Patent ID: 12247478

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

FIG.1shows a portion of a subsea template including a template slot2. The template rests on the seafloor9and the slot2is a large circular aperture in the base of the template, with an upstanding cylindrical support structure. Note that the invention is also applicable for free-standing wells. In this case there is no template structure2and the seafloor9is typically 1-2 metres lower with reference to the conductor housing4.

A bore hole3has been drilled through the template into the seafloor.

A conductor housing4is installed in the template slot2. The conductor housing is a cylindrical steel member of diameter slightly less than the slot2. The conductor housing4may have an outer diameter of about 30-42 inches (76-107 cm). It is supported in the template slot2by means of cooperating shoulder formations12,13on the template slot and conductor housing, respectively. In the case of a free-standing well, the conductor housing4is supported by cement which is placed between the conductor pipe5and borehole wall3up to a short distance from the seafloor9.

Welded to the conductor housing4are conductor tubulars, or just “conductor”5. Conductor5can have an outer diameter of about 26 to 36 inches (66 to 91 cm). Conductor5extends downwardly into the wellbore, to a depth of 40 to 230 feet (12 to 70 metres) depending on local soil conditions, at which point the wellbore narrows.

Installed in the conductor housing4is a wellhead housing7. The wellhead housing7can engage and align within the conductor housing4in different ways, one of which is via a mounting ring8. The mounting ring8can be engaged and/or supported on an internal shoulder14of the conductor housing4. Various rigid lock-down systems may be used to ensure appropriate load transfer between the outer and inner strings.

Surface casing6is welded to the lower end of the high-pressure wellhead housing7. Surface casing is a narrower steel tubular which extends downwardly beyond the end of the conductor5. Surface casing6can be approximately 18 to 24 inches in diameter (approximately 46 to 61 cm).

In an alternative structure, which is the subject of patent application No. 62/815,231, the conductor tubular may not be used, and the upper, larger diameter, portion of the wellbore can be avoided. Instead, the template slot2is sized and configured, equipped with conductor housing4without the conductor pipe5, to receive the high-pressure housing7and surface casing6directly at the level of the seafloor. The invention applies equally to this alternative structure. The contents of 62/815,231 are incorporated by reference.

Strain gauges11are mounted circumferentially around the outside of the surface casing6, with associated radio transmitter or transmitters15/16. The gauges are fitted immediately below the wellhead on the surface casing6in areas that are not sealing areas. A centralizing device may be used to protect the gauges/transmitters from being scraped/wiped off during landing of the wellhead7in the conductor housing4.

In this example, 4 strain gauges are used, but the number could be anything from 3 gauges to whatever number is required to get the required circumferential coverage, for example 10 or 20, to truly measure/calculate fatigue. For simplified one dimensional stress monitoring/measurement, one or two strain gauges with a transmitter to send data to an external receiver can be installed.

The strain gauges are a sensor type that measures dynamic strain with high resolution and accuracy, typically 1 micro-strain at 10 Hz or better. Such gauges are available on the open market and are well known devices.

The strain gauges are preferably oriented to give full circumferential coverage in order to calculate accumulated fatigue damage in the worst direction.

The gauges are arranged to measure the relative change in length (deformation) caused by a deforming force, thereby allowing the calculation of pipe stress, associated bending moment and the frequency (cycle) of the forces acting on surface casing just below the wellhead. From this, maximum stress and accumulated fatigue damage can be derived for critical fatigue hot spots, which typically are the welds between the forged steel wellhead components and the extension tubulars.

These types of strain often result from the movement of marine riser/BOP that vessels utilize to connect onto the well. The riser/BOP movement is caused by environmental forces that act on the vessel and/or riser and are also influenced by the station-keeping ability of the vessel in use. This movement is translated into a force where the riser/BOP is connected to the high-pressure wellhead housing7, which again is transferred to the well tubulars until the force is dissipated/absorbed by the external soil support.

Since the strain gauges are located just below seafloor level, they are in immediate proximity to a seabed receiver19that is placed on or adjacent the template structure. For free-standing wells, the receiver can be mounted on a bracket installed on the outer conductor. The receiver uses induction power or similar technology to wirelessly communicate with the gauge signal transmitter16to read strain data. The subsea receiver can comprise at minimum one or more data receiver(s), a storage memory, and a data communication/transmission system from seafloor to the surface through wire, acoustic technology or with ROV retrievable memory bank.

Once at the surface, strain data can be evaluated and analyzed to determine wellhead system performance under actual loading conditions (real-time or with a latency depending on data transfer technology used), and operational envelopes can be adjusted to suit.

Similarly, strain gauges10are also applied to the exterior surface of the conductor5, at a level just below the conductor housing4, evenly spaced around the circumference of the conductor5, and applied in the same way as to the surface casing. Additional gauges may be applied to additional pipe members immediately below the wellhead to evaluate maximum stress and accumulated fatigue damage in hot spots on the conductor pipe.

The measurement and data transmission is achieved by using combination or only batteries or induced power. Induced power applied on the template well slot, or the template well slot tail pipe allows a non-intrusive method to communicate and power sensors and achieve two-way communication of data, as well transmitting and powering up sensors transmission system for additional inner strings is wanted. Direct wired communication and powers is not possible through the conductor housing nor the wellhead housing, thus induction from the template slot inwards to the will enable non-intrusive powering and communication of collected data for the entire well life. Batteries carried will have a limited time window of operation, but may be satisfactory for some short duration wells, example exploration wells. Batteries will then power sensors and the transmission that may be acoustic or electromagnetic across the various pipes to a receiver/antenna placed on the template/well slot. se outer strain gauges may or may not utilize wireless data transfer technology depending on the physical arrangement.

FIG.2shows in highly schematic form the invention installed on the seafloor9. Where they show similar components, the same reference numerals are used inFIG.1andFIG.2.

A subsea template1has a number of slots2formed in it, two of which are shown inFIG.2. For clarity, only one of the slots2is shown with a conductor housing, etc., installed in it but normally all slots would be used.

In the left hand slot2inFIG.2, a conductor housing3is installed, with conductor attached to it and extending down into the well3. Installed within the conductor housing is a wellhead housing7from the lower end of which extends surface casing6. Attached to the upper end of the wellhead housing is a riser17which, depending on the circumstances may or not be present. If present, the riser would extend through the surface18of the sea to equipment on a producing platform (not shown). Lateral loads on the riser17are a source of stress on the wellhead and on the conductor and surface casing; these are measured with the strain gauges10,11at the position where normally the highest and most critical loads are located.

A seabed receiver19is shown adjacent the template. The seabed receiver incorporates a unit20for receiving data by radio signals from the strain gauges10,11. This may be stored in a digital memory21and transmitted by a radio transmitter22to a platform receiver23on a nearby platform24. Alternatively, a remotely operated unmanned vehicle25may be used to interrogate the seabed receiver19, in which case the vehicle25would be provided with some means26, e.g. a short range radio receiver, to received data from the seabed receiver19and to store it in digital memory27until it can be downloaded.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention.

Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.

REFERENCES

All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience:1. GB2402478A2. GB2450409B