阅读说明：本技术 一种致密碳酸盐岩声波速度估计方法及系统 (Method and system for estimating sound wave velocity of compact carbonate rock ) 是由 李博南 沈珲 李呈呈 马中高 杨丽 司文朋 王欢 于 2018-09-06 设计创作，主要内容包括：本发明提供了一种致密碳酸盐岩声波速度估计方法及系统,属于岩石物理领域。该致密碳酸盐岩声波速度估计方法利用致密碳酸盐岩的岩石物理实验数据或者邻井实测数据预测目标井的声波速度；所述岩石物理实验数据包括：利用岩石物理实验获得的纵波速度、横波速度、密度和孔隙度；所述邻井实测数据包括：通过邻井实测获得的纵波速度、横波速度、密度和孔隙度测井曲线。本发明方法充分利用了致密碳酸盐岩本身的一些岩石物理特征,保证了结果准确的前提下,在速度估算过程中做最大程度的参数简化。本发明计算效率高,精度好。(The invention provides a method and a system for estimating sound wave velocity of compact carbonate rock, and belongs to the field of rock physics. The method for estimating the acoustic velocity of the compact carbonate rock predicts the acoustic velocity of a target well by utilizing rock physical experiment data or adjacent well measured data of the compact carbonate rock; the petrophysical experimental data comprises: longitudinal wave velocity, transverse wave velocity, density and porosity obtained by rock physics experiments; the measured data of the adjacent well comprises: and (4) obtaining longitudinal wave velocity, transverse wave velocity, density and porosity logging curves through adjacent well actual measurement. The method fully utilizes some rock physical characteristics of the compact carbonate rock, and performs parameter simplification to the maximum extent in the speed estimation process on the premise of ensuring accurate results. The invention has high calculation efficiency and good precision.)

1. A method for estimating sound wave velocity of dense carbonate rock is characterized by comprising the following steps: the method comprises the steps of predicting the acoustic velocity of a target well by utilizing rock physical experiment data of compact carbonate rocks or measured data of an adjacent well; the petrophysical experimental data comprises: longitudinal wave velocity, transverse wave velocity, density and porosity obtained by rock physics experiments; the measured data of the adjacent well comprises: and (4) obtaining longitudinal wave velocity, transverse wave velocity, density and porosity logging curves through adjacent well actual measurement.

2. The tight carbonate sonic velocity estimation method of claim 1, characterized by: the method comprises the following steps:

(1) carrying out rock physical experiments on the compact carbonate rock to obtain longitudinal wave velocity, transverse wave velocity, density and porosity, or carrying out actual measurement on adjacent wells to obtain longitudinal wave velocity, transverse wave velocity, density and porosity logging curves;

(2) calculating to obtain a bulk modulus and a critical porosity value by using the data measured in the step (1);

(3) fitting the value of the volume modulus root opening number as an abscissa and the longitudinal wave velocity as an ordinate to obtain fitting constants b and c; fitting the transverse wave speed and the longitudinal wave speed by taking the transverse wave speed as an abscissa and taking the longitudinal wave speed as an ordinate to obtain fitting constants a and b, wherein a and c are slopes, and b is an intercept;

(4) calculating to obtain the bulk modulus of the target well by using the critical porosity value, the porosity of the target well and the mineral components of the target well;

(5) and predicting the longitudinal wave velocity and the transverse wave velocity of the target well by using the bulk modulus of the target well.

3. The tight carbonate sonic velocity estimation method of claim 2, characterized by: the operation of calculating the bulk modulus by using the data measured in the step (1) in the step (2) comprises the following steps: the bulk modulus was calculated using the formula:

wherein, V_P、V_SRho is the longitudinal wave velocity, the transverse wave velocity and the density measured in the step (1), K is the bulk modulus, and mu is the shear modulus.

