Jack-up drilling rigs are designed to elevate their working decks above the water by lowering large legs to the seabed and using those legs to support the weight of the rig. Before drilling begins, operators typically conduct preload operations to confirm that the seabed can support the anticipated loads.
One of the most dangerous failures that can occur during this process is known as a punch-through.
A punch-through occurs when one of the jack-up’s legs or footings suddenly penetrates farther into the seabed than expected. If one leg drops while the others remain relatively stable, the rig can tilt rapidly. The resulting imbalance can place tremendous forces on the legs, jacking system, hull, and other structural components.
In severe cases, a punch-through can cause a jack-up rig to lose stability entirely. Workers can be thrown from equipment, trapped by shifting machinery, forced to abandon the unit, or placed at risk if the rig begins to collapse or sink.
Understanding why punch-throughs occur requires examining both the seabed beneath the rig and the procedures used to position and preload the unit.
How a Jack-Up Rig Punch-Through Occurs
Most jack-up rigs use large footings at the bottom of their legs, commonly known as spudcans, to distribute the weight of the unit across the seabed.
When the legs first contact the bottom, the spudcans begin penetrating the soil. The amount of penetration depends on the weight applied to each leg and the strength of the underlying sediments. The danger arises when seabed conditions are not uniform.
A spudcan can initially encounter a relatively strong layer of soil that appears capable of supporting the rig. Beneath that layer, however, there may be much weaker material. As additional load is applied during preload, the upper layer can suddenly fail and allow the spudcan to break through into the softer sediment below.
Instead of gradually settling, the leg can drop abruptly.
If only one leg experiences that sudden penetration, the rig can immediately begin to list. Loads that were expected to be shared among several legs can shift dramatically, increasing stress on the remaining legs and the rig structure.
A punch-through therefore involves much more than a leg simply sinking deeper into the seabed. It is the sudden and unexpected loss of support beneath part of the rig that creates the greatest danger.
The same basic problem can occur in different seabed formations. Layered soils, weak clay beneath stronger material, sand over softer sediment, irregular seabed conditions, and previously disturbed soil can all complicate predictions concerning how a jack-up will behave when load is applied.
Why Preload Operations Are So Important
Preloading is performed before full drilling operations begin because the rig needs to demonstrate that the seabed can support the forces expected during the planned operation.
During preload, additional weight is deliberately placed on the rig. Water is commonly used as ballast to increase the load carried by the legs. The objective is to subject the seabed to forces equal to or greater than those expected during normal operations.
If the footing settles gradually and remains stable under the required load, the rig can then be elevated to its intended working position.
A punch-through during this process means the seabed did not behave as expected.
The consequences depend heavily on how rapidly the leg penetrates and whether rig personnel can control the resulting movement. A small amount of additional penetration may be manageable. A sudden drop of several feet can create a very different emergency.
Rig operators monitor leg penetration, hull elevation, jacking loads, ballast, and the behavior of each footing during preload. Abnormal movement can indicate that the soil is failing or that one leg is behaving differently from the others.
Preload procedures therefore have to account for the specific conditions at the location. A generic approach is not enough when seabed geology varies substantially from one drilling site to another.
Geotechnical information is particularly important. Soil borings, surveys, previous rig activity, nearby wells, bathymetric information, and engineering analyses can help identify conditions associated with punch-through risk before the rig begins jacking operations.
A serious punch-through can become an offshore platform accident before drilling ever begins.
What Happens When a Jack-Up Loses Stability
Once a leg suddenly penetrates the seabed, the situation can deteriorate quickly.
The first concern is the changing angle of the rig. Equipment and materials that were stable on a level deck can begin sliding or shifting. Cranes, pipe racks, tanks, drilling equipment, and other heavy machinery can create additional hazards as the structure lists.
Workers can lose their footing or be struck by moving equipment. Access routes and stairways can become difficult to use. Doors, hatches, and evacuation paths may no longer be positioned as expected.
The structural consequences can be even more serious.
Jack-up legs and jacking systems are designed to carry substantial vertical loads, but a sudden tilt can introduce forces that were not anticipated during normal operation. One leg can become overloaded while another loses support. Bracing and connections can experience extreme stress.
If the imbalance continues, a leg can buckle or the hull can contact the water. At that point, the rig can suffer progressive structural failure or sink.
The emergency can also affect nearby infrastructure. A jack-up working close to production equipment, pipelines, platforms, or subsea systems can create additional hazards if it moves unexpectedly.
Unlike an explosion, a punch-through begins as a stability and foundation problem. It can nevertheless develop into an emergency affecting the entire rig and everyone aboard.
