Capillary effects in sedimentary rocks: Application to reservoir water-flooding

The effect of water saturation on the mechanical properties of various sedimentary rocks of different lithologies is investigated. Experimental results show that the uniaxial compressive strength and Young’s modulus of a rock decreases with increasing water saturation. Moreover, water-flooding of low saturation rocks under constant stress conditions reveals a significant increase in rock compressibility when the rock is close to its plastic yield. A theoretical model based on capillary suction and Bishop’s effective stress principle for partially-saturated materials is presented and used for the calculation of the uniaxial compressive strength of the rock as a function of water saturation thus verifying the importance of the proposed mechanism.