Integrated approach to pore typing in complex carbonate reservoirs, Tengiz and Korolev fields, Kazakhstan

Abstract

Tengiz and Korolev fields are isolated carbonate buildups in western Kazakhstan, characterized by a range of primary rock types and fabrics in shallow-platform to slope depositional settings. These rock fabrics underwent extensive diagenetic modification from the time of deposition through deep burial, resulting in a complex paragenetic sequence with a variety of pore types. This study is focused on the Bashkirian–Serpukhovian–upper Visean interval (unit 1), which is the major oil-producing reservoir in Tengiz and Korolev fields. Most samples are from outer-platform and slope settings.Pore types are defined as collections or groups of micro- and macropores that may have different origins. These groups, which are linked to the paragenetic sequence, form characteristic assemblages that occur repeatedly in slope and platform settings. Pore types are classified based on the amount, distribution, and connectivity of micro- and macropores.Laser scanning confocal microscopy, which generates images of pores as small as 0.2 µm in diameter, provides an effective tool to visualize and quantify micropores (i.e., pores with pore diameter ≤10 µm). Confocal microscopy, combined with transmitted-light (TL) petrography, routine core analysis, and mercury injection capillary pressure (MICP) data were used to designate five pore types, which include micropore-dominated, macropore-dominated, and mixed micro- and macropore-bearing rocks with variable degrees of connectivity.This approach, which offers a new way to define complex pore families that correlate to reservoir-property groups, applies to any carbonate reservoir. This integrated petrographic and petrophysical classification links pore-body (confocal and TL) and pore-throat (MICP) size distributions. Future work includes prediction of pore types from logs and development of strategies for spatial distribution of pore types between wells in full-field geologic models.