Understanding reservoir compartmentalization - Strontium Isotope Residual Salt Analysis (SrRSA)
Summary:
Hundreds of wells have been studied using SrRSA since 1991 (initially as Isotopic Analytical Services (IAS) Ltd and since 2001 as Isotopic Ltd), and it is a routine core analysis reservoir characterization application for many oil companies. We have published a detailed review of the SrRSA method together with case studies (Mearns and McBride, 1999).
Constant monitoring of data quality ensures that newly measured SrRSA values are directly comparable with previous results. Thus, SrRSA results are always interpreted in the context of our large global database.
Core samples of any vintage can be studied by SrRSA. We have experience of obtaining optimum samples from cores cut under many different conditions.
We have been providing SrRSA data on a routine basis for oil company clients from around the world for 18 years.
PRINCIPLES OF Sr ISOTOPE RESIDUAL SALT ANALYSIS (SrRSA)
SrRSA data are the 87Sr/86Sr isotope ratios of the residual salts (and/or water) extracted from cores. These data reflect the Sr isotopic composition of the water (either the irreducible water in hydrocarbon saturated reservoir rocks or formation waters from water leg cores) present within the stata at the time the core was cut.
The 87Sr/86Sr isotope ratios of formation waters are modified by diagenetic and/or hydrodynamic processes. Once established, differences in 87Sr/86Sr isotope ratios within a given body will tend to be homogenized unless homogenization is prevented by some geological process or feature. Thus, the 87Sr/86Sr isotope ratios of residual salts within a hydrocarbon reservoir or aquifer are an effective means of investigating reservoir or aquifer compartmentalization.
Processes causing variations in 87Sr/86Sr isotope ratios of formation waters
The initial pore waters in sedimentary deposits will be determined by their depositional setting (ie. either meteoric or marine water). Upon subsequent burial, the 87Sr/86Sr isotope ratios of formation waters are likely to be modified by diagenesis (water - rock/mineral interactions) and/or large-scale subsurface fluid flow. Variations in 87Sr/86Sr isotope ratios of formation waters caused by natural radioactive decay (ie. 87Rb -> 87Sr + beta particle) are negligible owing to the extremely low concentrations of Rb and low Rb/Sr ratios in natural waters. Diagenetic reactions are essentially mineral dissolution and precipitation reactions which may alter formation water Sr concentrations and /or 87Sr/86Sr isotope ratios. Subsurface fluid flow may cause waters of differing composition to become inter-mixed on all scales causing 87Sr/86Sr isotope ratio variations. Fluid flow may occur in a sedimentary basin owing to combinations of many processes. It is likely that diagenesis driven by changes in formation pressure, temperature and fluid chemistry is closely inter-related with fluid flow. Because of the complex nature of these processes therefore, it is not possible to model their effects on 87Sr/86Sr isotope ratios in other than very general terms. eg. dissolution of silicate minerals such as detrital feldspars or micas is likely to increase the 87Sr/86Sr isotope ratio of formation waters because these minerals typically have very much higher 87Sr/86Sr isotope ratios than marine or meteoric waters.
Homogenization of 87Sr/86Sr isotope ratios of formation waters
Once variations in 87Sr/86Sr ratios in formation waters have been established, they will tend to become homogenized within a given hydrogeological system with time by mixing processes: small-scale fluid flow; and diffusion. Small-scale fluid flow is unlikely to independently homogenize compositions in the laminar flow regime, but may reduce the length scale of diffusion pathways and thus contribute to homogenization by diffusion (discussed in detail in Mearns and McBride, 1999; Figure 5). Chemical diffusion is driven by concentration gradients and so leads to homogenization of Sr concentrations but not 87Sr/86Sr isotope ratios. Tracer diffusion may be viewed as the exchange of neighbouring atoms by random atomic or molecular movements which will lead to homogenization of isotope ratios. Because it is an exchange process, tracer diffusion involves negligible mass transfer. For this reason, this is considered to be the more rapid process. Increased temperature will increase the rate of all of the above mixing processes.
Processes preventing homogenization of 87Sr/86Sr isotope ratios of formation waters
Variations in 87Sr/86Sr isotope ratio within a given hydrogeological system will tend to be homogenized over geological time unless mixing and/or diffusion within the system is prevented. This may be achieved by some form of "barrier" to diffusion or flow which either completely isolates a part of the system or which increases the tortuosity of the pathway between different parts of the system to an extent that prevents or hinders mixing and/or diffusion .
