Quantitative Discrimination of Effective Porosity Using Digital Image Analysis - Implications for Porosity-Permeability Transforms
Five relevant digital image analysis parameters for fluid flow are obtained from 2-D image analysis of carbonate rocks: 2-D image porosity, amount of pores, pore shape, total perimeter per area and dominant pore size range. Micro-porosity leads to low permeable, highly porous rocks. 2-D image porosity represents the macro-porosity because the resolution subtracts the small pores from the porosity. Compared to the total porosity, it improves the prediction of permeability by an order of magnitude in the high porosity range. Pore shape factor γ reduces the uncertainty in permeability prediction to 2 orders of magnitude. Pore shape factor analysis is restricted to samples with more than 4000 pores/cm. CT scans of plugs reveals that the pore shape factor γ is a relatively constant measure of the pore shape (+/0.2) throughout the sample plug. The larger the average pore size, the higher the velocity at a given porosity. The average pore size can be quantified by the upper limit of the dominant pore size range.
Novel microscopic imager instrument for rock and fluid imaging
Core analysis from reservoir rock plays an important role in oil and gas exploration as it can provide a large number of rock properties. Some of these rock properties can be extracted by image analysis of microscopic rock images in the visible light range. Such properties include the size, shape, and distribution of pores and grains, or more generally the texture, mineral distribution, and so on. A novel laboratory instrument and method allows for easy and reliable core imaging. This method is applicable even when the core sample is in poor shape. The capabilities of this technique can be verified by core images, image interpretation, and dynamic measurements of rock samples during flooding. A microscopic imager instrument is operated in video acquisition mode and can measure additional properties, such as fluid mobility, by detecting the emergence of injected fluids across the core sample.
Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil.
Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.