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Because of excellent superiorities, triple-electrode carbon nanotube sensor acts good in the detection of multi-component mixed gas. However, as one of the key factors affecting the accuracy of detection, the electrode separation of carbon nanotube gas sensor with triple-electrode structure is very difficult to decide. An optimization method is presented here to improve the mixed gas measurement accuracy. This method optimizes every separation between three electrodes of the carbon nanotube sensors in the sensor array when test the multi-component gas mixture. It collects the ionic current detected by sensor array composed of carbon nanotube sensors with different electrode separations, and creates the kernel partial least square regression (KPLSR) quantitative analysis model of detected gases. The optimum electrode separations come out when the root mean square error of prediction (RMSEP) of test samples reaches the minimum value. The gas mixtures of CO and NO2 are measured using sensor array composed of two carbon nanotube sensor with different electrode separations. And every electrode separation of two sensors is optimized by above-mentioned method. The experimental results show that the proposed method selects the optimal distances between electrodes effectively, and achieves higher measurement accuracy.

As the earth medium isn't perfect elastic actually, seismic waves traveling in the earth experience amplitude attenuation and velocity dispersion because of earth attenuation. In this paper, based on Futterman equation, we combine the quality factor Q, a parameter for quantitative characterization of absorption and attenuation, with the P wave propagation operator in elastic medium, to realize the numerical simulation of non-zero offset by one-way wave equation. Considering the principle that the common geophones propagate downward subsurface inefficiency, we use the reflected wave propagation upward theory, improving the computation efficiency greatly. In this paper we compare the one-way with full-way seismic wave-equation, and then we do pre-stack forward modeling based on viscoelastic medium by the former. The results of numerical simulation show that the amplitude of seismic wave is attenuated and dominant frequency shift to lower frequency in viscoelastic medium, at the same time, the spectral band become narrower and the time resolution decreased. Key ward one-way wave, attenuation medium, numerical simulation, computational efficiency

The exploration and development of tight-gas sandstone reservoirs have been paid more and more attention in recent years. However, it is difficult to identify them due to the low porosity and the slight change of geophysical characteristics caused by the change of oil and gas saturation. In this article, a more sensitive fluid-detection factor, which can be easily obtained from seismic inversion, is built by optimization of elastic parameters based on experimental data of tight sandstones from Daniudi gas field, This detection factor is applied to Daniudi gas field, showing its effectiveness and sensitiveness in highlighting the effects of fluid and better anti-noise ability.

This paper describes a deterministic method to compensate the attenuation of seismic wave caused by near surf ace , the compensation includes amplitude, frequency and phase, the compensation has two steps, first ,An accurate near surface Q was estimated from uphole survey in double hole, then a wide band , stable inverse Q filter was proposed and applied. The method has been tested in Daqing Oilfield, the result shown that the near surface Q estimation method is accurate and stable , the estimated Q-factor is reliable. the proposed inverse Q filer was applied to 3D seismic data, after inverse Q filter, the attenuated high frequency by near surface has been recovered reasonably ,the resolution of seismic data was enhanced ,signal to noise ratio was not decreased. Compared the result with OMEGA processing system , the proposed inverse Q filter has the more widen and flatten spectrum ,means the result has higher resolution.

This paper focuses on the 3D VSP data acquisition method of high-precision survey of VSP and 3D 3C surface seismic in LMD oilfield of Daqing. The first step is to design the geometry, to do ray tracing based on the 3D model, and to determine a reasonable geometry according to attributes analysis such as the fold and reflection angle. The second step is to develop a reasonable acquisition method, at the same time to improve the shooting equipment, the aim of which is to achieve synchronized recording of VSP and surface seismic. The last step is to acquire the data according to the designed geometry. The practice has shown that joint observation of VSP and surface seismic could reduce the acquisition costs significantly, and if the acquisition process is reasonable, it will affect neither the acquisition progress nor the quality, and it can get good acquisition results.

