Nonwetting phase retention and mobilization in rock fractures

Abstract

Perchloroethylene (PCE) was injected into fractured lime-stone samples (approximately 0.3 m x 0.3 m square) under controlled conditions to assess nonwetting phase fracture retention capacity. Testing was performed using two rock samples containing a single fracture in each, one fractured along a bedding plane and the other fractured along a prominent stylolitic joint. Residual PCE saturation decreased from 21% of the fracture volume at horizontal to 3% at completely vertical in the bedding plane fracture and decreased from 27% to 10% of the fracture volume under the same conditions in the stylolitic fracture. A portion of the retained residual was removed by waterflooding 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 absence of both buoyant and viscous forces. Residual PCE saturation decreased as the magnitude of N(C) + k(rW)N(B) increased; however, even at N(C) + k(rW)N(B) values approaching 10-2, all residual PCE was not completely removed from the fractures.