If the matrix composition remains constant over the formations under investigation, the basic measurement from the sonic, density, or neutron logs can be plotted directly vs. Rt with similar results.  This is possible because of the linear relationship between porosity and bulk density, sonic transit time, or neutron-hydrogen index response. 2. The transit time has been plotted against the induction resistivity for several levels. The northwesterly points define the 100% water saturation line. The transit-time value at the point where this line intersects the horizontal line of infinite resistivity is the matrix-transit time, tma In Fig. 2, tma is found to be approximately 47.5 ?s/ft (156 ?s/m). This corresponds to a matrix velocity of 21,000 ft/sec (6,400 m/s).
By knowing tma, a porosity scale, a scale of formation factor (e.g., from F = 1/? 2 ) can be easily derived. A vertical line drawn through F = 100 (or ? = 10) intersects the water line at R0 = 5 ohm•m; accordingly, Rw (= R0/F) is 0.05 ohm•m.
The lines for other Sw values are straight lines, determined as previously described, radiating out from the Rt =?, tma = 47.5 pivot point.
To have neutron logs, the intersection describes brand new matrix-hydrogen index, otherwise apparent matrix porosity
Density and neutron logs can be crossplotted against resistivity in a manner identical to the sonic logs. For density logs, the intersection of the 100% water line with the infinite-resistivity line yields the matrix-density value, ? Continue reading