Nonwetting phase retention and mobilization in rock fractures

Perchloroethylene (PCE) was injected into fractured limestone samples (appr oximately 0.3 m x 0.3 m square) under controlled conditions to assess nonwe tting phase fracture retention capacity. Testing was performed using two ro ck samples containing a single fracture in each, one fractured along a bedd ing plane and the other fractured along a prominent stylolitic joint. Resid ual PCE saturation decreased from 21% of the fracture volume at horizontal to 3% at completely vertical in the bedding plane fracture and decreased fr om 27% to 10% of the fracture volume under the same conditions in the stylo litic fracture. A portion of the retained residual was removed by waterfloo ding the fractures. The PCE retention capacity of both fractures exhibited a strong correlation with combined capillary and Bond number (N-C + k(rW)N( B)) provided that initial residual saturation (S-NWr*) was defined in the a bsence of both buoyant and viscous forces. Residual PCE saturation decrease d as the magnitude of N-C + k(rW)N(B) increased; however, even at N-C + k(r W)N(B) values approaching 10(-2), all residual PCE was not completely remov ed from the fractures.