Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-20
2003-06-17
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S259000, C525S263000, C524S505000, C524S824000, C524S071000
Reexamination Certificate
active
06579947
ABSTRACT:
The present invention relates to a hydraulic fracturing fluid comprising a block copolymer containing at least one water-soluble block and one hydrophobic block.
It is well known that production in petroleum, natural gas and geothermal wells can be greatly enhanced by hydraulic fracturing techniques. These techniques are known in the art and generally comprise introducing an aqueous solution of a water-soluble polymer (e.g. Guar Gum) in which “proppants” (e.g. coarse sand or sintered bauxite or synthetic ceramic materials) are suspended, through the well bore under extremely high pressures into the rock structure in which the petroleum, gas or steam is entrained. Minute fissures in the rock are thereby created and held open by the suspended particles after the liquid has drained off. The petroleum, gas or steam can then flow through the porous zone into the well. Examples of art relative to to fracturing techniques are U.S. Pat. Nos. 6,169,058, 3,974,077, and 3,888,312.
Polysaccharides, e.g. guar and guar derivatives, are the most commonly used water-soluble polymers for hydraulic fracturing. Examples of art relative to guar are U.S. Pat. Nos. 5,697,444, 5,305,837, and 5,271,466. Viscoelastic gels are formed by the chemical linking or cross-linking of the guar polymer chains. The result is a more ordered network structure which increases the effective molecular weight and thereby, the viscosity
(1)
. Surfactants and synthetic polymers have also been described in patent literature and are employed as gelling agents in fracturing fluids, when present in sufficient concentration to produce stable high viscosity viscoelastic gels. Examples of art relative to surfactants and synthetic polymers are U.S. Pat. Nos. 5,551,516, 6,013,185 6,004,466 and International Pat. WO/056497.
The viscosity stability of the various water-soluble polymer solutions, as a function of time and temperature, is crucial for successful hydraulic fracturing applications in the oil field area. They must retain sufficient suspension properties to deliver and place the proppant effectively to the targeted propagating fissure area, under typical high pressure and temperature conditions which are present down hole in the well bore. The fracturing process itself is relatively short lived, running typically from a few hours, but sometimes for a longer period in severe cases.
There are other important characteristics which must be met for a successful fracturing operation. The fracturing fluid must maintain sufficient proppant suspension and transport properties under a complex combination of rheological conditions presented by pressure, shear rate and temperature changes as the fracturing fluid is transported from the mixing stage, down through the well bore and into the propagating fractured rock fissures. It is necessary that the fluid exhibit predictable shear thinning and friction reduction properties in order the effectively transport it long distances down through the well bore at higher shear. Once in the propagating fissure area the fluid will encounter low shear under high pressure and temperature conditions. This is where its suspension properties are critical to ensure proper proppant packing within the fissure, with minimal dropout or settling of the proppant, which could cause an ineffective fracture once the pressure is released.
In addition to the Theological challenges under varying shear, pressure and temperature, the fluid is also exposed to a variety of chemical conditions which are dependent on the formation composition at the particular well site. These include pH (acidic or alkaline materials), brine (salt content), hardness (mineral content), crude oil and natural gas variations, which the fluid will contact and absorb as it travels through the propagating fracture.
The last major consideration is formation damage, once the fractured fissure has been completed and the proppant is properly placed. Great effort is made to remove as much of the gel-fluid component as possible, in order to reduce the amount of residue (polymeric or surfactant) left behind in the formation and proppant channel areas. A portion of it will naturally “leak-off” into the surrounding formation during the fracture process. This residue can reduce the effectiveness of the efficiencies gained by the fracturing process, by creating blockages in the minute porosity present in the fractured fissure face and channel. This is generally known as formation damage. It is desirable to minimize this condition in order to maximize the well production gain from the fracturing process. It is common to employ enzymatic or chemical “breakers” (example of that art: U.S. Pat. No. 5,697,444) when working with guar gels to depolymerize the polymer, which lowers the viscosity and allows a higher recovery of the fluid back through the well bore, although an amount of residual polymer is left behind. Surfactant systems most commonly known, rely on contact with the formation hydrocarbon (crude oil or liquefied gas) as a natural breaking mechanism to lower viscosity. Claims are made that this type of system leaves virtually no residue behind in the formation. The Industry generally refers to the term “permeability” to describe relative formation damage. A value of 100% return-permeability would denote that the formation permeability is equal to its original value, before exposure to a fracturing polymer or surfactant. A lower number would denote a reduction in formation permeability (formation damage) caused by polymer residue. In practice, the best traditional guar system cleanup will result in a maximum of 75% permeability, while surfactant systems claim values of 95-100%. The industry also uses the term “conductivity” to denote the relative permeability of the proppant filled fissure area, following a fracture job
One of the essential objectives of the present invention is to provide a fracturing fluid whose viscosity is stable as high temperatures as 190° C., preferably 200° C. and even higher.
Another objective of the invention is to provide a fracturing fluid with sufficient proppant suspension and transport properties.
Another objective of the invention is to provide a fracturing fluid causing no or almost no formation damage.
Another objective of the invention is to provide a fracturing fluid still efficient when exposed to a variety of chemical conditions.
These objectives and others which will appear subsequently, are attained by means of a hydraulic fracturing fluid comprising a block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature. More precisely, the invention relates to a hydraulic fracturing fluid composition comprising:
a) an aqueous liquid, and
b) a block copolymer comprising at least one block water-soluble in nature and containing hydrophobic units and at least one block predominantly hydrophobic in nature forming a viscoelastic gel in said aqueous liquid.
According to a first embodiment, the copolymer contains only a single hydrophobic block and a single water-soluble block. According to another embodiment, the copolymer contains a water-soluble block having a hydrophobic group at each end or the copolymer contains a hydrophobic block having a water-soluble group at each end.
In the description which follows, the expression “block water-soluble in nature” should be understood to mean a polymer block containing a number of hydrophilic groups sufficient to obtain a water soluble block well dissolved in water. Solubility in water of the water soluble block means a block copolymer containing such a water soluble block, when mixed with water, gives a translucent monophasic system. Usually such a translucent monophasic system is obtained from a water soluble block comprising at least 30%, preferably at least 50% by weight of hydrophilic units with respect to the totality of units of the water-soluble block. The block water-soluble in nature is therefore soluble in water. The term “unit” should be understood to mean that part of the block corresponding to a
Heitz Caroline
Joanicot Mathieu
Tillotson Robert J.
Asinovsky Olga
Rhodia Chimie
Seidleck James J.
LandOfFree
Hydraulic fracturing fluid comprising a block copolymer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic fracturing fluid comprising a block copolymer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic fracturing fluid comprising a block copolymer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3105125