Removing submerged piles of offshore production platforms

Certain aspects of removing submerged piles of offshore production platforms can be implemented as methods. A top deck of a fixed offshore platform installed on a mudline of a body of water is removed. An upper structure of the fixed offshore platform is removed. The upper structure is below the top deck. A lower structure is secured to the mudline by one or more structural piles remaining. The one or more structural piles, which are housed within one or more members of the lower structure, are driven below the mudline. The lower structure of the fixe offshore platform is removed. The one or more structural piles are left below the mudline.

TECHNICAL FIELD

This disclosure relates to offshore fixed platforms, for example, the installation or removal of such platforms.

BACKGROUND

Offshore platforms may need to be dismantled either for decommissioning after their useful lives or for installing new platforms at the same locations to accommodate more equipment or wells (both). Installing and commissioning an offshore platform can involve placing a large structure on a mudline, or seabed, within a body of water. In the case of a jacketed platform, a steel frame structure is secured to the mudline with piles. A portion of the structure surrounds, or “jackets” the piles. Dismantling involves removing the platform sufficiently so that it does not create a navigation hazard, cause any harm to the environment or facilitate installation of a slip-over platform. In the case of fixed offshore platforms, such removal often involves a near complete removal of the fixed platform since fixed platforms are often installed in shallow bodies of water. Removal of fixed platforms down to a mudline of a body of water is common.

In the case of a jacketed platform, removal often involves cutting a structural pile from within the pile a few feet below the mudline. This operation can involve cutting the pile from the pile's interior, lowering explosive charges into the piles, or other methods of cutting from the interior of the pile such as water jetting. The latter can disturb the seabed or degrade the seabed soil (or both).

SUMMARY

This disclosure describes technologies relating to removing submerged piles.

Certain aspects of the subject matter described here can be implemented as a method. A top deck of a fixed offshore platform installed on a mudline of a body of water is removed. An upper structure of the fixed offshore platform is removed. The upper structure is below the top deck. A lower structure is secured to the mudline by one or more structural piles remaining. The one or more structural piles, which are housed within one or more members of the lower structure, are driven below the mudline. The lower structure of the fixe offshore platform is removed. The one or more structural piles are left below the mudline.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. To remove the upper structure of the fixed offshore platform, shim plates, which are configured to attach the one or more structural piles within the one or more members of the lower structure, can be cut.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. To drive the one or more structural piles below the muddling, a chaser pile can be positioned to have a first end abut and be in-line with one of the one or more structural piles. The chaser pile can have a diameter sufficient to abut the structural pile. A hammer driver can be positioned at a second end of the chaser pile opposite the first end. The chaser pile can be hammered with the hammer driver to drive the structural pile below the mudline.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can include an insert at the first end to insert into the structural pile. The insert can centralize the chaser pile to be in-line with the structural pile.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can be retrieved prior to removing the lower structure of the fixed offshore platform.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can include an outer surface defining a central opening. To retrieve the chaser pile, an internal lifting tool can be inserted into the central opening.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The internal lifting tool can be a hydraulically actuated tool.

Certain aspects of the subject matter described here can be implemented as a method of clearing piles from a body of water. A chaser pile is positioned to have a first end of the chaser pile to be abut and in-line with an end of a structural pile. The chaser pile has a diameter sufficient to abut the structural pile. A hammer driver is positioned at a second end of the chaser pile opposite the first end. The chaser pile is hammered with the hammer driver to drive the structural pile below a mudline of a body of water.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile includes an insert at the first end configured to insert into the structural pile. The insert can centralize the chaser pile to be in-line with the structural pile.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can include an outer surface defining a central opening. To retrieve the chaser pile, an internal lifting tool is inserted into the central opening.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The internal lifting tool can be a hydraulically actuated tool.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The structural pile can secure a fixed offshore platform. A top deck of the fixed offshore platform, which is installed on the mudline of a body of water, can be removed. An upper structure of the fixed offshore platform, which is below the top deck, can be removed. A lower structure can be secured to the mudline by one or more structural piles remaining. The lower structure of the fixed offshore platform can be removed after the structural pile has been hammered below the mudline. To remove the upper structure of the fixed offshore platform, shim plates, which can attach the structural pile within a member of the lower structure, can be cut. The chaser pile can be removed prior to removing the lower structure of the fixed offshore platform. The chaser pile can include an outer surface defining a central opening. To retrieve the chaser pile, an internal lifting tool can be inserted into the central opening. The internal lifting tool can be a hydraulically actuated tool.

