970 resultados para Waveform inversion
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Crosshole Seismic tomography has been broadly studied and applied in the fields of resource exploration and engineering exploration because of its special observing manner and better resolution than normal seismic exploration. This thesis will state the theory and method of Crosshole Seismic tomography. Basing on the previous studies,the thesis studied the initial velocity model,ray-tracing method, and developed the three-dimension tomography software. All the cells that a ray passes through are of the same velocities if the paths from transmitters to receivers are straight. The cells that the each ray passes through are recorded, and rays that pass through each cell are calculated. The ray average velocity which passes through a cell is set as the cell velocity. Analogously we can make a initial node velocity model because the velocity sum is calculated on the all cells which own to a certain node, and the cell number is summed about each nodes,the ratio of the velocity sum to the all cells number is set as the node velocity. The inversion result from the initial node velocity model is better than that of the average velocity model. Ray-bending and Shortest Path for Rays (SPR) have shortcomings and limitations respectively. Using crooked rays obtained from SPR rather than straight lines as the starting point can not only avoid ray bending converging to the local minimum travel time path, but also settle the no smooth ray problem obtained by SPR. The hybrid method costs much computation time, which is roughly equal to the time that SPR expends. The Delphi development tool based on the Object Pascal language standard has an advantage of object-oriented. TDTOM (Three Dimensions Tomography) was developed by using Delphi from the DOS version. Improvement on the part of inversion was made, which bring faster convergence velocity. TDTOM can be used to do velocity tomography from the first arrival travel time of the seismic wave, and it has the good qualities of friendly user interface and convenient operation. TDTOM is used to reconstruct the velocity image for a set of crosshole data from Karamay Oil Field. The geological explanation is then given by comparing the inversion effects of different ray-tracing methods. High velocity zones mean the cover of oil reservoir, and low velocity zones correspond to the reservoir or the steam flooding layer.
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Ray tracing is a rapid and effective method for wave field calculation. Not only in the field of seismic-wave theory, but also in the field of seismic inversion and migration imaging,the seismic ray tracing method has become one of the most important methods. In anisotropic media, group velocity and phase velocity have different propagation directions. The seismic wave propagates along the direction of group velocity , it does not depend on the direction of phase velocity. Ray angle is a complex function with respect to phase angle, it is difficult to measure and calculate. But most rocks are weak anisotropic, so the expression of phase velocity can be simplified greatly. Based on the approximate expression of phase velocity this thesis for rotating axisymmetric weak anisotropic media deduces an expression of the partial derivative of phase velocity and an expression of group velocity with the method of linear approximation. This paper uses the fourth order Runge-Kutta method together with the two-dimensional interpolation and linear interpolation to obtain the parameters of the physical locations. At last the paths of seismic wave in rotating axisymmetric weak anisotropic media are computed. According to the analysis of the computational results, it indicates that the method developed in this paper has strong adaptability, high computational efficiency and high accuracy for rotating axisymmetric weak anisotropic media.
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With the develop ment of oil and gas exploration, the conventional struc ture exploration era has gradually been substituted by the concealed reser voir exploration technology. Hill poll becomes one of the most important areas in the future exploration. This paper is based on the three-dimensional seismic interpretation of Sudeerte structure. In terms of the overall character istics of Sudeerte structure, we use the coherent cube and the time slice to interpret the fault in plane. For the interpretation,we especially used the well to adjust the interpretation results. The results of seismic attribution analysis, spectrum decomposition and post- stack seismic inversion forecast that hill pools reservoir are dist ributed in several bands along the north-northeast to northeast-east. Xing'anling Group shows that the potential reser voirs are mainly distributed along Bei 14 –Bei 40 and De (99-212) - Bei (16-1) and Budate Group distributed along Bei 14 –Bei 40 in northwestern direction and De (99-212) - Bei (16-1) in north eastern direction. At the same time, by analyzing the structure and the reservoir, and combining with other data, three models are built. The characteristics of reservoirs dist ribution are concl uded,and potent ional favorable exploration dire ctions are predi cted.
