基于频陷理论的地震谱反演技术分析

我国陆相盆地广泛发育薄层砂体,但受地震分辨率限制,从地震剖面上难以直接识别薄层反射特征,为寻找岩性圈闭带来困难。谱反演技术的出现,为薄层砂体识别方法带来新的方向。该技术避开调谐振幅进行薄层识别的方法,采用在频率域中分析薄层频谱中出现的频陷特征,并且把地震信号分解为奇偶分量,进一步提高薄层的识别能力。通过模型分析,发现薄层厚度越小,对应信号频谱中频陷周期越大。地震信号奇偶分解后,其中偶分量能够提高地震资料的视分辨率。通过对谱反演目标函数的剖析,给出了具体实现过程。

基于频陷特征的薄层砂地比预测方法及应用——以阿尔及利亚X区块为例

已钻井揭示阿尔及利亚X区块河流相砂岩储层厚度较薄且横向变化快,高砂地比的“甜点”储层普遍具有较好的物性。由于储层埋藏较深,深层地震资料主频仅18Hz,为薄储层的“甜点”预测带来极大难度。调研分析发现,频率信息对薄层顶底的反射系数不敏感,对厚度更敏感,因此,在对储层砂地比的预测中,频域方法相比时域方法多解性更低,稳定性更好。理论上看,频陷特征与薄层的厚度有密切关系,在第1个频陷处,地震反射的能量谱和薄层的厚度呈反比关系,可以通过对薄地震反射频率特征的分析预测薄储层厚度的分布。以阿尔及利亚X区块为例,根据研究区储层段“砂包泥”的岩性组合特征,设计薄层楔形模型,运用正演模拟分析得出因调谐效应产生的频陷处能量与薄储层砂地比间具有反比关系,提出了利用第1个频陷处能量属性表征砂地比的思路;并运用该属性表征了研究区砂地比平面分布特征,识别出高砂地比的储层“甜点”区。相关研究为储层“甜点”预测和评价井部署提供支撑,取得了较好的应用效果。

基于纵向模态超声导波陷频特性的钢绞线拉力测量新方法

试验发现了钢绞线结构中L（0,1）模态导波存在陷频这一固有声学特性,由此提出一种钢绞线拉力检测新方法。为测试钢绞线中导波陷频特性与拉力的关系,研制了一款柔性低频磁致伸缩传感器,可在30~160 k Hz范围内激励/接收L（0,1）模态导波。在直径17.8 mm和15.2 mm的两种7芯钢绞线上进行导波陷频检测试验,结果表明陷频特征频率与拉力的自然对数值呈良好线性关系,陷频旁侧峰值比随拉力增大而线性增加。试验中1 k N的拉力增量（应力增量约3 MPa）引起的声学参数（陷频特征频率和陷频旁侧峰值比）变化可被检测到并较好的符合标定关系方程。在额定工作载荷内,拉力估算相对误差小于1.5%,这表明新方法具有较高的拉力检测精度。同时,依据试验所得结论,给出了钢绞线结构中L（0,1）模态导波陷频中心频率与拉力关系的修正公式。新方法实施过程简洁,具有很好的工程应用前景。

海底电缆鬼波压制及陷频补偿方法研究

受到海底、自由表面等强反射界面的影响,在海底电缆采集的地震资料中鬼波干扰往往非常发育,在频谱中表现为明显的陷频现象,严重影响地震剖面的质量,给后期的处理解释带来困难。为克服这一困难,根据海底电缆双检(陆检和水检)对下行波场的不同响应,在深入研究伪多道匹配滤波技术的基础上提出了伪多道双检合成方法。与传统的求取反射系数的双检合成方法不同,该方法完全数据驱动。在合成数据和渤海地震资料的实际应用中,鬼波成分得到了明显的压制,同时拓宽频带,补偿陷频,证明了该方法的有效性。

