Reservoir free gas saturation calculation method, device and medium

Abstract

The application discloses a reservoir free gas saturation calculation method, device and medium, considers different inhibiting effects of free gas geometric distribution types in the reservoir on acoustic wave signals, that is, compared with patchy distribution bubbles, uniform distribution small bubbles are more obvious in rapidly reducing acoustic wave velocity and acoustic wave signal attenuation, and a rock physical model based on the free gas geometric distribution types is constructed. The rock physical model based on the free gas geometric distribution types constructed by the application can accurately depict the P-wave velocity of the reservoir with different geometric distribution types of free gas, free gas saturation is calculated according to the P-wave velocity and the rock physical model based on the free gas geometric distribution types, and a basis is provided for quantitative analysis of free gas saturation of a free gas saturated water reservoir.

Description

Technical Field

[0001] This invention belongs to the field of applied geophysical logging technology, and more specifically, relates to a method, apparatus and medium for calculating reservoir free gas saturation. Background Technology

[0002] In lakebed, seafloor, and permafrost reservoirs, organic matter forms natural gas through biogenic or thermal degradation, and this natural gas exists extensively in the reservoir as free gas. Subsurface natural gas reservoirs also contain large quantities of natural gas in free gas form. Accurately assessing reservoir free gas saturation is one of the important tasks in geophysical logging. Currently, free gas saturation is mainly estimated based on Archie's formula and its improved versions, and sound velocity and sound velocity decay models are also important techniques. However, existing sound velocity and sound velocity decay models cannot accurately characterize the suppression effect of reservoir free gas on sound velocity and sound velocity decay, thus leading to significant errors in assessing free gas saturation.

[0003] Free gas is the primary cause of elastic wave dispersion and attenuation in saturated water reservoirs, and its geometric distribution has varying effects on sound velocity reduction and acoustic signal attenuation. Compared to patchy free gas distribution, free gas with a uniform distribution of small bubbles of the same volume exhibits a more significant effect on sound velocity suppression and acoustic signal attenuation. This implies that the geometric distribution characteristics of free gas are also a key factor influencing sound velocity and acoustic signal attenuation. Although existing sound velocity models (e.g., the Simplified Three Phase Equation, STPE model) have achieved some success in calculating sound velocity and acoustic signal attenuation in reservoirs containing free gas, these models do not consider the strong suppression effect of free gas geometric distribution characteristics on sound velocity. They cannot accurately describe the changes in sound velocity and acoustic signal attenuation in saturated water reservoirs containing free gas, and therefore cannot accurately characterize the velocity and attenuation characteristics of free gas reservoirs, affecting the accuracy of free gas saturation assessment. Summary of the Invention

[0004] This invention addresses the aforementioned problems in the prior art. Therefore, a method, apparatus, and medium for calculating reservoir free gas saturation are needed. Addressing the issue that existing technologies do not adequately consider the strong suppression effect of the geometric distribution characteristics of free gas in the reservoir on acoustic signals, this invention considers the geometric distribution characteristics of free gas and constructs effective bulk moduli for both uniform small bubble distribution and patchy bubble distribution types. The correspondence between the average acoustic velocity and free gas saturation is calculated, forming an acoustic rock physics modeling method that can accurately characterize the influence of free gas geometric distribution. The method calculates reservoir free gas saturation based on P-wave velocity. The rock physics model constructed by this method based on the free gas geometric distribution type can accurately calculate the P-wave velocity of reservoirs containing free gas, providing a technical basis for the quantitative interpretation of free gas saturation.

[0005] According to a first aspect of the present invention, a method for calculating reservoir free gas saturation is provided, the method comprising:

[0006] Establish a rock physics model based on the geometric distribution type of free gas;

[0007] A relative error objective function is constructed, and the reservoir free gas saturation is calculated based on the measured reservoir data.

[0008] Furthermore, a rock physics model based on the geometric distribution type of free gas is established, including:

[0009] Calculate the bulk modulus K of the solid particles constituting the reservoir framework using the Hill average formula. s and shear modulus μ s , represented as:

[0010]

[0011]

[0012] In the formula, m represents the number of components constituting the reservoir framework, and f i K is the volume percentage of component i. i It is the bulk modulus of component i, μ i It is the shear modulus of component i;

[0013] The bulk modulus of the reservoir dry skeleton is calculated based on the dry skeleton cementation model and the bulk modulus and shear modulus of the solid particles constituting the reservoir skeleton.

