Cédric Carpentier

Experimental simulation of chemomechanical processes during deep burial diagenesis of carbonate rocks

Chemomechanical processes involved in the deep burial diagenesis of carbonate petroleum reservoirs are still poorly understood. To better understand these processes and explain how porosity and permeability can be preserved at the great depth of DBRs (deeply buried reservoirs), we developed an experimental device allowing both the simulation of high-pressure/stresses/temperature conditions (80°C, 60 MPa of confining pressure, and differential stress up to 40 MPa) of DBR and the circulation of different fluids in rock samples. We tested (triaxial multistep creep tests) four core samples of a cemented limestone and analyzed creep deformations, fluids chemistry, and petrographical and petrophysical properties of samples. Different flow conditions (no flow and flow through) and chemical compositions (natural meteoric water with and without phosphate ions) were considered. Our study showed that the precipitation of calcite on free pore walls of micrites blocks the microporosity between micrite crystals, thus rendering the microporosity inaccessible to fluids. Hence, the connected porosity decreased strongly after experimentation. This is due to the PSC (pressure solution creep) which is the main process implied in the porosity reduction of a carbonate rock during deep burial. The preservation of macropores during PSC allows the preservation of permeability. In addition, calcite solubility is positively dependent on mechanical parameters (axial compaction and axial stress), thus suggesting that calcite can precipitate during decompression of deep basinal fluids, resulting in changes in porosity. A comparison of experimental results with theoretical calculations showed that the integration of the PSC process into calculation databases would greatly improve the modeling of DBR.

Erratum to: Microfossil assemblages and relative sea-level fluctuations in a lagoon at the Oxfordian/Kimmeridgian boundary (Upper Jurassic) in the eastern part of the Paris Basin

The Late Oxfordian–Early Kimmeridgian interval of the eastern part of the Paris Basin is characterized by a carbonate succession deposited in shallow-marine platform environments. The Gudmont-Villiers section is represented by deposits ranging from barrier to typical lagoonal environments often poor in macrofossils. Previously unpublished calcareous microfossils are more abundant and provide alternative paleoenvironmental indicators. They also provide a biostratigraphical framework across the Oxfordian–Kimmeridgian boundary. The evolution of microfossil associations (algae and benthic foraminifera) in the lower part of the section, based on statistical analyses, is correlated to the sea-level variations. The first highly diversified association composed of small agglutinated and calcitic foraminifera (miliolids, textulariids, Spirillina, Trocholina, Molherina basiliensis etc.) characterizes high sea-level deposits; a second association richer in large agglutinated foraminifera (Alveosepta jaccardi, Everticyclammina, Nautiloculina oolithica) is significantly abundant in low sea-level deposits. A third association characterizes beds with a significant occurrence of encrusting microorganisms and algae (Lithocodium aggregatum, Troglotella incrustans, Cayeuxia piae, dasycladaceans). The upper part of the section is marked by more argillaceous beds and by the occurrence of one opportunist taxon (Lenticulina). This study shows that the microfauna-flora evolution in an internal carbonate platform environment constitute an efficient tool to determine variations in the relative sea level.

Uncertainty management in stratigraphic well correlation and stratigraphic architectures: A training-based method

Abstract We discuss the sampling and the volumetric impact of stratigraphic correlation uncertainties in basins and reservoirs. From an input set of wells, we evaluate the probability for two stratigraphic units to be associated using an analog stratigraphic model. In the presence of multiple wells, this method sequentially updates a stratigraphic column defining the stratigraphic layering for each possible set of realizations. The resulting correlations are then used to create stratigraphic grids in three dimensions. We apply this method on a set of synthetic wells sampling a forward stratigraphic model built with Dionisos. To perform cross-validation of the method, we introduce a distance comparing the relative geological time of two models for each geographic position, and we compare the models in terms of volumes. Results show the ability of the method to automatically generate stratigraphic correlation scenarios, and also highlight some challenges when sampling stratigraphic uncertainties from multiple wells.

Assessing Uncertainty in Stratigraphic Correlation: A Stochastic Method Based on Dynamic Time Warping

We propose a method to manage uncertainties about the layering of 3D reservoir models, using stochastic correlations of sedimentary units identified along wells, according to the sequence stratigraphy paradigm. A stratigraphic model represents the architecture of the stratigraphic succession of an area. Sequence stratigraphy is a common paradigm in reservoir studies to interpret and correlate local high resolution observations (outcrops, well logs and core samples) and more exhaustive but lower resolution data such as 3D seismic. The incompleteness of these data, their quantity and their varying quality, added to the fact that the processes that control the geometry and the conformability of the sequences are complex and poorly known, lead to uncertainties. The proposed method aims at building stratigraphic models honoring 1D interpretations along wells together with conceptual sequence stratigraphic rules formulated quantitatively as correlation costs. The algorithm chosen is a modified version of the Dynamic Time Warping algorithm. More than finding the best correlation using a set of rules, it handles different orders of sequences, takes in account the conformability of the horizons, and its output is a set of different possible correlations, allowing for generating alternative stratigraphic layerings. This methodology is demonstrated on the Teapot Reservoir, Wyoming.