Characterization of tight and shale unconventional gas reservoirs using low field NMR
Date
2023-01-26
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Abstract
Unconventional petroleum resources, especially tight and shale reserves, constitute an increasing frontier of reserves additions as conventional production declines. In these sources, reservoir characteristics have significant value in reserve estimation and flow modelling. These characteristics are challenging parameters to measure. On the other hand, oil and gas sectors are continually looking for ways to do more with less environmental impact and greater operational efficiency. Nuclear Magnetic Resonance (NMR) offers fast and non-disruptive detection of the reservoir samples properties. The purpose of this research is to investigate the interactions between tight and shale rocks with hydrocarbons using NMR technique. This thesis mainly presents routine and new experimental and numerical methods of measuring porosity, permeability, residual saturations, and excess and absolute adsorption isotherms. The experiments were conducted on different porous media such as shale cores, tight sand cores, activated carbon, and sandpacks at pressures up to 7 MPa. In this thesis, for 150 cores, permeability was estimated using all existing NMR permeability correlations. In addition, irreducible saturations were presented for these cores. A new method to obtain residual saturation using the area under the NMR relaxation distribution curves was introduced. Permeability and irreducible saturation models are compared based of their standard error deviation from the independently measured ones. For organic porous media, the NMR decay curve of hydrocarbons exhibited a logarithmic behaviour at early times. Based on this observation, a new method of obtaining absolute adsorption was developed. The time when the decay curve shifts from logarithmic to multi-exponential behaviour was defined as sorption cut-off time. Adsorption isotherm hysteresis of methane in Duvernay shale samples was demonstrated using the newly developed method. In this research, for the first-time Low-Field NMR relaxometry with a frequency close to logging tools directly and without the use of correlations is used for quantitative determination of adsorption isotherms of methane in shale reservoirs. Isotherms derived by the new method better described the physical behaviour of hydrocarbon in organic porous media as it captures the effect of phase transition and measures critical pressure in organic porous media, which is different than the ones in non-organic porous media. Moreover, with this new fractal model, total hydrocarbon in place, adsorbed, and free hydrocarbon can be estimated from a single NMR experiment. This thesis is beneficial in understanding existing tight and shale reservoir characterization methods and introduces more advanced and reliable techniques to measure the properties of these reservoirs. In chapter 3 to 7 of this study, currently available methods of tight and shale reservoir characterization are presented. Then a new approach is provided for each case which is less computationally demanding, and calculations are easier to perform. Moreover, in most scenarios only a single NMR measurement is needed.
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Keywords
NMR, Shale, Unconventional, Petroleum, Adsorption
Citation
Solatpour, R. (2023). Characterization of tight and shale unconventional gas reservoirs using low field NMR (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.