Influence of the volume loss of framework grains on the quantitative analysis of diagenetic modification of the original intergranular porosity

The evaluation of the original intergranular porosity loss due to compaction (COPL) and cementation (CEPL) is an important tool for understanding the contribution of diagenetic processes to porosity reduction and permeability retention of sandstones and carbonate grainstones. The previous approach for computing CEPL and COPL assumed that the volume of framework grains remained constant during diagenesis. However, such assumption will introduce error in COPL and CEPL if diagenetic processes reduced the volume of framework grains. New equations are presented that account for such situations. Comparably, the previous approach underestimates COPL and the compaction index, but over-estimates CEPL in the case of volume loss of framework grains by dissolution or intergranular pressure solution (DIPL). The deviation of CEPL and COPL caused by DIPL rises with the increase in the intergranular volume and DIPL. Analysis of three published case studies suggests that DIPL values of just a few percentages will significantly impact COPL and CEPL values. The effects of DIPL can be greater than the effects of uncertainty in original porosity estimates and uncertainty in point count data.