A MOBILE OFFSHORE DRILLING AND PRODUCTION PLATFORM

FIELD OF INVENTION

The present invention relates to a mobile offshore oil drilling and production platform.

BACKGROUND OF INVENTION

The world's high energy demand has driven oil prices to unprecedented heights and put pressure on industry to produce more. Threshold levels for previously considered small or marginal fields have been lowered. A small or marginal field can be defined as a field that may not produce enough net income to make it worth developing at a given time; dependent upon a combination of technical, commercial, regulatory, production sharing terms and also company's own Internal Rate of Return.

High oil prices however brings with it new challenges. Development costs have been pushed to new highs. Competition for the same resources for e.g. skilled manpower, specialized plant and equipment and space in fabrication yards have also resulted in resource constraints. Typically these unexploited fields are often located in remote locations with little or no infrastructure. The biggest challenge, typically encountered in exploiting small or marginal fields are often due to uncertainty as it is often impossible to predict with certainty the amount or composition of recoverable oil in place. Consequently platforms have been over or under designed resulting in technicians, tools and equipment transported to site to carry out costly modifications.

Conventional offshore platforms are built from components that are transported separately from fabrication sites to offshore sites where they are put together utilizing barge mounted heavy lift cranes and/or jack-up drilling rig mounted derricks.

Due to the shortage of such crane barges and jack-up rigs, the mobilization or demobilization costs and day rates for these units have increased. Installation of platforms to extract hydrocarbons at small and marginal fields is no longer economically viable mainly due to this escalation in costs.

This led to the invention of self-installing platforms called Mobile Offshore Production Unit (MOPU) which can easily be re-locatable without the need for a derrick barge or a jack-up drilling rig. The MOPU is used adjacent to a wellhead platform that supports drilling operation. Hydrocarbons extracted via the wellhead platform are sent to the MOPU for separation and further conditioning before being returned to the wellhead platform for onward transportation to a pipeline network or a Floating Storage and Offloading (FSO) vessel.

The MOPU can only be operational where a pre-installed wellhead platform with risers linked to a pipeline network or if an FSO is present. For marginal fields and medium sized fields in remote locations where a pipeline network is non-existent, the high costs associated with the installation and de-installation of the wellhead platform and an FSO will not make the project economically viable.

Therefore, there is a need for the MOPU to be made versatile for use at small and marginal fields with solutions to overcome uncertainty and high costs associated with the installation of wellhead platforms for drilling and FSO for storage.

SUMMARY OF THE PRESENT INVENTION

Accordingly, there is provided a mobile offshore oil drilling and production platform wherein the platform includes a hull and a mat, wherein the mat is connected to at least one connecting leg substantially vertical upstanding from the mat to the hull and the mat includes at least one ballast compartment to be filled with sea water or compressed air in the platform characterized in that a drilling template attached to the hull and mat by connecting means wherein a drilling template is removeably attached to the hull and mat and the at least one connecting leg is provided with at least a stiffener, wherein the load of the platform is transferred over a substantially large area of the mat and then to seabed.

Also provided is a method of installing the mobile offshore oil drilling and production platform, wherein the method includes the steps of adjusting ballast levels in the hull and the mat's ballast chambers to achieve all required conditions for the platform to be towed to an offshore installation site, securing parts of the platform such as the legs and caisson by securing means such as sea-fastening for the tow, towing the platform to the site, removing the securing means such as seafastening, adjusting the ballast levels to achieve all required conditions, activating the heightening means so that the mat, legs and the caisson or the conductor subsea support frame to be lowered from underneath the hull to the seabed, de-activating a subsea clamp holding the caisson to the mat, to allow the caisson to self-penetrate, re-activating the clamp to provide lateral support for the caisson, fully de-ballasting the hull and activating the heightening means to elevate the hull to a desired height.

Furthermore, there is also provided a method of de-installing the mobile offshore oil production and processing platform, wherein the method of de-installing includes the steps of securing the wellhead deck to the caisson or conductors by a securing means, detaching the drilling template from the hull, de-activating a subsea clamp holding the caisson or the securing means to release the conductor subsea support frame from the mat, activating the heightening means so that the hull is lowered to substantially the sea level, removing any adhesion caused by soil-in areas surrounding the mat, activating the heightening means so that the mat and the legs are returned from the sea-bed to underneath the floating hull, and re-adjusting the platform to required conditions for towing to the next destination.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

FIG. 1 is a diagrammatic view of a Mobile Offshore Production Storage and Offloading Unit (MOPSU) platform with caisson according to the preferred embodiment of the present invention;

FIG. 2 is a diagrammatic view of the MOPSU platform with conductors according to the preferred embodiment of the present invention;

FIG. 3 is a cross-sectional view of the MOPSU platform with conductors;

FIG. 4 is a top view of the hull with the conductors;

FIG. 5 is a top view of the mat with the conductors; and

FIG. 6 is cross-sectional view of the connecting legs connected to the mat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a mobile offshore oil drilling and production platform. A detailed description of preferred embodiments of the invention is disclosed herein. It should be understood, however, that the disclosed preferred embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention.

