Eric J. Daniels

Isotope study on organic nitrogen of Westphalian anthracites from the Western Middle field of Pennsylvania (U.S.A.) and from the Bramsche Massif (Germany)

Abstract The objective of this study was to examine an aspect of the thermal cycling of organic nitrogen in sediments and metasediments. The cycling of organic nitrogen is important because sedimentary organic matter is a shuttle of nitrogen from the atmosphere to the lower crust and thermal decomposition of organic matter is a critical step in the recycling of nitrogen between the different nitrogen pools. Abundance and isotopic composition of organic nitrogen were determined in the particular case of two low sulfur Westphalian anthracites series from Pennsylvania and Bramsche Massif. They represent good examples of Euramerica coals spanning the whole range of anthractization in single fields. Gold cell experimental simulation of the denitrogenation process was conducted at moderate pressure to show that both suites make ideal metamorphic profiles without any shift due to change of facies or to hydrothermal disturbance. During anthracitization, organic nitrogen content decreases rapidly while organic nitrogen isotopic composition does not change with rank increase. The preservation of the isotopic signature implies that organic nitrogen isotopes could be used as indicators for the paleoecological and paleodepositional history reconstruction of the basins. The striking contrast between the rapid and sharp decrease of nitrogen organic content and the invariance of its isotopic composition during the whole anthracitization suggests that ammonia is an important product of the denitrogenation process.

Mineralogical responses of siliciclastic carbonate-cemented reservoirs to steamflood enhanced oil recovery

Abstract Rock–fluid interactions induced by steamflood enhanced oil recovery were investigated in laboratory simulations to determine the geochemical reactions and the effects of these reactions on reservoir permeability. Flow-through laboratory experiments using mixtures of quartz, kaolinite, and siderite were performed in a high temperature/high pressure permeameter at a confining pressure of 1200 psi and temperatures between 150–250°C. Fluid compositions used in the experiments simulated the vapor and residual liquid phases encountered in steamflood operations as well as an intermediate fluid composition. Effects of fluid pH, fluid salinity and flow rate were systematically investigated in the experiments. The most extensive fluid–rock interactions were observed in the vapor phase simulations and high temperature/high pH condition simulations. Smectite, chlorite, illite, mixed-layer clays, greenalite, analcime, and K-feldspar were all identified as products of rock fluid interaction in the experiments. Smectite was the dominant authigenic phase to reduce permeability in the experiments. The experiments showed that the formation of smectite in Fe-rich environments does not require a clay precursor. Smectite is likely the most damaging neoformed mineral to reservoir permeability under different hydrogeochemical conditions for several reasons including: (1) its relatively high surface area (including microporosity in the “honeycomb texture”), (2) its propensity to migrate and block pore throats during fluid flow in porous media because of its small particle size, pore-lining texture, and electrochemical surface properties, and (3) the wide range of stability of smectites in the physical and chemical conditions that exist in reservoirs undergoing steamflood EOR. The rapid precipitation of authigenic minerals in these experiments suggests that the period required for fluids and rock to reach equilibrium in diagenetic environments are extremely short when considering geologic time scales. The armoring of pre-existing minerals by grain-coating authigenic minerals appears to result in the attainment of local equilibrium conditions prior to when one would predict assuming a continuous supply of reactant minerals was present.

Diagnostic Tools to Assess Mass Removal Processes During Pulsed Air Sparging of a Petroleum Hydrocarbon Source Zone

During remediation of contaminated aquifers, diagnostic tools can help evaluate whether an intended mass removal process was successfully initiated and acted on specific contaminants of concern. In this study, several diagnostic tools were tested in a controlled-release in situ air sparging experiment that focused on the treatment of target hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xylenes). The tools included compound-specific isotope analysis (CSIA), expression of functional genes (mRNA), and metabolites characteristic of aerobic and anaerobic biodegradation. Total and compound-specific mass balances were established and used, along with traditional monitoring parameters, to validate the results from the various tools. CSIA results indicated biodegradation as the main process contributing to benzene and toluene removal. Removal process-specific isotope shifts were detected in groundwater as well as in the system effluent gas. CSIA, metabolite, and mRNA biomarkers consistently indicated that both aerobic and anaerobic biodegradation of benzene and toluene occurred, but that their relative importance evolved over time and were related to the treatment system operation. While the indicators do not allow quantif cation of the mass removed, they are particularly useful to identify if a removal process has been initiated, and to track relative changes in the predominance of in situ contaminant attenuation processes resulting from remediation efforts.