Geochemistry Of Formation Waters Research Articles

Chemical and isotopic tracers of the contribution of microbial gas in Devonian organic-rich shales and reservoir sandstones, northern Appalachian Basin

In this study, the geochemistry and origin of natural gas and formation waters in Devonian age organic-rich shales and reservoir sandstones across the northern Appalachian Basin margin (western New York, eastern Ohio, northwestern Pennsylvania, and eastern Kentucky) were investigated. Additional samples were collected from Mississippian Berea Sandstone, Silurian Medina Sandstone and Ordovician Trenton/Black River Group oil and gas wells for comparison. Dissolved gases in shallow groundwaters in Devonian organic-rich shales along Lake Erie contain detectable CH 4 (0.01–50.55 mol%) with low δ 13 C–CH 4 values (−74.68 to −57.86‰) and no higher chain hydrocarbons, characteristics typical of microbial gas. Nevertheless, these groundwaters have only moderate alkalinity (1.14–8.72 meq/kg) and relatively low δ 13 C values of dissolved inorganic C (DIC) (−24.8 to −0.6‰), suggesting that microbial methanogenesis is limited. The majority of natural gases in Devonian organic-rich shales and sandstones at depth (>168 m) in the northern Appalachian Basin have a low CH 4 to ethane and propane ratios (3–35 mol%; C 1 /C 2 + C 3 ) and high δ 13 C and δD values of CH 4 (−53.35 to −40.24‰, and −315.0 to −174.6‰, respectively), which increase in depth, reservoir age and thermal maturity; the molecular and isotopic signature of these gases show that CH 4 was generated via thermogenic processes. Despite this, the geochemistry of co-produced brines shows evidence for microbial activity. High δ 13 C values of DIC (>+10‰), slightly elevated alkalinity (up to 12.01 meq/kg) and low SO 4 values (<1 mmole/L) in select Devonian organic-rich shale and sandstone formation water samples suggest the presence of methanogenesis, while low δ 13 C–DIC values (<−22‰) and relatively high SO 4 concentrations (up to 12.31 mmole/L) in many brine samples point to SO 4 reduction, which likely limits microbial CH 4 generation in the Appalachian Basin. Together the formation water and gas results suggest that the vast majority of CH 4 in the Devonian organic-rich shales and sandstones across the northern Appalachian Basin margin is thermogenic in origin. Small accumulations of microbial CH 4 are present at shallow depths along Lake Erie and in western NY.

Hydrocarbon migration and accumulation along a long-term growth fault: Example from the BZ25-1 oilfield of Bohai basin, eastern China

Long-term growth faulting in the BZ25-1 oilfield of the Bohai basin, eastern China, plays a key role in hydrocarbon migration and accumulation in two types of petroleum pools that exist in the Minghuazhen and Shahejie Formations. The deep-seated pool shows normal mature crude oil, whereas the shallow-seated pool contains heavy, biologically degraded crude oil. Two types of crude oil and their properties indicate distinct oil characteristics and multi-periods of migration and accumulation along the No. 1 fault. Formation water geochemistry and overpressure transference also signify that the No. 1 fault was the main hydrocarbon migration pathway. Besides the long-term growth fault, early and late active faults also affect hydrocarbon migration and accumulation. The formation of the Shahejie oil pool is characterized as an autochthonous, hydrocarbon migration model controlled by overpressures; the Minghuazhen oil pool is dominated by an allothigenous hydrocarbon vertical-migration model through the fault system.

Geochemistry of formation water and its implication on overpressured fluid flow in the Dongying Depression of the Bohaiwan Basin, China

This study of the geochemistry of formation waters in the Dongying Depression of the Bohaiwan basin, East China, unravels a close relationship between vertical zonality and overpressured fluid flow. The zones have distinctive original pore waters because the sediments formed under different climate conditions. The highest value of the total dissolved solid in the formation water occurs in the ES4 member of Shahejie Formation due to the dissolution of halite and gypsum beds. In the overlying ES3 and ES2 members, low salinity water occurs, except for near syndepositional fault zones where a significant increase in salinity of formation water and a reduction in overpressure were observed. This fact indicates strong overpressured fluid flow where thermal anomalies have been observed, as evidenced from thermal gradient and fluid inclusion homogenization temperatures. The results indicate that the geochemistry of pore water may be used to help identify the main migration pathways for overpressured fluid flow with hydrocarbons.

