Patent Application
20230358918
The application claims priority to Chinese patent application No. 2022103441180, filed on Apr. 2, 2022, the entire contents of which are incorporated herein by reference.
The present invention belongs to the technical field of marine exploration, in particular to a forward physical simulation method for seismic response characteristics of a marine natural gas hydrate system.
Natural gas hydrates contain a lot of methane resources, about twice that of traditional conventional energy resources. They are considered to be a clean future new energy type with great potential, so they have been widely studied by scholars in China and abroad. The quantity of resources of the natural gas hydrates in Chinese offshore areas is as high as more than 80 billion tons of oil equivalents. In 2017, the natural gas hydrates were listed as the 173rd mineral variety in China by the Ministry of Natural Resources, while their commercial exploration, development and effective utilization, as a potential alternative energy type, are of great significance to relief of energy pressure in China.
In current research, seismic data are the most important data type used in the research of a natural gas hydrate system. Because of characteristics such as covering of three-dimensional space, low cost and high efficiency of delineating subsurface features, seismic data can provide cost-effective exploration services for hydrate development areas, which therefore have been most widely used in the field of natural gas hydrate research at present. Seismic research of the natural gas hydrate system means that staffs provide seismic interpretation, attribute analysis, inversion prediction, etc. to identify the natural gas hydrate system, including a hydrate-bearing reservoir, a Bottom Simulating Reflection (BSR) which indicates the base of a gas hydrate stability zone (GHSZ), and an underlying free gas zone (FGZ) below the BSR. It is generally considered that a BSR (Bottom Simulating Reflection) is a seismic sign of the bottom interface of the natural gas hydrate stability zone, which has the characteristics of high amplitude, negative in polarity, substantially parallel to a seabed, crosscutting isochronous strata. Marine natural gas hydrates usually exist in the shallow fine-grained, unconsolidated sediments, mostly argillaceous siltstone and fine-grained sandstone. Due to the cementation effect of the natural gas hydrates and existence of underlying free gas, petrophysical properties of a sedimentary stratum where the natural gas hydrate system is located are quite different from those of surrounding strata. Generally speaking, hydrate-bearing reservoirs are considered to have characteristics of high resistivity, high transverse wave and longitudinal wave speeds, low density, etc. In seismic data, gas hydrates are usually considered to manifest certain seismic response characteristics such as a high amplitude, an amplitude blank area, BSR, etc., while the underlying free gas zone (FGZ) shows high amplitude abnormal reflection directly blocked by the BSR. These characteristics mentioned above are widely applied in geophysical identification of the natural gas hydrates.
But in fact, it is still controversial whether there is a one-to-one corresponding relationship between a seismic reflection event and a real phase interface of the hydrate system (such as an interface between the hydrate-bearing stratum and the top and bottom of the underlying free gas) and whether a position of BSR directly indicates the bottom interface of the natural gas hydrate stability zone. In addition, distribution patterns of the natural gas hydrates in different sedimentary strata are variable controlled by different geological structures, gas source conditions, temperatures and pressures in the process of reservoir formation. Therefore, it is necessary to explore the seismic response characteristics corresponding to hydrate/free gas geological models with different saturations, and clarify the corresponding relationship between the seismic response characteristics and reservoir physical properties of the hydrate system (a hydrate reservoir and a free gas reservoir).
At present, forward research in the exploration field is mainly about conventional oil and gas reservoirs, with the aim of establishing a one-to-one corresponding relationship between the seismic reflection event and the underground real stratum interface. Through investigation of a large number of domestic and foreign literatures, it is found that there is little research work has been carried out on forward simulation performed on the natural gas hydrate system. At present, the forward simulation of the natural gas hydrate system is mainly based on numerical simulation; and forward physical simulation aiming at discovering the seismic response characteristics of the natural gas hydrates basically belongs to a research blank zone. In addition to a cost factor, another factor that restricts the forward physical simulation of the hydrates is core manufacturing. Usually, the natural gas hydrates exist in loose sediments with high porosity and semi-consolidation, and are mostly argillaceous cemented siltstone and fine siltstone, with a shallow burial depth, poor diagenesis, a low cementation degree and a very loose structure. However, the porosity of core samples manufactured by an existing artificial sandstone technology is generally below 30%; and they are completely consolidated samples, which have some shortcomings such as large differences, small sizes and poor pore uniformity compared with physical parameters of in-situ strata. Therefore, in order to solve above problems, it is necessary to explore a preparation technology of artificial sandstone with high porosity and weak cementation.
