In a modern marine 3-D seismic survey, typically, more than 100 000 traces per square km are recorded. Seismic Library Data Where You Need It Our expanding data library currently includes over 28,000 square miles of 3D onshore and in the Gulf of Mexico. Only one of these raypaths, CBG, is shown. Data quality can often be better than conventional 3D’s by an order of magnitude. But the language of the day still contained some disturbing phrases such as “Sideswipe” or “Out of the Plane”. The source-station and receiver-station spacings along this 2D profile both have the same value for Δx, which results in a stacking bin width of Δx/2. In particular, wide towed marine streamer data (multi-source, multi-streamer) after DMO had a very striped appearance. Overviews are often useful and this paper is written for the geophysicist who has not been deeply involved with the design and analysis of 3D seismic survey acquisition for the past 15 years or so, and would like to have an idea of what happened, what’s happening now and what is likely to happen in the future. Previous publications on the topic of seismic acquisition show that the trace spacing (i.e., the stacking-bin dimension) along a 2D seismic profile is one-half the receiver-station spacing (assuming the usual condition that the source-station spacing along the line is equal to or greater than the receiver-station spacing). Galbraith describes the parameters involved in onshore 3D seismic survey design. Starting in the late 80’s and early 90’s it became obvious that a lot of the 3D surveys contained more noise than signal - or, at least, more noise than previous 2D. Stated another way, the source-station and receiver-station spacings should be one-half the narrowest horizontal dimension that needs to be interpreted from the 3D data. Aram Aries - 1,000s of channels available. So the quest to kill the noise began. Offset and, to a lesser extent, azimuth distribution was recognized as the most important factor. The horizontal resolution a 3D seismic image provides is a function of the trace spacing within the 3D data volume. Contractors quickly tired of trying to shoot bricks through trees, so the slanted geometries were born. 1, each stacking bin has lateral dimensions of Δx and Δy. The stacking fold is shown by the sequence of numbers at the base of the diagram and, in this geometry, the maximum fold is 2. This method was an attempt to use a viable subset of the fully sampled 3D geometry. or. Progenitor of the wide vs. narrow debate. For a shallow target depth, Z1 , the stacking fold is low because there is only a small number, N1, of source-receiver pairs that can produce individual raypaths that reflect from point A. Austin, Texas: Bureau of Economic Geology, University of Texas. We were sold! In 2D acquisition geometry, the inline stacking fold, FIL, is a function of two geometrical properties: the number of active receiver channels and the ratio between the source-station interval and the receiver-station interval. Statics: How do geometries affect static calculations? Or is noise attenuation more important than signal? The imaging deficiencies of 2D seismic profiling were remedied by the implementation of 3D seismic data acquisition, which allows data processing to migrate reflections to their correct image coordinates in 3D space. The data obtained from such a survey is therefore very valuable, and if protected from disclosure constitutes a trade secret. 2D seismic Survey large areas with 2D seismic. In fact, Canadian geophysicists are internationally recognized as experts in the design, acquisition and processing of 3D seismic programs. Time will tell! Principles of Onshore 3-D Seismic Design. Imaging is often done using pre-stack time migration and results appear comparable to other geometries. Planning Land 3-D Seismic Surveys. 4 establishes the principle that inline stacking fold is one-half of the active receiver stations when the source-station interval equals the receiver-station interval. Lines displayed perpendicular to in-lines are called crosslines. ). Many random 3D surveys have now been conducted and the results indicate that this method does have considerable merit in reducing the seemingly ubiquitous footprint suffered by other geometries. Later it was realized that the largest minimum offset was also reduced. Galbraith, M. 1994. 2 – Example of the narrowest feature that must be seen in a 3D image. A seismic survey is used to investigate Earth’s subterranean structure and is mainly used for oil and gas exploration. Previously only very large companies were able to utilize this state-of-the-art, computer-intensive, 3-D The inline stacking fold is the number of independent reflection points that occur at the same subsurface coordinates, which is the same as the number of reflection points intersected by each vertical dashed line. Many articles were written extolling its virtues as the only 3D geometry you would ever need. New processing algorithms often appear to make a substantial difference to individual shots (or receiver line components of shots). A large volume of data is being converted to make this online archive. The raypath diagram in Fig. To coin a phrase, today’s geometries are Designer geometries! In the early 80’s orthogonal geometries were the norm. Moving shot and receiver lines one half ( or quarter, etc.) reads like this: This tried and true method persisted throughout. A prerequisite is equal sampling of shots and receivers for centre-spread land data acquisition and shot intervals half the receiver station intervals for marine end-of-spread acquisition. In the 90’s geophysics came to grips with this plethora of geometries. Near surface scatterers can cause each of the linear noise waves to be reflected. This was also predictable from theory and has been remarked on by a number of authors. Seismic survey consultation tailored to your imaging challenges. The raypath picture in Fig. The answer was 3D. As a programmer then, it was my task to build methods to process this data set. You must log in to edit PetroWiki. Offset analysis is a technical topic that goes beyond the scope of this discussion. The final CMP coverage extended from the edges of the loops to their center. Inline coordinates increase from west to east as shown. More information. Flexible 3-D seismic survey design Gabriel Alvarez1 ABSTRACT Using all available subsurface information in the design of a 3-D seismic survey, we can better adjust the acquisition effort to the demands of illumination of the target horizon. It began as early as 1964 when Hugh Hardy of Esso shot the world’s first cross-spread - before it even had a name! Geometry was the weapon of choice.  