GGU-SLUGTEST: Further boundary conditions
For a generally valid approach to the solution, applicable to numerous boundary conditions, the above differential equation introduces dimensionless variables in place of dimensioned variables. The dimensionless pressure or water level (hD) can be formulated as a function of time, location, system geometry and other influencing factors, and the dimensionless time (tD) as a function of the well radius, for example (EARLOUGHER, 1977):
hD = f (time, location, geometry,...)
tD = f (well radius, time,....).
This model has the advantage that the dimensionless variables are directly proportional to the dimensioned variables and can thus be mutually converted by simple transformations.
The complete description of the solution also consists of specification and formulation of boundary conditions. The type of input signal (e.g. the pressure impulse for a slug test) can be seen as one of the inner boundary conditions.
In addition, the influence of the borehole or the well itself must be considered. For a free groundwater level the wellbore storage of a well or borehole is defined as:
and
for an enclosed volume of water.
Where:
C : Storage constant [m³/m]
rB : Well radius [m]
g : Gravitational acceleration [m/s²]
cw : Compressibility of water [m²/N]
Vw : Volume of water column [m³]