Study Heterogeneous Shale Rocks by Simultaneous Neutron/X-ray Imaging & Small-Angle Scattering
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SPWLA Distinguished Speaker Series. Hydrocarbon production from shales using horizontal drilling and hydraulic fracturing has been the key development in the US energy industry in the past decade and has now become more important globally. Nevertheless, many fundamental problems related to the storage and flow of light hydrocarbons in shales are still unknown. It has been reported recently that the gas storage within the shale rocks is predominately associated with the organic component, the so-called kerogen, in the rocks, which is found to be imbedded within the inorganic matrix and has pores of characteristic length scale between 1 and 100 nm. The surface properties of these pores in the shale rocks are determinant factors for both reserve estimation and production-rate prediction in shale reservoir. In addition, the 3D connectivity of these kerogen pores and possibly with fractures from the micrometer to centimeter scale forms the flow path for light hydrocarbons. Therefore, to better model the gas-in-place and permeability in shales, it is necessary to quantify the surface properties of the kerogen pores and identify structural distribution of organic and inorganic components and fractures in shale rocks over a large breadth of length scales.
Simultaneous neutron and X-ray tomography offers a core-scale non-destructive method that can distinguish the organic matter, inorganic minerals, and open and healed fractures in 2.5 cm diameter shales with resolution of about 30 µm. Three shale samples from different locations were investigated using the simultaneous neutron and X-ray tomography. We were able to construct 3D images of shales and isolate 3D maps of organic matter and minerals including high-Z element unambiguously. The distribution of kerogen and fractures can be used in modeling hydrocarbon flow in core scale, a 109 upscaling from current methods that model the flow based on SEM images.A novel Generalized Porod’s Scattering Law Method (GPSLM) based on small-angle scattering was developed to quantify the heterogeneity of pore walls in porous materials. This method is non-destructive, model-independent, and gives statistically ensemble-average result efficiently. Three isolated kerogen samples isolated from shales with different maturity levels were studied with the GPSLM. The results indicate that more mature isolated kerogen has lower hydrogen content and more homogeneous chemical component distribution.
Dr. Wei-Shan Chiang is currently a postdoctoral researcher in University of Delaware and National Institute of Standards and Technology (NIST). She got her bachelor and master degrees from Chemical Engineering in National Tsing-Hua University in Taiwan. During her Ph.D. in Nuclear Science and Engineering in Massachusetts Institute of Technology, she used neutron and X-ray techniques to study chemical and physical properties of various systems such as block copolymers, protein solutions, colloidal suspensions, and cements. In her current research focus, she collaborates with the researchers at Aramco Research Center in Houston to study the structure of shale rocks, phase behaviors of hydrocarbons and hydrocarbon mixtures confined in nanopores, and methane storage and transportation in porous materials. She also establishes new methods to characterize heterogeneous materials. Her presentation of the work on shale rocks was recently selected as one of the 2017-2018 SPWLA Distinguished Speakers.
Start1. Intro and Outline (3:40)
Start2. What Neutrons are good at? (6:43)
Start3. 3D Structure of Shale Rocks Studied by NIST Neutron and X-ray Tomography (NeXT) (18:25)
Start4. Surface Heterogeneity Analysis of Kerogens Using Generalized Porod’s Scattering Law Method (GPSLM) (7:20)
Start5. Hydrocarbons Confined in Nanopores (5:48)
Start6. Conclusions (2:21)