Depending on their configuration and dimension within the reservoir, geological features such as coal beds, shale or argillaceous facies, pervasive authigenic carbonate cement, sealed faults, tar mats etc. may significantly affect homogenization of 87Sr/86Sr isotope ratios within a given hydrogeological system.
As hydrocarbons migrate into and become trapped in a reservoir compartment, the pore-filling formation waters become progressively displaced by the migrating hydrocarbons. At a certain critical level of hydrocarbon saturation the continuous pore-filling fluid phase must change from continuous formation water to continuous hydrocarbon. At this point, the water phase ceases to take any further part in significant diagenetic or hydrodynamic processes. As a reservoir becomes progressively saturated with hydrocarbon therefore, the 87Sr/86Sr isotope ratio of the irreducible waters may be considered as "fossilized" during reservoir filling. For this reason, the SrRSA profile through a reservoir interval is considered to yield useful information about the hydrocarbon filling history by giving an indication of the changes in formation water chemistry at the hydrocarbon-water contact through time (e.g. Lines and Auld, 2004)
Reservoir compartmentalization
The interpretative principles for SrRSA results are detailed in Mearns and McBride, 1999. Sharp steps or breaks in a SrRSA depth profile may reflect a significant difference in the timing of oil emplacement above and below the break. Where a step or break corresponds with a low permeability interval such as a mudstone, coal or tightly cemented bed the data can be interpreted to indicate that the low permeability interval may have been an up-dip sealing barrier at the time of oil emplacement. Alternatively, a step or reversal in a SrRSA profile can reflect the position of a hiatus in oil filling, for example at a paleo – oil-water contact (paleo-OWC). The timing of oil emplacement above and below a paleo–OWC might also be significantly different, but a paleo-OWC might not necessarily occur at a barrier to vertical connectivity (although it may reflect the spill-point of a barrier to lateral connectivity).
Within a water-leg, it is expected that variations in 87Sr/86Sr isotope ratios would be homogenized in geological time by mixing and diffusion. Therefore, a cored homogeneous water leg would be expected to have relatively invariant SrRSA 87Sr/86Sr isotope ratios. Significant variations in SrRSA 87Sr/86Sr isotope ratios within water leg cores may indicate that homogenization has been prevented. This may be achieved by active or relatively recent fluid movement and/or diagenesis in the aquifer. If significant changes in the profile style and values of 87Sr/86Sr isotope ratios occur across geological features within a cored section, then it may be concluded that the features are barriers which have acted to prevent or restrict homogenization of the water leg at that well location.
Lateral connectivity / compartmentalization of a reservoir may be investigated by comparison of SrRSA depth profiles obtained from cores in adjacent well sections plotted at a common TVDSS depth scale.
Salinity variation
The diagenetic and/or hydrodynamic processes that produce variations in the 87Sr/86Sr isotope ratios of formation waters may also cause variations in the water bulk chemistry and salinity. For this reason, variations in SrRSA 87Sr/86Sr isotope ratios through a reservoir section may also indicate that significant variations in formation water salinity exist. For example, Smalley et al (1995) demonstrate that variations in formation water 87Sr/86Sr isotope ratios (determined from SrRSA and centrifuged waters) correspond with a salinity variation of 80,000ppm through a well in the Machar oil field. It may not always be appropriate therefore, to apply a single salinity (and resistivity) value throughout a whole reservoir section that displays a varying SrRSA profile.
Age dating marine sediment - Strontium Isotope Stratigraphy
Summary:
There is an extensive published literature on global sea water strontium isotope studies which is a relatively long established method. We use the most recent calibration data available (e.g. McArthur et al. 2001 - Look-Up Table Version 4: 08/ 04).
Measured strontium 87Sr/86Sr isotope ratios of samples provide age dates for marine sediments using the global sea water calibration data.
Applicable to core, side wall core or cuttings. We have extensive experience of selecting optimum samples for strontium Isotope Stratigraphy analysis.
Specially developed procedures are used to measure strontium 87Sr/86Sr isotope ratios of carbonate and sulphate minerals to high precision, even in very small samples.
