Formation flow channel blocking

A method of blocking high permeability flow channels in a formation having flow channels of high permeability and having flow channels of lesser permeability extending along the formation, which comprises:

• (a) introducing an expandible blocking material in a carrier fluid into the flow channels of the formation through an injection zone;
• (b) introducing a buffer fluid into the formation through the injection zone to displace the carrier fluid and blocking material away from the injection zone to form a plug of blocking material and carrier fluid separated from the injection zone by a plug of buffer fluid, the buffer fluid being introduced to limit the degree of fingering thereof into the high permeability channels and thus provide a generally uniform interface between the two plugs;
• (c) allowing the blocking material to separate out from the carrier fluid and deposit in the channels to resist displacement by fluid flowing through the channels, the blocking material being such that it does not significantly interfere with the permeability of the channels;
• (d) introducing a quantity of an activating fluid into the channels at a sufficient rate for the activating fluid to present a sufficient velocity distribution between its velocity in the high permeability channels and its velocity in the lesser permeable channels for the activating fluid to finger into and reach the blocking material in the high permeability channels without reaching the blocking material in the lesser permeable channels, for the activating fluid to activate the blocking material which it reaches for the blocking material to expand to at least partially block the high permeability channels;
• and
• (e) controlling the quantity of activating fluid introduced into the channels to prevent the activating fluid from reaching the blocking material in the lesser permeable channels.