Cambridge Carbonates Ltd

Arc-sur-Tille, France

Cambridge Carbonates Ltd

Arc-sur-Tille, France
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Vincent B.,Cambridge Carbonates Ltd | Brigaud B.,University Paris - Sud | Emmanuel L.,CNRS Institute of Earth Sciences | Loreau J.-P.,CNRS Biogeosciences Laboratory
Sedimentary Geology | Year: 2017

The scope of this work is to investigate, at a high resolution, the oxygen isotope composition (δ18Ocarb) of diagenetic products (synsedimentary and burial calcite cements) in shallow-marine carbonates. SIMS (Secondary Ion Mass Spectrometry) microprobe analyses were performed on thin sections from Oxfordian and Kimmeridgian Formations of the eastern Paris Basin and compared to data obtained on the same diagenetic products by conventional mass spectrometry (acid digestion). Hereby obtained, δ18O are similar, but the SIMS dataset displays a larger range of values. The isotopic zonation obtained by SIMS transects through sequences of cements filling pores, reveals an (expected) isotopic depletion from older stage synsedimentary calcites to younger stage blocky calcites and that follows the CL (cathodoluminescence) zonation. SIMS analyses however show that synsedimentary cements precipitated in intra-skeletal pores, have heavier δ18O than their inter-particle counterparts, with an offset of + 4‰V-PDB, despite similar petrographical characteristics. This difference is maintained in the δ18O of the first stages of blocky calcite cements, intra-skeletal blocky calcites showing heavier δ18O than the time equivalent and petrographically identical inter-particle calcites, with an offset of + 5‰V-PDB. These offsets are tentatively explained by the precipitation of cements under non-equilibrium conditions in intra-skeletal pores, where organic matter decay may have played a key role, acting notably on the pH. The occurrence of isolated micro-diagenetic environments, co-existing at the thin section scale, is tentatively proposed as an explanation to these small scale and high amplitude δ18O heterogeneities. These results may question the sampling strategy for future works. Microdrilling may miss the observed range of variation, but averaging the values may not necessarily lead to real misinterpretations if a critical selection of samples is performed, targeting potentially similar micro-diagenetic environments and avoiding potentially specific ones, i.e. closed intra-skeletal pores. These results also definitely underscore the need for additional experiments to improve the reliability of SIMS, in order to develop the use of this very high resolution technique for carbonate diagenesis studies. © 2017 Elsevier B.V.

Vincent B.,Cambridge Carbonates Ltd | Fleury M.,French Institute of Petroleum | Santerre Y.,French Institute of Petroleum | Brigaud B.,University Paris - Sud
Journal of Applied Geophysics | Year: 2011

A set of carbonate outcrop samples, covering a wide range of the sedimentary textures and depositional environments existing on carbonate systems, was studied through an integrated petrographical and petrophysical approach. With the aim of improving the understanding of the NMR (Nuclear Magnetic Resonance) signal of carbonates, this work is: 1) providing an atlas for various carbonate reservoir rock-types, 2) providing a workflow for integrating geological and petrophysical data and, 3) documenting common shortfalls in NMR/MICP analyses in carbonates. The petrographical investigation includes thin section and SEM (Secondary Electron Microscope) observations, whereas petrophysical investigation includes porosity (φ), permeability (K), NMR, MICP (Mercury Injection Capillary Pressure), and specific surface area (BET) measurements.On the basis of NMR and MICP data, 4 groups of samples were identified: (1) microporous samples, (2) micro-mesoporous samples, (3) wide multimodal samples, and (4) atypical samples. The microporous samples allow us to define a maximum NMR threshold for microporosity at a T 2 of 200ms.NMR and MICP response of the investigated carbonates are often comparable in terms of modal distribution (microporous, micro-mesoporous and wide multimodal samples). In particular, micritization, a well known but underestimated early diagenetic process, tends to homogenize the NMR signal of primarily different sedimentary facies. A grainstone with heavily micritized grains can display well sorted unimodal NMR and MICP signatures very similar, even identical, to a mudstone-wackestone. Their signatures are comparable to that of a simple sphere packing model.On the contrary, several samples (labeled atypical samples) show a discrepancy between NMR and MICP response. This discrepancy is explained by the fact that MICP can be affected by the physical connectivity of the pore network, in case of disseminated and isolated molds in a micrite matrix for instance. Similarly, NMR can differentiate pore classes but with less resolution. It does not rely on connectivity but can be affected by diffusional pore coupling, i.e. the diffusion of water molecules carrying the magnetization between micropores and macropores. The pore-coupling phenomenon, through its impact on the T 2 distribution, may disturb the permeability calculations from NMR data.For core plug characterization, NMR appears to be a complementary tool to MICP and should be used to complete rock-typing analysis in carbonates. For reservoir rock-typing, the obvious advantage of developing a NMR based approach is the use of NMR logging data providing continuous records of pore size distributions. © 2011 Elsevier B.V.

