Experimental study on stress sensitivity in reservoirs with different permeability

Key words:  formation damage  stress sensitivity  pore structure  damage mode  damage mechanism

Abstract:

Stress sensitivity damage can reduce the permeability of oil and gas reservoirs, especially for low permeability reservoirs. Experimental study on the stress sensitivity was carried out using cores taken from natural rocks with different permeability. The relationship between the permeability and the net stress on rocks was established, and the mechanisms for the stress sensitivity damage were analyzed. The influence of stress sensitivity damage on the productivity of oil wells was studied based on a flow model of radial plane. The results show that the stress sensitivity in ultra-low to low permeability reservoirs is stronger than that in middle to high permeability reservoirs. The damage mode of stress sensitivity in a high permeability reservoir can be described as "gently dipping", while in an ultra-low permeability reservoir it is in a mode of "initially fast then slowly dipping". The damage caused by stress sensitivity is greatly affected by the structure and size distribution of pore throats in the rock. Nevertheless, the stress sensitivity has a negative effect on oil production because a permeability reduction zone can be formed near the wellbore.