A New Approach to Classify Microporosity in Miocene Carbonate Reservoirs of Offshore Sarawak, Malaysia

Abstract

Microporosity can occur in grain, cement or matrix and it is related to the depositional and diagenetic history of the carbonate reservoir. Depending on the crystallometry and morphometry of micrite particles, microporosity can vary both in amount and in nature. Different kinds of micrite microtextures may produce different kinds of microporosity. This study proposes a classification of micropores and micrite microtextures. We propose a classification that includes four micrite microtextures in Miocene Carbonate reservoirs, offshore Sarawak, Malaysia. Rounded, subrounded, microrhombic and polyhedral, and compact anhedral micrites have their distinct crystal morphology and crystal contacts. This microtexture classification of micrite particles can explain the occurrence, distribution and abundance of microporosity in Miocene carbonates. Based on the crystallometry, morphometry and textural arrangements of micrites a classification scheme is proposed that includes four different classes of micropores such as very fine, fine, medium and coarse micropores with a maximum pore diameter of 0.1 to 2 micrometer, 2 to 4 micrometer, 4 to 6 micrometer and 6 to 10 micrometer respectively. Microporosity affects the empirical porosity-permeability relationship in carbonate reservoirs and influences the assessment of ultimate recovery of hydrocarbon. The application of microtextural classification of microporosity can explain the scattering of data points in porosity-permeability crossplot.

Classification of Microporosity in Carbonates: Examples from Miocene Carbonate Reservoirs of Central Luconia, Offshore Sarawak, Malaysia

“…Based on the model of Folk's classification (1962), micrite particles are classified in three classes; fine, medium and coarse micrites, with a diameter (or maximum side length of the crystal) of 0.1-3μm, 3-6μm and 6-10 μm, respectively (Rahman et al, 2011). These classes are based on measurements on SEM photomicrographs taken at different magnifications using goldcoated thin sections (Figure 8 and 9).…”

“…rounded micrites, micro-rhombic micrites, and compact anhedral micrites. The study on Miocene carbonate reservoirs of offshore Sarawak proposes a classification for micrite microtextures that includes four classes: rounded micrites, subrounded micrites, microrhombic and polyhedral micrites, and compact anhedral micrites (Rahman et al, 2011).…”

“…The crystallometry, morphometry and texture of micrite particles control the occurrence and distribution of micropores (Rahman et al, 2011). Based on the occurrence and crystallometry of micrites, micropores in the Miocene carbonate reservoirs of Central Luconia, offshore Sarawak are grouped in four classes:…”