Brigaud B.,University of Burgundy | Brigaud B.,Andra Inc | Brigaud B.,University Paris - Sud | Vincent B.,Cambridge Carbonates Ltd | And 4 more authors.
Journal of Sedimentary Research | Year: 2010

Examination of petrophysical properties (acoustic velocity, porosity, permeability, and density) and petrographical characteristics (texture, facies composition, and diagenesis) of more than 250 core plugs from the Middle Jurassic carbonates of the eastern Paris Basin provides insights into the parameters controlling acoustic velocities in relatively low-porosity carbonate rocks (Φ < 20%). The pore-type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite, such that velocities in microporous mudstonewackestone (lagoonal) deposits are greater than in macroporous grainstone (shoal) samples, at a given porosity range (1520%). The standard Wyllie and Raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies. Marls and fine-grained deposits interpreted as lagoonal facies include statistically significant correlation (r = 0.9) between velocity and porosity. However, the data suggest that the wide scatter in velocityporosity relationship from grainstones are not the result of different sorting, grain size, pore type, dolomite content, or clay content. Instead, early cementation greatly influences acoustic properties during diagenesis, and are interpreted to account for the high variability of velocities over a given porosity range. Specifically, at a given porosity, acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early-cemented grainstone. Petrographic observations suggest that early cementation limits mechanical compaction, creating a heterogeneous medium from the earliest stages of diagenesis (non-touching grains, preservation of intergranular macropores that are partially to totally filled by later bločky calcite cement). The abundant interfaces between micritized ooids, early cement fringes, and blocky calcites in grainstones may induce significant wave attenuation. As a result, the standard time-average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity. Conversely, an absence of early cementation favors mechanical compaction, grain-to-grain contact, and suturing. The result is a homogeneous micritized grainsupported network that may facilitate wave propagation. Through demonstration of the key role of early cementation in the explanation of variability in acoustic properties, the results of this study illustrate the complicated factors influencing velocity transforms in carbonates (Wyllie and Raymer), i.e., classical tools for predicting reservoir properties. These insights on the interpretation of Vp and the refinement of velocityporosity transforms in grainstone units may be broadly applicable to enhancing seismic-based exploration in carbonate successions. Copyright © 2010, SEPM (Society for Sedimentary Geology).

Brigaud B.,University Paris - Sud | Vincent B.,Cambridge Carbonates Ltd | Durlet C.,French National Center for Scientific Research | Deconinck J.-F.,French National Center for Scientific Research | And 4 more authors.
Marine and Petroleum Geology | Year: 2014