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In the practical seismic profile multiple reflections tend to impede the task of even the experienced interpreter in deducing information from the reflection data. Surface multiples are usually much stronger, more broadband, and more of a problem than internal multiples because the reflection coefficient at the water surface is much larger than the reflection coefficients found in the subsurface. For this reason most attempts to remove multiples from marine data focus on surface multiples, as will I. A surface-related multiple attenuation method can be formulated as an iterative procedure. In this essay a fully data-driven approach which is called MPI —multiple prediction through inversion (Wang, 2003) is applied to a real marine seismic data example. This is a pretty promising scheme for predicting a relative accurate multiple model by updating the multiple model iteratively, as we usually do in a linearized inverse problem. The prominent characteristic of MPI method lie in that it eliminate the need for an explicit surface operator which means it can model the multiple wavefield without any knowledge of surface and subsurface structures even a source signature. Another key feature of this scheme is that it can predict multiples not only in time but also in phase and in amplitude domain. According to the real data experiments it is shown that this scheme for multiple prediction can be made very efficient if a good initial estimate of the multiple-free data set can be provided in the first iteration. In the other core step which is multiple subtraction we use an expanded multi-channel matching filter to fulfil this aim. Compared to a normal multichannel matching filter where an original seismic trace is matched by a group of multiple-model traces, in EMCM filter a seismic trace is matched by not only a group of the ordinary multiple-model traces but also their adjoints generated mathematically. The adjoints of a multiple-model trace include its first derivative, its Hilbert transform and the derivative of the Hilbert transform. The third chapter of the thesis is the application for the real data using the previous methods we put forward from which we can obviously find the effectivity and prospect of the value in use. For this specific case I have done three group experiments to test the effectiveness of MPI method, compare different subtraction results with fixed filter length but different window length, invest the influence of the initial subtraction result for MPI method. In terms of the real data application, we do fine that the initial demultiple estimate take on a great deal of influence for the MPI method. Then two approaches are introduced to refine the intial demultiple estimate which are first arrival and masking filter respectively. In the last part some conclusions are drawn in terms of the previous results I have got.
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Scale matching method means adjusting information with different scale to the same level. This thesis focuses on scale unification of information with different frequency bandwidth. Well-seismic cooperate inversion is an important component of reservoir geophysics; multiple prediction & subtraction is a development of multiple attenuation in recent years. The common ground of these two methods is that they both related to different frequency bandwidth unification. Well log、cross-hole seismic、VSP、3D seismic and geological information have different spatial resolution, we can decrease multi-solution of reservoir inversion and enhance the vertical and lateral resolution of the geological object by integrate those information together; Compare the predicted multiple generated by SRME with the real multiple, we find the predicted multiple convolutes at least one wavelet more, which brings frequency bandwidth difference between them. So the subtraction method also relates to multi-scale information unification. This thesis gives a method of well constrained seismic high resolution processing basing on auto gain control modulation. It uses base function method which utilizes original well-seismic match result as initial condition and processed seismic trace as initial model to extrapolate the high frequency information of the well logs to the seismic profiles. In this way we can broaden the bandwidth of the seismic and make the high frequency gain geological meaning. In this thesis we introduce the revised base function method to adaptive subtraction and verify the validity of the method using models. Key words: high frequency reconstruction, scale matching, base function, multiple, SRME prediction & subtraction
Resumo:
As a fast and effective method for approximate calculation of seismic numerical simulation, ray tracing method, which has important theory and practical application value, in terms of seismic theory and seismic simulation, inversion, migration, imaging, simplified from seismic theory according to geometric seismic, means that the main energy of seismic wave field propagates along ray paths in condition of high-frequency asymptotic approximation. Calculation of ray paths and traveltimes is one of key steps in seismic simulation, inversion, migration, and imaging. Integrated triangular grids layout on wavefront with wavefront reconstruction ray tracing method, the thesis puts forward wavefront reconstruction ray tracing method based on triangular grids layout on wavefront, achieves accurate and fast calculation of ray paths and traveltimes. This method has stable and reasonable ray distribution, and overcomes problems caused by shadows in conventional ray tracing methods. The application of triangular grids layout on wavefront, keeps all the triangular grids stable, and makes the division of grids and interpolation of a new ray convenient. This technology reduces grids and memory, and then improves calculation efficiency. It enhances calculation accuracy by accurate and effective description and division on wavefront. Ray tracing traveltime table, which shares the character of 2-D or 3-D scatter data, has great amount of data points in process of seismic simulation, inversion, migration, and imaging. Therefore the traveltime table file will be frequently read, and the calculation efficiency is very low. Due to these reasons, reasonable traveltime table compression will be very necessary. This thesis proposes surface fitting and scattered data compression with B-spline function method, applies to 2-D and 3-D traveltime table compression. In order to compress 2-D (3-D) traveltime table, first we need construct a smallest rectangular (cuboidal) region with regular grids to cover all the traveltime data points, through the coordinate range of them in 2-D surface (3-D space). Then the value of finite regular grids, which are stored in memory, can be calculated using least square method. The traveltime table can be decompressed when necessary, according to liner interpolation method of 2-D (3-D) B-spline function. In the above calculation, the coefficient matrix is stored using sparse method and the liner system equations are solved using LU decomposition based on the multi-frontal method according to the sparse character of the least square method matrix. This method is practiced successfully in several models, and the cubic B-spline function can be the best basal function for surface fitting. It make the construction surface smooth, has stable and effective compression with high approximate accuracy using regular grids. In this way, through constructing reasonable regular grids to insure the calculation efficiency and accuracy of compression and surface fitting, we achieved the aim of traveltime table compression. This greatly improves calculation efficiency in process of seismic simulation, inversion, migration, and imaging.