PRINCIPLES OF Sr ISOTOPE STRATIGRAPHY
Strontium Isotope Stratigraphy is performed on unaltered marine precipitates (e.g. carbonate and sulphate) and provides a means of dating and correlating marine strata. The technique is based on two principles:
1. That the 87Sr/86Sr ratio of seawater is uniform at any given time throughout the world’s oceans ;
2. That the 87Sr/86Sr ratio in seawater has varied systematically throughout geological time .
The first principle has been demonstrated for the modern oceans (eg. Burke et al, 1982) and is explained by the long residence time of Sr (5x10E6 years) compared with the relatively rapid mixing time of the oceans (approx. 1000 years).
The second principle was first reported by Peterman et al (1970) who documented the systematic variation in the 87Sr/86Sr ratio of unreplaced calcite fossil shells during Phanerozoic time.
Further work performed by the Mobil Research and Development Laboratories in Dallas greatly increased the database and improved the documentation of the variations of 87Sr/86Sr ratios of the oceans during Phanerozoic time (Burke et al, 1982). Subsequent studies have improved the resolution of the variation, particularly in the Cenozoic and upper Mesozoic and a recent comprehensive review has been performed by McArthur et al (2001). By reference to the calibration data, measured 87Sr/86Sr ratios in samples of unknown age may yield precise dates of precipitation of the marine sedimentary material.
This technique produces objective numerical data which have quantifiable levels of uncertainty. It may complement or provide an alternative to biostratigraphy, producing results unaffected by faunal provincialism, diachronism or facies variations and being applicable to strata without age-diagnostic fossil assemblages.
The method may be applicable to carbonate, phosphate or evaporite minerals which precipitated (biogenically or chemically) directly from seawater. Samples must preserve their original seawater 87Sr/86Sr ratio. The method is not applicable to cements which have undergone diagenetic alteration resulting in modified 87Sr/86Sr ratios.
The technique is most applicable to strata ranging from the Jurassic to Pleistocene because of the almost uninterrupted increase in seawater 87Sr/86Sr ratio during this interval. Its applicability in dating strata of Palaeozoic age is limited by cyclic fluctuations of the seawater 87Sr/86Sr ratio during that era. Cyclic fluctuations may however, be overcome by analysing suites of samples with a range of stratigraphic positions to observe trends of variation with increased depth / age.
Investigating diagenesis of authigenic carbonate cement - Strontium - Oxygen - Carbon Isotope Diagenesis
Summary:
Strontium (87Sr/86Sr isotope ratio), oxygen (delta 18O) and carbon (delta 13C) isotope analyses are well established in the study of authigenic carbonate cements.
Strontium, oxygen and carbon isotope compositions of authigenic carbonate cements provide information on reservoir and basin fluid composition at the time the cement formed.
Isotopic are experienced in the integration of isotope data with the results of specialist petrographic studies.
Profiles of strontium, oxygen and carbon isotope compositions through pervasive carbonate cement intervals in sandstone may help determine origin and geometry of the cemented layers.
PRINCIPLES OF Sr-O-C ISOTOPE DIAGENESIS OF CARBONATES
Delta notation
Stable isotope analysis of carbonates measures the ratio of the heavy to light isotopes of O and C in the mineral species under study (eg. The 18O/16O ratio and the 13C/12C ratio). In order that the results from different laboratories may be compared, these ratios are normalised relative to a fixed standard ratio of the isotopes and such results are conventionally prefixed with the delta symbol. The original standard that was used for carbonate analyses was carbon dioxide prepared from belemnites collected from the Peedee Formation (Cretaceous) of South Carolina, USA. This is known as the PDB standard. Actual material of the PDB is not used now and most labs use commercially available CO2 gas that has been calibrated by analysis of carbonate standards prepared by the American National Bureau of Standards (e.g the NBS 19 marble etc). Using the delta notation, the carbon isotope ratio of a sample is therefore reported as follows:
d13Csample = [(13C/12C)sample – (13C/12C)PDB] / (13C/12C)PDB x 10E3
Thus, if the sample has the same 13C/12C ratio as PDB then it will have a d13C = 0 per mil. Positive d13C values indicate a sample with a higher 13C/12C ratio than PDB and negative d13C values indicate a sample with lower 13C/12C ratios than PDB.
