Water saturation is the most significant characteristic for reservoir characterization in order to assess oil reserves; this paper reviewed the concepts and applications of both classic and new approaches to determine water saturation. so, this work guides the reader to realize and distinguish between various strategies to obtain an appropriate water saturation value from electrical logging in both resistivity and dielectric has been studied, and the most well-known models in clean and shaly formation have been demonstrated. The Nuclear Magnetic Resonance in conventional and nonconventional reservoirs has been reviewed and understood as the major feature of this approach to estimate Water Saturation based on T2 distribution. Artificial intelligence has recently been used to predict water saturation and other parameters in the reservoir characterization process using seismic data, so the main idea of this technique and a list of the author's researchers have been reviewed. In this review article, the reference approach using core analysis by distillation-extraction and retorting techniques have been explained, as well as the saturation-height method, which is based on the capillary pressure concept and wettability. Finally, alternative experimental approaches based on scanning are expressed in this manner.

A geological model was built for the Sadi reservoir, located at the Halfaya oil field. It is regarded as one of the most significant oilfields in Iraq. The study includes several steps, the most essential of which was importing well logs from six oil wells to the Interactive Petrophysics software for conducting interpretation and analysis to calculate the petrophysical properties such as permeability, porosity, shale volume, water saturation, and NTG and then importing maps and the well tops to the Petrel software to build the 3D-Geological model and to calculate the value of the original oil in place. Three geological surfaces were produced for all Sadi units based on well-top data and the top Sadi structural map. The reservoir has been divided into 85 sublayers in the vertical direction and 170*143 grid cells in the x-y direction, totalling 2,066,350 grid cells. The Sequential Gaussian Simulation technique is used to fill 3D grid cells with property values in locations far from wells after upscaling the well log data, then distributed across all reservoir zones. The standard original oil in place has been calculated, uncertainty evaluation was used to obtain more accurate results. Model Risk Analysis employs Monte Carlo Simulation to generate the pessimistic, most likely, and optimistic reserve values (P90, P50, and P10). The uncertainty was affected by the oil formation volume factor, oil depth, petrophysical model (porosity, water saturation, and NTG), and reservoir geometric structure (horizons and zones).

Tight gas sand is characterized for having low productivity and permeability in which low gas flow rate is provided. The application of hydraulic fracturing known as stimulation technique has been used to produce gas at economic rates. However, a common problem in tight gas reservoir simulation is the representation of hydraulic fracture in reservoir modelling. This is a crucial challenge for numerical simulation in which erroneous values of pressure distribution are generated, resulting in the calculation of unrealistic cumulative gas production. As a reliable solution, the use of Local Grid Refinement (LGR) simulation technique is applied around the wellbore and parallel to the fracture increasing the resolution of pressure behavior to adequate properly the hydraulic fracture in the reservoir modelling. In this paper, the results of simulation for Whicher-Range (WR), a tight gas field in Western Australia, were analyzed and used to generate the type curves for finite flow capacity in vertical fractured wells. Although the curves behavior was completely different to the type curves in conventional reservoirs, the development of engineering plot generated based on the same simulation results matched perfectly on the type curves predicting the gas production as well as validating the effectiveness of LGR method in numerical simulation of tight gas reservoir. The generation of type curves for hydraulic fractured wells in tight gas reservoir has never been presented and proven for Whicher Range field before. Also, the reformulated method based on the research by Argawal, Carter and Pollock of type curves are much faster than using numerical simulator which is time consuming and high CPU cost. In this paper, the successful method proven is a fast and effective way to predict the gas production for a single hydraulic fractured well in tight gas reservoir without any problem of using any commercial software.