Stylolite effect on geochemistry, porosity and permeability: Comparison between a limestone and a dolomite sample from Khuff-B reservoir in Eastern Saudi Arabia

Khuff formation constitutes the carbonate reservoirs in the Arabian Peninsula. In Saudi Arabia, subsurface Khuff is divided into five units (Khuff-A, B, C, D, and E). Stylolites are abundant in the Khuff-B gas reservoir of the Eastern Saudi Arabia. Two samples, one of oomodlic grainstone and another of dolomite, were selected from the Khuff-B reservoir for petrophysical and geochemical studies. SEM, X-ray line scan, X-ray mapping, helium porosimeter, and steady state gas probe permeameter techniques were utilized in this study. It is a well-known fact that stylolites are vertical permeability barriers. However, in this study, on a microstructural scale, it has been found that stylolite development completely destroys porosity and kills permeability (K_h and K_v) in the dolomite, while it enhances the horizontal permeability (K_h) in the oomoldic grainstone sample. This permeability enhancement in the oomoldic grainstone sample is associated with the introduction of new mineral assemblages.