3d Seismic Survey Design Software

Geophysics for Petroleum Engineers

Fred Aminzadeh , Shivaji N. Dasgupta , in Developments in Petroleum Science, 2013

3.6.1 Land Acquisition

Seismic surveys are conducted by deploying an array of energy sources and an array of sensors or receivers in an area of interest. Figure 3.9 shows a seismic survey on land. The source of seismic waves is either an explosive which directly generates the seismic wavelet or a mechanical source which is commonly a vibrator, which uses a steel base plate in contact with the ground and transmits seismic waves in the earth. The seismic waves with a vibrator are generated at controlled frequency ranges and a mathematical process of cross-correlation of the recorded signal with the source generated signal at the vibrator is used to create the seismic wavelet. The seismic waves that travel from the source into the earth are received on geophone sensors planted on the surface at different offsets or incremental distances away from the source point. The seismic traces are recorded as a function of time delay from the initiation of the source. For a 3D seismic survey, a network of sensors in a grid is planted and a network of source points is located. 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. Each source and receiver location is surveyed for accurate surface location and elevation.

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Exploration Geophysics

Swapan Kumar Haldar , in Mineral Exploration (Second Edition), 2018

6.2.6 Applications

The seismic survey can explain subsurface discontinuities, layering, and probable rocks/structures. It is suitable for the investigation of coal, oil and gas, groundwater, and massive metallic deposits. A 3D seismic survey outlined the basin configuration and resource estimate at Krishna-Godavari Basin, India, and a 2D seismic section mapping and establishment of a major structure for basement faults was applied successfully at Zeegt lignite coal mine in Mongol Altai coal basin. The other areas covered in metallic minerals are Munni Munni platinum-group element (PGE) deposit, Australia, Kevitsa Ni–Cu–PGE deposit, Finland, goldfields of Witwatersrand Basin, South Africa, and Bathurst zinc-gold Mining Camp, Canada. The ocean floor, otherwise unknown, was mapped precisely by marine seismic survey in the mid-20th century. The Mid-Atlantic Ridge at an average water depth of 5 km, and deep oceanic trenches in the Western Pacific, were discovered.

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Conceptual model of the copper–porphyry ore formation (Sorskoe copper–molybdenum ore deposit case study)

Viacheslav V. Spichak , in Computational Geo-Electromagnetics, 2020

10.5.1 Seismic survey

Seismic survey was carried out in the study area by Kadurin et al. (2008) by means of a joint registration of arrival times of compressional, shear and converted waves generated by local earthquakes. Seismic signals in the frequency range 0.5–10 Hz were recorded along a number of profiles by a Russian-made 4-channel digital recorder "Delta-Geon." The sampling of events was carried out from four recorders in a 3-min window. After appropriate preprocessing of the P-, S-, and PS-wave data the travel-time cross sections were built.

The reconstruction of seismic velocities was conducted by Kadurin et al. (2008) in the context of a block-layered isotropic model of the Earth crust with spacing 1 km in depth and 1 km in horizontal direction, which corresponds to the declared resolution at depth and horizontal site spacing. The accuracy of the reconstruction of seismic velocities is estimated as 0.1 km/s for both compressional (V_P) and shear (V_S) waves.

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Understanding Seismic Exploration

Enwenode Onajite , in Seismic Data Analysis Techniques in Hydrocarbon Exploration, 2014

4D (3D-Time Lapse) Seismic Surveys

4D seismic survey is a three-dimensional (3D) seismic data acquired at different times over the same area to assess changes in a producing hydrocarbon reservoir with time. Changes may be observed in fluid movement and saturation, pressure, and temperature.

The oil and gas industry uses 3D-time-lapse seismic survey to monitor the way fluids flow through a reservoir during production, by carrying out a baseline (pre-production) seismic survey (Figure 3.24) and then repeat surveys over the production lifetime of the reservoir (Figure 3.25). When 3D surveys are repeated in this way, they are often referred to as 4D seismic.

Typically, 4D seismic data are processed by subtracting the data from the baseline 3D survey from the data from the monitor 3D survey. The amount of change in the reservoir is defined by the difference between the two. If no change has occurred over the time period, the result will be zero.

Taking a closer look at both surveys in Figure 3.26, you will notice a remarkable difference between both surveys. This difference is called the 4D signature.

