Patent application title: Downhole Delivery Of Chemicals With A Micro-Tubing System
Yan P. Kuhn De Chizelle (Houston, TX, US)
Mathew M. Samuel (Sugar Land, TX, US)
Douglas Pipchuk (La Defanse Cedex, FR)
Don Williamson (Belding, MI, US)
Andrey Mirakyan (Katy, TX, US)
Andrey Mirakyan (Katy, TX, US)
Hemant K.j. Ladva (Missouri City, TX, US)
Richard D. Hutchins (Sugar Land, TX, US)
SCHLUMBERGER TECHNOLOGY CORPORATION
IPC8 Class: AE21B1720FI
Class name: Processes with indicating, testing, measuring or locating tracer
Publication date: 2013-10-24
Patent application number: 20130277047
A technique utilizes micro-tubing to facilitate performance of a well
treatment in which the micro-tubing is deployed for cooperation with a
larger tubing, such as a coiled tubing positioned in wellbore. The
micro-tubing is used to deliver a separated chemical downhole to modify a
property of a treatment fluid used in performing a desired well treatment
operation at a desired treatment region along the wellbore. A variety of
additional components may be combined with the micro-tubing to further
facilitate the treatment application.
1. A method of performing a well treatment, comprising: routing a
micro-tubing down through a coiled tubing deployed in wellbore; employing
a securing mechanism to secure a lower end of the micro-tubing proximate
a discharge region of the coiled tubing; positioning a communication line
within the micro-tubing; and delivering treatment fluids downhole through
the micro-tubing and through an interior of the coiled tubing located
between the micro-tubing and an interior surface of the coiled tubing,
the treatment fluids being dissimilar.
2. The method as recited in claim 1, wherein routing comprises pumping the micro-tubing down through the coiled tubing via a velocity booster coupled to a lead end fixture of the micro-tubing.
3. The method as recited in claim 1, wherein positioning comprises positioning a fiber optic communication line within the micro-tubing.
4. The method as recited in claim 1, wherein delivering comprises delivering a treatment fluid through the micro-tubing which alters the properties of the overall well treatment.
5. The method as recited in claim 1, wherein routing comprises routing a plurality of micro-tubings down through the coiled tubing.
6. The method as recited in claim 1, further comprising distributing treatment fluid from the micro-tubing, through a plurality of perforations, and into a mixing region for mixing with dissimilar treatment fluid delivered through the interior of the coiled tubing between the micro-tubing and the interior surface of the coiled tubing.
7. The method as recited in claim 1, further comprising providing a sensor system downhole coupled to the communication line.
8. The method as recited in claim 1, further comprising utilizing the communication line to power a downhole tool.
9. The method as recited in claim 2, wherein pumping comprises pumping down the micro-tubing with a pump-down plug having at least one burst disc which may be ruptured to enable delivery of at least one type of fluid.
10. The method as recited in claim 1, further comprising coupling the micro-tubing and the communication line to a retrievable delivery and electronics package.
11. The method as recited in claim 1, further comprising attaching a canister containing an additional treatment fluid to an end of the micro-tubing and controlling delivery of the additional treatment fluid with a valve.
12. A method of performing a well treatment, comprising: deploying a micro-coil tubing and a larger tubing downhole to a well treatment region of a wellbore; delivering a treatment fluid downhole through the larger tubing; using the micro-coil tubing to deliver a chemical downhole for combination with the treatment fluid at the well treatment region, the chemical being selected to modify a property of the treatment fluid; and communicating signals along the larger tubing via a communication line.
13. The method as recited in claim 12, wherein deploying comprises deploying the larger tubing in the form of coiled tubing.
14. The method as recited in claim 12, wherein deploying comprises pumping the micro-coil tubing down through an interior of the larger tubing.
15. The method as recited in claim 12, wherein deploying comprises deploying the micro-coil tubing along an exterior of the larger tubing.
16. The method as recited in claim 12, further comprising routing the communication line downhole through the micro-coil tubing.
17. The method as recited in claim 12, further comprising forming the micro-coil tubing from a thermoplastic material.
18. The method as recited in claim 12, wherein using comprises delivering the chemical downhole through the micro-coil tubing in the form of an additive comprising one of: a crosslinker, a breaker, an HT stabilizer, a corrosion inhibitor, a pH adjustor, a rheology enhancer, or an enzyme.
19. The method as recited in claim 12, wherein using comprises delivering the chemical downhole through the micro-coil tubing in the form of a tracer for monitoring the well and the well treatment.
20. The method as recited in claim 12, wherein using comprises delivering the chemical downhole into a mixing region with a desired turbulent flow pattern.
