--> Multiscale Characterization of Shale Oil Reservoirs Using XRF, SEM-EDS, Synchrotron-Based CT Imaging and DCM Modeling

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Multiscale Characterization of Shale Oil Reservoirs Using XRF, SEM-EDS, Synchrotron-Based CT Imaging and DCM Modeling

Abstract

Following the recent success in tapping the enormous unconventional hydrocarbon resources in North America, China has also made significant progress in the exploration and production of shale oil and gas over the past decade with some noticeable commercial discoveries in the Sichuan Basin, Ordos Basin and Junggar Basin. It has been well documented that unconventional reservoirs are primarily dominated by fine-grained sediments with multiscale, complex compositional and structural heterogeneities down to micro-nano scales, which control the storage and flowing capability of hydrocarbons in the unconventional reservoirs. This poses considerable challenges for the characterisation of unconventional reservoirs using the traditional visual and optical petrographic methods. As part of reservoir characterization of the shale oil reservoirs in the Jurassic Lucaogou Formation, Junggar Basin, northwest China, we employed a suite of state-of-art chemical and mineralogical speciation techniques including Micro X-ray Fluorescence Spectrometry (Micro-XRF), Field-Emission Scanning Electron Microscopy (SEM) with Energy Dispersion Spectroscopy (EDS), and synchrotron-based multi-energy micro-CT imaging coupled with Data Constrained Modelling (DCM). The effective integration of these techniques allows us to systematically mapping both the mineral compositions and pore structures of the reservoirs from nm to cm scales in three dimensions. It enables us to effectively identify and quantify the mineral species, pores and fractures, and predict the reservoir wettability and frackability for shale oil development purposes. Two sweet-spot intervals are delineated within the Jurassic Lucaogou Formation, where optimum combinations of brittle, fractured, strongly carbonate-cemented layers interbedded with dissolution-pore dominated and oil- and feldspar-rich layers are present. In the target reservoir, most of the shale oil are found to be stored in and migrated through pores and fractures of micro- to sub-micrometer scales.