Extensive microbial modification of formation water geochemistry: Case study from a Midcontinent sedimentary basin, United States

The Upper Devonian Antrim Shale in the Michigan Basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused. Oxygen and hydrogen stable isotope compositions of Antrim formation waters show that fresh waters, recharged from Pleistocene glaciation and modern precipitation, suppressed basinal brine salinity to great depths and enhanced methanogenesis. This paper presents results of integrated elemental and isotope analyses of Antrim Shale formation waters from the margins and center of the Michigan Basin, focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis. Cl-Br-Na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water, but also by halite dissolution where fluids recharged through underlying Devonian carbonate aquifers with localized evaporite deposits. Divalent cations, carbonate system parameters, and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis. Large decreases in formation water Ca/Mg and Ca/Sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production. Thermodynamic and reaction-path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis. Similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas. Microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution.

Regional variation of formation water chemistry and diagenesis reaction in underpressured system: example from Shiwu depression of Songliao basin, NE China

Geochemistry of formation waters in the Shiwu depression of the Songliao basin, northeast China, shows a distinct variation in different pressured systems. The study area is composed of terrigeneous clastics in fluvial-lacustrine environments, which contain formation water with salinity ranging from less than 1000 to 12,000 mg/l. Water composition varies with depth and hydrochemical regions. In the underpressured strata deposited during the rifting period, formation water is characterized by water type of CaCl 2 with higher salinity. NaHCO 3-dominanted water with lower salinity occurs in the normally pressured strata deposited during the post-rifting period. In the transition area between the normally pressured and underpressured zones, total dissolved solid (TDS) content ranges from 1000 to 7600 mg/1 and increases with depth. In this halite-free basin, brackish water may be attributed to the evaporation of formation water and water-rock interaction. In the deep buried underpressured water, a predominated diagenesis reaction resulting in Ca and Cl enrichment and reduction of Na may be related to albitization of plagioclase following the basinal fluid line (BFL). The results of this study indicate that salinity variation of formation water and diagenesis reaction is closely related to hydrochemical environments within different pressured systems.

Geochemistry of formation waters in the Pannonian Basin (southeast Hungary)

Twenty five deep-water samples collected in the southern part (Szeged area) of the Pannonian Basin were analysed for their chemical and isotopic compounds. Hydrogen and oxygen isotopes indicate that most of the waters have a palaeometeoric origin. They infiltrated during a cold period. Waters in the deepest lithostratigraphical positions are mixtures of palaeometeoric water and oil field water squeezed from the thick sequence of fine-grained sediments underlying the thermal water aquifer. Most of the waters are NaHCO 3 type with 1200–4400 mg/l of TDS. Na and HCO 3 increase with depth and/or temperature. Based on chemical and isotopic compositions, waters are divided into three groups and these reflect differences in the lithostratigraphy of the basin. The wide range of carbon stable isotope variation (−14.5<δ 13C<0) suggests the existence of different carbon sources. In the shallowest samples soil CO 2 and dissolved carbonate minerals could account for the dissolved inorganic carbon. In deeper layers additional carbon from the transformation of the sedimentary organic matter is required due to the increase of alkalinity with depth and δ 13C values. The evolution of the sediment organic matter starts with kerogen formation accompanied by a CO 2 production and is followed by the transformation of kerogen yielding CO 2 from its oxygen-containing functional groups. Such evolution and methane formation can explain the wide range of 13C contents measured in the total dissolved inorganic carbon.

The application of physical measurements to constrain reservoir-scale sequence stratigraphic models

Abstract Sequence and parasequence boundaries are characterized by lateral extents that are typically greater than development well spacings and frequently more extensive than individual oil and gas fields. These surfaces result from shifts of facies belts that generate laterally extensive changes over widespread areas. Commonly only facies interpretations of lithological signatures (e.g. hardgrounds) and biostratigraphic signatures (e.g. faunal changes) are used to identify these boundaries in both surface outcrops and subsurface reservoirs. However, a wide variety of physical measurements may also be made, especially in the subsurface, that may be used as additional criteria to recognize surfaces with sequence stratigraphic significance and hence to infer reservoir architectures. Palaeomagnetic reversal stratigraphies may assist in establishing a chronostratigraphic framework within which to identify significant hiatuses and to constrain sequence stratigraphic interpretations, of both outcrops and subsurface reservoirs. In reservoirs, sequence and parasequence boundaries may be detected by a variety of other methodologies, all of which rely upon the spatial coherence of changes across these significant stratal surfaces. The geochemistry of both formation waters, and hydrocarbons, may show significant changes across these surfaces as a consequence of original variations in pore-water chemistry and/or the inability of diffusive mixing processes to equilibrate chemical compositions across such laterally extensive barriers to vertical communication. Similarly, formation pressure profiles, measured after depletion from initial reservoir pressures, frequently show significant discontinuities across these surfaces. Seismic data record the varying strengths of reflections that emanate from geological interfaces as a consequence of varying contrasts in acoustic impedance across geological surfaces. These surfaces (seismic reflectors) are commonly assumed to be of chronostratigraphic significance. It follows that spatially coherent patterns of variation in the physical properties of sediments between these surfaces may serve to delineate the location of facies belts (systems tracts) during the period of geological time represented by the sediments between reflectors. In favourable circumstances these patterns are imaged with a high degree of spatial precision by 3D reflection seismic data. The integration of the geometry of reflections with variations in reflection strength or other seismic attributes, may therefore serve to define both the chrono- and lithostratigraphic framework of reservoir sequences. It follows that qualitative inferences regarding reservoir architecture that are derived from sequence stratigraphic principles may be tested, refined and given improved spatial definition by the careful integration of diverse measurements with conceptual sedimentological models.