The other widely used standard for oxygen isotope analyses is the mean 18O/16O isotope ratio obtained from ocean water (Vienna Standard Mean Ocean Water – VSMOW, so named as it was agreed at an international meeting to discuss stable isotope standards in Vienna in 1976).
Oxygen isotopes
The measured oxygen isotope composition of a mineral (d18O) is controlled by a temperature dependent fractionation of oxygen between the precipitating water and the mineral (a key reference for isotope systematics is Faure and Mensing, 2005).
The temperature dependence of the calcite - water fractionation used by Isotopic in carbonate diagenesis studies is as follows (using fractionation constants from Longstaffe, 1987):
1000ln alpha (fractionation factor) = (2.78x10E6 / TE2) - 2.89
[approximately equals d18O calcite - d18Owater]
i.e. the relationship between temperature and d18O of the precipitating water for the calcite - water system can be approximated as:
T (degrees C) = SQRT(2.78x10E6/(d18Ocalcite - d18Owater + 2.89)) – 273
(d18O values in VSMOW);
The temperature dependence of the dolomite -water fractionation used by Isotopic in carbonate diagenesis studies is:
T (degrees C) = SQRT(3.2x10E6/(d18Odolomite - d18Owater + 3.3)) – 273
(d18O values in VSMOW);
Therefore, using the measured d18O of the mineral and the appropriate fractionation constants, allows the range of possible precipitating temperatures and precipitating water oxygen isotope compositions to be constrained. Using these data it is possible to use a temperature of precipitation (e.g. from fluid inclusions) to determine the precipitating water oxygen isotope composition. It is also valid to make an assumption / interpretation about the precipitating water oxygen isotopic composition and determine a paleotemperature of cementation.
Carbon isotopes
Because the carbon isotope ratio 13C/12C is measured relative to the PDB standard, other similar primary marine carbonate material would be expected to have a d13C around 0 per mil PDB. However, secular variations within the range 0±5 per mil have occurred throughout geological time (e.g. Veizer et al 1999). Primary variations in d13C of authigenic carbonate cements occur as the result of different chemical processes acting on organic carbon.
For example, sulphate reduction and bacterial degradation of organic matter result in 12C enrichment of associated carbonate. Such processes occur directly below the sediment-water interface in the marine environment. Paragenetically early carbonate with low negative d13C values (e.g. -25 per mil PDB) are characteristic of this process.
Fermentation of low molecular weight acids or reduction of carbon dioxide by methanogenic bacteria can give rise to dissolved inorganic carbon (bicarbonate ions) enriched in 13C. Such processes occur at burial depths of a few tens of metres to approximately 1km. Carbonates with positive d13C (e.g. +10 to +15) are characteristic of these processes.
At increased burial depths and temperatures (e.g. above 80 degrees C), abiotic thermal decarboxylatiion of organic matter may release carbon enriched in the isotope 12C. Carbonate cement associated with these processes are characterised by “light” negative d13C values (e.g. -15).
Authigenic carbonate cements (particularly in sandstones) may yield d13C values intermediate between the extremes outlined above. Assuming the materials analysed are not multi-generation assemblages of cements, this would suggest the incorporation of bicarbonate derived from more than one primary source through dissolution and re-precipitation of earlier cements.
Petrographic study is essential prior to any isotopic work to determine whether mixed generations of cement are present and if so, the appropriate sampling procedure to be adopted (micro-drilling, sequential dissolution etc.).
Strontium isotope ratios (87Sr/86Sr) of carbonate minerals
Strontium is an alkaline earth element that behaves in a similar way to Ca in geological systems. The 87Sr/86Sr isotope ratio therefore, provides a means to characterise and investigate the origins of Ca in carbonate cements. The 87Sr/86Sr isotope ratio of seawater has varied systematically between 0.7068 and 0.7092 throughout Phanerozoic time. Carbonate minerals which precipitate directly from seawater or as a direct result of the dissolution and re-precipitation of marine biogenic carbonate, should exhibit the 87Sr/86Sr ratio of the sea water at the time of their precipitation (the basis of Sr Isotope Stratigraphy). In contrast, later burial diagenetic (mesogenetic) carbonates incorporate 87Sr released during the dissolution of detrital silicate minerals such as feldspars and micas. Such carbonate cements inherit the 87Sr/86Sr ratios of the evolved formation waters from which they crystallised which typically have 87Sr/86Sr ratios greater than contemporaneous seawater.
