There are now an increasing number of cases where both sources and receivers have been placed in well bores. At any given stacking-bin coordinate, the stacking fold inside that bin varies with depth. The problem was solved and confidence in the new exploration technology increased by leaps and bounds. The seismic tool must provide a cost efficient alternative to additional drilling. Some conclusions were clear. Invented and patented by PanCanadian. 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. Time-lapse 3D recording is becoming more widely used. The only real disadvantage is the minimal statics coupling between swaths (shots only). Science and sampling theory were applied and everyone came to realize that 3D’s were badly under-sampled. Tulsa, Oklahoma: Geophysical Developments, Soc. To coin a phrase, today’s geometries are Designer geometries! It began as early as 1964 when Hugh Hardy of Esso shot the world’s first cross-spread - before it even had a name! Today’s best geometries for noise attenuation seem to be wide azimuth slanted geometries with 18 degrees often emerging as the winning angle. Proven technology helps you reduce risk and improve your success rate. (Note that the absolute best answer is to use the fully sampled 3D geometry - this is the one design that will always exceed the budget.). 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. Logistically it was a very attractive, cheap method to acquire data in such areas. 3D seismic has become a common exploration and production tool. Time slice displays were just appearing in the literature at the time and none of us involved in the project had any good idea of what these new displays might show. 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. Cordsen, A., Galbraith, M., and Peirce, J. These were often referred to as drunken bricks (the terminology is clearly unrelated to the inventors!). 3D geometries differ in their ability to resolve 3D static delays. If you notice any problems with an article (examples: incorrect or missing figures, issue with rendering of formulas etc.) The final CMP coverage extended from the edges of the loops to their center. You must log in to edit PetroWiki. Thus the waves travel by a path from shot to scatterer to receiver. 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. PDF. 1997. More information. One of the most powerful geophysical technologies is 3D Seismic. Near surface scatterers can cause each of the linear noise waves to be reflected. 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. Geological Circular 97 – 5. honours degree in Mathematical Physics from University of Edinburgh (1967). Hardage, B.A. Multiples - is stack the best (the only effective?) The idea is to cover a large area with 3D and do it in the most cost-effective manner. In January 2007, Stewart purchased Tumbleweed Unit leases from BBC. 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. 3D surveys employing multiple sources and streamers are now the norm, although many shallow water high resolution geohazard surveys are still shot in 2D. However, in 3D profiling, the source-station spacing along a receiver line is the same as the source-line spacing, which is several times larger than the receiver-station spacing. 2 – Example of the narrowest feature that must be seen in a 3D image. It was rumored to be the geometry with the biggest footprint of all. 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. 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. Delays in travel times caused by near (or even far) surface anomalies can be a source of noise. And depth? At least three, and ideally four, stacking bins (that is, seismic traces) must lie within the narrowest dimension, W, of this channel if the channel is to be reliably seen in the seismic image during workstation interpretation. Recently we have partnered up with Dan A. Hughes Company in 2009 and have shot a 3D … Each shot is fired twice (or more depending on the salvo width). 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. This would cause a 200-ft channel to affect four adjacent traces. 2). When the stacking bin is kept at the same x and y coordinates but moved to shallower depth, Z1, the stacking fold decreases to the smaller number, N1. The imaging objective dictates how small a stacking bin should be. Logistically this is very attractive - 50% less receiver effort (increase the line spacing) for the price of adding a third vibrator crew. 3 shows, because N2 unique source-receiver pairs can be found that produce N2 distinct field traces that reflect from point B. A 3D seismic survey may cover many square miles of land and may cost $40,000 to $100,000 per square mile or more. Invented and patented by GEDCO. In other words, the stacking fold is the number of distinct reflection points that are positioned inside a bin because of the particular source-receiver grid that is used. The raypaths in Fig. Galbraith[4] describes the parameters involved in onshore 3D seismic survey design. 1, each stacking bin has lateral dimensions of Δx and Δy. A seismic survey is used to investigate Earth’s subterranean structure and is mainly used for oil and gas exploration. Once this minimum target dimension is defined, stacking bins with lengths and widths that are approximately one-fourth the minimum target width must be created if the target is to be recognized in a 3D data volume. Bin Spacing in Land 3-D Seismic Surveys and Horizontal Resolution in Time Slices. The nature of offset distribution and azimuth distribution and how they change with depth became crucial in studying the noise problem. 