Geophysical inversion is a computational process to restore subsurface geological structures and petrophysical properties from observed geophysical data.This paper outlined the evolution of seismic inversion technologies, from direct inversion tomodel based inversion, from linear inversion to nonlinear inversion, and from poststack inversion to prestack inversion. The inversion of elastic impedance will be one of directions of inversion development.Seismic inversion is on the way of integrating acoustic impedance with elastic impedance.

Although some progresses have been made in reservoir prediction and description by application of seismic reservoir inversion technology, complex seismic and geological conditions and inadequate research on its application conditions impedes the wider use of this technology. Eased on a classification of available inversion methods, the author summarized the application conditions for each method through theoretical modeling and data processing practice on a large quantity of real data. The key problems in the application of inversion technologies and policies in dealing with these problems are put forward.

Based on the seismic attribute classification proposed by Quincy Chen and others for reservoir characteristics, this paper discusses the methods of seismic time window selection and attribute pretreatment. The criteria and procedure of seismic attribute effectiveness analysis and algorithms of seismic attribute optimization are presented. An example of reservoir prediction in Block Fangshen2 of Songfangtun Oilfield in Daqing is also presented in the paper. The author believes that extraction and effectiveness analysis of seismic attribute is the prerequisite for high-precise seismic reservoir prediction, therefore much attention should be devoted.

Based on analysis of elastic impedance concept,the procedure of elastic impedance inversion was presented by use of the traditional poststack seismic inversion methodology and software package because of similarity between acoustic impedance and elastic impedance definition. Synthetic gathers generated by fluid replacement modeling and seismic verified the validity and reliability of this procedure forward modeling with elastic wave equation.The potential of elastic impedance in predicting lithology and fluid properties was analyzed. In the SLG area.due to good comparability between elastic impedance log with 16 incidence angle and gamma ray log the effective reservoir can be identified by elastic impedance inversion which provides a most efficient way of seismic reservoir description.

Field statics is one of vital processing for achieving high quality stacked sections in areas with drastic topographic relief and sharp lateral variations of LVZ velocity. The determination of LVZ velocity is deemed the key to statics. Conventional methods that are on basis of refraction arrival time or microlog cannot yield proper LVZ velocity or static quantities in areas with complex near surface conditions. This paper presents an approach that derives LVZ velocity and static correction values from the arrival time of first break by using tomography technology. Shortest path ray tracing is used in the forward step and SIRT in the inversion step. Results from real data processing show that the approach can substantially improve the quality of seismic stack sections in areas with complex near surface conditions such as desert and mountainous region.

The principles of wave equation pre-stack reverse-time migration method with high-order finitedifference approach are as follows:starting from 2D first-order hyperbolic seismic wave equation,the equation was discrete by a second-order finite-difference in time and an arbitrary high-order staggered-grid finite-difference scheme in space,the reverse extrapolation operator was obtained;the first-arrival travel time was computed by single-frequency full wave equation and was used as imaging condition for pre-stack reverse-time migration.Designed depression model and rift model verified the method.The numerical results indicate that the approach can image complex formation and remove low-frequency noises caused by reverse-time migration

The fundamental principles of static correction approaches being frequently applied, including elevation,model, refraction and tomography static corrections, are described and their suitability for complex near-surface conditions is discussed. The tomography static correction based on first breaking time is considered to be one of themost effectivemethods to deal with the long wavelength statics caused by variation of topography and low velocity zone (LVZ). The residual statics correction calculation based onmultiple domains statistics is thought to be a quit good approach for determining the short wavelength statics caused by geometry deviation and LVZmodel error, it is suitable for complex near-surface conditions through correct application. The conventional residual statics correction calculation based on reflection energy is of course indispensable in data processing. Time variable residual static correction can also be used if necessary. Real data examples give an explanation on above opinions.

Algorithms of neural nctworks,originatly studied in artificial intelligence,can be applied not only to gcophysical data processing, but also to geophysial inversion. This paper discusses the designing step and the algoeithm of back propagation neural network. The potential applications of the neural network algorithms are also pointed out.

The 3-D coherency cube is a recently developed seismi c interpretation t echnique. It uses the similarity of seismic signals between adjacent traces in 3 -D seismic volume to describe the lateral stratal and lithologic inhomogeneity. This paper introduces the mathematical basis of multi-trace coherency techniqu e. Real data test shows that the 3-D coherency technique can determine the faul t plane extent and its detailed features quickly and accurately, and the stratal occurrency information provided by the technique can be used to study the struc tural and sedimentary evolution system of object reservoirs.