Combined Sr-O-C data
As outlined above, Sr, O and C isotopes yield different information about the origin of formation water, dissolved ions and temperatures at points in time within reservoir compartments. By measuring combined Sr-O-C isotopes it may be possible therefore, to characterise, identify and correlate discrete generations of carbonate cement within a reservoir sequence in the context of a reservoir characterization and reservoir compartmentalization study. Contemporaneous cement forming in separate reservoir compartments may be petrographically similar but have different Sr-O-C isotope compositions reflecting differences in prevailing sources of water and ions.
One further application is to produce Sr-O-C profiles through carbonate cement intervals to investigate the growth history of the cement. Such information may allow interpretations of the geometry of pervasive carbonate cemented intervals to be made (in conjunction with SrRSA studies). Discrete nodular cement would be expected to have roughly symmetrical Sr-O-C profiles, whereas more laterally extensive layers of cement may be expected to isolate underlying from overlying formation waters thus giving rise to asymmetrical Sr-O-C profiles.
Provenance and Layering of Biostratigraphically Barren Clastic Sequences–Samarium–Neodymium Isotope Stratigraphy
Summary:
There is an extensive published literature on the use of the Samarium-Neodymium isotope system in provenance and correlation studies. We have published a case study in Dalland, Mearns and McBride, 1995.
The measured neodymium isotope ratios (143Nd/144Nd) and / or the Provenance Age calculated from the samarium-neodymium isotope ratios (147Sm/144Nd and 143Nd/144Nd) of samples are used to zone reservoirs and correlate strata.
Samarium – neodymium isotope data from clastic strata can also provide an indication of possible sediment source terrain compositions and hence may contribute to an understanding of sediment provenance.
This technique is applicable to core, side wall core or cuttings samples of sandstone and mudstone facies.
Isotopic have extensive experience of selecting optimum samples for samarium - neodymium isotope stratigraphy analysis.
Integration of the results with other chemostratigraphic techniques can provide robust correlations of biostratigraphically barren sequences.
PRINCIPLES OF SAMARIUM – NEODYMIUM ISOTOPE STRATIGRAPHY
Sm and Nd are Rare Earth Elements (REE). During partial melting of the upper mantle, the REEs as a group undergo extensive fractionation between mantle and crust. Crustal rocks are generally more enriched in the light REEs (including Sm and Nd) while the mantle residue is depleted in these elements. From the time that Sm and Nd are fractionated between crust and depleted mantle the 143Nd/144Nd ratio of the crustal component is modified by the long-lived radioactive decay reaction:
147Sm -> 143Nd + 4He (half life = 106 Ga)
Thus, the Sm-Nd isotopic composition of a mantle-derived crustal rock is controlled by the time since the rock first formed from the mantle.
Amongst the properties of REEs are extremely low solubilities in water. Upon weathering of crustal rocks therefore, Sm and Nd are transported in the detrital sediment mass and are not thought to be involved in most early diagenetic processes. Furthermore, because Sm and Nd are geochemically very similar, they probably undergo negligible fractionation between source and sediment in the sedimentary cycle (Mearns, 1988). For these reasons, a clastic sediment is considered to inherit the Sm-Nd isotopic composition of its source terrain(s). Once deposited and buried, the sedimentary rock is regarded as a closed system with respect to Sm-Nd isotopic composition, again owing to the low mobility of REEs in the mesogenetic realm. A sedimentary rock will therefore, always preserve the inherited Sm-Nd isotopic composition of its source terrain(s) regardless of diagenetic processes. Furthermore, sedimentary deposits derived from recycled older sedimentary material will inherit the Sm-Nd isotopic composition of the recycled sediments. i.e. the Sm-Nd isotope signatures of first-cycle sediments are transmitted through subsequent sedimentary cycles.
