These observations are eliminated from the regression by assigning weights of 0 to minimize their effects on estimates of well-loss coefficients. These anomalies result primarily from the analytical model not simulating wellbore storage. Transmissivity can be adjusted manually to best explain late-time drawdowns during each step, while visually ignoring anomalies from unsteady flow rates and wellbore storage. Transmissivity estimates are improved with the flow-normalized drawdown plot, because effects of transmissivity on drawdowns are isolated from well-losses (Figure 1). Were improved in the workbook, Pumping_StepDrawdown-2019.xlsm. Well-loss model and parameter estimation techniques Measured s/Qstep depart from straight lines at the beginning of each stepĭrawdowns were analyzed with a flow-normalized drawdown plot in a previouslyĪnd Kuniansky, 2002). Separately because of non-linear, well losses. T = 35.3 / Slopein field units of ft²/d, ft, and gpm. Slope (T/L²) estimated from flow-normalizedĮquation for transmissivity simplifies to, Q CONVERT converts flow to consistent units, e.g. T = 2.303 Q CONVERT / 4 / π / Slope or 0.1832 Q CONVERT Interpretation differs from Cooper-Jacob ( 1946) because discharge is incorporated in the estimated slope. Line, where transmissivity is inversely proportional to the slope ( Lee,ġ982). Transformed data theoretically should plot in a straight Figure 1.- Example of transformed drawdown (s) and flow-rate (Q) data and interpreted slope of s/Q that is inversely proportional to transmissivity. Drawdown ( s) and flow-rate ( Q) data are transformed by plotting drawdowns divided by flow rates ( s/Qstep) against flow-weighted, dimensionless times (Figure 1). The 2019 workbook accounts for linear and non-linear well losses while using graphical techniques to better estimate transmissivity ( Odeh and Jones, 1965). Transmissivity and well-loss coefficients can be estimated from step drawdown data with the workbook, Pumping_StepDrawdown-2019.xlsm. Pumping, during each step, and during recovery so that drawdowns can be Greater discharge rates are pumped during subsequent steps, where three to fiveĭischarge rates typically are tested. Water levels to change minimally at the end of each step ( Halford and Pumping rates are constant during steps which are of sufficient A step-drawdown test is a single-well test that isįrequently conducted after well development to determine well efficiency and correctly

Well drawdown test