bearing capacity of carbonate reservoirs using array acoustic logging, comprising the following steps: 1) converting the measured P-wave velocity of saturated carbonate samples into P-wave transit time and the measured S-wave velocity of saturated carbonate samples into S-wave transit time; 2) establishing a linear relationship between P-wave transit time, S-wave transit time, and core porosity based on geostatistical methods, and determining empirical formulas for calculating apparent porosity using P-wave and S-wave transit times; 3) calculating P-wave apparent porosity and S-wave apparent porosity using the P-wave and S-wave transit times obtained from carbonate reservoir logging based on the empirical formulas for apparent porosity; 4) constructing reservoir gas-bearing capacity characterization parameters based on the calculated P-wave and S-wave apparent porosity, and quantitatively evaluating the gas-bearing capacity of carbonate reservoirs based on these parameters. This method, based on the P-wave and S-wave transit times obtained from array acoustic logging, can quickly and accurately quantitatively evaluate the gas-bearing capacity of carbonate reservoirs, increasing the accuracy of identifying the fluid properties of carbonate reservoirs. Attached Figure Description

[0019] The present invention will now be described in further detail with reference to the accompanying drawings.

[0020] Figure 1 This is a graph showing the variation of longitudinal and transverse wave velocities with water saturation.

[0021] Figure 2 It is the formula for longitudinal wave time difference porosity;

[0022] Figure 3 It is the formula for transverse wave time difference porosity;

[0023] Figure 4 It is the response of longitudinal and transverse wave apparent porosity to water saturation;

[0024] Figure 5 This is a graph showing the relationship between reservoir gas content characterization parameters and carbonate reservoir water saturation.

[0025] Figure 6 This is a diagram illustrating the interpretation results of the velocity drop factor of an exploration well in the eastern area of ​​the X gas field in the Ordos Basin.

[0026] Figure 7 This is a comparison chart of the rate of decline factors of 10 carbonate reservoirs in the X layer of the X gas field in the Ordos Basin with the results of gas testing. Detailed Implementation

[0027] Example 1:

[0028] A method for determining the gas content of carbonate reservoirs using array acoustic logging includes the following steps:

[0029] 1) Convert the measured P-wave velocity of the carbonate saturated rock sample into P-wave transit time, and convert the measured S-wave velocity of the carbonate saturated rock sample into S-wave transit time.

[0030] 2) Based on geostatistical methods, a linear relationship was established between P-wave transit time, S-wave transit time and core porosity, and an empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time was determined.

[0031] 3) Based on the empirical formula for apparent porosity, the apparent porosity of the P-wave and the apparent porosity of the S-wave are calculated using the P-wave transit time and S-wave transit time obtained from well logging of carbonate reservoirs.

[0032] 4) Construct reservoir gas-bearing characterization parameters based on the calculated longitudinal wave apparent porosity and transverse wave apparent porosity, and quantitatively evaluate the gas-bearing capacity of carbonate reservoirs based on the reservoir gas-bearing characterization parameters.

[0033] Step 4) involves creating a scatter plot using reservoir porosity (P-wave apparent porosity and S-wave apparent porosity) and reservoir gas-bearing characterization parameters (rapid fall factor). The rapid fall factor is then used to evaluate the gas-bearing capacity of carbonate reservoirs based on the scatter plot (see [link to relevant documentation]). Figure 7 The value of the rapid decline factor varies between 0 and 1. This value is positively correlated with the water saturation of the reservoir and increases with the increase of water saturation. In other words, the closer the value is to 1, the lower the gas content of the reservoir, and the closer the value is to 0, the higher the gas content of the reservoir.

[0034] The technical principle behind this method for determining the gas content of carbonate reservoirs using array acoustic logging is as follows: the P-wave velocity increases with increasing reservoir water saturation, while the S-wave velocity remains essentially constant (see [link to related documentation]). Figure 1 The differential response characteristics of longitudinal and transverse wave velocities to changes in water saturation can be used to identify gas content.

[0035] Since the changes in longitudinal velocity and transverse wave velocity with respect to water saturation are relatively small compared to their own values, directly using the changes in longitudinal velocity and transverse wave velocity as parameters to determine the gas content of carbonate reservoirs has the disadvantages of low parameter values ​​and unclear response.