Based on above analysis, problems and defects existing in this research field are summarized as follows:
Aiming at the problems existing in this research field, the present invention provides a forward physical simulation method for seismic response characteristics of a marine natural gas hydrate system.
The present invention is implemented as follows: a forward physical simulation method for seismic response characteristics of a marine natural gas hydrate system comprises: comprehensively interpreting various data aiming at natural gas hydrate systems in different research areas; establishing a physical model according to an interpretation result of distribution characteristics of each hydrate system; simulating launching and receiving of seismic shot points; simulating seismic response characteristics of natural gas hydrates and underlying free gas; and correcting a seismic interpretation result of the natural gas hydrate system according to a forward physical simulation result, so that forward physical simulation of the marine natural gas hydrate system is realized.
Further, the forward physical simulation method for the seismic response characteristics of the marine natural gas hydrate system further comprises:
Specifically, the seismic response characteristics include seismic response characteristics of top and bottom interfaces of a hydrate-bearing reservoir, seismic response characteristics of top and bottom interfaces of a free gas-bearing reservoir, and whether a bottom interface of a natural gas hydrate stability zone between the hydrate-bearing reservoir and the underlying free gas reservoir strictly corresponds to BSR seismic reflection characteristics.
Further, the forward physical simulation method for the seismic response characteristics of the marine natural gas hydrate system further comprises the following steps:
Further, in step 2, according to characteristics that the hydrate is an organic crystal material, is in a solid state at normal temperature and pressure, can be prepared into powder, has similar elastic parameters to the hydrate, and has a high speed and low density, an alternative material highly similar to the natural gas hydrate is selected; and the reservoir speed and density parameters are analyzed.
Specifically, loose sediments have the characteristics of good porosity and relatively low speeds of longitudinal and transverse waves. After many tests, conditions of a small diagenetic pressure of 0.5-1.0 MPa, a low cement content of 5% and containing of formation water are finally selected for diagenesis; and the cores meeting requirements of the hydrate reservoirs are manufactured.
Further, a manufacturing method of the natural gas hydrate reservoir core in step 3 comprises the following steps:
Compared with the manufacturing method of the hydrate reservoir core sample, the artificial core sample of the free gas-bearing reservoir does not add the single crystal material, including stirring, pressing, firing, demolding and baking to complete a diagenetic process.
Further, in step 5, according to seismic main frequency and wavelet length parameters of the specific study area, relevant physical simulation parameters are set. For example: a longitudinal wave speed of the hydrate reservoir core is 2780 m/s; a transverse wave speed is 1790 m/s; a longitudinal wave speed of the free gas reservoir is 1780 m/s; a transverse wave speed is 1190 m/s; a dimension scale factor is set to 1:10000; a speed scale factor is 1:1; and a frequency scale factor is 10000:1. Sediment 1: a longitudinal wave speed is 2000 m/s; and a transverse wave speed is 1010 m/s. Sediment 2: a longitudinal wave speed is 2650 m/s; and a transverse wave speed is 1350 m/s.
Other parameters are set according to most natural gas hydrate stratum data in the research area. For example, a water depth can be set to 80 mm, which is equivalent to actual 800 m; the main frequency is 17 Hz; the number of shot points is 200; the number of channels received is 221; and a channel distance is 1 mm, which is equivalent to actual 10 m.
In an embodiment, the size of the stratum containing the natural gas hydrate and the free gas is set to 110 mm*30 mm, which is equivalent to actual 1100 m*300 m; and the overall size of the model is 300 mm*90 mm, which is equivalent to actual 3000 m*900 m.
Another purpose of the present invention is to provide a forward physical simulation system for seismic response characteristics of a marine natural gas hydrate system, which applies the forward physical simulation method for the seismic response characteristics of the marine natural gas hydrate system. The system comprises:
Further another purpose of the present invention is to provide a computer device, which comprises a memory and a processor, wherein the memory stores a computer program; and when the computer program is executed by the processor, the processor is made to perform the following steps:
Further another purpose of the present invention is to provide a computer-readable storage medium which stores a computer program, wherein when the computer program is executed by a processor, the processor is made to perform the following steps:
Further another purpose of the present invention is to provide an information data processing terminal, which is used to realize the forward physical simulation system for the seismic response characteristics of the marine natural gas hydrate system.