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Reservoir prediction techniques from prestack seismic are among the most important ones for exploration of lithologic hydrocarbon reservoir. In this paper, we set the turbidite fan sandstone reservoir in Liao-Zhong depress as our researching target, and aims to solve the apllication difficulties on pre-stack inversion in the area, where the drilling data is scarce and the reservoir is lateral varied. Meanwhile, AVO analysis and pre-stack inversion for gas-bearing detection is systematically researched. The seismic reflection characters of gas-bearing sandstone in turbidite fan with different fluid content are defined, after analyzing results from AVO seismic simulation and porous fluid replacement of real log data, and under the guides of the seismic characters from classical gas-bearing sandstone reservoir and numerical simulation for complicate gas-bearing sandstone. It is confirmed that detecting gas-bearing sandstone in turbidite fan via AVO technologies is feasible. In terms of AVO analysis, two AVO characters, fluid detection factor and product of intercept and gradient, can effectively identify top and bottom boundaries and lateral range of tuibidite gas sand by comparing real drilling data. Cross-plotting of near and far angle stack data could avoid the correlation existing in P-G analysis. After comparing the acoustic impedance inversions with routine stacked data and AVO intercept, impedance derived from AVO intercept attribute could reduce the acoustic impedance estimating error which is caused by AVO. On the aspect of elastic impedance inversion, the AVO information in the pre-stack gathers is properly reserved by creating partial angle stack data. By the far angle elastic impedance alone, the gas sand, with abnormally low range of values, can be identified from the background rocks. The boundary of gas sand can also be clearly determined by cross-plotting of near and far angle elastic impedances. The accuracy of far angle elastic impedance is very sensitive to the parameter K, and by taking the statistical average of Vp/Vs on the targeted section in key wells, the accuracy of low frequency trends is gurranteed; the intensive absorsion within the area of the gas sand, which tends to push the spectral of seismic data to the lower end, will cause errors on the inversion result of elastic impedance. The solution is to confine the inversion on the interested area by improving the wavelet. On the aspect of prestack AVA simultaneous inversion, the constraint of local rock-physical trends between velocities of P-wave、S-wave and density successfully removes the instability of inversion, thus improves the precision of the resulting elastic parameters. Plenty of data on rock properties are derived via AVO analysis and prestack seismic data inversion. Based on them, the fluid anomaly is analysized and lithological interpretation are conducted. The distribution of gas sand can be consistently determined via various of ways, such as cross-plotting of P and G attributes, near and far partial angle stack data, near and far angle elastic impedances, λρ and Vp/Vs, etc. The shear modulo and density are also reliable enough to be used for lithological interpretation. We successfully applied the AVO analysis and pre-stack inversion techniques to gas detecting for turbidite fan sand reservoir in Liao-Zhong depression.
