Derivative-assisted evaluation of well yields in a heterogeneous aquifer

Abstract

The evaluation of well yields conventional time–drawdown methods is based on the assumption of infinite-acting radial flow (IARF) of groundwater to a well. However, long-term well yields are controlled by heterogeneities and, as suggested here, by the presence of linear features and aquitard leakage, and the subsequent departures from IARF. Accurate prediction of long-term well yields therefore requires an evaluation of aquifer heterogeneities. Derivative techniques combined with aquifer geology and conventional methods aid in the evaluation of long-term well yields in the heterogenous aquifers. Our case study involves the estimation of long-term well yields from relatively short-term aquifer tests in an aquifer near Calgary, Alberta. The wells are completed in a gravel-floored cahnnel incised into bedrock. On the regional scale, the floor gravels appear to form a continuous and homogeneous aquifer. Aquifer-test responses indicate internal heterogeneity at a scale below the resolution attainable with the available well control. Reliable estimates of aquifer parameters are obtained by applying a derivative technique to the analysis of time–drawdown data. Derivative analysis allows us to isolate test segments for which the assumption of IARF is valid. Characteristic time–drawdown and derivative curves are then integrated with geology to identify the nature of heterogeneities and assess their impact on long-term aquifer response to pumping. Key words: aquifer-test, derivative, heterogeneity, well yield, buried valley aquifer.

The Unusual and Large Drawdown Response of Buried‐Valley Aquifers to Pumping

“…Slopes somewhat less than 1/2 are commonly reported, in part because most reported pumping tests for buried‐valley aquifers only had observation wells located near the pumped well, as is routine for sheet aquifers. For example, Andersen and Haman (1970, Figure 6); Shaver and Pusc (1992, Figure 6) and Parks and Bentley (1996, Figures 6 and 9) each presented pumping test results that have typical “straight‐line” strip aquifer behavior. The drawdown data for the Estevan Valley Aquifer (Figures 1 and 5) also illustrate such behavior.…”

“…Long and narrow strip aquifers in the form of buried‐valley deposits confined by low‐permeability aquitards are common in the glaciated terrain of northern North America and north‐western Europe (Andersen and Haman 1970; Kehew and Boettger 1986; Shaver and Pusc 1992; Parks and Bentley 1996; Maathuis and Thorleifson 2000; Desbarats et al 2001; Sandersen and Jorgensen 2003; Russell et al 2004; BurVal Working Group 2006; Seifert et al 2008; Ahmad et al 2009). These aquifers occur as long and narrow, highly transmissive, sand and gravel units that are incised into much less permeable clay‐rich formations or into the less permeable bedrock.…”

Derivative‐Assisted Classification of Fractured Zones Crossing a Deep Borehole

“…Because the logarithmic derivative is sensitive to slight changes of the drawdown curve, the derivative analysis allows us to find the well storage and skin effects in the drawdown curve, and to characterize the groundwater flow dimensionality and boundary conditions of an aquifer (Walker and Roberts ). Thus, it has been frequently used to conceptualize an oil reservoir in petroleum engineering (Bourdet et al ; Ramey ; Ehlig‐Economides et al ; Horne ) and to improve the estimation of the hydraulic properties of a heterogeneous aquifer in the subject of hydrogeology (Parks and Bentley ; Beauheim et al ; Samani et al ; Renard et al ).…”

A new method for aquifer system identification and parameter estimation

“…The use of derivative plots generated from drawdown data has become a common practice in the analysis of aquifer parameters for all types of aquifer settings and pumping test methodology. Parks and Bentley () used the derivative analysis to assess which sections of the drawdown data collected from short‐term aquifer tests in heterogeneous aquifers fall in the infinite acting radial flow. Pressure derivative type analysis was also used on slug tests within confined aquifers (e.g.…”