Surveys seismic

Exploration activities are potentially damaging to the environment. The cutting down of trees in preparation for an onshore seismic survey may result in severe soil erosion in years to come. Offshore, fragile ecological systems such as reefs can be permanently damaged by spills of crude or mud chemicals. Responsible companies will therefore carry out an Environmental Impact Assessment (EIA) prior to activity planning and draw up contingency plans should an accident occur. In Section 4.0 a more detailed description of health, safety and environmental considerations will be provided. 

Both survey methods are mainly employed to define large scale structures such as basins. Based on the resulting maps, seismic surveys are then carried out. 

It is fair to say that advances in seismic surveys over the last decade have changed the way fields are developed and managed. From being a predominantly exploration focused tool, seismic has progressed to become one of the most cost effective methods for optimising field production. In many cases, seismic has allowed operators to extend the life of mature fields by several years. 

Seismic surveys are traditionally an exploration and appraisal tool. However, 3-D seismic is now being used more widely as a development tool, i.e. applied for assisting in selecting well locations, and even in identifying remaining oil in a mature field. This was discussed in Section 2.0. Seismic data acquired at the appraisal stage of the field life is therefore likely to find further use during the development period. 

At the development planning stage, a reservoir mode/will have been constructed and used to determine the optimum method of recovering the hydrocarbons from the reservoir. The criteria for the optimum solution will most likely have been based on profitability and safety. The model Is Initially based upon a limited data set (perhaps a seismic survey, and say five exploration and appraisal wells) and will therefore be an approximation of the true description of the field. As development drilling and production commence, further data is collected and used to update both the geological model (the description of the structure, environment of deposition, diagenesis and fluid distribution) and the reservoir model (the description of the reservoir under dynamic conditions). 

If the original field development plan was not based on a 3-D seismic survey (which would be a commonly used tool for new fields nowadays), then it would now be normal practice to shoot a 3-D survey for development purposes. The survey would help to provide definition of the reservoir structure and continuity (faulting and the extension of reservoir sands), which is used to better locate the development wells. In some cases time-lapse 3-D seismic 4D surveys carried out a number of years apart, see Section 2) is used to track the displacement of fluids in the reservoir. 

Ground Penetrating Radar (GPR), Electromagnetic Conductivity (EM), Electrical Resistivity Surveys, or Seismic Surveys. 

Another type of technology that has influenced oil and gas exploration is the acquisition of 3-U surface seismic data. This technology produces so much information that modern interpreters have been forced to give up looking at paper sections and use computers just to view their data. The 3-U seismic surveys are very much like a solid section of the earth. An interpreter can sit at a workstation and literally slice through the data viewing the seismic picture of the earth in almost cvci y way possible. Some companies have assembled virtual reality rooms where the... 

When choosing an offshore drillsite, the primary considerations are the location of shipping lanes, foundation stability (for bottom-supported vessels), and the possible presence of shallow gas. Seismic surveys generally provide... 

Figure 10. Seismic survey based on vibroseis. Example of a seismic profile.

The main conclusion drawn from this study is that hydrocarbon- and fixed gas-based geochemical exploration methods in the Paradox Basin are cost-effective tools for pre-screening large areas to focus subsequent lease acquisition and seismic surveys for oil and gas exploration. Heavy metal anomalies are more difficult to link with the reservoir. 

Seismic Surveys. Gravity and magnetic measurements are considered preliminary. The principal detailing tool used is the seismograph.2... 

The type of experiment used to make a seismic survey in petroleum exploration will be determined by the type of information required, the types of rock strata anticipated, environmental considerations, the type of terrain, and, of course, the economic costs involved. 

In petroleum exploration, reflection seismic surveying is the method predominantly used. The seismograph records variations in the way rocks reflect sound waves sent downward from a surface source. The reflected sound waves vary with the type, depth, density, and dip of the rocks encountered. The returning sound waves made from a series of points along the survey path can then be displayed graphically to form a seismic record for interpretation by earth scientists. These principles are diagrammed and explained in Fig. 8. 

The principles of seismic surveying are the same regardless of the type of equipment used. As the waves strike the various strata, some are... 

Fig. 9, Seismic survey using a truck-mounted vibrator as the energy source for creating reflected aeons Lie sounds. This method is used in sensitive areas near cities and along highways because disturbance to the environment is minimal, (.American Petroleum Institute)...

Seismic Data Processing. Continuing advances in technology, such as fiber optics, have enabled the capabilities of seismic surveys to be markedly increased so that, where required, a 3-dimensional picture of the rocks in the subsurface can be obtained. Advanced processing has also enabled discrete anomalies in seismic data from individual rock horizons to be analyzed. Under certain conditions, the presence of hydrocarbons can be directly detected. This analysis, sometimes referred to as bright spot technology, has been responsible for numerous discoveries in the Gulf of Mexico in recent years. 

Raw data gathered from seismic surveys must be processed to compensate for and to remove a variety of distortions unwanted noises created by weathered near-surface rocks, normal time delays, and echoing by rebounding acoustic waves—to provide the clearest possible image of the strata below. Computers can restore these distortions in a fraction of the time that was formerly required to adjust the data painstakingly by hand. Advanced techniques not only permit presentations in three dimensions, but also in color, and to create contour maps and models of subterranean features. However, even with the use of sophisticated tools, there remains a large measure of uncertainty. History has shown repeatedly that a prospective area rejected by one petroleum firm has been accepted by another and proved to be successful. 

The Georgian onshore gas resources of Eocene and Cretaceous structures are assumed at 269 bcm. The proven Near-Tbilisi-region reserves in the Eocene structures of the Samgori, Rustavi and Ninotsminda fields approximately equal to 3.5 bcm. The data on gas prospective resources obtained by modem three-dimensional seismic survey over the Black Sea offshore structures are not available yet. 

The 8 UGS candidates were chosen among other oil and gas fields because these sites (with some variation) are well documented (e.g. 2D seismic surveys and a number of wells) and the reservoirs has a proven seal, which has been able to withhold a gas overpressure for million of years. This is important both for safety reasons and for operating the gas storage without risks of gas leaking away in the substrata. 

The reservoir structure was updated by shooting a 3D seismic survey. 

The first one is to the South of the 1 Karaiaz borehole, at the area of Upper Eocene sediments spreading. The aim would be a precise identification of the Upper Eocene sediment conditions in one section with seismic survey data. 

The second one is within the scope of East Mameuli anticline after carrying out detailed seismic survey works. 

Seismic Surveying The recording of echoes reflected to the surface from pulses of sound sent down into the earth. Used to determine underground geological structures. 

Structural Map A contour map detailing elevations of sub-surface rock layers, calibrated either in linear measure of feet or meters, or in time measure based on seismic surveys. 

Seismic surveys ice in the vicinity of Fresh water lakes, ponds and... 

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