Archie formula is the classical theory that describes the relationship between the resistivity and water saturation (Sw) of hydrocarbon-bearing sandstone reservoir. The application effect mainly depends on appropriate electrical parameters. Complex pore texture sandstone has low porosity, low permeability, more microporosity, more microfissure andhigh heterogeneity. Its electrical parameters are different evidently with conventional reservoir. On the basis of core electricity experiment data of low permeability sandstone of Upper Palaeozoic in Erdos Basin, the effects of complex pore structure on electrical parameter are investigated, the method to improve the precision of water saturation calculation through reservoir classification and using alterable m and n parameters are analyzed. Finally, a interpretation case of one well is presented.

Microseismic monitoring is a new technology emerged in recent two decades. This method consists mainly of 3 steps. Microseismic events induced by production are received with a geophone array deployed on the surface or in a borehole. They are inverted to determine parameters such as locations of microseismic sources. The resulted parameters are then used to guide the production activities.In the field of oil/gas developing,Microseismic monitoring is mainly used in dynamic imaging for hydraulic fracturing in low permeability reservoirs, and for monitoring of fluid injection. The basic principles of microseismic monitoring as well as acquisition and processing of microseismic data are discussed in the paper, and some application examples are also presented. The paper concluded with an analysis of application effects and the future of microseismic monitoring.

Fractured reservoir is an important reservoir of hydrocarbon. The carbonate fractured reservoirs in Tahe Oilfield, western China and the tight sandstone fractured reservoirs in the west of Sichuan are favorable reservoirs for hydrocarbon accumulation. We verified the presence of vertical fractures results in azimuthal anisotropy by physical modeling. Based on an analysis of the characteristics of azimuthal anisotropy (AVA analysis) , we developed an analytic resolution of 2-D azimuthal prediction and a least square method for 3-D azimuthal prediction. These methods have been used in prediction of carbonate fractured reservoirs in Tahe Oilfield. The results show that the predicted fracture orientation and density are well agreement with the geology. AVA analysis provides prediction and description of fractured reservoirs with an effective way.

With the development of oil & gas exploration, inversion and application of prestack seismic data is becoming the focus. Prestack simultaneous AVA inversion can simultaneously inverse P-wave and S-wave impedance and density data volume from small/middle/far angle stacked data volume. Based on the inversion result, the combined elastic parameters can be obtained. Being filled with gas, the compressional velocity of sandstone will usually decrease, the shear velocity does not change much, and the density decrease. If only the acoustic impedance is used, the combination of attributes of P-wave and S-wave impedance can improve the discriminating accuracy of fluid. So it is feasible to discriminate gas-bearing reservoir by using prestack simultaneous inversion technique. The basic principle of simultaneous inversion is introduced firstly and then the application of prestack simultaneous AVA inversion in exploration of middle-depth gas reservoir at Shengli oil field is discussed in some aspects, such as seismic data and well logs processing, angle wavelet extracting and calibrating, and inversion. The result shows that the method is effective in gas-bearing reservoir prediction.

Sichuan Xinchang area is one of the main gas-bearing fields in Sichuan province,and mainly is super-compactness sand fractured gas reservoir. The Xin 851 well shows the fairly good exploration prospect. In order to estimate azimuth, orientation and density, lithology identification of fracture with P-S wave, drilled into the reservoir formation pattern of super-compactness sand fractured gas reservoir. Meantime provide technology support and foundation data for 3-D 3-component seismic survey. 3-component seismic data of high quality are got at the first time. Demonstrating the acquisition parameter of field layout is problem for converted wave based on geophysics model and on increasing seismic data S/N ratio and resolution. The new seismic data is better reflecting the geologic feature than old seismic data.

Fracture identification and prediction is significant in hydrocarbon exploration. Corresponding theory and experiments have
shown that the anisotropy caused by fracture will affect seismic reflection features during wave propagation. For this
reason,it is feasible to characterize fracture trend,intensity and distribution by using seismic data. For fracture
prediction,seismic technology is characterized by low cost,extensive coverage area and large probing depth compared with
other methods,which can be divided into three types,including multi-component converted-wave fracture
characterization,azimuth anisotropy detection of P-wave response and post-stack seismic attribute analysis. Various
techniques have different popularity and efficiency because of the difference from data source,data requirement and technique
maturity. With the development of surveying and processing techniques,multi-component converted-wave fracture
characterization and azimuth anisotropy detection of P-wave response will be more widely used in fracture characterization.
For the same reason,seismic attribute anomaly detection will also be more important in using various dataset to recognize
fractured reservoirs.

Based on an analysis of conventional FFT, window FFT and wavelet transform, the paper points out the deficiency of conventional FFT and window FFT, and the advantage of wavelet transform in fine data processing at any detail and at any stage. Data sets are calculated for different frequency range by wavelet-transform-based frequency division processing. NMO and static corrections are then carried out on the resulting data. Finally wavelet reconstruction is performed. The proposed processes can decrease errors in the corrected quantity at different frequency and improves signal resolution.

