Gill Ranch Gas Storage Project, California

The Gill Ranch Gas Storage project, located 20 miles west of Fresno, California, US, was developed by Gill Ranch Storage, LLC (GRS), a subsidiary of NW Natural and Pacific Gas and Electric (PG&E) Company. GRS is the underground natural gas storage project’s initial operator, holding a 75% interest in the project, while 25% is held by PG&E.

The storage facility uses depreciated or reduced sandstone natural gas reservoirs of an existing gas field of GRS. The gas field is situated in Madera County in the central San Joaquin Valley, 25 miles west of the city of Frenso. The storage facility is located within the gas field and covers an area of approximately 5,020 acres.

NW Natural signed an agreement with PG&E to develop a natural gas storage project in 2007. The approval from the California Public Utilities Commission (CPUC) to develop and operate the project was received in October 2009.

A joint project development agreement was signed and the project moved ahead as its design was finalised, and preparation of regulatory documents and land-use filling were completed in 2008. The regulatory decision was approved in 2009 and construction started in January 2010.

The first phase of the project is estimated to have an initial capacity of around 20 billion cubic feet (bcf); 15bcf will be owned by GRS and 5bcf will be held by PG&E.

The project offers various benefits for Madera and Fresno counties by providing employment opportunities and tax revenues. Construction of the facility created hundreds of jobs with a peak on-site construction workforce of 500 during design and construction phases. It is expected to provide around $1.2m annually to support local services in the Madera County and approximately $0.6m for local services in the Fresno County.

Gill Ranch gas storage project geology

The Gill Ranch gas field was discovered in 1942 and consisted of different and geologically separate reservoirs. The first and second sands of the Starkey Formation, containing reservoirs to be developed for the project, lie at depth in the range of 5,700ft to 6,300ft below ground surface.

The Domengine / Kreyenhagen and Moreno formations, which could prove to be a potential future development phase, lie at depths of around 4,300ft to 4,600ft and 5,570ft below ground surface respectively.

Gas storage project construction and infrastructure

The Gill Ranch project involves underground reservoirs with high deliverability injection / withdrawal wells, and observation and monitoring wells. A flow line to connect injection and withdrawal (IW) wells to the compressor station, as well as the central compression and dehydration station with the storage field, was also developed.

The project includes a pipeline that connects the facility to customers throughout California. An electric substation and central compressor are also planned to be built. A 115kV line supplies the necessary power to the compressor station, and gathering lines were developed from Ithe W wells to the central compression facility.

The project started with an initial storage capacity of 20bcf, with the ability to expand its storage capacity later. The peak deliverability is 650mcf per day.

To reach the desired storage capacity of 20bcf and maximum design withdrawal rate of 650mcf per day, around 15 IW wells were drilled in three separate and second Starkey reservoirs. In addition, seven new observation and monitoring (OM) wells were also drilled into storage formations in an inactive gas portion of reservoirs.

The electric station is powered by electric motors. Power is supplied by a new nine mile-long electric power line. A 115kV electric power line extending from the central compressor station to tie-in with an existing PG&E line was also built. It is placed adjoining to the existing PG&E distribution lines.

The facility also has a central compressor offering 45,000bhp. Other infrastructure encompassed in the project includes a gas dehydration and processing facility, and a salt water disposal well.

The commissioning and testing of equipment was completed in June 2010. The natural gas injection began in August 2010. GRS commenced services from the facility in October 2010.

Gas transmitting pipeline

A 30in gas transmitting pipeline of around 27 miles in length was developed within the project site. The pipeline starts at PG&E line L401 interconnection, located around 0.5 miles southeast of PG&E’s Panoche Electrical Substation.

It is designed and developed for maximum allowable operating pressure of 1,415psig.

The pipeline is designed to support future additional deliverability planned.