Fluvial Systems
At any given point in geological time, individual clastic sediment source terrains may have unique Sm-Nd isotopic characteristics which may be transmitted to river sediments. Furthermore, adjacent source terrains may yield sediment with contrasting or similar Sm-Nd isotopic characteristics depending on the regional geology. Downstream from confluences however, the sediment from any number of different source terrains are mixed to give a weighted mean Sm-Nd isotopic composition for the combined source areas. At any point of deposition therefore, sediment may be deposited which has been derived from either a single or from multiple sources. Even in the case of a depositional system supplied by a single source, the isotopic composition of the sediment may vary through time owing to unroofing of different rock types or through expansion/contraction of the source terrains. Thus, these combined processes are likely to lead to variations in Sm-Nd compositions through a fluvial facies sedimentary sequence. It is these variations and their relationship to other geological features that are utilised for correlation by the Sm-Nd isotope technique.
Marine Systems
The likelihood of homogenization of sediment (and Sm-Nd isotope composition) from different clastic source terrains is greatly increased in the marine depositional environment. Thus, variation through a marine sedimentary sequence is expected to be less pronounced than through a fluvial section. Nevertheless, the Sm-Nd isotope technique may still be applicable as a correlation tool in these sequences if sufficient variations in Sm-Nd isotope composition are recorded. For example, in a submarine fan setting, sediment with different Sm-Nd isotope compositions may be transported by separate submarine channel systems. Stacking of such channels or submarine fans may thus result in measureable (and geologically meaningful) variations through a vertical reservoir section.
Provenance
Because the Sm-Nd isotope composition commonly represents the average composition of the source terrain (or terrains) of a sediment, it is seldom diagnostic of a specific provenance (at least in the North Sea basin). It is possible however, that this may not be the case in other depositional basins. Therefore, while changes in Sm-Nd isotope composition may be anticipated and recorded, it is not generally expected that these data will allow the location of actual clastic source areas to be determined.
An exception to this in the North Sea basin is the Upper Triassic - Lower Jurassic, Statfjord Formation of the Snorre and Gullfaks oilfields which contains fluvial facies sandstone members with distinct Sm-Nd isotope compositions which restrict their provenance to specific Erian Shield source terrains (and consequently constrains possible paleogeographies, sediment transport directions etc., Mearns, 1989; Mearns et al, 1989). Another example is the Middle Jurassic Ness and Tarbert Formations of the Gullfaks Field which contain sandstones with distinct Sm-Nd isotope compositions which restrict possible source terrains to areas containing Jurassic or older volcanic rocks (eg Rattray Formation volcanics in the central North Sea; Mearns, 1989, 1992, Dalland et al, 1999). It is possible that similar contrasting young volcanic and ancient Pre-Cambrian source terrains may exist for clastic sedimentary sequences in other depositional basins world-wide (e.g. West Africa).
RECENT STUDIES (2008–2009)
(to avoid repetition repeat and follow-on studies are not listed multiple times)
Strontium Isotope Stratigraphy age dating of marine sulphate strata from the Middle East
SrRSA reservoir compartmentalization of Permo-Carboniferous sandstone reservoir sequence, Southern North Sea
SrRSA reservoir compartmentalization of sandstone reservoir sequence, North Africa
Isotope characterization of produced water samples, North Africa
SrRSA reservoir compartmentalization of Cambro-Ordovician sandstone reservoir sequence, Middle East
SrRSA reservoir compartmentalization of Tertiary sandstone reservoir sequences, US Gulf Coast
Strontium Isotope Stratigraphy 87Sr/86Sr isotope ratios of fossil material, West Africa
Isotope Diagenesis and complementary specialist petrographic study of Jurassic Sandstones, UK North Sea.
SrRSA reservoir compartmentalization of Permo-Carboniferous sandstone reservoir sequences, UK and Netherlands Southern North Sea.
SrRSA reservoir compartmentalization of Triassic sandstone reservoir sequences, Norwegian North Sea.
SrRSA reservoir compartmentalization of Tertiary sandstone reservoir sequences, US Gulf Coast
Provision of 87Sr/86Sr isotope ratios of supplied water samples, Middle East
Produced water characterization (Sr-O-H isotope composition and complementary geochemical composition) of produced water samples, Far East.
SrRSA reservoir compartmentalization of Triassic sandstone reservoir sequences, UK North Sea
SrRSA reservoir compartmentalization studies of 3 different Tertiary sandstone reservoir sequences, for 3 different clients, UK North Sea
Provision of specialist isotope analyses (SIMS) of igneous rock samples, South America.
