Methods for making and using retarded acid compositions for well stimulation

Abstract

Described herein are methods for treating a subterranean formation penetrated by a wellbore with a retarded acidizing fluid containing an acid and an acid retarding agent, the concentrations of which are adjusted based on measured parameter values of the formation. Also described is a method for treating a subterranean formation by introducing an acid to the formation following the introduction of an acid retarding agent to the formation. Also described is a method for acid fracturing a subterranean formation including reducing the concentration of an acid retarding agent contained in a retarded acidizing fluid over the course of the acid fracturing operation.

What is claimed is: 
     
         1 . A method of treating a subterranean formation penetrated by a wellbore, the method comprising:
 a. measuring at least one parameter of the subterranean formation resulting in at least one parameter value;   b. forming a retarded acidizing fluid comprising an acid, and an acid retarding agent (RA) comprising at least one salt compound, by adjusting the concentrations of the acid and RA based on the at least one parameter value; and   c. contacting the subterranean formation with the retarded acidizing fluid at a pressure less than the fracture initiation pressure of the subterranean formation to treat the subterranean formation.   
     
     
         2 . The method of  claim 1  wherein a desired acid reactivity for the composition is determined based on the value of the at least one parameter; and wherein the concentrations of the acid and RA are adjusted in order to provide the desired acid reactivity. 
     
     
         3 . The method of  claim 1  wherein the at least one parameter is selected from the group consisting of temperature, pressure, calcite concentration, dolomite concentration, Mg concentration, formation fluid viscosity, formation capillary pressure, and combinations thereof. 
     
     
         4 . The method of  claim 2  wherein the subterranean formation comprises at least two sections, and wherein the at least one parameter is measured for at least one of the sections. 
     
     
         5 . The method of  claim 2  wherein the at least one parameter is measured at one or more points in time during the contacting of the composition with the subterranean formation resulting in at least one dynamic parameter value, and wherein the concentrations of the acid and RA of the composition are adjusted based on the at least one dynamic parameter value in order to provide the desired acid reactivity. 
     
     
         6 . The method of  claim 1  wherein the acid is one or more of hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen fluoride, sulfuric acid, nitric acid, phosphoric acid alkanesulfonic acids, arylsulfonic acids, acetic acid, formic acid, alkyl carboxylic acids, acrylic acid, lactic acid, glycolic acid, malonic acid, furnaric acid, citric acid and tartaric acid. 
     
     
         7 . The method of  claim 1  wherein the retarded acidizing fluid further comprises a surfactant, and wherein the salt compound comprises one or more cations selected from lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, mercury, boron, aluminum, gallium, indium, thallium, tin, ammonium, alkylammonium, dialkylammonium, trialkylammonium and tetraalkylammonium, and one or more anions selected from fluoride, chloride, bromide, iodide, sulfate, bisulfate, sulfite, bisulfite nitrate, alkanesulfonates, arylsulfonates, acetate and formate. 
     
     
         8 . The method of  claim 1  wherein the composition is formed by combining an acid-containing composition with a RA-containing composition within the subterranean formation. 
     
     
         9 . The method of  claim 8  wherein either or both of the acid-containing and RA-containing compositions are introduced to the subterranean formation prior to combination by a coiled tubing system. 
     
     
         10 . The method of  claim 8  wherein the RA-containing composition is introduced to the subterranean formation between separate introductions of the acid-containing composition into the subterranean formation, and wherein the acid-containing composition is combined with the RA-containing composition to form a first stage composition within the subterranean formation. 
     
     
         11 . The method of  claim 10  wherein the introductions of the RA-containing and acid-containing compositions are repeated at least n times to form subsequent (n+1)th stage compositions, and wherein n=1 through 10. 
     
     
         12 . The method of  claim 11  wherein the subterranean formation comprises first through nth number of sections, corresponding to the first through nth stage compositions. 
     
     
         13 . The method of  claim 12  wherein the at least one parameter value is measured for each of the first through nth sections, wherein desired acid reactivities are determined for the first through nth stage compositions based on the at least one parameter values measured for each of the first through nth sections; arid wherein the concentrations of the acid and RA are adjusted for each of the first through nth stage compositions in order to provide the desired acid reactivities. 
     
     
         14 . A method of treating a subterranean formation penetrated by a wellbore, the method comprising:
 a. introducing a first composition comprising an acid retarding agent (RA) to the subterranean formation at a pressure less than the fracture initiation pressure of the subterranean formation; and   b. following introduction of the first composition, introducing a second composition comprising an acid to the subterranean formation at a pressure less than the fracture initiation pressure of the subterranean formation to treat the formation.   
     
     
         15 . The method of  claim 14  wherein the RA comprises a salt compound. 
     
     
         16 . A method of treating a subterranean formation penetrated by a wellbore, the method comprising:
 a. utilizing a composition comprising an acid, a surfactant, and an acid retarding agent (RA) comprising at least one salt compound;   b. contacting the formation with the composition over a period of time at a pressure higher than the fracture initiation pressure of the subterranean formation to fracture and treat the formation; and   c. reducing the concentration of the RA relative to the acid in the composition during the period of time from an initial RA concentration to a final RA concentration lower than the initial RA concentration.   
     
     
         17 . The method of  claim 16  wherein at least one parameter of the subterranean formation is measured resulting in at least one parameter value, at least one desired acid reactivity for the composition is determined based on the value of the at least one parameter; and wherein the reduction of the concentration of the RA relative to the acid in the composition during the period of time is based on the at least one desired acid reactivity. 
     
     
         18 . The method of  claim 17  wherein the at least one parameter is selected from the group consisting of temperature, pressure, calcite concentration, dolomite concentration, Mg concentration, and combinations thereof. 
     
     
         19 . The method of  claim 17  wherein the at least one parameter is measured at one or more points in time during the contacting of the composition with the subterranean formation resulting in at least one dynamic parameter value, and wherein the concentrations of the acid and RA of the composition are adjusted based on the at least one dynamic parameter value in order to provide the desired acid reactivity. 
     
     
         20 . The method of  claim 16  wherein the composition is formed by combining an acid-containing composition with a RA-containing composition within the subterranean formation.