The nature of some water injection processes can cause unavoidable formation damage. In most cases, by optimal design of the process, the formation damage can be minimized or avoided. The estimation and assessment of formation damage on reservoir core samples is an important measurement which will be presented in this paper by monitoring rock permeability changes.

Laboratory tests were set up to investigate the effects of injection pressure, flow rate and also induced fracture on the rock sample with respect to formation damage. Reservoir core nature, structure and its heterogeneity make the phenomenon of formation damage more complex. In this research, selected rock samples from one of Iranian giant oil fields, which is undergoing water injection, were used as the laboratory physical model. Using injection water samples, different scenarios were performed on this model. Permeability reduction was observed for un-fractured samples: however, it was more interesting that no injection pressure build up was detected in fractured samples. It appears that fractures in sandstones, especially with weak cementation, can play the role of an agent for particle movement in causing damage to different parts of the formation. Over a long period of time, this phenomenon can cause more complicated situations in the reservoir, the degree of which being a function of several parameters, such as rock type and structure, pore size distribution and reservoir heterogeneity.

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