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. A partial list (who can remember them all?) The newly acquired seismic programs provide modern high-resolution imaging which encompass 1,606 square kilometers with an additional 632 square kilometers to be acquired in 2020. [1], Fig. Conversely, once a stacking-bin size is established, the narrowest stratigraphic feature that most interpreters can recognize will be a facies condition that spans at least three or four adjacent stacking bins. First appearing from Amoco’s Tulsa research, this geometry appeared to improve offset distribution considerably. Extremely high fold is also common. 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. However, many narrow patch surveys are still conducted. In 1978, a 3D survey was acquired near Calgary using orthogonal shot lines and receiver lines. Vermeer (SEG Convention, 2000) showed how common offset vector tiles (formed from symmetrically sampled orthogonal geometry) could be used to create a continuous migrated volume with minimal “edges”. Since 3D seismic is the most common type of seismic survey conducted (and the type TGS will be conducting), allow me to describe how these surveys are done. In the early 80’s orthogonal geometries were the norm. 5b shows the distribution of reflection points when the number of active receiver channels is the same as in Fig. Fig. 5a.) Until the beginning of the 1980s, 2D seismic surveys employing a single source and one streamer predominated in oil and gas exploration. offsets) to form a complete pre-stack time migrated volume is the subject of much current work. For a 3D seismic survey, a network of sensors in a grid is planted and a network of source points is located. 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. The dimension of the trace spacing in a given direction across a 3D image is the same as the horizontal dimension of the stacking bin in that direction. It is often the case that noise must be reduced before signal can even be seen. Rapid progress was made in understanding the algorithms needed for: On the question of noise attenuation, the jury is still out. The simple perspective is that if such static delays cannot be removed they will diminish the signal content. Figure 1 shows a typical 3D VSP situation, where the mode-converted wavefield, arising from surface sources, is recorded by downhole receivers. 1 – Oblique view of 3D stacking bins. Even back then, some said it was complete - at least for the purpose of finding oil and gas. The stacking fold associated with a particular 3D stacking bin is the number of field traces that are summed during data processing to create the single image trace positioned at the center of that bin (Fig. Offset analysis is a technical topic that goes beyond the scope of this discussion. The Brick was first invented to improve the offsets. ... 3D acoustic and viscoelastic, anisotropic finite difference modeling. Magnetic and Gravity Methods in Mineral Exploration: the Value of Well-Rounded Geophysical Skills, Knowledge True and False: Scientific Logic and Climate Change, Geomechanics: Bridging the Gap from Geophysics to Engineering in Unconventional Reservoirs, True Depth Conversion: More Than a Pretty Picture. Thus it is possible to have different shot statics at each shot position because of differing ray paths. 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. When it is critical to know the magnitudes and azimuth orientations of these offsets, commercial 3D seismic design software must be used. Significant cost savings can also be realized. This paper. Double or triple zigzags can work well against linear noise, but the imaging (migration) can have more “edges” than an orthogonal geometry and therefore appear less focused. Is it possible to extract more formation information by designing 3D geometries specifically to enhance the response of various AVO parameters (offset range, reflection angle, etc. Quality service begins with dedicated people. The small departure from orthogonal (18 degrees instead of zero) does not dramatically affect the imaging properties either. 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. Fig. Smaller stacking bins are required if the resolution of small stratigraphic features is the primary imaging requirement. New processing algorithms often appear to make a substantial difference to individual shots (or receiver line components of shots). Previously only very large companies were able to utilize this state-of-the-art, computer-intensive, 3-D 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. 2000. The grid of receivers and source point is moved over the survey area as the survey progresses until the entire area is covered by the survey. The answer was 3D. admin@csegrecorder.com. P-waves are only part of the wavefield. Eq. Practically it seems to be producing acceptable data. 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. 1 and 2 leads to the design equation for inline stacking fold: In 2D seismic profiling, the source-station interval is usually the same as the receiver-station interval, making the ratio term in the brackets in Eq. 2). Indications are that linear shot noise, backscatter and multiple energy are well attenuated by this geometry - perhaps better than by orthogonal. The bin dimensions should be no wider than W/3. The bin size, in turn, can be determined by developing a stratigraphic model of the target that is to be imaged and then using that model to define the narrowest feature that needs to be seen. Second that the size of a bin can determine resolution because of anti-alias criteria. 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