Considering Causes of Development and Effect of Non-Tectonic Fractures on Carbonate Reservoirs, Kangan and Dalan Formations, Central Persian Gulf

Abstract

Various types of non-tectonic fractures are considered in carbonate-evaporite Kangan and Dalan formations in central Persian Gulf in this study. Mud cracks have small sizes and low frequencies and have been formed in shallow water coastal (tidal and intertidal) environments exposed alternatively. Presence of syneresis and desiccation cracks show salinity change or dewatering. These fractures also have no major effect on reservoir properties such as the mud cracks but have higher frequency and show their original depositional environment. These fractures formed in sabkha environments. A lot of water has been released during gypsum-anhydrite transformations in these formations. In the case of low permeability, the rock can’t pass the fluid and so hydraulic fractures have been formed due to the mineral phase change. These fractures formed in burial diagenesis in tidal facies with high evaporation. Stylolite related fractures are vertical, perpendicular to the layering and stylolite surface. These fractures are also related to burial diagenesis, filled and prevent fluid flow in the studied formations. Loading fractures are vertical and have been filled by anhydrite in most cases. These fractures could enhance the permeability if they are open. Results show that except the last group, all detected fractures act as local fluid barriers in Kangan and Dalan formations in central Persian Gulf area.

Keywords

• Non-tectonic fractures
• Mud crack
• Syneresis
• Hydrolic fracture
• Stylolite