[0014] Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of uniformly distributed small bubbles to calculate the equivalent bulk modulus of a saturated water reservoir containing free gas.

[0015] Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of the patchy distribution bubble type to calculate the equivalent bulk modulus of the patchy distribution bubble type of the saturated water reservoir containing free gas.

[0016] Based on the equivalent bulk modulus of uniformly distributed small bubbles and the equivalent bulk modulus of patchy distributed bubbles, the equivalent bulk modulus of mixed distributed bubbles in a water-saturated reservoir containing free gas is calculated.

[0017] Based on the bulk modulus and shear modulus of solid particles in the reservoir framework, the bulk modulus and shear modulus of the dry reservoir framework, and the equivalent bulk modulus of mixed-distribution bubble-type reservoirs, the theoretical velocity v of a gas-saturated water reservoir based on the Biot two-phase wave characteristic equation is obtained using a petrophysical model of a gas-bearing reservoir with a free gas geometric distribution. p .

[0018] Furthermore, the bulk modulus K of the reservoir dry skeleton cementation m and shear modulus μ m Represented as:

[0019]

[0020]

[0021]

[0022] In the formula, φ is porosity, α is the cementing coefficient of the particles constituting the dry skeleton, and γ is the compatibility coefficient.

[0023] Furthermore, the formula for the equivalent bulk modulus of the uniformly distributed small bubbles is expressed as:

[0024]

[0025] In the formula, the modulus ratio Skeleton ratio φ s =1-φ,K w K is the bulk modulus of pore water. g S is the bulk modulus of the free gas. g r represents the free gas saturation. g The percentage of uniformly distributed small bubbles in the free gas is represented by J, where J is the uniformity index.

[0026] Furthermore, the formula for the equivalent bulk modulus of the patchy bubble distribution is expressed as follows:

[0027]

[0028]

[0029]

[0030] In the formula, K sat1 For the bulk modulus containing only pore water, K sat2 For the bulk modulus of gases containing only pores, K av2 It represents the bulk modulus of the patchy distribution.

[0031] Furthermore, the formula for the equivalent bulk modulus of mixed-distribution bubble type is expressed as follows:

[0032]

[0033] In the formula, w is the weight.

[0034] Furthermore, the theoretical formula for calculating the P-wave velocity based on a rock physics model of free gas geometric distribution type is expressed as follows:

[0035]

[0036] Among them, v p For the theoretical P-wave velocity in a rock physics model containing a free gas reservoir, Re(·) represents the real part, and ω represents the source frequency. The complex wave number is a characteristic root of Biot's biphase characteristic equation.

[0037] Furthermore, the Biot biphase characteristic equation is expressed as:

[0038]

[0039] In the formula, det(·) represents finding the eigenvalues ​​of the matrix, and ω represents the source frequency. This represents the complex wave number, where j is the imaginary unit;

[0040] It is the density matrix, where ρ 11 ρ 12 ρ 21 ρ 22 ρ represents the coupling density. 11 =(1-φ)ρ s -ρ 12 ,ρ 12 =-(α) inf -1)φρ l ,ρ 22 =φρ l -ρ 12 ,α inf =1+r(1 / φ-1), α inf S is the pore space compatibility coefficient. g ρ is the free gas saturation, J is the uniformity index, φ is the porosity, and ρ is the density of free gas. s ρ is the density of the skeletal particles. w ρ is the density of pore water.g Where is the free gas density, and r is the pore space tortuosity coefficient.

[0041] This is the friction coefficient matrix, where b represents the friction amount, and b = η. l φ 2 / κ, η l It is the viscosity coefficient of the mixed fluid, η g It is the gas viscosity coefficient, η w κ is the viscosity coefficient of the liquid, and κ is the effective permeability of the reservoir skeleton.

