Free-Product Recovery Using Skimmer and Dual-Pump Wells

Russell T. Johns, Larry W. Lake

Accidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake-like lens. Hydrocarbons in the aquifer that exist as a separate phase are termed free product or light nonaqueous phase liquids (LNAPL).

This project presents new analytical solutions for the effective design of long-term free-product recovery from aquifers with skimmer-, single- and dual-pump wells. The solutions are derived for steady-state flow based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow.

The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e. wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single or dual-pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table.