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Multi-waves and multi-component get more and more attentions from oil industry. On the basis of existent research results, My research focuses on some key steps of OBC 4C datum processing. OBC datum must be preprocessed quite well for getting a good image. We show a flow chart of preprocess including attenuation of noise on multi-component datum、elimination ghost by summing P and Z and rotation of horizontal components. This is a good foundation for the coming steps about OBC processing. How to get exact converted point location and to analyze velocity are key points in processing reflection seismic converted wave data. This paper includes computing converted point location, analyzing velocity and nonhyperbolic moveout about converted waves. Anisotropic affects deeply the location of converted wave and the nonhyperbolic moveout. Supposed VTI, we research anisotropic effect on converted wave location and the moveout. Since Vp/Vs is important, we research the compute method of Vp/Vs from post-stack data and pre-stack data. It is a part of the paper that inversing anisotropic parameter by traveltime. Pre-stack time migration of converted wave is an focus, using common-offset Kirchhoff migration, we research the velocity model updating in anisotropic media. I have achieved the following results: 1) using continued Fractions, we proposed a new converted point approximate equation, when the offset is long enough ,the thomsen’s 2 order equation can’t approximate to the exact location of converted point, our equation is a good approximate for the exact location. 2) our new methods about scanning nonhyperbolic velocity and Vp/Vs can get a high quality energy spectrum. And the new moveout can fit the middle and long offset events. Processing the field data get a good result. 3) a new moveout equation, which have the same form as Alkhalifah’s long offset P wave moveout equation, have the same degree preciseness as thomsen’s moveout equation by testing model data. 4) using c as a function of the ratio offset to depth, we can uniform the Li’s and thomsen’s moveout equation in a same equation, the model test tell us choice the reasonable function C can improve the exact degree of Li’s and thomsen’s equation. 5) using traveltime inversion ,we can get anisotropic parameter, which can help to flat the large offset event and propose a model of anisotropic parameter which will useful for converted wave pre-stack time migration in anisotropic media. 6)using our pre-stack time migration method and flow, we can update the velocity model and anisotropic parameter model then get good image. Key words: OBC, Common converted Point (CCP), Nonhyperbolic moveout equation, Normal moveout correction, Velocity analysis, Anisotropic parameters inversion, Kirchhoff anisotropic pre-stack time migration, migration velocity model updating
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The central-south Tibet is a part of the products of the continental plate collision between Eurasia and India. To study the deep structure of the study area is significant for understanding the dynamics of the continental-continental collision. A 3-D density model matched well with the observations in the central-south Tibet was proposed in this study. In addition, this study has also used numerical simulation method to prove that Quasi-Love (QL) wave is deduced by anisotropy variation but not by lateral heterogeneity. Meanwhile, anisotropy variation in the upper mantle of the Qiangtang terrane and Lhasa terrane is detected by the QL waves observed in recorded seismograms. Based on the gravity modeling, some results are summarized as follows: 1) Under the constrain of geometrical structure detected by seismic data, a 3-D density model and Moho interface are proposed by gravity inversion of the central-south Tibet. 2) The fact that the lower crustal densities are smaller than 3.2 g/cm3, suggests absence of eclogite or partial eclogitization due to delamination under the central-south Tibet. 3) Seismicity will be strong or weak in the most negative Bouguer gravity anomaly. So there is no a certain relationship between seismicity and Bouguer gravity anomaly. 4) Crustal composition are determined after temperature-pressure calibration of seismic P wave velocity. The composition of lower crust might be one or a mixture of: 1. amphibolite and greenschist facies basalt beneath the Qiangtang terrane; 2. gabbro-norite-troctolite and mafic granulite beneath the Lhasa terrane. Because the composition of the middle crust cannot be well constrained by the above data set, the data set published by Rudnick & Fountain (1995) is used for comparison. It indicated the composition of the middle crust is granulite facies and might be pelitic gneisses.Granulite facies used to be interpreted as residues of partial melting, which coincidences with the previous study on partial melting middle crust. Amphibolite facies are thought to be produced after delamination, when underplating works in the rebound of the lower crust and lithospheric mantle. From the seismology study, I have made several followed conclusions: 1) Through the numerical simulation experiment of surface wave propagating in heterogeneity media, we can find that amplitude and polarization of surface wave only change a little when considering heterogeneity. Furthermore, it is proved that QL waves, generated by surface wave scattering, are caused by lateral variation of anisotropy but not by heterogeneity. 2) QL waves are utilized to determine the variation of uppermost mantle anisotropy of the Tibetan plateau. QL waves are identified from the seismograms of the selected paths recorded by the CAD station. The location of azimuth anisotropy gradient is estimated from the group velocities of Rayleigh wave, Love wave and QL wave. It suggests that south-north lateral variation of azimuthal anisotropy locates in Tanggula mountain, and east-west lateral variation in the north of Gandese mountain with 85°E longitude and near the Jinsha river fault with 85°E longitude.
