A surfactant/foam process is described for the remediation of aquifers contaminated with dense nonaqueous phase liquid (DNAPL). Foam is used for mobility control to displace DNAPL from low permeability sands that are often unswept during a remediation process. Introduction An area where the technology developed for enhanced oil recovery can be applied to environmental remediation is the application of surfactant to remove nonaqueous phase liquid (NAPL) from aquifers. NAPL can be of two types, those which are less dense than water, called light nonaqueous phase liquid (LNAPL) and those which are more dense than water, called dense nonaqueous phase liquid (DNAPL). We concentrate on DNAPL because there are fewer viable alternatives to surfactant remediation. DNAPL will tend to migrate to the lowest accessible point in the aquifer and to enter lower permeability sediments if the capillary pressure becomes large enough. The challenge is to remove DNAPL from local depressions along the base of an aquifer and from low permeability layers in the presence of higher permeability layers. An approach to improve the sweep efficiency of a displacement process is to use mobility control so that the injected fluid is less mobile than the resident fluids. The common method of mobility control for surfactant flooding is through the generation of an inherently viscous microemulsion phase and through the addition of a polymer. However, Lawson and Reisberg introduced the concept of injecting gas with the surfactant solution to generate an in situ foam for mobility control. This approach has not been as popular because the mobility of foam is not as predictable as with polymers. However, much has been learned about the mobility of foam since that time and some publications on the use of foam for mobility control of surfactant flooding have appeared. Also foam has the potential of selectively reducing the mobility more in higher permeability layers in contact with lower permeability layers. Site Characterization The location for a field test of the surfactant/foam process for aquifer remediation is Hill Air Force Base near Ogden, Utah. This base has been the test site of many remediation technologies during 1996. The Operable Unit 2 (OU2) is a waste disposal site where unlined earthen trenches were used from 1967 to 1975 for the disposal of spent liquid degreasing solvents (primarily trichloroethylene). OU2 is currently being treated by "pump and treat" where the DNAPL and ground water are pumped out and the organic material removed by sedimentation and steam stripping. However, pump and treat treatment alone would have to continue for a very long time because of the low solubility of the contaminants in water and the large volume of DNAPL existing in pools and as a residual saturation. A surfactant flood without mobility control was conducted successfully by INTERA and the University of Texas at a site adjacent to where the surfactant/foam is to be tested. A steam flood test in an adjacent site is planned in the near future. Aquifer structure A structure map of the base of the unconfined aquifer is shown in Fig. 1. The aquifer consists of coarse-grained, unconsolidated sediments of recent alluvium and/or Provo Formation. It is about 50 ft thick and the water table is about 25 ft below ground level. The aquifer is underlain by more than 100 ft of the clay dominated Alpine Formation. This formation will be called the "aquitard". The structure of the aquitard and the water table helps to keep the aquifer confined in a trough or channel. Fig. 2 is a cross section along the long axis of the channel. The disposal trenches were located somewhere near the southern end of this cross-section. P. 471

