Acquisition Of Seismic Surveys Research Articles

Near Surface Characterization by Seismic Surface Wave Inversion

Surface waves are usually treated as unwanted coherent noise and steps are taken to remove them using geophone receiver arrays during seismic survey acquisition. During early data processing, attempts are made to further remove the ground roll. Recently, there has been a growing interest in using surface waves for estimating the near surface velocity model. Surface waves propagate in the shallow subsurface and can be used to derive shear wave velocities of the near surface.

Multidisciplinary analysis of hydraulic stimulation and production effects within the Niobrara and Codell reservoirs, Wattenberg Field, Colorado — Part 1: Baseline reservoir conditions

In the Wattenberg Field, the Reservoir Characterization Project at the Colorado School of Mines and Occidental Petroleum Corporation (Oxy) (formerly the Anadarko Petroleum Corporation) collected time-lapse seismic data for characterization of changes in the reservoir caused by hydraulic fracturing and production in the Niobrara Formation and Codell Sandstone member of the Carlile Formation. We have acquired three multicomponent seismic surveys to understand the dynamic reservoir changes caused by hydraulic fracturing and production of 11 horizontal wells within a 1 mi2section (the Wishbone Section). The time-lapse seismic survey acquisition occurred immediately after the wells were drilled, another survey after stimulation, and a third survey after two years of production. In addition, we integrate core, petrophysical properties, fault and fracture characteristics, as well as P-wave seismic data to illustrate reservoir properties prior to simulation and production. Core analysis indicates extensive amounts of bioturbation in zones of high total organic content (TOC). Petrophysical analysis of logs and core samples indicates that chalk intervals have high amounts of TOC (>2%) and the lowest amount of clay in the reservoir interval. Core petrophysical characterization included X-ray diffraction analysis, mercury intrusion capillary pressure, N2gas adsorption, and field emission scanning electron microscopy. Reservoir fractures follow four regional orientations, and chalk facies contain higher fracture density than marl facies. Integration of these data assist in enhanced well targeting and reservoir simulation.

Nodal land seismic acquisition: The next generation

Within the last two years six new land seismic nodal acquisition systems have been launched, a pace unmatched even during the oil boom of the late 2000s/early 2010s. Any acquisition system that utilizes recording instrumentation that does not incorporate cables is often referred to as a nodal system. Some instruments, however, are beginning to blur what initially appears to be a clear boundary. For example, the U-Node system from Seismic Instruments utilizes a node that records data from up to 24 different channels that can then be stored locally or transmitted via Wi-Fi to a central system. The reduction in cabling, which is usually cited as the core advantage of nodal recording, is therefore limited to the backbone connecting the central recording system to the field recording units. In this paper we will concentrate on nodes that are designed to record data from a single point and are thus typically limited to six or fewer channels. Over the history of nodes there have been six major categories developed (listed roughly in the order of their introduction): 1. Delayed data – Data is stored on the node and then transmitted after each shot, or stacked series of shots, is completed. 2. Remote-controlled – data is recorded internally but recording is initiated via radio messages. 3. Remote-synchronized – data is recorded continuously but the timing signal is issued via radio. 4. Real-time data – Data is transmitted in real-time. 5. Real-time QC – Status and or quality control data is transmitted in real-time. 6. Blind – the node records data internally and does not provide status or QC information in real-time. In this article we look at how nodal systems have evolved over the last 50 years. We begin with a historical overview starting from the early 1970s finishing in 2015. We then introduce the latest nodal systems and look at the implications of their use for seismic survey acquisition logistics. Finally, we will discuss the implications of these new systems and make some suggestions about where future developments should lie.

