报告人：George J. Hirasaki
NMR Response of Fluids in Organic Shale
George J. Hirasaki, Rice University
Oil production from unconventional formations (organic shale) has increased from about zero 15 years ago to about half of the U.S. production today. Although the growth of this production is remarkable, the formation evaluation technology for organic shale or source rock formations is evolving. The focus of this presentation will be on the interpretation of NMR well logging for organic shale formations.
Our approach to understanding the NMR log response of different fluids in organic shale is to measure the response of brine or hydrocarbon in isolated components of organic shale: clay, chalk, and kerogen. The NMR measurements include T1 and T2 relaxation times and diffusivity. Restricted diffusion significantly reduces diffusivity from that of bulk fluids. This effect is analogous to the formation-factor in electrical conductivity. The small pores of clay and kerogen greatly reduce the relaxation time of fluids compared to bulk values because of surface relaxation. The relaxation of hydrocarbon in kerogen isolates has two peaks, one due to inter-particle porosity and the other due to intra-particle porosity. The remarkable feature of the intra-particle peak is the large T1/T2 ratio.
Bitumen also has large T1/T2 ratios. One theory has hypothesized that it is due to paramagnetic components. We hypothesize that it is due to proton (hydrogen) dipole-dipole interactions. We test this hypothesis by comparing the NMR response of crude oil and bitumen with that of viscosity standards using NMR Larmor frequency from 2.3 to 400 MHz. Viscosity standards with undetectable paramagnetic material have the same limiting T1 and T2 behavior as bitumen. However, this limiting behavior is different from the observations and theory developed by Bloembergen, Purcell, and Pound in 1948. Considering internal motions and polydispersivity explains the observed behavior.
A 333,400 cp viscosity standard (polymer) is used as a model for kerogen to interpret the T1/T2 ratio of a simple hydrocarbon, n-heptane in kerogen. When the concentration of heptane is large, the surface relaxivity of heptane in the polymer is constant. However, when the heptane concentration is low, the T1/T2 ratio becomes large and is NMR frequency dependent. Molecular dynamics simulations are used to interpret NMR relaxation by proton (hydrogen) dipole-dipole interactions. The simulated and measured T1/T2 ratio agree. Thus, the large T1/T2 ratio of light hydrocarbons in kerogen is due to proton dipole-dipole interactions.
Bio. for George J. Hirasaki
A.J. Hartsook Professor Emeritus, Rice University
B.S. Chemical Engineering (1963) Lamar University
Ph.D. Chemical Engineering (1967) Rice University
George had a 26-year career with Shell Development and Shell Oil Companies before joining the Chemical Engineering faculty at Rice University in 1993. At Shell, his research areas were reservoir simulation, enhanced oil recovery, and formation evaluation. At Rice, his research interests are in NMR well logging, reservoir wettability, surfactant enhanced oil recovery, foam mobility control, gas hydrate recovery, asphaltene deposition, and emulsion separation. He received the SPE Lester Uren Award in 1989. He was named an Improved Oil Recovery Pioneer at the 1998 SPE/DOE IOR Symposium. In 2016 he was awarded the Offshore Technology Conference Heritage Award and the Lucas Medal from the SPE/AIME. He was the 1999 recipient of the Society of Core Analysts Technical Achievement Award. He is a member of the National Academy of Engineering and The Academy of Medicine, Engineering, and Science of Texas (TAMEST).