A novel approach to model water saturation in shaly sandstone petroleum reservoirs

Abstract Water saturation is a very important parameter in both the technical and commercial evaluation of petroleum reservoirs. Estimating water saturation in shaly sandstone reservoirs is considered one of the most challenging tasks in formation evaluation and petrophysics. Complexities arise from shale properties and composition as well as the pluralism of independent approaches and methods used in calculating water saturation. The problem is that these different approaches most of the time somehow result in different values of water saturation leading to under-estimation or over-estimation of the volumes of original oil in place (OOIP) and original gas in place (OGIP). The main challenge is resolving and understanding the differences between the water saturation values obtained using different approaches, and to arrive at the most accurate estimation of water saturation as well as its distribution throughout the reservoir. There are numerous shaly sandstone estimation models which are used frequently. These models can be divided into two main groups where the shale term of the first group is based mainly on shale volume while the other group depends on electric double layer effect. However, both approaches have drawbacks and limitations and don’t always give accurate results. This paper presents a novel hybrid approach between Vsh and EDL based models to determine water saturation in shaly sandstone reservoirs using well logs only and at the time is based on physical facts and reflects real current flow paths. This new approach was applied to three well logging datasets and the results were compared to that of counterpart existing models widely used in the oil and gas industry. Core analysis water saturation values were used as a baseline to validate the accuracy of the new model compared to counterpart models and the results were discussed. The new model is a series conductivity model which is based mainly on well logs reducing the need for any time-consuming and costly experiments. The results were promising and the new approach’s water saturation values showed great potential and consistency with core-derived water saturation values.