Changes

Zones having obviously low or high permeability as a result of their grain size, sorting, clay content, cement content, or extent of dissolution or fracturing, but which were not represented in the original suite of core plugs, should be sampled to evaluate their influence on flow properties. It is also important to assess the degree of vertical permeability across small scale potential permeability barriers such as stylolites, cemented zones, and healed fractures. If full diameter core analysis was conducted, a representative portion of each segment can be selected for analysis, and the porosity-permeability measurements for the whole segment can be assumed to apply to the portion sampled. Alternatively, core analysis and rock descriptive work can be conducted on plugs cut in selected segments of the full diameter core.

Zones having obviously low or high permeability as a result of their grain size, sorting, clay content, cement content, or extent of dissolution or fracturing, but which were not represented in the original suite of core plugs, should be sampled to evaluate their influence on flow properties. It is also important to assess the degree of vertical permeability across small scale potential permeability barriers such as stylolites, cemented zones, and healed fractures. If full diameter core analysis was conducted, a representative portion of each segment can be selected for analysis, and the porosity-permeability measurements for the whole segment can be assumed to apply to the portion sampled. Alternatively, core analysis and rock descriptive work can be conducted on plugs cut in selected segments of the full diameter core.

Petrographic analysis should be designed to generate quantitative data. Decisions as to which components should be measured separately in this analysis are based on several criteria. Generally, components that are relatively abundant (>10%) and whose abundance varies significantly in the interval being investigated should be measured separately. Porosity-permeability crossplots on which samples are plotted according to lithological data obtained from binocular microscope analysis may reveal relationships indicating the relative importance of certain components (Figure 3). Components that are finely crystalline, particularly diagenetic clays, may exert a major effect on permeability, even where their abundances are relatively low (3–5%).

Petrographic analysis should be designed to generate quantitative data. Decisions as to which components should be measured separately in this analysis are based on several criteria. Generally, components that are relatively abundant (>10%) and whose abundance varies significantly in the interval being investigated should be measured separately. Porosity-permeability crossplots on which samples are plotted according to lithological data obtained from binocular microscope analysis may reveal relationships indicating the relative importance of certain components ([[:file:evaluating-diagenetically-complex-reservoirs_fig3.png|Figure 3]]). Components that are finely crystalline, particularly diagenetic clays, may exert a major effect on permeability, even where their abundances are relatively low (3–5%).

Quantitative point count analysis is preferable to semiquantitative visual estimation. If such analyses are not feasible, use should be made of visual comparators. If microcrystalline components having sizes

Quantitative point count analysis is preferable to semiquantitative visual estimation. If such analyses are not feasible, use should be made of visual comparators. If microcrystalline components having sizes