Date(s) - 12/10/2019
11:30 am - 1:00 pm
Integration and Comparison of Physical and Digital Rock Properties from a Delaware Basin Well
Joel D Walls, Ingrain-Halliburton, Houston, TX
Gabriela Davalos, Ingrain-Halliburton, Houston, TX
A core analysis program was conducted on a Delaware basin well in west Texas. The 2nd Bone Spring and Wolfcamp formations were selected for a core testing program. The main objective was to understand reservoir quality, including porosity, fluid saturation, mineralogy, pore size, and pore type. An additional objective was to compare scanning electron microscope- (SEM) based digital rock analysis (DRA) results to physical laboratory tests, such as GRI crushed rock porosity and total organic carbon (TOC).
Plug samples were obtained for X-ray diffraction (XRD) mineralogy, pyrolysis, TOC, DRA, and retort analysis. DRA included Fourier transform infrared (FTIR) mineralogy, argon-ion milling, SEM imaging, image processing, and segmentation. The pore size and volume fraction of organic porosity, inter- and intra-granular porosity, and solid organic matter were computed. Rock material from near each plug was used for Dean-Stark extraction (Sw, So) and helium porosity. Thus, the relationships between key rock properties, such as clay content vs. TOC, bulk volume water vs. clay content, and bulk volume oil vs. porosity associated with organic matter (PAOM), were determined.
In these samples, TOC was observed to be related to clay content, but not linearly. Rather, TOC increases with clay content up to approximately 30% by weight clay, then begins to decrease. Total clay, silica, and carbonate from XRD and FTIR were in good agreement, although XRD indicated slightly higher clay content than FTIR. As reported elsewhere, SEM-derived porosity is generally lower than helium porosity. In addition, the difference between the two is strongly related to total clay, suggesting that clay-bound water may be a key factor. This is supported by GRI and XRD data that show bulk volume water is directly correlated to total clay with a near-zero intercept.
Understanding that a sweet spot for TOC exists at approximately 30% clay content in these formations may help to target the best reservoir.
Although image resolution and damage to organic porosity from ion-milling are commonly provided explanations for why SEM porosity on ion-milled samples is routinely lower than helium porosity, this work suggests a different reason: capillary-bound water on clay mineral surfaces. This water is driven off in Dean-Stark and retort methods, thus counted as part of total porosity. However, the SEM images do not resolve this adsorbed layer of water on clay surfaces.
When clay-bound water volume is added to SEM porosity and plotted vs. GRI porosity, a linear fit with a slope of near 1 and a correlation coefficient r2 of approximately 0.8 is obtained.
Director of Unconventional Technology
Dr. Joel Walls is a geophysicist and entrepreneur with extensive experience in the research, development, launch, and sale of advanced technology products and services for the upstream oil and gas industry. He joined Ingrain in 2010 as a Director of Unconventional Technology with responsibility for developing and commercializing services focused on shale and other unconventional reservoirs. Ingrain was acquired by Halliburton in 2017. Dr. Walls was a co-founder and the first president of the Society of Core Analysts, and is a member of AAPG, SPE, SPWLA, and SEG. He is the author of many industry publications and holds four U.S. patents in the fields of digital rock properties and seismic reservoir characterization. Education
Stanford University, Stanford, California, PhD, Geophysics/MS,
GeophysicsTexas A&M University, Commerce, Texas, BS, Physics
Cofounder & First President, Society of Core Analysts
Society of Exploration Geophysicists (SEG)
Society of Petroleum Engineers (SPE)
Society of Petrophysicists & Well Log Analysts (SPWLA)
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