In this paper we discuss our studies conducted on two California offshore fields that may be abandoned in near future. The purpose of the study was to examine the feasibility of re-purposing these fields to suitable offshore gas storage by utilizing the reservoir voidage and by using the existing pipeline facilities. These storage sites could offer a significant alternative to the current onshore sites located in highly populated urban areas of California.

Gas storage in certain California offshore fields producing from the fractured Monterey formation could eliminate the potential environmental risks associated with urban onshore storage of gas and prevent incidents such as the October 23, 2015 one in the Aliso Canyon Natural Gas Storage Facility in Los Angeles County. The 100,000 tonnes of methane emitted into the atmosphere resulted in the relocation of thousands of people from the areas proximal to the facility.

Study of the caprock and initial reservoir pressures encountered in these fields shows that a proposed 3000 psi storage pressure is safe for offshore storage purposes. Our computation of voidage caused by more than 3 decades of production shows that on a total basis, under a storage pressure cap of 3000 psi, these two fields together can help in storage of more than 3 TCF of gas. This is about 5 times the existing storage capacity of 0.6 TCF in California. On the long terms basis, the proposed offshore storage fields could provide a secure source of energy for the evolving market of California CNG based transportation, power generation and other consumer needs.

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