4. The tight carbonate sonic velocity estimation method of claim 3, characterized by: the operation of calculating the critical porosity value using the data measured in step (1) in step (2) includes: the critical porosity value is calculated using the formula:

wherein the content of the first and second substances,

K_pis a fluid induced additional modulus, in the dry state, K_pIs 0;

5. The tight carbonate sonic velocity estimation method of claim 4, characterized by: the steps of (A), (B), (C4) The operation of (1) comprises: calculating the bulk modulus K of the target well using the formula_sat：

K_sat＝K_dry+K_P

K_flIs the bulk modulus of the fluid phase suspension or mixture:

K_iand v_iRespectively representing the bulk modulus and the content of the ith fluid, wherein the values are obtained from a fluid saturation curve in a standard well logging interpretation;the porosity of the target well.

6. The tight carbonate sonic velocity estimation method of claim 5, wherein: the manipulating of the step (5) includes:

calculating the longitudinal wave velocity of the target well by using the following formula:

calculating the shear wave velocity of the target well by using the following formula:

V_Psat≈aV_Ssat+b。

7. a system for implementing the tight carbonate sonic velocity estimation method of any of claims 1-6, characterized by: the system comprises:

a data acquisition unit: carrying out rock physical experiments on the compact carbonate rock to obtain longitudinal wave velocity, transverse wave velocity, density and porosity, or carrying out actual measurement on adjacent wells to obtain longitudinal wave velocity, transverse wave velocity, density and porosity logging curves;

bulk modulus calculation unit: the device is connected with the data acquisition unit, and the volume modulus is calculated by utilizing the longitudinal wave speed, the transverse wave speed and the density sent by the data acquisition unit;

a critical porosity calculation unit: the device is connected with the data acquisition unit, and the critical porosity is calculated by utilizing the longitudinal wave speed, the transverse wave speed, the density and the porosity sent by the data acquisition unit;

a fitting unit: the device is respectively connected with the volume modulus calculation unit and the data acquisition unit, and for the volume modulus root opening number sent by the volume modulus calculation unit, the value after the root opening number is used as a horizontal coordinate, and the longitudinal wave speed sent by the data acquisition unit is used as a vertical coordinate, and the two are fitted to obtain fitting constants b and c; fitting the transverse wave speed sent by the data acquisition unit as an abscissa and the longitudinal wave speed sent by the data acquisition unit as an ordinate to obtain fitting constants a and b, wherein a and c are slopes and b is an intercept;

a target well volume modulus calculation unit: the critical porosity calculation unit is connected with the target well, and the porosity of the target well, the mineral composition of the target well and the critical porosity value sent by the critical porosity calculation unit are used for calculating to obtain the bulk modulus of the target well;

acoustic velocity prediction unit: and the device is respectively connected with the target well volume modulus calculating unit and the fitting unit, and predicts the longitudinal wave velocity and the transverse wave velocity of the target well by using the volume modulus of the target well sent by the target well volume modulus calculating unit and the values of a, b and c sent by the fitting unit.

8. The system of claim 7, wherein: the bulk modulus calculation unit calculates a bulk modulus using the following formula:

wherein, V_P、V_SRho is the longitudinal wave velocity, the transverse wave velocity and the density which are sent by the data acquisition unit respectively, K is the volume modulus, and mu is the shear modulus;

the critical porosity calculation unit calculates a critical porosity value using the following formula:

wherein the content of the first and second substances,

K_pis a fluid induced additional modulus, in the dry state, K_PIs 0;

the target well bulk modulus calculation unit calculates the bulk modulus K of the target well by using the following formula_sat：

K_sat＝K_dry+K_P

The subscripts V and R represent the Voigt limit and R, respectively, of the mineralAn euss limit;

K_flis the bulk modulus of the fluid phase suspension or mixture:

K_iand v_iRespectively representing the bulk modulus and the content of the ith fluid, wherein the values are obtained from a fluid saturation curve in a standard well logging interpretation;

the acoustic velocity prediction unit calculates the longitudinal velocity of the target well using the following equation:

calculating the shear wave velocity of the target well by using the following formula:

V_Psat≈aV_Ssat+b。

9. a computer-readable storage medium characterized by: the computer-readable storage medium stores at least one program executable by a computer, the at least one program when executed by the computer causing the computer to perform the steps in the tight carbonate sonic velocity estimation method of any of claims 1-6.

Technical Field

The invention belongs to the field of rock physics, and particularly relates to a method and a system for estimating sound wave velocity of compact carbonate rock.