These stacking bins can be square or rectangular, depending on an interpreter’s preferences. Significant cost savings can also be realized. 3D surveys employing multiple sources and streamers are now the norm, although many shallow water high resolution geohazard surveys are still shot in 2D. The vertical column shows the coordinate position of one particular stacking bin. Cordsen, A., Galbraith, M., and Peirce, J. In comparison, 30 pounds might be used for a large construction-site blast and 2,000 to 4,000 pounds for a medium-sized quarry or mine blast. ... 3D acoustic and viscoelastic, anisotropic finite difference modeling. A 3D seismic survey may cover many square miles of land and may cost $40,000 to $100,000 per square mile or more. Mike Galbraith is the President of Seismic Image Software Ltd., Calgary. The number of source-receiver pairs that can contribute to the image at B is typically confined to those source and receiver stations that are offset horizontally from B by a distance that is no larger than depth Z2 to reflection point B. In a 3D context, the stacking fold is the product of the inline stacking fold (the fold in the direction in which the receiver cables are deployed) and the crossline stacking fold (the fold perpendicular to the direction in which the receiver cables are positioned). With over 300 3D surveys and 22,000 miles of 2D, our library encompasses some of the most prolific oil and gas basins in the United States and the Gulf of Mexico. Barrett Corporation (BBC) completed 3D seismic surveys of the Tumbleweed Unit. Imagine the excitement as the display was unrolled and we walked down the corridor (and down in time) inspecting each slice as we went. A partial list (who can remember them all?) Fig. Geotec S.p.A. is a national leader when carrying out geophysical surveys using the 2D/3D seismic reflection method. This article talks about some of the basic concepts that it is important to understand to properly design a 3D seismic survey. Exploration Geophysics 25 (2): 71–77. 3D geometries differ in their ability to resolve 3D static delays. It will survey for hydrocarbons over a 5,000 km 2 area in the southern Atlantic for the Malvinas 3D programme in Argentina. Equally obvious is the question of what types of noise must be suppressed in this new wavefield environment? In the pre-stack domain, DMO was the algorithm of choice for many years (and still is in many parts of the world). Geophysical Pursuit is a relationship-driven seismic company specializing in the acquisition and licensing of seismic data critical to understanding oil and gas reservoirs. These were often referred to as drunken bricks (the terminology is clearly unrelated to the inventors!). In January 2007, Stewart purchased Tumbleweed Unit leases from BBC. Expensive but very interpretable! The design of geometries for such cases will carry different challenges than have been tackled so far. The distance between adjacent source points along a seismic line is the source-station spacing; the distance between adjacent receiver arrays along that same line is the receiver-station spacing. But the language of the day still contained some disturbing phrases such as “Sideswipe” or “Out of the Plane”. Ebrom, D., Li, X., and McDonald, J. On the question of reducing multiples, this is the most active area of research today. Using the results of the seismic surveys to help determine specific locations for exploratory drilling, Stewart has proposed up to six site-specific exploratory wells. In 1978, a 3D survey was acquired near Calgary using orthogonal shot lines and receiver lines. With this offset criterion to determine the number of source-receiver pairs that can contribute to the seismic image at any subsurface point, we see that the stacking fold at depth Z2 would be N2 , as Fig. Canceling shot noise (linear and backscatter) with effective geometries. The term inline is defined as the direction in which receiver cables are deployed, which is north/south in this example. Download Free PDF. State of the art equipment - 24 bit recording. The maximum stacking fold for this six-receiver geometry is 3. The 3D‐seismic survey would have proportionately fewer kilometers of camp‐move trails than the 2D survey because the seismic grid would be so closely spaced, but the 580 km of camp‐move trails stated in the SAExploration plan should be considered a minimum. Thus large bins set the limit on resolution and therefore on the maximum useful frequency. Seitel designs, markets, and executes new seismic surveys for leading oil and gas exploration companies. In Fig. This imaging principle causes the targeted stratigraphic anomaly to be expressed on three or four adjacent seismic traces. Post stack depth migration has also made an appearance in the past few years. Mike’s areas of interest are 3D Field Survey , analysis and determination of artefacts in 3D acquisition data, 3D field QC techniques and 3D processing algorithms. It was rumored to be the geometry with the biggest footprint of all. The main pieces of the puzzle involved modifying the existing 2D crooked line geometry software to handle the new concept of 3D CMP bins - and a new program to display time slices. To request a shapefile set for GPI’s 3D or 2D seismic library, please visit our contact page. Land 3-D Survey Design by Computer. Later, other post-stack methods were added to the arsenal - Finite Difference, Phase Shift and other more exotic variants. The nature of offset distribution and azimuth distribution and how they change with depth became crucial in studying the noise problem. Wide line spacing is the norm - up to one kilometer or more between shot and receiver lines. Once again if two is good, three must be better. In a similar vein, it is also worth remembering that if the CMP stack for one geometry attenuates the noise by 6dB when compared to the CMP stack for another geometry, the fold has again been effectively quadrupled. The resulting stacking fold is shown by the number written below each vertical dashed line, which is the number of reflection points intersected by each of those lines. Proven technology helps you reduce risk and improve your success rate. Download Full PDF Package. Could they ever be made to fit the budget? Download PDF Package. 3 – Vertical variation in stacking fold.. He holds a B.Sc. 5a shows the distribution of subsurface reflection points (the solid circles on the subsurface interface) when there are four active receiver channels and the source-station spacing equals the receiver-station spacing.