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.

Jacob (1947) 方程的系数B和C通常来自阶梯下降试验，通常分别归因于“含水层损失”和“井损失”。本文分析并区分了从含水层流向屏蔽井过程中发生的线性层流、非线性层流和湍流损失。由此，可以得出这两个系数的详细物理含义。系数B不仅包含含水层损失，还包含砾石充填和井眼表皮（如果存在）的线性损失。系数C包含来自砾石充填的非线性层流损失和由筛管流入和垂直流通过筛管和套管引起的湍流损失。在某些情况下，湍流损失小到可以忽略不计。对于较大时间的瞬态流动，含水层内线性层流损失的变化变得很重要。将 Jacob 方程的一个新的、明确的公式与长期现场逐步下降测试进行了比较，其中三个在受限的松散地层中，一个在破裂的岩石含水层中。Jacob CE (1947) 确定自流井有效半径的下降试验。反式。是。社会党。民事工程。112：1047–1070。