Generally, the present invention relates to a mobile offshore oil drilling, production and storage platform that allows a field operator to cope with uncertainty and economically develop a small or marginal oil field typically located in a remote location. More particularly, the invention relates to a versatile platform which includes a hull extending above the level of sea to house hydrocarbon extracting and scale up or scale down hydrocarbon processing system modules and equipment with provisions to drill new wells and work-overs using modular portable vertical drilling rigs or conventional rigs, connected to a mat acting as the foundation resting on the seabed which may or may not incorporate storage, using tubular legs, and provision to even abandon the field with minimal costs and disruption.

The present invention also relates to a method of installing and de-installing the oil drilling, production and storage platform.

The present invention provides a Mobile Offshore Production Storage and Offloading Unit (MOPSU) platform and seeks to overcome the challenges and uncertainties surrounding small and marginal field developments. The present invention also

eliminates the need for a FSO vessel by providing storage facility as an integrated feature of a mat.

As described briefly earlier, FIG. 1 is a diagrammatic view of a Mobile Offshore Production Storage and Offloading Unit (MOPSU) platform with caisson according to the preferred embodiment of the present invention, FIG. 2 is a diagrammatic view of the

MOPSU platform with conductors according to the preferred embodiment of the present invention, FIG. 3 is a cross-sectional view of the MOPSU platform with conductors, FIG.

4 is a top view of the hull with the conductors, FIG. 5 is a top view of the mat with the conductors and FIG. 6 is cross-sectional view of the connecting legs connected to the mat. These drawings will be referred to individually and collectively in the following detailed description of the preferred embodiment of the present invention.

As illustrated in the drawings, the MOPSU platform includes a hull (12) and a mat (14). The hull (12) and the mat (14) are connectable with legs (16).

Generally, the hull (12) includes facilities for drilling and processing hydrocarbons, accommodation quarters, offices and other facilities.

The legs (16) penetrate into the mat (14) and transfer the load through a reticulated network of stiffeners. This enables the mat (14) to take the load from topsides through the legs (16) to the sea bed. The mat comprises a minimum of one ballast chamber (20), each connectable to one terminal end region of each connecting leg (16) upstanding from the ballast chamber (20) to above the hull. The ballast chamber (20) is integrated to form a steel mat which will be used for stability during towing of the MOPSU. Once at installation site, the mat (14) is lowered by ballasting and strand-jacking until it reaches

the seabed. The mat (14) is then fully ballasted to allow it to sink into the seabed to attain equilibrium. The mat (14) will then serve as the foundation for the MOPSU, supporting the legs (16) and the facilities on the hull (12).

The present invention preferably includes four ballast chambers (20) and four connecting legs (16). The ballast chambers (20) are connected via piping rings and any one chamber can be by-passed or switched with another by operating the valves on the piping rings. The connecting means used are known in prior art and will not be described herein.

The ballast chambers (20) preferably should include at least one oil storage compartment, at least one air pressure compartment and at least one ballast compartment. The ballasting and de-ballasting operations can be performed by water/air and air/water displacement methods, respectively.

For ballasting, the air pressure compartment will be filled with water. When there is a need for de-ballasting, compressed air will be produced and channeled through the pipes to displace the water. The ballast chambers (20) are fitted with appropriate sensors for monitoring of the ballasting and de-ballasting processes. The oil storage compartment is for storing separated and stabilized crude oil. Extracted oil from the oil wells is transported to the hull for separation and stabilization processes. After that, the oil is transported to the mat (14) and stored in the oil storage compartment. The oil is then offloaded to a shuttle tanker via hoses on a periodic basis. The primary function of the legs (16) is to support the hull (12). Here, the legs (16) can also be used as conduits for piping, umbilical and cables between the hull (12) and the mat (14).

The MOPSU supports three different types of drilling systems. In addition to the provision of a wellhead deck for jack-up drilling, the hull (12) is designed to withstand loads imposed by tender assisted drilling rig and self-erecting modular drilling rig. Self- erecting drilling rigs, e.g. DrillTech produced by Streicher Group, are commonly used for onshore drilling works. However, these can be marinised and certified for offshore use. The entire drilling package can be modularized into six modules with each module the size of a 12.2m (40') container.

The use of the portable modular drilling rig eliminates the need for expensive jack up and self erecting drilling rigs. Once drilling has been completed, the modules are removed and replaced by hydrocarbon processing systems and equipment. The hydrocarbon processing systems and equipment is constructed in the form of compact modules that are easily handled, tested and integrated prior to being shipped to their offshore location. The hydrocarbon processing systems and equipment provide a stage by stage "building block" method of field development. As each modular processing unit is an integrated autonomous unit, it enables total integration testing to be undertaken in factory before deployment, thus increasing reliability and reducing installation and commissioning time.