In combination with the above technical solution and the technical problems solved, please analyze advantages and positive effects of the technical solution to be protected by the present invention from the following aspects:
The method for forward forecasting the seismic response characteristics of the natural gas hydrates by using laboratory physical simulation provided by the present invention analyzes relationships between seismic amplitudes, waveforms or the like and saturation, thickness and occurrence areas of the natural gas hydrates, explores the seismic response characteristics and modes of geological models of different natural gas hydrate systems, and guides identification and characterization of the natural gas hydrate systems in seismic interpretation work according to the forward physical simulation result.
The present invention provides a method for performing forward physical simulation research on the seismic response characteristics of the marine natural gas hydrate system. Aiming at special rock geophysical characteristics of the natural gas hydrate and underlying free gas reservoirs, the preparation technology of the artificial sandstone with the high porosity and weak cementation is developed; tests are performed mainly from aspects of diagenetic pressure, rock composition, particle size, cementation type and content, formation water content, etc.; and the appropriate cores meeting the requirements of the hydrate reservoirs are selected. Firstly, through the preparation technology of the artificial sandstone with the high porosity and weak cementation, after testing of the porosity repeatability, sample homogeneity and sample stability, the natural gas hydrate reservoir core and the free gas reservoir core that meet the requirements can be established; secondly, the dimension scale factor, the speed scale factor, frequency scale factor or the like are set; and the specific parameters of sedimentary strata are set according to the research areas, so as to establish the physical model of the natural gas hydrate and underlying free gas strata; and finally, a sedimentary model is established in the water tank with the device for simulating launching and receiving of the seismic shot points, so as to perform the seismic forward physical simulation. The method provided by the present invention can be used for analyzing research on the seismic response characteristics of the natural gas hydrate/underlying free gas geological models with different saturations; the geological model is established according to the real geophysical parameters of the specific study area; an arrangement manner of a seismic source and a geophone is close to an actual field acquisition mode; physical simulation work is performed by using a piezoelectric ultrasonic transducer; and according to the forward simulation result of the seismic response characteristics of the models containing the natural gas hydrates and free gas, the seismic interpretation result of the natural gas hydrate system in the corresponding study area is corrected so as to improve interpretation accuracy.
The seismic response characteristics obtained by the physical model provided by the present invention are as follows: a BSR interface shows obvious negative polarity, a high amplitude and a beveling stratum opposite to a seabed, which represents a phase interface between a hydrate stratum and a free gas stratum; a top interface of the upper hydrate-bearing stratum has positive polarity and a strong amplitude; and however, an amplitude of the underlying free gas bottom interface is relatively weak.
Secondly, regarding the technical solution as a whole or from the point of view of products, technical effects and advantages of the technical solution to be protected by the present invention are specifically described as follows:
The forward physical simulation method for the seismic response characteristics of the marine natural gas hydrate system provided by the present invention belongs to preliminary exploration and research under a background that forward physical simulation of the natural gas hydrate systems in China and abroad is in a primary stage, and has important guiding significance.
Thirdly, as creative auxiliary evidence of the claims of the present invention, it is also reflected in the following important aspects:
In order to explain the technical solution of embodiments of the present invention more clearly, drawings needing to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention; and other drawings can be obtained by those ordinarily skilled in the art according to these drawings without doing creative work.
In the figures: 1. initial geological model establishment module; 2. reservoir core manufacturing module; 3. artificial core testing module; 4. parameter setting module; 5. model establishment module; and 6. seismic forward simulation module.
In order to make the purposes, technical solution and advantages of the present invention clearer, the present invention will be further described below in detail in conjunction with embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but are not used to limit the present invention.
Aiming at the problems existing in this research filed, the present invention provides a forward physical simulation method for seismic response characteristics of a marine natural gas hydrate system; and the present invention will be described in detail with the drawings.
1. Embodiment explanation and illustration. In order to make those skilled in the art fully understand how to specifically implement the present invention, this part is an explanatory embodiment to illustrate the technical solution of the claims.
