The ability of a gas company to operate its storage fields efficiently requires the coordination of supply, sales and the capacity of the storage field or fields to accept or give up the required gas volumes. A model of a storage field's response to anticipated demand is the essential key in the development of a computer program which combines supply, sales and storage. The strength of the method described in this paper is its capability to calculate a daily injection or withdrawal rate pattern given a minimum of input data. On injection or withdrawal a target volume and pressure for a given date can be attained if the calculated daily rates are met.
As gas supplies decrease and high priority customers are added, the need for gas storage to accommodate large winter loads increases. Calculation of the storage system's reaction to varying weather patterns to meet these peak loads is desirable. Because patterns to meet these peak loads is desirable. Because the rate to or from a storage field is dependent on the field pressure, one must be able to predict field pressure accurately. pressure accurately. Field pressures must be known at the end of February and March to design facilities for peak day situations. It is also necessary to have both the maximum allowable Pressure and working gas volume occur on the same day which coincides with the end of the injection season, usually October 31 of any given year. The following examples specifically deal with the injection cycle. However, the methods described function equally well for withdrawal.
The methods described in Katz, et al, would require over 2,000,000 computations for a daily pressure profile covering one year of a gas storage field profile covering one year of a gas storage field operation which has been active for 30 years. The methods in this paper require less than 800 computations.
The equation developed by Tutt and Dereniewski is used as the basis for the predicted pressures in this paper. It has been modified somewhat to account for paper. It has been modified somewhat to account for varying storage volumes.
The primary equation to predict any day's pressure is:
coefficients a1 and a3 are essentially dependent on gas and water movement to and from the outer edges in the reservoir. Coefficient a2 is proportional to volume of gas present in the reservoir at any given pressure. Unlike the a2 in reference 2, this coefficient pressure. Unlike the a2 in reference 2, this coefficient is not constant. The coefficient a2 is allowed to vary according to:............................(2) Combining equation (1) with (2):
For simplicity throughout the rest of the paper equation (1) will be referred to. However, in the sample field problem following, equation (2) was substituted for a2. The average value of a2, calculated over the range of pressures the field would be subjected to, was used. What we wish to do with equation (1), which describes the field's pressure response to any given rate, is use it to predict the daily rates which would be needed so that the field is at a predetermined pressure and volume on a specified date. predetermined pressure and volume on a specified date. The first step is to determine under what measurable criteria a given field will attain the specified pressure and volume. pressure and volume.