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FIELD OF THE INVENTION 
   The invention relates to an injection apparatus for injecting an activated fluid (e.g. an activated chemical fluid mixture) into a well-bore. The invention also relates to an injection method for injecting an activated fluid into a well-bore. 
   A particular application of the invention relates to the oilfield industry, for example in cementing operation. 
   BACKGROUND OF THE INVENTION 
   During a hydrocarbon well drilling operation and after a hydrocarbon well has been drilled, various fluid injecting operations are generally carried out. The fluid injecting operations serves various purposes, for example delivering a chemical mixture into a fluid present in the borehole for consolidation purpose or fracturing purpose, or delivering a chemical mixture into a cement slurry for borehole cementing operation. These operations are well known in the oilfield industry and are described for example in U.S. Pat. No. 3,273,647, U.S. Pat. No. 4,415,269 and patent application EP 1223303.  FIG. 1  schematically shows a typical onshore hydrocarbon well location and equipments WE above a hydrocarbon geological formation GF after drilling operation has been carried out and after a casing string CS has been run. At this stage, the well-bore WB is a bore-hole generally filled with various fluid mixtures (e.g. the drilling mud or the like). The equipment WE comprises a drilling rig DR for running the casing string CS in the bore-hole, cementing equipment comprising cement silo CR and pumping arrangement CP, and a well head and stuffing box arrangement WH providing a sealing for deploying the casing string CS or pumping down the cement into the generally pressurized well-bore WB. 
   Subsequently, cementing operations are generally undertaken to seal the annulus AN (i.e. the space between the well-bore WB and the casing CS where fluid can flow). A first application is primary cementing which purpose is to achieve hydraulic isolation around the casing. Other applications are remedial cementing which purposes are to stabilize the well-bore, to seal a lost circulation zone, to set a plug in an existing well or to plug a well so that it may be abandoned. The cement may be pumped into the well casing through a casing shoe CI near the bottom of the bore-hole or a cementing valve installed in the casing so that the cement is positioned in the desired zone. 
   Cementing engineers prepare the cementing operations by determining the volume and physical properties of cement slurry and other fluids pumped before and after the cement slurry. In many situations, chemical additives are mixed with the cement slurry in order to modify the characteristics of the slurry or set cement. Cement additives may be broadly categorized as accelerators (i.e. for reducing the time required for the set cement to develop sufficient compressive strength to enable further operations to be carried out), retarders (i.e. for increasing the thickening time of cement slurries to enable proper placement), dispersants (i.e. for reducing the cement slurry viscosity to improve fluid-flow characteristics), extenders (i.e. for decreasing the density or increasing the yield of a cement slurry), weighting agents (i.e. for increasing or lightening the slurry weight), fluid-loss or lost-circulation additives (i.e. for controlling the loss of fluid to the formation through filtration) and special additives designed for specific operating conditions. 
   Because cement additives have an effect as soon as they are mixed with the cement slurry, it is important that cement additives are injected in the cement slurry at the proper time and at the desired location in the well-bore. 
   Apparatus for injecting cement additives are known. For example, U.S. Pat. No. 5,533,570 discloses an apparatus for injecting a fluid into a well-bore. This apparatus comprises a fluid holding chamber that is pumped down the well-bore, and a valve means for opening a port of the chamber and delivering the fluid at a desired time and location (for example through an opening of the casing shoe). However, this apparatus does not include an efficient additive dosing system. Further, the apparatus is non-retrievable. 
   SUMMARY OF THE INVENTION 
   One goal of the invention is to propose an apparatus for injecting an activated chemical fluid mixture into a well-bore that overcome at least one of the shortcomings of prior art apparatus. 
   According to the invention, the apparatus for injecting an activated chemical fluid mixture into a well-bore comprises a valve arrangement, an activation fluid reservoir and a dosing and mixing arrangement coupled to each other. The valve arrangement can be remotely activated from the surface. The apparatus is coupled to a standard drill-pipe string or a casing string in order to receive a flow of a first fluid and activation commands for the valve arrangement. The valve arrangement activates and controls the dosing and mixing arrangement so as to inject a determined quantity of activation fluid into the first fluid. The apparatus can be coupled to any casing, cementing or drilling equipments, and provides to these equipments a flow of a second fluid that may be constituted of an activated chemical fluid mixture. 
   More precisely, the present invention relates to an injection apparatus for injecting an activated fluid into a well-bore comprising a reservoir containing an activation fluid AF. The injection apparatus further comprises:
         a valve arrangement adapted to be coupled to a pipe (drill-stem or casing string) for receiving a first fluid flow,   a dosing and mixing arrangement coupled to the reservoir and to the valve arrangement.       

   The valve arrangement has a rest configuration in which the injection apparatus provides a non-activated fluid mixture and an activated configuration in which the injection apparatus provides an activated fluid mixture. 
   The dosing and mixing arrangement comprises an engine part mechanically coupled to a pumping part. The engine part runs the pumping part and the pumping part sucks the activation fluid of the reservoir when the valve arrangement is in the activated configuration. The dosing and mixing arrangement mixes the activation fluid with the first fluid and provides an activated fluid mixture flow at an outlet. 
