1. Document Overview
1.1 Nature and Status
This guide is an authoritative technical document issued by the China Classification Society (CCS) (GD002-2026), providing comprehensive analysis guidance for deepwater drilling and workover riser systems . The guide officially took effect on April 1, 2026, and serves as an important technical specification reference for deepwater offshore oil and gas development.
1.2 Scope of Application
| Application Scenario | Content |
|---|---|
| Floating Drilling Platform | Drilling vessels, semi-submersible drilling platforms |
| Subsea BOP System | BOP (Blowout Preventer) matching operations |
| New Riser Systems | Complete analysis and verification |
| In-Service/Reuse | Can be referenced for execution (historical data needs consideration) |
1.3 Analysis Purposes
- Predict Mechanical Behavior: Predict overall mechanical characteristics of the riser system under design conditions
- Determine Top Tension: Determine the required top tension settings for the riser
- Safety Assessment: Assess riser system safety under operating sea conditions
- Determine Operational Limits: Determine operational limit conditions through sea condition suitability analysis
2. Riser System Composition and Functions
2.1 Main System Components
Typical deepwater drilling riser system includes the following core components:
- Riser Pipe Joints: Main pipe structure
- Tensioner System: Provides top tension
- Buoyancy Modules: Provides additional buoyancy
- BOP Stack: Subsea wellhead protection device
- LMRP (Lower Marine Riser Package): Lower Marine Riser Package
- Flex Joint: At upper and lower ends, allows angle deflection
- Expansion Joint (Riser Tensioner): Compensates for platform movement
- Guiding System: Riser centering and guiding device
2.2 Four Major Operating Modes
| Operating Mode | Status Description |
|---|---|
| Drilling Mode | Normal drilling operations, riser connected to BOP |
| Connected Non-Drilling Mode | Riser connected to BOP but not conducting drilling operations |
| Hang-off Mode | Riser hung off (hard hang-off or soft hang-off) |
| Drift-off/Disconnect Mode | Platform requires emergency disconnect from wellhead |
2.3 Main Functions
The riser system is the key connection channel between floating drilling platforms and subsea wellheads. Main functions include:
- Provides flow channel for drilling fluid circulation (upward return)
- Provides entry channel for casing and oil pipes
- Provides channel for power/signal cables
- Provides wellhead pressure sealing
3. Design Basis and Loads
3.1 Design Load Classification
| Load Type | Specific Content |
|---|---|
| Environmental Loads | Wave force, sea current force, wind load |
| Pressure Loads | Internal pressure, external hydrostatic pressure, water level changes |
| Functional Loads | Riser self-weight, drilling fluid weight, buoyancy, tension |
3.2 Wave Force Calculation Key Points
- Applicable Theories: Flow function theory, Stokes wave theory, linear wave theory
- Calculation Method: Morison formula
- Key Parameters: Wave period, wave height, water depth - select appropriate wave theory
| Component | Drag Coefficient Cd | Inertia Coefficient Cm |
|---|---|---|
| Bare Pipe Joint (Vertical) | 0.6-1.2 | 1.5-2.0 |
| Bare Pipe Joint (Inclined) | 0.6-0.8 | 1.5-2.0 |
| With Choke/Kill Lines | 1.0-2.0 | 1.5-2.0 |
| BOP/LMRP Equipment | Requires special consideration | Requires special consideration |
3.3 Top Tension
Core Principle: Even if some tensioners fail, the riser bottom must still generate effective residual tension.
| Tensioner Type | Characteristics after Failure |
|---|---|
| Steel Wire Rope Tensioner | Sudden loss, large loss quantity |
| Direct-Acting Tensioner | Rod side pressure loss, tension loss relatively stable |
4. Response Analysis (Core of Overall Analysis)
4.1 Analysis Content Framework
Riser System Response Analysis
- Operability Analysis
- Launch & Recovery Analysis
- Hang-off Analysis
- Drift-off / Disconnect Analysis
- Weak Point Analysis
- Recoil Analysis
4.2 Operability Analysis
Determine operating ranges under different drilling fluid densities, define drilling mode and required top tension and allowable offset ranges for connected non-drilling mode.
