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. [4] 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