Water Injection Optimization Based on Operational KPIs

Abstract

Waterflood is one of the main techniques to improve the oil recovery. Besides displacing and producing incremental oil, water injection helps to maintain the reservoir pressure close to its original value, keeping productivity in a high level. In offshore fields, seawater is fully available although it needs to have several quality controls to avoid undesirable consequences. Others water sources can be used such as aquifers or produced water, each of which with its specific needs in terms of quality [Chappel, 2020]. In the last decades, injection water process treatment is including more advanced equipment and chemicals to improve the water quality. Therefore, large footprint, high power supply and hard logistic have been required for water injection. Separation process based on membranes is an example of technology that has its use increased recently, mainly for: Nanofiltration membranes for sulfate removal; low sulfate content in water injection may reduce significantly the scale precipitation potential. A side benefit is reducing the biogenic H2S generation (souring) when low SO4 water is injected.Ultrafiltration membranes for solids removal. High solids content can cause pore rocks plugging near wellbore, reducing injectivity. Ceramic ultrafiltration membranes have also been used to remove solids from produced water with the same target.Reverse osmoses membranes to reduce water salinity. Low salinity water may increase the oil recovery when compared with brines such as the seawater. Advanced technologies normally imply into more laborious or time-consuming maintenance. As space in an offshore unit is very limited, facilities design normally considers a set of equipment that allow full capacity even during maintenance, like 5×25% or 6×20%. Although all these cares, uptime can reach low values mainly for units with high volume rates or any critical operational problem. For some kind of equipment, it is possible to bypass it or still operate it far from design conditions. It means that you may keep the injection rate needed, but the water quality will be poor, and you should deal with the consequences. In this work, we will introduce a methodology to check the consequences and benefits of manage water injection with different KPIs (key performance index) and show some cases where this methodology was adopted with success.