Geology Reports⌕ Search

Geology topics

Y.K. Kharaka

Publications and source records attributed to Y.K. Kharaka.

29 records · Page 2Linked to original sources
USGS1987

Geochemistry of metal-rich brines from central Mississippi Salt Dome basin, U.S.A.

Oil-field brines are the most favored ore-forming solutions for the sediment-hosted Mississippi Valley-type ore deposits. Detailed inorganic and organic chemical and isotope analyses of water and gas samples from six oil fields in central Mississippi, one of the very few areas with high metal brines, were conducted to study the inorganic and organic complexes responsible for the high concentrations of these metals. The samples were obtained from production zones consisting of sandstone and limestone that range in depth from 1900 to 4000 m (70–120°C) and in age from Late Cretaceous to Late Jurassic. Results show that the waters are dominantly bittern brines related to the Louann Salt. The brines have extremely high salinities that range from 160,000 to 320,000 mg/l total dissolved solids and are Na Ca Cl-type waters with very high concentrations of Ca (up to 48,000 mg/l) and other alkaline-earth metals, but with low concentrations of aliphatic acid anions. The concentrations of metals in many water samples are very high, reaching values of 70 mg/l for Pb, 245 mg/l for Zn, 465 mg/l for Fe and 210 mg/l for Mn. The samples with high metal contents have extremely low concentrations (<0.02 mg/l) of H 2 S. Samples obtained from the Smackover Formation (limestone) have low metal contents that are more typical of oil-field waters, but have very high concentrations (up to 85 mg/l) of H 2 S. Computations with the geochemical code SOLMINEQ.87 give the following results: (1) both Pb and Zn are present predominantly as aqueous chloride complexes (mainly as PbCl 4 2− and ZnCl 4 2− , respectively); (2) the concentrations of metals complexed with short-chained aliphatic acid anions and reduced S species are minor; (3) organic acid anions are important in controlling the concentrations of metals because they affect the pH and buffer capacity of the waters at subsurface conditions; and (4) galena and sphalerite solubilities control the concentrations of Pb and Zn in these waters.

Applied Geochemistry↗
USGS1986

Uranium geochemistry in geopressured-geothermal aquifers of the U.S. Gulf Coast

Formation water from U.S. Gulf Coast geopressured-geothermal sandstone aquifers has been analyzed to determine the geochemistry of uranium in these systems. Results of chemical analyses and chemical equilibrium modeling indicate the formation waters are in equilibrium with uraninite (UO 2 ) and coffinite (USiO 4 ). The 234 U 238 U "> 234 U 238 U activity ratios in the formation waters range from 1.06 to 1.69. These isotopic data suggest that at formation temperatures uranium is continually reequilibrating chemically and isotopically between water, a solid phase of either UO 2 or USiO 4 and a component of 234 U supplied to solution from the aquifer matrix material by alpha recoil processes.

Geochimica et Cosmochimica Acta↗
USGS1984

Hydrogeochemistry of Big Soda Lake, Nevada: An alkaline meromictic desert lake

Big Soda Lake, located near Fallon, Nevada, occupies an explosion crater rimmed by basaltic debris; volcanic activity apparently ceased within the last 10,000 years. This lake has been selected for a detailed multidisciplinary study that will ultimately cover the organic and inorganic hydrogeochemistry of water and sediments because the time at which chemical stratification was initiated is known (~1920) and chemical analyses are available for a period of more than 100 years. Detailed chemical analyses of the waters show that the lake is at present alkaline ( pH = 9.7 "> pH = 9.7 ), chemically stratified (meromictic) and is extremely anoxic (total reduced sulfur—410 mg/L as H 2 S) below a depth of about 35 m. The average concentrations (in mg/L) of Na, K, Mg, Ca, NH 3 , H 2 S, alkalinity (as HCO 3 ), Cl, SO 4 , and dissolved organics (as C) in waters of the upper layer (depth 0 to 32 m) are 8,100, 320, 150, 5.0, &lt; 0.1 "> < 0.1 , &lt; 0.5 "> < 0.5 , 4,100, 7,100, 5,800, and 20 respectively; in the deeper layer (depth 37 to 64 m) they are 27,000, 1,200, 5.6, 0.8, 45, 410, 24,000, 27,500, 6,800, and 60, respectively. Chemical and stable isotope analyses of the waters, &#x3B4; 13 C "> δ13C and &#x394; 14 C "> Δ14C values of dissolved total carbonate from this lake and surface and ground waters in the area together with mineral-water equilibrium computations indicate that the waters in the lake are primarily meteoric in origin with the present chemical composition resulting from the following geochemical processes: 1. (1) evaporation and exchange with atmosphere, the dominant processes, 2. (2) mineral-water interactions, including dissolution, precipitation and ion exchange, 3. (3) inflow and outflow of ground water and 4. (4) biological activity of macro- and microorganisms, including sulfate reduction in the water column of the deeper layer at a very high rate of 6.6 μmol L −1 day −1 .

