Patent Application
20210404299
The exemplary embodiments disclosed herein relate generally to microencapsulated acid or acid generators for targeted delivery and dosing of acid at the site of perforation in hydraulic fracturing applications, device and method of using the same. The targeted delivery and dosing of acid at the site of perforation provides the benefit of, including but not limited to, eliminating over acidizing (limiting near wellbore formation damage) and optimizing the removal of perforation residue and formation materials for lowering break-down pressure.
Fracturing operations start with a well that has been drilled to a desired vertical and horizontal depth. Casing is cemented in place to isolate the well from the surrounding geology and groundwater zones. A perforating gun is lowered into the well to a designated location, and one or more charges are fired to perforate the casing, cement and formation. These perforations form the flowpath through which a subsequent stimulation treatment is applied.
Stimulation treatments involve creating or inducing fractures or enhancing natural fractures in the formation, and may be performed in multiple stages to achieve a desired network of fractures. A mixture of water, sand and chemicals is injected into the wellbore under high pressure to create and propagate the fissures or fractures in the formation. Other types of treatment fluids may also be used depending on the downhole operation, such as drilling operations, perforation operations, sand control treatments, water control treatments, wellbore clean-out treatments, organic scale deposits and inorganic scale treatments, and the like.
Acid may be used in a hydraulic fracturing process for many reasons including, for example, near wellbore clean out, remove perforation residue, to lower the formation breakdown pressure, and/or to “etch” channels in the rock that comprise the walls of the fracture. Without targeted delivery or dosing, the amount of acid normally required is in very large quantities, which requires shipment and storage of hazardous materials. Additional damage from excess acid can lead to corrosion, scale, and precipitate formation.
Therefore, there is a need for targeted delivering and dosing of acid at the site of perforation.
For a more complete understanding of the exemplary disclosed embodiments, and for further advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which:
The following discussion is presented to enable a person ordinarily skilled in the art to synthesize and use the exemplary disclosed embodiments. Various modifications will be readily apparent to those skilled in the art, and the general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the disclosed embodiments as defined herein. Accordingly, the disclosed embodiments are not intended to be limited to the particular embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein.
As mentioned above, the embodiments disclosed herein relate to microencapsulated acid or acid generators for targeted delivery and dosing of acid at the site of perforation in hydraulic fracturing applications, method and device of use the same. Although the term “microencapsulated” is used herein, it should be understood the disclosed microencapsulated particulates may range from 0.001 micrometer (μm) to about 5000 μm size particulates.
As used herein, the term “microencapsulated acid,” and grammatical variants thereof, refers to any substance that is able encapsulate or contain of all or a portion of one or more acids, or precursors thereof, to allow targeted placement and reaction of the acid at a perforation site.
As used herein, the term “acids,” or “acid precursors,” and grammatical variants thereof, refers to any acids (such as strong mineral acids like HCl, H2S04, HF, H3P04, and HNO3, or organic acids like acetic acid, tartaric acid, formic acid, or lactic acid) or precursors that has the capability of generating acid in-situ, such as TiCl3 (solid) or TiCl4 (liquid).
Polymer Microencapsulation
Materials: Polymer microencapsulation is used to create isolated solid, liquid, gas, or blends into individual particles. The polymer particles can be made from different blends of monomers in order to control the reactivity with the internal contents or external environment. Additionally, the polymer microparticles will have a range in internal and external dimensions which controls the weight percent of encapsulated materials, robustness of the barrier, and overall particle dimension and treating mass. Embodiments herein contemplate using encapsulated acids and acid precursors. Some examples of polymer materials that are inert enough to handle the reactive acids include 1-vinylimidazole with N,N-methylenebis(acrylamide), ACN/VDC (Poly(vinylidene chloride-co-acrylonitrile), polystyrene, n-butyl acrylate, acrylic acid and many others.
One or more embodiments contemplate an acid, such as HCl, HF, acetic acid, tartaric acid, formic acid, or lactic acid or acid precursor, e.g., TiCl4, to be loaded into the polymer microparticles. Loading the microparticles may be achieved using the following strategies in one or more embodiments.
