An efficient algorithm to compute transient pressure responses of slanted wells with arbitrary inclination in reservoirs

Compared with vertical and horizontal wells, the solution and computation of transient pressure responses of slanted wells are more complex. Vertical and horizontal wells are both simplified cases of slanted wells at particular inclination, so the model for slanted wells is more general and more complex than other models for vertical and horizontal wells. Many authors have studied unsteady-state flow of fluids in slanted wells and various solutions have been proposed. However, until now, few of the published results pertain to the computational efficiency. Whether in the time domain or in the Laplace domain, the computation of integration of complex functions is necessary in obtaining pressure responses of slanted wells, while the computation of the integration is complex and time-consuming. To obtain a perfect type curve the computation time is unacceptable even with an aid of high-speed computers. The purpose of this paper is to present an efficient algorithm to compute transient pressure distributions caused by slanted wells in reservoirs. Based on rigorous derivation, the transient pressure solution for slanted wells of any inclination angle is presented. Assuming an infinite-conductivity wellbore, the location of the equivalent-pressure point is determined. More importantly, according to the characteristics of the integrand in a transient pressure solution for slanted wells, the whole integral interval is partitioned into several small integral intervals, and then the method of variable substitution and the variable step-size piecewise numerical integration are employed. The amount of computation is significantly reduced and the computational efficiency is greatly improved. The algorithm proposed in this paper thoroughly solved the difficulty in the efficient and high-speed computation of transient pressure distribution of slanted wells with any inclination angle.

Pressure transient behavior of a slanted well with an impermeable fault

Analytical solution is obtained for the pressure response of a slanted well in a slab reservoir with an impermeable fault. Based on the basic point source solution in an infinite space, the basic point source solution is obtained by using the mirror image principle. Wellbore pressure response of a slanted well is obtained by integration of the basic point source solution along the trajectory of a slanted well and the type curves are computed. The dimensionless bottom hole pressure and type curves are obtained and the sensitivities of related parameters are discussed. The model presented in this paper could be used for the well test analysis of a slanted well in a reservoir bounded by an impermeable fault.

Workover String Mechanical Model and Calculation of Slanted and Horizontal Well

Force analysis and calculation of workover string in the slanted and horizontal well are the basis of designing and checking string strength, selecting tools and determining operation parameters, which determine the operation safety and success of engineering accidence treatment. In this paper, by comprehensive consideration of wellbore structure, string assembly, string load and workover operation conditions, the workover string mechanical model has been built under three kinds of working states of lifting, lowering and rotating. The downhole string mechanics has been analyzed and calculated. By field verification, the string assembly, tool selection and operation parameter optimization can be achieved, which can improve the safety and success rates of workover engineering accident treatment.

Influence of Wellbore Trajectory on Pressure Drop and Fluid Discharge

An experimental analysis has been conducted to study the process of fluid accumulation for different borehole trajectories.More specifically,five heel angles have been experimentally realized to simulate the borehole trajectory of the sloping section of the formation.The fluid-carrying capacity,pressure drop and fluid discharge volatility have been investigated for these conditions and,accordingly,the relationship between heel angle and wellbore pressure drop fluid-carrying capacity has been determined.The results show that while the reasonable roll angle can increase the pressure loss in the wellbore,it is beneficial to drainage.In terms of pressure loss and liquid-carrying capacity,when the heeling angle is 50°,the latter is increased while the former becomes very high,which indicates that when drilling and completing wells on site,a 50°roll angle should be avoided.It is found that the main reason for the increase of the total pressure drop in the wellbore is the increase of the local pressure loss in the inclined section.From the perspective of drainage stability,when there is heeling in the inclined section of the horizontal well,the fluctuation of the wellbore drainage tends to be enhanced.Through the comparison of the Beggs-Brill(B-B)and Mukherjee-Brill liquid holdup methods,it is found that B-B method better predicts liquid holdup.A new method for calculating the pressure drop in the inclined section in the presence of lateral inclination is obtained by taking into account the pressure drop in the curved section.Through comparison with experimental data,it is found that the error is within 20%,and the prediction accuracy is high.

Modeling of multi-depth slanted airgun source for deghosting

To obtain high-resolution of the subsurface structure, we modeled multidepth slanted airgun sources to attenuate the source ghost. By firing the guns in sequence according to their relative depths, such a source can build constructive primaries and destructive ghosts. To evaluate the attenuation of ghosts, the normalized squared error of the spectrum of the actual vs the expected signature is computed. We used a typical 680 cu.in airgun string and found via simulations that a depth interval of 1 or 1.5 m between airguns is optimum when considering deghosting performance and operational feasibility. When more subarrays are combined, preliminary simulations are necessary to determine the optimum depth combination. The frequency notches introduced by the excess use of subarrays may negatively affect the deghosting performance. Two or three slanted subarrays can be combined to remove the ghost effect. The sequence combination may partly affect deghosting but this can be eliminated by matched filtering. Directivity comparison shows that a multi-depth slanted source can significantly attenuate the notches and widen the energy transmission stability area.

Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence

On the basis of the extended Huygens-Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector,the characteristics of the partially coherent Gaussian Schell-model（GSM） beams propagating in slanted atmospheric turbulence are studied.Using the cross-spectral density function（CSDF）,we derive the expressions for the effective beam radius,the spreading angle,and the average intensity.The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically.The influences of the coherence degree,the propagation distance,the propagation height,and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.

拟齐次符号Slant H-Toeplitz算子的交换性

刻画了拟齐次符号的Slant H-Toeplitz算子在Bergman空间上的交换性,当不同次拟齐次符号Slant H-Toeplitz算子满足交换性,则必有一符号函数为0;相同非负次拟齐次符号Slant H-Toeplitz算子满足交换性,两符号函数线性相关.这与Bergman空间上具有相同符号的Toeplitz算子的交换性不同.

Nonlinear Trajectory SAR Imaging Algorithms:Overview and Experimental Comparison

The nonlinear characteristics of the motion trajectory of the synthetic aperture radar(SAR)flight platform can lead to severe two-dimensional space-variance characteristics of the signal,greatly affecting the imaging quality,and are currently considered as one of the difficulties in the field of SAR imaging.This paper first discusses the nonlinear trajectory SAR model and its space-variance characteristics and then discusses algorithms such as scaling-based algorithms,interpolation-based algorithms,time-domain algorithms,and hybrid algorithms.The relative merits and applicability of each algorithm are analyzed.Finally,computer simulation and actual data validation are conducted.

用于图像内容认证的半脆弱水印新算法

为了提升数字图像内容认证的准确性,提出一种新颖的半脆弱水印算法.引入相关块组的概念,并将相关块组进一步划分为子块组,轮流使用每个子块组内特定块生成水印,最终将水印嵌入到子块组内的其他块中.算法根据图像内容自适应选取量化步长,结合Slant变换高能量集中性及直流量化原理完成水印嵌入过程,认证过程中使用新的噪声过滤策略并通过投票方式确定篡改发生位置.实验表明:该算法能有效地提高含水印图像的质量及防止水印信息的未授权提取,在应对裁剪、替换等常规处理时定位精度提升明显.算法抵抗偶然攻击的能力强,新噪声策略有效地改善了针对篡改区域的识别效果.

一种基于Slant变换和SVD的稳健性数字水印算法

针对奇异值分解(SVD)存在的虚警错误和水印隐蔽性与鲁棒性的矛盾问题,提出了一种基于Slant变换和SVD的稳健性数字水印算法。对二值水印图像进行Arnold置乱和Logistic映射双因子加密预处理,增强水印信息安全性;将原始载体图像分成8×8不重叠子块分别对其进行Slant变换和块奇异值分解;然后将水印图像SVD后的左奇异矩阵和奇异值矩阵相乘作为水印主成分嵌入到每个子块的最大奇异值中。仿真实验结果表明,该算法不仅有效解决了传统SVD水印算法的虚警问题,提升了运行速度和水印安全性,在具有较好隐蔽性的同时,对JPEG压缩、噪声、滤波、几何攻击等也有较好的稳健性。

基于方向小波与Slant变换的鲁棒水印算法

设计了一种基于内容的数字水印算法。算法以方向小波变换提取的独立分块图像正则方向作为水印信息,根据图像噪声可见函数将水印信息量化嵌入分块图像Slant变换中频系数之中。实验结果显示,算法对于常见图像处理和几何攻击均具有很强的鲁棒性,与基于DCT和PST变换的算法相比,该算法能够更有效地抵抗一些恶意和非恶意操作同时实施的操作。

AN APPROACH TO IMPROVE PSEUDORANGE DIFFERENTIAL GPS

The pseudorange residual error of imperfect correction of the ionospheric time delay in pseudorange (PR) differential global positioning system (DGPS) is analyzed. The different vertical total electron content (TEC) and slant factors at the pierce points of satellite signals are the reasons of the residual error. An improved pseudorange differential approach is proposed and the effect of this new PR differential operation verified by using the simulation.

改进的Ridgelet变换图像去噪方法

提出了基于平移不变的ridgelet去噪方法,与平移不变小波去噪相比较,试验结果表明平移不变的ridgelet算法在消除和抑制噪声的同时能更好地保留图像边缘特征,并且显著改善了峰值信噪比。

结合图像归一化与Slant变换的鲁棒图像哈希

为了提高图像哈希算法抵抗几何攻击的性能,提出了一种结合图像归一化和Slant变换的图像哈希算法。使用几何不变矩将原始图像进行归一化操作得到仿射不变图像,仿射不变图像分块并进行Slant变换,根据用户密钥选择Slant变换中频系数极性并生成最终的图像哈希序列。实验结果表明该算法对常见图像操作处理和常见几何攻击鲁棒,对原始图像内容和用户密钥敏感,是一种有效的图像哈希算法。

与Slant矩阵相关的多通道滤波器的构造

为了构造多通道滤波器,研究了Slant矩阵各行元素和的特性.由该矩阵的第一行构造了一个低通滤波器,其它各行构造了一组高通滤波器.同时借助多相位分解,证明了多通道低通滤波器满足完全重构条件.给出了分解实例,验证了构造的多通道分解滤波器的有效性.