In accordance with the characteristics of Putaohua oil reservoir of thin deltaic interbeded sedimentary layers in Songliao basin, we study the relation among sandstones of different microfacies log characters, and seismic attributes to try qualitatively predict the sandstone reservoir development zone in terms of sedimentary microfacies and waveform characters. It is concluded that there is high degree of correlation between the total thickness of sandstone oil reservoir and seismic attributes. Thick sandstones can be predicted with high reliability and the thickness of sandstone reservoirs is predicted.

Practically, it is always hoped that such an ideal HF noise suppression filter could be acquired: which can absolutely suppress all the frequencies higher than a given value, and at the same time, it wouldn't bring any distortions to those which are lower than that of the given value. However, even up to now, we have never seen such a function which is smooth enough and can be used as this kind of filtering mentioned above. The smooth compensation filtering presented here is just for the purpose of solving this problem.As is well known, in frequency domain, though the fully smooth functions now available could suppress the HF frequencies ever so much, it suppresses, to some extent, the MF and the LF frequencies simultaneously. That shouldn't really be expected anyway.In order to decrease such kind of suppressions to minimum, a newfiltering method has thus been worked out at last--this is the so called"Smooth Compensation Filtering" described in this paper.

This paper discusses: (1) the relation of geophone na tural frequency, s purious frequency with quiet working bandwidth, (2) the relation between spuriou s frequency and anti-alias filter in recording system, (3) the influence of res o nance on seismic data due to spurious frequency in field tests, (4) the relation of geophone sensitivity, output resistance with input impedance of recording sy stem, and (5) the importance of geophone phase-frequency characteristic. It is pointed out that the geophone property is important in precise seismic explorati on.

In the paper, we introduce and implement a seismic ray tracing algorithm based on the linear travel-time interpolation put forward by Asakawa (called LTI algorithm for short). On the basis of these, the reflected wave LTI algorithm is proposed. The LTI algorithm is based on grid unit model, is adapted to arbitrary variable velocity media, and can be used to trace several kinds of raypaths such as direct wave,refracted wave and transmitted wave. The original LTI algorithm can process the first arrival type of seismic wave. In the paper, we spread it to the refected wave circumstances, making it usable to calcu-late the traveltimes of seismic reflected wave and trace the reflected wave raypaths. The comparison be-tween the calculation and physical model experiment results demonstrates that the algorithm is more pre-cise and more suitable to complicated conditions such as large velocity variation in calculating traveltimes and tracing raypath than other conventional methods (e. g. the finite-difference method). This kind of seismic ray tracing algorithm has a good prospect.

The absorbing boundary condition of acoustic perfectly matched layer (PML) in traditional displacement form should be established by three splitting displacement parameters and the third-order time derivative needs to be solved, which leads to a large computation amount and long computation time. Aiming at this problem, we proposed an improved acoustic splitting PML absorbing boundary condition. The establishment principles of traditional and improved PML absorbing boundary condition were described. Through numerical simulation, the absorbing effect of improved and traditional PML absorbing boundary and low-order Higdon absorbing boundary on boundary reflection was discussed. The results show that the absorbing effect of low-order Higdon absorbing boundary condition is undesirable and relatively strong boundary reflection exists in wave field snapshot and analog recording; the effect of traditional and improved PML absorbing boundary conditions are similar, which can effectively absorb and attenuate the boundary reflections from any angle. In the improved algorithm, the computation of three-order time derivative is replaced by convolution approximate calculation, which simplifies the computation process and reduces computation amount, and is high effective and robust.

The paper gives an overview on the fundamentals of exploring oil. gas and water using seismoeiectrie effects. The seismoelectric effects involved in the paper are limited to those caused by galvanie electrieity phenomina in fluid-bearing porous media. Exploring oil .gas and water using the method is thus refered to as the scismoelectrie method or electrie shock method, which is supposed to take on the features of high resolution and high selectivity theorctically. It's deduced from the seismoelectric effect that the oil. gas and water exploration could be carried forward in high selectivity by making use of the surface natural electromagnetic field. This paper will expound its physical basis and application conditions.

This paper discusses various high resolution seismic data processing techniques suitable for data acquired with high resolutionmeans. These techniques include prestack S/N ratio enhancement, heightening of the dominant frequency of reflected signals and spreading of the frequency band of significant signals, frequency divided processing, iterated optimal stack, signal direction constrained noise elimination, as well as predicted trace interpolation in 3-D FXY domain. Issues of enhancement of lateral resolution after stacking are also discussed. Desired results have been reached by the application of thesemethods to real seismic data.