Water in oil in water (W-O-W) double emulsion: Surfactant, acid/acid solution, monomer/polymer organic solutions are emulsified into an aqueous surfactant solution creating microcapsules or micro-sponges based on the polymerization process and solvent evaporation step. For example, in the first step of the encapsulation, aqueous acid (e.g., HCl) droplets is dispersed into a hydrophobic monomer phase to form a single emulsion. This is followed by dispersing the single emulsion phase into a second continues aqueous phase to generate a double emulsion. The resulting mixture is then subjected to polymerization of the monomers to form core-shell particles encapsulated with acids.
Expandable preformed hollow particles: Polymer microparticles will swell and become permeable with elevated temperatures or pressure. This allows acids to be added to the polymer microparticles after synthesis. For example, US 2018/0282609 discloses that fabricated polymeric nano- or microcapsules (e.g., from polystyrene) may be added to a volume of pure titanium chloride, or a corresponding solution of TiClx, and the resulting mixture may be subjected to one or more successive vacuum/fill cycles with an inert gas to diffuse the pure titanium chloride, or corresponding solution, through the shell to fill the cavities of the capsules in order to encapsulate the TiClx in the polymeric shell, which may subsequently produce about 53 wt. % of pure HCl.
Gas in oil in water (G/O/W) emulsion: surfactant, acid and organic based polymer solution are emulsified with an aqueous surfactant solution creating large swollen micro-sponges when the solvent is evaporated.
Cleaning excess acid/acid generators can be achieved through additional washes or with centrifugation and drying steps.
Post encapsulation modification of the polymer shell can also be performed through annealing (heat treatment) or coating will further isolate the acid and render the materials more inert. If the polymer barrier is more robust, then more drastic triggers would be used to release the acid payload.
In one aspect, acid may be target-delivered at the perforation site, and used in a hydraulic fracturing process to remove perforation residue. Preliminary calculations indicate that at most ˜1 L of pure HCl is required, per perforation, to effectively clean the cement and perforation residue. This can be generated from approximately 250 g of TiCl4 (a concentrated acid precursor), assuming enough water will ultimately be available for the reaction:
TiCl4+2H2O→4HCl+TiO2
This equates to 1.5 kg of TiCl4 to treat a 6-perforation cluster. If the TiCl4 is encapsulated as described above, this quantity could be contained in a cylindrical chamber approx. 5-ft. long (assuming 2½ in ID).
Release Mechanism
One of the applications of acids in hydraulic fracturing is to clean up the cement and perforation residue and lower the formation breakdown pressure, meaning that the acid is only needed within the perforation process. Additional damage from excess acid will lead to corrosion, scale, and precipitate formation. Therefore, there is a need for targeted delivering and dosing of acid at the site of perforation.
In one aspect of the present disclosure, release of acid can be triggered with time, temperature, pressure, or explosion (extreme heat/pressure). Controlled release of the acid can be achieved with tuning of the polymer compositions, thickness and acid loading amounts.
In one embodiment of the present disclosure, encapsulated acid is released by perforation guns.
In another aspect of the present disclosure, the acid is target-delivered into the perforation volume and damage zone, as illustrated in
Targeted Delivery of Acid to the Perforation Site
Delivering the microencapsulated acid to the path of the perforation gun can be achieved through various embodiments of the invention. In one embodiment, the microencapsulated acid is loaded in pumping fluid that is used to drive the perforation gun into place. This embodiment is suitable for a conventional perforating gun such as shown with respect to
In another embodiment, microencapsulated acid can be loaded into a perforation gun assembly, as shown in
The release of the acid from microencapsulates may be accomplished in still further embodiments. For example, with reference to
Another embodiment of the invention is with regard to
If sufficient overbalance does not exist to push the acid into the perforation volume or damage zone, the overbalance chambers 803, which contain propellant or similar material, can be activated to create a transient overbalance condition, thus pushing the recently-released acid or acid precursor into the perforation volume or damage zone. In one embodiment, the release of the overbalance chamber can be triggered by the same firing command from the surface, with another time delay if desired.
Various methods of delivering microencapsulated acid or precursor to treat formations in hydraulic fracturing applications are also provided according to embodiments of the invention. In one embodiment, by slowly pulling the perforation gun assembly uphole, the acid payload chamber, the perforation gun chamber, and the overbalance chamber can be activated sequentially and at substantially in the same location in the wellbore. This allows the microencapsulated acid to be target-released into the perforations.