[0042] It is the modulus coefficient matrix, A=((1-c)φ s ) 2 K av +K m -2μ m / 3, Q=(1-c)φ s φK av R = φ 2 K av N = μ m , A, R, Q, and N are the modulus components, and K... av For the equivalent bulk modulus of the mixed-distribution bubble type, w is the weight;

[0043] Furthermore, a relative error objective function is constructed, and the reservoir free gas saturation is calculated based on measured reservoir data, including:

[0044] Based on the natural gamma ray logging, porosity logging, and lithology density logging data of the target formation in the work area, the volume fraction of rock components was obtained. The bulk modulus and shear modulus of the reservoir skeleton granular solid phase were calculated using the Hill average equation. The measured P-wave velocity was calculated based on the sonic logging curves of the work area.

[0045] By substituting the free gas saturation and the proportion of uniform small bubbles in the free gas into a rock physics model based on the geometric distribution of free gas, the theoretical value of the longitudinal wave velocity of the reservoir in the work area is obtained. The measured velocity is compared with the theoretical velocity, and the reservoir free gas saturation is obtained when the error reaches the required accuracy.

[0046] Furthermore, the error between the measured speed and the theoretical speed is estimated using the following relative error objective function:

[0047]

[0048] In the formula, is Measured longitudinal wave velocity.

[0049] According to a second technical solution of the present invention, a reservoir free gas saturation calculation device is provided, the device comprising:

[0050] The model building module is configured to build a rock physics model based on the free gas geometry distribution type.

[0051] The saturation calculation module is configured to construct a relative error objective function to calculate the reservoir free gas saturation based on measured reservoir data.

[0052] According to a third technical solution of the present invention, a readable storage medium is provided, wherein the readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to implement the method described above.

[0053] The present invention has at least the following beneficial effects:

[0054] (1) The present invention provides a method for calculating reservoir free gas saturation based on a rock physics model of free gas geometric distribution type. The method calculates the elastic modulus of reservoir skeleton particles based on the Hill average equation; calculates the bulk modulus and shear modulus of the skeleton using the dry skeleton cementation model of the reservoir; calculates the equivalent bulk modulus of water-saturated reservoir containing free gas using the formula for the equivalent bulk modulus of uniformly distributed small bubble type; calculates the equivalent bulk modulus of water-saturated reservoir containing free gas using the formula for the equivalent bulk modulus of patchy distributed bubble type; calculates the equivalent bulk modulus of mixed distributed bubble type by combining the equivalent bulk modulus of uniformly distributed small bubble type and the equivalent bulk modulus of patchy distributed bubble type; and constructs a rock physics model based on free gas geometric distribution type by combining the elastic modulus of fluid phase, the elastic modulus of dry skeleton and the equivalent bulk modulus. The rock physics model constructed in this invention, based on the geometric distribution type of free gas, takes into account the strong attenuation mechanism of free gas geometric distribution on acoustic wave propagation in the reservoir. Compared with the existing theoretical models, it is more in line with the actual situation of free gas-bearing reservoirs and can characterize the acoustic response law of free gas-bearing water-saturated reservoirs. Then, acoustic logging can be used to detect and identify free gas-bearing water-saturated reservoirs.

[0055] (2) The method for calculating free gas saturation in a rock physics model reservoir based on the free gas geometric distribution type provided by the present invention can describe both uniform and non-uniform bubble morphology in the reservoir, which is consistent with the actual bubble distribution morphology of the actual free gas reservoir. It can accurately describe the longitudinal wave velocity of reservoirs with different free gas geometric distribution morphologies, and provides a technical basis for the quantitative interpretation and evaluation of free gas saturation.

[0056] (3) The quantitative analysis method of reservoir free gas saturation based on rock physics model of free gas geometric distribution type provided by the present invention can describe the longitudinal wave velocity of reservoirs containing free gas. The constructed rock physics model based on free gas geometric distribution type is applied to free gas detection, thereby providing a new method for free gas saturation detection using acoustic parameters (i.e. longitudinal wave velocity), which can provide a measurement method for the improvement and perfection of acoustic logging.

