Bacteria-based and enzyme-based mechanisms and products for viscosity reduction breaking of viscoelastic fluids

Abstract

It has been discovered that fluids viscosified with viscoelastic surfactants (VESs) may have their viscosities reduced (gels broken) by the direct or indirect action of a biochemical agent, such as bacteria, fungi, and / or enzymes. The biochemical agent may directly attack the VES itself, or some other component in the fluid that produces a by-product that then causes viscosity reduction. The biochemical agent may disaggregate or otherwise attack the micellar structure of the VES-gelled fluid. The biochemical agent may produce an enzyme that reduces viscosity by one of these mechanisms. A single biochemical agent may operate simultaneously by two different mechanisms, such as by degrading the VES directly, as well as another component, such as a glycol, the latter mechanism in turn producing a by-product (e.g. an alcohol) that causes viscosity reduction. Alternatively, two or more different biochemical agents may be used simultaneously. In a specific, non-limiting instance, a brine fluid gelled with an amine oxide surfactant can have its viscosity broken with bacteria such as Enterobacter colacae, Pseudomonas fluorescens, Pseudomonas aeruginosa, and the like.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a divisional application of U.S. Pat. No. 7,052,091 issued May 30, 2006, which in turn claims the benefit of U.S. provisional application No. 60 / 244,804 filed Oct. 31, 2000.FIELD OF THE INVENTION [0002] The present invention relates to gelled treatment fluids used during hydrocarbon recovery operations, and more particularly relates, in one embodiment, to methods of “breaking” or reducing the viscosity of aqueous treatment fluids containing viscoelastic surfactant gelling agents used during hydrocarbon recovery operations. BACKGROUND OF THE INVENTION [0003] Hydraulic fracturing is a method of using pump rate and hydraulic pressure to fracture or crack a subterranean formation. Once the crack or cracks are made, high permeability proppant, relative to the formation permeability, is pumped into the fracture to prop open the crack. When the applied pump rates and pressures are reduced or removed from the formation, the c...

AI Technical Summary

Benefits of technology

[0012] Accordingly, it is an object of the present invention to provide a method for breaking the viscosity of aqueous treatment fluids gelled with viscoelastic surfactants (VESs).

[0018] In another embodiment, the invention involves a method for breaking viscosity of aqueous fluids gelled with viscoelastic surfactants by adding to an aqueous fluid gelled with at least one viscoelastic surfactant, at least one bacteria type in an amount effective to reduce the viscosity of the VES-gelled aqueous fluid.

Problems solved by technology

When the applied pump rates and pressures are reduced or removed from the formation, the crack or fracture cannot close or heal completely because the high permeability proppant keeps the crack open.

The development of suitable fracturing fluids is a complex art because the fluids must simultaneously meet a number of conditions.

For example, they must be stable at high temperatures and / or high pump rates and shear rates that can cause the fluids to degrade and prematurely settle out the proppant before the fracturing operation is complete.

Further, such polymers tend to leave a coating on the proppant and a filter cake of dehydrated polymer on the fracture face even after the gelled fluid is broken.

The coating and / or the filter cake may interfere with the functioning of the proppant.

Studies have also shown that “fish-eyes” and / or “microgels” present in some polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and causing formation damage.

However, it is presently unknown to use bacteria and / or enzymes to break viscosities of fluids gelled using viscoelastic surfactants.

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