Objectives

The main objective of RDL porosity interpretation is to predict air porosity from OH logs.

The interpretation model is calibrated to air porosity on dried out lab cores.


Definition


Different OH sensors have complex correlation to effective porosity, shaliness and pore-saturating fluids.

The density, neutron, sonic and resistivity tools show a monotonous correlation to porosity and shaliness.

The density, and neutron tools exhibit a linear correlation while sonic  and resistivity tools exhibit non-linear correlation to porosity and shaliness.      



Density Porosity




Neutron Porosity




Sonic Porosity




Cross-Porosity Analysis



Neutron vs Density



\phi_e = \frac{ \phi_{ed} + \phi_{en}}{2}



for oil/water saturated formations


\phi_e = \sqrt{\frac{ \phi_{ed}^2 + \phi_{en}^2}{2} \ }



for gas saturated formations




Sonic vs Density


SPHI  is usually not sensitvie to second porosity development while DPHI  accounts for it proportionally.

This means formation units with secondary porosity development will show DPHI growing over SPHI.




Reference


[1]   http://petrowiki.org/Porosity_evaluation_with_acoustic_logging

[2]   http://pangea.stanford.edu/~jack/GP170/Reading%231.pdf 

BWLA - Porosity Logs.pdf

Open_Hole_Wireline_logging.pdf


Wyllie, M.R.J., Gregory, A.R., and Gardner, L.W. 1956. Elastic Wave Velocities in Heterogeneous and Porous Media. Geophysics 21 (1): 41–70. http://dx.doi.org/10.1190/1.1438217


Gardner, G.H.F., Gardner, L.W., and Gregory, A.R., 1974, Formation velocity and density -- the diagnostic basics for stratigraphic traps: Geophysics, 39, 770-780.


Raymer, L.L., Hunt, E.R., and Gardner, J.S., 1980, An improved sonic transit time-to-porosity transform: SPWLA 21 Ann. Logging Symp., July 8-11, 1980, 1-12.