Subterranean CNG Storage Vessel Using Cement Sheath
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Solution Overview
Problem
The high cost and space requirements for CNG storage tanks, along with the need for strong, leak-proof containers that can withstand high pressure and temperature cycling, pose challenges for widespread adoption of compressed natural gas (CNG) facilities, particularly in urban environments.
Innovation Solution
A method for forming a subterranean gas storage vessel by drilling a wellbore, inserting a casing, forming a cement sheath in the wellbore annulus, and sealing the casing interior to create a reliable storage and dispensing system for CNG, using settable cement and resin compositions that can withstand high pressures and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional above-ground CNG storage tanks are used, then CNG can be stored at high pressure, but the cost and space requirements increase significantly
Solution Approach 1:
The patent transitions CNG storage from above-ground surface facilities to subterranean underground storage. By drilling wellbores into subsurface formations and installing casing strings, the storage system moves to a different spatial dimension (underground), thereby reducing surface space requirements while maintaining high-pressure storage capability
Solution Approach 2:
The patent changes the physical environment parameters by creating an underground storage system with controlled temperature and pressure conditions. The subsurface formation provides natural thermal stability, and the casing with cement sheath creates a sealed environment that maintains different pressure conditions compared to surface storage
2Reliability
If conventional above-ground CNG storage tanks are used, then CNG can be stored at high pressure, but the cost increases significantly
Solution Approach 1:
The patent adapts proven well construction techniques from the oil and gas industry for CNG storage application. By using established methods for drilling wellbores, installing casing, and cementing annuli, the system leverages existing infrastructure and expertise, reducing development costs compared to creating entirely new above-ground storage facilities
Solution Approach 2:
The underground environment provides natural advantages including ambient temperature control that reduces thermal cycling stress on the storage vessel, and geological containment that reduces material requirements compared to above-ground steel or composite tanks
3Area of stationary object
If the casing is used as storage vessel, then space cost is reduced, but the casing must withstand repeated pressure and temperature cycling
Solution Approach 1:
The patent creates a composite storage system consisting of the metal casing string combined with the cement sheath material. This composite structure provides enhanced mechanical properties, including improved resistance to cyclic pressure and temperature stress, compared to the casing alone. The cement sheath acts as a protective and supporting layer
Solution Approach 2:
The cement sheath is installed beforehand to provide protective cushioning to the casing. This pre-installed protective layer absorbs and distributes mechanical stresses from pressure cycling and thermal expansion, preventing direct stress concentration on the casing walls and reducing fatigue damage
4Reliability
If the casing interior is sealed, then gas leakage is prevented, but the sealing material must withstand high pressure and temperature
Solution Approach 1:
The patent uses composite sealing systems including setting compounds (cement or resin) that are specifically formulated to withstand high pressure and temperature conditions. These composite materials provide both the sealing function and the mechanical strength required for the harsh underground storage environment
Solution Approach 2:
The setting compound acts as an intermediary material between the casing interior and the external environment. This intermediary provides the sealing function by filling micro-annuli and imperfections in the casing, while also being selected to have the thermal and pressure resistance properties needed for CNG storage conditions
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 method provides a robust and efficient solution for storing and dispensing CNG, addressing the challenges of tank cost and space while ensuring the integrity of the storage vessel under cyclic stress conditions.
Implementation Method 1
forming a cement sheath in the wellbore annulus
Implementation Method 2
sealing at least a portion of the interior of the casing
Data Source
AI summary
A method of forming a subterranean gas storage vessel is provided. A wellbore is drilled through the surface of the ground into the ground, and a casing is inserted into the wellbore, the casing having a size such that a wellbore annulus is formed between the outside surface of the casing and the wall of the wellbore. A cement sheath is then formed in the wellbore annulus, and the interior of the casing is sealed to help prevent gas from inadvertently escaping therefrom. The cemented and sealed casing can then be used as a storage vessel to store and dispense gas such as compressed natural gas (CNG).