A method and device for identifying the structure of a dolomite reservoir

Abstract

The present invention relates to a method and device for identifying the dolomite reservoir structure, belonging to the technical field of oil and gas exploration. The method includes: obtaining the different propagation distances of seismic waves at each CMP point in the target area and the frequencies corresponding to the propagation distances; fitting the different propagation distances of seismic waves and the frequencies corresponding to the propagation distances according to a first correspondence relationship to obtain fitting coefficients; the first correspondence relationship is the correspondence relationship between the propagation distance and the frequency; the first correspondence relationship is obtained according to the seismic wave amplitude propagation principle and the seismic energy principle; establishing a second correspondence relationship between the fitting coefficients and the dolomite reservoir structure; determining the dolomite reservoir structure in the target area according to the fitting coefficients and the established second correspondence relationship. The present invention uses prestack seismic data to identify the dolomite reservoir structure with large-scale dissolution pores, and the identification effect is good.

Description

Technical Field

[0001] The present invention relates to a method and device for identifying a dolomite reservoir structure, belonging to the technical field of oil and gas exploration. Background Art

[0002] The Lower Paleozoic dolomite reservoir refers to the Ordovician dolomite formation, which is a karst pore formation formed due to marine transgression, marine regression, stratum uplift, erosion and dissolution during the Ordovician period, and a gas-bearing reservoir formed under the action of later sedimentation and hydrocarbon generation. These reservoirs are usually the Ma 5-1 formation and the Ma 5-2 formation, with a thickness between 20 and 40 meters. The cap rocks above the Ma 5-1 and Ma 5-2 reservoirs are the dense limestone Ma 6 formation and bauxite mudstone, among which the bauxite mudstone is the uppermost cap rock. The stratigraphic sequence from top to bottom is: bauxite mudstone, limestone Ma 6 formation, Ma 5-1 formation, Ma 5-2 formation. The bauxite mudstone and the Ma 6 formation are not reservoirs, while the Ma 5-1 formation and the Ma 5-2 formation are reservoirs.

[0003] In oil and gas exploration, the identification of reservoir structure is a very important issue. Ultimately, it can be summarized as what proportion of the total thickness of the non-reservoir Ma 6 formation, bauxite mudstone and the reservoir Ma 5-1 formation, Ma 5-2 formation is occupied by the thickness of the non-reservoir Ma 6 formation and bauxite mudstone, and what proportion is occupied by the thickness of the Ma 5-1 formation and Ma 5-2 formation. Because according to existing investigations, the thickness of the Ma 5-1 and Ma 5-2 is relatively uniform, while the cap rock Ma 6 above is the first process of erosion and has obvious thickness changes. The uppermost cap rock, bauxite mudstone, is a laterally deposited formation and does not participate in the erosion process, with a relatively stable deposition process and small thickness changes. In actual oil and gas exploration, the thickness investigation of the non-reservoir bauxite mudstone and limestone Ma 6 is very important, because to drill to the reservoir, it is necessary to penetrate the non-reservoir. Therefore, the investigation of the reservoir and non-reservoir structure is of great significance in the exploration and development of oil and gas.

[0004] However, in the prior art, conventional reservoir prediction methods are basically based on post-stack inversion or waveform classification methods. Among them, the prediction method based on post-stack inversion is suitable for reservoir prediction of sandstone and mudstone with a large gamma value, but the gamma values of the reservoir dolomite and non-reservoir limestone in carbonates are not very different, and the prediction effect of this method is not good. The method based on waveform classification is simply a statistical classification of the post-stack seismic profile waveform into reservoirs and non-reservoirs. This method is essentially a representation of the seismic frequency and has many solutions, and it is impossible to specifically quantify the structural characteristics, etc.

[0005] Therefore, the existing reservoir structure identification methods are not applicable to the prediction of large-scale karst pore dolomite reservoirs. For this reason, a technical solution for identifying the dolomite reservoir structure needs to be proposed. Summary of the Invention

[0006] The purpose of this application is to provide a method and device for identifying dolomite reservoir structures, and to propose an effective technical solution for the identification of dolomite reservoir structures.