薄层陷频法

近来出现的谱分解法实际上就是已知的薄层陷频法。对砂泥岩薄互层段 ,用短时窗对地震道做傅里叶分析 ,可以显示薄层振幅谱和相位谱的周期性。对三维数据体目的层段做谱分析后 ,可以形成 (x ,y ,f)薄层振幅谱或相位谱数据体。非洲岸外的一个例子说明 ,在合适频率上做频率振幅切片有可能显示古河道。墨西哥湾的一个例子证明 ,做频率相位切片可以比党规三维振幅切片更清晰地显示断层。薄层谱还可用来估算薄层厚度及弹性参数。

立体气枪阵列对子波陷频的补偿分析

海上地震勘探中,为了获得较高信噪比的气枪子波,通常利用气枪阵列进行组合激发。将气枪阵列中的各个子阵沉放于不同的水深处并延迟激发,形成立体阵列,可以有效地压制震源虚反射,提高远场子波振幅谱的陷频点能量,从而拓宽子波频谱。本文从原理上分析了不同水深的气枪子阵列的陷频特性,总结出对陷频点振幅能量补偿较好的立体阵列设计方式,并进行实测,以达到指导海上立体阵列设计、改善气枪阵列子波频谱的目的。

应用反演谱分解去除调谐效应的分频AVO技术

传统的AVO分析是假设平面波入射到分开两个半空间的单界面,并没有考虑油藏厚度的影响。当地层为薄层时,调谐效应会使AVO的变化规律发生改变,影响储层的识别。谱分解能够将时间记录转换到不同频率,从而得到更多的储层信息。因此,可以利用谱分解进行分频AVO分析。在多种谱分解方法中,反演谱分解方法具有较高的时频分辨率,并且其直接得到的是反射系数谱,可去除子波的影响。依据这一特性,这里将反演谱分解方法用于去除调谐效应。根据实际薄层的物理参数和地质条件,设计不同厚度的薄层模型,正演得到合成地震道集;然后利用反演谱分解进行分频AVO分析。结果表明,该方法能够消除薄层调谐效应,同时还能避免陷频现象。

地震频谱分解技术应用中有关问题的讨论

薄层反射在频率域会出现陷频现象,其陷频周期的倒数等于薄层的时间厚度。频谱分解技术以此为理论基础对地层厚度进行预测。从此原理出发,阐述了频谱分解技术对原始地震数据体的高保真要求和定义频率范围的原则。实际应用时,利用沿层调谐体,通过求取频率域第一优势频带的频率进行地层厚度预测;利用各单一频率调谐体对薄层进行检测,利用调谐能量的变化对横向不连续的地质异常体空间分布特征进行描述。实际应用结果表明,频谱分解技术比传统的基于时间域地震主频的方法对地质体有更高程度的识别。

一种新型椭圆陷波特性的超宽带天线的设计

超宽带无线通信技术以其信道衰落不敏感,低能耗,抗干扰性强,系统设计复杂度较低等优点而备受重视。本文以椭圆片结构为基础设计了一种新型平面超宽带天线,并主要对该天线的陷波特性进行了研究。该天线由微带馈线,天线的制作是通过在介质基板上下面分别印刷一个椭圆形和矩形相结合,中间以蝶形天线过渡的金属片,下层矩形接地板来实现。仿真和实物实测结果都可以证实,该天线的工作频带为2.0～12GHz,具有超宽带特性和很好的全向辐射特性。同时,也对天线进行了双陷波特性设计,其性能更加优化,可用于无载波超宽带无线数据通信系统。

地震勘探时空域双曲滤波因子的特点与提高信噪比的能力

为改善强随机噪声背景中地震勘探资料信噪比(S/N),提出了混沌振子算法;该算法可实现对未知同相轴的确定.本文的时空域双曲滤波(hyperbolic ti me-distance relation filter,HTDF)是上述算法的后续处理,即处理得到存在的弱同相轴.HTDF的理论基础是最小平方滤波和混沌振子算法.为说明滤波过程与效果,对于包括一个反射同相轴的地震记录进行了多道滤波因子计算.结果表明,与一个输出道相应的双曲滤波因子组具有复杂的时频域结构,突出的特点是振幅谱"波动式陷频"表现;弥补或消除这个不足的方法是与输出道相应的多个滤波因子之间存在的振幅谱"互补"性.利用相同随机噪声背景下的共炮点理论记录,经与域双曲速度滤波、褶积滤波处理方法比较,在振幅谱、子波初至、零相位性、S/N改善等方面,HTDF的滤波效果优于另外两种.最后探讨了该滤波技术的机理,包括同相轴内各子波间的相似性,以及对组内因子实施的多次有效相加处理.

