Introduction
To understand reservoir rock–fluid interaction and to predict performance, reservoir systems can be subdivided into flow units and containers. Wellbore hydrocarbon inflow rate is a function of the pore throat size, pore geometry, number, and location of the various flow units exposed to the wellbore , the fluid properties, and the pressure differential between the flow units and the wellbore.
Reservoir performance is a function of the number,
quality, geometry, and location of containers within a reservoir system, drive
mechanism, and fluid properties. When performance does not match predictions,
many variables could be responsible , however, the number, quality, and location
of containers is often incorrect.
What is a flow unit?
A flow unites a reservoir subdivision defined on the basis of similar
pore type. Petrophysical characteristics, such as distinctive log character
and/or porosity–permeability relationships, define individual flow units.
Inflow performance for a flow unit can be predicted from its inferred pore
system properties, such as pore type and geometry. They help us correlate and
map containers and ultimately help predict reservoir performance.
What is a container?
A container is a reservoir system subdivision consisting of a pore
system, made up of one or more flow units, that responds as a unit when fluid
is withdrawn. Containers are defined by correlating flow units between wells.
Boundaries between containers are where flow diverges within a flow unit shared
by two containers . They define and map reservoir geology to
help us predict reservoir performance.
Defining flow units
To delineate reservoir flow units, subdivide the wellbore into intervals
of uniform petrophysical characteristics using one or more of the following:
• Well log curve character
• Water saturation (SW–depth plots)
• Capillary pressure data (type curves)
• Porosity–permeability cross
plots
The diagram below shows how flow units are differentiated on the basis
of the parameters listed above.
Defining containers within a reservoir system is relative to the flow quality of the rock. Flow units with the largest connected pore throats dominate flow within a reservoir system. Follow the steps listed in the table below as a method for defining containers.
· Correlate flow units between wells in strike and dip-oriented structural and stratigraphic cross sections.
· Identify the high-quality flow units from rock and log data.
· Draw boundaries between containers by identifying flow barriers or by interpreting where flow lines diverge within flow units common to both containers.