Abstract:
A mudline tubing hanger is disclosed in which the tubing hanger is provided as an integral part of the tubing string and is set within the casing by an hydraulic setting mechanism driven through an external control line and actuated by a wireline shifted sleeve. Further manipulation of the sleeve isolates the setting mechanism from the tubing and external control line, establishing a chemical injection conduit with access to the tubing bore through the external control line.

Description:
BACKGROUND OF THE INVENTION 
     Several deepwater oil and gas fields have been recently discovered which necessitate new methods and apparatus in order to produce them. The depth of the water at these locations may range from 2000 to 7000 feet of water. Two of the proposed methods for developing such oil and gas fields are known as ocean floor completions and the production facilities on tension leg platforms. In ocean floor completions, a well would be drilled from a floating vessel on the surface of the ocean subsequently be completed by hanging strings of casing and production tubing from a wellhead that is positioned on the ocean floor or at the mudline. In the second method, a tension leg platform floats in an anchored position on the surface of the water while conducting well drilling operations and subsequently production operations. In the later case, the wellheads are positioned on one of the decks of the tension leg platform and a production riser extends from each of the wellheads down to the ocean floor and downwardly into the formation to the hydrocarbon producing zone. In both cases, it is often desirable to remove some of the weight of the tubing pipe string from the wellhead by providing it with a tubing hanger which may be set deep in the well. 
     A second problem exists in the production of hydrocarbons, especially in gas wells, in that hydrates are often formed in the tubing string under the right combination of pressure and/or temperature. These hydrates tend to restrict the flow of hydrocarbons in the tubing string or block it altogether. Thus, it is desirable to add a chemical into the tubing string at a depth in the well which is below that at which hydrates form in the tubing string. Any of several chemicals which prevent the formation of hydrates and are well known to the art may be injected into the tubing string. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to develop an hydraulically actuatable tubing hanger which would be included as an integral part of the tubing string and lowered into the well thereby. The apparatus would act as a mudline tubing hanger which would support the weight of the tubing pipe string below the hanger after it had been set in the well by means of an externally connected control line. After the apparatus had been set in a well casing, the externally connected control line used to pressure up the tubing hanger latches would then be converted to a chemical injection device by a wireline tool. The tubing hanger of the present invention would be used when there is no shoulder in the casing on which it could be seated. 
     Another object of the present invention is to provide a tubing hanger that can be set in a well without manipulation of the tubing string and serves to reduce the load on a wellhead. 
     In accordance with the present invention the tubing hanger is connected into a tubing string between two sections thereof and lowered into a well together with a small quarter-inch tubing which would be strapped to the tubing string above the hanger in a manner well known to the art and extend to the surface where it could be connected to a source of hydraulic pressure fluid used to actuate the latching dogs of the hanger. If hydrates formed in the production fluid coming from the well, a determination would be made by means of calculations, experiments, or tests to determine the location or depth in the tubing string that hydrate formation would occur. The tubing hanger of the present invention would be connected into the tubing string at a point so that when the hanger and tubing string were run into the well, the hanger and chemical injection sub of the present invention would be positioned below the zone of hydrate formation in the well. After setting the hanger at the selected depth, the hanger would be pressurized to anchor it to the inner wall of the surrounding casing string and subsequently a wireline tool would be lowered through the tubing string to move a sleeve valve in the tubing hanger so that a corrosion inhibitor or a hydrate inhibiting chemical could be injected from the surface down the pressure tubing and into the bore of the tubing string. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross sectional view of the tubing hanger of the present invention connected into a tubing string and positioned within a well casing before it has been actuated and latched to the casing. 
     FIG. 2 is a cross sectional view of the tubing hanger after the dogs have been latched to the inner wall of the casing and after the central sleeve valve has been shifted so that a chemical fluid can be injected into the bore of the tubing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 of the drawing, a hanger body member 10 is shown as being positioned within a well casing 11. The casing 11 may be the production casing in the well and may be of any suitable size, say for example, 75/8&#34; or 95/8&#34; in diameter. The hanger body 10 is provided at the lower end with suitable connector means such as screw threads 12 for connecting the body 10 to a section of production tubing 13. The production tubing may have a diameter of, say, 27/8&#34; or 31/2&#34;. In a like manner, the upper end of the body member 10 is provided with screw threads 14 for connecting into the lower end of the tubing string 13. 
     The upper end of the hanger body 10 is also provided with an inlet port 15 having a screw-threaded connection 16 for securing the lower end of a small diameter pressure tubing 17. The pressure tubing 17 is bent over against the outer wall of the tubing string 13 and is secured thereto in any suitable manner well known to the art, as by straps (not shown). The inlet port 15 forms one end of a manifold 17a formed within the hanger body 10 which is provided with spaced-apart outlet ports 18 and 19. 
     Formed within the lower part of the body member 10 are a plurality of vertically-extending and radially-directed slots 20 and 21 in which a pair of latching dogs 22 and 23 are slidably mounted for extension therefrom to contact the inner surface of the well casing 11. The faces of the latching dogs 22 and 23 are preferably serrated as at 24 and 25. The serrations may take the form of a plurality of horizontal teeth on the outer surface of the latching dogs 22 and 23. Preferably, the serrations are downwardly and outwardly sloping teeth so that in the event of failure of the apparatus, the hanger body could be pulled upwardly out of the well casing 11. 
     Formed within the lower portion of the hanger body 10 are a pair of piston chambers 26 and 27 in which pistons 28 and 29 are slidably mounted. The lower parts of the pistons 28 and 29 are preferably wedge-shaped in form and are provided with camming surfaces 30 and 31 which cooperate with camming surfaces 32 and 33 on the inner side of the latching dogs 22 and 23. 
