In this paper we present a partitioning interwell tracer test (PITT) technique for the detection, estimation, and remediation performance assessment of the subsurface contaminated by nonaqueous phase liquids (NAPLs). We demonstrate the effectiveness of this technique by examples of experimental and simulation results. The experimental results are from partitioning tracer experiments in columns packed with Ottawa sand. Both the method of moments and inverse modeling techniques for estimating NAPL saturation in the sand packs are demonstrated. In the simulation examples we use UTCHEM, a comprehensive three‐dimensional, chemical flood compositional simulator developed at the University of Texas, to simulate a hypothetical two‐dimensional aquifer with properties similar to the Borden site contaminated by tetrachloroethylene (PCE), and we show how partitioning interwell tracer tests can be used to estimate the amount of PCE contaminant before remedial action and as the remediation process proceeds. Tracer tests results from different stages of remediation are compared to determine the quantity of PCE removed and the amount remaining. Both the experimental (small‐scale) and simulation (large‐scale) results demonstrate that PITT can be used as an innovative and effective technique to detect and estimate the amount of residual NAPL and for remediation performance assessment in subsurface formations.

Summary We report results for a number of promising enhanced-oil-recovery (EOR) surfactants based upon a fast, low-cost laboratory screening process that is highly effective in selecting the best surfactants to use with different crude oils. Initial selection of surfactants is based upon desirable surfactant structure. Phase-behavior screening helps to quickly identify favorable surfactant formulations. Salinity scans are conducted to observe equilibration times, microemulsion viscosity, oil- and water-solubilization ratios, and interfacial tension (IFT). Cosurfactants and cosolvents are included to minimize gels, liquid crystals, and macroemulsions and to promote rapid equilibration to low-viscosity micro-emulsions. Branched alcohol propoxy sulfates (APS), internal olefin sulfonates, and branched alpha olefin sulfonates (AOS) have been identified as good EOR surfactants using this screening process. These surfactants are available at a low cost and are compatible with both polymers and alkali, such as sodium carbonate and, thus, are good candidates for both surfactant-polymer and alkali-surfactant-polymer EOR processes. One of the best formulations was tested in both sandstone and dolomite cores and found to give excellent oil recovery and low surfactant retention with a west Texas (WT) crude oil.

No abstract

No abstract

Partitioning interwell tracer tests (PITTs) have emerged as a useful tool in characterizing the volume of nonaqueous phase liquids (NAPLs) in contaminated aquifers. More than 40 PITTs have been conducted in various NAPL-contaminated sites for both initial estimation of NAPL volume and postremediation performance assessment of various cleanup technologies. An effective interpretation of PITT results requires an accurate determination of the confidence limits of the volume of NAPL estimated from PITT data. This necessitates a description of the various errors, both systematic and random, associated with the measurement and analysis of PITT data. In this paper, an approach for performing this error analysis for both vadose-zone and saturated-zone PITTs is presented. This approach is based upon identifying the various sources of errors in both the measurement of PITT data and the errors from the data analysis using the method of temporal moments. Results are illustrated using our data from several soil column studies and two field PITTs, one saturated and one unsaturated.

The physicochemical characteristics of five nonaqueous phase liquids (NAPLs) recovered from contaminated alluvial aquifers are presented. The five include two chlorinated degreasing solvents, one chlorinated dry-cleaning solvent and two weathered fuel hydrocarbons. In addition to density, viscosity, and interfacial tensions, the equivalent alkane carbon number (EACN), spreading coefficients and Amott-Harvey and USBM wettability indices with respect to alluvial aquifer materials are used as a means to characterize three of these NAPLs. Experimentally measured spreading coefficients of four of these NAPLs illustrate that field NAPLs can have positive initial spreading coefficients. Furthermore, capillary desaturation curves for two NAPLs with alluvial aquifer material collected from the NAPL zone are presented as an additional and important means to infer the practical implications of the wetting characteristics on the efficacy of NAPL recovery. The results from the wettability and capillary desaturation experiments show that these NAPLs are mixed-wet to oil-wet when measured in the alluvium from their respective field sites. Furthermore, these results indicate that the displacement of NAPLs from soils by water is more difficult for mixed-wet or oil-wet soils than it is for water-wet or weakly water-wet soils. Finally experimental data indicate that adding anionic surfactants to the water shifts the wettability toward water-wet and makes the NAPL easier to displace and recover.

Chlorinated degreasing solvents are multicomponent liquids containing not only the chlorinated hydrocarbons with which their name is associated (e.g., trichloroethylene or |TCE]. perchloroethylene or [PCE], 1,1,1‐trichlorocihane [TCA]) but also a number of organic additives included as corrosion inhibitors and antioxidants. The additives, such as 1,4‐dioxane, are likely to be of significant public‐health importance as ground water contaminants due to their toxicity, solubility, and mobility. Following their use in vapor degreasing systems by industry, chlorinated degreasing solvents will also contain about 25% solubilized oil and grease. A number of physical‐chemical properties become especially important in the light of the multicomponent nature of these solvents. First, the higher aqueous solubility and lower sorption of the additives makes it is reasonable to expect that faster moving plumes of these solvent additives will precede plumes of the chlorinated hydrocarbons. Second, due to high losses of chlorinated hydrocarbons by volatilization from vapor degreasers during years in the middle of the century, it is probable that background concentrations of these hydrocarbons are present in ground water flow systems due to their downwind washout. Finally, the solubilized oil and grease may cause profound changes to the wettability of aquifer materials contacted by the solvents during their subsurface migration. It is argued, therefore, that the wettability of aquifer materials contaminated by chlorinated degreasing solvents needs to be experimentally determined before remediation of DNAPL at each site, rather than being simply assumed as water wet.

No abstract