   Advantageously, the injection apparatus further comprises a pressure adjusting arrangement for adjusting the pressure inside the reservoir to the pressure inside the pipe (a reservoir comprising a piston or a reservoir comprising an equalization port). 
   Advantageously, the valve arrangement comprises a sliding sleeve having a first dart catcher for remotely activating the valve arrangement from the rest configuration to the activated configuration. 
   Other characteristics of the injection apparatus will be further described in the detailed description herein below. 
   The apparatus for injecting an activated chemical fluid mixture into a well-bore of the invention is adapted to be connected to a drill-string or a casing string. The apparatus is fully retrievable: it can be removed from the well-bore when operations are completed and re-used for subsequent operations. Alternatively, it can be drilled if rig-time needs to be saved. It enables a truly proportional dosing of an activation fluid into a fluid to be activated. Finally, it can be remotely controlled. 
   Consequently, the apparatus of the invention is flexible, cheap and efficient to use in various oilfield industry oriented applications. 
   In particular, the apparatus can be used in casing stab-in situation (i.e. injecting a chemical activator into a cement slurry directly at the casing shoe), in drilling situation (i.e. injecting a chemical activator into a reactive fluid pumped through the drill-string) for well-bore walls or plugs voids consolidation, in cement plug situation (i.e. injecting a chemical activator into a fluid for temporary of permanent sealing inside the well-bore), in casing-drilling situation, or in coiled-tubing operation (i.e. injecting a chemical activator into the main fluid for coiled tubing fracturing or remedial cementing). 
   The invention also relates to an injection method for injecting an activated fluid into a well-bore. The method comprises the steps of:
         running the injection apparatus of the invention at a proper location in the well-bore, the valve arrangement being in a rest configuration,   letting flow a first fluid through the apparatus into the well-bore,   activating the valve arrangement of the injection apparatus in an activated configuration in which a first portion of the first fluid activates a pumping part sucking the activation fluid of the reservoir,   mixing the sucked activation fluid with the first portion of the first fluid, and   injecting an activated fluid mixture flow at an outlet.       

   Optionally, the method further comprises the steps of activating the valve arrangement of the injection apparatus in a by-pass position in which a second portion of the first fluid flows directly to the outlet (non activated fluid flow). 
   Advantageously, the activating steps are remotely controlled from a surface equipment. 
   Thus, the invention provides an efficient apparatus and method which can be run at a desired location in a well-bore and remotely activated at a particular moment for injecting an additive contained in a reservoir into the well-bore. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limited to the accompanying figures, in which like references indicate similar elements: 
       FIG. 1  schematically shows a typical onshore hydrocarbon well location and equipments; 
       FIG. 2  schematically illustrates an apparatus for injecting a chemical fluid mixture into a well-bore according to the invention; 
       FIGS. 3.A ,  3 .B and  3 .C schematically illustrate the valve arrangement of the apparatus of  FIG. 2  and its various positions during operation; 
       FIG. 4.A  schematically illustrates a first embodiment of the dosing and mixing arrangement of the apparatus of  FIG. 2 ; 
       FIG. 4.B  schematically illustrates a second embodiment of the dosing and mixing arrangement of the apparatus of  FIG. 2 ; 
       FIG. 5.A  schematically illustrates a first application of the invention; 
       FIGS. 5.B  and  5 .C are detailed cross-section views of the first application of  FIG. 5.A ; 
       FIG. 6.A  schematically illustrates a second application of the invention; 
       FIGS. 6.B  and  6 .C are detailed cross-section views of the second application of  FIG. 6.A ; 
       FIG. 7.A  schematically illustrates a third application of the invention; and 
       FIGS. 7.B  and  7 .C are detailed cross-section views of the third application of  FIG. 7.A . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  was already described in relation with the background of the invention. 
     FIG. 2  schematically illustrates an apparatus  1  for injecting an activated chemical fluid mixture into a well-bore. 
   The apparatus  1  for injecting a chemical fluid mixture is fitted into the casing CS. The apparatus is coupled by its upper part to a standard drill-pipe string  6 . The apparatus is coupled by its lower part to any equipment such as a standard float equipment of a stab-in casing, a casing drilling or casing shoe, or left as such for other drilling or cementing applications. The apparatus receives through an inlet  7  a flow of a first fluid F 1  from the drill-pipe string  6  and provides through an outlet  8  a flow of a second fluid F 2 . 
   The apparatus  1  for injecting a chemical fluid mixture comprises a valve arrangement  2 , a reservoir  3 , a dosing and mixing arrangement  4  and shunt tubes  9 ,  10 . 