21. The method as recited in claim 12, further comprising detecting electrical properties of a surrounding formation by using conductive and nonconductive portions of the micro-coil tubing.
22. A system for treating a well, comprising: a coiled tubing deployed in a wellbore; a micro-tubing sized to enable deployment along an interior of the coiled tubing; a securing mechanism to secure a downhole end of the micro-tubing proximate an end of the coiled tubing; and an end fixture coupled to the micro-tubing and located downhole to control the discharge and mixing of chemicals separately delivered downhole through the coiled tubing and the micro-tubing to modify a well treatment.
23. The system as recited in claim 22, wherein the micro-tubing is a non-metallic tubing deployed in the coiled tubing and held by the securing mechanism.
24. The system as recited in claim 22, wherein the end fixture comprises a plurality of openings located at positions 360.degree. around a mixing chamber.
25. The system as recited in claim 22, wherein the end fixture comprises a plurality of vanes oriented to facilitate mixing of a chemical additive, delivered through the micro-tubing, with a separate well treatment fluid delivered through the coiled tubing.
 During and after many downhole wellbore operations, such as hydraulic fracturing, a controlled release of chemicals may be desired. In many applications, however, treatment fluids travel to substantial depths which can affect properties of the chemicals delivered downhole. The detrimental effects on the treatment chemicals often are exacerbated when certain chemicals are mixed at the surface and then delivered downhole to the substantial depths.
 Coiled tubing has been employed to deliver well treatment fluids downhole for enhancing hydrocarbon production. Examples of well treatment applications employing coiled tubing include the pumping of stimulation fluids, e.g. acids, solvent washes, scale dissolvers, and/or fracturing fluids; and the pumping of cleanout fluids, e.g. nitrogen, CO2, polymer-containing aqueous brines (xanthan and diutan), and mixed metal hydroxides to lift sand, debris or drill cuttings. However, challenges have arisen in delivering the chemicals in a controlled manner to the desired depths with conventional coiled tubing systems. A number of solutions have been proposed, such as the use of fluid plugs, canisters, and encapsulation. Additionally, the use of micro-coil chemical delivery has been attempted, but such techniques incur various difficulties.
 For example, difficulties arise in retrofitting existing coiled tubing systems with micro-coil tubing. Additionally, existing systems are inadequate for delivering and mixing the desired chemicals to modify properties of the well treatment system. Furthermore, existing systems may not be capable of sufficient interaction with monitoring systems and other downhole systems employed during a given well treatment application.
 In general, a system and method is described for facilitating performance of a well treatment in which a micro-tubing, e.g. a micro-coil or micro-capillary tubing, is deployed for cooperation with a larger tubing, such as a coiled tubing positioned in a wellbore. The micro-tubing is used to deliver a separated chemical downhole for modifying a property of a treatment fluid used in performing a desired well treatment operation at a desired treatment region along the wellbore. Additional components may be combined with the micro-tubing to further facilitate the treatment application. For example, a securing mechanism may be used to selectively secure a lower end of the micro-tubing proximate a lower end of the larger tubing. In some embodiments, a communication line also is routed downhole along the micro-tubing to facilitate transmission of signals, e.g. power and/or data, between downhole and surface locations. The communication line may be used in cooperation with a sensor system.
BRIEF DESCRIPTION OF THE DRAWINGS
 Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
 FIG. 1 is a schematic front elevation view of one embodiment of a well system having a micro-tubing deployed in a wellbore for a well treatment application;
 FIG. 2 is a bottom view of the micro-tubing illustrated in FIG. 1;
 FIG. 3 is a front view of one embodiment of a treatment system employing a micro-coil tubing having an end fixture;
 FIG. 4 is a cross-sectional, schematic view of another embodiment of a treatment system employing a micro-tubing having a different type of end fixture used in cooperation with a larger tubing;
 FIG. 5 is a cross-sectional, schematic view of another embodiment of a treatment system employing a micro-tubing used in cooperation with a larger tubing;
 FIG. 6 is a cross-sectional, schematic view of another embodiment of a treatment system employing a micro-tubing used in cooperation with a larger tubing; and
 FIG. 7 is a schematic view of another embodiment of a treatment system employing a micro-tubing used in cooperation with a larger tubing.
 In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it will be understood by those of ordinary skill in the art that the present disclosure may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
 The embodiments described herein generally relate to a system and method for improving the performance of a well treatment at a downhole location. According to one embodiment, a treatment fluid, e.g. a fracturing fluid, stimulation fluid, or other treatment fluid, may be modified by separately delivering one or more chemicals downhole through a micro-tubing. By way of example, the micro-tubing may comprise a micro-coil tubing which is pumpable along a larger tubing, e.g. a larger coiled tubing, deployed in a wellbore. In some applications, the micro-tubing is pumped down through an interior of the larger tubing with the aid of a pump-down plug and/or velocity booster.