Geochemistry of formation waters and hydrodynamic evolution of a young and restricted sedimentary basin (Mahakam Delta Basin, Indonesia)

AbstractChemical and isotopic data on formation waters of oil‐fields from two parallel anticline axes of the Mahakam Delta Basin provide information about the present‐day mass transfers in the sedimentary sequence of this basin. Depletions in Ca, Sr and K, enrichment in Rb, and the Sr/Ca ratios in the waters are related to illitization of smectite and precipitation of carbonate minerals, as well as dissolution of K‐feldspar and precipitation of albite. These short‐lasting processes seem to have been more pronounced in the deeper segments of the proximal anticline. The Sr, oxygen and hydrogen isotopic data emphasize occurrence of lateral migrations of the formation waters within permeable units from Borneo Island to the proximal anticline under continental influence, and further to the distal anticline under marine influence.Description of a combined process including illitization of smectite, precipitation of carbonate minerals, dissolution of K‐feldspar and precipitation of albitic feldspar, during lateral migrations of the formation waters was only possible because of the young age and the restricted volume of the basin. In addition, the chemical signatures in the formation waters were not obscured by water‐rock interactions during long‐distance migrations that occur systematically in large sedimentary basins.

Geochemistry of deep formation waters in the Canning Basin, Western Australia, and their relationship to Zn‐Pb mineralization

The Canning Basin contains several Mississippi Valley‐type Zn‐Pb sulphide prospects and deposits in Devonian carbonate reef complexes on the northern edge of the Fitzroy Trough, and in Ordovician and Silurian marine sequences on the northern margin of the Willara Sub‐basin. This study uses the ionic composition and 5D, δ18O, δ34S, 87Sr/86Sr isotopic data on present‐day deep formation waters to determine their origin and possible relationship to the Zn‐Pb mineralizing palaeofluids. The present‐day Canning Basin formation waters have salinity ranging from typically less than 5000 mg/L up to 250 000 mg/L locally. The brines are mixtures of highly saline water, formed by seawater which evaporated beyond halite saturation (bittern water), with meteoric water ranging in salinity from low (<5000 mg/L) to hypersaline water (up to about 50 000 mg/L) formed by re‐solution of halite and calcium sulphate minerals. The original marine chemical composition of the bittern‐dominated brines was changed to that of a Na‐Ca‐Cl water by addition of Ca and removal of Mg and SO4, initially by bacterial sulphate reduction and later by dolomitization of carbonate. Other reactions with terrigenous components of the sediment have provided additional Ca and Sr, including a small proportion of 87Sr‐rich material. The δ34S values of the bittern‐containing waters are within the range over which marine sulphate has fluctuated from the Ordovician to the Holocene, although one of the hypersaline waters has a value of +6.8%, indicating SO4 of non‐marine origin. The pH of the bittern‐containing waters is low (about 5) and they contain significant concentrations of dissolved Fe (up to 120 mg/L). The Canning Basin bitterns appear similar in origin and chemical composition to highly saline marine brines in the Mississippi Salt Dome Basin, USA, which are known to be either metal or sulphide‐rich depending on the organic content of the host rock. In the Canning Basin, mixing of the bittern water with the various types of meteoric water has resulted in decreases in salinity, Na, Ca, Mg, K, Sr, Li and Fe, and increases in HCO3, SO4 and pH. Mixing of the bitterns with other types of metalliferous fluids and/or with sulphate‐containing hypersaline meteoric waters formed from the same marine evaporite sequence should produce ore‐precipitating fluids which are relatively hot and saline, and the resulting ore deposit should be of high grade and contain abundant sulphate minerals. In the southern Canning Basin, this type of mixing and the corresponding style of ore deposit is evident in the evaporite‐associated areas of Zn‐Pb mineralization near the Admiral Bay Fault. If the bitterns mix with low salinity HCO3‐waters in near‐surface environments, then the ore‐precipitating fluids should have relatively low salinities and carbonate minerals would precipitate during later stages of mixing. In the Lennard Shelf, the present‐day formation waters, the style of the Zn‐Pb deposits, and range of salinity and temperature of the ore‐forming palaeofluids are consistent with this type of mixing.