     The other side of each of the pistons 28 and 29 near the lower ends thereof are provided with serrated faces 34 and 35. These serrated faces 34 and 35 are arranged to engage the outwardly-extending serrated faces 36 and 37 of cooperating wedge-shaped locking latches 38 and 39 which are slidably mounted in radially-extending slots in the hanger body 10. The locking latches 38 and 39 are arranged to be energized for outward movement in any suitable manner, as by the use of springs 40 and 41. Thus, when a pressure fluid is applied through conduits 40 and 41 to the piston chambers 26 and 27, the pistons 28 and 29 will be forced downwardly. At this time the camming faces 30 and 31 on the pistons engage the cooperating camming faces 32 and 33 of the latching dogs 22 and 23 to drive the dogs 22 and 23 outwardly until they engage the inner wall of the well casing 11. At that time the serrated faces 34 and 35 on the inner wall of the piston will be forced down across the serrated faces 36 and 37 of the locking latches 38 and 39 forcing them inwardly. With the locking latches and 38 and 39 positioned in this manner, the pistons 28 and 29 are locked against any movement upwardly which would tend to release the latching dogs 22 and 23 from the casing wall. Once the latching dogs 22 and 23 are in engagement with the inner wall of the casing 11, the tubing string 13 at the surface is allowed to move downwardly so that the weight of the string forces the teeth of the latching dogs 22 and 23 further into the well casing 11. The body member 10 of the hanger is provided with a central chamber 42 in which a sleeve valve is slidably mounted for limited vertical movement. Mounted in the bottom of the central chamber 42 and extending up into the sleeve valve 43 are a pair of tubes 44 and 45 which are in communication at their lower ends with the fluid passageways 40 and 41 and are in communication at the upper end with the outlet port 19. It is to be understood that flow passageways 46 and 47 are circular in form and extend around the sleeve valve 43. 
     The sleeve valve 43 is also provided with a series of fluid passageways 48, 49 and 50 which are subsequently moved down with the sleeve valve to cooperate with the outlet port 18 of the manifold, as shown in FIG. 2. The upper end of the sleeve 43 is also provided with a latching groove 51 and/or a shoulder 52. After the hanger body 10 has been set by hydraulic pressure applied through the tubing 17, a wireline running tool of any suitable design well known to the art is lowered through the tubing string to engage the recess 51 or shoulder 52 to force the sliding sleeve valve 43 from its position shown in FIG. 1 to its position shown in FIG. 2. In the position shown in FIG. 2 the outlet port 19 is blocked off by the sleeve valve body so there is no further communication between the pressure tubing 17 and the piston chambers 26 and 27. At the same time the fluid ports 48, 49 and 50 in the upper part of the sleeve valve 43 are brought into communication with the outlet port 18 of the manifold. In orginally setting the hanger, water or glycol or any other fluid may be pumped down through tubing 17 to actuate the pistons of the hanger and set the dogs against the casing. After changing the sliding sleeve valve 43 to the position shown in FIG. 2 a corrosion inhibitor or a hydrate inhibitor fluid may be pumped from the surface down through tubing 17, out the outlet 18 and through the fluid passageways 48, 49 and 50 to be discharged in the bore of the tubing 13. 
     As previously pointed out, in order to effectively prevent the formation of hydrates in a well tubing, it will be necessary to introduce a hydrate inhibiting fluid in a well below that point or depth at which the hydrates form. Thus, in using the apparatus of the present invention to provide for a method of preventing the formation of hydrates in a well, a determination would be made after studying the well as to what depth in the well the hydrates formed. If the hydrates were found to form in a particular well at a depth of 3500 feet, a tubing string for that well would be made up by screwing together sections of tubing in a manner well known to the art. At a point in the tubing which would be below the hydrate-forming point, say, 3600 feet, the apparatus of the present invention would be connected into the tubing string and the entire tubing string with its hanger would be run into the well. With the hanger on the tubing string positioned at 3600 feet below the surface, a pressure fluid such as ethylene glycol, would be pumped down through tubing 17 and into the tubing hanger and piston chambers 26 and 27 to set the dogs 22 and 23 against the casing 11. With the tubing anchored in place, the valve 43 would be moved downwardly to the position shown in FIG. 2 by use of a wireline 2, well known to the art. After withdrawing the wireline 2 from the tubing string, a hydrate preventing chemical in fluid form would be pumped down the tubing 17 and discharged into the bore of the tubing to return to the surface with the production fluid from the well. 
     It may be seen that in utilizing the present invention in this manner the weight of all of the tubing string below the tubing hanger would not have to be supported from a wellhead, say, one that is buoyantly supported by a tensin leg platform. Since in a 20,000 foot well, the tubing may weigh about 250,000 pounds, it may be seen that most of this weight would be removed from the floating platform and supported by the tubing hanger of the present invention. 
     In one example of a deepwater well completion, a 20,000-foot well may have a bottom hole pressure of 13,500 psi and a pressure of 10,000 psi at the mudline. The bottom hole temperature is 250 degrees F. while the temperature at the mudline can be as low as 40 degrees F. Hydrates are known to form in production fluids from 40 degrees F. to as high as 70 degrees F. Thus, in this case, a 31/2&#34; diameter tubing string equipped with the mudline hanger of the present invention would have the hanger set at between 4000 and 5000 feet. After setting the tubing hanger the injection of various chemicals would take place. Such chemicals may be methanol, glycol, certain paraffin solvents such as toluene and diesel, amine based corrosion inhibitors, calcium bromide, zinc bromide, calcicum chloride, seawater and nitrogen.