[0057] (4) The quantitative analysis method of reservoir free gas saturation based on rock physics model of free gas geometric distribution type provided by the present invention utilizes the rock physics model based on free gas geometric distribution constructed by the present invention to determine free gas saturation using longitudinal wave velocity. Compared with the free gas saturation calculation method based on STPE elastic wave rock physics model and resistivity Archie formula, the new saturation calculation method based on acoustic parameters provided by the present invention avoids the problem of inapplicability when free gas saturation is less than 1%, greatly expands the free gas saturation calculation method of free gas reservoirs, and solves the evaluation and interpretation of free gas saturation in weakly diagenetic strata to a certain extent. Attached Figure Description

[0058] Figure 1 A flowchart of a method for calculating reservoir free gas saturation according to an embodiment of the present invention is shown;

[0059] Figure 2 A schematic diagram showing the variation curve of longitudinal wave velocity with free gas saturation in a water-saturated reservoir containing free gas according to an embodiment of the present invention is shown.

[0060] Figure 3 A structural diagram of a reservoir free gas saturation calculation device according to an embodiment of the present invention is shown. Detailed Implementation

[0061] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and specific examples, but this is not intended to limit the present invention. If there is no necessary sequential relationship between the various steps described herein, the order in which they are described as examples should not be considered a limitation. Those skilled in the art should understand that the order can be adjusted, as long as it does not disrupt the logical consistency between them and render the entire process impossible.

[0062] This invention provides a method for calculating reservoir free gas saturation, such as... Figure 1 As shown, the specific steps are as follows:

[0063] S1. Establish a rock physics model based on the geometric distribution type of free gas. The specific steps are as follows:

[0064] S11. Calculate the bulk modulus K of the solid particles that constitute the reservoir skeleton. s and shear modulus μ s ,

[0065] In some embodiments, in step S11, the bulk modulus K of the solid particles of the reservoir framework s and shear modulus μ s Represented as:

[0066]

[0067]

[0068] In the formula, m represents the number of components constituting the reservoir framework, and f i K is the volume percentage of component i. i It is the bulk modulus of component i, μ i It is the shear modulus of component i.

[0069] S12. Based on the dry skeleton cementation model and the bulk modulus and shear modulus of the reservoir skeleton solid particles obtained in step S11, calculate the bulk modulus and shear modulus of the reservoir dry skeleton.

[0070] In some embodiments, the bulk modulus and shear modulus of the reservoir dry skeleton cementation in step S12 are expressed as follows:

[0071]

[0072]

[0073]

[0074] In the formula, φ is porosity and α is the cementation coefficient of the particles constituting the dry skeleton.

[0075] S13. Substitute the bulk modulus parameters of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton obtained in step S12, into the formula for the equivalent bulk modulus of uniformly distributed small bubbles to calculate the equivalent bulk modulus of the saturated water reservoir containing free gas.

[0076] In some embodiments, the formula for the equivalent bulk modulus of uniformly distributed small bubbles in step S13 is expressed as:

[0077]

[0078] In the formula, the modulus ratio Skeleton ratio φ s =1-φ,K w K is the bulk modulus of pore water. gS is the bulk modulus of the free gas. g r represents the free gas saturation. g The percentage of uniformly distributed small bubbles in the free gas is represented by J, where J is the uniformity index.

[0079] S14. Substitute the bulk modulus parameters of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton obtained in step S12, into the formula for the equivalent bulk modulus of the patchy distribution bubble type to calculate the equivalent bulk modulus of the patchy distribution bubble type of the saturated water reservoir containing free gas.

[0080] In some embodiments, the formula for the patchy distributed bubble type equivalent bulk modulus in step S14 is expressed as:

[0081]

[0082]

[0083]

[0084] S15. Combining the uniformly distributed small bubble type equivalent bulk modulus obtained in step S13 and the patchy distributed bubble type equivalent bulk modulus obtained in step S14, the mixed distributed bubble type equivalent bulk modulus can be obtained.

[0085] In some embodiments, the equivalent bulk modulus of the mixed-distribution bubble type is expressed as:

[0086]

[0087] In the formula, w is the weight.

[0088] S16. Combining the bulk modulus and shear modulus of the reservoir dry skeleton cementation in step S12 with the equivalent bulk modulus of the mixed-distribution bubble type in step S15, the P-wave velocity type v of the rock physics model of the free gas reservoir is calculated according to the Biot two-phase wave characteristic equation. p .

[0089] In some embodiments, the formula for calculating the P-wave velocity in a rock physics model containing a free gas reservoir is expressed as follows:

[0090]

[0091] Among them, v p Let Re(·) denote the longitudinal wave velocity of a reservoir containing free gas, and let Re(·) denote the real part. These are the characteristic roots of Biot's biphase characteristic equation.