 The well treatment system also may comprise a communication line for conveying sensor data which enables monitoring of the treatment application. In some applications, the monitoring may be performed in real-time by, for example, a fiber optic system deployed downhole adjacent the micro-tubing. The communication line may be protected by the micro-tubing via placement of the communication line along an interior of the micro-tubing. Depending on the application, the communication line may utilize an optical fiber in the form of a distributed sensor (for sensing temperature, vibration, and/or pressure) and/or the communication line may be coupled to downhole sensor systems. Additionally, the communication line may be an individual line or multiple lines for carrying data signals and/or power signals between the downhole sensor or sensor systems. If the communication line is designed for power, power signals may be directed downhole to power one or more components of the well treatment equipment located downhole.
 According to one specific embodiment, the micro-tubing employed with the overall well treatment system is a pumpable tubing formed of a non-metallic material, such as a thermoplastic material. One example of a suitable thermoplastic material is a polyetheretherketone (PEEK) material which is delivered along an interior of coiled tubing to an end of the coiled tubing via pumping. A downhole end of the micro-tubing is fitted with an end fixture in the form of a plug, e.g. an expandable or inflatable plug. The plug may be designed as a securing mechanism to secure the micro-tubing within the coiled tubing or casing and to seal the micro-tubing with respect to the coiled tubing or casing. In an embodiment, the micro-tubing may be formed from a composite material containing metals or formed from a non-metallic material comprising a coating of metallic paint or nano materials
 As illustrated and described in greater detail below, one embodiment of the plug is fitted with burst discs, such as a first burst disc which enables inflation or expansion of the plug to facilitate pumping of the micro-tubing, and another burst disc to open the coil for flow of chemicals once the thermoplastic micro-tubing has been fully inserted to the end of the surrounding coiled tubing. In some embodiments, the plug is designed to fit into a securing mechanism having the form of a tool receptacle attached at the end of the coiled tubing. The tool receptacle helps lock the micro-tubing in place. The securing mechanism also may be integrated with a mixing device to facilitate mixing of fluids delivered through the micro-tubing and through the coiled tubing. By way of example, the mixing device may be designed with openings oriented to create a vortex effect which facilitates mixing of fluids, and thus modification of the treatment fluid at the downhole location. The plug and/or other securing features enable retrofitting of coiled tubing with a much smaller micro-tubing by allowing deployment of the micro-tubing to a desired location within the coiled tubing via pumping followed by securing the micro-tubing.
 Referring generally to FIG. 1, one embodiment of a well system 20 is illustrated as having a well treatment system 22 deployed in a wellbore 24. The wellbore 24 extends down from a surface location and into or through a subterranean formation 26. By way of example, the wellbore 24 may be cased with a casing 28 having perforations 30 which allow injection of the treatment fluid into the surrounding subterranean formation 26 at a desired well treatment region 32.
 The well treatment system 22 is illustrated schematically and may comprise a variety of configurations and components. By way of example, the well treatment system 22 comprises a micro-tubing 34, which may be a micro-coil tubing or a micro-capillary tubing, for delivering an additive/chemical 35 to the well treatment region 32. The micro-tubing 34 is deployed along a larger tubing 36, which in many applications comprises coiled tubing. In the example illustrated, the micro-tubing 34 is deployed along an interior 38 of the larger tubing 36, e.g. coiled tubing. Depending on the application, the micro-tubing 34 may comprise an individual tubing or multiple tubings, as represented by the additional tubing shown in dashed lines in FIG. 1. If the micro-tubing 34 comprises multiple tubings, a plurality of different chemicals 35 may be selectively delivered downhole to the well treatment region 32 via the multiple tubings for mixing with a treatment fluid 39. Treatment fluid 39 is delivered separately along the interior 38 of larger tubing 36 outside of micro-tubing 34.
 By way of example, the well treatment fluid 39, e.g. a fracturing fluid, may be delivered downhole through tubing 36 in the annulus formed between micro-tubing 34 and an interior surface 40 of tubing 36 before exiting at a discharge region 41 of tubing 36. One or more chemical additives 35 may be simultaneously, but separately, delivered down through micro-tubing 34 for mixing with treatment fluid 39 at a desired downhole mixing region 42, e.g. a mixing chamber. This at depth mixing allows the well treatment fluid to be modified in a desired manner at the downhole region 42 for injection into the well treatment region 32 of formation 26.