   The valve arrangement  2  is coupled to the drill-pipe string  6  or directly to a casing element of the casing string and receives the flow of the first fluid F 1 . The valve arrangement is also coupled to the reservoir  3  through a first reservoir conduit  3 D and to the dosing and mixing arrangement  4  through a first shunt tube  9 . The valve arrangement may also be coupled directly after the mixing arrangement  5  through a second shunt tube  10 . The valve arrangement can be remotely activated (i.e. opening or closing of valves and ports) from the surface. Depending on the configuration of the valve arrangement  2 , the fluid F 1  may be divided into a first portion F 1 ′ flowing through the shunt tube  9 , or a second portion F 1 ″ flowing through the second shunt tube  10  and a third portion F 1 ′″ flowing though the reservoir conduit  3 D. 
   The reservoir  3  contains an activation fluid AF. The activation fluid may be pressurized by means of a piston  3 B when submitted to the pressure of the third flow portion F 1 ′″ flowing through the conduit  3 D to an upper port  3 A into an upper part of the reservoir. The activation fluid AF may flow through a lower port  3 C and a second reservoir conduit  3 E into the dosing and mixing arrangement  4 . The piston  3 B also acts as a mechanical plug separating the activation fluid AF from the third fluid portion F 1 ′″. The reservoir has for example a cylindrical shape and the piston is a plug similar to the standard plugs used in primary cementing. The reservoir volume (diameter, length) can be very easily adapted to each situation of use of the apparatus, namely quantity of activation fluid to be injected or available place within the casing string, etc. . . . 
   Alternatively, the conduit  3 D, the upper port  3 A and the piston  3 B may be replaced by an equalization port for automatically adjusting the pressure inside the reservoir  3  to the pressure inside the drill-pipe or the casing string. In this case, the reservoir may be a rubber bladder. The bladder membrane submitted to the tubing pressure through the equalization port plays the role of the piston relatively to the activation fluid. 
   The dosing and mixing arrangement  4  is coupled to the first shunt tube  9 . It is also coupled to the lower port  3 C of the reservoir by the conduit  3 E and may receive a portion of the activation fluid AF contained in the reservoir. The dosing and mixing arrangement determines the ratio of activation fluid AF injected into the first fluid flow F 1  (in fact into the first portion F 1 ′ of the first fluid flow). 
   The dosing and mixing arrangement  4  provides the second fluid flow F 2  to the outlet  8 . It insures a proper mixing of the injected activation fluid AF with the first portion F 1 ′ of the first fluid flow. 
   Alternatively, a complementary mixing arrangement may be coupled downstream to the dosing and mixing arrangement. 
   The second shunt tube  10  couples the valve arrangement directly to the outlet  8 . It acts as a side conduit for providing, at the outlet  8 , a second portion F 1 ″ of the first fluid flow that does not need to be activated by the activation fluid. In this case, the second fluid F 2  flowing through the outlet  8  is chemically identical to the first fluid F 1  flowing through the inlet  7 . 
   The first and second shunt tubes  9 ,  10  are conduits by-passing the reservoir  3  and attached to its periphery. The shunt tubes can be designed with various diameters and lengths adapted to the various specific use of the apparatus. 
   The operation principle of the apparatus  1  for injecting an activated fluid mixture into a well-bore will be explained herein below in relation with  FIGS. 3 and 4 . 
     FIGS. 3.A ,  3 .B and  3 .C schematically illustrate the valve arrangement  2  and its various positions during operation. 
   The valve arrangement  2  comprises a sliding sleeve  21 . The sliding sleeve  21  is hollow so as to let flow the first fluid F 1 . It also comprises a side opening  24  for letting flow a portion of the first fluid F 1 . The sliding sleeve comprises a first dart catcher  22  and optionally a second dart catcher  23 . The dart catcher can be remotely activated by a dart sent from the surface in the first fluid F 1  through the drill-pipe string  6  or the casing string CS. This activation of the dart catcher determines different operating configuration or position of the valve arrangement. 
   The valve arrangement  2  comprises a first side conduit  25  connected to the first reservoir conduit  3 D and the first shunt tube  9 , and optionally a second side conduit  26 . 
   According to another embodiment, the second shunt tube is omitted. This embodiment is advantageous when the apparatus does not need to be fastened to a casing shoe. 
     FIG. 3.A  shows the valve arrangement  2  in a first configuration (rest configuration) before activation of the first dart catcher  22  by a first dart. In this configuration, the sliding sleeve closes the first  25  and second  26  side conduits, and the first fluid flows though the hollow sliding sleeve directly into the second shunt tube  10  as fluid flow F 1 ″. 
     FIG. 3.B  shows the valve arrangement  2  in a second configuration (activated configuration) after activation of the first dart catcher  22  by a first dart  27 . In this configuration, the sliding sleeve  21  opens the side opening  24  and the dart closes one end of the sliding sleeve so that the flow of the first fluid F 1  is mainly diverted through the side opening  24  into the first side conduit  25 . Subsequently, the first fluid flow F 1  splits as a third portion F 1 ′″ flowing into the reservoir conduit  3 D and a first portion F 1 ′ flowing into the first shunt tube  9 . The third portion F 1 ′″ flowing into the reservoir conduit  3 D pressurizes the reservoir  3  by acting on the piston  3 B (see  FIG. 2 ). 
   The first portion F 1 ′ flowing into the first shunt tube  9  activates the dosing and mixing arrangement  4  as it will be further described herein below. 
