Cushion gas is the capital that never comes back. A portion of the gas injected into a storage reservoir must remain permanently to maintain the pressure required for deliverability, and in depleted field storage it commonly represents half or more of total inventory. That gas is purchased at the start of the project and recovered, if at all, only at the end of the facility's life. Determining the minimum cushion consistent with the required deliverability is one of the more valuable calculations in storage development, and using inert gas as partial cushion is one of the few ways to reduce it.

Deliverability is a curve, not a number. At full inventory a storage field can deliver at high rate; as gas is withdrawn, pressure falls and deliverability with it. Storage contracts specify rates that must be met at defined inventory levels, and meeting them at low inventory is the binding design case. Characterising the deliverability curve, verifying it in operation, and maintaining it as wells degrade is the central operational discipline.

Cyclic service is harder on wells than production service. A storage well is injected into and produced from at high rate every year, reversing flow direction and cycling pressure and temperature. Tubulars, completions, packers, cement and casing all experience fatigue that a production well does not, and integrity failures in storage wells have caused major incidents with substantial consequence. Well integrity management is a more prominent discipline in storage than in production operations.

Finally, inventory verification is genuinely difficult and commercially important. The gas in the reservoir cannot be measured directly; it is inferred from injected and withdrawn volumes, from pressure behaviour and from material balance, and the three do not always agree. Discrepancies may indicate measurement error, gas migration out of the storage volume, or an incorrect understanding of the storage geometry, and distinguishing between them matters for both operations and commercial accounting.

By the end of this training, participants will be able to:

• Compare storage types and select the appropriate option against deliverability, capacity and cycling requirements
• Determine cushion and working gas volumes and evaluate options for reducing cushion requirement
• Characterise deliverability as a function of inventory and verify it against operating data
• Analyse injection and withdrawal cycling behaviour and its effect on reservoir performance
• Verify inventory using material balance, pressure behaviour and volumetric methods
• Diagnose gas migration and loss and distinguish it from measurement error
• Design wells and completions for high rate cyclic storage service
• Assess well and caprock integrity requirements and design monitoring programmes
• Describe salt cavern development, behaviour and operation
• Specify surface facilities and evaluate storage commercial performance

The training works through storage engineering using operating data from storage facilities. Participants determine cushion and working gas, construct and verify deliverability curves, perform inventory verification by multiple methods and diagnose discrepancies. Well design for cyclic service is developed against the loads involved. Storage incidents including well integrity failures and gas migration events are examined for their cause and their consequences. Commercial performance measures are calculated for a storage operation across a withdrawal season.

Organisations sending participants to this training will:

• Improve deliverability performance and contract compliance
• Reduce cushion gas investment through better technical determination
• Improve inventory accounting accuracy and reduce unexplained discrepancies
• Reduce well integrity failures in cyclic service
• Improve storage facility design and conversion project outcomes
• Strengthen the technical basis of storage commercial commitments

Participants will:

• Determine cushion, working gas and deliverability for a storage facility
• Verify inventory and diagnose discrepancies
• Design wells for cyclic storage service
• Assess integrity risk and specify monitoring
• Understand storage commercial drivers and their technical basis
• Build a specialist capability in a growing sector as gas systems balance renewables

• Reservoir engineers working on gas storage facilities
• Production and operations engineers running storage operations
• Well and completion engineers designing storage wells
• Integrity engineers responsible for storage well and caprock integrity
• Facilities engineers supporting storage surface plant
• Project engineers developing or converting storage facilities
• Commercial staff requiring technical understanding of storage performance

Upon successful completion of this training course, delegates will be awarded an official Certificate of Completion issued by the Petroleum Engineers Association (PEA), an ISO 9001:2015 certified training organization. The certificate carries 10 Credits and formally records the total learning hours completed.

Each certificate is signed by the Course Facilitator and the CEO of the Petroleum Engineers Association, and serves as verifiable proof of professional training that delegates can present to employers and professional bodies worldwide.