海上常规拖缆采集的地震数据存在受海水面虚反射(鬼波)引起的陷波特性,而近年发展的上/下缆采集技术可以压制鬼波,但仍然存在等效陷波。为此,提出了基于f-k域上/下缆合并算子确定上/下缆沉放深度的方法,进而分析了历年来国内外油公司采用的上/下缆沉放深度的合理性。针对目前国内拖缆沉放深度的最大范围,通过对不同上/下缆沉放深度下上/下缆合并算子的等效陷波特征分析,确定出等效陷波出现的频带范围在目的层有效频带范围以外的上/下缆最优沉放深度组合,系统优选出了12组上/下双缆以及3组上/中/下三缆陷波作用相对较小些的上/下缆沉放深度最优组合,为实际上/下缆采集时缆深选择提供了理论依据。

David Hill, Leendert Combee, and John Bacon, WesternGeco, introduce a new configuration for towed-streamer seismic data acquisition. They argue that the ver/under technique is a major advance on conventional techniques providing previously unattained signal bandwidth, where the low-frequency content gives deeper penetration, and therefore, improved imaging beneath basalt, salt, and other highly absorptive overburdens. In a conventional towed-streamer marine acquisition configuration, shallow sources and shallow cables increase the high-frequency content of the seismic data needed for resolution. However, shallow sources and shallow cables attenuate the low frequencies, which are necessary for stratigraphic and structural inversion, and for imaging deep objectives. Towing shallow also makes the data more susceptible to environmental noise. In contrast deep sources and deep cables enhance the low frequencies, but attenuate the high frequencies. In addition, the data recorded via a deep tow have a higher signal-to-ambient-noise ratio due to the more benign towing environment. A conventional towed-streamer survey design therefore, attempts to balance these conflicting aspects to arrive at a tow depth for the sources and cables that optimizes the bandwidth and signal-to-noise ratio of the data for a specific target depth or two-way travel time, often at the expense of other shallower or deeper objectives. An over/under, towed-streamer configuration is a method of acquiring seismic data where cables are typically towed in pairs at two different cable depths, with one cable vertically above the other. The depths of these paired cables are typically significantly deeper than would be used for a conventional towed-streamer configuration. In conjunction with these paired cables, it is possible to acquire data with paired sources at two differing source depths. Again, the depths of these paired sources are typically significantly deeper than would be used for a conventional towed-streamer configuration. The seismic data recorded by the over/under towed-streamer configuration are combined in data processing into a single dataset that has the high-frequency characteristics of conventional data recorded at a shallow towing depth and the lowfrequency characteristics of conventional data recorded at a deeper towing depth. This combination process is commonly referred to in the geophysical literature as deghosting. The current benefits of over/under data compared with conventional data can be summarized as: - A significantly broader signal bandwidth, where the lowfrequency content gives deeper penetration, and therefore, improved imaging beneath basalt, salt, and other highly absorptive overburdens. Moreover, the bandwidth extension to lower frequencies makes seismic inversion less dependent upon model-based methods - A simpler signal wavelet with the bandwidth extension to higher frequencies giving enhanced resolving power, allowing for a more detailed stratigraphic interpretation - Higher signal-to-ambient-noise ratio as a consequence of the deeper towed-cable pairs - An extended weather window enabled by the deeper towed-cable pairs.

David Carlson, Andrew Long, Walter S02llner, Hocine Tabti, Rune Tenghamn, and Nils Lunde discuss the theory behind a towed dual-sensor developed by Petroleum Geo-Services to operate at deeper depths and deliver de-ghosted data.

Robert Soubaras and Robert Dowle explain how a broadband solution leveraging thebenefits of towing variable depth solid streamers and proprietary deghosting processing techniques can resolve a longstanding challenge in marine seismic acquisition.

We considered the importance of low frequencies in seismic reflection data for enhanced resolution, better penetration, and waveform and impedance inversion. We reviewed various theoretical arguments underlining why adding low frequencies may be beneficial and provided experimental evidence for the improvements by several case studies with recently acquired broadband data. We discussed where research and development efforts in the industry with respect to low frequencies should be focusing.

