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Summary The uphole time t is a kind of important parameter containing abundant near-surface information and it has the characteristics that include a large quantity of shots. The t value directly reflects the depth and the lithology of each shooting well. Studies show that application of the uphole time t has the advantages, the improvement of the static correction precision, the establishment of the near-surface velocity dataset, and quality control of the shooting well depth.
Introduction The uphole time t has been recorded during operation in the field, but it has not been used. Recently, along with the increasing of shooting hole depth, the application of uphole time t has been greatly enhanced. Detailed study of the application of uphole time t value has its great significance. The static correction of shot point and receiver point includes corrections for weathering layer, hole depth and the datum plane. In the past, when doing the hole depth correction, the t value was not used directly, but was applied after doing the conversion of the hole depth. If using velocity, so the precision is influenced. If the uphole time t value is directly used, the precision of the static correction will be greatly improved. Analysis indicates that various static correction methods have to use the near-surface velocity, but up to now the near-surface velocity field is obtained by near-surface investigation in the field. Because the investigation points are not very dense, the velocity variation can not be controlled. Using the t value, the high density control points can be realized, and accordingly, the precision of velocity will be improved. It can also be used as an initial velocity model in the first break refraction static correction, the tomography static correction method and the wave equation continuation static correction method.
The theory The applications of uphole time t value are mainly in the following three aspects: 1) Improving the precision of static correction Because the hole depth in most areas is generally greater than the thickness of the weathering layers, the information of uphole time t can completely reflect the time variation, which is needed when seismic waves are traveling through the weathering layer. 2) Establishing the near-surface velocity information Dataset; The near-surface velocity field has mainly been obtained by using the near-surface investigation method in the field, however, because the investigation points are not very dense, the velocity variation can not be controlled. By using the t value of the shot point, the near-surface velocity control with high density control points can be realized. The idiographic method is as follows: First we validate the correctness of the t value, deal with the abnormal points, and then calculate the near-surface velocity, V0, by using the hole depth, H0, and t value. 3) Monitoring the depth of shooting hole In high precision exploration, no matter whether in 2D or 3D operation, the shot interval along the shot line direction is not very large and the near-surface structure of adjacent shot points is the same.
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