[0036] Therefore, the P-wave transit time and S-wave transit time are first calculated using the P-wave velocity and S-wave velocity of the saturated rock sample, and then converted into P-wave apparent porosity based on geostatistical methods (see...). Figure 2 ) and transverse wave apparent porosity (see Figure 3 ).

[0037] P-wave apparent porosity increases with increasing gas saturation (decreasing water saturation) in carbonate reservoirs, while S-wave apparent porosity remains essentially unchanged. The response of both P-wave and S-wave apparent porosity to gas saturation is more pronounced (see [reference needed]). Figure 4 and Figure 5 ).

[0038] Based on the apparent porosity of longitudinal and transverse waves, a reservoir gas-bearing characterization parameter is constructed and defined as the rate-decline factor. The reservoir gas-bearing characterization parameter varies between 0 and 1, and the variation trend is positively correlated with the water saturation. It can be used to identify changes in reservoir gas-bearing.

[0039] This method, based on the P-wave and S-wave time differences obtained from array acoustic logging, can quickly and accurately quantitatively evaluate the gas content of carbonate reservoirs, increasing the accuracy of fluid property identification in carbonate reservoirs.

[0040] Example 2:

[0041] Based on Example 1, the formula for converting the measured P-wave velocity of the carbonate saturated rock sample into P-wave transit time in step 1) is as follows:

[0042] The formula for converting the measured shear wave velocity of a saturated carbonate rock sample into shear wave transit time is as follows:

[0043] Where: Δt p Longitudinal wave time difference, s / m; V p Longitudinal wave velocity, m / s; Δt s Transverse wave time difference, s / m; V s : Shear wave velocity, m / s.

[0044] This formula is characterized by its simple and easy-to-understand principle, few operation steps, ease of construction, and high accuracy.

[0045] Preferably, the specific steps of step 2) are as follows: First, convert the P-wave transit time units and S-wave transit time units of all carbonate rock saturated samples from s / m to μs / m; then, establish a linear relationship between all P-wave transit time units and S-wave transit time units in μs / m and the corresponding analytical porosity, thereby determining the empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time.

[0046] This formula is characterized by its simple and easy-to-understand principle, few operation steps, ease of construction, and high accuracy.

[0047] Preferably, in step 3), the P-wave transit time and S-wave transit time obtained from the carbonate reservoir logging are continuous data that vary with well depth, obtained from array acoustic logging.

[0048] Based on continuous data of P-wave and S-wave time differences that vary with well depth, the apparent porosity of P-wave and S-wave in a continuous incline can be calculated.

[0049] Preferably, the formula for constructing reservoir gas-bearing characterization parameters based on the calculated P-wave apparent porosity and S-wave apparent porosity in step 4) is as follows: Where, φ s Shear wave apparent porosity, %; φ c : Pending wave apparent porosity, %; Δφ: The difference between the Pending wave apparent porosity and the Transverse wave apparent porosity, Δφ = φ c -φ s ,%;S d : Parameters characterizing reservoir gas content.

[0050] The reservoir gas-bearing characteristic parameter is the rate-decline factor. Based on the apparent porosity of the longitudinal and transverse waves that varies with well depth, continuous gas-bearing characteristic parameters can be calculated, which facilitates a fine evaluation of the vertical gas-bearing capacity of the reservoir.

[0051] Preferably, in step 4), the reservoir gas content characterization parameter is between 0 and 1, and the variation trend of the reservoir gas content characterization parameter is positively correlated with the water saturation of the carbonate reservoir.

[0052] This parameter, ranging from 0 to 1, facilitates lateral reservoir correlation and can also be used to determine reservoir gas content without relying on lateral correlation. It can also serve as a substitute parameter for water saturation.

[0053] Experimental data for this method of determining the gas content of carbonate reservoirs using array acoustic logging are available in [link to relevant documentation]. Figure 6 and Figure 7 : Figure 6 The first track from the right is the comprehensive well logging interpretation result; the second track from the right is the lithological analysis.