The wavelet transform is a new branch of mathematics, which has been widely used in seismic exploration. In the paper, we use the wavelet transform to perform the potential field data processing, andderive 2-D wavelet transform formula form 1-D wavelet transform formla. A good processing result forthe model data and practical data has been achieved. It proves that 2-D wavelet transform can play animportant role in extracting areal regional anomaly and local anomaly and removing high-fraquency weakmagnetic interference.

The reef flat facies reservoir of Changxing formation is widely distributed in the southwest Sichuan province and is abundant in gas. However, the forecast of reef reservoir is always a difficult thing in hydrocarbon exploration and most of the wells in which the reef is found by accident. Aiming at this problem, the distribution of reef flat facies reservoir in Changxing stage is forecast based on the high signal-to-noise ratio seismic data and the known gas field forecast model First, structure and depositional setting of the area are described and response characteristic of the reef flat facies reservoir of Changxing formation is analyzed; then, through analyzing seismic response characteristic and sequence stratigraphy feature of the reef flat facies reservoir of Changxing formation in Puguang oilfield, the methods of forecasting reef flat facies reservoir is established and the seismic response characteristic and sequence stratigraphy feature of reef flat facies reservoir in Tongnanba structure and in Tongnanba structure belt-the south of the Jiulongshan structure are specially analyzed. On the basis of this, the distribution of reef flat facies of these two geological structures is predicted. Finally, the hydrocarbon exploration perspective is evaluated.

Velocity model building for prestack depth migration is a model-based iteration process. Besides velocity inversion algorithm, the static correction in complex near-surface condition and irregular geometries may also impact the velocity modeling. Based on integrating seismic processing and interpretation, aimed at different seismic-geological conditions, the strategy of accurate velocity model establishment is proposed. In some high degree exploration areas, the initial macro interval velocity model is firstly established by u-sing the logging-constrained method, and then, the double-iteration method in multi-domains is applied on velocity model updating to meet the accuracy of prestack imaging. In addition, based on some problems in velocity modeling in the foreland basin of west China, the thought and strategy for velocity modeling are proposed and the development tendency of this technique is analyzed.

The reservoir of Xujiahe Formation in west Sichuan depression is deep buried, super-tight, less changeable in lithological parameters, and strongly in-homogeneous and anisotropic. Practice has proved that fracture helps enhance the porosity and permeability of the deep tight reservoirs, thus controls the concentration and production of natural gas. P-wave amplitude has been successfully applied to detect vertically oriented fractures by foreign colleagues. Essentially, this technique makes use of the fact that P-wave amplitude changes periodically with the orientation and density of the fractures. Taking the characteristics of the fractured reservoir of Xujiahe Formation into account, the author developed a suite of P-wave azimuthally anisotriopic fracture detection methods (AVA) to detect fracture azimuth and fracture density on wide azimuth 3D seismic data. The AVA technology has been successfully used in the 3D seismic exploration in JM area

This paper presents a data processing method for nois e removal which ca n decrease the damage to the effective waves to the minimum. For signals in freq uency segments without coherent disturbance the wavelet frequency-division is a d opted to remove noises. For signals with coherent disturbance the window-divisi o n is adopted to make the noise removal processing performed only within segments with disturbance. The picking of coherent disturbance is based on the mean valu e weighting technique, which is new, precise, and practical for noise picking. R eal data processing demonstrates that the method can eliminate coherent disturba nce while fully preserving effective waves from loss and its negative effect is very small.

The shape of seismic trace is the synthetic reflection of amplitude, frequency, and phase for seismic wave. The waveform classification technology was adopted for trace-by-trace contrast classification through neural network in some geological strata on seismic section, which can portray the lateral changes of seismic signals in detail and obtain seismic phase diagram corresponding to the geological stratum to predict the sand bodies and lithologic reservoirs. Waveform classification technology was used to predict the sedimentary microfacies of Putaohua formation in Gulongbei area. The predicted result coincides with the macro sedimentary environment of the area, the matching degree is high with sedimentary microfacies of a single well, and the detailed changes of properties agrees with the sedimentary rules. Two wells were deployed by predicted results and industrial oil flow was obtained after drilling. Lithologic deposit with large scale of scales was discovered recently.

TIME-FREQUENCY ANALYSIS is a new technique for thin interbeds examination. The technique is based on the ground of time-frequency variation of seismic response. In this paper,the fundamental ideas about the time-frequency analysis was expounded,effects resulted from the seismic wavelet,the window length,the step length as well as the other processing parameters were discussed. Also discussed were the effects of the multiple,the absorption and the attenuation. The time-frequency responses for sedimentary texture of different types were developed by means of the theoretical model. The principle and technique for data interpretation were delineated by comparision. Application shows that the thin interbeds were distinguished very well In northern Songliao basin.