Page 14 - Fundamentals of Enhanced Oil and Gas Recovery

2 Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi

Surface tension reduction, oil swelling, relative permeability improvement, wettability
alteration, etc. are different mechanisms that can work together simultaneously or
separately.
Today, using progressive EOR processes is unavoidable, particularly in reservoirs
that are in their second half of life or cannot produce oil naturally. Achievement
and prosperity of EOR methods definitely depend on comprehensive studying of
rock and fluid properties and reservoir condition. These features describing reser-
voirs are the main controlling parameters on which an appropriate EOR method is
selected.

1.2 RESERVOIR ROCK PROPERTIES

A reservoir rock is a rock providing a condition to trap oil in porous media.
The reservoir rock contains pores and throats, creating flow path and an accumulat-
ing system for hydrocarbon and also consist of a sealing mechanism for prohibiting
hydrocarbon penetration to surface layers. The reservoir rock appears in different
forms, from loose sands to dense and tight rocks. Reservoir rocks are totally classi-
fied as conventional and unconventional rocks. In the case of conventional type,
the rock consists of grains bound together by a bunch of material such silica, cal-
cite, and clay. These rocks provide appropriate storativity and conductivity for accu-
mulating and flowing hydrocarbon. To evaluate and understand reservoir behavior
and also improvement of reservoir performance, studying reservoir rock properties
is vital.
Most reservoir rock properties are determined by lab-based works. In order to
perform experimental tests, the reservoir rock should be sampled. The special sample
of reservoir rocks is called the core. The lengths of cores are varied, from a few inches
in core plugs to several meters in whole cores. For the following experimental tests
these cores are maintained under reservoir condition (temperature, pressure), other-
wise the cores are aged to reservoir condition.
Rock properties analysis is mainly subcategorized to advanced core analysis or
special core analysis (SCAL) and routine core analysis (RCAL). In SCAL all
saturation-dependent or multiphase flow properties including relative permeability,
capillary pressure, compressibility, and wettability are determined, and other para-
meters such as porosity, permeability, saturation and lithology are characterized by
RCAL. The abovementioned properties significantly influence hydrocarbon distribu-
tion along reservoirs, thus a comprehensive analysis of reservoir rock properties is
definitely essential, especially in the case of EOR methods selection.