Milad Kheirinasab - Master Student of Petroleum Exploration, University of Tehran
Hossein Mohammadrezaei - Iranian Offshore Oil Company
Bita Arbab - Iranian Offshore Oil Company
Abbas Bahrudi - Assistant Professore, Faculty of Engineering University of Tehran

Pore pressure which exists in the reservoir bear part of the earth stress and keeps the pores open. So the pore pressure is one of the factors affecting the compressive strength of rock. When the pore pressure is being reduced by production process, so that effective stress increase. Changing in effective stress can cause elastic and inelastic deformations. Faulting is one of this deformations. Depend on type of faulting systems(strikeslip,normal and reverse), when stress path is being passed its critical,therefore faulting occur. Compaction is another deformations that include normal compaction and abnormal compaction. Normal compaction is being occurred when rock deformation is elastic in this case increase in effective stress cause closure of pores. In abnormal compaction increase in effective stress can continues considerably to porosity and permeability reduse gradually during the production period in this case rock deformation is inelastic with shear enhance compaction, the phenomenon is known as pore collapse. In this article, we study the effective stress changes as a result of the production and reasons of occurrence of each deformation mentioned. Then ways to prevent the occurrence of these events is checked.

Depletion Effect, Elastic Deformation, Inelastic Deformation, Effective Stress