Method and Apparatus for Completing Underwater Well Heads

The invention refers to a method of completion of one or a plurality of grouped undersea oil wells, and a structure for use in carrying out the method.

Amongst the main known methods of completion there are those which require crews of divers. Such methods have the disadvantage of being useable only at relatively small depths. In order to avoid this disadvantage other methods use mechanisms enabling vertical or lateral connections to be carried out automatically.

The mechanisms employed are, however, complex, costly and cumbersome. Moreover complete supervision of the well head cannot be carried out. In certain cases this is corrected by carrying out lateral connections of the well head by means of an undersea enclosure provided with an airlock for access to a personnel transfer apparatus. After having exhausted the water inside the enclosure and replaced it by air at atmospheric pressure, the connection is carried out and the transfer apparatus is withdrawn. One method offering greater safety uses an enclosure at atmospheric pressure enabling the well to be controlled as it lies in the water. In this method, however, the connection had still to be effected from the outside of the enclosure so that the interest afforded by this method is counterbalanced by the usual difficulties encountered in carrying out such connections.

It is an object of the present invention to provide a method of completion of at least one undersea oil well, according to which the production head is temporarily withdrawn from the ambient medium which is replaced by a gaseous medium at atmospheric pressure, wherein prior to the installation of the well head, a structure is lowered vertically on to the sea bed where the gathering is to be carried out, the structure including an enclosure at atmospheric pressure and housing a manifold, and as many compartments, capable of communicating with the enclosure, receiving a production head and being rendered watertight, as there are well heads to be installed, installing a well head in a compartment, lowering a production head into the compartment and on to the well head, rendering the compartment watertight, removing water from the compartment from the inside of the enclosure, substituting for the water a mixture of gases at the pressure of the enclosure, connecting the production head to the manifold through a connector plate which separates the compartment from the enclosure in a watertight manner after connection, and refilling the compartment with water.

This method has the advantage that, by use of it, connection of the production head to the manifold can be carried out from the inside of the enclosure. It consequently enables the working party to remain in a zone of safety. Each compartment may be of relatively small dimensions in order to be separated from the enclosure only by a wall provided with an opening which can be shut off, rendering easily accessible the elements for connection of the production head to the manifold.

It is another object of the invention to provide a structure for carrying out the above method, the structure comprising an enclosure at atmospheric pressure and at least as many compartments as there are production heads to be installed, each compartment being connected to the enclosure by a removable watertight separator plate, being capable of receiving a production head and being rendered watertight.

The structure may be constructed of a mass of concrete which is sufficiently heavy to remain on the sea bed and increases the rigidity of the assembly of casings, tubings and preventers during the operations of drilling and completion. Advantageously the structure includes in an upper portion at least one airlock for connection to a submarine and a passageway for a delivery pipe connected to the manifold.

Use of the above method by means of such a structure enables easy solution not only of the problems of connection of the various well heads installed in the compartments of the enclosure structure to the manifold but also that of the connection of the delivery pipe to the manifold which is effected inside the enclosure. In addition the problem of protection of the undersea well heads is solved since each well head lies inside a compartment which forms part of a whole which it is sufficient to arrange below the level of the sea bed in order for it to escape the action of foreign bodies, such for example as icebergs, the bottom of which can hit unprotected installations.

Another object of the invention is to facilitate completion of the wells by providing in each compartment grinding means enabling the connections of the production pipes and various controls to be easily oriented with respect to the enclosure during the installation of the well head.

Another object is to provide the bottom of each compartment with a shape adequate for serving as a receptacle or seat for the first casing of the well, and to give the top portion a shape suitable for supporting a guide-structure and receiving a closure device ensuring watertightness of the compartment.

Thus the present method enables easy completion of the wells, ensures perfect safety of the working parties during connections and sure protection of the well heads in water of relatively little depth.

Other advantages and features of the invention will become apparent from the following description of an embodiment of a structure for use in completion of a group of wells according to the invention given by way of example only, with reference to the attached drawings.

