Methods of Controlled Release pH Adjustment for Oilwell Stimulation

Abstract

A method for treating subterranean formations by the use of delayed release pH control agents in subterranean formations during fracturing operations includes providing a fracturing fluid comprising a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material. The delayed release pH-adjusting material includes a pH-adjusting agent and a binder. The fracturing fluid is introduced into a subterranean formation, and the pH of the fracturing fluid is changed through at least partial degradation or disassociation of the delayed release pH-adjusting material, thereby allowing the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent.

Description

BACKGROUND[0001]The present invention relates to methods for treating subterranean formations. More particularly, the present invention relates to the use of delayed release pH control agents in subterranean formations during fracturing operations.[0002]Hydrocarbons (e.g., oil, natural gas, etc.) in a subterranean formation can be recovered by drilling a well into the subterranean formation. Hydrocarbons in the subterranean formation are driven into the well to be produced by, for example, pressure gradients that exist between the formation and the well, the force of gravity, displacement of the fluids using pumps or the force of another fluid injected into the well. The production of hydrocarbons is commonly increased by stimulating the subterranean formation.[0003]One stimulation technique is fracturing which involves pumping a fluid down the well at a sufficient flow rate and pressure to overcome the fracture gradient pressure and create or enhance fractures in the rocks of the s...

AI Technical Summary

Benefits of technology

[0009]In some embodiments, the present invention provides a method comprising providing a fracturing fluid comprising: a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material, the delayed release pH-adjusting material comprising a pH-adjusting agent and a binder; introducing the fracturing fluid into a subterranean formation; changing the pH of the fracturing fluid through at least partial degradation or disassociation of the delayed release pH-adjusting material; and allowing the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent.

[0010]In other embodiments, the present invention provides a method comprising providing a fracturing fluid comprising: a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material, the delayed release pH-adjusting material comprising a basic pH-adjusting agent and a binder; introducing the fracturing fluid into a subterranean formation; raising the pH of the fracturing fluid through at least partial degradation of the delayed release pH-adjusting material; and allowing the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent.

[0011]In still other embodiments, the present invention provides a method comprising providing a fracturing fluid comprising: a base fluid, a viscosifying agent, a pH sensitive crosslinking agent, and a delayed release pH-adjusting material, the delayed release pH-adjusting material comprising an acidic pH-adjusting agent and a binder; introducing the fracturing fluid into a subterranean formation; lowering the pH of the fracturing fluid through at least partial degradation or disassociation of the delayed release pH-adjusting solid material; and allowing the viscosifying agent to be crosslinked through activation of the pH sensitive crosslinking agent.

Problems solved by technology

Such a procedure requires high pumping pressures due to the high viscosity of the gelled fluid as it is pumped down the wellbore, and results in high friction losses within the bore and pipes.

In fact, the viscosity of the gel prepared on the surface might often be lower than the viscosity desired within the fracture due to limitations imposed by the pumping abilities of the equipment used.

Further, fully crosslinked fluids may suffer irreparable viscosity degradation from the high shear environment during the pumping stages.

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