 In the example illustrated, micro-tubing 34 is pumped down through the interior of coiled tubing 36 which enables retrofitting of existing coiled tubing systems. However, the micro-tubing 34 may be pumped down through larger tubing in a variety of applications and systems. The pumping down may be facilitated by providing the micro-tubing 34 with an end fixture 44 which may comprise (or work in cooperation with) a securing mechanism designed to secure micro-tubing 34 at a desired position within coiled tubing 36, such as at a downhole end of coiled tubing 36.
 According to one embodiment, end fixture 44 comprises a pump-down plug 46 having a seal 48 designed to seal against interior surface 40 of tubing 36. The pump-down plug 46 helps pull micro-tubing 34 down through the interior 38 of tubing 36 when fluid is pumped down from a surface location. The plug 46 may be selectively expanded or inflated against the interior surface 40 to facilitate pumping of micro-tubing 34 to the desired downhole location within larger tubing 36. In some applications, the pump-down plug 46 serves as a securing mechanism via selective expansion into engagement with the surrounding tubing 36. However, in other applications a separate securing mechanism 50 may work alone or in cooperation with plug 46 to secure the micro-tubing 34 at the desired location in tubing 36. For example, the securing mechanism 50 may comprise a landing feature, latch, collett, or other securing mechanism designed to grip and hold the lead end of micro-tubing 34 at a desired location, e.g. at a downhole end of tubing 36.
 As further illustrated in FIG. 2, the pump-down plug 46 may comprise one or more controllable openings 52, e.g. valves or burst discs, which allow the plug 46 to be pressurized and inflated or otherwise expanded against interior surface 40. In one example, application of sufficient pressure causes the disc 52 to rupture which enables flow of chemicals 35 down through micro-tubing 34 and into mixing region 42. In some applications, an additional burst disc or valve 52 may be used to prevent expansion of the pump-down plug 46 until a desired stage of the process. Other burst discs or valves 54 also may be used in plug 46 to selectively control the flow of well treatment fluid 39 through the plug from the annulus surrounding micro-tubing 34 within larger tubing 36. In other embodiments, however, the flow of well treatment fluid 39 may be enabled by deflating or otherwise disengaging pump-down plug 46 from interior surface 40.
 In some applications, the communication line 56 of well treatment system 22 comprises one or more communication lines, as further illustrated in FIG. 1. The communication line 56 may comprise an optical fiber cable, however the communication line also may comprise other signal carriers to carry data signals and/or electrical power signals. In some embodiments, communication line 56 enables transmission of data signals to and/or from an electronics and sensor system 58 deployed downhole to monitor the mixing and application of treatment fluids and additives. By way of example, sensor system 58 may comprise downhole sensors for measuring fluid pH, pressure, temperature, viscosity, acoustic measurements, salinity, and/or other parameters. The communication line 56 also may comprise electric lines designed to transfer electrical power signals to a downhole tool 60 of the downhole equipment employed to carry out the well treatment operation. For example, downhole tool 60 may comprise one or more components of an injection system employed to inject fracturing fluids into the surrounding formation 26. In some embodiments, downhole tool 60 comprises one or more of actuatable valves, sleeves, and/or ports. A control system 62, such as a computer-based processing system, may be employed at a surface location with suitable surface equipment or at another suitable location to control the delivery of signals downhole and to receive/process data received from the downhole components.
 In the embodiment illustrated, communication line 56 is deployed within micro-tubing 34, although the communication line may be routed downhole within the coiled tubing 36 outside of micro-tubing 34 or at other suitable locations. In some applications, the communication line 56 is embedded in a wall of the micro-tubing 34 or in a wall of the larger tubing 36. By placing the communication line 56 within micro-tubing 34, the communication line is protected. Depending on the application, the communication line 56 may be pumped down through tubing 36 while within micro-tubing 34. In other applications, however, the communication line 56 may be pumped down through micro-tubing 34 after deployment of the micro-tubing downhole. If the communication line 56 is an optical fiber used as a distributed sensor system, the optical fiber may simply be pumped down and returned to a surface location, as with other distributed sensor systems deployed downhole. In other applications, the communication line 56 is coupled to downhole equipment, such as sensor system 58 and/or downhole tool 60, via appropriate wet connectors or other types of available connectors.
 As discussed briefly above, some treatment applications benefit from forming micro-tubing 34 from a thermoplastic material, such as PEEK. Such materials have high temperature limits and high tensile strength while being exceptionally chemically resistant. In this specific example, the pump-down plug 46 is made of a plastic or metal material with concentric seals 48 along its outside diameter. The seals 48 serve as wipers and prevent undesirable fluid communication across the plug. Pressurizing fluid above the plug 46 causes the plug to expand and then to move downhole along the interior of tubing 36 until it is received in securing mechanism 50, e.g. a landing tool. In some applications, the plug 46 is designed to latch into a receptacle attached to the end of the coiled tubing 36 so as to secure the lead end of the PEEK tubing.
