Abstract: A method for selectively reducing the permeability of one or more relatively permeable geological layers of an oil-bearing formation, to inhibit breakthrough of driving fluid from a driving fluid injection well via at least one of said layers into an oil production well, which method comprises the steps of injecting a driving fluid comprising a first compound into the formation via the injection well; detecting the first compound in well fluid of the oil production well; upon detection, injecting a second compound into the formation via the oil production well, to react with the first compound in order to provide a flow restriction generated by a third compound which comprises a reaction product of the first and second compounds in at least one relatively permeable geological layer through which breakthrough of the driving fluid into the oil production well has occurred.

Abstract: A method of injecting a stream of treatment fluid into an earth formation in the course of drilling a borehole into the earth formation, using an assembly having a drill string provided with at least one sealing means arranged to selectively isolate a selected part of the borehole from the remainder of the borehole, the drill string further being provided with a fluid passage for the stream of treatment fluid into the selected part of the borehole, the method involving: operating the drill string, and stopping the drilling operation when a zone for which treatment is desired is arranged adjacent to the part of the selected part of the borehole; isolating the selected part of the borehole using the sealing means so as to seal the drill string relative to the borehole wall; and, pumping the stream of treatment fluid via the fluid passage into the selected part of the borehole and from there into the treatment zone.