Building Time-Depth Curves: The Shift/Drift Methodology

The Checkshot is a well acquisition technique whose data are used to try to establish a correlation among depth of geological layers in well to the time of seismic events in a seismic section. In a petroleum company, it is a routine to discuss about bad quality in seismic to well correlation, regardless the commercial tool in use. This correlation may be done by using synthetic seismograms. The first perception trying to do this correlation is that there is a time shift that must be solved. In general this time shift may be observed correlating good geological markers that are also good seismic events: the time of events in seismic section doesn’t agree with the time of checkshot readings. By the time the initial correlation is assumed good enough, the technician involved in the task may note also that there is an increasing uncoupling among geological markers and seismic events, starting from the initial point of correlation. Also it is easy to observe that amplitude, frequency and phase of seismic events doesn’t match the same properties in the synthetic seismogram. The scope of this paper is to investigate and establish an acceptable solution to the correlation between geological markers in well and the correlative seismic events in seismic section.