[0007] To achieve the above purpose, this application proposes a technical solution for a method of identifying dolomite reservoir structures, including the following steps:

[0008] 1) Obtain pre-stack seismic data for each CMP point in the target area, where the pre-stack seismic data includes different propagation distances of seismic waves and the frequencies corresponding to the propagation distances;

[0009] 2) Fit the different propagation distances of seismic waves and the frequencies corresponding to the propagation distances according to a first correspondence relationship to obtain fitting coefficients; the first correspondence relationship is the correspondence relationship between propagation distance and frequency; the first correspondence relationship is obtained based on the seismic wave amplitude propagation principle and the seismic energy principle;

[0010] 3) Establish a second correspondence relationship between the fitting coefficients and the dolomite reservoir structure. The process of establishing the second correspondence relationship is as follows:

[0011] Determine the thickness of reservoir Ma51, the thickness of reservoir Ma52, the thickness of non-reservoir bauxitic mudstone, and the thickness of the Lower Paleozoic reservoir cap rock Ma6 in the dolomite reservoir at the known well according to the drilling data of the known well in the target area; at the same time, obtain the fitting coefficients corresponding to the known well according to the pre-stack seismic data of the CMP points near the known well and the first correspondence relationship;

[0012] Determine the dolomite reservoir structure at the known well according to the thickness of reservoir Ma51, the thickness of reservoir Ma52, the thickness of non-reservoir bauxitic mudstone, and the thickness of the Lower Paleozoic reservoir cap rock Ma6;

[0013] Establish a second correspondence relationship according to the fitting coefficients corresponding to the known well and the dolomite reservoir structure at the known well;

[0014] 4) Determine the dolomite reservoir structure in the target area according to the fitting coefficients obtained in step 2) and the second correspondence relationship established in step 3).

[0015] In addition, this application proposes a technical solution for a dolomite reservoir structure identification device. The device includes a processor, a memory, and a computer program stored in the memory and operable on the processor. The processor implements the above-mentioned dolomite reservoir structure identification method when executing the computer program.

[0016] The beneficial effects of the technical solution of the dolomite reservoir structure identification method and device of the present invention are as follows: Based on the seismic wave amplitude propagation principle and the seismic energy principle, the present invention establishes a first correspondence relationship between the propagation distance and the frequency, and then establishes a second correspondence relationship between the dolomite reservoir structure and the fitting coefficient according to the pre-stack seismic data of the CMP points of the known well, the drilled well data, and the first correspondence relationship. Finally, after obtaining the fitting coefficient through the pre-stack seismic data of each CMP point in the target area, the reservoir structure of the dolomite in the target area is determined in combination with the second correspondence relationship. The present invention uses pre-stack data for reservoir structure identification, without complex post-stack data processing, reduces the errors caused by data processing, has good stability, and has a good identification effect on the dolomite reservoir structure with large-scale dissolution holes.

[0017] Further, in the above dolomite reservoir structure identification method and device, the first correspondence relationship is:

[0018]

[0019] where f is the frequency; α is the fitting coefficient; r is the propagation distance of the seismic wave; and E1 is the corrected seismic energy.

[0020] Further, in the above dolomite reservoir structure identification method and device, the reservoir structure of the dolomite is:

[0021] K = m5 12 / (T9 + m6 + m5 12 );

[0022] where K is the reservoir structure of the dolomite; m6 is the thickness of the Lower Paleozoic reservoir cap rock Majiagou Formation Member 6; m5 12 is the sum of the thicknesses of reservoir Majiagou Formation Member 51 and reservoir Majiagou Formation Member 52; and T9 is the thickness of the non-reservoir bauxitic mudstone.

[0023] Further, in the above dolomite reservoir structure identification method and device, the fitting coefficient is the attenuation coefficient during the propagation of the seismic wave amplitude, and the seismic wave amplitude propagation principle is:

[0024] A = A0e -αr ;

[0025] where A is the amplitude of the seismic wave at the propagation distance r; A0 is the initial amplitude of the seismic wave; α is the attenuation coefficient; and r is the propagation distance of the seismic wave.

[0026] Further, in the above dolomite reservoir structure identification method and device, the corrected seismic energy is obtained from the seismic energy before correction, and the seismic energy before correction is:

[0027] E ∝ ρA 2 f 2 W;

[0028] Among them, E is the seismic energy before correction; ρ is the medium density; A is the amplitude of the seismic wave at the propagation distance r; f is the frequency; W is the volume of the propagation medium.