Removing the receiver ghost before migration provides better low and high frequency response as well as a higher signal-to-noise ratio for preprocessing steps such as multiple suppression and velocity analysis. We propose a bootstrap approach that self-determines its own parameters for receiver deghosting. The recorded data in shot domain are first used to create mirror data through a 1D ray tracing based normal moveout correction method; then both the recorded and mirror data are used to jointly invert for the receiver-ghost-free data. We demonstrate with both synthetics and real data that our deghosting method can, in many situations, reliably remove the receiver ghost for marine towed streamer data in the premigration stage. Here, this technique is used to partially improve the bandwidth of conventional streamer data but for optimal broadband seismic, a full broadband system (like BroadSeis) is necessary.

Conventional marine acquisition uses a streamer towed at a constant depth. The resulting receiver ghost notch gives the maximum recoverable frequency. To push this limit, the streamer must be towed at a quite shallow depth, but this compromises the low frequencies. Variable-depth streamer (VDS) acquisition is an acquisition technique aimed at achieving the best possible signal-to-noise ratio at low frequencies by towing the streamer very deeply, but by using a depth profile varying with offset in order not to limit the high-frequency bandwidth by notches as in conventional constant-depth streamer acquisition. The idea is to use notch diversity, each receiver having a different notch, so that the final result, combining different receivers, will have no notches. The key step to process VDS acquisitions is the receiver deghosting. We found that the optimal receiver deghosting, instead of being a preprocessing step, should be done postimaging, by using a dual-input, migration and mirror migration, and a new joint deconvolution algorithm that produces a 3D real amplitude deghosted output. This method can be applied poststack, the inputs being the migration and mirror migration images and the output being the deghosted image. Using a multichannel joint deconvolution, the inputs are the migrated and mirror migrated image gathers and the outputs are the prestack deghosted image gathers. This method preserves the amplitude-versus-offset behavior, as the deghosted output can be seen on synthetic examples to be equal to a reference computed by migrating the data modeled without any reflecting water surface. A real data set was used to illustrate this method, and another one was used to check the possibility of performing prestack elastic inversion on the deghosted gathers.

Variable-depth streamer acquisition is an acquisition technique aiming at achieving the best possible signal-to-noise ratio at low frequencies by towing the streamer very deeply, but by using a depth profile varying with offset in order not to limit the high frequency bandwidth. Previous papers have shown how a joint deconvolution allows the post-stack deghosting of such variable-depth streamer acquisitions, and the purpose of this paper is to show how this can be generalized to a multichannel joint deconvolution that allows pre-stack though post-imaging deghosting of such acquisitions. After computing migrated gathers as well as mirror migrated gathers, a deghosted gather is computed through joint deconvolution by assuming a parametrical form in offset for the events. This method preserves the AVO behaviour. Synthetic and real data examples are shown.

斜缆地震采集采用水下电缆变深度施工方式,从而产生连续变化的鬼波陷波频率,有利于最大程度地压制鬼波,获得高信噪比和高保真的宽频地震数据.针对珠江口盆地白云凹陷深水复杂构造区斜缆三维地震资料,采用了不同于常规拖缆地震资料处理的子波处理、三维水面相关多次波去除（3D SRME）、镜像偏移和联合反褶积去鬼波、Q补偿等斜缆地震资料处理关键技术,有效地去除了多次波,压制了鬼波,拓宽了低频和高频信息,提高了地震资料信噪比和分辨率.斜缆地震资料处理显著改善了中深层复杂构造成像效果,更好地满足了白云凹陷深水复杂构造区地震反演和解释的需求.

Variable depth towed streamer acquisition results in receiver ghost diversity leading to an increase in temporal bandwidth. This paper describes a pre-migration processing algorithm that derives a surface datum ghost free model of the data. The model may be used to receiver de-ghost and re-datum so that conventional flat streamer algorithms can be used.