Abstarct: Fractured carbonate reservoirs are one of the most important sources of hydrocarbons in the world. In fractured carbonate reservoirs, porous media and joints, there are major routes for fluid transfer to the well, while mostly hydrocarbons are placed in the porous media and a small amount of fluid is stored in the joints. In order to investigate the fluid flow path in fractured reservoir as well as to estimate the permeability of the fluid in the vicinity of the permeable rock, it is necessary to understand exactly how the fluid moves through the rough fractures. Fracture permeability is generally estimated from the cubic law, which is valid under laminar flow conditions and perfectly smooth joint surfaces. But the actual topography of joints and fractures is very complex, and the joint surfaces are irregularly connected to the opposite side. These factors cause the fluid to move through the joint and the fractures to be twisted, resulting in a different permeability value than that obtained from the cubic law. Numerical modeling of natural fractured reservoirs is one of the important issues in estimating fluid movement in carbonate reservoirs for which several methods have been proposed. One of the common methods in modeling slotted reservoirs is to use the equivalent continuous model for the reservoir. In this modeling, the joint is modeled with elements similar to the rock matrix, with the similarity that their hydraulic properties are selected equivalent to the properties of the joint. One of the weaknesses of this type of modeling is the lack of consideration of joint geometry and its effect on the path of fluid movement. Perhaps the most important drawback of this type of modeling is that it keeps the seam permeability constant over time. By discharging hydrocarbons from the reservoir, the initial stress is disturbed and the stress redistribution occurs. Joints that were previously closed or open are likely to open and close under the new stress distribution conditions. Changing the joint opening is equivalent to changing the permeability of the reservoir joints. Therefore, assuming a constant amount of joint permeability will have problems in reservoir design in terms of determining the location of wells and drilling wells. In order to address the problems presented in the modeling of fractured reservoirs, in this study, the effect of confinement stress on the permeability of the porous medium is investigated. Then, by creating artificial joints, the effect of roughness and lateral pressure on the behavior of the fluid inside the matted joint has been investigated, which shows the nonlinear behavior (Forchmier equation) of the fluid in the rough joint. Due to laboratory limitations, it is not possible to investigate the behavior of the fluid in the joint with the adjacent porous medium and inevitably this has been investigated numerically. The results of this study showed that if the media around the rough joint is permeable porous; the behavior of the fluid inside the joint is also nonlinear. The effect of permeable porous medium on the behavior of the fluid inside the joint with the change in permeability is evident as increasing the permeability of the lateral media increases the rate of fluid passage through the joint. This is very effective at low mechanical aperture values, so that at a constant mechanical aperture value, if the permeability of the peripheral increases from 1 millidarcy to 100 millidarcy, only the amount of current passing through the joint will be 50 to 100 times greater. Also, the hydraulic aperture of the joint changes with increasing permeability of the adjacent media and becomes closer to the amount of mechanical aperture. In the last chapter, the results obtained from laboratory studies are implemented in a three-dimensional model with simultaneous hydromechanical behavior in 3DEC software that has the ability to model leak off behavior. In the numerical model, two wells in a reservoir are modeled separately and the fluid behavior in them is investigated. The results of this modeling confirm the dual permeability behavior. It also shows the effect of joint closure with fluid outflow in relation to the geometric characteristics of the joints, the double permeability behavior of the reservoir and the simultaneous hydromechanical behavior of the media.