Methods of treating subterranean formations using low-molecular-weight fluids

Abstract

The present invention relates to systems and methods useful in subterranean treatment operations. More particularly, the present invention relates to systems and methods for treating subterranean formations using low-molecular-weight fluids. Examples of methods of the present invention include methods of treating a subterranean formation intersected by a wellbore; methods of enhancing production from multiple subterranean formations penetrated by a well bore during a single trip through the well bore; methods of enhancing production, in real time, from multiple subterranean formations penetrated by a well bore during a single trip through the well bore; and methods of reducing the cost of enhancing production from multiple formations penetrated by a well bore by stimulating multiple formations, on a single trip through the well bore, with a fluid that minimizes damage to the formation.

Description

BACKGROUND OF THE INVENTION TECHNOLOGY [0001] The present invention relates to systems and methods useful in subterranean treatment operations. More particularly, the present invention relates to systems and methods for treating subterranean formations using low-molecular weight treatment fluids. [0002] Hydrocarbon-bearing subterranean formations penetrated by well bores often may be treated to increase their permeability or conductivity, and thereby facilitate greater hydrocarbon production therefrom. One such production stimulation treatment, known as “fracturing,” involves injecting a treatment fluid (e.g., a “fracturing fluid”) into a subterranean formation or zone at a rate and pressure sufficient to create or enhance at least one fracture therein. Fracturing fluids commonly comprise a proppant material (e.g., sand, or other particulate material) suspended within the fracturing fluid, which may be deposited into the created fractures. The proppant material functions, inter alia...

AI Technical Summary

Benefits of technology

[0011] Another example of a method of the present invention is a method of reducing the cost of enhancing production from multiple formations penetrated by a well bore by stimulating multiple formations, on a single trip through the well bore, with a fluid that minimizes damage to the formation comprising: lowering a work string having a first packer apparatus connected to a lower end of the work string to a desired location in the wellbore, the work string being communicated with the wellbore through a longitudinal opening defined by the first packer apparatus, the first packer apparatus comprising: a packer mandrel; and an expandable packer element disposed about the packer mandrel; compressing the expandable packer element by lowering the packer mandrel relative to the expandable packer element thereby expanding the packer element outward to engage and seal a casing in the wellbore below the formation, wherein the compressing step seals the longitudinal opening to prevent communication therethrough; displacing a low-molecular-weight fluid down the work string and into the wellbore through a flow port defined in the work string above the first packer apparatus, so as to create or enhance at least one fracture in the subterranean formation, the low-molecular-weight fluid having the capability of enhancing the regain permeability of the formation; unsealing the longitudinal opening after the displacing step to communicate a portion of the wellbore above the expandable packer element with a portion of the wellbore below the expandable packer element through the longitudinal opening to equalize a pressure in the wellbore above and below the expandable packer element; disengaging the expandable packer element from the casing; and moving the packer apparatus to another formation in the well bore and repeating the step of displacing a low-molecular-weight fluid down the work string and into the wellbore to create or extend at least one fracture in the formation.

[0012] Another example of a method of the present invention is a method of enhancing production, in real time, from multiple subterranean formations penetrated by a well bore during a single trip through the well bore, comprising: lowering a work string having a first packer apparatus connected to a lower end of the work string to a desired location in the wellbore, the work string being communicated with the wellbore through a longitudinal opening defined by the first packer apparatus, the first packer apparatus comprising: a packer mandrel; and an expandable packer element disposed about the packer mandrel; compressing the expandable packer element by lowering the packer mandrel relative to the expandable packer element thereby expanding the packer element outward to engage and seal a casing in the wellbore below the formation, wherein the compressing step seals the longitudinal opening to prevent communication therethrough; displacing a low-molecular-weight fluid down the work string and into the wellbore through a flow port defined in the work string above the first packer apparatus, so as to create or extend at least one fracture in the subterranean formation, the low-molecular-weight fluid having the capability of enhancing the regain permeability of the formation; unsealing the longitudinal opening after the displacing step to communicate a portion of the wellbore above the expandable packer element with a portion of the wellbore below the expandable packer element through the longitudinal opening to equalize a pressure in the wellbore above and below the expandable packer element; determining, in real time, at least one parameter related to the creation or enhancement of the at least one fracture; disengaging the expandable packer element from the casing; and moving the packer apparatus to another formation adjacent the well and repeating the step of displacing a low-molecular-weight fluid down the work string and into the wellbore to create or extend at least one fracture in the formation.

