Page 37 - Primer on Enhanced Oil Recovery

28 Primer on Enhanced Oil Recovery

goes without saying that if we know and control more parameters we will get more
oil but the question is what price we will pay for the knowledge, exerted influence
and what the profit will be.
For the future clarity we will provide few definitions here. One needs to take
into the account that in many cases, and this book is no exception, the definitions
are linked to an application area. Here we will provide the definitions which are
more suitable for oil and gas industry and also sometimes use more ubiquitous
terms.
The matter exists in different, so named, states. Each state has set of physical
parameters. Regarding hydrocarbon extraction, the matter (hydrocarbons) can be in
solid, liquid or gaseous state. In some cases we can have vapor which can be a mix-
ture of gaseous and liquid state (small droplets of liquid in gas) in the state of ther-
modynamics equilibrium.
In general description fluid is a matter which does not have permanent shape. It
is also said that a fluid deforms under shear stress. A fluid flow is a special case of
deformation. In principle fluid term includes liquids, gases and supercritical fluids.
For the purpose of this book we will only concentrate and talk about liquids.
In order for fluid, liquid from this point, to flow one needs to apply and main-
tain pressure (differential, e.g. sheer force). If there is no sheer force liquid flow
will cease (albeit only after inertia energy of the motion has been zeroed). This is
due to the fact that liquid “resists” deformation. One can observe that various
layers of liquid during deformation move with the different speed. Interaction of
those layers between themselves appears like internal friction. The value of this
“internal friction” is represented by a value of viscosity. Liquid almost always,
except few very special case, interacts with the surfaces which defines liquid
shape (a pipe wall, for instance). For the majority of liquids, when the liquid
moves the liquid layers very near solid surface has much smaller speed than the
liquid layers in the middle of the flow (we assume here that the liquid moves in
the pipe and that the liquid moves relatively slowly so that the flow is laminar).
In accordance with the above liquid layer will start to experience “internal fric-
tion” and we will observe the viscosity. More accurately, in this case, it is so
named dynamic viscosity.
The dynamic viscosity can be defined as this

σ F
μ 5 5 =@υ=@y
γ A

where μ is viscosity. It is obtained then as a ratio of stress to gradient of flow
speed. Given that the speed of movement near the pipe wall is very small, then
small gradient of speed means that all liquid moves slowly in all volume and the
viscosity is high. We can say that liquid with high viscosity flows slowly! Actual
laws of liquid flow through a pipe are quite complex. Many parameters need to be
taken into the account but the fact remains viscous fluids flow slowly and one
needs to maintain high pressure (differential) to maintain the flow.