Key Outputs:
- Tension vs.drilling fluid density relationship curves
- Floating platform "warning circle" boundary (red-yellow-green circle diagram)
- Recommended maximum/minimum top tension
4.3 Drift-off/Disconnect Analysis (Core Safety Analysis)
Ensure that in emergency situations, the platform can safely drift off or be disconnected from the wellhead, while the riser system will not be damaged.
Design Requirement: Establish complete Emergency Disconnect Sequence (EDS), ensuring reliable disconnection of LMRP and BOP connectors.
4.4 Key Design Criteria (Connected State)
| Design Parameter | Drilling Operation Condition | Connected Non-Drilling Condition | Extreme Condition |
|---|---|---|---|
| Riser Effective Stress/Yield Stress | 0.67 | 0.8 | 1.0 |
4.5 Hang-off Operating Mode Classification
| Hang-off Type | Description | Characteristics |
|---|---|---|
| Hard Hang-off | Remove tensioner, lock expansion joint, rigidly hang riser on riser spider | No tension compensation capability |
| Soft Hang-off | Hang off through tensioner/bumper sub, with tension compensation capability | Can absorb platform movement |
5. Fatigue Analysis
5.1 Wave-Induced Fatigue
Mainly caused by circulation loads induced by irregular waves.
- Focus on riser stress concentration areas (weld seams, connections)
- Use spectrum analysis method or time domain simulation method for assessment
5.2 Vortex-Induced Vibration (VIV) Fatigue
When sea current flows past the riser, periodic vortices are generated, causing lateral vibration.
- Fatigue damage is closely related to flow velocity, riser diameter, and natural frequency
- VIV analysis is required to optimize riser arrangement and buoyancy configuration
6. Special Requirements for Workover Riser Systems
Compared with drilling risers, workover riser systems have the following special analysis requirements:
- Shorter Operation Cycles: Frequent connect/disconnect operations
- BOP Configuration Differences: BOP types used in workover operations may differ from drilling
- Tensioner Requirements: Tensioner configuration may be simplified in workover mode
- Special Working Conditions: Riser hang-off weight calculation methods differ in workover mode
- LMRP Disconnect Procedures: Conditions for LMRP and BOP disconnect are more stringent in workover mode
7. Analysis Software Requirements
Commonly used software includes:
- OrcaFlex (Most widely used in industry)
- ABAQUS
- MOSES
- SAPE (Domestic self-developed software)
8. Key Abbreviations Reference
| Abbreviation | Full Name | Chinese |
|---|---|---|
| CCS | China Classification Society | China Classification Society (CCS) |
| BOP | Blowout Preventer | Blowout Preventer (BOP) |
| LMRP | Lower Marine Riser Package | Lower Marine Riser Package (LMRP) |
| VIV | Vortex-Induced Vibration | Vortex-Induced Vibration (VIV) |
| EDS | Emergency Disconnect Sequence | Emergency Disconnect Sequence (EDS) |
| DP | Dynamic Positioning | Dynamic Positioning (DP) |
| Morison | Morison Equation | Morison Equation |
9. Core Key Points Summary
Value for Drilling Equipment Export Business
Client Technical Communication
When deepwater oil and gas field project clients (CNOOC, Sinopec, Rosneft, Kazakhstan National Oil Company, etc.) procure drilling platforms or riser systems, referencing CCS guidelines can enhance the professionalism of technical communication.
Technical Threshold Awareness
Deepwater riser systems are one of the components with the highest technical threshold and most complex systems in offshore oil and gas development. Mastering this knowledge helps understand the technical depth of client procurement requirements.
Industry Compliance Standards
As China's official classification society, CCS guidelines, together with IMO and API standards, constitute the industry compliance system, helping understand technical access requirements for international oil and gas projects.
Central Asian Market Connection
Caspian Sea oil and gas projects in Kazakhstan and Uzbekistan (Kashagan, Kara gas, etc.) involve floating platform operations, where riser systems are key supporting equipment.
