TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOccurrence of asphaltene deposition in producing formation constitutes one of the most serious problems currently encountered in the petroleum industry in many areas of the world. Reversibility of asphaltene deposition represents crucial argument and controversy in laboratory research of the petroleum industry. Deep understanding of this phenomenon is the key for treatment the problem of asphaltene deposition.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractContinued research and field application of steam flooding have confirmed an early conclusion that the process is a powerful method for recovering heavy and intermediate gravity crude oils.

Crude oils produced in many parts of the world contain asphaltene. Asphaltene plugging is a known cause of near-wellbore formation damage. The deposition phenomenon of asphaltene has been extensively investigated in homogenous porous media. However, we have not found any reported experimental work on asphaltene plugging in naturally or artificially fractured reservoirs. The main objective of this study is to investigate the effect of fracture characteristics on reduction of permeability by asphaltene deposition in carbonate formation. A single fracture system is made with different fractures characteristics such as porosity, permeability, and fracture angel using saw-cut limestone core samples with metallic plate. The fracture aperture was kept constant for most of the studied systems. The effect of flow rate, fracture angel, matrix to fracture permeability, asphaltene concentration and the state of stress on the retained permeability is presented. Different fracture angle orientations of 45°, 90°, and 180° relevant to the axis of the flow were investigated. A non-invasive imaging technique-Scanning Electron Microscopy (SEM) was employed to visualize changes on the surface of the fracture as a result of aspheltenic crude oil flow through the system. Introduction Fractured reservoirs are comprised of matrix blocks and fractured networks. One may view these reservoirs as the extreme case of heterogeneous reservoirs. Natural and artificially induced fractures are channels through which fluid can flow towards a production well. Natural and artificially induced fractures may have a positive or negative effect on reservoir ultimate recovery. In the case of single-phase production, the fractures act as a conduit path for the oil that exists in the matrix and reduces the pressure drop between the well and the reservoir. This results in an improvement in the well productivity. However, in the case of two-phase flow (oil and water or gas), the presence of a fracture network may result in fluid bypassing, early water or gas breakthrough, reduction of volumetric sweep efficiency, and overall poor recovery efficiency. Since fractured reservoirs contain a large fraction of the world supply of oil, a substantial amount of work devoted by many researchers on the flow of a single and multi-phase through fractured system. Early studies in the literature centered on viscous cross flow in layered porous media 1,2. Firoozabadi et al.3 studied the gravity and capillary cross-flow in fractured porous media. They concluded that the contribution of the capillary cross-flow from the side faces of the matrix rock increases as the tilt angel increases, where as the effect of gravity decreases with an increase in tilt angel. Pope et al.4 discussed the damage to fracture conductivity resulting from channeling or viscous fingering. Makurat and Gutierrez5 investigated the effect of shear displacement and fracture normal stress on fracture flow and bulk flow. They showed that fracture flow can increase with increasing shear displacement, even when rather weak rocks are sheared under high stress to strength ratio.