 After landing in the securing mechanism 50, plug 46 may be opened to the flow of additives/chemicals by opening the controllable opening 52. The plug 46 also may be removed, e.g. dissolved, or otherwise opened up to enable the flow of well treatment fluid down through tubing 36 along the exterior of micro-tubing 34. To remove micro-tubing 34 from the wellbore, the tubing may simply be pulled from the plug 46 and from securing mechanism 50, if present. After removal, the PEEK tubing 34 can be retooled for the next deployment. Alternatively, the micro-tubing 34 may be left within larger tubing 36 and used for future delivery of desired chemicals.
 Referring generally to FIG. 3, another embodiment of end fixture 44 is illustrated as located at the lower end of micro-tubing 34. In this embodiment, the end fixture 44 comprises one or more velocity boosters 64 designed to catch fluid as end fixture 44 and micro-tubing 34 are pumped down through larger tubing 36 to the securing mechanism 50. The velocity boosters 64 may be in the form of cups or flaps designed to catch the pump-down fluid and to speed movement of micro-tubing 34 through the surrounding tubing 36. In some applications, the pump-down fluid may comprise a treatment fluid.
 End fixture 44 further comprises an enlarged portion 66, such as an enlarged cylinder, having a plurality of perforations 68. The perforations 68 are oriented to discharge the desired chemical 35 delivered through micro-tubing 34 into mixing region 42. Initially, the perforations 68 may be sealed to protect against leakage during deployment of the micro-tubing 34 through coiled tubing 36. By way of example, the perforations may be sealed with a dissolvable or removable material 70. Similarly, the velocity booster or boosters 64 also may be dissolvable or removable. In some applications, the velocity boosters 64 are frangible so they can be selectively shattered and removed. Removal of the velocity boosters 64 is often desirable to facilitate flow of well treatment fluid through interior 38 of coiled tubing 36 for mixing with the chemical additives 35 delivered through micro-tubing 34. In a similar manner, the seals 48 and/or plug 46 illustrated in FIG. 1 also may be dissolvable or removable.
 The end fixture 44 can be constructed with additional features to facilitate the well treatment application. For example, one or more valves 72 may be employed to control the flow of chemicals from micro-tubing 34 to perforations 68. This valving enables control over the additive dosage as additives 35 are delivered to modify the well treatment fluid 39 routed externally of micro-tubing 34 within tubing 36. The one or more valves 72 may be controlled via signals, e.g. hydraulic or electric signals, delivered through communication line 56. The end fixture 44 also may comprise a jetting tool 74. Additional features may comprise a magnet 76 positioned to minimize movement of the communication line 56. In some applications, the magnet 76 is exposed by dissolving or otherwise removing the surrounding velocity boosters 64 after positioning micro-tubing 34 and communication line 56 in the well. The magnet 76 may be used to facilitate connection and/or communication of signals between the communication line 56 and downhole components, such as sensor system 58 and downhole tool 60.
 As discussed above, communication line 56 may be constructed in a variety of forms and may be coupled with other devices/systems downhole via a variety of available wet connectors, inductive couplings, and other types of connectors. The type of connector employed (if a connector is needed) depends on the application and use of communication line 56. In some applications, for example, communication line 56 comprises an optical fiber 78 which may be used to take measurements of the duration of the treatment, flowback, and production. By way of example, optical fiber 78 may comprise a distributed sensor system, such as a distributed temperature sensor system. In some applications, the optical fiber 78 is designed to relay signals back and forth between the downhole components and control system 62, including instruction signals from the control system 62 to the downhole component(s). The optical fiber 78 also may be used to deliver light, e.g. UV light, for activation of additives delivered through micro-tubing 34 and/or to cause treatment fluid reaction. In some applications, the optical fiber 78 may even be used in cooperation with the micro-tubing 34 to measure fluid properties by illuminating a sample of fluid using a colorimetric method.
 Communication line 56 also may comprise additional signal carriers, such as one or more electrical lines 80 designed to carry data and/or power signals. For example, power signals may be delivered through electric line 80 to power downhole tool 60 (see FIG. 1). The electric line 80 also may be used to deliver voltage for the purpose of generating heat to initiate reactions downhole. In some applications, downhole tool 60 is an acoustic tool and electric line 80 powers the tool 60 to provide acoustic or ultrasound effects which help initiate downhole reaction of chemicals.
