PROCESS FOR HYDRAULIC FRACTURING WITH pH CONTROL

Abstract

A process for hydraulic fracturing including the steps of (a) providing a fracturing fluid by combining water, proppant, an oxidizing biocide, and a friction reducer; (b) introducing the fracturing fluid into a well; and (c) controlling the pH of the fracturing fluid to a pH of at least about 4.5.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the stimulation of the production of subterranean hydrocarbon formations or stimulation of fluid injection into subterranean formations in a hydraulic fracturing process. More particularly, the present invention relates to an improved process for hydraulic fracturing in which performance of additives, in particular, friction reducers, is enhanced.BACKGROUND OF THE INVENTION[0002]The production of oil and natural gas from an underground well (subterranean formation) can be stimulated by a technique called hydraulic fracturing in which a fracturing fluid is introduced into an oil or gas well via a conduit, such as tubing or casing, at a flow rate and a pressure to create, reopen and / or extend a fracture into the well, allowing access to the oil or gas within the formation.[0003]The fracturing fluid is typically a water based solution and may comprise components such as suspended proppants (e.g., sand, bauxite); biocides to i...

AI Technical Summary

Benefits of technology

[0024]In the hydraulic fracturing process large volumes of water are used. An advantage of the present invention is that when pH is suitably controlled, at least a portion of the water used for fracturing, which can average about 3000 gallons (11,000 liters) per minute, or more, can be flow back and produced water. Flow back water that is recovered from the fracturing operation and produced water may comprise metal salts including ferrous and ferric metal salts, hydrocarbons, and residual biocide, friction reducer and other additives. In the absence of pH control as set forth herein, the presence of metal salts in the produced water interferes with performance of the friction reducer. In certain regions, such as in the Marcellus Shale region, produced water is characterized as having a high iron content.

[0025]Proppant, which keeps an induced hydraulic fracture open during or following a fracturing treatment, is most commonly sand but can also be any other such particulate material with adequate mechanical properties to withstand closure stresses including, for example, ceramic, glass, and bauxite.

[0026]The fracturing fluid may comprise other components, including, for example, polymers, breaking agents, scale inhibitors, corrosion inhibitors, etc. These other components may be added to the biocide or to the water, or still other options for adding are available.

[0027]The process of this invention comprises providing a fracturing fluid by combining water, proppant, an oxidizing biocide, and a friction reducer. This combining step may be in a single step or multiple steps.

[0028]For example, the water may be treated with the biocide and with other components such as a scale inhibitor and a corrosion inhibitor prior to combining the treated mixture with proppant and the friction reducer. The biocide treated water may be stored, for example for periods of time of about 30 minutes or less prior to combining with friction reducer. The water used may consist of all fresh water, usually from a local stream, pond, or potable water supply, or a mixture of fresh water and produced water. The fresh and produced water may be supplied to treatment manifold in a single stream or in multiple streams.

[0029]“Frac tanks” are often used as a source of water to supply a constant flow of water to the fracturing process. Water may be supplied to a blending / mixing device, such as a ribbon mixer into which friction reducer, proppant and biocide or biocide mixture are added to produce the fracturing fluid.

Problems solved by technology

Problems have been encountered in the performance of organic polymer friction reducers such as anionic polyacrylamide polymers (either hydrolyzed to produce acid functionality or copolymerized with acrylic acid).

It has been theorized that use of oxidizing biocides in combination with these polymers causes the polymers to degrade and therefore increasing pumping pressure is necessary during the fracturing operations.

However, many non-oxidizing biocides are not acceptable due to environmental concerns and low efficacy.

At low pH, protonation of the polyacrylamide friction reducers can inhibit its ability to hydrate and unwind rapidly, thus, reducing its friction-reducing ability.

Because of the shortage of fresh water and the cost of treatment and / or disposal of produced water it is desirable to re-use at least a portion of the produced water in subsequent hydraulic fracturing treatments; however, the presence of contaminants, which include oxidizable, acid-producing metal ions, such as soluble Fe2+ and Mn2+, also negatively affects performance of the friction reducers.

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