基于谱分析的谱峰数预测薄互层砂岩厚度

通过陷频分析,在讨论单层厚度地震谱特征基础上,针对利用多层地层的地震谱方法预测厚度这一难题,在研究各类多层模型的谱特征后,总结出砂岩厚度、岩性与地震谱谱极值大小变化规律,并以此分析方法为依据,研究了利用谱峰数预测砂岩厚度的方法.

薄层的二阶功率谱特征研究及厚度预测

常规的薄层厚度估算技术都是基于地震子波为零相位的假设而发展起来的,在非零相位情况下进行估算往往误差较大。为此,从薄层振幅调谐具有周期性陷频谱特征出发,提出了二阶功率谱的概念,从理论上对薄层的二阶功率谱特征进行了研究,建立了薄层厚度与二阶功率谱极大值之间的对应关系,给出了利用二阶功率谱进行薄层厚度预测的理论依据和方法,即根据薄层厚度和二阶功率谱的能量关系制作二阶功率谱图,图上强能量团对应的时间即为薄层时间厚度。楔状模型试验结果表明,通过二阶功率谱进行薄层厚度估算更加直观有效,且不受子波相位的影响,适应能力更强。

基于地震叠前大角度道集的调谐压制提高分辨率方法

地震叠前成像的叠加数据受大角度道集干涉调谐作用影响,子波特征模糊、分辨率降低。对此,利用正演模拟首先明确大角度数据干涉的形成机理,即随着入射角的增大,地层时间厚度减小,导致数据发生干涉调谐效应。在此基础上进一步分析地层顶底干涉的陷频周期条件、正演模拟陷频和假陷频特征,明确了提高分辨率应在资料的原始频带内实施。依据叠前共成像道集的同源性理论,通过构建叠前大角度数据与小角度数据的匹配关系,求解匹配因子用以压制大角度数据的调谐效应,从而提高地震叠前成像的叠加数据的分辨率。在胜利油田CD地区的实际应用表明,该方法能有效提高大角度数据的分辨率,处理的成像道集叠加后分辨率得到了明显提高。

Research on the imaging of concrete defect based on the pulse compression technique

When the synthetic aperture focusing technology （SAFT） is used for the detection of the concrete, the signal-to-noise ratio （SNR） and detection depth are not satisfactory. Therefore, the application of SAFT is usually limited. In this paper, we propose an improved SAFT technique for the detection of concrete based on the pulse compression technique used in the Radar domain. The proposed method first transmits a linear frequency modulation （LFM） signal, and then compresses the echo signal using the matched filtering method, after which a compressed signal with a narrower main lobe and higher SNR is obtained. With our improved SAFT, the compressed signals are manipulated in the imaging process and the image contrast is improved. Results show that the SNR is improved and the imaging resolution is guaranteed compared with the conventional short-pulse method. From theoretical and experimental results, we show that the proposed method can suppress noise and improve imaging contrast, and can also be used to detect multiple defects in concrete.

海底电缆双检资料合并处理技术

针对海底电缆勘探资料因鸣震干扰产生的陷频问题,采用了双检合并处理技术。由于压力、速度检波器的物理机制不同,在同一位置接收的鸣震干扰极性相反。在对两种资料进行一致性处理、提高信噪比处理、反褶积处理以及选择合适的合并方法等关键性处理后,鸣震干扰得到了有效压制,提高了海底电缆勘探资料的分辨率。

Superfluid Fermi Gases in a Rotating Anharmonic Trap

The quadrupole mode frequency, the monopole mode frequency, and the critical rotational frequency for stirring a single vortex nucleation along the BEC-BCS crossover are obtained. The results show that, in a rotating anisotropic anharmonic trap, the quadrupole mode frequency and the critical rotational frequency for stirring a single vortex nucleation are modified significantly when the system crosses from the BEC side to the BCS side： the anisotropy of the trap induces a downshiff of the quadrupole mode frequency and the critical rotational frequency and helps the vortex formation in the system, while an anharmonic trap induces an upshift of the quadrupole mode frequency and the critical rotational frequency and suppresses the vortex formation in the system.

