The Role of Stylolites and its Pattern Attribute on Porosity and Permeability: Evidence from a Lower Cretaceous Carbonate Oil Reservoir, Abadan Plain, SW Iran

Abstract

Stylolites are localized dissolution surfaces commonly found in sedimentary rocks. Stylolites have been extensively studied for their important role in controlling porosity and permeability through dissolution, precipitation, deformation, and fluid transport in rocks. Prevalent views are that they act as permeability barriers, although laboratory studies are scarce. Here, we report on a systematic laboratory study of the influence of stylolites on permeability in carbonates. Our data demonstrate that the studied stylolites do not act as barriers to fluid flow. When a stylolite occurs perpendicular to the flow direction, the permeability follows the same power law porosity-permeability trend as the stylolite-free material. Stylolite surfaces can play an effective role as open pathways in increasing the effective porosity of reservoir rock, and due to the wide amplitude range of stylolites, it is necessary to ensure that the permeability of facies increases. The stylolites have been classified into three main types based on their properties such as genesis, general shape, size, the difference in amplitude, amount of accumulated insoluble material in their seams, discontinuity of their seam material, and, most importantly, to predict their role in conducting fluid flow has been explained. However, the direction of dominant stress that determines the genetic type of stylolites and all the effective parameters in the burial diagenetic stage, including the pressure, temperature, and soluble ion-rich fluids, can increase or decrease the porosity and permeability values by draining or blocking the pathway produced by this process through quality assessment of carbonate host rock reservoir. Ultimately, based on this, stylolites in some facies of the Fahliyan Formation in the Abadan Plain Zone act as a continuous and connected porosity for fluid flow and, according to their amplitude and morphology, stylolites increased the effective permeability and reservoir quality, especially in the mud-supported facies in this formation. However, our data affirm that all conditions, especially the nature of morphology, are the most influential parameters determining the porosity and permeability of the Fahliyan Formation facies.

Keywords

• stylolite
• morphology
• porosity
• permeability
• fluid flow
• fahliyan reservoir