[0029] Furthermore, in the above dolomite reservoir structure identification method and device, the relationship between the corrected seismic energy and the seismic energy before correction is:

[0030]

[0031] Among them, E1 is the corrected seismic energy; E is the seismic energy before correction; ρ is the medium density; A0 is the initial amplitude of the seismic wave. Brief Description of the Drawings

[0032] Figure 1 is a flowchart of the dolomite reservoir structure identification method of the present invention;

[0033] Figure 2 is a curve graph of the reservoir structure and fitting coefficient at the known well of the present invention;

[0034] Figure 3 is a schematic structural diagram of the dolomite reservoir structure identification device of the present invention. Detailed Embodiments

[0035] Embodiment of the dolomite reservoir structure identification method:

[0036] The main concept of the present invention is that, based on practice, when seismic waves propagate through reservoirs with different thickness capping layers, the frequency will change abnormally, which will be manifested in the periodic signal of the seismic wave. Conversely, by investigating the frequency characteristics of the pre-stack seismic periodic signal, the reservoir characteristics of the formation can also be identified. Therefore, the present invention first obtains the first corresponding relationship between the propagation distance and frequency of the seismic wave based on the seismic wave amplitude propagation principle and the seismic energy principle. Secondly, a second corresponding relationship between the dolomite reservoir structure and the fitting coefficient is established according to the drilling data of the known well and the pre-stack seismic data of the CMP point at the known well; finally, the dolomite reservoir in the target area is identified according to the pre-stack seismic data of the CMP point in the target area, the first corresponding relationship and the second corresponding relationship.

[0037] Specifically, the dolomite reservoir structure identification method is as Figure 1 shown, and includes the following steps:

[0038] 1) Establish the first corresponding relationship between the propagation distance and frequency of the seismic wave based on the seismic wave amplitude propagation principle and the seismic energy principle.

[0039] The seismic wave amplitude propagation principle is:

[0040] A = A0e -αr (1)

[0041] Wherein, A is the amplitude of the seismic wave at the propagation distance r; A0 is the initial amplitude of the seismic wave; α is the attenuation coefficient (in subsequent calculations, the attenuation coefficient is the fitting coefficient); r is the propagation distance of the seismic wave.

[0042] The seismic energy is:

[0043] E ∝ ρA 2 f 2 W (2)

[0044] Wherein, E is the seismic energy (i.e., the seismic energy before correction); ρ is the medium density; A is the amplitude of the seismic wave at the propagation distance r; f is the frequency; W is the volume of the propagation medium.

[0045] Substituting formula (1) into formula (2), we get: E ∝ ρ(A0e -αr ) 2 f 2 W = ρA0 2 e -2αr f 2 W;

[0046] Wherein, ρA0 2 is a constant, so let We get: E′ ∝ e -2αr f 2 W;

[0047] In the above formula, W is the volume of the propagation medium, that is, the propagation volume of the seismic wave from the ground excitation point to the lower hemisphere, which can be calculated from the propagation distance r, and then we get:

[0048]

[0049] Since is a constant, so let We get:

[0050] E″ ∝ e -2αr f 2 r 3 (3)

[0051] Taking the logarithm of both sides of formula (3), we get:

[0052] lnE″ ∝ -2αr + 2lnf + 3lnr (4)

[0053] Dividing both sides of formula (4) by 2, we get:

[0054]

[0055] Let the corrected seismic energy That is, we get:

[0056] For the convenience of subsequent calculations, replace "∝" with "=" to obtain:

[0057] Furthermore, the first correspondence relationship is obtained: From the above equivalent process, it can be seen that the relationship between the corrected seismic energy and the seismic energy before correction is:

[0058]

[0059] 2) Collect the drilling data of the known wells in the target area and the prestack seismic data of the CMP points near the known wells, and establish the second correspondence relationship between the reservoir structure of dolomite and the fitting coefficient in combination with the first correspondence relationship.