Compound specific isotope analysis (CSIA) study of gas samples, North Africa
Strontium, oxygen and carbon (Sr-O-C) isotope diagenesis study of pervasive carbonate cemented Jurassic sandstone sequence, UK North Sea. Investigation of possible origins of pervasive authigenic carbonate cement in a reservoir sequence.
Elemental Residual Salt Analysis (ERSA) research study investigating methodologies for studying the salinity (cation and anion concentrations) of formation waters from core samples. The results of this research work are to be published later this year by our clients and collaborators.
2001 to 2007 Isotopic Ltd = over 400 separate isotope geochemistry studies.
1991- 2001 Isotopic Analytical Services Ltd = hundreds more isotope geochemistry studies for over 80 different clients worldwide.
REFERENCES
(apply to all articles)
Burke W.H., Denison R.E., Hetherington E.A., Keopnick R.B., Nelson H.F. and Otto J.B., 1982. Variation of seawater 87Sr/86Sr throughout Phanerozoic time. Geology 10, p. 516-519.
Dalland, Mearns and McBride, 1995. The application of samarium-neodymium (Sm-Nd) Provenance Ages to correlation of biostratigraphically barren strata: a case study of the Statfjord Formation in the Gullfaks Oilfield, Norwegian North Sea. Geol. soc. Spec. Pub. 89, p. 201-222.
Faure and Mensing (2005). Isotopes. Principles and Applications. Third Edition. Wiley.
Lines M.D. and Auld H. A., 2004. A petroleum charge model for the Judy and Joanne Fields, Central North Sea: application to exploration and field development. Geol. Soc. Spec. Pub. 237, p. 175-206.
Longstaffe, 1987. Stable isotope studies of diagenetic processes; In Kyser, T.K. ed. Short course in stable isotope geochemistry of low temperature fluids. Mineralogical Association of Canada, 13, p. 187-257.
McArthur J.M., Howarth R.J., and Bailey T.R., 2001. Strontium isotope stratigraphy: LOWESS Version 3. Best-fit line to the marine Sr-isotope curve for 0 to 509 Ma and accompanying look-up table for deriving numerical age. Journal of Geology, 109, 155-169, 2001.
Mearns E.W., 1988. A Samarium-Neodymium isotopic survey of modern river sediments from northern Britain. Chemical Geology (Isotope Geoscience Section), 73, p. 1-13.
Mearns E.W., Knarud R., Reastad N., Stanley K.O. and Stockbridge C.P., 1989. Samarium-Neodymium isotope stratigraphy of the Lunde and Statfjord Formations of Snorre Oil Field, northern North Sea. Jour. Geol. Soc. Lond., 146, p. 217-228.
Mearns E.W., 1989. Neodymium isotope stratigraphy of Gullfaks Oil Field. In: Collinson J.D. (ed.) Correlation in Hydrocarbon Exploration. Graham & Trotman, London, p. 201-215.
Mearns E.W., 1992. Samarium-neodymium isotopic constraints on the provenance of the Brent Group. In: Morton A.C., Haszeldine R.S., Giles M.R. and Brown S. (eds.), 1992, Geology of the Brent Group. Geol. Soc. Spec. Pub., 61, p. 213-225.
Mearns E.W. and McBride J.J., 1999. Hydrocarbon filling history and reservoir continuity of oil fields evaluated using 87Sr/86Sr isotope ratio variations in formation water, with examples from the North Sea. Petroleum Geoscience, 5, p. 17-27.
Mearns E.W. and McBride J.J., 2001. Strontium Isotope Analysis can help define compartmentalization. Oil & Gas Journal, 99, issue 35, Aug 27th.
Peterman Z.E., Hedge C.E. and Tourtelot H.A., 1970. Isotopic composition of strontium in seawater throughout Phanerozoic time. Geochim. Cosmochim. Acta, 34, p. 105-120.
Smalley P.C., Dodd T.A., Stockden I.L., Raheim A. and Mearns E.W., 1995. Compositional heterogeneities in oilfield formation waters: identifying them, using them. Geol. Soc. London Special Publication, 86, p. 59-69.
Veizer et. al., 1999. 87Sr/86Sr, d13C and d18O evolution of Phanerozoic sea water. Chem. Geol., v. 161, p. 59-88.