Delamination Damage Detection in Laminated Composite by LDR-Based Multi-frequency Method

Local defected resonance(LDR)is a recently-developed non-destructive testing method,which identifies damage by detecting the vibrational response of the structural surface under the wideband ultrasonic excitation. The concept of LDR is studied and applied for damage imaging of delamination in composite laminates. Aiming at the problem of poor anti-noise ability and inaccurate damage identification in traditional detection process,an LDR-based multi-frequency method is proposed. Experimental results show that the proposed method can realize the localization and imaging of delamination damage in composite materials.

Defective recovery of QT dispersion following transcatheter aortic valve implantation： frequency, predictors and prognosis

Background Corrected QT dispersion （cQTD） has been correlated with non-uniform ventricular repolarisation and increased mortality. In patients with aortic stenosis, cQTD has been shown improved after surgical valve replacement, but the effects of transcatheter aortic valve implantation （TAVI） are unknown. Therefore, we sought to explore the frequency, predictors and prognostic effects of defective cQTD recovery at 6 months after TAVI. Methods A total of 222 patients underwent TAVI with the Medtronic-CoreValve System between November 2005 and January 2012. Patients who were on class Ⅰ or Ⅲ antiarrhythmics or on chronic haemodialysis or who developed atrial fibrillation, a new bundle branch block or became pacemaker dependent after TAVI were excluded. As a result, pre-, post- and follow-up ECG （median： 6 months） analysis was available in 45 eligible patients. Defective cQTD recovery was defined as any progression beyond the baseline cQTD at 6 months. Results In the 45 patients, the mean cQTD was 47 ± 23 ms at baseline, 45 ±17 ms immediately after TAVI and 40 ± 16 ms at 6 months （15% reduction, P = 0.049）. Compared to baseline, cQTD at 6 months was improved in 60% of the patients whereas defective cQTD recovery was present in 40%. cQTD increase immediately after TAVI was an independent predictor of defective cQTD recovery at 6 months （per 10 ms increase; OR： 1.89, 95% CI： 1.15-3.12）. By univariable analysis, defective cQTD recovery was associated with late mortality （HR： 1.52, 95% CI： 1.05-2.17）. Conclusions Despite a gradual reduction ofcQTD after TAVI, 40% of the patients had defective recovery at 6 months which was associated with late mortality. More detailed ECG analysis after TAVI may help to avoid late death.

Simplified Method of Designing FIR Filter with Controllable Center Frequency

A novel simplified method is presented to design FIR filter with controllable center frequency. The properties of transfer curves for all-phase filters are illustrated under 3 windowing conditions. By combining single-window all-phase filter design steps and double phase-shift combination, a series of design formulas for point-pass filter, notch filter, band-pass filter and band-stop filter are derived, thus the design computation complexity is greatly reduced. Experiments prove that the center frequency of all the filters can be accurately specified at arbitrary position by adjusting frequency parameters m and λ.

TIME-VARYING AR MODELING AND ADAPTIVE IIR NOTCH FILTER FOR ANTI-JAMMING DSSS RECEIVER

Using Time-Varying AR (TVAR) model and adaptive notch filter is a new method for the non-stationary jammer suppression in Direct Sequence Spread Spectrum (DSSS). The performance of TVAR model for Instantaneous Frequency (IF) estimation will be affected by some factors such as basis functions. Focusing on this problem, the optimal basis function of TVAR model for the IF estimation of the LFM signal is obtained in this paper. Besides the depth and width of notching, the phase properties of notch filter affect the Signal-to-Interference plus-Noise Ratio (SINR) of correlation output to the narrowband jammer suppression in DSSS, in response to the problem the closed solution of correlation output SINR improvement has been derived when a single frequency jammer passes through direct IIR notch filter, and its performance has been compared with those of five coefficient FIR filters. Later, a novel method for LFM jammer suppression based on Fourier basis TVAR model and direct IIR notch filter is proposed. The simulation results show the effectiveness of the proposed method.