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Recovering seismic velocities and electrical resistivity from the EM sounding data and seismic tomography

Viacheslav V. Spichak , in Computational Geo-Electromagnetics, 2020

13.3.2 Seismic survey

Seismic survey was carried out by Kadurin et al. (2008) using the converted-waves method based on a joint registration of arrival times of compression, shear, and converted waves generated by local earthquakes (see location of some hypocenters on Fig. 13.2).

The seismic signals in the frequency range 0.5–10 Hz were recorded along the profile shown in Fig. 13.1 by Russian made 4-channel digital recorder "Delta-Geon." The sampling of events was carried out from four recorders in the 3-min window. After appropriate preprocessing of the P-, S-, and PS—waves' data the travel-time cross-sections were built. The local earthquakes' hypocentral parameters were determined using the code HYPOELLIPSE (Lahr, 1999), while the two-dimensional forward modeling was fulfilled using the technique proposed by Zelt and Smith (1992).

The seismic velocities' reconstructions were conducted in the context of a block-layered isotropic model, which, in the opinion of the authors, is most suitable for the observed wave field in the upper crust. The accuracy of the seismic velocities' reconstruction is estimated as 0.1 km/s for both compressional and shear waves while the resolution at depth is around 1–1.5 km. Fig. 13.4B and C shows the velocity cross-sections of compressional and shear seismic waves, respectively.

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Geophysical monitoring at the Nagaoka pilot-scale CO2 injection site in Japan

Takahiro Nakajima , Ziqiu Xue , in Active Geophysical Monitoring (Second Edition), 2020

6.3.3.4 3D seismic surveys

3D seismic surveys are a powerful tool to monitor spatial distribution of injected CO ₂ (Ringrose et al., 2013; Jenkins et al., 2015). It is difficult to design the onshore survey plan in Japan because of human activities. Furthermore, the amount of injected CO₂ was small at the Nagaoka site compared to other commercial-scale sites. Therefore visualizing the CO₂ plume from the time-lapse 3D seismic survey at the Nagaoka site presented a challenge.

Fig. 6.3.9 shows the time slices and cross-sections obtained at the 2003 and 2005 surveys. There are small differences in the seismic traces around the wells. They may be partly due to the uneven shot points and observation lines for 3D seismic surveys. Ignoring this nonrepeatable noise, the vertical resolution of these surveys was about 20–27 m at the reservoir depth by assuming that the average velocity was 2.2 km/s, frequency was 20–30 Hz, and 1/4 of the wavelength was the limit of vertical resolution. Sakai (2013) used a sophisticated technique to highlight the difference caused by CO₂ injection at this site. He pointed out that the shape of the CO₂ plume was elongated because of the heterogeneity of the reservoir heterogeneity.

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Methods of Exploration

Richard C. Selley , Stephen A. Sonnenberg , in Elements of Petroleum Geology (Third Edition), 2015

3.3.4.2 Data Acquisition

Seismic surveys are carried out on land and at sea in different ways. On land, the energy source may be provided by detonating explosives buried in shot holes, by dropping a heavy weight off the back of a lorry (the thumper technique is actually a rather sophisticated procedure), or by vibrating a metal plate on the ground (Vibroseis). The returning acoustic waves are recorded on geophones arranged in groups. The signals are transmitted from the geophones along cables to the recording truck. Equipment in this truck controls the firing of the energy source and records the incoming signals from the geophones on magnetic tapes.

The shot points and the receiving geophones may be arranged in many ways. Many groups of geophones are commonly on line with shot points at the end or in the middle of the geophone spread. Today, common depth point, or CDP, coverage is widely used. In this method the shot points are gradually moved along a line of geophones. In this way, up to 48 signals may be reflected at different angles for a common depth point.

In Arctic conditions, a different technique is employed. Bundles of geophones are rowed on a cable, termed a streamer, behind a snowmobile that contains the recording gear. The energy source is detonating cord laid on top of the snow ahead of the snowmobile. Care is taken to ensure that explosions occur before the arrival of the recording vehicle. Used carefully, this technique can acquire a large amount of information quickly. It is faster than conventional onshore seismic because it does not require jug hustlers to lay and pick up geophones (Rygg et al., 1992). In wetlands, such as the swamps of Louisiana, hovercraft are used for seismic surveys.

