API PUBL 4760 VOL 2-2007

The American Petroleum Institute (API) Publication Number 4682, Free-Product Recovery of Petroleum Hydrocarbon Liquids (Charbeneau et al., 1999), provides an overview of recovery technologies for petroleum hydrocarbon liquids that are released to the subsurface environment and accumulate near the water table. The primary recovery technologies include skimmer wells that produce hydrocarbon liquids and single- and dual-pump wells that produce both water and hydrocarbon liquids. Hydrocarbon liquid recovery rates may also be enhanced by applying a vacuum pressure to the well to increase the gradient towards the well within the hydrocarbon layer. API Publ 4682 describes two (Excel spreadsheet) models that may be used to characterize the subsurface distribution and mobility of liquid hydrocarbon (lighter-than-water nonaqueous phase liquids, LNAPL), and to calculate the potential recovery rate and time using single- and dual-pump wells, and vacuum-enhanced wells.

API Publication Number 4729, Models for Design of Free-Product Recovery Systems for Petroleum Hydrocarbon Liquids (Charbeneau, 2003) describes scenario-based models for LNAPL liquid recovery using skimmer wells, water and vacuum enhanced recovery wells, and trenches. Soil capillary pressure characteristics are described using the van Genuchten (1980) capillary pressure model (soil characteristics in API Publ 4682 are described using the Brooks and Corey (1964) capillary pressure model). Implementation of the models through use of four separate spreadsheets is presented, based on single or two-layer heterogeneity, and on selection of relative permeability model (Burdine, 1953, or Mualem, 1976).

The objective of the present manuscript is to provide necessary background and user information for application of scenario-based models describing LNAPL liquid recovery. Volume 1 of this two-volume series provides model background information including the effects of capillarity in porous media, distribution of LNAPL saturation under conditions of vertical equilibrium, potential movement of LNAPL liquid, and mathematical model formulation and solution. The model scope is similar to that presented in API Publ 4729, though the model formulation has been generalized and additional capabilities have been added. The present Volume 2 describes model implementation through a single executable program. This is a User Guide and includes information and guidance on parameter selection and model testing.