Earth boring – well treating – and oil field chemistry – Well treating
Reexamination Certificate
2000-10-13
2003-09-02
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
C507S100000, C507S103000, C507S203000, C507S902000, C507S922000, C507S925000, C507S933000, C507S939000, C166S300000, C166S305100, C166S308400
Reexamination Certificate
active
06613720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of hydrocarbon production from hydrocarbon-bearing formations. More particularly, it concerns fluid compositions that can be useful in improving hydrocarbon production and methods of introducing such fluid compositions into a hydrocarbon-bearing formation.
2. Description of Related Art
Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geologic formation (e.g., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation. This provides a partial flowpath for the oil to reach the surface. In order for oil to be “produced,” that is travel from the formation to the well bore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the well bore. Unobstructed flow through the formation rock (e.g., sandstone, carbonates) is possible when rock pores of sufficient size and number are present for the oil to move through the formation.
A common reason for a decline in oil production is “damage” to the formation that plugs the rock pores and impedes the flow of oil. Often such damage is a result of methods and chemicals used in establishing the well or in remedial operations performed on it. Another reason for lower than expected production is that the formation is naturally “tight” (e.g., a low permeability formation), with pores sufficiently small that the oil migrates toward the well bore only very slowly.
In general, techniques used to increase the permeability of the formation are referred to as “stimulation.” Essentially, one can perform a stimulation technique by: (1) injecting chemicals into the well bore to react with and/or dissolve damage; (2) injecting chemicals through the well bore and into the formation to react with and/or dissolve small portions of the formation to create alternative flowpaths for the hydrocarbon (thus rather than removing the damage, redirecting the migrating oil around the damage); or (3) injecting chemicals through the well bore and into the formation at pressures sufficient to fracture the formation, thereby creating a channel through which hydrocarbon can more readily flow from the formation and into the well bore.
Acids or acid-based fluids, and fluids containing strong chelants have been found to be useful both for the removal of damage and the creation of alternative flowpaths due to their ability to dissolve certain formation minerals and/or certain contaminants introduced into the well bore and formation during drilling or subsequent operations. The most common agents used in acid treatments of wells are mineral acids, though organic acids are also used. Hydrochloric acid is the preferred acid treatment in carbonate formations. For sandstone formations, the preferred fluid is a hydrochloric/hydrofluoric acid mixture. When the treatment is designed to remove damage resulting from a drilling mud filter cake, it is important to moderate the reaction of the fluid with the filter cake. When a strong acid is delivered in a low-viscosity fluid, often the action of removing the low permeability filter cake is localized, and much of the remainder of the acid is lost to the formation without further removal of the filter cake across the damaged zone. Often drilling mud is designed with a combination of polymers and dissolvable minerals, such as calcium carbonate. An emulsion formulated with an internal acid or internal strong chelant can be used to remove the mineral on a moderated basis by slow release. Dissolution of the mineral compromises cake strength making it more easily removed by production pressures. Acids are also utilized in the process called “acid fracturing” for improving permeability in carbonate reservoirs through an etching technique.
At present, such acid-based and chelant-based treatments have several serious limitations: lack of uniform radial and axial (along the wellbore) coverage; corrosion of the pumping equipment and well bore tubing; and reaction rates at higher temperatures that are too rapid. An improved well stimulation fluid that has a moderated reactivity and that is less damaging to equipment is a highly desirable goal.
Hydraulic fracturing involves literally breaking or fracturing a portion of the surrounding strata, by injecting a specialized fluid into the well bore directed at the face of the geologic formation at pressures sufficient to initiate and extend a fracture in the formation. Actually, what is created by this process is not always a single fracture, but a fracture zone, that is, a zone in the formation having multiple fractures, through which hydrocarbon can more easily flow to the well bore.
Certain commonly used fracturing treatments generally comprise at least three principal components: a carrier fluid (usually water or brine), a polymer, and a proppant. Many further comprise a crosslinker. Other compositions used as fracturing fluids include water with additives, viscoelastic surfactant gels, and gelled oils. The purpose of these fracturing fluids is to first create and extend a fracture, and then once it is opened sufficiently, to deliver proppant into the fracture, which keeps the fracture from closing once the pumping operation is completed. The carrier fluid is the means by which proppant and breaker are carried into the formation. A typical fracturing fluid can be prepared by blending a polymer with an aqueous solution (sometimes an oil-based or a multi-phase fluid is desirable); often, the polymer is a solvatable polysaccharide. The purpose of the polymer is to increase the viscosity of the fracturing fluid which aids in the creation.of a fracture; and to thicken the aqueous solution so that solid particles of proppant can be suspended in the solution for delivery into the fracture. In many fracturing treatments, a crosslinking agent is added which further increases the viscosity of the fluid composition by crosslinking the polymer.
In addition to being useful in fracturing, fluids that comprise a polymer and crosslinker can also be useful in the workover of a hydrocarbon producing well to improve production. Such workover fluids (e.g., those used in conformance control and zone abandonment operations, among others) with increased viscosity through polymer crosslinking, especially those that become a gel after crosslinking, are useful for isolating particular zones for subsequent treatment by acids, scale removers, or asphaltene diluents, among others. After the treatment, a gel formed by the workover fluid can be intentionally degraded to remove the barrier. In other cases, the gel permanently plugs the zone.
A chemical or biological agent (e.g., crosslinked polymer, acid, or biocide, among others) that is a useful component of a stimulation or workover fluid can, in certain cases, be neutralized or degraded before reaching the site at which it is to have its effect. Therefore, in certain instances, more of the agent is used in order to be effective and to compensate for agent that is lost in delivering the agent to the site. Thus, there is a need for a more efficient way to deliver useful chemical and biological agents to a desired location in a well.
SUMMARY OF THE INVENTION
The present invention is directed to fluid compositions that can be used in improving hydrocarbon production and methods of introducing such fluid compositions into a hydrocarbon-bearing formation. The invention relates to delaying the action of at least one chemical or biological agent that is sequestered in the discontinuous phase of an emulsion. Upon exposure to one or more destabilizing conditions, the emulsion is disrupted, releasing the sequestered chemical or biological agent into the bulk fluid of the composition, permitting the agent to have its desired effect.
One embodiment is a method of delivering a well treatment fluid composition into a hydrocarbon-bearing formation. In this method, a well treatment fluid that comprises a surfactant stabilized emulsion is pumped into a well. The emulsion comprises a continuous phas
Dismuke Keith
Feraud Jean Pierre
Hutchins Richard D.
McConnell Stanley Bruce
Nelson Erik B.
Jeffery Brigitte
Menes Catherine
Ryberg John J.
Schlumberger Technology Corporation
Tucker Philip
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