Nuclear magnetic resonance (NMR), stable isotope geochemistry of micro-sampled cores, NMR well-logs and 3D modeling are used to investigate the carbonate permeability-porosity heterogeneity along 230m-thick limestones of the Paris Basin. Despite the global low porosity and permeability of the limestones, two aquifers units with porosity greater than 15% were identified. These two aquifers are very different in terms of pore through radii and NMR signal. The first one (A1: Aquifer 1) is a 7m-thick mudstone unit, dominated by extended microporosity with pore throat radii of 0.25μm to 0.3μm. The second one (A2: Aquifer 2) is a 15m-thick oolitic grainstone units showing macropores reaching 100μm and pore throat radii of 32μm. From core descriptions and wireline logs on 26 wells, a 3D static geological model is build. The fine tuning of permeability calculations from NMR logs realized along 12 of the wells, allows porosity and permeability heterogeneity to be distributed within a 3D model at the reservoir scale (area of about 2000km2) which match the flow behavior illustrated by well tests. Associated with early meteoric calcite cements and poorly developed burial blocky calcite cements, the porous and permeable intervals may be predicted in two stratigraphic and diagenetic considerations. Firstly, the syn-sedimentary meteoric dissolution or neomorphism of the initial high magnesium calcite and aragonite particles or clasts into low magnesium calcite particles or cements prevented most mechanical and chemical compaction during the first steps of burial. Secondly, the regional stratigraphic architecture reveals the presence of local permeability barriers, which prevented Early Cretaceous lateral meteoric water circulation and the associated burial calcite cementation. © 2014 Elsevier Ltd.

Tucker M.,Durham University | Garland J.,Cambridge Carbonates Ltd
Geologica Belgica | Year: 2010

The sequence stratigraphic approach has evolved into an important tool for stratigraphic analysis and does have an element of prediction. Several sequence models have been proposed and are in use, but there have been emotive discussions in the literature over these, as well as systems tracts and key surfaces. Metre-scale cycles (parasequences) are the building blocks of sequences and are an essential component of carbonate successions throughout the stratigraphic record. Their thickness and facies patterns, reflecting the longer-term changes in accommodation that affected deposition, enable the various systems tracts in a sequence to be recognised. There have been many arguments over the origin of parasequences with orbital forcing, tectonic and sedimentary mechanisms all having their proponents. Devonian carbonates of the Ardennes-Eifel-Aachen area are dominated by a suite of parasequence types deposited in ramp and shelf-interior locations. They show thickness patterns and trends in facies, which on a broad scale can be correlated across the region, whereas individual cycles cannot. Some packaging of cycles is seen, which could indicate an orbital-forcing control. However, there is clear evidence for a tectonic control on regional thickness patterns in some parts of the succession, as a result of deposition across syn-sedimentary extensional faults. As with many areas of Earth Science, explanation involves a combination of several hypotheses and here one mechanism does not seem to have been responsible for the Devonian cyclicity.

Garland J.,Cambridge Carbonates Ltd | Neilson J.,University of Aberdeen | Laubach S.E.,University of Texas at Austin | Whidden K.J.,U.S. Geological Survey
Geological Society Special Publication | Year: 2012

The development of innovative techniques and concepts, and the emergence of new plays in carbonate rocks are creating a resurgence of oil and gas discoveries worldwide. The maturity of a basin and the application of exploration concepts have a fundamental influence on exploration strategies. Exploration success often occurs in underexplored basins by applying existing established geological concepts. This approach is commonly undertaken when new basins 'open up' owing to previous political upheavals. The strategy of using new techniques in a proven mature area is particularly appropriate when dealing with unconventional resources (heavy oil, bitumen, stranded gas), while the application of new play concepts (such as lacustrine carbonates)to new areas (i.e. ultra-deep South Atlantic basins) epitomizes frontier exploration. Many low-matrix-porosity hydrocarbon reservoirs are productive because permeability is controlled by fractures and faults. Understanding basic fracture properties is critical in reducing geological risk and therefore reducing well costs and increasing well recovery. The advent of resource plays in carbonate rocks, and the long-standing recognition of naturally fractured carbonate reservoirs means that new fracture and fault analysis and prediction techniques and concepts are essential. Akey area of progress has been integration of stratigraphic, structural, geomechanical and diagenetic analysis to populate reservoir models accurately. Dramatic increases in computing and digital imaging capabilities are being harnessed to improve spatial analysis and spatial statistics in reservoirs and ultimately improve 3D geocellular models. © The Geological Society of London 2012.