Background

Acoustic velocity is the most important elastic parameter in seismic exploration, and for carbonate rocks there are two main categories of prediction methods currently used most widely in the industry: empirical formula method and equivalent medium model method. Empirical formula has the advantage of being computationally efficient (e.g., Castagna's formula and Krief's formula), but in principle tends to attribute differences in rock velocity simply to changes in porosity. This assumption is more applicable in sandstone reservoir segments. In the case of carbonate rock, the pore structure also has a great influence on the speed, and the application effect of the method is difficult to avoid and is limited. The equivalent medium model method describes the microstructure of the whole rock in great detail (such as a DEM model, a KT model and an SCA model), and the comprehensive influence of various internal mineral components, fluid flow, pore scattering and other factors is considered in sound wave velocity prediction. However, these microscopic parameters are difficult to obtain in actual production. In addition, many iterative processes are usually hidden in the models, the calculation efficiency is low, and the models cannot be used in a large scale under the condition of large data volume.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a compact carbonate rock acoustic velocity estimation method which can calculate the target well site acoustic velocity according to regional rock physical experiment data or adjacent well measured data.

The invention is realized by the following technical scheme:

a tight carbonate rock sound wave velocity estimation method is characterized in that the sound wave velocity of a target well is predicted by utilizing rock physical experiment data or adjacent well measured data of tight carbonate rock; the petrophysical experimental data comprises: longitudinal wave velocity, transverse wave velocity, density and porosity obtained by rock physics experiments; the measured data of the adjacent well comprises: and (4) obtaining longitudinal wave velocity, transverse wave velocity, density and porosity logging curves through adjacent well actual measurement.

The method comprises the following steps:

(1) carrying out rock physical experiments on the compact carbonate rock to obtain longitudinal wave velocity, transverse wave velocity, density and porosity, or carrying out actual measurement on adjacent wells to obtain longitudinal wave velocity, transverse wave velocity, density and porosity logging curves;

(2) calculating to obtain a bulk modulus and a critical porosity value by using the data measured in the step (1);

(3) fitting the value of the volume modulus root opening number as an abscissa and the longitudinal wave velocity as an ordinate to obtain fitting constants b and c; fitting the transverse wave speed and the longitudinal wave speed by taking the transverse wave speed as an abscissa and taking the longitudinal wave speed as an ordinate to obtain fitting constants a and b, wherein a and c are slopes, and b is an intercept;

(4) calculating to obtain the bulk modulus of the target well by using the critical porosity value, the porosity of the target well and the mineral components of the target well;

(5) and predicting the longitudinal wave velocity and the transverse wave velocity of the target well by using the bulk modulus of the target well.

The operation of calculating the bulk modulus by using the data measured in the step (1) in the step (2) comprises the following steps: the bulk modulus was calculated using the formula:

wherein, V_p、V_SRho is the longitudinal wave velocity, the transverse wave velocity and the density measured in the step (1), K is the bulk modulus, and mu is the shear modulus.

The operation of calculating the critical porosity value using the data measured in step (1) in step (2) includes: the critical porosity value is calculated using the formula:

wherein the content of the first and second substances,

critical porosity;

the porosity measured in the step (1);

K_pis a fluid induced additional modulus, in the dry state, K_pIs 0;

the subscripts V and R represent the Voigt and reus limits of the mineral, respectively;

the operation of the step (4) comprises the following steps: calculating the bulk modulus K of the target well using the formula_sat：

K_sat＝K_dry+K_P

K_flIs the bulk modulus of the fluid phase suspension or mixture:

K_iand v_iRespectively representing the bulk modulus and the content of the ith fluid, wherein the values are obtained from a fluid saturation curve in a standard well logging interpretation;

porosity of the target well;

the manipulating of the step (5) includes:

calculating the longitudinal wave velocity of the target well by using the following formula:

calculating the shear wave velocity of the target well by using the following formula:

V_Psat≈aV_Ssat+b。

the invention also provides a tight carbonate rock acoustic velocity estimation system, comprising:

a data acquisition unit: carrying out rock physical experiments on the compact carbonate rock to obtain longitudinal wave velocity, transverse wave velocity, density and porosity, or carrying out actual measurement on adjacent wells to obtain longitudinal wave velocity, transverse wave velocity, density and porosity logging curves;

bulk modulus calculation unit: the device is connected with the data acquisition unit, and the volume modulus is calculated by utilizing the longitudinal wave speed, the transverse wave speed and the density sent by the data acquisition unit;

a critical porosity calculation unit: the device is connected with the data acquisition unit, and the critical porosity is calculated by utilizing the longitudinal wave speed, the transverse wave speed, the density and the porosity sent by the data acquisition unit;

a fitting unit: the device is respectively connected with the volume modulus calculation unit and the data acquisition unit, and for the volume modulus root opening number sent by the volume modulus calculation unit, the value after the root opening number is used as a horizontal coordinate, and the longitudinal wave speed sent by the data acquisition unit is used as a vertical coordinate, and the two are fitted to obtain fitting constants b and c; fitting the transverse wave speed sent by the data acquisition unit as an abscissa and the longitudinal wave speed sent by the data acquisition unit as an ordinate to obtain fitting constants a and b, wherein a and c are slopes and b is an intercept;

a target well volume modulus calculation unit: the critical porosity calculation unit is connected with the target well, and the porosity of the target well, the mineral composition of the target well and the critical porosity value sent by the critical porosity calculation unit are used for calculating to obtain the bulk modulus of the target well;

acoustic velocity prediction unit: and the device is respectively connected with the target well volume modulus calculating unit and the fitting unit, and predicts the longitudinal wave velocity and the transverse wave velocity of the target well by using the volume modulus of the target well sent by the target well volume modulus calculating unit and the values of a, b and c sent by the fitting unit.

The bulk modulus calculation unit calculates a bulk modulus using the following formula:

wherein, V_p、V_SRho is the longitudinal wave velocity, the transverse wave velocity and the density which are sent by the data acquisition unit respectively, K is the volume modulus, and mu is the shear modulus;

the critical porosity calculation unit calculates a critical porosity value using the following formula:

wherein the content of the first and second substances,

critical porosity;

porosity transmitted for the data acquisition unit;

K_pis a fluid induced additional modulus, in the dry state, K_PIs 0;

the subscripts V and R represent the Voigt and reus limits of the mineral, respectively;

the target well bulk modulus calculation unit calculates the bulk modulus K of the target well by using the following formula_sat：

K_sat＝K_dry+K_P

K_flIs the bulk modulus of the fluid phase suspension or mixture:

K_iand v_iRespectively representing the bulk modulus and the content of the ith fluid, wherein the values are obtained from a fluid saturation curve in a standard well logging interpretation;porosity of the target well;

the acoustic velocity prediction unit calculates the longitudinal velocity of the target well using the following equation:

calculating the shear wave velocity of the target well by using the following formula:

V_Psat≈aV_Ssat+b。

the present invention also provides a computer-readable storage medium storing at least one program executable by a computer, the at least one program, when executed by the computer, causing the computer to perform the steps in the tight carbonate sonic velocity estimation method of the present invention.

Compared with the prior art, the invention has the beneficial effects that: the method fully utilizes some rock physical characteristics of the compact carbonate rock, and performs parameter simplification to the maximum extent in the speed estimation process on the premise of ensuring accurate results. The theoretical curve comparison and the embodiment comparison prove that the quantitative relation provided by the invention generally exists in practice, and the method has high calculation efficiency and good precision.

Drawings

FIG. 1 is a theoretical verification of the computational effectiveness of the present invention;

FIG. 2 validation of the invention with petrophysical experimental data on core scale;

FIG. 3 illustrates the verification of the present invention with acoustic velocity profiles at the well log scale;

FIG. 4 is a block diagram of the steps of the method of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings:

according to the rock physical characteristics of the compact carbonate rock, the invention provides a method capable of calculating the sound wave speed of the target well position according to rock physical experimental data or adjacent well actual measurement data, the method can simplify input parameters to the greatest extent on the premise of ensuring the accuracy of the result, the analysis process of a large number of microscopic parameters or mineral components is omitted, the cost is greatly saved, and the efficiency is improved. According to theoretical comparison, the results of core measured data comparison and well logging measured data comparison, the method disclosed by the invention is high in calculation precision, simple and feasible.