Field Demonstration of the Surfactant/Foam Process for Aquifer Remediation G.J. Hirasaki, SPE, C.A. Miller, SPE, R. Szafranski, D. Tanzil, SPE, and J.B. Lawson, SPE, Rice University, H. Meinardus, M. Jin (SPE), J.T. Londergan, and R.E. Jackson, Duke Engineering and Services, and G.A. Pope (SPE) and W.H. Wade, University of Texas Abstract The first field demonstration of the surfactant/foam process for removal of DNAPL from a heterogeneous alluvial aquifer was conducted during the spring of 1997 at Hill Air Force Base in Utah. The surfactant solution was designed to mobilize and solubilize the contaminant, which was located in the lowest part of the aquifer. During the demonstration, air was injected to form an in situ "foam" in the zones of highest permeability, the purpose being to divert surfactant solution to zones of lower permeability and thereby improve the efficiency of the removal process, as compared to continuous surfactant injection without foam generation. The process was successful in reducing the average DNAPL saturation of the swept pore volume to 0.03%. Introduction and Summary The EPA defines a DNAPL (Dense NonAqueous Phase Liquid) site as "a site where DNAPL has been released and is now present in the subsurface as an immiscible phase", i.e., either free-phase and residual DNAPL or simply residual DNAPL alone. Residual DNAPL is that immiscible liquid trapped by capillary forces within the pore spaces of the sand and silt that comprise the aquifer system. In the saturated zone, it consists of discrete drops or ganglia and is immobile. In contrast, by definition, the free-phase DNAPL is present along continuous pathways through the aquifer and is mobile. The accumulation of DNAPL in an aquifer is a persistent source of contamination that cannot be remediated by the traditional method of "pump and treat". Even if it was possible to detect and produce all of the free-phase DNAPL, the aquifer will continue to be contaminated by the residual DNAPL. Thus, complete remediation will require removal of all of the DNAPL, including residual DNAPL and unswept DNAPL due to aquifer heterogeneities. Surfactant-enhanced aquifer remediation (SEAR) is a promising technology for removal of DNAPL because of its history of recovering residual oil that remains after waterflooding. A common problem with surfactant flooding, both for recovery of petroleum and in aquifer remediation, is the effect of heterogeneities on the performance of the process. The effect of heterogeneity is mitigated by application of mobility control. Mobility control in surfactant flooding has been accomplished by addition of polymer, generation of a viscous microemulsion, and in situ generation of foam by injection of gas. The first field demonstration of the surfactant/foam process for removal of DNAPL from heterogeneous alluvial aquifers was conducted during the spring of 1997 at Hill Air Force Base (AFB) in Utah. The surfactant solution was designed to mobilize and solubilize the contaminant, which was located in the lowest part of the saturated zone of an alluvial aquifer contained in a buried paleo-channel eroded into thick clay deposits. The clay provided a capillary barrier to contaminant migration. During the demonstration, air was injected to form an m situ 'foam' in the zones of highest hydraulic conductivity or permeability, the purpose being to divert surfactant solution to zones of lower conductivity and thereby improve the efficiency of the removal process as compared continuous surfactant injection without foam generation. The demonstration was conducted in a 6.1-meter (20-foot) line drive well pattern with three injection and three extraction wells spanning the width of the buried channel (approximately 3.7 meters, or 12 feet). Hydraulic conductivity ranged from 10–4 m/s (permeability: 10 darcy) to more than 10-–3 m/s (permeability: 100 darcy) with the contaminated zones near the bottom of the channel being in the lower portion of this range. The bottom of the buried channel was some 13.7 meters (45 feet) below the ground surface. The contaminant itself contained approximately 70% trichloroethene (TCE), and smaller amounts of other solvents and dissolved greases.

No abstract

No abstract

No abstract

No abstract

No abstract

TX 75083-3836, U.S.A., fax +1-972-952-9435. AbstractOver the past several decades the oil and gas industry has developed full-system approaches for safe and cost-effective injection of methane, carbon dioxide and acid gas. Projects have been executed successfully in formations spanning a full range of depths, reservoir quality, pressures and temperatures. Injection has been into both aquifers and hydrocarbon bearing intervals. Lessons learned about site selection, storage design and site monitoring are directly applicable to current and future CO 2 geo-sequestration projects. The standard for performance for geo-sequestration projects, as defined by the USA National Energy Technology Laboratory, is for 99+% permanence of storage and 30+% efficiency of pore space utilization.The focus of this paper will be on project design and well completion options to manage plume growth and promote safe, efficient and reliable storage in different geologic settings. Safe and reliable long term storage of carbon dioxide within a defined permit area will require knowledge and observance of limits on cap rock fracture pressures, formation stratigraphy and properties, knowledge of formation spill points and calculation of maximum rates of injection. Optimum design will achieve both permanence of storage and efficient use of pore space to mitigate adverse sweep related to gravity override of injected gas. To manage these issues in deep saline formations, with or without closed anticline structures, may require inclusion of brine withdrawal as part of the project design. Options for achieving the above will be discussed in the context of a staged development process.By use of specific examples across a range of possible storage scenarios this paper will illustrate that site specific data, combined with detailed dynamic modeling, is very important to a complete assessment of storage site capacity and to design well completions that will achieve project objectives. Year Aquifer Pressure, psiCentral Basin GI Area East Basin