In search of the well tie: What if I don’t have a sonic log?

A petrophysical approach to the investigation of shallow marine geology

“…The Gardner equation (Gardner, Gardner and Gregory ) allows estimation of Vp from , or vice versa; the Faust equation (Faust ), along with variants such as the Kim–Rudman equation (Kim ; Rudman et al . ) and Smith’s equation (Adcock ), describes the relationship between resistivity and Vp, and the relationship between Vp and Vs is described by Greenberg–Castagna (Castagna, Batzle and Eastwood ; Greenberg and Castagna ) and the Krief equation (Krief et al . ).…”

“…However, all of these relationships are ultimately based on elastic rock properties, to which model the immediate sub‐seabed does not necessarily conform. It was shown by Ayres and Theilen () that, in the upper 9 m of sediment in a continental slope setting, Vs became highly sensitive to changes in lithology and other mechanical properties, whereas Vp is more tightly constrained and Reidel and Theilen () demonstrated the limitations of elastic AVO models in the shallow sub‐seabed. However, Richardson and Briggs () found reliable correlations between “Index of Impedance” (i.e., AI) and velocity, density, and porosity in seafloor sediments.…”

“…In the absence of in situ measurement of Vp, Vs, and ρ values, a set of empirically derived relationships allows each of these to be estimated from either or both of the other two or from other data sources. The Gardner equation (Gardner, Gardner and Gregory 1974) allows estimation of Vp from ρ, or vice versa; the Faust equation (Faust 1951), along with variants such as the Kim-Rudman equation (Kim 1964;Rudman et al 1975) and Smith's equation (Adcock 1993), describes the relationship between resistivity and Vp, and the relationship between Vp and Vs is described by Greenberg-Castagna (Castagna, Batzle and Eastwood 1985;Greenberg and Castagna 1992) and the Krief equation (Krief et al 1990). In addition to empirical relationships derived from well-log analysis, there are further empirically derived relationships for Vs (Hegazy and Mayne 1995;Paoletti et al 2010) and ρ (Mayne, Peuchen and Bouwmeester 2010;Robertson and Cabal 2010) from CPT cone resistance (qt) and sleeve friction (fs) data.…”

Tying seismic data to geologic information from core data: an example from ODP Leg 177

“…With a dominant frequency of the data from the seismic survey below 100 Hz, this means that the resolution of the data from the seismic survey is considerably lower than that for the ODP data. Detailed information on the relationship between depth and time is needed to perform a conversion, for which velocity information can be obtained from sonic logs or measured from core samples in case sonic log data are not available (Adcock 1993). Velocities measured on sediment cores originating from depths shallower than a few hundred metres tend to be up to 5% lower than corresponding down-hole measurements (Blum 1997).…”

“…For the deeper parts of the wells, however, only density information is available (Fig. 6), in which case an empirical relationship to estimate the missing variable, such as Gardner's (Gardner et al 1974;Adcock 1993), has to be used. Internal reflections in the sediment layer were included in the calculation of the synthetic traces, although their influence is very small due to the small reflection coefficients.…”