In the drawings:

FIG. 1 represents the general diagrammatic view, partially in section, of the structure after completion of the group of wells;

FIG. 2 is a plan of the structure before installation;

FIG. 3 is a diagrammatic view partially in section of a compartment provided with a guide-structure of vertical columns supporting the preventers;

FIG. 4 is a diagrammatic view of a variant of the structure of FIG. 3;

FIG. 5 is a diagrammatic view partially in section of a compartment after lowering of the well head and putting in place of a closure device;

FIG. 6 is a diagrammatic view partially in section of a well head after connection to the manifold in the enclosure;

FIG. 7 is a diagrammatic view in section of a compartment before drilling;

FIG. 8 is a partial view of the inside of a compartment in the direction of the arrow VIII in FIG. 7;

FIG. 9 is a diagrammatic view partially in section of a variant arrangement of the side outlet of the production head; and

FIG. 10 is a detail of the assembly of the guide structure of the compartment of FIG. 3.

To enable connection of one or, as shown, a plurality of well heads 1, FIG. 1, to a manifold 2 without having to have access directly to the or each well head, a structure 3 is provided. The structure 3 is made of a mass of concrete which defines a central enclosure 5 and peripheral compartments 6, FIG. 2. Recesses 7 surrounding the upper ends of compartments 6 are provided to create clearances for putting in place guide means, such as guide means 8, FIG. 3, or guide means 9, FIG. 4, necessary for the drilling and completion of the wells, and for protecting the top portion of attachment means 10 (FIGS. 1, 7 and 10). The structures 8 and 9 either include guide lines 28 or a simple cone for guidance of the first tools of the first casings and of the preventers. They may also be provided with release means shown diagrammatically at 31, which cooperate with the attachment means 10, FIGS. 7 and 10. In the case where it would be required to put the structure 3 in position using floats, these recesses also enable seating of the bottoms of the floats (not shown), which may be of any type. These floats are preferably attached at their bottoms by means of a remote-controlled connector device to the attachment means 10 at the top portion of a casing 11, FIG. 7, of each compartment 6. Hence the structure 3 may be conveniently lightened during the course of its descent, the floats being recovered after the structure has been placed in position by remote control of the connectors. In the case where more accurate guidance of the structure 3 is required, for example, on to the centre of an excavation, a tube 13 (FIG. 1) is placed at the centre of the excavation. An anchorage 14 surmounted by a pulley 15 around which a guide cable (not shown) has previously been passed is located in the tube 13. The cable passes through a central guide column 12 integral with the structure and passing in a watertight manner through the enclosure 5. Hence it is sufficient to attach one side of the cable to the structure and to wrap the other side round a winch at the surface in order to lower the structure 3 on to the centre of the excavation, the embankment 17 of the excavation may be used to bury a delivery pipe 18 which may be buried in the sea bed.

After lowering the structure and withdrawal of the floats or cable, the pipe 18 may be connected to the manifold 2. This connection is carried out from the inside of the enclosure 5 to which access may be gained by employing a suitable submarine 20 which is connectable to the enclosure through an airlock 21 integral with the structure 3 and a door 22 normally closing the airlock 21. The enclosure 5 is at atmospheric pressure, watertight doors 13, FIG. 3, closing passageways 37 between the enclosure and the compartments, isolating the enclosure from the compartments 6. A cable 24 wrapped round a winch 40 in the submarine 20 enables the pipe 18 to be dragged through a watertight passageway 25 which extends in any known manner through the structure. During the course of this operation the cable 24 passes round a pulley (not shown for greater clarity in the drawing) the plane of which is the vertical plane passing through the delivery pipe 18 and the way 25.

When the pipe has been sufficiently drawn into the enclosure 5, a valve 26 at the end of the pipe 18 is connected to the manifold by means of a connector 27.

The wells are then drilled according to a conventional method except that special guide structures 8 or 9 and an extension pipe 29 are employed. The pipe 29 is provided with centering lugs 30, intended to reduce the bending moment transmitted by the preventers 38 and the riser 42 to the bottom of the extension pipe 29, and is connected to the well head 71 by a connector 39.