[0092] In some embodiments, the Biot biphase characteristic equation is expressed as:

[0093]

[0094] In the formula, det(·) represents finding the eigenvalues ​​of the matrix, and ω represents the source frequency. This represents the complex wave number, where j is the imaginary unit.

[0095] In some embodiments, It is the density matrix, ρ 11 =(1-φ)ρ s -ρ 12 ,ρ 12 =-(α) inf -1)φρ l ,ρ 22 =φρ l -ρ 12 ,α inf =1+r(1 / φ-1), ρ s ρ is the density of the skeletal particles. w ρ is the density of pore water. g Where is the free gas density, and r is the pore space tortuosity coefficient.

[0096] In some embodiments, It is the friction coefficient matrix, with preference given to b = η l φ 2 / κ, η g It is the gas viscosity coefficient, η w κ is the liquid viscosity coefficient, and κ is the effective permeability of the reservoir skeleton.

[0097] In some embodiments, It is the modulus coefficient matrix, A=((1-c)φ s ) 2 K av +K m -2μ m / 3, Q=(1-c)φ s φK av R = φ 2 K av N = μ m It is the modulus component.

[0098] S2. Construct a relative error objective function and calculate the reservoir free gas saturation based on measured reservoir data:

[0099] S21. Based on the natural gamma ray logging, porosity logging, and lithology density logging data of the target formation in the work area, obtain the volume fraction of rock components. Calculate the bulk modulus and shear modulus of the reservoir skeleton granular solid phase using the Hill average equation. Calculate the measured P-wave velocity based on the sonic logging curves of the work area.

[0100] S22. Then, substituting the free gas saturation and the proportion of uniform small bubbles in the free gas into the rock physics model based on the geometric distribution of free gas, the theoretical value of the P-wave velocity of the reservoir in the work area can be obtained. Substituting the measured velocity and the theoretical velocity into the relative error objective function...

[0101]

[0102] In the formula, It is the measured longitudinal wave velocity. The velocity of the adjacent bubble-free reservoir is taken as the target velocity. Specifically, when the relative error objective function is less than the error threshold of 0.001, the calculated free gas saturation meets the accuracy requirements. Otherwise, the iterative algorithm is used to update the free gas saturation until the accuracy requirements are met.

[0103] Specifically, the iterative algorithm uses the particle swarm optimization algorithm. The initial particle swarm consists of 1000 groups of particles, i.e., within the range s... g ∈[0,0.2],r g 1000 values ​​are uniformly and randomly generated within the range [0.4, 0.6] and [0.1, 0.7]. The theoretical P-wave velocity is obtained by substituting each particle's value into the calculation formula. Take the measured P-wave velocity at the first position and substitute it into the objective function I(S) g ,r g The particle with the smallest calculated result (w) is the current optimal particle. The update direction for each particle is the direction from which the particle points to the optimal particle, and the update step size for each particle is 1 / 200 of the distance between the particle and the optimal particle. Take the maximum value among all measured P-wave velocities, recalculate the current optimal particle, and stop updating the current optimal particle after 50 iterations.

[0104] Figure 2 The variation trend of P-wave velocity with free gas saturation in reservoirs containing free gas is presented and compared with experimental data. Figure 2 The results show that the P-wave velocity calculated based on the free gas-enhanced rock physics model is consistent with the experimentally measured data.

[0105] The aforementioned method constructs a rock physics model based on the geometric distribution type of free gas, which considers the strong suppression effect of the free gas geometric distribution type on acoustic velocity. Compared with existing theoretical models, it better reflects the actual situation of free gas-bearing reservoirs, can more accurately describe the P-wave velocity of reservoirs with different free gas saturation, and provides more accurate calculations. This is of great significance and value for the acoustic detection and identification of free gas-bearing reservoirs, and provides a theoretical basis for the quantitative interpretation of free gas saturation in free gas-bearing reservoirs. Applying this free gas-enhanced rock physics model to free gas detection provides a new method for free gas detection using acoustic parameters (i.e., P-wave velocity and attenuation coefficient), improving and refining acoustic logging.

