Unraveling the Causes of Well Inefficiencies

Well efficiency is a topic that is of interest to well designers, constructor and owners.  Well inefficiency is associated with increased ownership costs and reduction of service life.  Increased ownership costs associated with inefficient wells include increased pumping costs, increased maintenance costs and down time.  In addition, inefficient wells tend to have shorter service lives due to increased well aging as compared to efficient wells.

Rorabaugh (1953) developed a method to determine the laminar and non-laminar components of drawdown in a pumping well, expresses as:

S_w = BQ + CQⁿ

Where:

S_w = 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.