Certain aspects of the subject matter described here can be implemented as a method. A top deck of a fixed offshore platform installed on a mudline of a body of water is removed. An upper structure of the fixed offshore platform is removed. The upper structure is below the top deck. A lower structure is secured to the mudline by one or more structural piles remaining. A chaser pile is positioned to have a first end of the chaser pile be abut and in-line with an end of a structural pile. The chaser pile has a diameter sufficient to abut the structural pile. A hammer driver is positioned at a second end of the chaser pile opposite the first end. The chaser pile is hammered with the hammer driver to drive the structural pile, housed within one or more members of the lower structure, below the mudline of the body of water. The lower structure of the fixed offshore platform is removed. The one or more structural piles are left below the mudline.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile includes an insert at the first end that can insert into the structural pile. The insert can centralize the chaser pile to be in-line with the structural pile.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can include an outer surface defining a central opening. To retrieve the chaser pile, an internal lifting tool is inserted into the central opening.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. To remove the upper structure of the fixed offshore platform, shim plates configured to attach the one or more structural piles within the one or more members of the lower structure are cut.

Other aspects, taken alone or in combination with any of the other aspects, can include the following features. The chaser pile can be retrieved prior to removing the lower structure of the fixed offshore platform.

DETAILED DESCRIPTION

Dismantling jacketed platforms requires the removal of the structural piles that secure the jacket to a mudline of a body of water. Traditional removal methods can include the use of dangerous materials, such as explosives, and working under dangerous conditions for workers, such as diving and cutting in a confined space. These dangerous tasks are often necessary to completely remove a fixed platform structure so that no structure extends above the mudline. Other dismantling methods can include water jetting that can disturb the seabed or degrade the seabed soil (or both). Many jurisdictions require such removal to ensure that there are no navigation hazards in the body of water that the platform inhabited.

This disclosure relates to a method for dismantling a fixed offshore platform. The method includes removing the top deck and upper structure with conventional methods, hammering down the existing piles with a chaser pile and a driver until the original pile is below the mudline, removing the driver and chaser pile, then removing the remaining jacket. The original piles remain buried in the seabed.

FIG. 1Ashows a perspective view of a schematic diagram of an example fixed offshore platform100. The fixed platform includes a top deck102that sits atop a main platform structure104. The main platform structure104rests above a mudline within a body of water. The body of water can include a lake, river, ocean, or any other body of water. The fixed platform can include a steel structure configured to support the top deck102. The top deck102can include processing equipment for oil and gas production, pipeline infrastructure, power generating facilities, recreation facilities, or any combination.

FIG. 1Bis a side cross-sectional view of an example jacketed leg of the example platform100. The fixed offshore platform100is installed on a mudline302of a body of water304. At202, the top deck102of the platform100is removed. Removing the top deck102can include heavy lifts, cutting, or any other removal steps. For example, an operator or team of operators can remove the top deck102with an offshore barge with suitable cranes. At204, a structure306of the fixed offshore platform100is removed. The transition piece308that is configured to redirect a load from one direction to another. For example, as illustrated, the transition piece308redirects the load from a vertical load to an angled load. In some implementations, the transition piece308includes a hollow steel tube with a bend towards the middle of the tube. In some instances, the transition piece308rests on a structural pile312. Removing the transition piece308can include heavy lifts, cutting, un-bolting, or any other removal steps. In some implementations, the upper structure306and transitional piece308are connected and can be considered an effective single structure. In some implementations, before driving the structural pile312, it is detached from jacket or lower structure314by cutting the shim plates310. The lower structure314is secured to the mudline302by one or more structural piles312. The piles312are held in place by the pressure and friction of the soil that surrounds the piles below the mudline302. The lower structure314is secured to the piles by shim plates310. The structural pile312itself can include a long, hollow steel tube that is open at one or both ends. The lower structure314remains in place after the top deck102, the transition piece308and shim plates310are removed. While the illustrated implementation shows a waterline316being below the transition piece308, upper structure306, and shim plates310, the waterline316can land anywhere between the mudline302and the shim plate310without departing from this disclosure.