Embodiments of the inventive method are described more fully with regard to
In yet another embodiment, the microencapsulated acid/precursor could be packaged within the perforating gun chamber itself, rather than separate dedicated acid chambers. Further, the acid payload chamber, and propellant/overbalance chamber (if required), could be combined into a single physical chamber serving both functions.
Thus, the targeted delivery and dosing of acid at the site of perforation in hydraulic fracturing applications disclosed herein provides a number of benefits over existing acid delivery mechanism. These benefits include, for example, eliminating over acidizing, limiting near wellbore formation damage, optimizing the removal of perforation residue and formation materials for lowering break-down pressure, and eliminating the need of transportation and storage of corrosive acids, among others.
Accordingly, as set forth above, the embodiments disclosed herein may be implemented in a number of ways. For example, in general, in one aspect, the disclosed embodiments relate to a perforation gun assembly, comprising a microencapsulated acid payload chamber and a perforating gun payload chamber, or a chamber containing both a microencapsulated acid payload and a perforating gun payload, and optionally an overbalance payload chamber. In another aspect, the disclosed embodiments relate to a method for fracturing operation using the perforation gun assembly disclosed in accordance with any one or more of the foregoing embodiments.
In accordance with any one or more of the foregoing embodiments, the acid payload chamber or the chamber containing both an acid payload and a perforating gun payload contains a microencapsulated acid, an overbalance payload chamber contains propellant or similar material and can be activated to create a transient overbalance condition, and/or the acid payload comprises microencapsulated acid particulates with a polymeric shell and an acid or acid precursor core.
In accordance with any one or more of the foregoing embodiments, an acid payload chamber and a perforating gun payload chamber are present, wherein the acid payload comprises microencapsulated acid particulates with a polymeric shell and an acid or acid precursor core, and an overbalance payload chamber is present, wherein the overbalance payload chamber contains propellant or similar material, and can be activated to create a transient overbalance condition.
In accordance with any one or more of the foregoing embodiments, acid release occurs simultaneously with creating a perforation, and/or an acid precursor is released by perforating microencapsulated acid particulates and simultaneously creating a perforation.
In accordance with any one or more of the foregoing embodiments, a perforation gun assembly is used, and the perforating operation comprises releasing an acid payload from the acid payload chamber, activating the perforating gun payload chamber, and simultaneously, releasing acid or acid precursor by creating a perforation.
In accordance with any one or more of the foregoing embodiments, performing a perforating operation comprises releasing microencapsulated acid payload from the acid payload chamber, and activating the perforating gun payload chamber, and simultaneously, releasing acid or acid precursor by perforating microencapsulated acid particulates and creating a perforation.
In accordance with any one or more of the foregoing embodiments, the acid payload chamber and the perforation gun chamber can be released/activated sequentially and substantially in the same location, and the acid and/or acids precursor can be target-released into the perforation.
In accordance with any one or more of the foregoing embodiments, performing a perforating operation comprises using the perforation gun assembly, releasing an acid payload from the acid payload chamber, activating the perforating gun payload chamber, and simultaneously, releasing acid or acid precursor by creating a perforation, and activating the overbalance payload chamber, pushing the released acid or acid precursor into the perforation.
In accordance with any one or more of the foregoing embodiments, performing a perforating operation comprises releasing a microencapsulated acid payload from the acid payload chamber, activating the perforating gun payload chamber, and simultaneously, releasing acid or acid precursor by perforating microencapsulated acid particulates and creating a perforation, and activating the overbalance payload chamber, pushing the released acid or acid precursor into the perforation. The acid payload chamber, the perforation gun chamber, and the overbalance chamber can be released/activated sequentially and substantially in the same location, and the acid and/or acid precursor can be target-released into the perforation.
In accordance with any one or more of the foregoing embodiments, the perforation gun assembly comprises an acid payload chamber and a perforating gun payload chamber, wherein the acid payload comprises microencapsulated acid particulates with a polymeric shell and an acid or acid precursor core, the microencapsulated acid particles range from 0.001 micrometers to 5000 micrometers, the microencapsulated acid particles comprise one of HCl, H2S04, HF, H3P04, or HNO3, the microencapsulated acid particles comprise an organic acid, the organic acid comprising one of acetic acid, tartaric acid, formic acid or lactic acid, and/or the microencapsulated acid particles are encapsulated in an inert polymer material.
While the invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the description. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/038237 | 6/20/2019 | WO | 00 |
