Method of Heterogeneous Etching of Sandstone Formations

Abstract

The invention provides a method of treating a sandstone-containing subterranean formation penetrated by a wellbore. The method is carried out by forming a slurry of a carrier fluid containing a viscosifying agent and encapsulated particles of a hydrogen fluoride source without settling of the particles. The carrier fluid may be an acid-based carrier fluid. The encapsulated hydrogen fluoride source may be encapsulated with a solid polymer acid precursor. The hydrogen fluoride source is present within the slurry in an amount of about 10% or more by weight of the slurry. The slurry is introduced into the wellbore at a pressure above the fracture pressure of the formation under conditions wherein the hydrogen fluoride source is released.

1 . A method of treating a sandstone-containing subterranean formation penetrated by a wellbore comprising:
 forming a slurry of a carrier fluid containing a viscosifying agent and encapsulated particles of a hydrogen fluoride source, the encapsulated hydrogen fluoride source being dispersed within the slurry without settling of the particles and to provide heterogeneous placement of the particles, the hydrogen fluoride source being present in the slurry in an amount of about 10% to about 60% by weight of the slurry; and   introducing the slurry into the wellbore at a pressure above the fracture pressure of the formation under conditions wherein the hydrogen fluoride source is released in a portion of the formation containing sandstone.   
   
   
       2 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is encapsulated within a polylactic acid solid polymer acid precursor.   
   
   
       3 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is encapsulated within a solid polymer acid precursor comprising at least one of homopolymers of lactic acid, glycolic acid, hydroxybutyrate, and hydroxyvalerate, random copolymers of at least two of lactic acid, glycolic acid, hydroxybutyrate, hydroxyvalerate, L-serine, L-threonine, L-tyrosine, block copolymers of at least two of polyglycolic acid, polylactic acid, hydroxybutyrate, hydroxyvalerate, L-serine, L-threonine, L-tyrosine, homopolymers of ethylenetherephthalate (PET), butylenetherephthalate (PBT) and ethylenenaphthalate (PEN), random copolymers of at least two of ethylenetherephthalate, butylenetherephthalate and ethylenenaphthalate, block copolymers of at least two of ethylenetherephthalate, butylenetherephthalate, ethylenenaphthalate and combinations of these.   
   
   
       4 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is encapsulated within at least one of acrylics, halocarbon, polyvinyl alcohol, aqueous dispersions, hydrocarbon resins, polyvinyl chloride, enteric coatings, hydroxypropyl cellulose (HPC), polyvinylacetate phthalate, hydroxypropyl methyl cellulose (HPMC), polyvinylidene chloride, hydroxylpropyl methyl cellulose phthalate (HPMCP), proteins, fluoroplastics, rubber (natural or synthetic), caseinates, maltodextrins, shellac, chlorinated rubber, silicone, polyvinyl acetate phtalate coatings, microcrystalline wax, starches, coating butters, milk solids, stearines, polyvinyl dichloride latex, molasses, sucrose, dextrins, nylon, surfactants, combined polymer/plasticizer coating systems, a combination of film-forming polymer/plasticizer/stabilizers, enterics, paraffin wax, fluorocarbons, polymethacrylates, phenolics, waxes, ethoxylated vinyl alcohol, vinyl alcohol copolymer, polylactides, zein, fats, polyamino acids, fatty acids, polyethylene gelatin, polyethylene glycol, glycerides, polyvinyl acetate, vegetable gums and polyvinyl pyrrolidone.   
   
   
       5 . The method of  claim 1 , wherein:
 the encapsulating material makes up from about 0.1% to about 30% by weight of the slurry.   
   
   
       6 . The method of  claim 1 , wherein:
 the carrier fluid is an acid-based fluid.   
   
   
       7 . The method of  claim 6 , wherein:
 the carrier fluid includes hydrochloric acid, nitric acid, hydroiodic acid, hydrobromic acid, sulfuric acid, sulfamic acid, phosphoric acid, formic acid, acetic acid, halogenated derivatives of acetic acid, citric acid, propionic acid, tartaric acid, lactic acid, glycolic acid, aminopolycarboxylic acids, sulfamic acid, malic acid, maleic acid, methylsulfamic acid, chloroacetic acid, 3-hydroxypropionic acid, polyaminopolycarboxylic acid, bisulfate salts and combinations of these.   
   
   
       8 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is selected from ammonium fluoride, ammonium bifluoride, fluoroboric acid, hexafluorophosphoric acid, difluorophosphoric acid, fluorosulfonic acid, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, sodium tetrafluoroborate, ammonium tetrafluoroborate, salts of hexafluoroantimony, polytetrafluoroethylene polymers, and combinations of these.   
   
   
       9 . The method of  claim 1 , wherein:
 the encapsulated particles have a particle size of from about 0.1 mm to about 2 mm.   
   
   
       10 . The method of  claim 1 , wherein:
 the hydrogen fluoride source makes up from about 50% to 99% by weight of the encapsulated particles.   
   
   
       11 . The method of  claim 1 , wherein:
 the pressure is maintained above the fracture pressure for a period of from one hour or more after the slurry is introduced into the well.   
   
   
       12 . The method of  claim 1 , wherein:
 the treatment results in an increased production of fluids from the wellbore.   
   
   
       13 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is present in the slurry in an amount of from about 10% to about 50% by weight of the slurry.   
   
   
       14 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is present in the slurry in an amount of from about 15% to about 50% by weight of the slurry.   
   
   
       15 . The method of  claim 1 , wherein:
 the hydrogen fluoride source is present in the slurry in an amount of from about 20% to about 45% by weight of the slurry.   
   
   
       16 . A method of treating a sandstone-containing subterranean formation penetrated by a wellbore comprising:
 forming a slurry of an acid-based carrier fluid containing a viscosifying agent and encapsulated particles of a hydrogen fluoride source, with the encapsulating material making up from about 0.1% to about 50% by weight of the encapsulated particles and wherein   the encapsulated hydrogen fluoride source is dispersed within the slurry without settling of the particles and to provide heterogeneous placement of the particles, the hydrogen fluoride source being present in the slurry in an amount of about 10% to about 60% by weight or more of the slurry; and   introducing the slurry into the wellbore under conditions wherein the hydrogen fluoride source is released in a portion of the formation containing sandstone to provide heterogeneous etching of faces of said portion of the formation.   
   
   
       17 . The method of  claim 16  wherein the slurry is introduced into the wellbore at a pressure above the fracture pressure of the formation under conditions wherein the hydrogen fluoride source is released. 
   
   
       18 . The method of  claim 16 , wherein the hydrogen fluoride source is encapsulated within a polylactic acid solid polymer acid precursor. 
   
   
       19 . A method of treating a sandstone-containing subterranean formation penetrated by a wellbore comprising:
 forming a slurry of a carrier fluid containing a viscosifying agent and particles of a hydrogen fluoride source encapsulated with a solid polymer acid precursor, the encapsulated hydrogen fluoride source being dispersed within the slurry without settling of the particles and to provide heterogeneous placement of the particles, the hydrogen fluoride source being present in the slurry in an amount of about 10% to about 60% by weight; and   introducing the slurry into the wellbore under conditions wherein the hydrogen fluoride source is released in a portion of the formation containing sandstone.   
   
   
       20 . The method of  claim 19  wherein the slurry is introduced into the wellbore at a pressure above the fracture pressure of the formation under conditions wherein the hydrogen fluoride source is released.