Unraveling the Causes of Well Inefficiencies
Rorabaugh (1953) developed a method to determine the laminar and non-laminar components of drawdown in a pumping well, expresses as:
Sw = BQ + CQn
Sw = drawdown in the pumped well,
B = formation factor,
C = well-loss constant,
Q = discharge of the pumped well, and
n = exponent for turbulent flow.
However, the CQn term contains all of the combined non-linier aquifer head losses, resulting from water moving from the aquifer to the well, and wellbore loss. The loss from water moving from the aquifer can be further broken down to include skin effects of wellbore damage, converging flow and turbulent flow through the filter pack and screen. The contributing factors to the well loss will be discussed from the inside of the well into the aquifer unraveling the items that form the non-liniar head loss in a well.
A case history of an inefficient well will be discussed and the identification of the issues associated with turbulent flow using a stepped-rate pumping test and evaluation of the efficiency of the well along with corrective actions to enhance the efficiency.