[0106] This invention provides a reservoir free gas saturation calculation device, such as... Figure 3 As shown, the device 300 includes:

[0107] Model building module 301 is configured to build a rock physics model based on the free gas geometric distribution type;

[0108] The saturation calculation module 302 is configured to construct a relative error objective function to calculate the reservoir free gas saturation based on the measured reservoir data.

[0109] In some embodiments, the model building module is further configured to calculate the bulk modulus K of the solid particles constituting the reservoir framework according to the Hill average formula. s and shear modulus μ s , represented as:

[0110]

[0111]

[0112] In the formula, m represents the number of components constituting the reservoir framework, and f i K is the volume percentage of component i. i It is the bulk modulus of component i, μ i It is the shear modulus of component i;

[0113] The bulk modulus of the reservoir dry skeleton is calculated based on the dry skeleton cementation model and the bulk modulus and shear modulus of the solid particles constituting the reservoir skeleton.

[0114] Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of uniformly distributed small bubbles to calculate the equivalent bulk modulus of a saturated water reservoir containing free gas.

[0115] Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of the patchy distribution bubble type to calculate the equivalent bulk modulus of the patchy distribution bubble type of the saturated water reservoir containing free gas.

[0116] Based on the bulk modulus and shear modulus of solid particles in the reservoir skeleton, the bulk modulus and shear modulus of the dry reservoir skeleton, the equivalent bulk modulus of uniformly distributed small bubbles, and the equivalent bulk modulus of patchy distributed bubbles, the theoretical velocity v of a rock physics model based on the free gas geometric distribution type is obtained according to the Biot two-phase wave characteristic equation. p .

[0117] In some embodiments, the bulk modulus K of the reservoir dry skeleton cementation m and shear modulus μ m Represented as:

[0118]

[0119]

[0120]

[0121] In the formula, φ is porosity, α is the cementing coefficient of the particles constituting the dry skeleton, and γ is the compatibility coefficient.

[0122] In some embodiments, the formula for the equivalent bulk modulus of uniformly distributed small bubbles is expressed as:

[0123]

[0124] In the formula, the modulus ratio Skeleton ratio φ s =1-φ,K w K is the bulk modulus of pore water. g S is the bulk modulus of the free gas. g r represents the free gas saturation. g The percentage of uniformly distributed small bubbles in the free gas is represented by J, where J is the uniformity index.

[0125] In some embodiments, the formula for the equivalent bulk modulus of the patchy bubble distribution is expressed as:

[0126]

[0127]

[0128]

[0129] In the formula, K sat1 K is the equivalent bulk modulus of liquid only. sat2For problems involving only gases, K is the modulus. av2 It is the equivalent bulk modulus of the bubble-like distribution.

[0130] In some embodiments, the equivalent bulk modulus of mixed-distribution bubbles is expressed as:

[0131]

[0132] In the formula, w is the weight.

[0133] In some embodiments, the Biot biphase characteristic equation is expressed as:

[0134]

[0135] In the formula, det(·) represents finding the eigenvalues ​​of the matrix, and ω represents the source frequency. This represents the complex wave number, where j is the imaginary unit;

[0136] In some embodiments, It is the density matrix, ρ 11 =(1-φ)ρ s -ρ 12 ,ρ 12 =-(α) inf -1)φρ l ,ρ 22 =φρ l -ρ 12 ,α inf =1+r(1 / φ-1), ρ s ρ is the density of the skeletal particles. w ρ is the density of pore water. g Where is the free gas density, and r is the pore space tortuosity coefficient.

[0137] In some embodiments, It is the friction coefficient matrix, with preference given to b = η l φ 2 / κ, η g It is the gas viscosity coefficient, η w κ is the liquid viscosity coefficient, and κ is the effective permeability of the reservoir skeleton.

[0138] In some embodiments, It is the modulus coefficient matrix, A=((1-c)φ s ) 2 K av +K m -2μ m / 3, Q=(1-c)φ s φK av R = φ2 K av N = μ m It is the modulus component.

[0139] In some embodiments, the formula for calculating the P-wave velocity in a rock physics model containing a free gas reservoir is expressed as follows:

[0140]

[0141] Among them, v p Let be the theoretical longitudinal wave velocity of a reservoir containing free gas, and Re(·) denotes taking the real part.

