Speaker: Ravinath Kausik K.V. - Schlumberger-Doll Research
Speaker Bio:
Ravinath Kausik
K.V. is a Senior Research
scientist at Schlumberger-Doll Research in Cambridge, USA where he has focused
on the development of novel NMR and petrophysical techniques for porous media, especially
unconventional shale gas and tight oil formations. His work has led to the
development of techniques such as TGIP-NMR and RPI for unconventional plays. He
has also worked on the development of next generation NMR diffusion and
relaxation measurements for both laboratory and downhole applications. He has
served as a SPWLA distinguished speaker both in 2015-16 and 2016-17 and is the
current president of the Boston SPWLA chapter. He obtained a M.Sc. from IIT
Madras, India and Ph.D. degree in physics from Universität Ulm, Germany. He
worked as a postdoctoral fellow at the University of California, Santa Barbara
before joining Schlumberger-Doll Research in 2009. He has co-authored more than
30 peer-reviewed publications and several patent applications and is a
scientific reviewer for more than 10 international journals.
TEMPERATURE DEPENDENCE OF 2D NMR T1-T2 MAPS OF SHALE
Abstract: Paper JJ
Two-dimensional
nuclear magnetic resonance (NMR) T1-T2 maps are fast becoming the industry
standard for fluid typing in unconventional shale rocks due to their
sensitivity to molecular mobility (Kausik et al., 2011, 2014, 2016; Rylander et
al., 2013). The increasing mobility of the different components of
unconventional plays—ranging from solid kerogen to the fluid components of
viscous bitumen, clay-associated water, oil in oil-wet organic pores to fluids
(oil and water) in the mixed-wet inorganic pores and natural fractures—is
measured by this methodology to determine the fluid types and their confining
environments for the construction of universal 2D maps of different wells. One
of the biggest challenges for the universal application of this methodology is
that the impact of variation in the temperature between different basins,
wells, or even multiple depths within a well, on the 2D NMR T1-T2 maps needs to
be well understood.
The main
objective of this paper is to understand the changes in molecular mobility of
the different fluids in shale rocks as a function of temperature and their
influence on 2D NMR T1-T2 maps. For this purpose, we performed NMR relaxation
experiments on the extracted bulk components of shale rocks, such as kerogen,
bitumen, and light oil, and also investigated them under confinement, such as
bitumen and oil in organic kerogen pores, oil and water in inorganic pores,
other than clay-associated water. This enabled us to obtain a universal picture
of the different fluids in both bulk state and under oil-wet or water-wet
confinement, with different pore sizes and surface relaxivity.
The multi-temperature
NMR relaxometry experiments were conducted on both low- and high-frequency NMR
systems to enable comparison with the logs and to obtain the highest-resolution
data, respectively. It has been demonstrated that the relaxation-time
dependence of light oil is proportional to viscosity over temperature. The
temperature dependence of bitumen or heavy viscous oil relaxation times is
proportional to viscosity over temperature with a power law of –0.45. Both the
heavy oil and light oil in the oil-wet organic pores of the kerogen show a much
weaker dependence on temperature. This can be explained by the fact that fluids
in the wetting environments are constrained in their motions by the surface
interactions (and residence times), and if these are not significantly changed
by increases in temperature. We also compare this relaxation behavior with that
of the oil or water in mixed-wet inorganic matrix, where a much stronger
temperature dependence due to the lower reduction in the bulk phase mobility
can be observed.
In conclusion, we
investigated the 2D NMR T1-T2 response of different shale rock components such
as bitumen, oil, and water in a bulk state as well as in oil-wet (organic
kerogen) or mixed-wet (mineral matrix) confinements. The hybrid Bakken petroleum
system was used as the template for these experiments, with the behavior of the
upper Bakken organic mudstone interval contrasted with that of the middle
Bakken inorganic matrix. Based on these studies we propose a more universal
understanding of fluid typing based on 2D NMR T1-T2 logging.
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