Main objective of this study is dealing with a real case study of an Iranian gas condensate reservoir for the purpose of underground gas storage. Doing such a study in this reservoir will aid developing this technology and also demonstrates new concept of underground gas storage in partially depleted gas reservoirs.
After gathering some data about the reservoir and preparing a geological model for the field, a simulation plan considered for this field. Static model converted to a dynamic one by assigning reservoir fluid data. Finally, compositional model of the reservoir prepared and verified to be accurate through a history matching process.
After being sure about accuracy of the model and validating it, different scenarios for underground gas storage developed. Depletion and gas storage scenarios made for the field and results obtained. Gas storage in partially depleted gas reservoir considered in scenarios for developing this field too. After comparing different scenarios some practical results achieved and best scenario for developing this field chosen.
An underground gas storage system can be defined as a combination of a constant supply with a variable demand for economic advantages[1]. In other words, it helps to combine low-demand summer season and high-demand winter season. The whole process is injecting natural gas or rarely other gases into subsurface reservoirs in the periods that demands fall bellow the gas supply. When demands exceed the supply, the gas will be withdrawn from the reservoir. Fluctuating demands due to temperature and climate make it an economic process that is necessary in many cases for efficient use of the pipelines. It also helps to have an effective delivery during peak demand seasons. This process can also help producing oil or condensate and can be considered as an IOR method too. By increasing demand of gas in many areas of the world, developing storage plans and effective use of existing storage sources is a priority for engineering and economic advantages. Figure 1 illustrates natural gas supply and demand relation and clarifies importance of having some gas stored in low demand periods in order to use in high demand periods.
Figure 1- Natural gas supply and demand. (Source from [2]) (Available in full paper)
Depleted gas reservoirs called to be the best choice of underground gas storage and almost all early projects were developed in depleted gas reservoirs. There are of course other types of underground gas storage that are storing gas in aquifers and in caverns and salt structures.
Peak load natural gas consumption has become a problem in big cities in Iran, especially in Capital. Underground gas storage technology seems to be a helpful key to overcome this trouble.
A gas condensate reservoir is chosen for the purpose of underground gas storage that is located in central Iran. This field discovered in 1955 and its production started in 1959. It has a structure that is a northwest-southeast trending anticline approximately 25 kilometers long and about five kilometers wide. The structure is investigated by surface and seismic surveys and eight wells drilled on the field.
