Scales and Characteristics of Heterogeneity in Sandstone Reservoirs, Miri Field, Sarawak

Reservoir is a porous and permeable underground formation containing an
individual and separate natural accumulation of producible hydrocarbons, oil or gas,
which is confined by impermeable rock or water barriers and is characterized by a
subsurface, porous, permeable rock body in which oil and gas are stored (Oil Gas
Glossary, 2007). A good reservoir is influenced by two important factors. These are the
porosity to host oil or gas and the permeability to allow the movement of fluids in the
reservoir rock (Allen, 1982). Most reservoir rocks are limestone, dolomites, sandstones,
or a combination of these three types of rocks. Dan and Edward (2000) stated that
sandstone and carbonate are the dominant reservoir rocks. In particular, sandstone is
commonly porous and permeable and therefore a likely type of rock in which to find a
petroleum reservoir.
The quality of reservoir is determined by interrelationship between porosity,
permeability, thickness, mineral composition, lateral distribution of rock. Therefore, a
detailed study on reservoir properties must be derived from the characteristics of
reservoir heterogeneity and interpretation of geological and petrophysical data. Reservoir
heterogeneity is a formation with different specific and relative permeability
characteristics (Ambastha, 1995). Reservoir heterogeneity is variation in rock properties
within a single reservoir that affuct the flow of hydrocarbons. A number of factors such
as pore size distribution, core-scale heterogeneity and the geological structure of rock are
known to affect the measured petrophysical properties in core plug samples.