Inorganic scale precipitation and deposition in oil and gas wells can cause significant production loss, which results in additional operational expenditure (OPEX) and health safety and environmental (HSE) risks. Scale management requires a detailed understanding of production rates, hydrocarbon and produced water compositions as well as reservoir conditions. Accurate real-time analysis of produced water compositions can immediately identifiy scaling risks in a production well and can lead to significantly reduced production loss, optimized chemical dosages, and fewer workovers, consequently lowering OPEX and mitigating HSE risk. This paper introduces development of a device capable of measuring the most critical parameters associated with inorganic scale in flowing produced water including pH, alkalinity, strontium, barium, sulfate, total hardness, total dissolve solids (TDS) and others.
In order to measure these water properties with the device, different methods were tested, but eventually, a combination of spectrophotometric and other methods were determined effective. One of the challenges of using spectrophotometric methods is the reagent stability over time. Hence, customized reagents were prepared for this application and the stability of these reagents was tested over time. Specific calibration methods were designed in order to extend the usage of the reagents.
Static measurements were initially performed and the results showed precise measurements of all the parameters. Results from dynamic tests utilizing real time flow and static test were in agreement and the accuracy was confirmed by traditional methods. Once the device prototype was built in our laboratories, production fluids were used to test the complete device. This device can be placed at various attachment points from the wellhead to the separator. This automated device is capable of collecting a discrete production fluid sample, separating produced water from the bulk phase and measuring various properties of produced water. These properties are reported electronically and used as part of a combined real time scale risk prevention system. In addition, this device measures parameters while maintaining wellhead pressure and temperature in order to eliminate the potentials errors in measurements, for instance pH of water changes due to degassing and precipitation as a result of changes in pressure and temperature.
A field trial is planned to test the device under full flowing conditions. This will be the first automated real-time produced water composition monitoring device with high measurement accuracy while maintaining pressure and temperature of samples, which can be attached at various points from wellhead to separator. This can be beneficial to identify the scaling risk in production wells before severe scaling occurs. The device is designed to enhance reliability of water properties measurements, provide real-time measurements, and reduce downtime and costs associated with scale problems and sampling.