The basic method of acquiring seismic data offshore is much the same as that of onshore, but it is simpler, faster, and, therefore, cheaper. A seismic boat replaces a truck as the controller and recorder of the survey. This boat trails an energy source and a cable of hydrophones, again termed a streamer (Fig. 3.58). It is possible for one boat to operate several energy sources, but experience has shown that, in this instance, more bangs is not necessarily the best. Streamer lengths can extend for up to 6000 m to the annoyance of fisher folk. Currently, survey vessels, such as the Ramform Explorer, can operate up to three energy sources whose signals are received by hydrophones on 8–12 streamers, up to 3000 m in length, with a total survey width of 800 m.

In marine surveys, dynamite is seldom used as an energy source. For shallow, high-resolution surveys, including sparker and transducer surveys, high-frequency waves are used. In sparker surveys, an electric spark is generated between electrodes in a sonde towed behind the boat. Every time a spark is generated, it implodes after a few milliseconds. This implosion creates shock waves, which pass through the sea down into the strata. Transducers alternately transmit and receive sound waves. These high-resolution techniques generally only penetrate up to 1.0-s two-way time. They are useful for shallow geological surveys (e.g., to aid production platform and pipeline construction) and can sometimes indicate shallow gas accumulations and gas seepages (Fig. 3.59).

For deep exploration, the air gun is a widely used energy source. In this method, a bubble of compressed air is discharged into the sea; usually a number of energy pulses are triggered simultaneously from several air guns. The air guns can emit energy sufficient to generate signals at between 5- and 6-s two-way travel time. Depending on interval velocities, these signals may penetrate to >5 km.

The reflected signals are recorded by hydrophones on a cable towed behind the ship. The cable runs several meters below sea level and may be up to 6 km in length. As with land surveys, the CDP method is employed, and many recorders may be used. The reflected signals are transmitted electronically from groups of hydrophones along the cable to the recording unit on the survey ship. Other vital equipment on the ship includes a fathometer and position fixing devices. The accurate location of shot points at sea is obviously far more difficult than it is on land. Formerly this was done either by radio positioning, or by getting fixes on two or more navigation beacon transmitters from the shore. Nowadays, satellite navigation systems enable pinpoint accuracy to be achieved.

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Methane Hydrates

R. Matsumoto , in Encyclopedia of Ocean Sciences, 2001

Submersible Dives

Neither seismic surveys nor drilling is useful to investigate ocean floor hydrate, but direct observation, sampling, and monitoring by submersible dives provide critical information for the study of gas hydrate exposed on the seafloor. Recent submersible dives to Hydrate Ridge of Cascadia and the continental slope of the Gulf of Mexico identified dense occurrence of gas hydrate on and within bottom sediments. Repeated dives in the Nankai Trough off central Japan by 'Shinkai 2000' and 'Shinkai 6500' ('Shinkai' means deep-sea) observed active, methane-bearing seeps and associated chemosynthetic communities, and carbonate crusts and chimneys, perhaps linked with dissociation of subsurface gas hydrate and migration of fluids.

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Hydraulic Fracturing

A.M. Dayal , in Shale Gas, 2017

6.10 Hazard Management

A seismic survey for subsurface study is responsible for induced seismicity and emission to environment. In shale gas exploration, initially, a small quantity of water is used for drilling a bore well and later a measured amount is used for hydraulic fracturing. For the transportation of water and heavy equipment, road infrastructure is used. In fracking fluid, chemicals are added, and flowback water is highly contaminated. These are the measured hazard in shale gas exploration. Induced seismicity is a major hazard during hydraulic fracturing compared to the seismic survey. During hydraulic fracturing, monitoring of induced seismicity is necessary, and a proper log book should be maintained by the operator. All the seismic stations should have networking in a control room so that the fracking area can be monitored from the control room for any accident. Monitoring is also necessary while injecting flowback water into deep wells. These are two major hazards for induced seismicity. Seismicity and their impact are given in the following table:

Magnitude	Impact from the Seismic Event
<2.5	Usually not felt, but recorded by seismograph
2.5–5.0	It is felt, but no damage is reported
5.0–6.0	It is felt, and there is damage to the structure
6.0–7.0	Felt strongly and may be minor damage to the structure
7.0–8.0	Felt strongly and major damage to the building and road
>8.0	Earthquake at a large scale can produce a tsunami and severe damage to infrastructure

The next hazard is contamination of shallow water aquifers by fracking fluid while hydraulic fracturing. During hydraulic fracturing the injection of fracturing fluid at high pressure activates small fractures, and many cracks in the upper rock will allow the fracking fluid to migrate upward, and later this fluid may contaminate the groundwater being used by the community. This is a major hazard, and a good amount of precaution and monitoring is necessary. If some small event is reported, immediate action is must, and that is possible only when base data of the shale gas play area is available and there is proper monitoring of all the shallow water aquifers in the operation area. For the safety of the human/living beings and aquatic animals, protection of shallow water aquifers is necessary to avoid any major health hazard. It is necessary that chemicals added in the fracking water as additives should not be hazardous to the community.