 The micro-tubing 34 is used to deliver a variety of chemicals 35 downhole, e.g. additives used to modify properties of the treatment system/treatment fluid 39 when mixed with the treatment fluid at mixing region 42. By way of example, micro-tubing 34 may be used to deliver additives comprising one or more of crosslinkers, breakers, breaker aids, HT stabilizers, corrosion inhibitors, rheology enhancers, enzymes, oxygen scavengers, scale control additives, H2S scavengers, viscosity boosters, activators, clay stabilizers, buffers, emulsifiers, demulsifiers, pH adjusters, reaction activators, catalysts, and/or other chemical additives. Additionally, the additive may be delivered in a desired physical state, such as a liquid, a solution, an emulsion, a colloid, a slurry, a foam, or a gas. The type of additive chemical 35 delivered through micro-tubing 34 may be selected according to the type of well treatment fluid 39 separately delivered downhole. Well treatment fluid 39 may comprise fracturing fluid, but the fluid 39 also may comprise a variety of other types of fluids, including slurries, acids, stimulants, and other well treatment fluids. In an embodiment, the additive chemical 35 comprises a gas that may be delivered through the micro-tubing 34 to create a foam with fluids at the mixing region 42. In an embodiment, an additive chemical 35 may be delivered downhole through the micro-tubing 34 to the mixing region 42 using energized gas.
 Furthermore, individual additives or multiple additives may be delivered downhole to mixing region 42 via a single micro-tubing 34. In alternate embodiments, multiple additives may be delivered downhole separately through multiple micro-tubings 34. The amount of chemical additives added to the well treatment fluid in mixing region 42 may be metered and controlled by, for example, one or more of the valves 72. Additionally, the micro-tubing 34 may be employed to inject tracers which are used for monitoring the well application, such as the well treatment and/or well production. In some applications, the micro-tubing 34 may even be employed for fluid sampling by reversing the flow of fluid through the micro-tubing.
 Referring generally to FIG. 4, another embodiment of well treatment system 22 is illustrated. In this embodiment, micro-tubing 34 is routed down through larger tubing 36 at an off-center position generally along the interior surface 40. The micro-tubing 34 is joined with end fixture 44 via a tubing connector 82. In this embodiment, end fixture 44 is generally cylindrical and has an outer surface 84 which lies generally along interior surface 40 of tubing 36. The end fixture 44 further comprises an interior surface 86 which defines mixing region or chamber 42.
 A flow passage 88 is disposed between outer surface 84 and interior surface 86 and delivers the additive 35 to a plurality of injection ports 90. Injection ports 90 may be in the form of openings/perforations formed through interior surface 86 to introduce the chemical 35 into mixing region/chamber 42. The injection ports 90 are oriented to impart a desired mixing flow. In one embodiment, the injection ports 90 are distributed over the full 360° circumference along interior surface 86 around the mixing region 42 (or along a circumference less than the 360°) to provide a distributed injection of chemical 35 from micro-tubing 34. The injection ports 90 also may be oriented to induce turbulent flow to enhance mixing with the well treatment fluid 39. In other applications, the injection ports 90 may be oriented to induce a vortex similarly designed to enhance mixing with the primary well treatment fluid 39. The mixing also may be enhanced by employing a plurality of mixing vanes 92 along the interior surface 86 of end fixture 44. The mixing vanes 92 may be designed to act as an inline static mixer at the end of the micro-tubing 34.
 In the embodiment illustrated in FIG. 4, the end fixture 44 is pumped down through larger tubing 36 along with its micro-tubing 34. The pumping down may be facilitated by providing a temporary restrictor 94, e.g. a burst disc, across the end fixture 44, as illustrated. The end fixture 44 is pumped down until a lower end of the fixture/micro-tubing is captured by securing mechanism 50. By way of example, the securing mechanism 50 may comprise a combined landing nipple and lock 96 located at a bottom end 98 of tubing 36 to lock the micro-tubing 34 in place. Additionally, the sensor assembly 58 may be located in end fixture 44 and may comprise a plurality of sensors 100 for detecting and/or monitoring a variety of fluid and mixing related parameters, as discussed above.