[0013] Yet another method of the present invention is a method of enhancing production from multiple subterranean formations penetrated by a well bore during a single trip through the well bore, comprising: lowering a work string having a first packer apparatus connected to a lower end of the work string to a desired location in the wellbore, the work string being communicated with the wellbore through a longitudinal opening defined by the first packer apparatus, the first packer apparatus comprising: a packer mandrel; and an expandable packer element disposed about the packer mandrel; compressing the expandable packer element by lowering the packer mandrel relative to the expandable packer element thereby expanding the packer element outward to engage and seal a casing in the wellbore below the formation, wherein the compressing step seals the longitudinal opening to prevent communication therethrough; displacing a low-molecular-weight fluid down the work string and into the wellbore through a flow port defined in the work string above the first packer apparatus, so as to create or extend at least one fracture in the subterranean formation, the low-molecular-weight fluid having the capability of enhancing the regain permeability of the formation; unsealing the longitudinal opening after the displacing step to communicate a portion of the wellbore above the expandable packer element with a portion of the wellbore below the expandable packer element through the longitudinal opening to equalize a pressure in the wellbore above and below the expandable packer element; disengaging the expandable packer element from the casing; and moving the packer apparatus to another formation adjacent the well and repeating the step of displacing a low-molecular-weight fluid down the work string and into the wellbore to create or extend at least one fracture in the formation.

Problems solved by technology

While the use of gelled and crosslinked polysaccharide-containing fracturing fluids has been successful, such fracturing fluids often have not been thermally stable at temperatures above about 200° F. That is, the viscosity of the highly viscous gelled and crosslinked fluids may decrease over time at high temperatures.

To offset the decreased viscosity, the concentration of the viscosifier often may be increased, which may result in, inter alia, increased costs and increased friction pressure in the tubing through which the fracturing fluid is injected into a subterranean formation.

This may increase the difficulty of pumping the fracturing fluids.

However, the use of thermal stabilizers also may increase the cost of the fracturing fluids.

Certain types of subterranean formations, such as certain types of shales and coals, may respond unfavorably to fracturing with conventional fracturing fluids.

For example, in addition to opening a main, dominant fracture, the fracturing fluid may further invade numerous natural fractures (or “butts” and “cleats,” where the formation comprises coal) that may intersect the main fracture, which may cause conventional viscosifiers within the fracturing fluid to invade intersecting natural fractures.

When the natural fractures re-close at the conclusion of the fracturing operation, the conventional viscosifiers may become trapped therein, and may obstruct the flow of hydrocarbons from the natural fractures to the main fracture.

This may be problematic, inter alia, where the production of hydrocarbons from the subterranean formation involves processes such as desorption of the hydrocarbon from the surface of the formation.

However, this may be problematic, inter alia, because such fluids may prematurely dilate natural fractures perpendicular to the main fracture a problem often referred to as “near well bore fracture complexity,” or “near well bore tortuosity.” This may be problematic because the creation of multiple fractures, as opposed to one or a few dominant fractures, may result in reduced penetration into the formation, e.g., for a given injection rate, many short fractures may be created rather than one, or a few, lengthy fracture(s).

This may be problematic because in low permeability formations, the driving factor to increase productivity often is the fracture length.

Furthermore, the use of less viscous fracturing fluids also may require excessive fluid volumes, and / or excessive injection pressure.

Excessive injection pressure may frustrate attempts to place proppant into the fracture, thereby reducing the likelihood that the fracturing operation will increase hydrocarbon production.

There are a number of difficulties associated with the present methods of isolating formations utilizing packers lowered into a wellbore on coiled tubing.

There are some difficulties associated with such a method, including leak-off and compression, and safety concerns because of the gasified fluids communicated to the surface.

It is also sometimes necessary to reverse-circulate fluids to reduce the differential pressure used to set the cup packers.

There are environments, however, where it is difficult to reverse-circulate.

Although some opposing cup tools have a bypass which will allow the pressure above and below the tools to equalize, the bypasses cannot handle environments wherein fluids have a high solids content.

Compression packers utilized on coiled tubing to isolate a section of a wellbore typically have a solid bottom such that communication with the wellbore through the lower end of the packer is not possible and the only way to equalize pressure and unset the packer is by flowing the well or by pressurizing the wellbore.

This presents many of the same problems associated with a dual cup packer system.

If the tools are moved when differential pressure exists, damage may occur and such operations can be time-consuming and costly.

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