Fluid distribution in a tight gas reservoir using the saturation-height model

The development of tight gas reservoirs requires detailed knowledge of gas volumes and their distribution in three-dimensional space. This information can be obtained using a Saturation Height Model (SHM) developed by combining mercury injection capillary pressure analysis and well logging data. The SHM is constructed using core data from two wells in the tight gas reservoir of Amin formation in Oman. The saturation-height model is represented by a tangent line function linked with porosity. The developed SHM accurately simulates water saturation from well logs in seven wells. The curve fitting procedure determines three baselines, designated as free water levels (FWL), increasing with depth in the order of FWL0, FWL1 and FWL2. In three wells, the best match for the water saturation curve is obtained using FWL1 for Upper Amin formations and FWL2 for Low and Middle Amin formations. Different FWLs in the wells indicate differences in well placement within blocks and depending on tectonic history. The described tight gas reservoir can rather be characterized as a composite type because gas accumulations are not only found in high positions, but they also exist deeper over a wide range of depths. The developed SHM and the determined FWLs can be used for 3D reservoir modeling, in situ gas volumetric analysis and S_w calculation in undrilled areas to formulate a field development plan and fracturing program. This information makes it possible to estimate the consumption of water and chemicals required for hydraulic fracturing operations, which, in turn, makes it possible to estimate the required capacities for treatment of produced water and gas and to identify the places of possible contamination and gas losses.