Patent Publication Number: US-2011048697-A1

Title: Sonically activating settable compositions

Description:
TECHNICAL FIELD 
     This invention relates to cementing operations and, more particularly, to sonically activating settable compositions. 
     BACKGROUND 
     Some wellbores, for example, those of some oil and gas wells, are lined with a casing. The casing stabilizes the sides of the wellbore. In a cementing operation, cement is introduced down the wellbore and into an annular space between the casing and the surrounding earth. The cement secures the casing in the wellbore, and prevents fluids from flowing vertically in the annulus between the casing and the surrounding earth. Different cement formulations are designed for a variety of wellbore conditions, which may be above ambient temperature and pressure. In designing a cement formulation, a number of potential mixtures may be evaluated to determine their mechanical properties under various conditions. 
     SUMMARY 
     The present disclosure is directed to a system and method for sonically activating cement slurries. In some implementations, a composition for treating a subterranean formation includes a settable composition and an activator. The activator is released in response to a sonic signal to initiate setting of the settable composition. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an example well system for producing fluids from a production zone; 
         FIGS. 2A and 2B  are example cementing process in the well system of  FIG. 1 ; 
         FIGS. 3A and 3B  illustrate an example activation device for activating cement slurry in a wellbore; 
         FIGS. 4A and 4B  illustrate example processes for releasing activators in cement slurries; 
         FIG. 5  is a flow chart illustrating an example method for activating deposited cement slurry; 
         FIG. 6  is a flow chart illustrating an example method for fabricating capsules; 
         FIGS. 7A-F  illustrate example capsules for activating a cement slurry in the system of  FIG. 1 ; 
         FIG. 8  is another example well system for producing fluids from a production zone; and 
         FIGS. 9A-H  illustrate example graphs demonstrating affects of sonic signals on cement slurries. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The present disclosure is directed to one or more well systems having an on-command cement delivery system that selectively controls setting of a cement slurry. For example, the described systems may use sonic irradiation (e.g., ultrasound, terahertz), such as in the range from about 20 Hz to 2 MHz, to release activators to initiate or accelerate the cement setting (see  FIG. 1 ) and/or may use ultrasound to directly activate or accelerate cement slurries (see  FIG. 8 ). In some instances, the described systems may include a cement slurry and capsules that release activators into the cement slurry in response to ultrasound. An activator typically includes any chemicals that activate and/or accelerate the setting process for a cement slurry in the described systems. An activator may also retard or otherwise affect the setting or properties of the cement slurry. For example, the described systems may include one or more of the following activators: sodium hydroxide, sodium carbonate, calcium chloride, calcium nitrite, calcium nitrate, and/or others. In some implementations, the capsules may include elements that substantially enclose one or more activators and that release the activator in response to at least sonic signals. For example, the sonic signal may break or otherwise form an opening in the encapsulating element to release the one or more activators. 
     In regards to directly activating cement slurries, the described systems may directly activate the cement slurry using one or more different mechanisms responsive to sonic signals. The one or more different mechanisms may include modifying chemical properties, releasing chemicals, modifying physical properties (e.g., particle size), updating operating conditions (e.g., pressure, temperature), and/or other mechanisms responsive to sonic signals. For example, described systems may use sonic signals to directly minimize or otherwise reduce the effect of hydrophobic surfactants to, for example, enable the surfactants to enter into suspension and/or partially hydrate. In these instances, the described systems may directly activate cement slurries using sonic signals independent of introducing or adding chemicals to the cement slurry. In addition, the systems may include free-radical dopants in cement slurries that release autocatalytic free radicals in response to at least ultrasonic signals. Alternatively or in combination, the sonic signals may trigger or otherwise activate a polymerization process in the cement slurry to provide in-situ polymerization. In general, the described systems include a cement slurry in an annulus formed between a casing and a wellbore, and when the cement is set, the cement secures the casing in place. By selectively controlling the setting of a cement slurry, the described systems allow cement properties to be tailored once the cement slurry has been pumped down the borehole. 