For a long time in Midwest area of China, migration imaging is affected by multiple factors such as complex surface condition and high-steep structure with weak reflected signal and low SNR in target zone. It is difficult to get satisfied migration result. CRS stack is one of effective method to improve SNR, but it injuries diffraction wave and causes amplitude distortion. In this article, through theoretical analysis, develop an extended CRS based processing technology from CRS stack, and give a PSTM processing flow based on extended CRS, this flow is applied to real data in western oilfields and obviously improved imaging result.

Forward modeling of the underground propagation process of seismic waves is performed with the numerical simulation method by taking strata as viscoelastic media. Based on the simulation result, the absorption and attenuation of seismic waves passing through each interval involving surfaces, shallow and deep layers is estimated quantitatively; in addition, after absorption and attenuation of seismic waves, the variation of their amplitude, phase and form, main frequency and frequency bandwidth are estimated, and based on the variation of the main frequency and frequency bandwidth, the reduction of seismic wave resolution is analyzed after absorption and attenuation in surface, shallow and deep layers. Several common viewpoints on seismic data resolution improvement by absorption compensation can be obtained as follow: (1)the surface layer has very low Q value and large abruption attenuation, so it is necessary to attach importance to the compensation for surface absorption and attenuation; (2) the absorption and attenuation of a layer is the function of Q and the travel time in it. A surface layer has very low Q value but very short travel time, and a deep layer has high Q value but long travel time; by comprehensively considering the two factors, the absorption and attenuation of the surface layer is still smaller than that of the deep layer, so it is required to make compensation for both surface and deep absorption and attenuation instead of compensation for only surface in order to improve seismic data resolution; (3) the surface layer has higher transverse non-uniformity than the deep layer and also large transverse variation of Q value. Consistent compensation for surface absorption and attenuation is also very important to seismic exploration aimed at mainly probing into the transverse variation of strata. In addition, the estimation of the transverse variation of surface absorption and attenuation property also helps select an appropriate seismic source excitation position and improve seismic data resolution from the very beginning.

Frequency slice wavelet transform (FSWT) is a new kind of time-frequency analysis method. Compared to traditional short time Fourier transform (STFT), it can be implemented by translation and dilation in the frequency domain. FSWT decomposes signals by frequency slice function (FSF), which is similar to mother wavelet, and it can reconstruct the original signal without the strict reconstruction condition of wavelet transform. This new method can get a good balance between time and frequency resolution through introducing a new scale parameter. In this paper, FSWT is used to do time-frequency analysis on the synthetic seismic data the first time and the seismic data of GG reservoir from a certain marine block is selected to do the spectral decomposition. From the synthetic analysis results, we can get that the new method can effectively detect the low frequency shadow of the reservoir and distinguish gas-bearing sandstone and water-bearing sandstone. The real data analysis results show that FSWT has the good effect on seismic data time-frequency analysis and provides a new kind of method for the reservoir prediction and hydrocarbon detection.

The Gaussian beam is high-frequency approximate solution that wave equation centralized around the ray, which closely combines wave equation with the ray theory to get raypath through kinematical ray tracing and to get high-frequency energy near central ray through dynamic ray tracing.The individual Gaussian beam is used to carry out the wavefield propagation and it retains the kinematical characteristics, while it keeps the dynamic features of wavefield at the same time. Gaussian beam depth migration (GBM), propagating each ray by a Gaussian beam form and summing the contributions from all the individual beams to produce the wavefield, is an accurate, flexible and efficient migration method, with the ability to image steeply dipping reflectors and anisotropic medium, and also, to extract Angle Domain Common Imaging Gathers (ADCIGs) directly through wavefield direction vector by computing traveltime gradient which is restricted in the effective region of a Gaussian beam. In this paper, the basic principle and strategy of GBM are introduced; the technology to yield ADCIGs by Gaussian beam migration is also shown. Numerical tests on synthetic data and real data sets demonstrate the Gaussian beam migration method is effective.

