Subsea Riser Inert Gas Injection for Explosive Atmosphere Control
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Solution Overview
Problem
Subsea mudlift pump systems face the challenge of preventing the accumulation of explosive atmospheres in open top risers due to entrained wellbore gas mixing with air, which poses safety risks.
Innovation Solution
Introducing drilling fluid at a controlled rate into the upper portion of the riser to maintain a fluid level and operate the subsea pump to manage pressure, thereby inhibiting the accumulation of explosive gases and preventing flame propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the upper portion of the drilling riser is left open to enable subsea mudlift drilling, then drilling depth and wellbore diameter are improved, but the risk of explosive atmosphere accumulation increases due to air-filled space above drilling fluid
Solution Approach 1:
The patent introduces an inert gas (nitrogen or carbon dioxide) into the air-filled portion of the riser to displace oxygen and prevent formation of explosive atmospheres. This creates an inert environment that eliminates the harmful combustion risk while maintaining the open riser configuration needed for deep drilling operations.
Solution Approach 2:
The patent uses an inert gas as an intermediary substance between the drilling fluid and the atmosphere. This intermediary layer prevents direct contact between flammable gases (entrained in drilling fluid) and oxygen, thereby eliminating explosive risks without requiring the riser to be closed or pressurized.
2Length of moving object
If drilling fluid is pumped at high pressure to enable deep wellbore drilling, then drilling depth is improved, but the pressure gradient in the wellbore annulus increases which requires additional casings
Solution Approach 1:
The patent segments the riser into two distinct zones: a lower zone filled with drilling fluid under pressure for wellbore support, and an upper zone filled with inert gas at atmospheric pressure. This segmentation allows the system to achieve deep drilling capabilities while maintaining lower overall pressure gradients in the annulus, reducing the need for additional casings.
Solution Approach 2:
The patent employs a dynamic fluid level control system that actively adjusts the interface between drilling fluid and inert gas in the riser. By dynamically maintaining the optimal fluid level, the system enables deep drilling operations while controlling pressure gradients to minimize casing requirements.
3Ease of operation
If the riser is kept open for mud return operations, then operational simplicity is improved, but safety risks increase due to potential flame propagation in air-filled space
Solution Approach 1:
The patent maintains the operational simplicity of an open riser configuration while eliminating flame propagation risks by filling the upper portion with inert gas. The inert atmosphere prevents combustion throughout the entire riser length, allowing continuous mud return operations without safety compromises.
Solution Approach 2:
The patent ensures continuous suppression of explosive atmospheres by maintaining a persistent inert gas layer in the riser throughout drilling operations. This continuous protective action eliminates intermittent safety risks while preserving the uninterrupted mud return flow needed for operational simplicity.
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 prevents the formation of explosive mixtures in the riser by ensuring a downward flow of drilling fluid, thereby maintaining safety and preventing accidents.
Implementation Method 1
pump drilling fluid into the well at such rates and pressures as to enable lifting the drilling fluid all the way from the bottom of the wellbore and back to the drilling unit
Implementation Method 2
A rate of introducing the fluid is selected to inhibit an explosive atmosphere in the space in the riser above the drilling fluid level therein
Data Source
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AI summary
A method for inhibiting an explosive atmosphere in a wellbore drilling system, including a riser connected to a wellbore above a top thereof wherein the riser has a fluid outlet below a surface of a body of water in which the wellbore is drilled, and wherein the fluid outlet is connected to a subsea pump to return drilling fluid to a drilling platform on the water surface and wherein a space in the riser above the drilling fluid level filled with air includes pumping drilling fluid into a drill string extending from the drilling platform into the wellbore. Fluid is introduced proximate an upper end of the riser. A rate of introducing the fluid is selected to inhibit an explosive atmosphere in the space in the riser above the drilling fluid level. The subsea pump to remove fluid from the riser outlet is operated at a rate selected to maintain the fluid level or to maintain a selected wellbore pressure.