Assessment of Permeability and Porosity Using High Resolution CT and NMR: An Example From The Central Tengiz Platform Reservoir, Pricaspian Basin , Kazakhstan

Kenter, J.A.M.¹, O. Vizika², E. Rosenberg², M. Skalinski³, P.M. Harris⁴, M. Buoniconti⁴ (1) Chevron ETC, Voorburg, Netherlands (2) Institut Français du Pétrole, Paris, France (3) TengizChevroil, Atyrau, Kazakhstan (4) Chevron Energy Technology Company, San Ramon, CA

The central platform in the Tengiz buildup contains a succession of cyclic shallow water deposits ranging from Famennian to Bashkirian in age. The upper Visean, Serpukhovian, and Bashkirian form the main hydrocarbon-bearing interval and contain cyclic, depositional cycles ranging from dm- to m-scale to 10's of meters in. The distribution of reservoir rock types in the central platform is determined by a combination of primary deposition and burial diagenetic modification and includes spatial variations of both porosity enhancing (corrosion) as well as porosity filling (reducing) effects.

A pilot study using a combination of pore network modeling of the petrophysical properties from high resolution (~1 micron) CT microscanner imagery of several selected plug samples resulted in spatial pore and pore-throat size distributions, level and type of pore interconnectivity as expressed by the aspect ratio as well as the coordination numbers (number of pore throats per pore). Porosity, permeability, capillary pressure and formation factors were estimated from CT and NMR analyses and show a close match with those derived from analytical measurements. Most strikingly, the CT imagery allowed the extraction of the 3D distribution of pore type and connectivity as well as cement types, information essential to reservoir quality assessment but very difficult to reconstruct using the classic petrographic approach.

High resolution CT and NMR imagery of key reservoir intervals provide reliable data on rock properties and, more importantly, they fill the essential link between petrophysics and geology at the scale of even small pore types (~1-3 microns) and pore filling cements.