Principal Investigator

Dr Cédric John

I am a Senior Lecturer in the Department of Earth Science and Engineering at Imperial College London. Broadly speaking, I am interested in neritic and pelagic carbonates, what they tell us about the history of climate and paleo-fluid flow, and what controls the architecture of carbonate platforms. I am notably keen on applying novel isotopic techniques to carbonate material in order to extract relevant proxy data. My research group is currently working on clumped isotope paleothermometry. This new paleotemperature proxy is very promising, tricky to master, and (let’s admit it) fun to work with. Now is an exciting time to work on clumped isotope because a number of labs are finally able to run the technique (making inter-laboratory calibration possible) and new studies suggest additional interesting kinetic controls on the clumping of heavy isotopes in carbonates.

Finally, a completely different aspect of my research interests is to explore the interaction through time between carbonate rocks and the surrounding fluids: this interaction promotes dissolution of the original phases, and/or precipitation of new cement, i.e. carbonate diagenesis. An interesting approach is to link the depositional environment of carbonate platform (climate, eustasy, paleoceanography, biological constraints, etc…) with the diagenetic potential of carbonate rocks, the potential for fracturation, and the resulting fracture network with diagenetic fluid circulation and further modifications of the carbonate rocks. This approach is multidisciplinary, and because diagenesis impacts on the porosity and permeability of carbonate rocks, our research has tremendous implications for oil and gas reservoirs, and for safe carbon capture and storage (CCS) in carbonate rocks.

Research Associates/Assistants

Dr Simon Davies

Postgraduate Students

Maria Gusarevich

Claire Veillard

The Qatar Stable Isotope laboratory started in 2010, and was officially opened in 2012 with the suite of other QCCSRC laboratories. The laboratory operates three mass spectrometers dedicated to developing, calibrating and testing clumped isotopes for application to subsurface reservoirs. These state-of-the-art machines are complemented by dedicated vacuum lines that were developed in the context of the QCCSRC project, as well as an automated clumped isotope line (the IBEX) destined to become the first commercially available preparation device for clumped isotopes.

Clumped isotopes is a new method to reconstruct palaeotemperatures, and it contributes to the geoscientists tool box for interpreting past environments of deposition and diagenesis. It allows the determination of the accurate temperature of precipitation of carbonate minerals, which helps in understanding the geological history of the reservoir and thus improving its management.

One of the three mass spectrometers in the laboratory is also equipped with a Kiel IV carbonate device, which allows measurement of conventional stable isotopes of carbon and oxygen on small samples (down to 20 µg of carbonate) with great accuracy and an excellent sample throughput. In addition, the laboratory and carbonate group are equipped with state of the art petrographic and cathodoluminescence microscopes.

The combination of all of the above analytical facilities ensures that isotope data are collected with an accurate geological context in place, and helps guiding interpretation of the data. It enables novel research that will benefit the oil and gas industry in general and the State of Qatar in particular.

The clumped isotope paleothermometer has emerged as one of the most promising isotopic tools, enabling the reconstruction of the temperature of precipitation of carbonate phases as diverse as calcite, aragonite, dolomite, ankerite, magnesite and even carbonate-fluoro apatite.

One of the main new research directions undertaking within QCCSRC was to set up a clumped isotope laboratory, and to explore systematically the application of clumped isotopes to realistic reservoir conditions. Most of the work on clumped isotopes had been confined to low-temperature, surface conditions. The first step in our research efforts was the creation of a new calibration that would bracket the temperature encountered in oil and gas reservoirs. This was achieved by building a new precipitation rig where pressure was controlled, allowing the precipitation of carbonates at controlled temperatures of up to 250˚C.

Armed with the new calibration, the group now tackles questions related to burial recrystallization of carbonates and how this can be used to understand the burial history of petroleum basins. We also work on the effects of salinity on clumped isotopes, the origin of fault-related and early dolomite, and the effect of pH on clumped isotopes.

The most recent research efforts will attempt to pair radiogenic isotope dating with clumped isotope temperatures on the same carbonate phases. This novel approach, if successful, would yield a powerful tool to reconstruct the thermal history of basin and constrain burial curves. This data is crucial to understand the maturation of oil in petroleum provinces, but also to understand the relative timing of oil emplacement and diagenetic transformations within carbonate and clastic reservoirs.

Structural geology and fracture-related work in reservoirs and seals analogues

The QCCSRC project also has an important component of outcrop-related work. Some of the questions addressed pertain to fracture propagation and fluid movements along faults, as well as the resulting diagenetic transformations within the rock matrix. For instance, the group has worked intensively over the past four years on fracture-related dolomitization in Oman, focusing on stratigraphic units ranging from the Precambrian to the Jurassic.

This work continues in Oman, and is augmented by fracture-related dolomitization research in Spain. Another major focus of past and current research has been to understand what controls the fracture network of the Jebel Madar salt dome in Oman, and what fluids led to the precipitation of the calcite and barite minerals infilling the fractures.

Finally, a major concern for CCS operations is the reliability of the overlying seal or caprock, notably its ability to prevent the propagation of fractures that could act as conduit to fluids and result in CO2 escaping containment. Since the caprock in Qatar (the Hith Formation) comprises mostly anhydrite, the team is currently working at understanding fracture propagation within anhydrite lithologies, and what prevents fractures from developing in this type of lithology.

Sedimentary geobodies of reservoirs and seal analogues at the inter-well scale

The issue of the scale of observations is a crucial one for the petroleum geologist. Usually, the very large, regional scale geological view is available through the interpretation of seismic images of the subsurface. The very small-scale observations can be done on wells that were cored or where cuttings are available, as well as on thin sections if these are available.

 The real issue though is to bridge these two scales, especially at the 100 to 1000 meter lateral scale where the control on reservoir unit connectivity and heterogeneity is poorly constrained. This is a crucial scale because it corresponds to the typical spacing between wells.

A significant portion of QCCSRC research has been devoted to investigating reservoir analogues at the outcrop in order to understand inter-well scale sedimentary heterogeneities in 2D and pseudo-3D. Considerable work has been done on the Cretaceous Jurf and Qishn Formation in Central East Oman, where tidal-flat facies outcrop in the desert and are good analogues for the subsurface oil-bearing Kharaib Formation.

Current research efforts on understanding sedimentological heterogeneities at the inter-well scale focus on reservoir analogues facies of Jurassic age outcropping in the United Arab Emirates (analoguous to the Arab formation in the subsurface), and on Jurassic anhydrite deposits that can be accessed in deep mines in the United Kingdom (and that are analogues to the Hith Formation in Qatar). These efforts shed light on the sedimentary processes that operated during deposition, and offer a solid database of the type and scale of heterogeneities that could be expected between wells in the Middle East, thus informing the reservoir geologist on what could potentially impact on flow during CCS or EOR operations.

Looking forward: areas under investigation

  1. Calibrate clumped isotopes for reservoir applications at up to 250˚C and 30 bars
  2. Explore the feasibility of pairing radiometric age-dating with clumped isotope temperatures
  3. Providing an understanding of inter-well scale heterogeneities of Cretaceous and Jurassic carbonate reservoirs
  4. Exploring the origins and geometries of fault-related dolomite and other diagenetic bodies
  5. Improving our understanding of small scale heterogeneities in Jurassic anhydrite seals
  6. Understand the propagation of fractures in fine-grained caprocks such as anhydrite and mudstones