The invention relates to Voigt-reus-Hill mean, Wood mean, Critical Porosity Model (CPM) and Gassmann equations. The method can quickly and accurately estimate the sound wave velocity of the compact carbonate rock under the condition of only a small amount of rock physical experiment data or adjacent well data. According to the method, effective elastic moduli of the mineral components and the fluid compound are respectively calculated by applying the Voigt-Reuss-Hill average and the Wood average, and then the saturated rock bulk modulus is calculated based on experimental data or adjacent well data. And finally, calculating the acoustic wave velocity of the rock according to the deduced approximate relation. For compact carbonate rocks, the method of the invention is theoretically based mainly on the following petrophysical relations:

first, it is assumed that the compressional and shear wave velocities propagating in carbonate rock satisfy the mathematical relationship:

V_P≈aV_S+b (1)

wherein a and b are empirical constants. Furthermore, a large amount of experimental data shows that for tight reservoirs, the compressional-shear velocity ratio of saturated rocks is close to that of minerals (Mavko,2006), so for saturated rocks:

wherein, V_PIs the velocity of longitudinal wave, V_SFor shear wave velocity, the subscripts sat and m represent the parameters for saturated rock and mixed minerals, respectively, and σ is the poisson's ratio of the mineral matrix.

In addition, the true velocity of longitudinal wave propagation in rock can also be expressed in terms of bulk and shear moduli, i.e.:

wherein rho is density, K and mu are volume modulus and shear modulus respectively, and the three equations are combined to obtain:

based on the theoretical derivation process, the invention provides a method for rapidly estimating the carbonate rock sound wave velocity by further approximating and deforming the formula (4), and the complete theoretical derivation and the specific operation steps are shown in fig. 4, and the method comprises the following steps:

(1) calculating mineral and fluid moduli:

the modulus of elasticity of the solid mineral mixture is generally calculated according to the Voigt-reus-Hill mean theory (1952):

where K and U are the bulk and shear moduli, respectively, the subscript m indicates the mixed mineral parameter, and V and R represent the Voigt and reus limits of the mineral, respectively. Carbonate rocks usually have the characteristic of single rock-making minerals, generally only contain calcite, dolomite and clay, and the specific volume content can be estimated according to laboratory analysis or Gamma logging interpretation results. At this time, the properties of the solid phase mineral mixture were calculated by the following formula:

ρ_m＝v_calρ_cal+v_dolρ_dol+v_clayρ_clay

K_V＝v_calK_cal+v_dolK_dol+V_clayK_clay

U_V＝v_calU_cal+v_dolU_dol+v_clayU_clay

v is the volume content and the indices cal, dol and clay represent the parameters for calcite, dolomite and clay minerals, respectively.

Bulk modulus K for fluid phase suspensions or mixtures_flCalculated from Wood (1955) formula:

K_iand v_iRespectively, the bulk modulus and the content of the ith fluid.

(2) And (3) calculating the volume modulus of the saturated rock:

the Gassmann equation speed form rewritten by Murphy (1991):

K_sat＝K_dry+K_P. (8)

wherein K_satIs the saturated rock bulk modulus, K_dryIs the dry rock modulus, K_pIs the fluid induced additional modulus, which is a function of porosity, dry rock bulk modulus and fluid bulk modulus:

since the laboratory conditions are controlled, Kp can be considered to be 0 as long as it is measured in a dry state.

