Wetting collapse analysis on partially saturated oil chalks by a modified cam clay model based on effective stress

This paper presents an interpretation of wetting collapse in partially saturated oil chalks subjected to water flooding. For this purpose, two competitive mechanisms, namely, compressive plastic strains and elastic swelling, have been analyzed through a modified Cam Clay model based on effective stress. The resulting simulation shows that, mechanical behaviors of oil chalks upon wetting have been captured with good accuracy. The interpretation detects the possibility of wetting compaction/swelling for oil chalks under different stress states, emphasis is also placed on specific conditions for the occurrence of wetting collapse. Inspections on effective stress and preconsolidation stress paths show that, the distance between two streams plays the main role on the magnitude of accumulated compressive plastic strain. Since wetting process generally leads to two competitive deformation, elastic swelling due to the diminution of suction and additional plastic flow due to the diminution of plastic yield stress (contraction of yield surface), the plastic compaction would outweigh elastic swelling if a threshold value of suction can be achieved.