     FIG. 3.C  shows the valve arrangement  2  in an optional third configuration (by-pass configuration) after activation of the second dart catcher  23  by a second dart  28 . In this configuration, the sliding sleeve  21  opens the second side conduit  26  and closes the side opening  24  so that the first fluid F 1  is mainly diverted through the second side conduit  26 . The first fluid flows directly into the second shunt tube  10  as fluid flow F 1 ″ which corresponds to a non-activated fluid chemically identical to the first fluid F 1 . 
   The first and second darts and the corresponding dart catchers are sized so that the first dart activates the first dart catcher and cannot activate the second dart catcher. The first and second darts of the above described embodiment are of spherical shape. However, it will appear obvious for a man skilled in the art that others kinds of shape are possible, and that others kinds of catcher (e.g. plug catcher) can also achieve the same remote activation function (e.g. see the application examples hereinafter). 
     FIGS. 4.A  and  4 .B schematically show the dosing and mixing arrangement  4  according to a first and a second embodiment respectively. 
   The dosing and mixing arrangement  4  comprises an engine part  31 , a pumping part  32  and a gearing part  33 . 
   The engine part  31  is coupled to the valve arrangement by the first shunt tube  9 . The pumping part  32  is coupled to the reservoir by the second reservoir conduit  3 E. When the valve arrangement is in the activated configuration, the flow of the first portion F 1 ′ of the first fluid activates the engine part  31 . The engine part  31  produces a mechanical movement that activates the pumping part  32  through the gearing part  33  (schematically illustrated by the dotted lines). When activated, the pumping part  32  sucks the activation fluid FA from the reservoir (that may be pressurized by the third portion F 1 ′″ of the first fluid flow). The gearing part  33  allows selecting the volume ratio of the two flows, namely the activation fluid FA and the first portion F 1 ′ of the first fluid. 
   Advantageously, the engine part and the pumping part are progressive cavity or helical rotor type pumps. These types of pump are also known as Moineau pump and consists of a helical rotor which rotates inside a helical stator. The geometry and dimensions of the rotor and stator are designed so that a double string of sealed cavities are formed when the rotor turns into the stator. The cavities progress axially from the suction to the discharge port of the pump, thus carrying the fluid. The rotation rate of the rotor is proportional to the fluid flow rate. 
   Alternatively, the pumping part may also form a peristaltic pump, the pumping part being coupled to a simple flexible tube compressed and released by the movement of the pumping part run by the engine part. 
   According to the first embodiment shown in  FIG. 4.A , the dosing and mixing arrangement  4  further comprises a complementary mixing arrangement  5 . 
   The first portion F 1 ′ of the first fluid flows out of the engine part  31 , while the activation fluid FA flows out of the pumping part  32 . 
   The complementary mixing arrangement  5  comprises a flow splitter  34 , a pre-mixing chamber  35  and a final-mixing chamber  36 . The mixing arrangement insures a proper mixing of the first fluid flowing out of the engine part with the activation fluid FA flowing out of the pumping part. 
   The first portion F 1 ′ flows through the flow splitter  34 . The flow splitter  34  is coupled to an inlet of the pre-mixing chamber  35  and to an inlet of the final-mixing chamber  36 . 
   The pre-mixing chamber  35  is also coupled to the pumping part through an injecting conduit  37 . It insures a first mixing of the split portion F 1 ′ of the first fluid with the activation fluid FA. For improving the mixing process, the injecting conduit may be a Venturi tube producing a jet of activation fluid in the pre-mixing chamber. 
   The final mixing chamber  36  is also coupled to outlet of the pre-mixing chamber. It insures a second mixing of the other split portion F 1 ′ of the first fluid with the pre-mixed fluid mixture. The outlet of the final mixing chamber delivers a second fluid flow F 2 , namely an activated fluid mixture. 
   The final mixing chamber outlet may include a float valve, preventing any back flow from the well-bore. 
   According to the second embodiment shown in  FIG. 4.B , the engine part  31  is positioned downstream of the pumping part  32 . The activation fluid flows FA into the engine part  31  by its superior part. Thus, the movement of the engine part insures a proper mixing of the fluid to be activated F 1 ′ with the activation fluid flow FA. In this embodiment, the complementary mixing arrangement is not necessary as mixing already occurred properly in the dosing and mixing arrangement  4 . 
   Three different applications will be described hereinafter in relation with  FIGS. 5 ,  6  and  7 . 
     FIGS. 5.A ,  5 .B and  5 .C relate to a first application of the invention corresponding to a cement plug located in a lost circulation zone (i.e. the activation fluid is used so that the fluid injected into the annulus can become thick enough, or the cement setting time can be shortened to limit losses). The injecting apparatus  101  is run at the bottom of the drill stem  106 . It is activated by a dart  127  sent from the surface into the drill stem. The injecting apparatus  101  can be retrieved at the end of the injection operation. 
     FIGS. 5.B  and  5 .C shows a detailed cross-section view of the injecting apparatus  101  in a rest configuration and in an activated configuration respectively. 
