By the 70’s it became a search for better, more accurate signal. Thus large bins set the limit on resolution and therefore on the maximum useful frequency. These were often referred to as drunken bricks (the terminology is clearly unrelated to the inventors!). Recently many acquisition geophysicists have made attempts to reduce linear and backscatter noise before it reaches the recorder. But the CMP stacks with and without the noise removal algorithm often look distressingly similar, leading to the conclusion that CMP stacking is still the best weapon in the anti-noise armory. An equal number of articles extolling the virtues of the wide patch were written. Shothole and vibroseis. Inline coordinates increase from west to east as shown. Many articles were written extolling its virtues as the only 3D geometry you would ever need. Contractors quickly tired of trying to shoot bricks through trees, so the slanted geometries were born. 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. 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. Each source and receiver location is surveyed for accurate surface location and elevation. Phrases like “Cross well tomography” and “3D VSP” are becoming part of the exploration vocabulary. Combined, these create one of the largest seismic databases in the United States, currently containing 39,000 square miles of 3D data and 512,000 linear miles of 2D data. 1 – Oblique view of 3D stacking bins. 5 expands the inline stacking-fold analysis to show that for geometries in which the source-station interval does not equal the receiver-station interval, then. Ideally, they should be approximately W/4. Imaging in the early days was all done post stack - typically through 3D Kirchhoff or FK migration. It became clear fairly quickly that the best way to attack noise was through the act of CMP stacking. For a deep target at depth Z2, the stacking fold in this bin is a high number because there is a large number, N2, of source-receiver pairs that each produce a raypath that reflects from subsurface point B. Moving shot and receiver lines one half ( or quarter, etc.) Designing 3D seismic surveys 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 quick answer is that time has favored the wide patch - mostly because of better offset distribution for noise attenuation and generally reduced artifacts due to the wide sampling. 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. Very tight shot and receiver line spacing is the norm here. New processing algorithms often appear to make a substantial difference to individual shots (or receiver line components of shots). 3D seismic programs are generally a uniform and evenly spaced grid of lines. [1], Fig. Reduce uncertainty associated with structure or stratigraphy to accurately position wells or … The data obtained from such a survey is therefore very valuable, and if protected from disclosure constitutes a trade secret. Predictions as to the demise of 2D were everywhere. Galbraith, M. 1994. PDF. 2000. Practically it seems to be producing acceptable data. The stacking-fold numbers at the bottom of the diagram define the number of distinct source-receiver pairs that create a reflection image at each subsurface point, that is, the number of reflection points that each vertical dashed line intersects. 3 – Vertical variation in stacking fold.[1]. 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. To request a shapefile set for GPI’s 3D or 2D seismic library, please visit our contact page. [1] A variation in seismic reflection character on three to four adjacent traces is usually noticed by most interpreters, whereas anomalous behavior on fewer traces tends to be ignored or may not even be seen when a 3D data volume is viewed. The current thinking is that 18 beats 26 which beats 45. Egdon Resources has provided an update on the timing of the 3D seismic survey over the Resolution gas discovery in offshore licences P1929 and P2304. Bin Spacing in Land 3-D Seismic Surveys and Horizontal Resolution in Time Slices. As a programmer then, it was my task to build methods to process this data set. The Brick was first invented to improve the offsets. The double zigzag cured that and is still a popular geometry in desert regions. 4a show the distribution of reflection points (the solid circles on the subsurface interface) when there are four active receiver channels and the source-station interval is the same as the receiver-station interval. Tulsa, Oklahoma: Geophysical Developments, Soc. At the conclusion of 3D data processing, the area spanned by a 3D seismic image is divided into a grid of small, abutted subareas called stacking bins. The raypaths in Fig. The horizontal resolution a 3D seismic image provides is a function of the trace spacing within the 3D data volume. Other factors like unequal shot and receiver line spacing and slanted lines are currently under investigation. The 4 line patch was only a few hundreds of metres wide - and very long - and cheap! 