     Referring to  FIG. 1 , the system  100  is a cross-sectional well system  100  that initiates or accelerates the setting of cement slurring using encapsulated activators. In the illustrated implementation, the well system  100  includes a production zone  102 , a non-production zone  104 , a wellbore  106 , a cement slurry  108 , and capsules  110 . The production zone  102  may be a subterranean formation including resources (e.g., oil, gas, water). The non-production zone  104  may be one or more formations that are isolated from the wellbore  106  using the cement slurry  108 . For example, the zone  104  may include contaminants that, if mixed with the resources, may result in requiring additional processing of the resources and/or make production economically unviable. The cement slurry  108  may be pumped or selectively positioned in the wellbore  106 , and the setting of the cement slurry  108  may be activated or accelerated using the capsules  110 . In some implementations, the capsules  110  may release activators in response to ultrasound initiated by, for example, a user of the system  100 . By controlling the setting, a user may configure the system  100  without substantial interference from the setting of the cement slurry  108 . 
     Turning to a more detailed description of the elements of system  100 , the wellbore  106  extends from a surface  112  to the production zone  102 . The wellbore  106  may include a rig  114  that is disposed proximate to the surface  112 . The rig  114  may be coupled to a casing  116  that extends the entire length of the wellbore or a substantial portion of the length of the wellbore  106  from about the surface  112  towards the production zones  102  (e.g., hydrocarbon-containing reservoir). In some implementations, the casing  116  can extend past the production zone  102 . The casing  116  may extend to proximate a terminus 118 of the wellbore  106 . In some implementations, the well  106  may be completed with the casing  116  extending to a predetermined depth proximate to the production zone  102 . In short, the wellbore  106  initially extends in a substantially vertical direction toward the production zone  102 . In some implementations, the wellbore  106  may include other portions that are horizontal, slanted or otherwise deviated from vertical. 
     The rig  114  may be centered over a subterranean oil or gas formation  102  located below the earth&#39;s surface  112 . The rig  114  includes a work deck  124  that supports a derrick  126 . The derrick  126  supports a hoisting apparatus  128  for raising and lowering pipe strings such as casing  116 . Pump  130  is capable of pumping a variety of wellbore compositions (e.g., drilling fluid, cement) into the well and includes a pressure measurement device that provides a pressure reading at the pump discharge. The wellbore  106  has been drilled through the various earth strata, including formation  102 . Upon completion of wellbore drilling, the casing  116  is often placed in the wellbore  106  to facilitate the production of oil and gas from the formation  102 . The casing  116  is a string of pipes that extends down wellbore  106 , through which oil and gas will eventually be extracted. A cement or casing shoe  132  is typically attached to the end of the casing string when the casing string is run into the wellbore. The casing shoe  132  guides the casing  116  toward the center of the hole and may minimize or otherwise decrease problems associated with hitting rock ledges or washouts in the wellbore  106  as the casing string is lowered into the well. The casing shoe  132  may be a guide shoe or a float shoe, and typically comprises a tapered, often bullet-nosed piece of equipment found on the bottom of the casing string  116 . The casing shoe  132  may be a float shoe fitted with an open bottom and a valve that serves to prevent reverse flow, or U-tubing, of cement slurry  108  from annulus  122  into casing  116  after the cement slurry  108  has been placed into the annulus  122 . The region between casing  116  and the wall of wellbore  106  is known as the casing annulus  122 . To fill up casing annulus  122  and secure casing  116  in place, casing  116  is usually “cemented” in wellbore  106 , which is referred to as “primary cementing.” In some implementations, the cement slurry  108  may be injected into the wellbore  106  through one or more ports  134  in the casing shoe  132 . The cement slurry  108  may flow through a hose  136  into the casing  116 . In some instances where the casing  116  does not extend the entire length of the wellbore  106  to the surface  112 , the casing  116  may be supported by a liner hanger  138  near the bottom of a previous casing  120 . 
     In some implementations, the system  100  may activate the setting of the cement slurry  108  using the capsules  110  during, for example, conventional primary cementing operation. In conventional primary cementing implementations, the capsules  110  may be mixed into the cement slurry  108  prior to entering the casing  116 , and the cement slurry  108  may then be pumped down the inside of the casing  116 . For example, the capsules  110  may be mixed in the cement slurry  108  at a density in the range of 4-24 pound per gallon (ppg). As the slurry  108  reaches the bottom of casing  116 , it flows out of casing  116  and into casing annulus  122  between casing  116  and the wall of wellbore  106 . As cement slurry flows up annulus  122 , it displaces any fluid in the wellbore. To ensure no cement remains inside casing  116 , devices called “wiper plugs” may be pumped by a wellbore servicing fluid (e.g., drilling mud) through casing  116  behind the cement