Furthermore, according to Nur (1995) Critical porosity model, K_dryCan be further expressed as critical porosity

Porosity of

Can be estimated from the core or logging speed:

wherein the content of the first and second substances,is porosity, critical porosity

Is a parameter which describes the relationship between the pore structure of the rock and the rigidity of the skeleton. The critical porosity of carbonate rock is generally in the range of 0.01-0.4, and dolomite is larger than limestone, and hard pores are larger than soft pores. The method can be used for calculating according to actually measured speed data (such as a rock core and well logging) of the same stratum in the same region, for example, the acoustic logging data of a target position is missing or the experimental data is insufficient, and the critical porosity value of the corresponding depth can be calculated through curves of the same layer of an adjacent well. The calculation formula is as follows:

when calculated using equation (10), mineral composition information, saturated rock velocity, density and porosity are required, these parameters are obtained directly from the laboratory or from well logging, for V_p、V_SRho, gThe formula (10) is as follows:

(3) rock acoustic velocity estimation:

through the above steps, equation (4) can be further approximated. Rho of dense reservoirs of dolomites and limestone, which are composed of them, due to their similar densities_dryUsually in the range of 2.65 to 2.75g/cm³In the narrow region in between, the calculation results are influenced little (Sain et al, 2008; Mavko et al, 2008).

In addition, the constants a and b can also be obtained by simply fitting well log data or experimental data (linear fitting vp and vs is sufficient, that is, formula (1), the following formula (12) is directly used only for b, and a is converted into a part of parameter c by formula (11)), so that the coefficient of the first term on the right of the approximate number in formula (4) can be regarded as a constant, that is:

thus, for dense carbonate rock, the longitudinal wave velocity can be approximately expressed as the mineral matrix Poisson's ratio σ, porosity φ and critical porosity φ_cA function of three parameters. The final approximate calculation formula of the longitudinal wave velocity provided by the invention is as follows:

equation (12) can be abbreviated as:

the shear wave velocity of the saturated rock can then be calculated using the following equation:

V_Psat≈aV_Ssat+b。

the invention also provides a tight carbonate rock acoustic velocity estimation system, comprising:

a data acquisition unit: carrying out rock physical experiments on the compact carbonate rock to obtain longitudinal wave velocity, transverse wave velocity, density and porosity, or carrying out actual measurement on adjacent wells to obtain longitudinal wave velocity, transverse wave velocity, density and porosity logging curves;

bulk modulus calculation unit: the device is connected with the data acquisition unit, and the volume modulus is calculated by utilizing the longitudinal wave speed, the transverse wave speed and the density sent by the data acquisition unit;

a critical porosity calculation unit: the device is connected with the data acquisition unit, and the critical porosity is calculated by utilizing the longitudinal wave speed, the transverse wave speed, the density and the porosity sent by the data acquisition unit;

a fitting unit: the device is respectively connected with the volume modulus calculation unit and the data acquisition unit, and for the volume modulus root opening number sent by the volume modulus calculation unit, the value after the root opening number is used as a horizontal coordinate, and the longitudinal wave speed sent by the data acquisition unit is used as a vertical coordinate, and the two are fitted to obtain fitting constants b and c; fitting the transverse wave speed sent by the data acquisition unit as an abscissa and the longitudinal wave speed sent by the data acquisition unit as an ordinate to obtain fitting constants a and b, wherein a and c are slopes and b is an intercept;

a target well volume modulus calculation unit: the critical porosity calculation unit is connected with the target well, and the porosity of the target well, the mineral composition of the target well and the critical porosity value sent by the critical porosity calculation unit are used for calculating to obtain the bulk modulus of the target well;

acoustic velocity prediction unit: and the device is respectively connected with the target well volume modulus calculating unit and the fitting unit, and predicts the longitudinal wave velocity and the transverse wave velocity of the target well by using the volume modulus of the target well sent by the target well volume modulus calculating unit and the values of a, b and c sent by the fitting unit.

The bulk modulus calculation unit calculates a bulk modulus using the following formula:

wherein, V_p、V_SRho is the longitudinal wave velocity, the transverse wave velocity and the density measured in the step (1), K is the volume modulus, and mu is the shear modulus;

the critical porosity calculation unit calculates a critical porosity value using the following formula:

wherein the content of the first and second substances,

critical porosity;

the porosity measured in the step (1);

K_pis a fluid induced additional modulus, in the dry state, K_pIs 0;

the subscripts V and R represent the Voigt and reus limits of the mineral, respectively;

the target well bulk modulus calculation unit calculates the bulk modulus K of the target well by using the following formula_sat：

