Pore size distribution characterization in carbonates by correlating NMR, MICP and micro-CT data

Resumo

From laboratory tests on pre-salt plugs, it is possible to obtain information such as pore body and pore
throat size distributions, that may indicate the storage capacity and potential for extraction of fluids from a
reservoir. This paper correlates data from NMR, MICP and micro-CT tests in order to characterize the pore body
to pore throat ratios (BTR) for coquinas from Morro do Chaves Formation, in the Sergipe-Alagoas Basin. MICP
data was converted to pore throat size distributions using Washburn equation and compared with pore body sizes
computed from micro-CT data analyzed with image processing software. The comparison between MICP and
micro-CT data yields the pore body to throat ratios, which are known to vary considerably in carbonates due to
the heterogeneity of the pore structure. Next, the NMR T2 distributions were scaled to pore size distributions using
the surface relaxivity parameter (ρe) and compared to both MICP pore throat size distributions and micro-CT pore
body size distributions. The results indicate a good correlation between MICP pore throat distributions and T2
distributions, but when comparing T2 distributions with micro-CT distributions, allowance must be made for the
low resolution limit of the micro-CT (20 microns) and the effect of bulk relaxation on larger pores.