slurry  108 . The wiper contacts the inside surface of casing  116  and pushes any remaining slurry  108  out of casing  116 . When cement slurry reaches the earth&#39;s surface  112 , and annulus  122  is filled with slurry  108 , pumping is terminated. In connection with pumping the cement slurry  108  into the annulus, an ultrasonic signal may be transmitted before, during, and/or after the pumping is complete to activate the capsules  110 . In response to at least the signal, the capsules  110  may release activators that initiate and/or accelerate the setting of the cement slurry  108  in the annulus  122 . Some or all of the casing  116  may be affixed to the adjacent ground material with set cement  202  as illustrated in  FIGS. 2A and 2B . In some implementations, the casing  116  comprises a metal. After setting, the casing  116  may be configured to carry a fluid, such as air, water, natural gas, or to carry an electrical line, tubular string, or other elements. 
     After positioning the casing  116 , a settable slurry  108  including capsules  110  may be pumped into annulus  122  by a pump truck (not illustrated). While the following discussion will center on the settable slurry  108  comprising a cement slurry  108 , the settable slurry  108  may include other compounds such as resin systems, settable muds, conformance fluids, lost circulation, and/or other settable compositions. Example cement slurries  108  are discussed in more detail below. In connecting with depositing or otherwise positioning the cement slurry  108  in the annulus  122 , the capsules  110  may release activators to activate or otherwise increase the setting rate of the cement slurry  108  in response to at least ultrasound. In other words, the released activators may activate the cement slurry  108  to set cement in the annulus  122 . 
     In some implementations, the capsules  110  may release an activator that initiates or accelerates the setting of the cement slurry  108 . For example, the cement slurry  108  may remain in a substantially slurry state for a specified period of time, and the capsules  110  may activate the cement slurry in response to ultrasound. In some instances, ultrasound may crack, break or otherwise form one or more holes in the capsules  110  to release the activators. In some instances, the ultrasound may generate heat that melts one or more holes in the capsules  110 . The capsules  110  enclose the activators with, for example, a membrane such as a polymer (e.g., polystyrene, ethylene/vinyl acetate copolymer, polymethylmethacrylate, polyurethanes, polylactic acid, polyglycolic acid, polyvinylalcohol, polyvinylacetate, hydrolyzed ethylene/vinyl acetate, or copolymers thereof). The capsule  110  may include other materials responsive to ultrasound. In these implementations, the capsule  110  may include a polymer membrane that ultrasonically degrades to release the enclosed activators. In some examples, an ultrasonic signal may structurally change the membrane to release the activators such as, for example, opening a preformed slit in the capsules  110 . In some implementations, at least one dimension of the capsules  110  may be microscopic such as in range from 10 nanometers (nm) to 15,000 nm. For example, the dimensions of the capsules  110  may be on a scale of a few tens to about one thousand nanometers and may have one or more external shapes including spherical, cubic, oval and/or rod shapes. In some implementations, the capsules  110  can be shells with diameters in the range from about 10 nm to about 1,000 nm. In other implementations, the capsules  110  can include a diameter in a range from about 15 micrometers to about 10,000 micrometers. Alternatively or in combination, the capsules  110  may be made of metal (e.g., gold) and/or of non-metallic material (e.g., carbon). In some implementations, the capsules  110  may be coated with materials to enhance their tendency to disperse in the cement slurry  108 . The capsules  110  may be dispersed in the cement slurry at a concentration of 10 5  to 10 9  capsules/cm 3 . In some implementations, the capsules  110  are a shell selected from the group consisting of a polystyrene, ethylene/vinyl acetate copolymer, and polymethylmethacrylate, polyurethanes, polylactic acid, polyglycolic acid, polyvinylalcohol, polyvinylacetate, hydrolyzed ethylene/vinyl acetate, and copolymers thereof. 
     The release activator may include sodium hydroxide, sodium carbonate, amine compounds, salts comprising calcium, sodium, magnesium, aluminum, and/or a mixture thereof. The capsule  110  may release a calcium salt such as calcium chloride. In some implementations, the capsule  110  may release a sodium salt such as sodium chloride, sodium aluminate, and/or sodium silicate. The capsule  110  may release a magnesium salt such as magnesium chloride. In some examples, the capsule  110  may release amine compounds such as triethanol amine, tripropanol amine, tri-isopropanol amine, and/or diethanol amine. In some implementations, the capsule  110  may release the activator in a sufficient amount to set the cement slurry  108  within about 1 minute to about 24 hours. In implementations including sodium chloride as the released activator, the concentration may be in the range of from about 3% to about 30% by weight of the cement in the cement slurry  108 . In implementations including calcium chloride as the released activator, the concentration may be in the range of from about 0.5% to about 5% by weight of the cement in the cement slurry  108 . In the case that the settable slurry  108  comprises resin, the release activator may include amine accelerators for a epoxy/novalac resins. 
