A method for plugging the more permeable strata of a subterranean formation of nonuniform permeability in which an aqueous solution of a gelling agent and an aqueous solution containing both a gelling agent and an alkali metal silicate are injected into the formation.
The two solutions can be injected in any order, and are separated by a slug of an inert aqueous spacer liquid. The first injected solution preferably also contains a polymer thickener. Field of the Invention. This invention relates to the plugging of the more permeable strata of subterranean formations of nonuniform permeability. More particularly, the invention relates to an improved method for forming a plug covering a substantial areal extent of the more permeable strata.
The method of this invention is especially useful in promoting more uniform fluid injection patterns, such as are desirable in the enhanced recovery of petroleum by displacement with flood water, and in achieving water shutoff in producing wells. Since only a portion of the oil contained in a petroleum reservoir can be recovered by primary methods, it has become conventional practice to employ various enhanced recovery techniques to produce additional quantities of oil not economically recoverable by primary methods.
Of the various enhanced recovery methods available, one of the most widely practiced techniques is the displacement of oil from the reservoir with a driving fluid such as flood water injected for that purpose. Normally, in carrying out the flooding process, a series of input wells spaced apart from one or more producing wells are drilled into and opened to the oil-producing strata. The injection well locations with reference to the production wells are selected to afford a desired flood pattern, the selected pattern depending in part upon field conditions, the location of existing wells, and the operator's preference.
Aqueous drive fluid, such as water, brine, or a viscous aqueous polymer solution, is forced into the input wells under pressure, and out into the surrounding oil-bearing strata towards the producing well or wells.
