Oral Presentation Australian & New Zealand Society of Magnetic Resonance Conference 2017

Dynamics of asphaltene adsorption and deposit morphology in aged sandstone through evolution of diffusionally coupled relaxation using nmr cryoporometry and relaxation exchange techniques (#73)

Igor Shikhov 1 , Rupeng Li 1 , Yin Yao 2 , Shuang Xiao 1 , Christoph H. Arns 1
  1. School of Petroleum Engineering, University of New South Wales, Sydney, NSW, Australia
  2. EMU/MWAC, University of New South Wales, Sydney, NSW, Australia

Asphaltene aggregation in oil bearing rocks subjected to onset conditions leads to reduction of reservoir transport properties through compartmentalisation, wettability change and decrease of relative permeability. Asphaltenes may be accumulated in variety of morphological types, e.g. covering layers and aggregates, which are multi-scale porous structures. Understanding of the effect of these structures on transport in rocks would contribute to improved modelling of petroleum reservoirs and aids in designing representative laboratory core analyses. Various NMR techniques have been established for petrophysical characterisation of rocks, petroleum fluids and asphaltenes flocculation dynamics: diffusometry, relaxometry, relaxation dispersion and variety of correlation techniques. Nowadays several of these techniques are available for downhole measurements, therefore, improvements in NMR signal interpretation providing detailed information about asphaltenes behaviour are of a high practicality.

We created a set of core plugs aged over specific time intervals and accumulated various amounts of asphaltene deposits. This provides a coarse reference bulk adsorption dynamics. A set of analytical techniques (BET gas adsorption, FESEM, MIP) and NMR cryoporometry [1] were applied to obtain elements of the deposit structure and evolution, such as pore-size distribution of deposits and surface area change over time. Diffusion relaxation exchange in aged cores was measured directly using T2-store-T2 relaxation experiment [2,3]. This technique aids to uncover several properties of asphaltene deposits - volumetric fraction and porosity estimate of macroscopic aggregates and a fraction in a covering layer [4]. Additional information about relaxation exchange processes between porous aggregates and marcopores in aged sandstone (tortuosity, effective diffusion and connectivity to macropore space) is inferred utilising detailed numerical nano-scale model of deposits developed using Poisson particle process [5], a simulated magnetisation exchange using a simplified uniform 2D model of the medium [6,7] and simulated NMR relaxation experiment on 3D voxelised image [8].

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