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Pre-stack seismic inversion has become the emphasis and hotspot owing to the exploration & exploitation of oil field and the development of seismic technology. Pre-stack seismic inversion has the strongpoint of making the most of amplitude versus offset compared with the post-stack method. In this dissertation, the three parameters were discussed from multi-angle reflectance of P-wave data based on Zoeppritz’s and Aki & Richard’s equation, include P-wave velocity, S-wave velocity, and density. The three parameters are inversed synchronously from the pre-stack multi-angle P-wave data, based on rockphysics model and aimed at the least remnant difference between model simulation and practical data. In order to improve the stability of inversion and resolution to thin bed, several techniques were employed, such as the wavelet transform with multi-scale function, adding the Bayesian soft constraint and hard constraints (the horizon, structure and so on) to the inversion process. Being the result, the uncertainty of the resolution is reduced, the reliability and precision are improved, the significance of parameters becomes clearer. Meeting to the fundamental requirement of pre-stack inversion, some research in rockphysics are carried out which covered the simulation and inversion of S-wave velocity, the influence of pore fluids to geophysical parameters, and the slecting and analyzing of sensitive parameters. The difference between elastic wave equation modeling and Zoeppritz equation method is also compared. A series of key techniques of pre-stack seismic inversion and description were developed, such as attributes optimization, fluid factors, etc. All the techniques mentioned above are assembled to form a technique sets and process of synchronous pre-stack seismic inversion method of the three parameters based on rock physics and model simulation. The new method and technology were applied in many areas with various reservoirs, obtained both geological and economic significance, which proved to be valid and rational. This study will promote the pre-stack inversion technology and it’s application in hidden reservoirs exploration, face good prospects for development and application.
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To improve the efficiency of boundary-volume integral equation technique, this paper is involved in the approximate solutions of boundary-volume integral equation technique. Firstly, based on different interpretations of the self-interaction and extrapolation operators of the resulting boundary integral equation matrix, two different hybrid BEM+Born series modeling schemes are formulated and validated through comparisons with the full-waveform BE numerical solutions for wave propagation simulation in a semicircular alluvial valley and a complex fault model respectively. Numerical experiments indicate that both the BEM+Born series modeling schemes are suitable for complex geological structures and significantly improve computational efficiency especially for the cases of high frequencies and multisource seismic survey. Then boundary-volume integral equation technique is illuminated in detail and verified by modeling wave propagation in complex media. Furthermore, the first-order and second-order Born approximate solutions for the volume-scattering waves are studied and quantified by numerical simulation in different random medium models. Finally, preconditioning generalized minimal residual method is applied to solve boundary-volume integral equation and compared with Gaussian elimination method. Numerical experiments indicate this method makes the calculations more efficient.
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Junggar Basin has a large amount of recoverable reserves, However, due to the unfavorable factors, such as bad seismic data quality, complex structure with many faults and less wells, the exploration of oil and gas is still relatively limited, so advanced theoretical guidance and effective technical supports are desirable. Based on the theories of sedimentology, as well as comprehensive studies of outcrops, seismic data, drilling data and setting of this area, the paper establishes the isochronous correlation framework, and analyzes the sedimentary facies types and provenance direction, and obtains the profile and plain maps of the sedimentary facies combined with the logging constrained inversion. Then the paper analyzes the reservoir controlling factors, reservoir lithology attribute, 4-property relationship and sensibility based on the sedimentary facies research, and sets up a 3D geological model using facies controlled modeling. Finally, the paper optimizes some target areas with the conclusions of reservoir, structure and reservoir formation.Firstly, the paper establishs the isochronous correlation framework by the seismic data, drilling data and setting of this area. The sedimentary facies in Tai13 well block are braided river and meandering river according to the analysis of the lithology attribute, logging facies and sedimentary structure attribute of outcrop. The concept of “wetland” is put forward for the first time. The provenance direction of Badaowan and Qigu formation is obtained by the geology setting, sedimentary setting and paleocurrent direction. The paper obtains the profile and plain maps of the sedimentary facies from the sand value of the wells and the sand thickness maps from the logging constrained inversion. Then, this paper takes characteristics and control factors of the Jurassic reservoirs analysis on thin section observation, scanning transmission electron microscope observation and find out the petrology characteristics of reservoir, space types of reservoir and lithofacies division. In this area, primary pores dominate in the reservoir pores, which believed that sedimentation played the most important roles of the reservoir quality and diagenesis is the minor factor influencing secondary porosity. Using stochastic modeling technique,the paper builds quantitative 3-D reservoir Parameter. Finally, combined the study of structure and reservoir formation, the reservoir distribution regularity is concluded: (a) structures control the reservoir formation and accumulation. (b) Locating in the favorable sedimentary facies belt. And the area which meets these conditions mentioned above is a good destination for exploration.