[0142] In some embodiments, the saturation calculation module is further configured to:

[0143] Based on the natural gamma ray logging, porosity logging, and lithology density logging data of the target formation in the work area, the volume fraction of rock components was obtained. The bulk modulus and shear modulus of the reservoir skeleton granular solid phase were calculated using the Hill average equation. The measured P-wave velocity was calculated based on the sonic logging curves of the work area.

[0144] By substituting the free gas saturation, weights, and the proportion of uniform small bubbles in the free gas into the rock physics model based on the geometric distribution of free gas, the theoretical value of the longitudinal wave velocity of the reservoir in the work area is obtained. The measured velocity is compared with the theoretical velocity, and the reservoir free gas saturation is obtained when the error reaches the required accuracy.

[0145] In some embodiments, the saturation calculation module is further configured to estimate the error between the measured velocity and the theoretical velocity using the following relative error objective function:

[0146]

[0147] In the formula, is Measured longitudinal wave velocity.

[0148] It should be noted that the device described in this embodiment and the method described earlier belong to the same technical concept and can achieve the same technical effect, which will not be repeated here.

[0149] This invention provides a readable storage medium that stores one or more programs, which can be executed by one or more processors to implement the methods described in the above embodiments.

[0150] The above description is intended to be illustrative and not restrictive. For example, the above examples (or one or more of them) can be used in combination with each other. Other embodiments can be used by those skilled in the art when reading the above description. Furthermore, in the above detailed description, various features may be grouped together to simplify the invention. This should not be construed as an intention that a feature of an unclaimed invention is necessary for any claim. Rather, the subject matter of the invention may be less than all the features of a particular embodiment of the invention. Thus, the following claims are incorporated herein by reference as examples or embodiments, wherein each claim is an independent, separate embodiment, and these embodiments are contemplated to be combined with each other in various combinations or arrangements. The scope of the invention should be determined by reference to the appended claims and the full scope of their equivalents.

Claims

1. A method for calculating reservoir free gas saturation, characterized in that, The method includes: Establish a rock physics model based on the geometric distribution type of free gas; Construct a relative error objective function and calculate the reservoir free gas saturation based on measured reservoir data; Establish a rock physics model based on the geometric distribution type of free gas, including: Calculate the bulk modulus of the solid particles constituting the reservoir dry framework using the Hill average formula. and shear modulus , represented as: In the formula, The number of components that make up the reservoir framework, It is a component Volume ratio It is a component bulk modulus, It is a component shear modulus; Based on the dry skeleton cementation model and the bulk modulus and shear modulus of the solid particles constituting the reservoir skeleton, the bulk modulus and shear modulus of the reservoir dry skeleton are calculated. Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of uniformly distributed small bubbles to calculate the equivalent bulk modulus of a saturated water reservoir containing free gas. Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of the patchy distribution bubble type to calculate the equivalent bulk modulus of the patchy distribution bubble type of the saturated water reservoir containing free gas. Based on the equivalent bulk modulus of uniformly distributed small bubbles and the equivalent bulk modulus of patchy distributed bubbles, the equivalent bulk modulus of mixed distributed bubbles in a water-saturated reservoir containing free gas is calculated. Based on the bulk modulus and shear modulus of solid particles in the reservoir framework, the bulk modulus and shear modulus of the dry reservoir framework, and the equivalent bulk modulus of mixed-distribution bubble-type reservoirs, the theoretical velocity of a petrophysical model of a gas-saturated water reservoir with free gas geometric distribution is obtained according to the Biot two-phase wave characteristic equation. .

2. The method according to claim 1, characterized in that, Cemented bulk modulus of reservoir dry skeleton and shear modulus Represented as: In the formula, It is porosity. It is the cementing coefficient of the particles that make up the dry skeleton. It is the coordination coefficient.

3. The method according to claim 2, characterized in that, The formula for the equivalent bulk modulus of uniformly distributed small bubbles is expressed as follows: In the formula, the modulus ratio skeleton proportion , The bulk modulus of pore water. The bulk modulus of free gas. Free gas saturation The proportion of small bubbles evenly distributed in the free gas. It represents the uniform distribution index.

4. The method according to claim 3, characterized in that, The formula for the equivalent bulk modulus of the patchy bubble distribution type is expressed as follows: In the formula, For bulk modulus containing only pore water, For the bulk modulus of gases containing only pores, It represents the bulk modulus of the patchy distribution.