In FIG. 7 there is shown one of the compartments 6. Below the watertight door 23 a pipe 34 is provided connecting the compartment 6 to a valve 35 which is connected to a pump (not shown) for subsequent emptying of the compartment 6. At the bottom of the compartment there is a seating 36 of any suitable known type which is used for suspension of the first casing, the assembly of the heads of these casings forming the well head 71. A guide groove 32 is provided opposite the pipe 34 and the passageway 37. The groove serves to orientate a production head 43 accurately. The preventers 38 are attached to the upper portion of the extension pipe 29 with respect to the passageway 37. The bottom connector 39 may be of any type as may units 41 for control and connection of the riser 42.

After drilling, putting in place the casings and tubings as well as plugs enabling withdrawal of the preventers 38, the connector 39 is disconnected from the well head 71 and a production head 43, FIGS. 5 and 6, is lowered on to the well head. The head 43 is connected to the well head 71 by a connector 44 already connected to the production head 43. The lines for control of the top valve 45 and the connector 44 are attached to a hydraulic control lines connector 46. The control line for the master valve 47 is connected to a double-acting valve 48 which enables control of the master valve 47 either from the surface by way of the connector 46 or by a direct line 49. A side outlet valve 50 for effluent is controlled by a direct line 51. A control line 52 enables, where necessary, measurement of the pressure in the annulus.

During the course of lowering, the control lines 49, 51 and 52 are attached to the production well head 43 and, as soon as the connector 44 is connected to the well head, the top aperture of the compartment 6 is shut off by a special plug 53 which locks on to the attachment means 10. By connecting the valve 35 to the pump (not shown) in the enclosure 5 the compartment 6 is emptied and the pressures between the enclosure and the compartment are equalized.

The passageway 37 can then be opened by opening or removing the door 23 so that access may be gained to the control lines 49, 51 and 52. It will be observed that it is unnecessary to enter the interior of the compartment 6 in order to carry out the connection of the well to the manifold 2 and that it is sufficient to be able to withdraw the ends of the control lines. By means of any suitable handling device with which the enclosure is equipped, a pipe 54 provided with a connector 55 is connected to the side outlet 56 controlled by the valve 50 on the production head. Connection may be carried out by means of the control line 57. This line may have already been attached to a shut-off connector-plate 58 through which the pipe 54 passes. This plate is attached to a flange on the passageway 37 by means of conventional clamp and sealing means 59. The plate 58 comprises connectors, such as 61, for easy connections of the control lines 49, 51, 52 and 57, connector valves 62 to 65 enabling operation and control of the production head 43 from the inside of the enclosure 5. Watertightness of the pipe 54 with the plate 58 is ensured after connection of the connector 55 by means of watertight sealing means 66 which are clamped against the pipe 54 and between a flanged cylindrical member on the plate 58 and a cylindrical member carrying a flange 67 by means of bolts and nuts 68. At least one valve 69 completes the connection between the pipe 54 and the manifold 2.

Thus contrary to known methods, connection of the well head to the manifold is carried out inside an enclosure without having to enter the space directly surounding the well head.

When connection has been completed the valve 35 is connected to a water-introduction circuit (not shown) and, after filling the compartment 6 with water, the plug 53 is withdrawn. Tubing (not shown) leading up to the surface may be put into production after fishing up the plugs by the so-called "wire-line" technique of intervention by cables.

The valves 45 and 47 are then closed and the production pipe may be disconnected. A protector cap 70 may be lowered on to the top portion of the head 43 and the connector 46, this lowering being again guided by the groove 32.

Although only one embodiment of the structure 3 has been described it will be understood that it may take a number of forms as also may the production heads, the side outlet 56 of which may form an acute angle with the top portion of the head 43. FIG. 9, in order to enable employment of the so-called "through the flow line" technique of intervention via the delivery pipe. In this latter case, the pipe 54 is curved for the passage of pumped tools which are sent into the well from the enclosure 5 and pass through the plate 58 at an angle. Similarly a number of side outlets may be provided on one head, all of these outlets and their controls being connected through a shut-off plate to the enclosure manifold and to control members in the enclosure 5.