Purposefully built underground natural gas storage

The volumes of natural gas that are needed for a wide variety of industrial processes plus domestic uses vary significantly with respect to time, location, and demand. Thus, mechanical storage of natural gas in manufactured containers is not economically feasible or even logistically possible. Although much of the storage and withdrawal have been associated with seasonality, storage is becoming essential in an integrated natural gas supply network. It is particularly important in large operations, such as being a backup fuel in power generation and in sustaining the rate for liquefied natural gas (LNG) production. Therefore, the design of underground natural gas storage becomes essential.Important components of natural gas storage engineering include capacity which is affected by reservoir volume and tolerable pressure; injection or producing rates which are affected by reservoir permeability, natural reservoir drive mechanism, well completion/stimulation; and the impact of cyclical losses.We present here a new sequence of calculations and estimations for monitoring and forecasting gas movements through an underground gas storage reservoir:
• Maximum capacity estimation with a new type of graphical construction, blending concepts of the classical p/Z vs. cumulative recovery straight line in natural gas production.
• Prediction of withdrawal rates and time, constrained by decreasing storage pressure.
• Determination of maximum or sustainable withdrawal rate for a period of time. In all cases considered, the injecting and producing wells are hydraulically fractured. The hydraulic fractures are designed for the withdrawal rate. Thus, the required number of wells is determined.We apply these concepts to an underground natural gas storage facility and forecast the injection and production rates, cumulative storage and withdrawal, pressure buildup and decline as a function of time.A case study is presented here to demonstrate an appropriate sequence for designing an underground natural gas storage facility so that it can meet certain functionalities. In this case, the underground storage facility needs to provide enough gas to support a 1000 MW gas-fired power plant for continuous 90-day operating period (in the case of emergency).

► A new sequence of calculations and estimations demonstrating salient elements of storage design.
► Maximum capacity estimation with a new type of graphical construction.
► Prediction of withdrawal rates and time.
► Determination of maximum or sustainable withdrawal rate for a period of time.
► Determination of the required number of hydraulically fractured injecting and producing wells.