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Gas storage reservoirs are used worldwide to store produced natural gasduring periods of low demand for use during periods of high demand. These formations are often depleted natural gas reservoirs. Proper selection of a gas storage reservoir is important to allow proper and economic operation of the project on a long-term basis. This paper describes issues which need to betaken into consideration from a reservoir perspective when considering the development of a gas storage reservoir. These issues include the proper containment of the injected gas, maintaining injectivity and productivity overlong-term operations, and problems which may be associated with the presence of free water or hydrocarbons in the storage reservoir (both mobile and immobile)as well as formation damage issues that often surround the drilling andcompletion of new wells in the gas storage reservoirs for development purposes. Introduction Gas storage reservoirs are used on a worldwide basis for the storage ofnatural gas for use in periods of peak consumption, generally in the colder portions of the year when gas demand for heating is higher. Storage reservoirs are also used to buffer periods of peak demand and prevent disruption of supplies during mechanical or other problems in producing fields. Gas storage reservoirs generally consist of good to excellent quality formations which are often located spatially close to the ultimate demand source (i.e. major population centers). Most of these reservoirs represent natural gas pools which have been depleted below their abandonment pressureduring normal production operations, but are now used on a seasonal basis forgas storage. For a reservoir to be a candidate for gas storage, the following criteria must be satisfied:Sufficient reservoir volume to allow for storage of the required amountof gas without exceeding containment pressure constraints and without requiringun economic compression to high pressure levels.Satisfactory containment of the gas by competent upper and lower sealing caprock.Sufficient inherent permeability to allow injection and production at required delivery rates during peak demand periods.Limited sensitivity to reductions in permeability (and injectivity/productivity) due to:–presence of in-situ water (mobile or immobile)–presence of liquid hydrocarbons (mobile or immobile)–plugging of the near injector region by compressor lubricants or otherintroduced fluids–reservoir stress fluctuations during successive pressure cyclesAbsence of hydrogen sulphide gas (in-situ or bacterially generated)We must be able to drill an dcomplete additional wells in the formationas required with causing servere formation damange (due to the highly depleted pressure condition which may often exist in these reservoirs). The Typical Gas Storage Reservoir Gas storage reservoirs are generally high permeability clastics or carbonates (1000–10,000 mD in-situ permeability is common) existing at intermediate depths and temperatrues. In general, these reservoirs are depleted formations which originally contained dry (non-retrograde), sweet (no H2S) natural gas. Typically, these zones do not contain mobile water or active or partially active aquifers, oil legs or residual liquid hydrocarbon saturations, although this is not always the case.

Forward osmosis (FO) is a technical term describing the natural phenomenon of osmosis: the transport of water molecules across a semi-permeable membrane. The osmotic pressure difference is the driving force of water transport, as opposed to pressure-driven membrane processes. A concentrated draw solution (DS) with osmotic pressure draws water molecules from the feed solution (FS) through a semi-permeable membrane to the DS. The diluted DS is then reconcentrated to recycle the draw solutes as well as to produce purified water. As a major disadvantage, nature of FO membranes (asymmetrical structure) causes international concentration polarization (ICP) which promotes the decrease in water flux. Therefore, the number of studies related to improving both active and support layers of FO membranes is increasing in the applications. The purpose of the chapter is to bring an overview on the FO membrane manufacturing, characterizing and application area at laboratory or full scales. This chapter is published in two parts. In the first part, which appears here, the overview of membrane technologies and the definition of forward osmosis process are stated. The manufacturing methods of support and active layers forming FO membranes are described with common and/or new modification procedures.