[0060] The establishment process of the second correspondence relationship is as follows:

[0061] Collect the drilling data of the known wells in the target area and the prestack seismic data of the CMP points near the known wells; the prestack seismic data includes different propagation distances of seismic waves and the corresponding frequencies of the propagation distances;

[0062] Determine the thickness of reservoir Mawu I, the thickness of reservoir Mawu II, the thickness of non-reservoir bauxitic mudstone, and the thickness of the Lower Paleozoic reservoir cap rock Mawu VI in the dolomite reservoir at the known well according to the drilling data; determine the reservoir structure K of dolomite at the known well according to the thickness of reservoir Mawu I, the thickness of reservoir Mawu II, the thickness of non-reservoir bauxitic mudstone, and the thickness of the Lower Paleozoic reservoir cap rock Mawu VI:

[0063] K = m5 12 / (T9 + m6 + m5 12 )

[0064] where K is the reservoir non-reservoir structure; T9 is the thickness of non-reservoir bauxitic mudstone; m6 is the thickness of the Lower Paleozoic reservoir cap rock Mawu VI; m5 12 is the sum of the thicknesses of reservoir Mawu I and reservoir Mawu II.

[0065] Substitute the prestack seismic data of the CMP points near the known well into the first correspondence relationship for fitting to obtain the fitting coefficient α (i.e., the attenuation coefficient) corresponding to the known well;

[0066] Establish the second correspondence relationship according to the fitting coefficient α corresponding to the known well and the reservoir structure K of dolomite at the known well.

[0067] During the fitting process of the fitting coefficient α, transform the formula into:

[0068] With For fitting as a whole, in this embodiment, taking a certain target area A as an example, the second corresponding relationship is determined.

[0069] Obtain the pre-stack seismic data of CMP points near the known wells in a certain target area A, where one CMP point and r are shown in Table 1:

[0070] Table 1 of a certain CMP point

[0071]

[0072]

[0073] Fit the pre-stack seismic data of all CMP points of the known wells in a certain target area A according to the first corresponding relationship, and obtain the fitting coefficients corresponding to each CMP point as shown in Table 2:

[0074] Table 2 Fitting coefficients obtained by fitting the pre-stack seismic data of each CMP point

[0075]

[0076]

[0077] Determine the thickness of the reservoir Ma 5-1, the thickness of the reservoir Ma 5-2, the thickness of the non-reservoir aluminous mudstone, and the thickness of the lower Paleozoic reservoir caprock Ma 6 at the known wells according to the drilling data of the known wells in a certain target area A, and then determine the reservoir structure K of dolomite at each known well. Each reservoir structure corresponds to a fitting coefficient α, as shown in Table 3:

[0078] Table 3 List of reservoir structures and fitting coefficients

[0079]

[0080]

[0081] The data in Table 3 are represented by curves as Figure 2 shown. Figure 2 The upper curve is the curve after normalizing the fitting coefficient, and the lower curve is the reservoir structure curve. Combining with other data in Table 3, it can be seen that there is a good correlation between the reservoir structure K of dolomite and the fitting coefficient. Therefore, the second corresponding relationship between the reservoir structure K and the fitting coefficient is obtained.

[0082] 3) Obtain the pre-stack seismic data of each CMP point in the target area, fit the pre-stack seismic data according to the first corresponding relationship, and obtain the fitting coefficients of the corresponding each CMP point.

[0083] 4) Determine the dolomite reservoir structure of the target area according to the fitting coefficient and the second corresponding relationship.

[0084] The present invention can make a good indicative prediction of the reservoir structure around the local well area. The present invention indicates the reservoir structure well through the characteristics of the frequency change when seismic waves propagate in the reservoir structure, and has the characteristics of being robust, independent, and reliable.

[0085] Embodiment of the dolomite reservoir structure identification device:

[0086] The dolomite reservoir structure identification device, as Figure 3 shown, includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the dolomite reservoir structure identification method.

[0087] The specific implementation process and effects of the dolomite reservoir structure identification method are introduced in the above embodiments of the dolomite reservoir structure identification method, and will not be elaborated here.

[0088] That is to say, the method in the above embodiments of the dolomite reservoir structure identification method should be understood that the process of the dolomite reservoir structure identification method can be implemented by computer program instructions. These computer program instructions can be provided to a processor (such as a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices, etc.), so that by executing these instructions by the processor, the functions specified by the above method process are generated.

[0089] The processor referred to in this embodiment refers to a processing device such as a microprocessor MCU or a programmable logic device FPGA;

[0090] The memory referred to in this embodiment is used to store the computer program instructions formed for implementing the dolomite reservoir structure identification method, including a physical device for storing information, usually storing the information after digitization and then using a medium such as electricity, magnetism, or optics. For example: various memories that store information by electrical energy, such as RAM, ROM, etc.; various memories that store information by magnetic energy, such as hard disks, floppy disks, magnetic tapes, magnetic core memories, bubble memories, USB flash drives; various memories that store information by optical means, such as CDs or DVDs. Of course, there are also other types of memories, such as quantum memories, graphene memories, and so on.