5b is two times greater than the flag movement in Fig. Invented and patented by PanCanadian. For example, if the interpretation objective is to image meandering channels that are as narrow as 200 ft, then the stacking bins should have lateral dimensions of approximately 50 ft (Fig. Planning Land 3-D Seismic Surveys, Vol. 3, when the stacking bin is centered around deep reflection point B, the stacking fold is at its maximum because the largest number of source and receiver pairs can be used to produce individual reflection field traces that pass through the bin. This led the seismic industry from laboriously – and therefore rarely – acquiring small 3D surveys in the 1980s to routinely acquiring large-scale high resolution 3D surveys. [1], Fig. The seismic tool must provide a cost efficient alternative to additional drilling. Even back then, some said it was complete - at least for the purpose of finding oil and gas. 2D seismic Survey large areas with 2D seismic. Even back then, some said it was complete - at least for the purpose of finding oil and gas. This year, about 1200 3D programs will be recorded in Canada. Delays in travel times caused by near (or even far) surface anomalies can be a source of noise. Our understanding of 2D seismic surveys - their acquisition, processing and interpretation - was extremely comprehensive. One of the most powerful geophysical technologies is 3D Seismic. The bin dimensions should be no wider than W/3. Crossline fold, FXL, is given by. Only N1 source-receiver pairs generate field traces that reflect from A and still satisfy the geometrical constraint that these pairs are offset by distance DE (or EF) that does not result in critical wavefield refractions at interfaces above A. It is worth remembering that if shot noise can be reduced by 6dB using a better array, this is equivalent to quadrupling the CMP stack fold! For example, the petroleum industry’s Stone Cabin 3D seismic survey scheduled for this summer near Nine Mile Canyon in Carbon County will use 10 and 20 pounds of explosives in shot holes. There is today an increasing interest in the other forms of energy that arrive at the surface spread. The answer to the same question for other geometries is still unresolved. Imagine the excitement as the display was unrolled and we walked down the corridor (and down in time) inspecting each slice as we went. Significant cost savings can also be realized. Indications are that linear shot noise, backscatter and multiple energy are well attenuated by this geometry - perhaps better than by orthogonal. 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. In the past few years there has been a decline in the use of DMO and an increasing emphasis on pre-stack time migration. The only real disadvantage is the minimal statics coupling between swaths (shots only). While there is no shortage of anecdotal knowledge, there is still a lack of broadly based experiential knowledge about the use of arrays in 3D. When the geology involves steep dips or large changes in rock velocity across a fixed horizontal plane, rigorous calculations of station spacing (or bin size) should be made with commercial 3D seismic design software rather than by following the simple relationships described here. 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. 9. In the pre-stack domain, DMO was the algorithm of choice for many years (and still is in many parts of the world). These other forms of energy may be mode converted from a down-going impulsive source or may arise from a shear wave source capable of outputting both compressional and shear waves. honours degree in Mathematical Physics from University of Edinburgh (1967). In particular, wide towed marine streamer data (multi-source, multi-streamer) after DMO had a very striped appearance. Some rights reserved. Geophysical Pursuit is a relationship-driven seismic company specializing in the acquisition and licensing of seismic data critical to understanding oil and gas reservoirs. As a general rule, there should be a minimum of three stacking bins, and preferably at least four bins, across the narrowest stratigraphic feature that needs to be resolved in the 3D data volume. to repeat a 3D in an economic and effective manner). 5a; that is, there are four receiver groups, but the source-station spacing is now twice the receiver-station spacing. Then, many of us noticed the noise. Unfortunately such 3D’s have high noise content and can be difficult to interpret. TGS will use BGP Prospector for the 3D seismic survey for a multitude of exploration and production companies, increasing its coverage in the region to 18,000 km 2. People often use specialized software for this task, as the process requires a lot of math and the careful construction and interpretation of data. [email protected] A short summary of this paper. Wide line spacing is the norm - up to one kilometer or more between shot and receiver lines. 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