Retrievable Plug Dead String for Gas Well Liquid Loading
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Solution Overview
Problem
Natural gas wells face reduced production due to liquid loading, where the critical velocity required to lift liquids to the surface is not adequately reduced by existing dead string configurations, limiting access and intervention capabilities for wellbore issues like sand accumulation.
Innovation Solution
A dead string apparatus with a retrievable plug and ported member allows selective fluid communication between the tubing string and the annulus, reducing critical velocity while enabling access below the dead string for intervention and reagent delivery, using sliding sleeve valves or ported flow subs to manage fluid flow and isolate sections as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a dead string with a permanent plug or bull plug is used to reduce critical velocity, then liquid loading is reduced, but access to the wellbore below the dead string is blocked preventing intervention capabilities
Solution Approach 1:
The plug is made retrievable rather than permanent, allowing it to be removed when wellbore access is needed. This dynamic configuration enables the system to switch between liquid loading prevention mode (plug installed) and intervention mode (plug removed), resolving the contradiction between maintaining productivity and enabling operational access.
Solution Approach 2:
The plug can be discarded (removed) temporarily to allow wellbore access for interventions such as sand removal or reagent delivery, then recovered and reinstalled to resume liquid loading prevention. This temporary discarding and recovery cycle allows both functions to be performed at different times.
2Productivity
If holes are drilled in ported tubing to allow fluid crossover, then critical velocity is reduced, but ability to deliver reagents to the bottom of the wellbore is limited
Solution Approach 1:
The ported member incorporates a sliding sleeve valve that can dynamically open or close the ports. When ports are closed, reagents can be delivered through the tubing to the bottom of the wellbore without escaping through the ports. When ports are open, critical velocity reduction is achieved. This dynamic control resolves the contradiction between productivity enhancement and operational flexibility.
3Productivity
If a bull plug is used to force flow up to the ported section, then liquid loading is prevented, but circulation fluids cannot reach the bottom of the production tubing
Solution Approach 1:
The sliding sleeve valve in the ported member can be opened to allow circulation fluids to pass through the ported section to the bottom of the production tubing. When the valve is closed, liquids are forced to flow up the annulus to the ported section, preventing liquid loading. This dynamic switching capability resolves the contradiction between liquid loading prevention and circulation capability.
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
The apparatus effectively decreases the critical velocity required to lift liquids, allowing for improved wellbore access and intervention, including sand management and reagent delivery, thereby enhancing natural gas well production and operational flexibility.
Implementation Method 1
The critical velocity is the flow velocity or flow rate(mcf/d) required to overcome this pressure differential needed to lift produced fluids to surface
Implementation Method 2
The ported member is configured to selectively permit or prevent fluid communication between the interior of the ported member and the annular region between the tubing string and a wall of the wellbore
Data Source
AI summary
Disclosed herein is a system for enhancing the recovery of gas in a perforated interval of a gas well. The system features a tubing string having a dead string attached for reducing the flow area of the annulus in the perforated interval, thereby reducing the critical velocity of the gas, i.e., the velocity required to overcome backpressure due to fluids in the well column. The system includes a ported member for receiving gas from the annulus into the tubing string. The ported member and the dead string are isolated from each other by a retrievable plug. The disclosed system provides access from the surface through the dead string for diagnostic or corrective operations. The system also provides delivery of reagents such as foamers to the perforated region to further reduce the critical velocity.