Geochemistry of Formation Waters from the Lower Silurian Clinton Formation (Albion Sandstone), Eastern Ohio (1)

Waters of the petroleum-bearing Clinton formation (Albion Sandstone) of eastern Ohio are highly concentrated brines with average total dissolved solids (TDS) of 250,000 ppm. Sodium, calcium, and chloride account for 97% of the TDS. Distribution of divalent metal chlorides (MCl[2]) allows inference of an up-dip paleoflow direction, although present-day flow is probably down-dip. Solute distribution may have been emplaced during early basin development; it thus provides a snapshot of paleoflow. Formation structure alone can not explain MCl[2] trends; they probably also are controlled by regional variation in salt thickness. Major constituent data do not indicate that membrane filtration affected the waters. High bromide content (mean = 1860 ppm) of the waters indicates that they originated from evaporating seawater. They probably are related genetically to the Salina evaporite group. Calculations show that several subsequent diagenetic reactions can account for the observed major ion composition. Recrystallization of aragonite and dolomitization of calcite probably occurred as the waters moved through the Big Lime and/or the Packer Shell carbonates. Cation exchange and chlorite formation probably altered water composition during interaction with shales of the Cabot Head formation and within the Clinton. Minor constituents of the waters appear to be controlled by reactions with clays.

Geochemistry of Saline Formation Waters, Miocene, Offshore Louisiana: ABSTRACT

Geochemistry of Saline Formation Waters, Miocene, Offshore Louisiana: ABSTRACT

The geochemistry of formation waters in the molasse basin of upper Austria

The geochemistry of formation waters in the Molasse basin of Upper Austria has been investigated to ascertain the extent of meteoric water replacement of the connate interstitial fluids in these sediments. The chemistry, isotopic composition, and dissolved gas contents of the groundwaters and of oil and gas associated brines have been determined. The most superficial sediments of the basin, the Innviertel (Miocene), have been completely flushed by meteoric waters within the last 200 ka. The underlying Hall and Puchkirchen formations (Miocene/Oligocene) form gas reservoirs for biogenic methane, and the associated formation waters are chemically and isotopically modified connate brines of the original marine deposition. In the northeastern part of the basin, the connate brines of the deeper sediments (Cretaceous/Jurassic) have been partially or completely replaced by meteoric waters, whereas in the south of the basin these sediments contain high salinity fluids which are substantially of connate origin. These conclusions are supported by the stable isotope composition of the various brines. Oil-associated brines from the Eocene sediments contain large amounts of dissolved radiogenic40Ar, which suggests that the oils have migrated from high-temperature environments. This is in contrast with the Puchkirchen, for which the observed absence of radiogenic40Ar suggests that the biogenic methane has been formed in situ. The4He contents of these brines and of the Cretaceous/Jurassic groundwaters are, however, less than those in the overlying Puchkirchen formation and suggest that He has been removed from the deeper sediments as a result of flushing by meteoric water. The ratios of dissolved methane and nitrogen to argon increase with increasing ammonium content of the formation waters. All of these parameters may be used as indices for the maturation of the system. The heavy noble gases, Kr and Xe, are abnormally abundant in the dissolved gases, and this is attributed to geochemical concentration of these gases by adsorption onto shales in the sediment sequence. The overall geochemical situation confirms the existence of separate hydraulic systems with little interconnection in the several overlying geological horizons.

Formation waters and hydrodynamics

Abstract Formation water geochemistry and hydrodynamics, referred to in this article as “fluid geology”, have been used, for a long time, as an efficient exploration tool. In the first part of this paper, a review is made of the three domains in which this tool can be used: evaluation of fields and pools (hydrocarbon distribution, tilt phenomena, production and salinity anomalies, genesis), evaluation of their prospects (hydrodynamic gradients, petroleum indicators) and basin evaluation (hydrodynamic pattern, invasion by meteoric waters, type of reservoir cementation). The second part explains the role played by fluid geology in the discovery of the Meillon-St. Faust field and in the exploration of the Lacq Meillon Basin (Aquitaine, south-western France).

