L., Relationships between compressional and shear-wave velocities in elastic silicate rocks: Geophysics, 50, p Fatti, J.L., mith, G.C., ail.j., trauss.j. The Fluid Factor is thus the reflectivity of the oisson Impedance, where the hear Impedance has been additionally scaled so that amplitudes are close to 0.ġ6 REFERENCE Castagna, J., Batzle, M.L., and Eastwood, R. Using the mudrock line, c was defined as 1.16 in both the mith (1987) and Fatti (1994) papers. (1994) to include the density term and write it in terms of acoustic and shear impedance reflectivities: ΔRp Δ F = c (7) Rp R ΔR (6) Where c represents the slope of the wet clastic reservoir trend. ρ σ (4) (5)ġ5 The Fluid Factor was defined as the difference between the actual p reflectivity and the reflectivity calculated from the mudrock line, i.e., ΔF = Δp p c Δ This was modified by Fatti et al. The pseudo-oisson s Ratio reflectivity can thus be defined as: Δ( I / / ) = Δ = ρ( c ) = 1/ 2 Δ Note that reflectivity equation above would be the same as the reflectivity of the previously derived oisson elocity. From mith and Gidlow (1987)ġ4 We can derive the following relationship between p/s and oisson s Ratio as follows: 1 σ = 1/ 2 σ This is a direct linear relationship with p/s increasing with increasing σ. The mudrock line equation is given as : p = 1.16 s m/s The simple idea of the Fluid Factor is that points that lie further away from the brine wet trend are more likely to have hydrocarbons. The basic idea of the Fluid Factor is that brine-saturated clastic silicate rocks define a mudrock line trend on the p-s cross-plot space (Castagna et al., 1985). The Fluid Factor concept was first introduced in a paper by mith and Gidlow in a paper called Weighted stacking for rock property estimation and detection of gas, 1987, Geophysical rospecting. The I log is spliced into the section.ġ3 The oisson Impedance has a very close relationship with the Fluid Factor attribute. Implementing this relationship within Hampson-Russell oftware is quite easy to do and involves some simple Trace Maths scripts.ġ2 Here is the output oisson Impedance volume with the low blue values indicating the gas zone. The inverse of the slope is 1/0.77 = 1.3 which is an approximation to the square root of 2 (i.e., 1.41). For example, the Greenberg-Castagna p- s equation is s = 0.77 p 869 m/s. (2006) Where c is the term that optimizes the rotation.Ĥ Recall that the oisson s Ratio can be written as: σ = 2( ) = 2( ) ( p 2s) (1) If we rewrite the I=AI ci in terms of velocities and density, then we can define the so-called oisson elocity I = ρ c ρ = ρ( c ) = ρ Notice that we can now relate the oisson s Ratio (1) with the oisson elocity (2) and if we define c=sqrt(2) and a scaling factor, D, then σ = D σ (3) σ (2)ĥ The significance of the c term is that it is the inverse of the slope of the litho-fluid trends. The method for defining the oisson Impedance can be written as: I = AI ci From Quakenbush et al. But rotating the axis to be parallel with the trends would ensure a distinct discrimination of the litho-fluid distributions. In the Acoustic Impedance / hear Impedance cross-plot, it is difficult to discriminate the litho-fluid distributions on the horizontal and vertical axes. 3 The idea of the oisson Impedance is illustrated in the figure on the left.