Use of a Fully Coupled Reservoir Simulation Approach for Deliverability and Cycle Enhancement in a Gas Storage Field
Authors: Guoynes John , Laude Larry , Squire Ken , Jones Frank , Hampton David , Wells John 
Published: December 2007

Successful optimization of a gas storage field begins with proper reservoir description and evaluation of deliverability and storage capacity in the reservoir. Once true reservoir potential is determined, the effects of surface piping and surface-facility pressure constraints can be integrated to quantify a more accurate estimate of the actual deliverability, injectivity, and working gas capacity of the gas storage field. This paper discusses the integration of previously used deliverability enhancement methods with a new reservoir solution simulation package, fully coupled to include surface pipelines and field facilities. The process allows reservoir capacity, reservoir deliverability/injectivity potential, and the surface constraints imposed by pipeline interconnects and facilities to be modeled, allowing the storage operator to improve cycle performance of the entire storage asset.

A gas-storage field in Pennsylvania with approximately 50 injection/withdraw wells completed in a pressure-drive sandstone reservoir was studied. The field was converted from a depleted gas producing field to storage in the 1940's. The operator wanted to evaluate the capability to improve deliverability and cycle performance of the field. To accomplish this, geologic modeling was integrated into a reservoir simulation package that incorporated modeling of the subsurface reservoir, the completion piping of the wells, and the complete surface gathering system to the mainline interconnect. Deliverability decline was evaluated using the deliverability indexing method and well test analysis. Skin damage determined from well testing was integrated into the reservoir simulation. After determining the reservoir uplift potential of the field from damage remediation, improvement opportunities were assessed, based on the results of a fully coupled simulation model of the reservoir, including pressure restrictions throughout the piping and facilities.

This project demonstrates how modeling the full reservoir, including field facilities and piping, can economically determine incremental levels of improvement associated with mitigation or complete removal of restrictions that compromise the full potential of the gas-storage reservoir. Some of the field restrictions are naturally occurring reservoir rock characteristics while others result from skin damage and pressure restrictions in surface lines or facilities. Direct quantifiable and cost-effective field performance opportunities are determined with a surface and subsurface full-field reservoir simulation package.

Results of this field optimization and reservoir study were applied to remediate 18 wells in the storage field in 2001. The performance of this remediation program, including the delta pressuring of the field, demonstrates that the fully coupled reservoir characterization study was successful in 1) improving overall field operation efficiencies, and 2), demonstrating that this process can be applied to future evaluation of many gas storage fields. After two seasons of withdrawal, results of actual performance are compared to the simulation modeling predictions used in the optimization study.