 Referring generally to FIG. 5, another embodiment of well treatment system 22 is illustrated. In this embodiment, the end fixture 44 is similar to the embodiment of end fixture 44 described with reference to FIG. 4, and corresponding components have been labeled with corresponding reference numerals. In the embodiment illustrated in FIG. 5, however, the micro-tubing 34 is delivered along an outside of tubing 36, e.g. coiled tubing. The micro-tubing 34 comprises a stinger end 102 which may be stung into a corresponding receptacle 104 disposed on end fixture 44. A variety of communication lines 56, e.g. fiber-optic cable 78 and/or electrical line 80, may be deployed within micro-tubing 34. Furthermore, the end fixture 44 may have a variety of configurations designed to facilitate mixing of the additive chemical 35 with the well treatment fluid 39 to effectively modify the well treatment fluid at the downhole mixing region 42. Similar to the previously described embodiment, the sensor package 58 may comprise a variety of sensors coupled to one or more communication lines 56 for detecting and monitoring a variety of treatment system related parameters.
 Another embodiment of well treatment system 22 is illustrated in FIG. 6. In this embodiment, micro-tubing 34 is combined with an end fixture 44 having a delivery and electronics package (DEP) 106 which combines the electronics and sensor package 58 with a chemical delivery section 108 designed to deliver the chemical additive 35 into mixing chamber 42. The DEP 106 is deployed down through tubing 36 with micro-tubing 34 until the DEP 106 has landed in a corresponding securing mechanism 50, e.g. landing and locking nipple 96. The DEP 106 may be landed inside a tubing tailpipe 110 which has an internal diameter greater than the diameter of the micro-tubing 34 and its end fixture 44. Once the DEP 106 is landed, it may be latched in place.
 During a well treatment operation, e.g. a well stimulation operation, chemicals are delivered down through the micro-tubing 34 into the DEP 106 and out through openings 112, e.g. jets, integrated into the DEP at the chemical delivery section 108. The openings 112 may be positioned to evenly disperse the chemical 35 into the surrounding interior of tubing tailpipe 110. A variety of mixing vanes 114 may be employed within the tubing tailpipe 110 to help homogenize the chemicals 35 and well treatment fluids 39 before exiting the tailpipe assembly.
 In some applications, communication line 56 may be added in the form of a wireline attached to the DEP 106. The electronics and sensor package 58 within the DEP 106 provides data back to the surface through the communication line 56 as described above. For example, sensor package 58 may be designed to detect and/or monitor various well treatment operation parameters, including pH, temperature, pressure, viscosity, depth, electrical conductivity, fluid velocity, sound and/or vibration, and/or other parameters related to the fluids and well treatment operation. Other types of data, such as quality control data, also may be included in the data stream delivered to control system 62 from electronics and sensor package 58. As described with respect to other embodiments herein, the communication line 56 may again comprise electric lines, e.g. electric lines 80, to deliver data and/or power to downhole mixing equipment incorporated into the DEP 106 or positioned at other locations in the downhole equipment.
 Once the well treatment operation is completed, a signal may be sent downhole to initiate release of the DEP 106 from the securing mechanism 50. The DEP 106 may then be retrieved to the surface. In this example, the tubing tailpipe 110 remains in the well without interfering with production operations. If subsequent well treatments are desired, the DEP 106 can be redeployed down through tubing 36 to securing mechanism 50 for delivery of desired chemicals and/or gathering of data prior to and/or during the subsequent well treatment operation. It should be noted that if a stimulation treatment is delivered down the casing without tubing 36, a wireline retrievable packer assembly having a securing mechanism/landing nipple for the DEP 106 may be placed and set prior to deployment of the DEP. The DEP 106 may then be deployed and locked in place at the securing mechanism 50.
 Referring generally to FIG. 7, another embodiment of well treatment system 22 is illustrated. In this embodiment, the end fixture 44 is enlarged and contains a canister 116 with a controllable valve 118. The canister 116 contains an additional chemical 120 which may be delivered through valve 118 for mixing with additive chemical 35 and with well treatment fluid 39. When valve 118 is closed, there is no mixing of the chemical additive 35/well treatment fluid 39 and the additional chemical 120. The additive chemical 35 can simply flow past the canister 116 for mixing with well treatment fluid 39. When the valve 118 is opened, the additional chemical 120 is released for mixing with the other chemicals. In some embodiments, valve 118 is positioned to enable flow of chemical 35 from micro-tubing 34 through canister 116, thus allowing on demand release of the second chemical from canister 116. Depending on the type of chemical contained by canister 116, the mixing can be accomplished internally or externally with respect to the canister. Switching of valve 118 may be accomplished by signals delivered through communication line 56 or by other communication modes, such as pressure pulses, pumping down a ball or dart, or by other suitable methods for communicating instructions to the valve. In an embodiment, the micro-tubing 34 may be utilized to activate the contents of the canister 116 pumping a device or fluid to dissolve or otherwise open an opening or openings in the canister 116 to release the contents 120 of the canister 116.