Term explanation: a natural gas hydrate is an ice-like crystalline substance formed by hydrocarbon gases such as methane and water at conditions of a high pressure and a low temperature. Because of low permeability of hydrate-bearing layers, the natural gas hydrate can be used as a seal layer to trap free gas in the lower part. BSR (bottom simulating reflection) is considered as a seismic sign of a bottom interface of a natural gas hydrate stability zone and has the characteristics of being strong in amplitude, negative in polarity, substantially parallel to a seabed, beveling in isochronous strata etc. Forward simulation: in geophysical exploration research, according to geophysical parameters such as the shape of a target geological body, physical parameters and an acoustic wave speed, by establishing a numerical model or a physical model, theoretical seismic response characteristics are calculated or actual seismic response characteristics generated thereby are observed, which is called forward simulation.
As shown in
As shown in
The present invention provides a forward physical simulation method for research on the seismic response characteristics of the marine natural gas hydrate system, which performs seismic forward simulation by establishing the physical model meeting geophysical characteristics of reservoirs of the natural gas hydrate system, and establishes relationship research between each interface in the natural gas hydrate system and the seismic response characteristics. Specifically, the characteristics include (1) seismic response characteristics of top and bottom interfaces of a hydrate-bearing reservoir, (2) seismic response characteristics of top and bottom interfaces of a free gas-bearing reservoir, and (3) whether a bottom interface of a natural gas hydrate stability zone between the hydrate-bearing reservoir and the underlying free gas reservoir strictly corresponds to BSR seismic reflection characteristics. The method can establish different physical models for distribution characteristics of hydrate systems in different research areas, perform research on the seismic response characteristics of the natural gas hydrates and underlying free gas, and correct a previous seismic interpretation result of the natural gas hydrate system according to a forward physical simulation result. Specific method steps are:
The seismic response characteristics obtained by the physical model are as follows: a BSR interface shows obvious negative polarity, a high amplitude and a beveling stratum opposite to a seabed, which represents a phase interface between a hydrate stratum and a free gas stratum; a top interface of the upper hydrate-bearing stratum has positive polarity and a strong amplitude; and however, an amplitude of the underlying free gas bottom interface is relatively weak.
2. Embodiment application. In order to prove creativity and technical values of the technical solution of the present invention, this part is an application embodiment of the technical solution of the claims in specific products or related art.
The physical model established by the embodiment of the present invention is shown in
Finally, the seismic response characteristics obtained from this physical model are as follows: the BSR interface is horizontally distributed, which is consistent with the phase interface between a hydrate stratum and a free gas stratum in an actual geological model; the BSR characteristics show obvious negative polarity, a high amplitude and a beveling stratum opposite to a seabed; a top interface of the upper hydrate-bearing stratum has positive polarity and a strong amplitude; and however, an amplitude of the underlying free gas bottom interface is relatively weak.
It should be noted that implementations of the present invention can be realized by hardware, software, or a combination of software and hardware. The hardware part can be realized by special logic; and the software part can be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or specially designed hardware. Those skilled in the art can understand that the above-mentioned devices and methods can be implemented using computer-executable instructions and/or containing in a processor control code. For example, such code is provided on a carrier medium of a magnetic disk, a CD or a DVD-ROM or the like, a programmable memory such as a read-only memory (firmware) or a data carrier such as an optical or electronic signal carrier. The device and modules thereof of the present invention can be realized by VLSI or gate arrays or the like, semiconductors such as logic chips and transistors, or hardware circuits of programmable hardware devices such as field programmable gate arrays and programmable logic devices, or by software executed by various types of processors, or by a combination of the above hardware circuits and software such as firmware.
3. Evidence of relevant effects of the embodiment. The embodiment of the present invention has achieved some positive effects in the process of research and development or use, and has great advantages compared with the prior art. The following contents are described in combination with data, charts and the like during the test.
The forward physical simulation result of the embodiment shows that the seismic response characteristics obtained by the physical model show that the BSR interface is horizontally distributed, which is consistent with the phase interface between the hydrate stratum and the free gas stratum in the actual geological model. In addition, the seismic reflection characteristics of the top and bottom interfaces of the hydrate reservoir in the hydrate system are obvious. The BSR characteristics show obvious negative polarity, a high amplitude and a beveling stratum opposite to a seabed; a top interface of the upper hydrate-bearing stratum has positive polarity and a strong amplitude without occurrence of a blank reflection zone proposed by predecessors; and however, an amplitude of the underlying free gas bottom interface is relatively weak, which may be related to setting of the petrophysical parameters of the free gas.
The above is only the specific implementation of the present invention, but the protection scope of the present invention is not limited to this. Any modification, equivalent substitution and improvement or the like made by any of those skilled and familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be included in the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022103441180 | Apr 2022 | CN | national |