   The injecting apparatus  101  comprises a valve arrangement  102 , a reservoir  103  and a dosing and mixing arrangement  104 . The injecting apparatus  101  is installed inside a standard casing or a special housing. The length of the injecting apparatus should be almost the same as a casing length. 
   The valve arrangement  102  comprises a mandrel  109  and a sliding sleeve  121 . 
   The mandrel  109  is a tube having substantially the same diameter or less than the drill stem  106 . It is coupled by a top part to the drill stem and receives through the inlet  107  the fluid flowing through the drill stem. It is coupled by a bottom part to at least one shunt tube  110 . The bottom part also comprises an abutment  109 A. The sliding sleeve  121  is guided within the mandrel. 
   The sliding sleeve  121  comprises a dart catcher  122 , first  124  and second  124 ′ openings and a top part  121 A. 
   The valve arrangement can be in a rest configuration ( FIG. 5.B ) or in an activated configuration ( FIG. 5.C ). 
   In the rest configuration, the first openings  124  enable the fluid flowing into the mandrel to be diverted into the shunt tube  110 . The sliding sleeve  121  can be maintained in the rest position by, for example, a pin mechanism  121 B. 
   In the activated configuration, the second openings  124 ′ enable the fluid flowing into the mandrel to be diverted into the dosing and mixing arrangement  104 . The sliding sleeve  121  can be maintained in the activated configuration when, for example, the top part  121 A is in contact with the abutment  109 A. 
   The dart catcher  122  enables to activate the valve arrangement from the rest configuration to the activated configuration. 
   The reservoir  103  is an annular bladder. The annular bladder is installed around the mandrel  109 . 
   The top extremity of the bladder comprises a filling hose  103 B closed by a top plug  103 A. The bottom extremity of the bladder comprises an evacuation hose closed by a bottom plug  103 D. The extremities of these hoses are secured in the injecting apparatus near both extremities of the mandrel. The plugs can be removed to fill or flush the reservoir. The top plug  103 A or the bottom plug  103 D may be equipped with a relief valve for automatically venting the air trapped in the bladder. 
   The reservoir  103  is connected to the dosing and mixing arrangement  104  by a reservoir conduit  103 E. 
   The pressure of the reservoir  103  is automatically adjusted to the pressure inside the drilling stem (hydrostatic pressure plus surface pressure) and/or in the mandrel by means of at least one equalization port  103 C drilled in the mandrel  109 . The equalization port  103 C operates as follows: the fluid in the mandrel penetrates in the equalization port and exerts its pressure onto the reservoir, thus pressurizing the reservoir. When the reservoir is an annular bladder, it is deformed until the pressures outside and inside the reservoir are equilibrated. 
   The dosing and mixing arrangement  104  comprises an engine part  131  mechanically coupled to a pumping part  132 . Advantageously, the engine part  131  is a progressive cavity or helical rotor type pump and the pumping part  132  is a peristaltic pump. The progressive cavity pump is coupled to the peristaltic pump by a driving shaft  133 . The end of the reservoir conduit  103 E is a flexible tube coupled to the peristaltic pump. 
   The engine part  131  namely the progressive cavity pump is driven by any fluid flowing through it. When a fluid flows through the engine part  131 , it makes the pumping part  132  namely the peristaltic pump to rotate. The rotation of the peristaltic pump alternatively compresses and releases the flexible tube of the reservoir conduit  103 E, thus sucking the activation fluid AF out of the reservoir. 
   The engine part  131  is positioned downstream of the pumping part  132  in order to ensure a better mixing of the fluid to be activated and the activation fluid. 
   The peristaltic pump is well adapted as long as the required activation fluid injection rate is a few percents of the main flow rate. 
   The activated fluid is injected into the well-bore through the outlet  108 ″ downstream of the engine part  131 . 
   The injecting apparatus  101  for the first application operates as follows. 
   In the rest configuration shown in  FIG. 5.B , the injecting apparatus  101  can be used to deliver a non activated fluid F 1 ″ into the well-bore. The sliding sleeve  121  of the valve arrangement  102  is positioned into the mandrel  109  so that the fluid flowing into the mandrel is diverted through the first openings  124  into the shunt tube  110  towards the shunt tube outlet  108 ′. 
   In order to activate the valve arrangement, a dart  127  is launched from the surface and transported by the fluid that is to be activated. 
   In the activated configuration shown in  FIG. 5.C , the injecting apparatus  101  is used to deliver an activated fluid F 2  into the well-bore. 
   The dart catcher  122  of the sliding sleeve receives the dart transported by the fluid. The dart catcher  122  is for example a particular profile of the sliding sleeve (narrow area) for stopping and sealing the dart  127 . When the dart lands in the dart catcher, the sliding sleeve acts as a plug and blocks the fluid flow. Consequently, the upstream pressure rises, thus creating a downward load that moves the sleeve in the activated configuration. When the sliding sleeve is maintained in the rest configuration by a pin mechanism, the downward load shears the pins  121 B and releases the sliding sleeve. The sliding sleeve  121  slides downward in the mandrel and the top part  121  A of the sliding sleeve bumps into the abutment  109 A of the mandrel. 