Smart DAS upholes for simultaneous land near-surface characterization and subsurface imaging

A novel integrated land seismic imaging system that uses distributed acoustic sensing (DAS) in a grid of shallow upholes is proposed. This system allows simultaneous land near-surface characterization and subsurface imaging in a cost-efficient manner. Using this fiber-optic system, uphole velocity surveys can be acquired at any time with a single shot, since all depth levels are recorded simultaneously. Dense grids of smart DAS upholes accurately characterize long-wavelength statics and reduce uncertainty in exploration for low-relief structures. In addition, connecting multiple upholes with a single fiber enables efficient acquisition of seismic surveys with buried vertical arrays, which can provide superior images of the deeper subsurface than surface seismic, but with improved accuracy, since they bypass most of the near-surface complexities. The smart DAS upholes can deliver on-demand surveys that simultaneously characterize the near surface and perform deep reflection imaging of oil and gas targets for exploration, development, or reservoir monitoring. We have performed successful field testing of the smart DAS system on an onshore field in Saudi Arabia. Such a system is long overdue for land regions that have complex near-surface conditions.

How a new cable-less land seismic survey acquisition system was born

John Flavell Smith recounts how Scottish company Vibtech is winning over the sceptics with its cable-less onshore seismic acquisition system in which key ingredients are technologies originating from the mobile communications and Internet communities. The Vibtech story started quite by chance. Vibtech co-founders Bill Park and John Flavell Smith had worked together at GECO in the UK during the late 1980s and both had subsequently returned to Scotland. In 1995, Flavell Smith saw a small advertisement that Park had placed in the press looking for field personnel and called him. They arranged to meet up and that was the starting point for the Vibtech journey. Both recognized the need to rid land and transition zone seismic systems of the messy and problematic digital cables and connectors which are responsible for huge logistical, troubleshooting and HSE issues. If this could be done, then system channel counts could increase and explorationists could concentrate once more on data quality and not on the logistics of moving massive recording systems. To achieve this, they had the idea of applying techniques from the burgeoning mobile telephone and internet markets to seismic instrumentation. Vibtech was founded to explore those ideas and the world’s first Cellular Seismic acquisition system was born. This would be the first time that a seismic acquisition system capitalized on technologies developed for other industries and integrated them into the system architecture, breaking the mould of seismic instrumentation design, which had historically used bespoke engineering solutions. The great advantage of this design philosophy was that emerging new technologies could be incorporated into the system without the need to completely re-design the system. Vibtech has constantly seized upon these opportunities to refine its systems. The huge operational benefits of cable free and light weight systems are obvious and are the holy grail for the seismic designer and operator alike. These benefits have been widely discussed previously in this publication, by Burger (2000), Jack (2003), and Heath (2004), to name a few. It is interesting to note that Vibtech’s competitors have recognized that its approach to delivering a cable free system is on the right path and have recently changed their plans to follow. Vibtech has now designed, developed, and commercialized a full-scale seismic acquisition system from the ground up, something which many have tried but few have managed. In the process, Vibtech has raised well in excess of $20 million in venture capital, built the workforce to more than 30 personnel, including an in-house R&D team of engineers, opened offices in London and Houston, and has representation in all of the major exploration regions of the world. Vibtech systems have now recorded more than 100 3D surveys in North America, Australia, and China.

Some considerations on the interpretation of seabed images based on commercial 3D seismic in the Faroe‐Shetland Channel

AbstractCommercial three‐dimensional (3D) seismic surveys now cover much of the continental slope and basin floor areas of the Faroe‐Shetland Channel. A mosaic of the seabed picks derived from these data sets and enhancement with visualisation techniques has resulted in detailed relief images of the seabed that testify to the action of a number of sedimentary processes such as glaciation, downslope and alongslope processes. The wealth of detail in these images is remarkable and extremely valuable for the identification and interpretation of seabed features. However, the level of detail can seduce the interpreter into treating the image purely as an aerial photograph. The interpreter needs to understand the limitations and artefacts inherent in such images to use them appropriately. This paper will present the major artefacts observed in the images and how certain aspects of 3D seismic survey acquisition and processing have contributed to their presence. The vertical and horizontal resolution of the images will also be discussed. Although primarily focused on seabed imagery these comments are equally pertinent to the application of 3D seismic surveys for shallower objectives than for which they were primarily designed.

