Using Petrophysical Rock Types for Variable Electrical properties (m & n exponents) in Archie Water Saturation Modeling

ABSTRACT:

Economically important unconventional reservoirs provide many challenges for accurate petrophysical interpretation. While accurate estimate of the complex mineralogical composition, organic matter content (TOC), and total porosity has been well documented, water saturation modelling of the “non-Archie” rock types provide unique challenges and remains “Achilles’ heel” of the petrophysical assessment for the unconventional reservoirs. Unconventional reservoirs are characterized by low porosity and very complex pore structures ranging from nano porosity including organic porosity in kerogen, connected and non-connected micro porosity, very fine pore structure of the tight sands, and in some cases having pore structure resembling conventional sandstone reservoirs (e.g.,1st BSPG only). Numerous types of reservoirs can be found across Permian basin including “low resistivity” siltstone/ sandstone reservoirs (e.g., BSPG, Dean, Jo Mill and Spraberry sandstone), interbedded “hybrid” reservoirs, tight carbonates / carbonate debris flow intervals, as well as the high-resistivity, organic-rich, mudstones reservoirs of the Wolfcamp and Avalon. Moreover, pronounced vertical heterogeneity (i.e., presence of many different rock types) can be observed within most formations. For all these reasons traditional approach of using resistivity based “Archie” water saturation, requiring ever-changing Archie electrical properties is challenging and inherently unreliable. We propose a new method using facies (rock type) driven electrical properties to improve water saturation estimation. This process relies on using petrographic and sedimentologic facies descriptions from core, SEM, and thin sections to derive a continuous, log scale, facies model. This approach captures the pronounced reservoir heterogeneity. In the next step we relate core derived electrical properties to continuous log facies and use them as input in petrophysical modeling.

BIOGRAPHY:

Mitch Pavlovic is currently the Principal Petrophysicist & Manager of the Rock and Fluids team for Oxy. He is responsible for core acquisition planning, execution, and analysis program & quality control. In this role Mitch introduced several petrophysical workflow improvements for petrophysical evaluation of unconventional reservoirs, assuring consistency and standardization by reducing subjectivity in petrophysical interpretation.

Prior to this position, Mitch worked as Onshore petrophysical Manager/ Sr. Petrophysical advisor for Anadarko and held various positions with Baker Hughes. He holds a B.S. and M.Sc. Degree in Geology and Geophysics from the Belgrade University.