   In this configuration, the sliding sleeve  121  simultaneously closes the shunt tube  110  and diverts the flow through the second opening  124 ′ towards the engine part  131 . The engine part  131  begins to rotate and makes the pumping part  132  to rotate, thus sucking the activation fluid AF out of the reservoir  103 . 
   The activation fluid flow FA and the fluid flow F 1 ′ to be activated mixes together downstream of the pumping part  132  (i.e. in the engine part  132 ). An activated fluid flow F 2  is delivered in the annulus AN of the well-bore WB. 
     FIGS. 6.A ,  6 .B,  6 .C relate to a second application corresponding to a casing cementation (i.e. the activation fluid is used so that the cement setting time can be shortened to save rig time). The injecting apparatus  201  is incorporated between the two casing elements CS 1 , CS 2 . It is activated by a dart  227  sent from the surface through the casing. The injecting apparatus  201  may be drilled out at the end of the cementing operation. 
     FIGS. 6.B  and  6 .C shows a detailed cross-section view of the injecting apparatus  201  in a rest configuration and in an activated configuration respectively. 
   The injecting apparatus  201  comprises a valve arrangement  202 , a reservoir  203  and a dosing and mixing arrangement  204 . The injecting apparatus  201  is installed inside two standard casings between casing element CS 1  and CS 2  by means of a nipple CSN. The casing element CS 2  may be a casing shoe. 
   The valve arrangement  202  comprises a mandrel  209  and a sliding sleeve  221 . 
   The mandrel  209  is a tube having an inferior diameter than the casing CS 1 , CS 2  diameter. It receives the fluid flowing through the casing. Because of the significant difference between the casing internal diameter and the mandrel inside diameter, a double dart assembly DD is used for the activation operation. The mandrel  209  is coupled by a top part to a superior dart catcher  222 C having a size substantially corresponding to the internal size of the casing. The superior dart catcher  222 C is adapted to receive the double dart assembly DD transported by the fluid. The mandrel  209  is coupled by a bottom part to at least one shunt tube  210 . The bottom part also comprises an abutment  209 A. The sliding sleeve  221  is guided within the mandrel. 
   The sliding sleeve  221  comprises a inferior dart catcher  222 A, first  224  and second  224 ′ openings and a top part  221 A. 
   The valve arrangement can be in a rest configuration ( FIG. 6.B ) or in an activated configuration ( FIG. 6.C ). 
   In the rest configuration, the first openings  224  enable the fluid flowing into the mandrel to be diverted into the shunt tube  210 . The sliding sleeve  221  can be maintained in the rest configuration by, for example, a pin mechanism  221 B. 
   In the activated configuration, the second openings  224 ′ enable the fluid flowing into the mandrel to be diverted into the dosing and mixing arrangement  204 . The sliding sleeve  221  can be maintained in the activated configuration when, for example, the top part  221 A is in contact with the abutment  209 A. 
   The inferior dart catcher  222 A enables to activate the valve arrangement from the rest configuration to the activated configuration. 
   The reservoir  203  is an annular bladder  203 . The annular bladder is installed around the mandrel  209 . 
   The top extremity of the bladder comprises a filling hose  203 B closed by a top plug  203 A. The bottom extremity of the bladder comprises an evacuation hose closed by a bottom plug  203 D. The extremities of these hoses are secured in the injecting apparatus near both extremities of the mandrel. The plugs can be removed to fill or flush the reservoir. The top plug  203 A or the bottom plug  203 D may be equipped with a relief valve for automatically venting the air trapped in the bladder. 
   The reservoir is connected to the dosing and mixing arrangement  204  by a reservoir conduit  203 E. 
   The pressure of the reservoir  203  is automatically adjusted to the pressure inside the casing and/or in the mandrel by means of at least one equalization port  203 C drilled in the mandrel  209 . The equalization port  203 C operates as follows: the fluid in the mandrel penetrates in the equalization port and exerts its pressure onto the reservoir, thus pressurizing the reservoir. When the reservoir is an annular bladder, it is deformed until the pressures outside and inside the reservoir are equilibrated. 
   The dosing and mixing arrangement  204  comprises an engine part  231  mechanically coupled to a pumping part  232 . Advantageously, the engine part  231  is a progressive cavity or helical rotor type pump and the pumping part  232  is a peristaltic pump. The progressive cavity pump is coupled to the peristaltic pump by a driving shaft  233 . The end of the reservoir conduit  203 E is a flexible tube coupled to the peristaltic pump. The engine part  231  is driven by any fluid flowing through it. When a fluid flows through the engine part  231 , it makes the pumping part  232  to rotate. The rotation of the peristaltic pump alternatively compresses and releases the flexible tube of the reservoir conduit  203 E, thus sucking the activation fluid AF out of the reservoir  203 . The engine part  231  is positioned downstream of the pumping part  232  in order to ensure a better mixing of the fluid to be activated and the activation fluid. 
   The activated fluid is injected into the well-bore through the outlet  208  downstream of the engine part  231  via for example a typical casing shoe CS 2 . 