Breesch L.,Copenhagen University | Swennen R.,Catholic University of Leuven | Dewever B.,PanTerra Geoconsultants BV | Roure F.,Institute Francais du Petrole IFP | Vincent B.,Cambridge Carbonates Ltd.
GeoArabia | Year: 2011

The diagenesis and fluid system evolution of outcrop analogues of potential subthrust Cretaceous carbonate reservoirs in the Musandam Peninsula, northern United Arab Emirates, is reconstructed during the successive stages of the Oman Mountains development. Detailed petrographic and geochemical analyses were carried out on fracture cements in limestones and dolomites mostly situated close to the main faults, which were the locations of major fluid fluxes. The main result of this study is a generalised paragenesis subdivided into four diagenetic time periods. Based on analyses of syn-tectonic veins and dolomites a large-scale fluid system is inferred with migration of hot brines with H 2O-NaCl-CaCl2 composition along Cenozoic reverse faults. These brines were sourced from deeper formations or even from the basal decollement and infiltrated in the footwall. These results are compared with similar studies, which were carried out in other regions worldwide. Furthermore some implications for reservoir characteristics and hydrocarbon scenarios could be postulated. It must be noted that the majority of the analysed rocks do not have sufficiently high porosities to be regarded as reservoir rocks. However, some diagenetic processes that can improve the reservoir quality were observed. For example dolomite recrystallisation occurred in patches at the carbonate platform border, which created poorly connected reservoirs. Other possible exploration targets could be the footwall blocks of the Cenozoic reverse fault zones. When the migration of hot brines along these faults and into the footwall would be combined with petroleum migration, the footwall block could act as a potential hycrocarbon trap sealed by the fault. The fluid system evolution is incorporated in a schematic model of the geodynamic framework of the region in order to summarise the different diagenetic and fluid events, which took place during the northern Oman Mountains evolution up to now.

Maurer F.,Maersk Oil | Van Buchem F.S.P.,Maersk Olie og Gas A S | Eberli G.P.,University of Miami | Pierson B.J.,Petronas University of Technology | And 4 more authors.
Terra Nova | Year: 2013

Compelling physical evidence for a Late Aptian lowstand with an amplitude of at least 50m is presented in subsurface seismic and core data from the Arabian Plate. Biostratigraphic dating indicates that the fall and rise bracketing this lowstand were rapid, and that the lowstand lasted for around 5ma with distinctly cyclic sedimentation at the 0.4-0.5ma scale (eccentricity band). A glacio-eustatic mechanism is invoked as the most likely cause, which is supported by cooling indicated in oxygen isotope shifts and by evidence for a global expression of this lowstand from a number of locations at the mid and high latitudes. Hence, the Late Aptian data presented here document the longest Cretaceous sea-level lowstand, interpreted as the longest cooling phase during the Cretaceous greenhouse. © 2012 Blackwell Publishing Ltd.

Horbury A.D.,Cambridge Carbonates Ltd.
2nd Arabian Plate Geology Workshop 2010: Albian/Cenomanian/Turonian Carbonate-Siliciclastic Systems of the Arabian Plate | Year: 2010

Albian-Turonian carbonates in NE Arabia show a progressive retreat of their shelf margins towards palaeohighs. This retreat is controlled by localised tectonic collapse of the pre-existing platforms and relocation of platform margins onto structurally high areas.

Horbury A.D.,Cambridge Carbonates Ltd
2nd EAGE Workshop on Iraq: Field Development and Emerging Technologies | Year: 2013

Subsurface geology of Iraq is generally poorly understood away from the main petroleum producing areas of the SE and the foldebelt of the NE. Relatively little interpretation has been made and published using regional 2-D seismic coverage, whilst data from wells is scattered and of variable quality; and outcrop studies are still in their infancy. Largely this is due to a perception that the broad down-to-the east regional dip across this whole region, precludes the development of significant traps and therefore the petroleum industry has focused its resources elsewhere. As a first pass strategy this is undoubtedly sensible but as acreage and fields in parts of the country with existing production are allocated to operators, attention will inevitably focus updip in a westerly direction.

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