Temperature and Frequency Dependence of 2D NMR T1-T2 Maps Of Shale

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SPWLA Distinguished Speaker Series. 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.

Your Instructor

Ravinath Kausik, PhD, SPWLA
Ravinath Kausik, PhD, SPWLA

Ravinath Kausik K.V. is a Senior Research scientist at Schlumberger-Doll Research. At Schlumberger he has focused on the development of novel NMR and petrophysical techniques for porous media, especially unconventional gas and tight oil organic shale plays. He has developed new NMR pulse sequences and petrophysical workflows for better understanding various fractions of unconventional plays such as the stored gas, bitumen, producible oil, kerogen and bound water. He is also involved in the development of the next generation NMR relaxometry and diffusometry measurements for both laboratory and logging applications. He obtained a M.Sc. from IIT Madras, India and Ph.D. degree in physics from the University of Ulm, Germany. He worked as a postdoctoral fellow at the University of California, Santa Barbara before joining Schlumberger-Doll Research in 2009.