K_sat＝K_dry+K_P

K_flIs the bulk modulus of the fluid phase suspension or mixture:

K_iand v_iRespectively representing the volume mode of the ith fluidQuantities and contents, the values of which are obtained from the fluid saturation curves in the standard well log interpretation;

porosity of the target well;

the acoustic velocity prediction unit calculates the longitudinal velocity of the target well using the following equation:

calculating the shear wave velocity of the target well by using the following formula:

V_Psat≈aV_Ssat+b。

the speed estimation effect and accuracy proposed by the present invention can be confirmed by comparison with a complete theoretical model, as shown in fig. 1, the solid line in fig. 1 is an exact speed calculation method (formula 3); the dotted line is the approximation method proposed by the present invention (equation 12). The dark color represents pure dolomite matrix, and the light color curve is pure limestone matrix; it can be seen that the calculated results are very close, and the theoretical error of the approximation formula does not exceed 2%.

The examples of the invention are as follows:

FIG. 2 shows the cross plot of the dry rock modulus and the longitudinal wave velocity test results as the petrophysical experimental data points. The dashed curve is the combination of pure dolomite matrix and hard pores, which can be considered as the upper velocity limit; the light solid curve is a combination of pure limestone matrix and soft porosity and can be considered as the lower velocity limit; the middle dark solid curve is the final estimation result of the speed, and the coefficients determined by the rock physics experiment are as follows: where b is 1859.6 and c is 0.0178 (i.e., c (σ) in equation (12), the determination method in the experiment is as shown in fig. 2, the bulk modulus open root (Ksat shown in fig. 2, K is set as an independent variable instead of K in fig. 2 for convenience of display, and the result is consistent) and the velocity of the longitudinal wave are fitted, and the modulus is directly calculated from the velocity and the density by equation 3, and the velocity is directly measured). It can be seen that the calculated results are highly consistent with the experimental values, and the regression coefficient is as high as 0.9610, thus proving the effectiveness of the invention.

The rock velocity can be predicted by substituting equation (12) according to parameters b and c obtained in fig. 2. The first two red curves in fig. 3 show the estimation of the logging acoustic velocity according to the present invention, the black curve is the measured acoustic velocity curve, and the last two columns are the intermediate process parameters used. It can be seen that for dense carbonate rock, the present invention can achieve accurate estimation of velocity without requiring too many microstructural parameters of the rock and mineral composition analysis results.

The speed of sound in rock is the most important elastic parameter in seismic exploration and contains a large amount of useful information about reservoir minerals, pores and fluids. However, in actual operation, the condition that acoustic logging data is lost frequently occurs. Aiming at the problem, according to the rock physical characteristics of the compact carbonate rock, the invention provides an approximate relation capable of calculating the sound wave speed of a target well position according to rock physical experiment data or adjacent well measured data. The new expression can simplify the input parameters to the greatest extent on the premise of ensuring the accuracy of the result, thereby avoiding the analysis process of a large number of microscopic parameters or mineral components, greatly saving the cost and improving the efficiency. According to the theoretical comparison, the comparison of the actually measured data of the rock core and the comparison result of the actually measured data of the well logging, the invention is high in calculation precision, simple and easy to implement

The geological conditions in the middle and western regions of China are favorable for the formation and the preservation of compact carbonate reservoirs. In the view of strategic eyes, the reservoirs are very widely distributed and rich in reserves, and are potential exploration targets. The speed of sound in rock is the most important elastic parameter in seismic exploration and contains a large amount of useful information about reservoir minerals, pores and fluids. However, in actual operation, the condition that acoustic logging data is lost frequently occurs. The method fully utilizes some rock physical characteristics of the compact carbonate rock, and performs parameter simplification to the maximum extent in the speed estimation process on the premise of ensuring accurate results. The comparison of theoretical curves and the comparison of examples prove that the quantitative relationship provided by the invention generally exists in practice, and has high calculation efficiency and good precision.

The above-described embodiment is only one embodiment of the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be easily made based on the application and principle of the present invention disclosed in the present application, and the present invention is not limited to the method described in the above-described embodiment of the present invention, so that the above-described embodiment is only preferred, and not restrictive.