Abstarct: Permeability of fractured rock masses is one of important issues in many studies such as geothermal engineering, mining, geological engineering and underground hydrocarbon storage. Due to lack of enough experince in determination of appropriate leakage system for designation and construction of unlined rock caverns for underground storage of crude oil in iran, this study is carried out in order to developing this issue. Rock mass permeability is not only effected by geometric properties of discontinuities system, it is also effected by stress field and it’s changes. Parametric studies and sensitivity analysis provide the possibility of knowing effective key factors to locate and controling leakage system of unlined rock caverns. Due to employer decision (Iranian oil terminals company) in order to construction study of unlined rock cavern for storage of crude oil in Asmari formation and also because of locating Karoon 4 dam and cavern site in Asmari formation, this study carried out with Karoon 4 site’s datas. This study is a guidline to determine appropriate methodology for similar studies in other sites. In the first step, field studies carried out at Karoon 4 site that is including joint survey and then this datas analyzed via DIPS and EASY-FIT softwares in order to determine governing distribution functions on fracture properties. In the second step, three dimensional discrete fracture network is constructed baxsed on mentioned datas via discrete element software, 3DEC. In the third step, representative elementary volume is estimated under hydromechanical coupling process. In the fourth step, a comparison is done between calculated values in two conditions of coupled and un-coupled process and then is validated by insitu values calculated via lugeon test in Karoon 4 site’s. In the fifth step, unlined rock cavern with standard dimensions is excavated in calibrated block and then stability conditions under hydromechanical coupling is assessed. Next, pore pressure and water flowrate into cavern via intersected discontinuities with cavern boundary is estimated. Then similar assessments is carried out with sensitivity analysis of parameters such as water table and cavern depth. In the final step, by creating artificial water curtain system and changing water curtain boreholes properties such as distance from cavern’s crown and water pressure in this boreholes, the modeling is carreid out in order to estimate water flowrate into cavern and also calculate pore pressure in intersected discontinuities with cavern boundary in comparison with lack of water curtain system.