5. The method according to claim 4, characterized in that, The formula for the equivalent bulk modulus of the mixed-distribution bubble type is expressed as follows: In the formula It's the weight.

6. The method according to claim 5, characterized in that, The theoretical formula for calculating the P-wave velocity based on a rock physics model of free gas geometric distribution is expressed as follows: in, The P-wave velocity is based on the theoretical values ​​of a rock physics model for a reservoir containing free gas. Indicates taking the real part, Indicates the frequency of the wave source. These represent the characteristic roots of Biot's biphase characteristic equation; The Biot biphase characteristic equation is expressed as follows: In the formula, This indicates finding the eigenvalues ​​of a matrix. Indicates the frequency of the wave source. It is a virtual unit; It is the density matrix, where , , , Indicates coupling density. , , , , , The pore space compatibility coefficient, Free gas saturation The uniform distribution index, Porosity The density of the skeletal particles. The density of pore water, For free gas density, It is the pore space curvature coefficient; This is the friction coefficient matrix, where b represents the amount of friction. , , It is the viscosity coefficient of the mixed fluid. It is the viscosity coefficient of the gas. It is the viscosity coefficient of the liquid. It is the effective permeability of the reservoir framework; It is the modulus coefficient matrix. , , , , , Q and N are the modulus components. It is the equivalent bulk modulus of mixed-distribution bubble type.

7. The method according to claim 6, characterized in that, Construct a relative error objective function and calculate the reservoir free gas saturation based on measured reservoir data, including: Based on the natural gamma ray logging, porosity logging, and lithology density logging data of the target formation in the work area, the volume fraction of rock components was obtained. The bulk modulus and shear modulus of the reservoir skeleton granular solid phase were calculated using the Hill average equation. The measured P-wave velocity was calculated based on the sonic logging curves of the work area. ; The error between the measured velocity and the theoretical velocity is estimated using the following relative error objective function: In the formula, is Measured longitudinal wave velocity; By substituting the free gas saturation, weights, and the proportion of uniform small bubbles in the free gas into the rock physics model based on the geometric distribution of free gas, the theoretical value of the longitudinal wave velocity of the reservoir in the work area is obtained. The measured velocity is compared with the theoretical velocity, and the reservoir free gas saturation is obtained when the error reaches the required accuracy.

8. An apparatus for calculating reservoir free gas saturation, characterized in that, The device includes: The model building module is configured to build a rock physics model based on the free gas geometry distribution type, including: Calculate the bulk modulus of the solid particles constituting the reservoir dry framework using the Hill average formula. and shear modulus , represented as: In the formula, The number of components that make up the reservoir framework, It is a component Volume ratio It is a component bulk modulus, It is a component shear modulus; Based on the dry skeleton cementation model and the bulk modulus and shear modulus of the solid particles constituting the reservoir skeleton, the bulk modulus and shear modulus of the reservoir dry skeleton are calculated. Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of uniformly distributed small bubbles to calculate the equivalent bulk modulus of a saturated water reservoir containing free gas. Substitute the bulk modulus of pore water and pore free gas, as well as the bulk modulus of the reservoir dry skeleton, into the formula for the equivalent bulk modulus of the patchy distribution bubble type to calculate the equivalent bulk modulus of the patchy distribution bubble type of the saturated water reservoir containing free gas. Based on the equivalent bulk modulus of uniformly distributed small bubbles and the equivalent bulk modulus of patchy distributed bubbles, the equivalent bulk modulus of mixed distributed bubbles in a water-saturated reservoir containing free gas is calculated. Based on the bulk modulus and shear modulus of solid particles in the reservoir framework, the bulk modulus and shear modulus of the dry reservoir framework, and the equivalent bulk modulus of mixed-distribution bubble-type reservoirs, the theoretical velocity of a petrophysical model of a gas-saturated water reservoir with free gas geometric distribution is obtained according to the Biot two-phase wave characteristic equation. ; The saturation calculation module is configured to construct a relative error objective function to calculate the reservoir free gas saturation based on measured reservoir data.

9. A readable storage medium, characterized in that, The readable storage medium stores one or more programs, which can be executed by one or more processors to implement the method as described in any one of claims 1 to 7.

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