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Post-stack seismic impedance inversion is the key technology of reservoir prediction and identification. Geophysicists have done a lot of research for the problem, but the developed methods still cannot satisfy practical requirements completely. The results of different inversion methods are different and the results of one method used by different people are different too. The reasons are due to the quality of seismic data, inaccurate wavelet extraction, errors between normal incidence assumption and real situation, and so on. In addition, there are two main influence factors: one is the band-limited property of seismic data; the other is the ill-posed property of impedance inversion. Thus far, the most effective way to solve the band-limited problem is the constrained inversion. And the most effective way to solve ill-posed problems is the regularization method assisted with proper optimization techniques. This thesis systematically introduces the iterative regularization methods and numerical optimization methods for impedance inversion. A regularized restarted conjugate gradient method for solving ill-posed problems in impedance inversion is proposed. Theoretic simulations are made and field data applications are performed. It reveals that the proposed algorithm possesses the superiority to conventional conjugate gradient method. Finally, non-smooth optimization is proposed as the further research direction in seismic impedance inversion according to practical situation.
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Datuming which has not been well solved in complex areas is a long-existing problem in seismic processing and imaging. Theoretically, Wave-equation datuming(WED) works well in the areas with substantial surface topography and areas of complex velocity structure. However, many difficulties still exist in practice. There are three main reasons: (1) It’s difficult to obtain the velocity model. (2) The computational cost is high and the efficiency is low. (3) Reflection waveform distortions are introduced by low S/N ratio in seismic data. The second and third problems are involved in the paper. To improve computational efficiency, DP1 proposed by Fu Li-Yun is applied in WED. Some quantitative and semi-quantitative conclusions of assessing the computational accuracy and efficiency have been obtained by comparing the adaptation of three operators( PS, SSF, DP1) to the surface topography and the lateral velocity variation. Moreover, the impacts of near surface scattering associated with complex surface topography on WED is analyzed theoretically. According to the analysis results, the following conclusions have been obtained. WED is stable and effective when the field data has high S/N ratio and velocity model is accurate. However ,it doesn’t work well when S/N ratio of field data is low. So denoising techniques in process of WED is important for low S/N data. The paper presents the theoretical analysis for the issues facing WED, which is expected to provide a useful reference to the further development of this technology.
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With the deepening development of oil-gas exploration and the sharp rise in costs, modern seismic techniques had been progressed rapidly. The Seismic Inversion Technique extracts seismic attribute from the seismic reflection data, inverses the underground distribution of wave impedance or speed, estimates reservoir parameters, makes some reservoir prediction and oil reservoir description as a key technology of Seismic exploration, which provides a reliable basic material for oil-gas exploration. Well-driven SI is essentially an seismic-logging joint inversion. The low, high-frequency information comes from the logging information, while the structural characteristics and medium frequency band depend on the seismic data. Inversion results mainly depend on the quality of raw data, the rationality of the process, the relativity of synthetic and seismic data, etc. This paper mainly research on how the log-to-seismic correlation have affected the well-driven seismic inversion precision. Synthetic, the comparison between middle –frequency borehole impedance and relative seismic impedance and well-attribute crossplots have been taken into account the log-to-seismic correlation. The results verify that the better log-to-seismic correlation, the more reliable the seismic inversion result, through the analysis of three real working area (Qikou Sag, Qiongdongnan basin, Sulige gas field).