Pore pressure variation at constant confining stress on water-oil and silica nanofluid-oil relative permeability

摘要

Studies on stress sensitivity of relative permeability in the laboratory were mostly carried out by varying overburden pressure at constant pore pressure(PP).However,in a real oilfield situation,changes in net stress are induced by changes in PP rather than overburden pressure.This research presents the effect of PP variation at a confining stress of 25 MPa on water-oil and silica nanofluid-oil relative permeability curves.Results showed that,at low PP variations of 0.1,2,and 5 MPa,two-phase flow parameters exhibited distinct trends.Thus,for water-oil relative permeability,initial water(S_(wi))and residual oil(S_(or))saturations both decreased as PP increased.End-point oil K_(ro)(S_(wi))and water K_(rw)(S_(or))relative permeabilities both increased for water flooding.Similar trends were observed for nanofluid flooding.End-point mobility ratio and displacement efficiency both increased with increase in PP within this range for water and nanofluid flooding.At 10 MPa PP,S_(wi)decreased compared to low PP variations,while S_(or)increased significantly.Similar observation was made for nanofluid flooding except for S_(or)which had moderate increment.End-point mobility ratio increased significantly for water flooding,but had a slight increase for nanofluid flooding compared to low PP variations.Displacement efficiency decreased for both water and nanofluid flooding compared to low PP variations.At the same PP,water-oil and nanofluid-oil relative permeabilities showed similar S_(wi)and K_(ro)(S_(wi))but differing S_(or)and K_(rw)(S_(or)).The findings provide insights into the effect PP variation on relative permeability and would be important in flooding design considerations.