Towards a Balance of Pore Size Distribution in Non-Conventional Hydrocarbon Reservoirs: a Combination of Bulk Techniques Applied to Comparable Sub-Samples Localized by 3D X-ray Tomography

Matskova, N. (Universite de Poitiers) | Pret, D. (Universite de Poitiers) | Gaboreau, S. (BRGM) | Cosenza, P. (Universite de Poitiers) | Brechon, R. (Universite de Poitiers) | Gener, I. (Universite de Poitiers) | Fialips, C. I. (Total E&P) | Dubes, G. (Total E&P) | Gelin, F. (Total E&P)



Non-conventional shale reservoirs are characterized by multi-scaled pore systems closely associated with a variable spatial distribution of mineral grains and organic matter. Therefore, only an integrated multi-technique approach can provide a quantitative balance in pore size distribution. Such a balance is not achievable when each of the different methods is applied on different samples that are randomly selected within the formation being studied. In this multi-technique study, the initial cores were first scanned by μ-tomography with an achieved resolution of 78.8 μm to visualize potential spatial heterogeneities at the core scale. This approach identified similar and homogenous areas of interest for localized bulk measurements. In particular, the sub-sample positions were selected, in the 3D views, in areas presenting (i) similar non-clay grain amounts, (ii) similar X-ray linear attenuation coefficients, and (iii) no cracks or macro-heterogeneities.

This approach was applied to seven core samples (dimensions of ~7x7 cm) from the Vaca Muerta formation (Argentina), taken from three different exploration wells in zones with various hydrocarbon types (condensate gas, dry gas, and oil). These samples were chosen on the basis of well log data and their petrophysical interpretations. Lithofacies with similar mineral distribution but contrasting physical properties (resistivity, porosity, and density) and organic matter content were selected.

Conventional bulk methods were used to characterize the pore network of the selected sub-samples: mercury intrusion porosimetry, gas adsorption, nuclear magnetic resonance spectroscopy and helium pycnometry. Some of these methods are generally applied to non-localized crushed powder samples, which is inappropriate for evaluating preserved microstructure from the micro- to the macro-porosity range. For this reason, most of the acquisitions were performed on preserved core blocks, including nitrogen gas adsorption experiments, which were performed with kinetic control of adsorption equilibrium. This innovative approach has provided, for the first time ever, a full set of truly comparable data, localized on 3D views, displaying quantitative balances of pore size distribution in shale reservoirs.

  Country: North America > United States (0.68)
  Industry: Energy > Oil & Gas > Upstream (1.00)