 Depending on the specific treatment application and environment, the well treatment system 22 may be constructed according to a variety of configurations. Various micro-tubing and coiled tubing arrangements can be combined with a number of end fixtures, sensor systems, and other components to facilitate the delivery and mixing of chemicals at the downhole mixing region. In some applications, for example, the micro-tubing 34 may be constructed of non-conductive materials and conductive materials to form non-conductive sections 122 and conductive sections 124 which may be employed to measure electrical properties of the surrounding formation, as illustrated in FIG. 7. In other applications, the micro-tubing 34 may be designed to operate in conjunction with optical fibers of communication line 56 to measure gas hold up. By way of additional examples, the micro-tubing 34 may be used in selectively treating one or more well treatment regions 32 disposed along wellbore 24. The micro-tubing also may be used to assist the detection and monitoring of a variety of parameters, e.g. the micro-tubing may be employed as a pipe rheometer to measure fluid viscosity downhole. In an embodiment, the micro-tubing 34 may be constructed of a material that may subsequently degrade with time after having delivered a specific chemical downhole. In an embodiment, the micro-tubing 34 may be constructed of a high strength composite material.
 Additionally, control over the chemical mixing may be automated via control system 62. In this example, signals are provided to control system 62 from the various sensors 100 located downhole, and the control system 62 automatically responds by controlling delivery of the desired chemical additives to optimize fluid chemistries of mixed fluids delivered into the surrounding formation. The shape, configuration, and materials used to construct the various components of the overall well treatment system 22 may be adjusted as desired for a given well treatment operation and the characteristics of the surrounding environment.
 In an embodiment, the micro-tubing 34 is utilized to pump air or fluid in the same direction within the micro-tubing. In an embodiment, the micro-tubing 34 is loaded utilizing vacuum or negative pressure from one end of the micro-tubing 34. In an embodiment, the micro-tubing 34 defines one or more compartments of similar outside diameter or different radii, whereby the amount of material delivered by the micro-tubing 34, such as the chemical/additive 35, may be controlled by selected the compartments of different radii. In an embodiment, the chemical/additive 35 may be pumped through the micro-tubing 34 at the time of treatment in order to modify treatment fluid 39, such as at the mixing region 42. In an embodiment, the chemical/additive 35 may be pumped after the treatment during flowback, such as a corrosion inhibitor to reduce the corrosion tendency due to the hot unspent acid coming back after an acid treatment. In an embodiment, the chemical/additive 35 and/or the treatment fluid 39 may comprise two treatment fluids or chemical additives that individually will not affect the fluid properties and a third, intermediate fluid or additive that will react with the two fluids and change the fluid properties, such as, but not limited to, by a fluid pumped through annulus outside the tubing 36, another fluid pumped down inside the tubing 36 and a fluid which is mixed after injection from the micro-tubing 34.
 In an embodiment, the micro-tubing 34 it utilized to perform depth measurements, such as by using the fiber optic, temperature/vibration correlation against known perforation depth or by recording deployed length of the micro-tubing 34 from surface. In an embodiment, pressure measurements may be performed by the micro-tubing 34, especially while not pumping through the micro-tubing 34. The micro-tubing 34 may be used as a very effective "dead string". The micro-tubing 34 which will carry reasonably clean & homogeneous fluids 35 may be used as a very effective pressure guide to transmit transient pressure information either upwards or downwards, which may be utilized for telemetry purposes, or reservoir interpretation, such as well testing, fracture closure pressure determination, etc. In an embodiment, the larger tubing 36 comprises coiled tubing having long perforated intervals in an end of the tubing 36. The micro-tubing 34 and plug 46 may then be dynamically positioned up or down the perforated interval to change the ratio (and the location) of treated fluid vs. untreated fluid. The well treatment system 22 may be utilized to treat multiple zones at the same time with different fluid rheologies, such as by pumping fluid through annulus outside the tubing 36, pumping fluid down inside the tubing 36, and by pumping another fluid 35 through the micro-tubing 34. In an embodiment, fluids (treatment fluids or reservoir fluids) may be backflowed into the micro-tubing 34 in order to take fluid samples during or after treatment. In an embodiment, positioning, actuating, and measuring of the plug 46 may be handled via slickline or wireline deployed in a coiled tubing 36.
 Accordingly, although a few embodiments of the present disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.
Patent applications by Andrey Mirakyan, Katy, TX US
Patent applications by Hemant K.j. Ladva, Missouri City, TX US
Patent applications by Mathew M. Samuel, Sugar Land, TX US
Patent applications by Richard D. Hutchins, Sugar Land, TX US
Patent applications by SCHLUMBERGER TECHNOLOGY CORPORATION
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