[0054] The first channel is for analysis, containing the mineral composition of carbonate rock strata; the second channel is for porosity; the third channel is for array acoustic wave 5 gas-bearing characterization parameters, where the velocity drop factor is the calculated apparent porosity based on the P-wave and S-wave porosity in this case.

[0055] Porosity is used to characterize reservoir gas-bearing properties; the fifth channel represents logging and coring data; the sixth channel represents P-wave and S-wave transit times; the other channels represent conventional logging curves. From Figure 6 It can be seen that the array acoustic gas-bearing characterization parameters have a good negative correlation with the comprehensive interpretation conclusions of well logging, and can be used to indicate the gas-bearing properties of carbonate reservoirs.

[0056] Figure 7 This is a cross-plot of porosity and rate drop factor in carbonate reservoirs based on gas testing results. The rate drop factor 0 in the plot represents the gas-bearing characteristic parameter of array acoustic wave in this invention, indicating gas-bearing layers, gas-water co-layers, poorly gas-bearing layers, and gas-bearing layers.

[0057] The water layer represents the results of reservoir gas testing. This cross plot shows that the array acoustic gas-bearing characterization parameters are in good agreement with the results of carbonate reservoir gas testing. The array acoustic gas-bearing characterization parameters for gas layers are less than 66%, for gas-water co-layers and differential gas layers are between 66% and 86%, and for gas-water layers are greater than 86%.

[0058] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for determining the gas content of carbonate reservoirs using array acoustic logging, characterized in that: Includes the following steps: 1) Convert the measured P-wave velocity of the saturated carbonate rock sample into P-wave transit time, and convert the measured S-wave velocity of the saturated carbonate rock sample into S-wave transit time. 2) Based on geostatistical methods, a linear relationship was established between P-wave transit time, S-wave transit time and core porosity, and an empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time was determined. 3) Based on the empirical formula for apparent porosity, the apparent porosity of the P-wave and the apparent porosity of the S-wave are calculated using the P-wave transit time and S-wave transit time obtained from well logging of carbonate reservoirs. 4) Construct reservoir gas-bearing characterization parameters based on the calculated P-wave and S-wave apparent porosity, and quantitatively evaluate the gas-bearing capacity of carbonate reservoirs according to these parameters; the formula for constructing reservoir gas-bearing characterization parameters based on the calculated P-wave and S-wave apparent porosity in step 4) is as follows: ;in: s Shear wave apparent porosity, % c Longitudinal wave apparent porosity, % The difference between the apparent porosity of longitudinal waves and the apparent porosity of transverse waves. ,%; S d : Reservoir gas content characterization parameters; The variation trend of reservoir gas content characterization parameters is positively correlated with the water saturation of carbonate reservoirs; In step 4), the reservoir gas content characterization parameters are between 0 and 1. The closer the value is to 1, the lower the gas content of the reservoir. The closer the value is to 0, the higher the gas content of the reservoir.

2. The method for determining the gas content of carbonate reservoirs using array acoustic logging as described in claim 1, characterized in that: The formula for converting the measured P-wave velocity of the carbonate saturated rock sample into P-wave transit time in step 1) is as follows: ; The formula for converting the measured shear wave velocity of a saturated carbonate rock sample into shear wave transit time is as follows: ;in: t p Longitudinal wave time difference, s / m; V p Longitudinal wave velocity, m / s; t s Transverse wave time difference, s / m; V s : Shear wave velocity, m / s.

3. The method for determining the gas content of carbonate reservoirs using array acoustic logging as described in claim 2, characterized in that: The specific steps of step 2) are as follows: First, convert the units of P-wave transit time and S-wave transit time of all carbonate rock saturated samples from s / m to μs / m; then, establish a linear relationship between all P-wave transit time and S-wave transit time in μs / m and the corresponding analytical porosity, so as to determine the empirical formula for calculating apparent porosity using P-wave transit time and S-wave transit time.

4. The method for determining the gas content of carbonate reservoirs using array acoustic logging as described in claim 3, characterized in that: In step 3), the P-wave and S-wave transit times obtained from the carbonate reservoir logging are continuous data that vary with well depth, obtained from array sonic logging.

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