     In some implementations, the capsule  110  may “flash-set” the cement slurry  108 . As referred to herein, the term “flash-set” will be understood to mean the initiation of setting of the cement slurry  108  within about 1 minute to about 15 minutes after contacting the released activator. In some implementations, the previously identified activators may flash set the cement slurry  108 . Flash-set activators may include sodium hydroxide, sodium carbonate, potassium carbonate, bicarbonate salts of sodium or potassium, sodium silicate salts, sodium aluminate salts, ferrous and ferric salts (e.g., ferric chloride and ferric sulfate), polyacrylic acid salts, and/or others. In some implementations, the following activators can flash-set the cement slurry  108  based on these activators exceeding a specified concentration: calcium nitrate, calcium acetate, calcium chloride, and/or calcium nitrite. In some implementations, the capsule  110  may release a solid activator. 
     In some implementations, the cement slurry  108  may comprise a “delayed set” cement compositions that remain in a slurry state (e.g., resistant to setting or gelation) for an extended period of time. In such implementations, a delay-set cement slurry  108  may include a cement, a base fluid, and a set retarder. In these and other implementations, activation may change the state of the cement slurry from delay set to neutral, to accelerated, or to less delayed. The cement slurry  108  may include other additives. The delayed-set cement slurry  108  typically remains in a slurry state for in range of about 6 hours to about 4 days under downhole or other conditions. That said, the cement slurry  108  may include components that result in a slurry state for a greater, or shorter, amount of time. For example, the cement slurry  108  may be mixed or otherwise made well ahead of positioning the slurry  108  in the annulus  122 . The delayed-set cement slurry  108  can, in some implementations, include a cement, a base fluid, and a set retarder. The delayed-set cement slurry  108  may be set at a desired time, such as after placement, by activating the capsules  110  to release one or more activators. 
     In regards to cements included in the cement slurry  108 , any cement suitable for use in subterranean applications may be suitable for use in the present invention. For example, delayed-set cement slurry  108  may include a hydraulic cement. In general, hydraulic cements typically include calcium, aluminum, silicon, oxygen, and/or sulfur and may set and harden by reaction with water. Hydraulic cements include, but are not limited to, Portland cements, pozzolanic cements, high aluminate cements, gypsum cements, silica cements, high alkalinity cements, and/or Sorel cements. In addition, the delayed-set cement slurry  108  may include cements based on shale or blast furnace slag. In these instances, the shale may include vitrified shale, raw shale (e.g., unfired shale), and/or a mixture of raw shale and vitrified shale. In some implementations, the settable composition  108  includes a polymer additive comprising at least one of a monomer, a pre-polymer, an oligomer, or a short chain polymer that polymerizes in response to the sonic signal 
     In regards to base fluids included in the cement slurry  108 , the delayed-set cement slurry  108  may include one or more base fluids such as, for example, an aqueous-based base fluid, a nonaqueous-based base fluid, or mixtures thereof. Aqueous-based may include water from any source that does not contain an excess of compounds (e.g., dissolved organics, such as tannins) that may adversely affect other compounds in the cement slurry  108 . For example, the delayed-set cement slurry  108  may include fresh water, salt water (e.g., water containing one or more salts), brine (e.g., saturated salt water), and/or seawater. Nonaqueous-based may include one or more organic liquids such as, for example, mineral oils, synthetic oils, esters, and/or others. Generally, any organic liquid in which a water solution of salts can be emulsified may be suitable for use as a base fluid in the delayed-set cement slurry  108 . In some implementations, the base fluid exceeds a concentration sufficient to form a pumpable slurry. For example, the base fluid may be water in an amount in the range of from about 25% to about 150% by weight of cement (“bwoc”) such as one or more of the following ranges: about 30% to about 75% bwoc; about 35% to about 50% bwoc; about 38% to about 46% bwoc; and/or others. 
