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Controlled Rocking Derrick

IP.com Disclosure Number: IPCOM000241476D
Publication Date: 2015-May-04
Document File: 2 page(s) / 101K

Publishing Venue

The IP.com Prior Art Database

Abstract

Earthquake hazards pose a design challenge in several regions of the world with oil and gas resources. The drilling derrick is one element of offshore oil and gas platforms that is particularly vulnerable. It is a tall, slender structure intended to resist primarily vertical loading — the forces imposed by earthquake excitation are horizontal and may lead to the need to substantially modify standardized derrick designs and the supporting structure below. Typical approaches have been to strengthen the structural members of the derrick. The added weight has direct cost impact with respect to the derrick itself, but also knock-on effects in the remainder of the topsides design. The fact that the derrick weight is “high weight” above the center of gravity also leads to design challenges and cost implications. Examples of projects where seismic design of the derrick led to substantial project challenges include the Berkut and Hebron platforms. Another approach on the Orlan platform has been to protect the derrick using a tuned mass damper at the top, a solution also with cost and weight implications.

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Problem Statement

Earthquake hazards pose a design challenge in several regions of the world with oil and gas resources. The drilling derrick is one element of offshore oil and gas platforms that is particularly vulnerable. It is a tall, slender structure intended to resist primarily vertical loading - the forces imposed by earthquake excitation are horizontal and may lead to the need to substantially modify standardized derrick designs and the supporting structure below.

Typical approaches have been to strengthen the structural members of the derrick. The added weight has direct cost impact with respect to the derrick itself, but also knock-on effects in the remainder of the topsides design. The fact that the derrick weight is "high weight" above the center of gravity also leads to design challenges and cost implications. Examples of projects where seismic design of the derrick led to substantial project challenges include the Berkut and Hebron platforms. Another approach on the Orlan platform has been to protect the derrick using a tuned mass damper at the top, a solution also with cost and weight implications.

Description of the Invention

The proposed invention is called a controlled rocking derrick. Rather than fixing the base, it is allowed to uplift and rock as horizontal force is applied. The business benefit of such an approach is that improved performance is achieved via subtraction of materials (and accordingly cost) rather than addition. Horizontal seismic demands are reduced as the base restraint is relieved when the derrick uplifts - in contrast to large accelerations and large reaction forces that are induced when the derrick is base connected.

The favorable performance of tall slender structures allowed to rock was first noticed by...