Management of flowback water and proper treatment is a major part of the shale gas exploration as this water is major hazard to the community. Proper monitoring and guidelines for treatment are required, and disposal of this water to surface water should be permitted only when this water has been cleaned as per the required guidelines. Water is the largest used substance, and very strong guidelines are required to protect it for any contamination by any means. There should be a specific tax to the industry using water in their processing that includes power generation, chemical industry, hydrocarbon industry (which includes shale gas exploration), food industry, paper industry, alcohol industry, etc. To protect water from major hazards, it is necessary for the industry to have a water treatment plant, and they can dispose the water from their industry only after the required treatment as per the guidelines issued by the civic authority.

One of the important parts of any process industry is the hazards to the people associated with the various processes. It is necessary to provide them prior training for the work so they can monitor it, and in case of emergency, they can take appropriate action. Persons working in handling flowback water should know about the chemicals being added and their impact to living beings. Associated people should take all required precaution while handling fracturing fluid and flowback water. Flowback water comes with high pressures with lots of semisolids as well as volatile material. Operation of flowback water needs trained people who are well aware about the associated hazards. In a shale gas operation, this is a major hazard, and well-trained personal are required for this operation.

As the hydraulic fracturing work is carried out with high air pressure [18,000–20,000 per square inch (psi)] the problem related with high pressure could be hazardous in case of any accident. For shale gas exploration and exploitation, training of the workers for various processes is most important for the sake of various hazards. As the system is associated with flammable gases and air at high pressure, various volatiles released after fracking need specific handling. To avoid any major accident, all the major high pressure lines should be designed with a bypass system, so in case of any accident, the bypass system can be used, and if possible under the monitoring system, this bypass should be a self-operating system. Inspection of all the necessary checkpoints is necessary for starting any process. It is also important to follow the regular maintenance schedule for all the equipment and other process systems. Such precautions will prevent any major accidents during the operation. There should be an arrangement for fire extinguishers as there is emission of flammable and volatile material that is hazardous. Storage of diesel and other flammable material should be at a specific location with a clearly marked boundary and proper security. All the shale gas play areas should be marked with a big display board for various cautions for the general community in the region. The area should be restricted for any flammable materials like match boxes, smoking, any acid battery, mobile phones, and other devices.

To avoid any gas leakage, a safety system should be fixed at all the necessary points at the well pad. In case of any excess gas or volatile materials, the alarm system should be actived to alert the workers. For excess pressure, there should be a provision for an alarm, and it should inform the operator for taking necessary action. For all the equipment, there should be a display board for starting and shutdown procedures for safety reasons. There should be a dress code for various operators including flame-resistant clothing for the people working near a fire hazard area.

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International Handbook of Earthquake and Engineering Seismology, Part A

Kiyoshi Suyehiro , Kimihiro Mochizuki , in International Geophysics, 2002

3.1.2.1 Eastern Nankai District

OBS seismic surveys in the Nankai Trough began in 1992 (Nakanishi et al., 1998). Figure 3 represents a cross section off Tokai district from 25 OBSs where the Zenisu Ridge is approaching the trough (Nakanishi et al., 1998). The seismic velocity structures on both flanks suggest the Ridge to be oceanic crust. The igneous crust section is about 8 km thick. The subduction of the Philippine Sea plate is imaged to about 34° N, where the top of the subducting igneous crust reaches about 12 km depth. The dip angle is only about 4°. Strong seismic coupling occurs below this depth. A dip angle of about 10° can be inferred from seismicity north of 34° N.

Beneath the south flank of the Zenisu Ridge, the Moho seems to become discontinuously shallower landward with an offset of 5 km in depth. This discontinuity coincides with the deeper extension of a major fault zone identified in reflection seismic record near the sea floor (Le Pichon et al., 1996). Such a major fault suggests that the plate motion is accommodated in a much wider area than previously thought. Again, this sort of feature can only be identified by marine seismological techniques.

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