An enhanced accuracy method for monitoring formation water salinity utilizing elemental spectroscopy logging

The accurate determination of formation water salinity is crucial for petroleum exploration and development, as it plays a significant role in determining reservoir parameters. The salinity of formation water affects physical parameters such as resistivity and Sigma, which are essential in calculating reservoir oil saturation. Therefore, this paper proposes an effective calculation method of formation water salinity based on elemental spectroscopy logging technology. The method starts by accurately calculating the formation chlorine (Cl) content through a combination of inelastic and capture energy spectrum analyses. Subsequently, a high-precision calculation model of formation water salinity is constructed by utilizing formation density and porosity information. Compared to the traditional oxide closure model, the joint bispectral method improves the calculation accuracy of Cl content by an order of magnitude and keeps the calculation error of formation water salinity within 2 g/L. The field logging example further demonstrates the high agreement between the calculated results of formation water salinity and laboratory analysis results, validating the accuracy of the joint bispectral method. This method is not affected by the mineral composition of the formation, making it suitable for a wide range of applications and highly versatile, which provides valuable technical support for the exploration and development of oil and gas in saltwater-bearing reservoirs.