Punch-Through Accidents Can Trigger an Immediate Abandonment
A sudden loss of stability can leave little time for offshore workers to react. Emergency alarms may be activated while personnel are still trying to understand what is happening. Workers can be required to leave their work areas and report to designated muster locations while the deck is already listing. If the unit continues losing stability, evacuation can become necessary.
Offshore emergency planning is intended to provide several methods for getting personnel away from a rig. Lifeboats, life rafts, rescue vessels, personal flotation devices, and other equipment can become critical if a jack-up has to be abandoned.
Locating personnel afterward can be equally important. An EPIRB can transmit a distress signal to assist search-and-rescue authorities in identifying the location of a maritime emergency.
The effectiveness of any evacuation depends heavily on how quickly the casualty develops. A slowly developing problem can provide time to organize personnel and prepare survival equipment. A rapid punch-through can produce a severe list almost immediately, making ordinary escape routes more difficult to use. For that reason, emergency procedures have to account for the possibility that a jack-up will not remain level during an evacuation.
Investigating a Jack-Up Punch-Through
After a serious punch-through, identifying the immediate event is only the beginning of the investigation. Investigators need to determine why the footing lost support. That analysis generally starts with the geotechnical information available before the rig was positioned. Investigators can compare predicted soil conditions with the actual penetration experienced by each leg.
They can also review the preload plan and the sequence used to increase loads on the rig. Important questions include whether the expected leg penetration was calculated correctly, whether the soil profile showed weak layers, whether previous operations had disturbed the seabed, and whether any unexpected movement occurred before the major punch-through.
Rig data can provide a detailed picture of the casualty. Jacking records, ballast levels, leg loads, penetration measurements, alarms, and other operating information can show how the unit behaved as the preload progressed.
The investigation can also address whether warning signs were recognized and whether operations should have been stopped or modified before the stability loss occurred.
A punch-through does not automatically establish negligence. Some seabed failures can be difficult to predict even after substantial engineering work. The legal and safety analysis depends on what information was available, what the responsible companies did with that information, and whether appropriate procedures were followed.
Multiple Companies Can Be Involved in Jack-Up Operations
Modern offshore drilling operations frequently involve several businesses. The rig can be owned by one company, operated by another, and contracted to an exploration or production company. Engineering firms, geotechnical consultants, marine warranty surveyors, drilling contractors, and other specialists can also participate in selecting and evaluating the location.
That division of responsibility becomes important after a punch-through. One company may have performed the seabed investigation. Another may have developed the preload procedure. Rig personnel may have been responsible for carrying out the jacking operation, while the operator or another contractor supplied information concerning the drilling location.
When a casualty occurs, determining responsibility requires understanding what each company was required to do and what information it possessed.
For an injured maritime worker, the legal remedies can depend on the worker’s employer, job duties, connection to the rig, location of the accident, and which company caused the unsafe condition.
An injury occurring during jacking or preload operations can therefore involve both maritime employment issues and claims against third parties whose conduct contributed to the accident.
Preventing Punch-Through Accidents
The most effective way to address a punch-through is to identify the risk before the rig is fully loaded. That begins with reliable seabed information. Geotechnical studies should provide enough information to understand the strength and layering of the soil beneath the proposed leg locations. Engineering analysis can then estimate expected penetration and identify formations that create a heightened risk of sudden failure.
The planned preload procedure should reflect those conditions.
Personnel also need to monitor how the rig actually behaves. Unexpected penetration, unusual leg loads, or differences between predicted and actual conditions can require reevaluation before additional load is applied.
Prior rig activity at the location can also be important. Previous spudcan footprints can alter the seabed and create uneven conditions for a later installation. A new rig positioned close to an existing footprint can experience lateral movement or uneven support.
The goal is not simply to complete preload. The purpose is to demonstrate that the rig can safely remain supported throughout the drilling operation. A jack-up that cannot maintain stable footing presents a danger to every person aboard.
Speak With a Maritime Injury Lawyer After a Jack-Up Rig Accident
Spagnoletti Law Firm represents offshore and maritime workers injured in jack-up rig accidents and other serious offshore casualties.
A maritime injury lawyer can evaluate the circumstances of a punch-through accident, explain the legal remedies available to an injured worker, identify potentially responsible contractors and offshore companies, handle insurance issues, and pursue compensation when negligent conduct causes injury or death.
We offer a free consultation to discuss an offshore accident and the legal options that may be available. Our firm represents clients on a contingency fee basis, meaning clients do not pay attorney’s fees unless we obtain a recovery.
If you have been impacted by a jack-up rig accident, call Spagnoletti Law Firm at 713-804-9306 or contact us online.