Subsea Riser Gas Influx Control via Dual Closure and Fluid Injection
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Solution Overview
Problem
Deep water drilling operations face hazards due to uncontrolled gas releases above subsea blowout preventers, leading to rapid pressure drops and potential hydrostatic collapse of riser pipes, with existing diverter systems being inadequate in controlling gas expansion and maintaining bottom hole pressure.
Innovation Solution
A method involving the operation of first and second riser closure apparatuses to manage gas influx by maintaining constant pressure in the riser through fluid pumping and choke control, utilizing annular blowout preventers and a riser gas handling manifold to direct fluids to a mud gas separator for gas separation and pressure regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a diverter is used to vent gas overboard, then gas is diverted away from personnel, but the release of gas is not controlled and bottom hole pressure is not managed
Solution Approach 1:
A riser closure apparatus is introduced as an intermediary device between the gas influx and the diverter. This apparatus includes a closure element that can seal within the riser to isolate the gas, and a fluid injection system that injects fluid into the riser to maintain pressure control. The intermediary closure apparatus enables controlled management of gas release while maintaining bottom hole pressure, rather than allowing uncontrolled venting.
Solution Approach 2:
The system incorporates automatic detection and response mechanisms where gas detection triggers automated closure of the riser and activation of fluid injection. The system serves itself by automatically maintaining pressure control through coordinated operation of closure elements and fluid injection without requiring manual intervention, ensuring reliable pressure management during gas influx events.
2Productivity
If the diverter closes rapidly to secure the well, then gas release is controlled faster, but the reaction time is still too slow to fully protect the drill crew
Solution Approach 1:
The riser closure apparatus is pre-positioned within the riser structure, with closure elements ready to seal immediately upon detection of gas influx. The fluid injection system is pre-configured with injection lines extending into the riser, allowing immediate fluid injection to maintain pressure control. This preliminary positioning eliminates delays associated with deploying control devices during an emergency.
Solution Approach 2:
The system replaces manual mechanical operation with automated detection and actuation systems. Gas detection sensors trigger automated closure mechanisms and fluid injection systems, eliminating the time delay associated with manual reaction and mechanical operation. The automated system responds instantaneously to gas influx conditions.
3Reliability
If fluid is pumped into the riser to maintain pressure, then bottom hole pressure is controlled, but the complexity of the pressure control system increases
Solution Approach 1:
The fluid injection system serves multiple functions: it maintains bottom hole pressure control, provides hydrostatic support to prevent riser collapse, and works in coordination with the closure apparatus to manage gas influx. The closure apparatus itself serves dual purposes of isolating gas and working with the injection system for pressure control. This multi-functionality reduces the need for separate dedicated systems.
Solution Approach 2:
The closure apparatus and fluid injection system are merged into a single integrated pressure control assembly. The closure elements and injection lines are positioned and coordinated within the same structural framework, allowing simultaneous operation for pressure management. This merging reduces overall system complexity compared to having separate independent systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively controls gas expansion, maintains hydrostatic pressure, and prevents riser collapse by rapidly sealing the riser and pumping fluid to manage pressure, thereby ensuring safer drilling operations and reducing the risk of uncontrolled gas releases.
Implementation Method 1
pumping fluid into an inlet line which extends into the riser at a point above the second point but below the flow spool
Implementation Method 2
operating a choke provided in the riser gas handling manifold to maintain the pressure in the inlet line or the riser between the first and second points at a substantially constant pressure
Implementation Method 3
operating a first riser closure apparatus to close the riser at a first point above a flow spool provided in the riser
Implementation Method 4
utilizing annular blowout preventers and a riser gas handling manifold to direct fluids to a mud gas separator for gas separation and pressure regulation
Data Source
AI summary
A method of operating a system for handling an influx of gas into a marine riser during the drilling of a well bore includes the steps of operating a first riser closure apparatus to close the riser at a first point above a flow spool provided in the riser, there being a riser gas handling line extending from the riser at the flow spool to a riser gas handling manifold, operating a second riser closure apparatus to close the riser at a second point below the flow spool, pumping fluid into an inlet line which extends into the riser at a point above the second point but below the flow spool, and operating a choke provided in the riser gas handling manifold to maintain the pressure in the inlet line or the riser at a substantially constant pressure.