     In regards to set retarders in the cement slurry  108 , the cement slurry  108  may include one or more different types of set retarders such as, for example, phosphonic acid, phosphonic acid derivatives, lignosulfonates, salts, organic acids, carboxymethylated hydroxyethylated celluloses, synthetic co- or ter-polymers comprising sulfonate and carboxylic acid groups, and/or borate compounds. And In some implementations, the set retarders used in the present invention are phosphonic acid derivatives. Examples of set retarders may include phosphonic acid derivatives commercially available from, for example, Solutia Corporation of St. Louis, Mo. under the trade name “DEQUEST.” Another example set retarder may include a phosphonic acid derivative commercially available from Halliburton Energy Services, Inc., under the trade name “MICRO MATRIX CEMENT RETARDER.” Example borate compounds may include sodium tetraborate, potassium pentaborate, and/or others. A commercially available example of a suitable set retarder comprising potassium pentaborate is available from Halliburton Energy Services, Inc. under the trade name “Component R.” Example organic acids may include gluconic acid, tartaric acid, and/or others. An example of a suitable organic acid may be commercially available from Halliburton Energy Services, Inc. under the trade name “HR® 25.” Other examples of set retarders may be commercially available from Halliburton Energy Services, Inc. under the trade names “SCR-100” and “SCR-500.” Generally, the set retarder in the delayed-set cement slurry  108  may be in an amount sufficient to delay the setting in a subterranean formation for a specified time. The amount of the set retarder included in the cement slurry  108  may be in one or more of the following ranges: about 0.1% to about 10% bwoc; about 0.5% to about 4% bwoc; and/or others. 
     In some implementations, the cement slurry  108  may not include a set retarder. For example, the system slurry  108  may include high aluminate cements and/or phosphate cements independent of a set retarder. In these instances, the activators may initiate setting of the slurry  108 . For example, these activators may include alkali metal phosphate salts. High aluminate cement may comprise calcium aluminate in an amount in the range of from about 15% to about 45% by weight of the high aluminate cement, Class F fly ash in an amount in the range of from about 25% to about 45% by weight of the high aluminate cement, and sodium polyphosphate in an amount in the range of from about 5% to about 15% by weight of the high aluminate cement. In certain embodiments of the present invention wherein a cement composition comprising a phosphate cement is used, a reactive component of the cement composition (e.g., the alkali metal phosphate salt) may be used as an activator. 
       FIGS. 2A and 2B  illustrate a cross sectional view of the well system  100  including activated set cement  202  in at least a portion of the annulus  122 . In particular, the capsules  110  released activators in at least a portion of the cement slurry  108  to form the set cement  202 . In  FIG. 2A , the cement slurry flowed into the annulus  122  through the casing  116 , and in response to at least a signal, the capsules  110  in the slurry  108  released an activator. In the illustrated example, substantially all capsules  110  in the annulus  122  released activators to form the set cement  202  along substantially the entire length of the annulus  122 . Referring to  FIG. 2B , the cement slurry  108  flowed into the annulus  122  through the casing  116 , and in response to at least an ultrasonic signal, the capsules  110  in the slurry  108  released activators within a specified location  204 . In the illustrated example, the region or location  204  is located proximate the zone  102 . In other words, the capsules  110  proximate the zone  102  may release activators and form the set cement  202  located in the region  204 . The ultrasonic signal may be localized to the region identified by  204 , and in response to at least the localized signal, the set cement  204  forms. In some implementations, an initial amount of the cement slurry  108  may be exposed to an ultrasonic signal such that the setting period may be substantially equal to a period of time for the setting cement slurry  108  to flow to the location  204 . In these examples, the cement slurry  108  may be exposed to the ultrasonic signal as the slurry  108  including the capsules  110  enters the casing  116 . As the leading edge of cement slurry  108  begins to set, fluid flow through the annulus  122  may become more restricted and may eventually cease. Thus, the cement slurry  108  may be substantially prevented from flowing onto the surface  112  through the annulus  122 . The remainder of the cement slurry  108  may set in the annulus  122  behind the leading edge as illustrated in  FIG. 2A  or the cement slurry  108  may set at a later time as illustrated in  FIG. 2B . In the later, the remaining cement slurry  108  may be exposed to ultrasonic signals at a later time to initiate or accelerate the setting processes. 
       FIGS. 3A and 3B  illustrates an example capsule  110  of  FIG. 1  in accordance with some implementations of the present disclosure. In this implementation, the capsule  110  is spherical but may be other shapes as discussed above. The capsule  110  is a shell  302  encapsulating one or more activators  304  as illustrated in  FIG. 3B . The capsule  110  releases one or more stored activators  304  in response to at least an ultrasonic signal. For example, the capsule  110  may crack or otherwise form one or more holes in response to at least the ultrasonic signal. The illustrated capsule  110  is for example purposes only, and the capsule  110  may include some, none, or all of the illustrated elements without departing from the scope of this disclosure. 
       FIGS. 4A and 4B  illustrate example implementations of the capsules  110  releasing one or more activators. The capsules  110  may release activators by heating one or more portions to form at least one opening, destroying or otherwise removing one or more portions, and/or other processes. The following implementations are for illustration purposes only, and the capsules  110  may release activators using some, all or none of these processes. 
