Temporarily plugging a subterranean reservoir with a self-foaming aqueous solution

A process for treating a subterranean reservoir into which a well is completed comprising:

• compounding an aqueous solution in which the solutes consist essentially of at least one each of (a) a reactive compound for generating nitrogen gas at a rate affected by the temperature and pH of the solution, (b) a surface-active compound for causing the solution to be converted to a relatively immobile foam as gas is generated within the solution, (c) a pH-controlling system for initially maintaining a relatively high pH at which the gas-generating reaction rate is relatively slow at temperatures less than the reservoir temperature and subsequently maintaining a barely acidic pH at which that reaction rate is only moderately fast at temperatures near the reservoir temperature and, (d) a relatively slowly reactive acid-yielding compound for relatively slowly reducing the solution pH from said relatively high value to said barely acidic value;
• and,
• injecting the compounded solution into the reservoir at a rate such that (a) a significant portion of injected solution flows into at least the largest pores or other openings in or along the reservoir rock before that portion of solution has generated a significant fraction of the amount of gas it is capable of generating and (b) said portion of injected solution remains within said openings until it becomes converted into a relatively immobile foam.