Tender Mooring For Infill Drilling Operations: A Case Study
Authors: Muhammad Ramli , McCollum Frank L. , Kwan C.T. , Loong Chin Vun , Cheah Andrew 
Published: December 2007

Ramli Muhammad, SPE, Esso Production Malaysia Inc.; Frank L. McCollum, SPE, Esso Production Malaysia Inc. and C. T. Kwan, SPE, Exxon Production Research Co.; Chin Vun Loong, Esso Production Malaysia, Inc.; Andrew Cheah, Tioman Drilling Company

Abstract
In preparation for an infill drilling program in the South China Sea, Esso Production Malaysia, Inc. recognized the complexity of mooring a drilling tender among eleven pipelines in the platforms' vicinity. In preparation for this work, a scenario based risk assessment was conducted to identify the various hazards that would exist during the initial mooring and subsequent drilling operations. Following the risk assessment, an initial mooring plan was developed and analyzed for its effectiveness in the anticipated environmental conditions. The prevention and mitigation measures identified in the risk assessment were then used to modify the plan to insure acceptable risk. An iterative planning and analysis process ultimately led to a final mooring plan that prevented mooring line contact with the pipelines when the tender was moored in either the lifting or drilling positions. The required mooring equipment was then procured and installed using a flotilla of six anchor handling vessels, two cargo boats, a dedicated emergency tow vessel and a survey vessel.
This paper summarizes the risk assessment techniques used and the results that were obtained; the key findings during the iterative planning and analysis process; and the field organization and operational procedures used to safely control the mooring operation and implement the plan.

Introduction
Production from Esso Production Malaysia Inc. (EPMI) wells in the South China Sea offshore oil fields is shipped onshore via pipeline from the Tapis Pump platform, a four leg jacket structure, located about 230 ft. south of the Tapis-D platform and connected to it by a walkway bridge. All production from EPMI's wells drilled in the South China Sea offshore Terengganu is piped to this platform for pumping to an onshore terminal (Fig. 1). The Tapis Pump/Tapis-D complex is located about 125 miles east of Kerteh, Terengganu.
The Tapis Pump platform is the heart of EPMI operations. The continuous operation of this platform is essential to the pumping of EPMI's total daily crude production of about 360,000 barrels.
The Tapis-D platform is a manned production platform which also acts as a Central Communication Center and Emergency Response Command Center for EPMI's offshore operations in the South China Sea.
A total of nine wells are planned for an infill drilling program at the Tapis-D platform. Tapis D has twenty-one conductor slots, ten of which were used for the initial development drilling in 1981/1982, and ten more slots which were available for the infill program. The rig selected for this infill drilling program is a self erecting tender assisted rig which utilizes an eight point wire rope mooring system.
There are a total of eleven pipelines connected to the Tapis Pump/Tapis-D platform complex. All of these pipelines were laid on the seafloor without any special external protection and were not tied down or anchored.

Risk Assessment
EPMI recognized the complexity of mooring a drilling tender in the midst of eleven pipelines. In preparation for this work, a risk assessment was performed to identify the various hazards that would exist during the initial mooring and subsequent infill drilling operations.
Formal risk assessment is the process of analyzing and evaluating risk to provide input for risk management.
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