     Referring to  FIG. 4A , the capsule  110  forms an opening through heat formed from ultrasonic signals. For example, the ultrasonic signals may directly heat the membrane of the capsule  110  and/or heat the surrounding cement slurry  108  to a temperature above the melting point. The capsule  110  may be a gold shell that when vibrated at its natural frequency melts at least a portion of the shell to release the enclosed activators. In these instances, the generated heat may melt or otherwise deform the shell to form an opening. In addition to metal membranes, the capsule  110  may be other materials such as a polymer. Referring to  FIG. 4B , the capsule  110  forms cracks, breaks, or openings in response ultrasonic signals. For example, the ultrasonic signal may crack or otherwise destroy portions of the capsule  110 . In some implementations, the ultrasound may form defects in the membrane of the capsule and, as a result, form one or more openings as illustrated. 
       FIGS. 5 and 6  are flow diagrams illustrating example methods  500  and  600  for implementing and manufacturing devices including one or more activators. The illustrated methods are described with respect to well system  100  of  FIG. 1 , but these methods could be used by any other system. Moreover, well system  100  may use any other techniques for performing these tasks. Thus, many of the steps in these flowcharts may take place simultaneously and/or in different order than as shown. The well system  100  may also use methods with additional steps, fewer steps, and/or different steps, so long as the methods remain appropriate. 
     Referring to  FIG. 5 , method  500  begins at step  502  where capsules are selected based, at least in part, on one or more parameters. For example, the capsules  110  and the enclosed activators may be based, at least in part, on components of the cement slurry  108 . In some implementations, the capsules  110  may be selected based on downhole conditions (e.g., temperature). At step  504 , the selected capsules are mixed with a cement slurry. In some examples, the capsules  110  may be mixed with the cement slurry  108  as the truck  130  pumps the slurry into the annulus  122 . In some examples, the capsules  110  may be mixed with dry cement prior to generating the cement slurry  108 . Next, at step  506 , the cement slurry including the capsules are pumped downhole. In some instances, the cement slurry  108  including the capsules  110  may be pumped into the annulus  122  at a specified rate. One or more ultrasonic signals are transmitted to the at least a portion of the downhole cement slurry at step  508 . Again in the example, the transmitter may be lowered into the casing to transmit signals at a portion of the cement slurry  108 . In this example, the transmitted signals may activate the capsules  110  proximate the shoe  132  to set that portion of the cement slurry  108  as illustrated in  FIG. 2B . In some instances, the casing  116  may be moved (e.g., up/down) to assist in distributing the activators as desired. 
     Referring to  FIG. 6 , the method  600  begins at step  602  where a first emulsification step is performed. For example, a polystyrene dissolved in CH 2 Cl 2  where saturated aqueous CaCl 2  may be emulsified using WS-36 (Sorbitan Monooleate). Next, at step  604 , the first emulsification may then again be emulsified in a second step. In the example, the first emulsion may then be subsequently emulsified into a large volume (e.g., 10× excess) of a 2% polyvinylalcohol solution. 
       FIGS. 7A-F  illustrate an example implementation of the capsules  110  in accordance with some implementations of the present disclosure. In this example, implementation, the capsules  110  encapsulate activators, and power ultrasound may break the capsules to release the activators on command. The illustrated capsules  110  are polystyrene microcapsules encapsulating aqueous CaCl 2 . Though, the capsules  110  may be formed from other materials such as ethylene/vinyl acetate copolymer, polymethylmethacrylate, and/or others. In some instances, these types of capsules  110  may be created using a double emulsion technique. For example, the technique may include a polystyrene dissolved in CH 2 Cl 2  where saturated aqueous CaCl 2  was emulsified using WS-36 (Sorbitan Monooleate). Next, this emulsion may then be subsequently emulsified into a large volume (e.g., 10× excess) of a 2% polyvinylalcohol solution. The double emulsion was stirred and heated to about 30° C. to drive off CH 2 Cl 2  and concentrate the polystyrene ultimately forming liquid filled microcapsules. To evaluate these capsules, four different cement slurries were tested and the results are graphed in  FIGS. 7C-F . A retarded slurry, a retarded slurry with CaCl 2 , a retarded slurry with the microcapsules, and a retarded slurry with the microcapsules treated with sonication were evaluated. A 20 kHz ultrasonic horn was used for ten minutes at 50% power to treat the sonicated sample. The composition and results are listed in Tables 1-3 below. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Slurry 1 
                 Slurry 2 
                 Slurry 3 
                 Slurry 4 
               
