Efficient and robust produced water treatment technology is necessary for many oilfield explorations because of increasingly strict discharge regulations, but also for applications to debottleneck mature fields, as well as for subsea applications with produced water re-injection.
The performance of produced water treatment systems can be improved by using mixedflow hydrocyclone technology. In this novel design an even flow inlet distribution is created which can be used to reduce the pressure drop as well as to enable an increased throughput. The mixed flow technology offers high separation performance and reliability for a wide range of operating conditions, including highly demanding produced water streams containing heavy crude.
A testing campaign of the mixedflow hydrocyclone was performed on a dedicated test loop located at the Federal University of Itajuba in Brazil. Goal is to determine the performance (i.e. separation efficiency) for a wide operating range, including varying crude types, flow rates, inlet oil-in-water concentrations and reject rates. Based on this work, a performance prediction tool and capacity curves have been established which allow for robust design of produced water treatment facilities.
The upstream oil industry spends a considerable amount of capital and operation effort providing and maintaining produced water treating systems. More and more the produced water treatment systems influence the overall economics of offshore oil field exploration as in many cases the produced water rate increases continuously.
Challenging design cases are especially found when dealing with low API crudes (i.e. heavy oil) where the driving force behind cyclonic separation is significantly lower than for light crudes. Furthermore, ongoing strengthening of environmental specifications on produced water discharge, has a challenging impact on the design, as the allowable Oil-in-Water (OiW) content before discharge, measured as parts-per-million (ppm), is reduced further and further. Therefore, treatment of produced water with hydrocyclones is of high importance to enable produced water discharge and even more important for reinjection purpose into the wells.
The understanding of the dependency of hydrocyclone performance (efficiency) on droplet size distributions, crude density, reject flow rates and inlet OiW concentrations is fundamental to allow for proper design of produced water treatment facilities. Furthermore, this understanding is essential in order to have performance prediction tools established for the purpose of the process design of these facilities. Moreover, more developments are now considering subsea separation, whereby produced water can be separated and re-injected into the wells and thus avoiding produced water to be transported in the flowlines and risers to the surface facilities for treatment. For such subsea applications, there is a need for robust high performance technology with proper qualification work done.