Recent oil and gas exploration has shown that large hydrocarbon reserves are available in deeper water. As the water depth increases, anchoring methods may also develop due to economic and logistical issues.
Two "Deep Penetrating Anchors" before installation. Photo: Deep Sea Anchors.
In this way, torpedo anchors have great potential for the oil and gas industry in deeper water not only due to economic and logistical issues, but also due to design and performance reliability. Torpedo anchors have been introduced to the offshore oil and gas industry as a cost effective deepwater anchoring solution with simple installation and relatively inexpensive fabrication.
NGI, Inc. has developed predictive models for:
Calculation of impact velocity
The velocity of a torpedo anchor at impact is a governing parameter to assess final penetration depth. The free fall phase for a torpedo pile contains three force components including self weight, buoyancy force, and drag force. To compute the impact velocity of the torpedo anchor, an iterative calculation procedure is developed using a finite difference method to solve Newton's 2nd law of motion. More complex computational fluid dynamics approaches may also be applied.
Embedment depth predictions
Torpedo anchor penetration depth is important to assess the subsequent holding capacity, which is then largely governed by the shear strength of soil. The penetration is resisted by a combination of components including buoyancy, frictional resistance, end bearing and drag.
Evaluation of holding capacity
Pullout capacity is provided by the submerged weight, reverse end bearing, frictional resistance and components for the fluke and padeye. The ultimate capacity also includes time related set-up effects, similar to a driven pile or suction anchor. Predictive relationships are currently based on limited data, and further research is ongoing together with our sister company NGI in Oslo, Norway.
The calibration of these predictive models against full-scale tests data has improved the degree of confidence in the geotechnical performance of torpedo anchors. So far, this technology has been used for commercial projects in Brazil, with other test projects in areas such as the North Sea. Relatively little test data has been made available within the public domain for detailed evaluation, and the future availability of such field test results for different soil profiles and anchor geometries is an important prerequisite for future use of torpedo anchors in commercial projects.