FIG. 2is a flowchart of an example method200that can be used with aspects of this disclosure. Steps of this method will be referenced throughout the remainder of this disclosure.

FIG. 3is a side cross-sectional view of the example structural pile312being driven below the mudline302of the body of water304. Referring back toFIG. 2, at206, a chaser pile402is positioned to have a first end404aof the chaser pile402to be abut and in-line with an end406of the structural pile312. The chaser pile402has a diameter sufficient to abut the structural pile312. In some implementations, the chaser pile402can include an insert410at the first end404aof the chaser pile402. For example, the insert can be a stabbing guide or a rolled bar. The insert410is configured to insert into the structural pile312and centralize the chaser pile402to be in-line with the structural pile312. That is, a central longitudinal axis of the central chaser pile402is aligned with a central longitudinal axis of the structural pile312. At208, a hammer driver408is positioned at a second end404bof the chaser pile402opposite the first end. At210, the chaser pile402is hammered with the hammer driver408to drive the structural pile312below the mudline302of the body of water304. In some implementations, the hammer driver408includes an anvil and a ram (not shown). For example, the structural pile312can be driven so that the end406of the structural pile312is a few feet below the mudline302, so long as the structural pile312is sufficiently below the mudline to prevent any navigational hazard or obstruction to installing the new slip-over platform. In some implementations, the structural piles may not be fully driven below the mudline302, so long as they are driven to a sufficient depth to prevent navigational hazards. In some instances, prior to hammering the structural pile312, a pile drivability analysis is performed to ensure that the structural pile312can be hammered below the mudline302. In some instances, drivability may not be possible, such as if the hammer doesn't has have enough energy, or the pile stresses during driving increase beyond yield strength of steel. The former can be addressed by using higher energy hammers, but since the piles are existing, stresses are limited the below yield strength of the steel. This in turn will not allow the use higher energy hammer beyond a certain limit. The drivability analysis provides both the hammer energy required as well as the stresses in the pile. The structural pile312is housed within the member of the lower structure314during hammering operations. After the structural pile312is driven below the mudline302, the chaser pile402is retrieved. That is, the chaser pile402is retrieved prior to removing the lower structure314.

FIG. 4is a side cross-sectional view of an example chaser pile402being retrieved from lower structure314. The chaser pile402includes an outer surface that defines a central opening502. Retrieving the chaser pile402includes inserting an internal lifting tool504into the central opening502. In some implementations, the internal lifting tool504is a hydraulically actuated tool. In such an implementation, the tool extends gripping members506from a central core508of the tool504to grip an inner surface of the chaser pile402. Once the internal lifting tool504has a hold of the chaser pile402, the tool504and the chaser pile402are retrieved by a crane, winch, or other retraction mechanism. In some instances, the internal lifting tool504is used to help position the chaser pile402prior to driving operations.

FIG. 5is a perspective schematic diagram of an example lower structure314of the fixed offshore platform100being lifted. Referring back toFIG. 2, at212, the lower structure314of the fixed offshore platform100is removed. The lower structure314is removed, for example, by an offshore crane sufficient of rated capacity to lift the lower structure314. After the lower structure314is removed, at214, any structural piles312that once secured the platform100are left below the mudline. As the structural piles312are below the mudline302, the structural piles312no longer pose a navigation risk to passing vessels or obstruction to the installation of the new slip-over platform.