Offshore oil and gas exploration has become the main field at present and in the future; however, the information about offshore deepwater exploration is less than onshore. At present, the offshore oil and gas exploration is mainly based on seismic data, thus, it is significant to use seismic data to detect hydrocarbon in offshore deepwater exploration. Using seismic data to do hydrocarbon detection is a process of inversion, and it has ambiguity and uncertainty. This paper illustrated five methods to detect hydrocarbon, namely, seismic amplitude attribute, frequency attribute, spectrum decomposition method, waveform classification and cross plot analysis of far offset stack data and near offset stack data. The combined application of those methods can greatly reduce the ambiguity and uncertainty. According to the study of deepwater sediment in Equatorial Guinea, the results of hydrocarbon detection coincide with drilled wells and the known hydrocarbon distribution. The combined using of those methods has achieved better effect in this study area, and has formed a series of methods of hydrocarbon detection in offshore deepwater oil and gas exploration.

Oil exploration has proven that, about half the world oil and gas reserves and productions existed in the carbonate reservoir. Although carbonate reservoir widely distributes in China, it has a very low level of exploration and development. Compared to the global distribution of carbonate oil and gas resources, there is a huge potential for improvement about exploration and development of carbonate reservoir in China. In this paper, high-order staggered finite-difference numerical simulation method is used to model the different equivalent seism-geological cave models of carbonate reservoir. Such as, a series models of different scales, different fillings, different source dominant frequencies, and different combinations of caves. And then, we conducted a comprehensive analysis about its reflection characteristics and reflection amplitude of the synthetic wave field. Studies have shown that: (1) with the width of the cave increases, the amplitude increases rapidly; while, height has less effect on the amplitude than width, but it is more complex. (2) The greater the source dominant frequency, the greater the amplitude, and the higher the resolution. (3) If cave fillings become dense, the amplitude will decrease and the overall response characteristics will become simple. (4) Vertical double-cave model in the migrated section easily form a "string beads" phenomenon. We have systematically summarized the influence of width, height and distance on the "string beads " phenomena. And we also found that a single large cave cannot cause obvious "string beads" phenomenon. As a result, the forward modeling suggests that the multi diffraction is the key factor to produce the "string beads" phenomenon.

Seismic data excited by low frequency vibrator has the characteristic of low start frequency of sweeping and broad frequency bandwidth. The purpose of this paper is to analyze and draw some conclusions about their difference of key processing steps by processing and comparing low frequency data and conventional data. ①Low frequency data has the advantage of strong low frequency signal and broad frequency bandwidth, but low frequency noises are some stronger, which has negative effect on the image of low frequency signal; ②The final migration of low frequency data has much rich low frequency signal, and deep fracture and basement become much clear. Low frequency signal has the good ability of penetrating, which is very useful to image of deep target layer. Consistency between migration ③ of low frequency data and well is very good, and the result of inversion is reasonable, its resolution is higher than conventional data. The ability of solving reservoir exploration and development problem using by frequency seismic data is also discovered.

In anisotropy media, every reflecting body sets each impact wave split into two distinct shear waves, and the fast and slow shear wave after the first division has once again meet anisotropy media will happen then split. The actual data exists many splitting and re-splitting, finally made the reflection coefficient array extremely complex, and shallow anisotropy has great influence to anisotropy parameters of deep target stratum. In order to eliminate this effect, you should calibrate shallow layer's shear wave re-splitting so that it requires shallow anisotropy layer convert to the isotropic layer. Firstly, convert the anisotropic layer to the isotropic layer by eliminating time difference between fast and slow S-wave caused by shallow anisotropy, then eliminating anisotropy from shallow to deep to analyze the anisotropy layer by layer and eliminate the influence of overlying strata until the objective stratum. This article does research on model trial and practical application, which made the ideal effect.