               
                   
                 Base  
                 Retarded w/  
                 Encapsulated  
                 Sonicated  
               
               
                 Description 
                 Retarded 
                 CaCl 2   
                 CaCl 2   
                 Encap CaCl 2   
               
               
                   
               
             
            
               
                 Water 
                 39.4% bwc 
                 39.4% bwc 
                 39.4% bwc 
                 39.4% bwc 
               
               
                   
                   332 g 
                   332 g 
                   332 g 
                   332 g 
               
               
                 Class H 
                  100% bwc 
                  100% bwc 
                  100% bwc 
                  100% bwc 
               
               
                   
                 842.5 g 
                 842.5 g 
                 842.5 g 
                 842.5 g 
               
               
                 HR-800 
                 0.25% bwc 
                 0.25% bwc 
                 0.25% bwc 
                 0.25% bwc 
               
               
                   
                  2.1 g 
                  2.1 g 
                  2.1 g 
                  2.1 g 
               
               
                 CaCl 2   
                   
                 0.27% bwc 
                   
                   
               
               
                   
                   
                  2.3 g 
                   
                   
               
               
                 Encapsulated 
                   
                   
                 0.27% bwc 
                 0.27% bwc 
               
               
                 CaCl 2   
                   
                   
                  2.3 g 
                  2.3 g 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 Density- 
                 16.4 ppg 
               
               
                   
                 Yield- 
                 1.07 ft 3 /sk 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Slurry 1 
                 Slurry 2 
                 Slurry 3 
                 Slurry 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pump time 
                 14:19 
                  9:17 
                 12:20 
                  7:35 
               
               
                   
                 (70BC) 
                   
                   
                   
                   
               
               
                   
                 Hydration Heat 
                 16:00 
                 11:00 
                 16:00 
                 11:20 
               
               
                   
                   
               
            
           
         
       
