Step-drawdown tests: linear and nonlinear head loss components

Coefficients B and C of the Jacob (1947) equation, usually derived from step-drawdown tests, are commonly attributed to aquifer losses and well losses, respectively. This paper analyzes and separates the linear laminar, nonlinear laminar and turbulent losses occurring during flow from an aquifer to a screened well. From this, one can derive a detailed physical meaning for both coefficients. The coefficient B does not contain only aquifer losses but also linear losses from the gravel pack and wellbore skin, if present. Coefficient C contains nonlinear laminar losses from the gravel pack and turbulent losses caused by screen inflow and vertical flow through the screen and casing. In some cases, the turbulent losses are small enough to be omitted. For transient flow at larger times, the changes in linear laminar losses within the aquifer become important. A new, explicit formulation of the Jacob equation was compared to long-duration field step-drawdown tests, three in confined unconsolidated formations and one in a fractured rock aquifer. Jacob C.E. (1947) Drawdown test to determine effective radius of artesian wells. Trans. Am. Soc. Civil Eng. 112:1047-1070.

Automated summary

This paper analyzes the coefficients B and C of the Jacob (1947) equation, indicating that coefficient B includes linear losses from the gravel pack and wellbore skin in addition to aquifer losses, while coefficient C contains nonlinear laminar and turbulent losses from the gravel pack, screen inflow, and casing.