Geochimica et Cosmochimica Acta↗
USGS1983

Thermal decarboxylation of acetic acid: Implications for origin of natural gas

Laboratory experiments on the thermal decarboxylation of solutions of acetic acid at 200°C and 300°C were carried out in hydrothermal equipment allowing for on-line sampling of both the gas and liquid phases for chemical and stable-carbon-isotope analyses. The solutions had ambient pH values between 2.5 and 7.1; pH values and the concentrations of the various acetate species at the conditions of the experiments were computed using a chemical model. Results show that the concentrations of acetic acid, and not total acetate in solution, control the reaction rates which follow a first order equation based on decreasing concentrations of acetic acid with time. The decarboxylation rates at 200°C (1.81 × 10 −8 per second) and 300°C (8.17 × 10 −8 per second) and the extrapolated rates at lower temperatures are relatively high. The activation energy of decarboxylation is only 8.1 kcal/mole. These high decarboxylation rates, together with the distribution of short-chained aliphatic acid anions in formation waters, support the hypothesis that acid anions are precursors for an important portion of natural gas. Results of the δ 13 C values of CO 2 , CH 4 , and total acetate show a reasonably constant fractionation factor of about 20 permil between CO 2 and CH 4 at 300°C. The δ 13 C values of CO 2 and CH 4 are initially low and become higher as decarboxylation increases.

Geochimica et Cosmochimica Acta↗
USGS1980

Stable carbon isotopes of HCO3- in oil-field waters-implications for the origin of CO2

The δ 13 C values of dissolved HCO 3 − in 75 water samples from 15 oil and gas fields (San Joaquin Valley, Calif., and the Houston-Galveston and Corpus Christi areas of Texas) were determined to study the sources of CO 2 of the dissolved species and carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The reservoir rocks are sandstones which range in age from Eocene through Miocene. The δ 13 C values of total HCO 3 − indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin. The range of δ 13 C values for the HCO 3 − of these waters is −20–28 per mil relative to PDB. This wide range of δ 13 C values is explained by three mechanisms. Microbiological degradation of organic matter appears to be the dominant process controlling the extremely low and high δ 13 C values of HCO 3 − in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low δ 13 C values (< −10 per mil) are obtained in waters where concentrations of SO 4 2− are more than 25 mg/l and probably result from the degradation of organic acid anions by sulfate-reducing bacteria ( SO 4 2− + CH 3 COO − → 2 HCO 3 − + HS − ). The high δ 13 C values probably result from the degradation of these anions by methanogenic bacteria ( CH 3 COO − + H 2 O ai HCO 3 − + CH 4 ). Thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO 2 and CH 4 is probably the major source of CO 2 for production zones with subsurface temperatures greater than 80°C. The δ 13 C values of HCO 3 − for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO 2 and CH 4 . At these high temperatures, δ 13 C values of HCO 3 − decrease with increasing temperatures and decreasing concentrations of these acid anions.

Geochimica et Cosmochimica Acta↗
USGS1976

Hydrogen and oxygen isotope exchange reactions between clay minerals and water

The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100–350° for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100°. Exchange rates were 3–5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure. Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O 18 exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O 18 exchange. At 350° kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O 18 exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor.

Geochimica et Cosmochimica Acta↗
USGS1975

Short chain aliphatic acid anions in oil field waters and their contribution to the measured alkalinity

High alkalinity values found in some formation waters from Kettleman North Dome oil field are due chiefly to acetate and propionate ions, with some contribution from higher molecular weight organic acid ions. Some of these waters contain no detectable bicarbonate alkalinity. For waters such as these, high supersaturation with respect to calcite will be incorrectly indicated by thermodynamic calculations based upon carbonate concentrations inferred from traditional alkalinity measurements

Geochimica et Cosmochimica Acta↗
USGS1973

Isotopic composition of oil-field brines from Kettleman North Dome, California, and their geologic implications

Deuterium and O 18 analyses were made on 25 formation-water samples from Miocene (Temblor Formation) and Eocene (McAdams Formation) reservoir rocks at Kettleman North Dome oil field, California, and on three surface water samples from Reef Ridge located about three miles to the west of the field. The δO 18 values obtained generally increase with depth and most probably are due to temperature controlled exchange reactions with carbonate cement and dissolved carbonate species. The δD values obtained seem to be controlled primarily by the membrane behavior of shales modifying the assumed original values. The contribution of isotopic exchange between water and clays cannot be evaluated at present. The isotopic data support the conclusions based on a detailed study of geology, hydrodynamics, and formation water geochemistry ( Kharaka , 1971) which indicate that: 1. The Temblor Formation waters are probably meteoric in origin concentrated chemically and isotopically by shale membranes, and 2. The McAdams Formation waters were most probably obtained by squeezing the original interstitial marine connate waters of deposition from the underlying Mesozoic sediments.

California↗
USGS1973

Simultaneous flow of water and solutes through geological membranes-I. Experimental investigation

The relative retardation by geological membranes of cations and anions generally present in subsurface waters was investigated using a high pressure and high temperature ‘filtration cell’. The solutions were forced through different clays and a disaggregated shale subjected to compaction pressures up to 9500 psi and to temperatures from 20 to 70°C. The overall efficiences measured increased with increase of exchange capacity of the material used and with decrease in concentration of the input solution. The efficiency of a given membrane increased with increasing compaction pressure but decreased slightly at higher temperatures for solutions of the same ionic concentration. The results further show that geological membranes are specific for different dissolved species. The retardation sequences varied depending on the material used and on experimental conditions. The sequences for monovalent and divalent cations at laboratory temperatures were generally as follows: Li < Na < NH 3 < K < Rb < Cs Mg < Ca < Sr < Ba. The sequences for anions at room temperature were variable, but at 70°C, the sequence was: HCO 3 < I < B < SO 4 < Cl < Br. Monovalent cations contrary to some field data were generally retarded with respect to divalent cations. The differences in the filtration ratios among the divalent cations were smaller than those between the monovalent cations. The passage rate of B, HCO 3 , I and NH 3 was greatly increased at 70°C.

Geochimica et Cosmochimica Acta↗