Produced Water Analysis by X-Ray Fluorescence with and without the Presence of Crude Oil

Abstract

Abstract Scaling and corrosion are two common problems during oil and gas production which can cause severe safety issues and significant decrease in production. Analysis of produced water is widely applied to evaluate scaling and corrosion by monitoring parameters such as pH, alkalinity, cation concentrations, sulfate concentration, total dissolved solids (TDS) and conductivity/resistivity. Produced water sampling is usually performed at the wellhead for on-shore wells and can be done relatively easily if unpressurized samples are required. However, temperature and pressure drop as well as CO2 degassing during sampling dramatically affect pH and alkalinity measurements. As a result, carbonate scales may precipitate during degassing. For offshore wells, produced water sampling on site is costly and time consuming and mainly performed after abnormal observation of production rate. Thus, scale monitoring and prediction based on analysis of surface produced water is not reliable and analysis under temperature and pressure is required for accurate results. In this paper, X-ray fluorescence (XRF) is used for monitoring water composition for scale and corrosion prediction with or without the presence of crude oil. To our best knowledge, XRF has not been reported as an analytical approach for water analysis with the presence of crude oil. This technique measures various metal cation concentration quantitatively in oil and water emulsions. It allows for a fast analysis of the water composition without the need for oil and water separation. Combined with automatic water analysis device developed previously, all important water parameters including, but not limited to, pH, alkalinity, sulfate, total hardness, TDS and cation concentrations can be measured for scale and corrosion monitoring and prediction. Measured results will be transfered and automatically incorporated into scale prediction software for scaling risk evaluation and scale inhibitor selection. In addition, concentration of other metal ions (Na, Mg, Fe, Mo, Ni, Co, Mn, etc.), heavy metal ions (Pb, Zr, Hg, Cd, etc.) and nonmetal elements (S, P, As, etc.) can also be measured. Concentration of Fe, Mo, Ni, Co and Mn has been accurately measured. In situ measurement of transition metal concentrations can be a useful tool for monitoring potential corrosion during production. The technology developed in this paper allows for automatic online monitoring of scale and corrosion risks under real production conditions. This system accurately measures various parameters and provides valuable produced water information without user interferences and with little maintenance.