基于数字脊波和样条权神经网络的高光谱图像融合分类

提出了一种基于数字脊波和样条权神经网络的高光谱图像融合分类新算法。在特征级融合中,针对数字脊波的特点,对不同分辨率的脊波系数采用局部信息熵进行融合,并运用样条权神经网络实现了分类。在决策级融合中,提出了先用样条权神经网络进行预分类,然后用主体投票法进行决策融合的算法,为避免作为局部分类器的神经网络结构过于复杂,对输入数据先进行了像素层的融合实现数据降维,这实质上体现了一种多层次融合的思想。实验结果表明,这两种方法都能有效的实现高光谱图像的融合及分类,在较少的训练样本下分类精度能达到92%以上,其中特征级融合可达到95.87%。

Preliminary Results of 4-D Water Vapor Tomography in the Troposphere Using GPS

Slant-path water vapor amounts （SWV） from a station to all the GPS （Global Positioning System） satellites in view can be estimated by using a ground-based GPS receiver. In this paper, a tomographic method was utilized to retrieve the local horizontal and vertical structure of water vapor over a local GPS receiver network using SWV amounts as observables in the tomography. The method of obtaining SWV using ground-based GPS is described first, and then the theory of tomography using GPS is presented. A water vapor tomography experiment was made using a small GPS network in the Beijing region. The tomographic results were analyzed in two ways： （1） a pure GPS method, i.e., only using GPS observables as input to the tomography, （2） combining GPS observables with vertical constraints or a priori information, which come from average radiosonde measurements over three days. It is shown that the vertical structure of water vapor is well resolved with a priori information. Comparisons of profiles between radiosondes and GPS show that the RMS error of the tomography is about 1-2 mm. It is demonstrated that the tomography can monitor the evolution of tropospheric water vapor in space and time. The vertical resolution of the tomography is tested with layer thicknesses of 600 m, 800 m and 1000 m. Comparisons with radiosondes show that the result from a resolution of 800 m is slightly better than results from the other two resolutions in the experiment. Water vapor amounts recreated from the tomography field agree well with precipitable water vapor （PWV） calculated using GPS delays. Hourly tomographic results are also shown using the resolution of 800 m. Water vapor characteristics under the background of heavy rainfall development are analyzed using these tomographic results. The water vapor spatio-temporal structures derived from the GPS network show a great potential in the investigation of weather disasters.

SLANT IMMERSIONS OF COMPLEX SPACE FORMS AND CHEN'S INEQUALITY

A submanifold in a complex space form is called slant if it has constant Wirtinger angles. B. Y. Chen and Y. Tazawa proved that there do not exist minimal proper slant surfaces in CP2 and CH2. So it seems that the slant immersion has some interesting properties. The authors have great interest to consider slant immersions satisfying some additional conditions, such as unfull first normal bundles or Chen’s equality holding. They prove that there do not exist n-dimensional Kaehlerian slant immersions in CPn and CHn with unfull first normal bundles. Next, it is seen that every Kaehlerian slant submanifold satisfying an equality of Chen is minimal which is similar to that of Lagrangian immersions. But in contrast, it is shown that a large class of slant immersions do not exist thoroughly. Finally, they give an application of Chen’s inequality to general slant immersions in a complex projective space, which generalizes a result of Chen.

基于超混沌和Slant变换的鲁棒水印算法

为进一步提高水印算法的安全性和抗攻击能力,结合超混沌和Slant变换的优点,提出一种基于超混沌和Slant变换的鲁棒水印算法。首先,在隐藏水印之前采用超混沌系统对水印图像进行加密,提高了待隐藏图像的安全性;其次,将原始载体图像划分成大小为8×8的不重叠分块并对各个分块分别进行Slant变换;最后,将加密后的水印图像隐藏到Slant变换后的直流系数和中频系数中。大量的仿真结果表明,本文算法具有较好的隐蔽性,对JPEG压缩、噪声、滤波、缩放、对比度调整等攻击具有较好的抗攻击能力。与相似算法相比,本文算法具有更好的鲁棒性能。

Tropospheric Wet Refractivity Tomography Based on the BeiDou Satellite System

This paper presents a novel approach for assessing the precision of the wet refractivity field using BDS （BeiDou navigation satellite system） simulations only,GPS,and BDS＋GPS for the Shenzhen and Hongkong GNSS network.The simulations are carried out by adding artificial noise to a real observation dataset.Instead of using the δ and σ parameters computed from slant wet delay,as in previous studies,we employ the Bias and RMS parameters,computed from the tomography results of total voxels,in order to obtain a more direct and comprehensive evaluation of the precision of the refractivity field determination.The results show that：（1） the precision of tropospheric wet refractivity estimated using BDS alone （only 9 satellites used） is basically comparable to that of GPS; （2） BDS＋GPS （as of current operation） may not be able to significantly improve the data＇s spatial density for the application of refractivity tomography; and （3） any slight increase in the precision of refractivity tomography,particularly in the lower atmosphere,bears great significance for any applications dependent on the Chinese operational meteorological service.