1996-03 - Geophone checking for 3-C seismic surveys...

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Geophone checking for 3-C seismic surveys CREWES Research Report — Volume 8 (1996) 3-1 Geophone orientation, location, and polarity checking for 3-C seismic surveys Henry C. Bland and Robert R. Stewart ABSTRACT A method to compute geophone orientation and location is introduced. This method analyses the horizontal components of 3-C geophones and estimates the azimuth of the source with respect to the geophone. Based on these azimuths for several shots, a solution for the true geophone orientation and location is determined. INTRODUCTION A major delay in laying out 3-C seismic programs is the task of correctly orienting the 3- C geophones. This requires considerable time and care in the field, leading to higher costs. Miswiring or misconnection of geophones can also lead to data unknowingly having a reversed polarity. This too leads to data error. A correctly oriented geophone could also be used to check for source-receiver geometry. It would be very useful to have a technique that could allow arbitrarily oriented geophone deployment which would also determine the orientation, polarity and geometry of the geophone. Such a procedure is important in 2-D as well as 3-D multicomponent surveying. This paper proposes a technique to do such an analysis. THEORY Orientation error and trace reversal There are many assumptions that could be made with respect to the geophone orientation problem: That the geophones are level, that the elements have equivalent output, that they are "welded" or totally coupled to the ground surface. In this discussion we shall assume that the geophone is correctly located but incorrectly oriented. Since geophone locations are usually confirmed by survey measurements one finds that poor geophone orientation is more common than incorrect geophone placement. Even experienced 3-C acquisition crews have difficulty orienting geophones with less than 10 degrees error. Given a single shot and a single 3-C geophone, one would expect that the shot azimuth could be determined by analysing the signal from the two horizontal elements. Assuming this is possible, one can then compare the observed shot/receiver azimuth to the shot/receiver azimuth based on the survey geometry and obtain a value for the angular orientation error (Figure 1.).
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This note was uploaded on 05/09/2010 for the course EARTH SCIE APPLIED GE taught by Professor Es during the Spring '09 term at IIT Bombay.

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1996-03 - Geophone checking for 3-C seismic surveys...

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