Influence of faulting on porosity and permeability features of carbonate rocks, Kardeh fault, NE Iran

Abstract

In the southern part of the Kopeh Dagh basin, NE Iran, outcrop of the Kardeh fault damage zone in Mozduran carbonate formation provides an opportunity for investigation of the impact of faulting on permeability and porosity. For this purpose, three methods were focused on: 1) gas injection in oriented cores prepared parallel and perpendicular to fault strike and parallel to fault dip, 2) microscopic analysis and 3) determining variation of the degree of fractures connectivity in the fault damage zone. Results of tests show air-porosity and air-permeability increase from fault core toward host rock. Using microscopic studies, we attribute these variations to bioclasts destruction and filling, precipitation of calcite cement in fractures and pores, development of compaction structures such as stylolites and particle abrasion. Analyzing variation of the fractures connectivity in the fault damage zone in macro-scale shows degree of connectivity increases from host rock toward fault core (Y and X nodes). Clear dependence between this parameter and fluid flow is reflected by connected linear springs developed in the damage zone in close proximity to the fault core. Results of this study show that permeability in a fault zone is a scale dependent feature.