Tolmount Wellhead Platform

Block 42/28d, Southern North Sea – 50km NE of Easington, Humberside

The Tolmount Development Project establishes a Minimum Facilities Platform in the Southern North Sea for Premier Oil E&P UK Ltd. Following successful exploration drilling, the platform serves as a central hub for the Greater Tolmount Area, integrating wellhead operations with production gathering capabilities for current and future field developments.

The platform addresses North Sea operational challenges through robust structural design, accommodating multi-well operations and subsea tie-back capabilities. The unmanned facility design ensures operational flexibility for phased development of additional prospects in the Greater Tolmount Area.

Project Scope

Detailed Design of a fixed offshore platform in 51.5m water depth, integrating jacket, piles, topside structures, and subsea infrastructure for current and future field expansion.

Platform Structural System

• Four-legged jacket with eight driven piles (two per leg) using grouted sleeve connections
• Three-level NUI topsides at elevation +21m LAT (cellar, main, and weather decks)

Wellhead and Drilling Facilities

• Six conductor slots in 2×3 array (2.5m spacing) for four planned production wells
• 13⅜-inch diameter conductor system with integrated drilling support structure
• Platform orientation optimized for drilling rig approach

Riser and Pipeline Systems

• 20-inch export gas riser with piggy-backed 3-inch methanol import line
• Four future import risers (two 12-inch, two 8-inch) for subsea tie-backs
• All risers pre-installed on west face, away from cargo operations to minimize dropped object risks
• Complete structural analysis including in-place strength, fatigue, and transient phases

J-Tube and Caisson Infrastructure

• 1,120mm J-tube caisson with four 12-inch and one 8-inch J-tubes for subsea umbilicals and control lines
• 30-inch produced water caisson for formation water discharge

Topside Integration and Life Safety Systems

• Emergency overnight accommodation for twelve personnel
• Helideck for Augusta AW-139 helicopter operations
• Platform crane for cargo handling and maintenance
• SOLAS-compliant lifeboat system and two walk-to-work landing areas

Engineering Approach

The design follows the performance standards in accordance with API RP2A-WSD 22nd Edition with ISO 19902 and DNV-GL standards. The design integrates comprehensive metocean analysis, geotechnical investigation data, and finite element modeling of the complete platform system.

Structural analysis covers operational conditions, 100-year storm events, installation phases, and fatigue life assessment using spectral methods with site-specific wave data.

Foundation design utilizes advanced soil-structure interaction analysis with grouted pile-sleeve connections. Installation engineering addresses lift analysis, transportation, upending operations, and post-installation grouting to ensure structural integrity throughout the platform’s operational life.