METHOD FOR REVERSE CEMENTING OF CASING IN WELL Russian patent published in 1996 - IPC

FIELD: mining, particular, cementing of casings in wells. SUBSTANCE: method for reverse cementing of casing in well includes shutting off of wellhead, injection of grouting mortar into casing string-borehole annulus and forcing of drilling mud present in borehole; and in the wake of it, grouting mortar is forced into highly permeable formations. The value of excessive pressure at the wellhead in casing string-borehole annulus is determined from empirical relation. In so doing, injection of grouting mortar to these formations is continued to build up the pressure Pk at the wellhead determined from the expression Pk=0.3 Phs, where Phs is hydrostatic pressure produced by column of grouting mortar in casing string-borehole annulus exerted on highly permeable formations, MPa, with flow rate of grouting mortar equalling 0.003 cu.m/s. After it, casing string-borehole annulus at wellhead is temporary opened until grouting mortar reaches the end of casing string. EFFECT: higher quality of cementing in the presence of highly permeable formations with different characteristics due to provision of full replacement of drilling mud with grouting mortar; excluded dilution of grouting mortar with formation fluids during its injection into casing string-borehole annulus and provision of design height of grouting mortar in casing string-borehole annulus.