     
     The illustrated parameters including operating conditions are for illustration purposes only. The system  100  may use some, all or none of the values without departing from the scope of this disclosure. 
       FIG. 8  is another example system  100  that directly activates the cement slurry  108  using ultrasonic signals. For example, ultrasonic transducers  802   a  and  802   b  may be affixed to the exterior of the casing  116  and emit ultrasound to sonically activate the cement slurry. By sonically activating the cement slurry, the system  100  may set cement on-demand. For example, the system  100  may set the cement slurry  108  in a period of the range from 1 hour to 1 day. The sonic transducers  802  may directly activate the cement slurry  108  using one or more different mechanisms responsive to sonic signals. The one or more different mechanisms may include modifying chemical properties, releasing chemicals, modifying physical properties (e.g., particle size), updating operating conditions (e.g., pressure, temperature), and/or other mechanisms responsive to sonic signals. For example, the sonic transducers  802  may reduce the particulate size in the cement slurry  108  and, as a result, may increase the surface area. By increasing the surface area, the setting process may be initiated, accelerated, or otherwise activated. Alternatively or in combination, the sonic signals may increase the pressure and/or temperature and, as a result, may initiate, accelerate, or otherwise activate the setting process. In some implementations, the ultrasonic transducers  802  may activate accelerators in the cement slurry  108  and/or deactivate cement retarders in the cement slurry  108  to set the cement on demand. For example, the ultrasonic transducers  802  may generate ultrasonic or acoustic waves to initiate the setting process of the cement slurry  108  through, for example, the selective activation of accelerators in the cement slurry  108  such as CaCl 2  and/or the deactivation of cement retarders in the cement slurry  108  such as xylose. In some implementations, cement hydration inhibitors (in relatively low concentration) can work to alter the surface energy of the tricalcium aluminate, silicate and/or other compounds in the cement slurry  108 , which can make the compounds more hydrophobic. The transducers  802  may ultrasonically agitate the cement slurry  108  to reduce the effect of hydrophobic surfactants, which may enable the compounds to enter into solution and/or partially hydrate. The transducers  802  may generate ultrasonic signals having a frequency that substantially matches the resonant conditions for inhibitor neutralization. In some implementations, the system  100  may execute frequency tuning to substantially optimize frequency and power combinations for a given geometry and inhibitor chemistry. In these instances, a user of the system  100  may remotely control the initiation of cement hydration. In addition, the system  100  may initiate an autocatalytic process. For example, the transducers  802  may generate ultrasonic signals that sets off an autocatalytic free-radical release that propagates through the cement slurry  108 . In these instances, this process may initiate from a single point. The cement slurry  108  may include additives (e.g., free-radical dopants) that release free-radical species through out the slurry  108  in response to at least ultrasonic initiation or hydration. 
       FIGS. 9A-H  illustrate example graphs demonstrating affects of sonic signals on cement slurries. In these examples, measurements were made on cement slurries that were sonically activated in comparison to cement slurries not sonically activated. In particular, ultrasound was used to accelerated the set of retarded cement slurries. The cement slurries were retarded using one of the following three retarders: EDTA; a combination of FDP-C742A and EDTA; and a combination of FDP-C742A and Component R. Without exposure to ultrasound, the cement slurries pumped between 6.5 hours to 80 hours. After exposure to 20 kHz of ultrasound, the pump times for these slurries may be reduced 40-50%. In addition, a control pump time using neat cement with and without exposure to ultrasound was run. The ultrasound exposure did not appear to affect the pump time of the neat cement. Based, at least in part, on the data, the ultrasound appears to target the retarders and may be accelerating the setting process as a result. 
     Referring to  FIG. 9A , the graph  910  plots data for cement slurry comprising 16.4 PPG (Class H cement, neat) operating at 120° F. and 3600 PSI in 30 minutes. The cement slurry was not exposed to ultrasound. The graph  910  includes a peak  912  indicating the pump time to be 2 hours and 23 minutes. Referring to  FIG. 9B , the graph  920  plots data for the same cement slurry as graph  910  including exposure to 20 kHz ultrasound for seven minutes. In this experiment, the ultrasound was shut off after 5 minutes to due to an increase in the cement-slurry temperature. The cement slurry was exposed to an additional 2 minutes of the ultrasound once cooled. The graph  920  includes a peak  922  indicating the pump time to be 2 hours. 
     Referring to  FIG. 9C , the graph  930  plots data for cement slurry comprising 16.4 PPG (Class H cement, 1% EDTA) operating at 120° F. and 3600 PSI in 30 minutes. The cement slurry was not exposed to ultrasound. The graph  930  includes a peak  932  indicating the pump time to be 7 hours and 45 minutes. Referring to  FIG. 9D , the graph  940  plots data for the same cement slurry as graph  930  including exposure to 20 kHz ultrasound for 7 minutes (5 minutes on, 2 minutes off, 2 minutes on). In this experiment, the ultrasound was shut off after 5 minutes due to an increase in the cement-slurry temperature. The cement slurry was exposed to an additional 2 minutes of the ultrasound once cooled. The pump time was 4 hours 15 minutes. 
     Referring to  FIG. 9E , the graph  950  plots data for cement slurry comprising 16.4 PPG (Class G cement w/35% SSA-1; 10.4 SSA-1; 1% CFR-3; 0.8% Halad-200; 0.4 gal/sk Gascon 469; 1.8% FDP-C742A; 1.8% EDTA; 0.3 gal/sk NF-6) with the % in bwoc. The operating conditions were 400° F. and 13100 PSI in 90 minutes. The cement slurry was not exposed to ultrasound. The pump time was 6 hours and 46 minutes. Referring to  FIG. 9F , the graph  960  plots data for the same cement slurry as graph  950  including exposure to 20 kHz ultrasound for 15 minutes (10 minutes on, 1 minutes off, 5 minutes on). In this experiment, the ultrasound was shut off after 10 minutes due to an increase in the cement-slurry temperature. The cement slurry was exposed to an additional 5 minutes of the ultrasound once cooled. The pump time was 3 hours 15 minutes. 
     Referring to  FIG. 9G , the graph  970  plots data for cement slurry comprising 16.4 PPG (Class G cement w/35% SSA-1; 10.4 SSA-1; 1% CFR-3; 0.8% Halad-200; 0.4 gal/sk Gascon 469; 1.8% FDP-C742A; 0.8% Compound R; 0.3 gal/sk NF-6) with the % in bwoc. The operating conditions were 422° F. and 13100 PSI in 90 minutes. The cement slurry was not exposed to ultrasound. The pump time was 79 hours. Referring to  FIG. 9H , the graph  980  plots data for the same cement slurry as graph  970  including exposure to 20 kHz ultrasound for 15 minutes (5 minutes intervals). The pump time was 50 hours. 
     The present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.