Julien Bourdet

Hydrocarbon charge history of the Tazhong Ordovician reservoirs,Tarim Basin as revealed from an integrated fluid inclusion study

Abstract This paper presents an integrated workflow for investigating hydrocarbon charge history using fluid inclusions using the Ordovician reservoirs from the Tazhong Oilfield, Tarim Basin as an example. The work flow involves the delineation of fluid inclusion assemblage (FIA) using fluid inclusion petrography and spectroscopy for microthermometric analysis. The interpretation of microthermometric data is based on data derived from synthetic inclusion experiments and takes consideration of the P-T re-equilibration of fluid inclusions in carbonate and over pressure effect on fluid inclusion trapping. The workflow also emphasizes on the requirements of adequate sample preparation, FIA identification, quantitative spectroscopic data (CIE), coeval petroleum and aqueous fluid inclusions, adequate number of microthermometric measurements and integrated interpretation using borehole temperature. In the study reservoirs in the Tazhong area, fluid inclusion spectroscopy reveals the presence of three groups of oil inclusions of near yellow, near blue and near white fluorescence colours. The fluid inclusion microthermometry data indicate the presence of at least two predominant hydrocarbon fluid inclusion assemblages including: homogenous liquid phase yellow fluorescence inclusions and liquid phase oil and condensate fluid inclusion assemblages with homogenous near blue, near white and near yellow fluorescence colours. The aqueous inclusions from the Ordovician reservoirs in the Tazhong area reveal the presence of low, moderate, high and very high salinities in the reservoirs. The extremely high salinity is believed to be caused by regional brine intrusions relating to regional structural movement and deformation.

Organic matter network in post mature Marcellus Shale: Effects on petrophysical properties

Shale samples of the Marcellus Shale from a well drilled in northeastern Pennsylvania were used to study diagenetic effects on the mineral and organic matter and their impact on petrophysical response. We analyzed an interval of high gamma ray and anomalously low electrical resistivity from a high thermal maturity (mean maximum vitrinite reflectance > 4%) part of the shalehgas play. A suite of microanalytical techniques was used to study features of the shale down to the nanoscale and assess the level of thermal alteration of the mineral and organic phases. The samples are organic rich, with total organic carbon contents of 3–7 wt. %; the vast majority of the organic matter was identified as highly porous pyrobitumen. Matrix porosity is also present, especially within the clay aggregates and at the interface between rigid clasts and clay minerals. Mineral- and organic-based thermal maturity indices suggest that during burial the sediment had been exposed to temperatures as high as 285°C (545°F). Under these conditions, the residual, migrated organic matter assumed a partially crystalline habit as confirmed by the identification of turbostratic structures via electron microscopy imaging. Experimental dielectric measurements on organic matter–rich samples confirm that the anomalous electrical properties observed in the wire-line logs can be ascribed to the presence of an electrically conductive interconnected network of partially graphitized organic matter. The preservation of porosity suggests that this organic network can contribute not only to the electrical properties but also to the gas flow properties within the Marcellus Shale.

Petroleum migration in the Bight Basin: a fluid inclusion approach to constraining source, composition and timing

The Bight Basin in southern Australia is a vast under-explored offshore area with promise of, but as of yet, limited proof for hydrocarbons. Fluid inclusions (FIs) offer a unique method to test for petroleum migration, composition and timing, which would otherwise remain hidden in the rocks, and more direct evidence to calibrate basin models. A reconnaissance-scale FI study, using CSIRO’s Grain with Oil Inclusion (GOI™) technique, was undertaken to detect liquid hydrocarbons in Jurassic to Cretaceous sandstones. Oil-bearing, and in some cases gas-rich, inclusions were detected at low abundance, and their presence provides proof of oil generation and migration in the Ceduna Sub-basin. Geochemical fingerprinting of FI oil was undertaken using the Molecular Composition of oil Inclusions (MCI) technique on an intra-Coniacian interval in Gnarlyknots-1A and a Cenomanian interval in Greenly-1. The results show differences in the type of organic matter input, with algal co-sourcing significant for the central Ceduna Sub-basin. The timing of oil migration from pressure-temperature (PT) reconstructions was interpreted in Gnarlyknots-1A, Greenly-1, Duntroon-1 and Potoroo-1. The results indicate oil charge during the Late Cretaceous in the basin depocentres, explained by sediment loading of the Upper Cretaceous succession by the Hammerhead Supersequence and oil, gas-condensate and gas charge to the depocentres and basin margins during the Miocene. The Great Australian Bight Research Program is a collaboration between BP, CSIRO, the South Australian Research and Development Institute (SARDI), the University of Adelaide and Flinders University. The Program aims to provide a whole-of-system understanding of the environmental, economic and social values of the region, providing an information source for all to use.

Generation of amorphous carbon and crystallographic texture during low-temperature subseismic slip in calcite fault gouge

Identification of the nano-scale to micro-scale mechanochemical processes occurring during fault slip is of fundamental importance to understand earthquake nucleation and propagation. Here we explore the micromechanical processes occurring during fault nucleation and slip at subseismic rates (∼3 × 10−6 m s–1) in carbonate rocks. We experimentally sheared calcite-rich travertine blocks at simulated upper crustal conditions, producing a nano-grained fault gouge. Strain in the gouge is accommodated by cataclastic comminution of calcite grains and concurrent crystal-plastic deformation through twinning and dislocation glide, producing a crystallographic preferred orientation (CPO). Continued wear of fine-grained gouge particles results in the mechanical decomposition of calcite and production of amorphous carbon. We show that CPO and the production of amorphous carbon, previously attributed to frictional heating and weakening during seismic slip, can be produced at low temperature during stable slip at subseismic rates without slip weakening.

Texture, Porosity and Diagenesis - A Marcellus Shale Case Study

Marcellus Shale samples were used to quantify mineralogy and texture, evaluate the abundance and thermal maturity of organic matter, describe porosity and interpret the diagenetic history of this post‐mature shale‐gas reservoir. A multidisciplinary approach was adopted comprising X-ray diffraction to quantify the mineralogy, neutron diffraction to quantify the texture of the rock-forming minerals, electron microscopy to visualise porosity in the shale and distinguish between detrital and diagenetic phases and Raman spectroscopy to quantify thermal transformation in the organic matter. Results indicate that the samples are composed of quartz, illite, calcite, chlorite, albite, and pyrite with a total organic content ranging between 3 and 7 wt %. There is a significant crystallographic preferred orientation in the diagenetic illite and calcite that can be well modelled assuming transverse isotropy; quartz shows random texture. Nano sized pores are observed within the organic matter as well as at mineral junctions. Raman geothermometry indicate that the sediment witnessed maximum temperatures of approximately 250°C commensurate with the high optical reflectance (R0 > 4.5%) reported on the same material. This and the analysis of illite cristallinity indicate that the Marcellus Shale has been exposed to prehnite-pumpellyite metamorphic facies and a maximum burial depth of 6-8 km