Abstract
The analogous behaviors of capillary pressure and 1/T2 decay versus saturation data provide a methodology for deriving synthetic capillary pressure information directly from NMR logs even if core data are not available. Estimations of irreducible water saturation4 from NMR log-based synthetic capillary pressure profiles have numerous benefits. One benefit is the enhanced accuracy of permeability estimations by using synthetic bulk volume irreducible in the bound water model. Availability of synthetic bulk volume irreducible data from capillary pressure modeling eliminates the requirements for determining the T2cutoff time from core analysis data or assuming generally accepted constants for it (33 ms for clastics and 92 ms for carbonates). In addition to the bound water model, an alternative permeability profile can also be generated from Purcell's7 capillary pressure-permeability relation. Another benefit derived from a synthetic capillary pressure profile is the determination of Oil Water or Gas Water Contact (OWC, GWC) by simply converting the capillary pressure information to height above free water level. This information can also be compared with the Free Water Level (FWL) from formation test tools. The relative positions of FWL and OWC assist in inferring wettability14 and the degree of wettability magnitude for the subject reservoir.
Relative permeability estimations from synthetically created capillary pressure data provide an avenue to make the firstapproximation profiles of the effective permeability values to the phases contained in the pore space. Consequently, effective permeability profiles in conjunction with other petrophysical and fluid properties and the pressure information lead to the anticipated production rates and overall evaluation of the economic viability of a well(s) and field. Applications of the technique with inherent assumptions, limitations, and remedies for the limitations are reviewed and explained through a case study presented in this paper.