How to optimize pilot sweep of vibratory sources in seismic surveys

Prof Yuriy Tyapkin, of the Ukrainian State Geological Prospecting Institute, and Enders A. Robinson, Maurice Ewing and J. Lamar Worzel professor emeritus of geophysics, Columbia University, New York City, have been developing a solution to what they believe is a longstanding omission in the effectiveness of the pilot sweep of vibratory sources in seismic survey acquisition. Successful application of high-resolution seismic methods requires the evaluation of each element in the seismic system to ensure that each part makes an optimal contribution. This principle extends from seismic signal radiation through to data processing where good performance and correct parameter selections are required. Unfortunately, unlike the data processing stage, this important field operation is not usually optimised. The purpose of our study was to eliminate the obvious non-co-ordination of field operations with data processing so that both stages co-operate fully and optimally. We addressed not only the beginning of the seismic system, the source of the seismic signal, but the system as a whole. To validate its feasibility, this optimisation was based upon the Vibroseis technique, primarily because of its versatility in controlling the signal spectrum. The method illustrated here for optimising a pilot sweep signal, using synthetic data as examples, allows the best data quality to be achieved with limited energy expenses. The reflectivity function, also called the impulse response, allows geophysicists to investigate structural and reflective properties of geologic boundaries in the subsurface. Unfortunately the response is always distorted by the filtering (smoothing) effect of a wavelet radiated by a seismic source (Robinson and Treitel, 1980). In order to remove or, more exactly, to reduce the impact of this factor, special processes known as deconvolution are widely used. Unless such procedures have been implemented, seismic data cannot be interpreted in detail and with confidence. Importantly, the deconvolution methods, among which the Wiener filters are most widespread, usually have an optimum character. Favourable conditions for the subsequent resolution improvement should be created, even in the field, so that both stages of the seismic system, field operations and data processing, blend harmoniously and concur in achieving their common objective. The problem, easily solved in this case, is most germane to Vibroseis systems, controllable and hence adaptable to the seismic properties of any area. The Vibroseis technique, conceived more then 40 years ago, is now mature and deployed by a large variety of users in the oil industry. In recent years, vibrators have been the energy sources for over half of the 2D/3D seismic crews operating worldwide. Strangely enough, however, most if not all of them have not benefited from real optimisation of the sweep signal, the most important parameter of vibratory sources. As a matter of fact, any attempt to optimise the pilot sweep at the input to the seismic system made without reference to the properties of the system (Goupillaud, 1976; Dougherty and Justice, 1988) is doomed to fail. This is because it bears no relation to the optimum result at the output of the system. Instead of special preliminary quantitative estimations, a testing of various sweep parameters – the frequency band and the type of non-linearity with associated characteristics foremost among them – followed by visual (so, subjective) analysis of the results is implemented in order to choose a suitable vibratory signal (e.g. Pritchett, 1994). This conventional approach sometimes causes a highly inefficient distribution of the generated energy along the frequency axis, for example, groundless significant extra expenses, on the one hand, and deterioration of the data quality compared with the best (optimum) that should and could be attained, on the other. A method that takes the properties of the entire seismic exploration system into account was first developed in Widess (1982) for optimisation of the pilot sweep. It supposed a special filter to be used for optimising a local criterion for the vertical resolving power of the system. However, the Wiener deconvolution filter, which has enjoyed widespread use for source wavelet deconvolution in exploration seismology, is certain to be more helpful in such a case. Preoptimisation of the signal spectrum at the input to the Wiener deconvolution filter was described in Franks (1969). To avoid some obstacles, however, the solution was simplified and reduced to a band-limited form. A method for optimisation of the spectrum of the pilot sweep which overcomes the shortcomings of the Vibroseis technique described above is the subject here enabling the most efficient use of the radiated energy as a result of its rational distribution along the frequency axis. Emitting the optimum pilot sweep along with finishing Wiener deconvolution filtering at the very end of processing provides the best data quality under a natural restriction on the source energy available.