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.

Geochemistry and origin of formation waters in the western Canada sedimentary basin—III. Factors controlling chemical composition

Twenty major and minor chemical components are reported for 78 formation waters from oil fields and gas fields in Alberta, Canada. Using published pore volume and chlorinity distribution data, a volume-weighted mean composition of formation waters in the western Canada sedimentary basin is presented. The results of Q-mode, R-mode, and second-order R-mode factor analyses are tabulated and interpreted. The volume-weighted mean composition is similar to that of present day sea water and is compelling evidence for an ultimate origin from sea water of the major portion of the dissolved salts in the formation waters. Dilution by fresh water recharge and concentration by membrane filtration are the major factors controlling chemical composition. Together, they produce a chemical population ranging from freshwater to brines which is confirmed by the Q-mode analysis. Compared to sea water, the volume-weighted mean formation water has gained NaCl, which occurs as a separate factor in the R-mode analysis, and quantitative calculations demonstrate that sufficient halite has been dissolved from Middle Devonian evaporite beds to account for the observed gain in NaCl, and that the balance of halite dissolved from bedded evaporites in the basin has been, and is being, lost to the surface. The presence of Mg and Ca in separate factors, together with quantitative calculations, indicate that the ionically balanced loss of Mg and gain of Ca in the volume-weighted mean formation water cannot be attributed to dolomitization. Similarly, the total loss of SO 4 is not due to conversion of H 2S. Chlorite formation could account for the loss of Mg. Other factors controlling chemical composition and suggested by the factor study include cation exchange on clays, a probable contribution of Br and I by desorption from the clay fraction of argillaceous rocks, as well as from organic matter, and solubility control of Ca-CO 3 and Sr-SO 4 concentrations.

Geochemistry and origin of formation waters in the western Canada sedimentary basin—I. Stable isotopes of hydrogen and oxygen

Stable isotopes of hydrogen and oxygen, together with chemical analyses, were determined for 20 surface waters, 8 shallow potable formation waters, and 79 formation waters from oil fields and gas fields. The observed isotope ratios can be explained by mixing of surface water and diagenetically modified sea water, accompanied by a process which enriches the heavy oxygen isotope. Mass balances for deuterium and total dissolved solids in the western Canada sedimentary basin demonstrate that the present distribution of deuterium in formation waters of the basin can be derived through mixing of the diagenetically modified sea water with not more than 2.9 times as much fresh water at the same latitude, and that the movement of fresh water through the basin has redistributed the dissolved solids of the modified sea water into the observed salinity variations. Statistical analysis of the isotope data indicates that although exchange of deuterium between water and hydrogen sulphide takes place within the basin, the effect is minimized because of an insignificant mass of hydrogen sulphide compared to the mass of formation water. Conversely, exchange of oxygen isotopes between water and carbonate minerals causes a major oxygen-18 enrichment of formation waters, depending on the relative masses of water and carbonate. Qualitative evidence confirms the isotopic fractionation of deuterium on passage of water through micropores in shales.

Geochemistry and origin of formation waters in the western Canada sedimentary basin, 2. Alkali metals

The population statistics for Cl, Br, I, HCO 3, SO 4, Na, Ca, Mg, K, Rb, Li, Sr, Mn, Zn, Fe, Ni, Co, Cr and Cu in formation waters from the western Canada sedimentary basin are presented, together with weighted, mean composition. Five types of formation waters are present in the basin but only two are considered in detail: (1) a membrane-concentrated formation water; and (2) a formation water formed either by mixture of #1 and very small amounts of bitterns resulting from halite precipitation or by hyperfiltration. Investigation of the alkali metals indicates that the membrane is selective and leads to a relative concentration pattern in the solution of: Rb > K > Na > Li. The movement of alkalies through the filter is primarily by site-hopping and the relative rate is controlled by the ion's ease of replacibility in the order: Li > Na > K > Rb. The composition, and thus ionratios, are set by mineral-solution reactions, particularly during early diagenesis. Modification of the composition then occurs by selective filtration, further chemical reaction, and mixing during the subsequent fluid migration resulting from hydrodynamic drive.

Geochemistry of Tertiary and Cretaceous age oil-bearing formation waters

Geochemistry of Tertiary and Cretaceous age oil-bearing formation waters