The modular processing units, may be of the general type forming part of modular system for sub-sea use designed by Alpha Thames limited of Essex, United Kingdom, and referred to as AlphaPRIME. The modular processing units can be of two-phase and/or three-phase separation module and a booster pump with single well flow measurement. The modular processing unit for separation fluid mixtures is described in EP 1555387. Furthermore, the modular processing unit can accommodate sand removal as described in WO 03/041838 A1 and possibly a gas compressor. In fact, due to the

AlphaPRIME system-modular design approach, any new technology can be included into an existing system at a later date, when it becomes available, whilst production continues uninterrupted. The modular processing unit can be progressively exchanged in the same way, in order to re-configure in response to changes of field characteristics or in order to incorporate the latest technology for optimum production.

A self-installing drilling template (22) which can be removeably attached to be a standalone wellhead platform has been added to the MOPSU as an enhanced feature. The self-installing drilling template is made up of a wellhead deck (24) removeably attached to the hull (12) of the MOPSU and a caisson subsea clamp or a conductor subsea support frame (32) removeably attached to the mat (14) of the MOPSU.

The self-installing drilling template (22) is to be used to support conductors (26) or a caisson (28) containing drilling casings. A caisson (28) can be pre-installed onto the MOPSU at the fabrication site and towed to the offshore site together with the MOPSU. The caisson (28) is clamped at the mat (14) and secured at the wellhead deck (24) during tow. Alternatively, instead of pre-installing a drilling caisson (28) onto the MOPSU, drilling conductors (26) can be driven or drilled through the drilling template (22), and casings run inside the drilling conductors (26) instead of the caisson (28). The MOPSU platform supports both the above options for drilling template.

The MOPSU is self-installing and thus the timing for installation and de-installation does not have to coincide with availability of a derrick barge or a jack-up drilling rig.

The method of installing the MOPSU is now described. The MOPSU, comprising of the hull (12), mat (14), legs (16), caisson (28), wellhead deck (24) and sub-sea support

clamp (for MOPSU with caisson) / frame (32) (for MOPSU with conductors), is constructed and assembled at a fabrication yard and its quayside before towing to an offshore installation site as an integrated unit.

Once the MOPSU is assembled and ready for the tow, strand jacks are installed and the ballast levels in the hull (12) and the mat's ballast chambers are adjusted to achieve the required draft and trim for the tow to offshore installation site. Then the legs (16), caisson (28), flare tower, etc. are secured for the tow by sea-fastening. The fully assembled MOPSU is then towed by one or two tugs. Upon reaching the destination, the sea- fastening is removed and ballast levels adjusted to achieve even trim. The strand jacks are then activated and ballasting commences to lower the mat (14), legs (16) and the caisson (28) to the seabed. All the ballast chambers (20) in the mat (14) are then fully ballasted to allow the mat (14) to sink. Once the mat (14) sinks into the seabed to achieve equilibrium, the sub-sea clamp holding the caisson (28) is released to allow the caisson (28) to self-penetrate into the soil until it becomes self-standing. The sub-sea clamp will then be re-activated to provide lateral support for the caisson (28).

The hull (12) is then fully de-ballasted and jacked-up to the desired height to provide adequate air gap. The strand jacks are then deactivated and disconnected for use at another MOPSU. The platform is then secured and prepared for drilling activities to extract hydrocarbons from the target reservoirs.

The extracted hydrocarbons are transported to the hull (12) for separation and stabilization before storing the crude oil in the mat. When all the oil compartments fill-up, a shuttle tanker is mobilized and the crude oil is offloaded using hoses.

The method of de-installing the MOPSU will now be described. After drilling and production operations, the wellhead deck (24) can be secured to the drilling caisson (28) by way of welding or any other securing means and is then detached from the hull (14). The sub-sea clamp will then be de-activated and the MOPSU de-installed to leave the offshore site. The caisson (28) will then be self-standing and supporting the wellhead deck (24) for further well intervention and workovers. Where conductors (26) are used instead of the caisson (28), after drilling and production operations, the wellhead deck (24) can be welded to the conductors (26) and detached from the hull (12). The guide frame at the mat (14) can similarly be released and the MOPSU can be de-installed to leave the conductors free-standing to support the hull (12).

The de-installation of the MOPSU is essentially a reverse of the installation procedure. However, before the de-ballasting can take place, water jets will have to be used to break-out the consolidated clay layer below the mat (14). Strand jacks are then activated and the mat (14) and legs (16) jacked-up. The hull (12) is then jacked down to sea level, draft and trim adjusted and tug (s) connected for the tow to the next destination.

The caisson (28) or conductors (26) that support the wellhead deck (24) will then be stand-alone for further well intervention and workovers or abandonment. Further production can be planned with much higher certainty based on the performance achieved via the MOPSU.

The MOPSU clearly from the descriptions above offers total flexibility at optimal cost by providing drilling to be carried out and upon completion allowing hydrocarbon processing to be carried out with the stabilized crude stored in the integrated storage tanks, all by

the same unit. The self installing drilling template further offers scaling up or cost effective abandonment with the MOPSU deployed elsewhere.