   The injecting apparatus  201  for the second application operates as follows. 
   In the rest configuration shown in  FIG. 6.B , the injecting apparatus  201  can be used to deliver a non activated fluid F 1 ″ into the well-bore. The sliding sleeve  221  of the valve arrangement  202  is positioned into the mandrel  209  so that the fluid flowing into the mandrel is diverted through the first openings  224  into the shunt tube  210  towards the outlet  208 . 
   In order to activate the valve arrangement, a double dart assembly DD is launched from the surface and transported by the fluid that is to be activated. 
   In the activated configuration shown in  FIG. 6.C , the injecting apparatus  201  is used to deliver an activated fluid F 2  into the annulus AN of the well-bore WB. 
   The superior dart catcher  222 C receives the double dart assembly DD transported by the fluid. When the double dart assembly DD lands in the superior dart catcher, the double dart assembly acts as a plug and blocks the fluid flow. Consequently, the upstream pressure rises, thus creating a downward load that liberates a small dart  227 . The inferior dart catcher  222 A receives the dart  227  transported by the fluid. The dart catcher  222 A is for example a particular profile of the sliding sleeve (narrow area) for stopping and sealing the dart  227 . Once again, when the dart lands in the dart catcher  222 A, the sliding sleeve acts as a plug and blocks the fluid flow. Consequently, the upstream pressure rises, thus creating a downward load that moves the sleeve in the activated configuration. When the sliding sleeve is maintained in the rest configuration by a pin mechanism, the downward load shears the pins  221 B and releases the sliding sleeve. The sliding sleeve  221  slides downward in the mandrel and the top part  221  A of the sliding sleeve bump into the abutment  209 A of the mandrel. 
   In this configuration, the sliding sleeve  221  simultaneously closes the shunt tube  210  and diverts the flow through the second opening  224 ′ towards the engine part  231 . The engine part  231  begins to rotate and makes the pumping part  232  to rotate, thus sucking the activation fluid AF out of the reservoir  203 . 
   The activation fluid flow FA and the fluid flow F 1 ′ to be activated mixes together downstream of the pumping part  232 . An activated fluid flow F 2  is delivered in the annulus AN of the well-bore WB. 
   As shown on the Figures, the double dart assembly may comprise an additional valve avoiding the activated fluid (e.g. cement) in the annulus of greater density than fluid (generally mud) within the casing to flow back to the surface in the casing. 
     FIGS. 7.A ,  7 .B,  7 .C relate to a third application corresponding to a casing cementation in a casing-drilling configuration. The casing CS 3  is already in place and the injecting apparatus  301  is pumped through the casing and lands above the casing shoe CS 4 . The injecting apparatus  301  is activated by a dart  327  sent from the surface through the casing. The injecting apparatus  301  may be drilled out at the end of the cementing operation. 
     FIGS. 7.B  and  7 .C shows a detailed cross-section view of the injecting apparatus  301  in a rest configuration and in an activated configuration respectively. 
   The injecting apparatus  301  comprises a valve arrangement  302 , a reservoir  303  and a dosing and mixing arrangement  304 . 
   The valve arrangement  302  comprises a mandrel  309  and a sliding sleeve  321 . 
   The mandrel  309  is a tube having an inferior diameter than the casing CS 3  diameter. It receives the fluid flowing through the casing via the inlet  307 . Because of the significant difference between the casing internal diameter and the mandrel inside diameter, a double dart assembly DD′ is used. The mandrel  309  is coupled by a top part to a superior dart catcher  322 C having a size substantially corresponding to the internal size of the casing. The superior dart catcher  322 C is adapted to receive the double dart assembly DD′ transported by the fluid. The mandrel  309  is coupled by a bottom part to a shunt tube  310 . The shunt tube comprises an abutment  309 A under the bottom part of the mandrel. The sliding sleeve  321  is guided within the mandrel. The sliding sleeve  321  comprises an inferior dart catcher  322 A. 
   The valve arrangement can be in a rest configuration ( FIG. 7.B ) or in an activated configuration ( FIG. 7.C ). 
   In the rest configuration, the fluid flowing into the mandrel flows through the sliding sleeve and is diverted into the shunt tube  310 . The sliding sleeve  321  can be maintained in the rest configuration by, for example, a pin mechanism or sealing mechanism. 
   In the activated configuration, enable the fluid flowing into the mandrel is diverted through an opening  324  into the dosing and mixing arrangement  304 . The sliding sleeve  321  is maintained in the activated configuration when it is in contact with the abutment  309 A. 
   The inferior dart catcher  322 A enables to activate the valve arrangement from the rest configuration to the activated configuration. 
   The reservoir  303  is an annular bladder, for example made in rubber material. The annular bladder is installed around the mandrel  309 . 
   The top extremity of the bladder comprises a filling hose  303 B closed by a top plug  303 A. The bottom extremity of the bladder comprises an evacuation hose closed by a bottom plug  303 D. The extremities of these hoses are secured in the injecting apparatus near both extremities of the mandrel. The plugs can be removed to fill or flush the reservoir. The top plug  303 A or the bottom plug  303 D may be equipped with a relief valve for automatically venting the air trapped in the bladder. 
