The use of a hydrophobically modified water soluble polymer is described capable of being chemically cross-linked so as to produce a stable gel for blocking a water-bearing formation from a hydrocarbon-producing well. The polymer is essentially linear having hydrophilic side groups located at random positions along its backbone.

This invention relates to a method of treating oil- and water-bearing formations to stimulate the production of oil while simultaneously retarding the production of water-producing passages by employing a composition comprising a solution of an acid salt of a fatty amine containing, when necessary, a wetting agent to allow the solution to be pumped with ease into the formation. The compositions, which are generally dissolved in an organic solvent such as a hydrocarbon solvent to facilitate easy handling, are employed as preflush compositions to plug water-bearing passages while leaving oil-bearing passages open. Thereupon an acid solution is pumped into the formation to selectively acidize and stimulate the oil-bearing passages.

In well treatments such as workovers, fracturing processes, etc., permeable subterranean earth formations are temporarily plugged by contacting them with self thickening-and-thinning liquid systems. The systems initially contain unhydrated cellulose ether dispersed in aqueous liquid solutions of buffering agents, pH-increasing reactants and pH-decreasing reactants. The system components are arranged so that the cellulose ether hydration is first delayed by a buffer-maintained acidity, then is accelerated by an increasing pH and, subsequently, the high viscosity due to the dissolved hydrated cellulose ether is reduced by an acid-induced hydrolysis of the ether.

A method to reduce water influx into a producing well is described comprising the steps of pumping a chemical composition into a production interval and into surrounding formation; said composition being capable of forming, firstly, a physically stabilized structure and, secondly, a chemically stabilized structure, wherein said physically stabilized structure being dissolvable by hydrocarbon containing fluids; letting said composition form said physically stabilized structure within the formation surrounding said production interval; changing pressure condition in said production interval such that the fluid flow within the surrounding formation is reversed; letting thereby in some portions of the formation hydrocarbon containing fluids dissolve said physically stabilized structure and chemically stabilize said structure in the remaining portions by a cross-linking reaction. The time constants of the two stabilizing reactions are selected such that the physical stabilization is essentially completed before the pumping direction is reversed and the chemical stabilization is essentially completed after the pump-out/cleaning operation.

A method of reducing the water produced from a subterranean formation penetrated by a wellbore without appreciably reducing the oil produced therefrom is provided. In accordance with the method, the formation is contacted with a hydrocarbon treating solution having dissolved therein a surface active agent comprosed of one or more fatty acid imidazolyl compounds.