[0091] The dolomite reservoir structure identification device composed of a memory storing computer program instructions for implementing the dolomite reservoir structure identification method and a processor is implemented in a computer by the processor executing corresponding program instructions. The computer can use the Windows operating system, Linux system, or others, such as implementing in an intelligent terminal using Android, iOS system programming languages, and implementing based on the processing logic of a quantum computer, etc. As other embodiments, the dolomite reservoir structure identification device may further include other processing hardware, such as a database or a multi-level cache, GPU, etc. The present invention does not specifically limit the structure of the dolomite reservoir structure identification device.

Claims

1. A method for identifying the structure of a dolomite reservoir, characterized in that, Including the following steps: 1) Obtain the pre-stack seismic data of each CMP point in the target area, where the pre-stack seismic data includes different propagation distances of seismic waves and the frequencies corresponding to the propagation distances; 2) Fit the different propagation distances of seismic waves and the frequencies corresponding to the propagation distances according to the first correspondence relationship to obtain the fitting coefficient; the first correspondence relationship is the correspondence relationship between the propagation distance and the frequency; The first correspondence relationship is obtained according to the seismic wave amplitude propagation principle and the seismic energy principle; 3) Establish a second correspondence relationship based on the fitting coefficient and the reservoir structure of dolomite. The process of establishing the second correspondence relationship is as follows: Determine the thickness of reservoir Ma51, the thickness of reservoir Ma52, the thickness of non-reservoir aluminous mudstone, and the thickness of Lower Paleozoic reservoir cap rock Ma6 at the known well in the dolomite reservoir according to the drilling data of the known well in the target area; at the same time, obtain the fitting coefficient corresponding to the known well according to the pre-stack seismic data of the CMP point near the known well and the first correspondence relationship; Determine the reservoir structure of dolomite at the known well according to the thickness of reservoir Ma51, the thickness of reservoir Ma52, the thickness of non-reservoir aluminous mudstone, and the thickness of Lower Paleozoic reservoir cap rock Ma6; Establish a second correspondence relationship according to the fitting coefficient corresponding to the known well and the reservoir structure of dolomite at the known well; 4) Determine the reservoir structure of dolomite in the target area according to the fitting coefficient obtained in step 2) and the second correspondence relationship established in step 3).

2. The dolomite reservoir structure identification method according to claim 1, characterized in that The first correspondence relationship is: Among them, f is the frequency; α is the fitting coefficient; r is the propagation distance of the seismic wave; E1 is the corrected seismic energy.

3. The dolomite reservoir structure identification method according to claim 1, characterized in that The reservoir structure of dolomite is: K = m5 12 / (T9 + m6 + m5 12 ); Among them, K is the reservoir structure of dolomite; m6 is the thickness of the Lower Paleozoic reservoir caprock Maliu; m5 12 is the sum of the thicknesses of reservoir Mawuyi and reservoir Mawuer; T9 is the thickness of the non-reservoir aluminous mudstone.

4. The dolomite reservoir structure identification method according to claim 2, characterized in that, The fitting coefficient is the attenuation coefficient in the propagation process of the seismic wave amplitude. The seismic wave amplitude propagation principle is: A = A0e -αr ; Among them, A is the amplitude of the seismic wave at the propagation distance r; A0 is the initial amplitude of the seismic wave; α is the attenuation coefficient; r is the propagation distance of the seismic wave.

5. The dolomite reservoir structure identification method according to claim 2, characterized in that The corrected seismic energy is obtained according to the seismic energy before correction. The seismic energy before correction is: E ∝ ρA 2 f 2 W; Among them, E is the seismic energy before correction; ρ is the medium density; A is the amplitude of the seismic wave at the propagation distance r; f is the frequency; W is the volume of the propagation medium.

6. The dolomite reservoir structure identification method according to claim 5, characterized in that The relationship between the corrected seismic energy and the seismic energy before correction is: Among them, E1 is the corrected seismic energy; E is the seismic energy before correction; ρ is the medium density; A0 is the initial amplitude of the seismic wave.

7. A dolomite reservoir structure identification device, characterized in that, Including a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the dolomite reservoir structure identification method according to any one of claims 1-6.

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