   The reservoir is connected to the dosing and mixing arrangement  304  by a reservoir conduit  303 E. 
   The pressure of the reservoir  303  is automatically adjusted to the pressure inside the casing and/or in the mandrel by means of at least one equalization port  303 C drilled in the mandrel  309 . The equalization port  303 C operates as follows: the fluid in the mandrel penetrates in the equalization port and exerts its pressure onto the reservoir, thus pressurizing the reservoir. When the reservoir is an annular bladder, it is deformed until the pressures outside and inside the reservoir are equilibrated. 
   The dosing and mixing arrangement  304  comprises an engine part  331  mechanically coupled to a pumping part  332 . Advantageously, the engine part  331  is a progressive cavity or helical rotor type pump and the pumping part  332  is a peristaltic pump. The progressive cavity pump is coupled to the peristaltic pump by a driving shaft  333 . The end of the reservoir conduit  303 E is a flexible tube coupled to the peristaltic pump. The engine part  331  is driven by any fluid flowing through it. When a fluid flows through the engine part  331 , it makes the pumping part  332  to rotate. The rotation of the peristaltic pump alternatively compresses and releases the flexible tube of the reservoir conduit  303 E, thus sucking the activation fluid AF out of the reservoir  303 . The engine part  331  is positioned downstream of the pumping part  332  in order to ensure a better mixing of the fluid to be activated and the activation fluid. Thus the engine part  331  also acts as a mixing arrangement  305 . 
   The activated fluid is injected into the well-bore through the outlet  308  downstream of the engine part  331  via for example a typical casing shoe CS 4 . 
   The injecting apparatus  301  for the third application operates as follows. 
   In the rest configuration shown in  FIG. 7.B , the injecting apparatus  301  can be used to deliver a non activated fluid F 1 ″ into the well-bore. The sliding sleeve  321  of the valve arrangement  302  is positioned at the bottom of the mandrel  309  so that the fluid flowing into the mandrel flow through the sliding sleeve into the shunt tube  310  towards the outlet  308 . 
   In order to activate the valve arrangement, a double dart assembly DD′ is launched from the surface and transported by the fluid that is to be activated. 
   In the activated configuration shown in  FIG. 7.C , the injecting apparatus  301  is used to deliver an activated fluid F 2  into the annulus AN of the well-bore WB. 
   The superior dart catcher  322 C receives the double dart assembly DD′ transported by the fluid. When the double dart assembly DD′ lands in the superior dart catcher, F the double dart assembly acts as a plug and blocks the fluid flow. Consequently, the upstream pressure rises, thus creating a downward load that liberates a small dart  327 . The inferior dart catcher  322 A receives the dart  327  transported by the fluid. The dart catcher  322 A is for example a particular profile of the sliding sleeve (narrow area) for stopping and sealing the dart  327 . Once again, when the dart lands in the dart catcher  322 A, the sliding sleeve acts as a plug and blocks the fluid flow. Consequently, the upstream pressure rises, thus creating a downward load that moves the sleeve in the activated configuration. The sliding sleeve  221  slides downward and bumps into the abutment  309 A. 
   In this configuration, the sliding sleeve  321  simultaneously closes the shunt tube  310  and diverts the flow through the opening  324  towards the engine part  331 . The engine part  331  begins to rotate and makes the pumping part  332  to rotate, thus sucking the activation fluid AF out of the reservoir  303 . 
   The activation fluid flow FA and the fluid flow F 1 ′ to be activated mixes together downstream of the pumping part  332 . An activated fluid flow F 2  is delivered in the annulus AN of the well-bore WB. 
   As shown on the Figures, the double dart assembly may comprise ah additional valve avoiding the activated fluid (e.g. cement) in the annulus of greater density than fluid (generally mud) within the casing to flow back to the surface in the casing. 
   It is to be noted that the peristaltic pump described in relation with the embodiments of  FIGS. 5 to 7  may, alternatively, be equipped with several flexible tubes. In this case, the peristaltic pump may be designed to press simultaneously the several flexible tubes. Each tube may be fitted with a valve in order to adjust, for a given application, the activation fluid flow-rate to be injected in the fluid. 
   It is to be mentioned that the invention is not limited to onshore hydrocarbon well and can also be used in relation with offshore hydrocarbon well. 
   Also, a particular application of the invention relating to the oilfield industry has been described. However, the invention is also applicable to other kind of industry, e.g. the construction industry or the like. 
   The drawings and their description hereinbefore illustrate rather than limit the invention. 
   Any reference sign in a claim should not be construed as limiting the claim. The word “comprising” does not exclude the presence of other elements than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such element.

Summary:
An injection apparatus for injecting an activated fluid and an activated chemical fluid mixture into a well-bore is disclosed. Then, an injection method for injecting an activated fluid into a well-bore is also disclosed. A particular application to the oilfield industry, for example in cementing operation is encompassed. The apparatus and the method of use is fully automatic.