Selective stimulation with selective water reduction

#1. Field of the Invention

#The present invention relates to a method of treating a subterranean formation. More specifically, the invention is a method for selectively acidizing a primarily oil producing zone in a formation comprised of a primarily hydrocarbon producing zone and a primarily water producing zone.

#2. Description of the Prior Art

#FIG. 1 shows an oil and water producing formation following injection of a water shut-off composition.

#FIG. 2 shows the formation of FIG. 1 following injection of a brine solution.

#FIG. 3 shows the formation of FIG. 2 following the injection of a VES fluid.

#The method of the present invention selectively increases the oil production from a water and oil bearing formation and decreases the water production from the same formation. It should be understood that oil producing zones may produce a certain amount of water or other fluid or gas. Similarly, water producing zones may produce a certain amount of oil or other fluid or gas. By providing a WSO gel that preferentially penetrates the water producing layers of the formation, in conjunction with a VES gel that is broken or degraded by contact with hydrocarbons, the water producing layers may be effectively isolated and protected prior to treatment of the formation with a reactive fluid, such as an acid.

#FIG. 1 shows a subterranean formation 10 having a wellbore 12 there through. The formation 10 comprises a plurality of layers or zones 14, 16. Particularly, the formation comprises at least one oil producing zone 14 and at least one water producing zone 16. In addition to the water and oil producing zones 14, 16 the formation may also include gas producing zones, not shown. The wellbore 12 preferably extends into or through at least one oil producing zone and one water producing zone.

#The first step of the treatment method of the present invention involves providing or pumping a water shut-off composition or gel 18 into the formation. The WSO composition 18 may be any suitable fluid or material capable of forming a thickened gel or gel-like plug or barrier in a zone of the formation. In a preferred embodiment, the WSO composition preferentially or selectively enters or penetrates the water producing zones 16. Although it is preferred that the WSO composition be placed prefentially in the water producing zones, it should be understood that a certain portion of the composition may enter or be deposited into the oil producing zones as well. The placement of the WSO gel is determined by a number of factors including the viscosity of the gel itself, the pressure in each layer, the injectivity of each layer and the injectivity ratio between oil and water layers. The WSO composition may be either organic or inorganic, but is preferably solids-free. Suitable WSO compositions include, but are not limited to: delayed inorganic precipitation systems, delayed organic precipitation systems, monomer or polymer base delayed cross-linking systems, monomer or polymer base reservoir rock absorption or coating systems, resin base delayed gelling systems, foamed gel systems and thixotropic gel systems. Where the formation is sandstone, an acid-based WSO composition is preferred. More preferably, the WSO composition will be water-based, have a viscosity of about less than about 10 cP at 100 s−1 (i.e., substantially similar to that of water) and will be acid soluble. Without limiting the foregoing, the following systems are particularly useful in the present invention: polyacrylamide-based fluid in conjunction with an organic crosslinker; polyacrylamide-based fluid in conjunction with chromium; aluminum hydroxychloride-based fluid or relative permeability modifiers, including polyacrylamide polymers, block polymers and copolymers, and terpolymers.