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Soil Mechanics
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Porosity and permeability both depend on opening between grains but do not always correlate. A bucket of marbles, for example, may have the same porosity as a piece of Swiss cheese, but the marble bucket has high permeability and the cheese does not. Many carbonate rocks have high porosity due to vugs formed by dissolution. Often, however, they have quite low permeabilities. Porous materials only have high permeabilities if their pores are well connected. So, some engineers, especially petroleum engineers, define different kinds of porosity, such as:total porosity—as defined aboveprimary porosity—porosity of the rock resulting from original depositional processessecondary porosity—porosity resulting from diagenesiseffective porosity (also called connected porosity)—ratio of the connected pore volume to the total volumefracture porosity—porosity resulting from fractures in the rock at all scalesvug porosity—porosity associated with vugs, commonly in carbonate rocks
Accelerator Technology for Well Logging: Advances, Challenges, and Opportunities
Published in Nuclear Science and Engineering, 2023
The LINAC tool had successfully provided the density but was challenged in providing the lithology due to the low-energy tail of the bremsstrahlung contributing directly to the signal. Also, it required considerable power. As for the INGD, it was less accurate than the 137Cs-based density even in database calibration. The errors, respectively, were ±0.025 g/cm3 in clean formations (shale-free) and ±0.045 g/cm3 in shale, versus ±0.015 g/cm3 with the 137Cs tool for both clean and shale formations.55 These would translate to porosity errors of ±1.5 pu in a sandstone formation and ±2.7 pu in shale versus less than ±0.06-pu error using a 137Cs source in both. In the petroleum industry, an error in porosity of ±1 pu or lower is desired for accurate determination of reserves. The INGD performed much worse in the field with an error of ±0.2 g/cm3 (versus ±0.01 g/cm3 desired) in a vuggy carbonate reservoir.56 A vug is a small cavity in a rock or vein, often lined with crystals.