Abstract

Produced water re-injection (PWRI) is an important strategy for deriving value from waste water but its implementation can face challenges related to injectivity and safety issues. Re-injection in fracturing regime is often the only option to guarantee the sustainability of injectivity but it can present some risks to be anticipated early during the design phase.

The first objective of a PWRI design study is to supply water quality specifications to petroleum architects (in terms of solid and oil contents) to allow designing water treatment facilities. The second objective is to supply injection pressure specifications allowing designing injection pumps and network. These specifications must allow sustaining well injectivity over field life while preventing any risk of cap rock failure.

The specification of water quality is of prime importance as a maximum of contaminant injection is sought in order to minimize the cost related to water treatment, but at the same time it must prevent any injectivity loss or excessive increase of pressure beyond which fracture confinement is no more possible.

Water quality and injection pressure are thus linked to each other. They are deduced by simulation on a case by case basis. The modeling approach used by Total was presented in previous publications. The objective of this paper is to detail how the two parameters are deduced when uncertainties on input data are considered. Indeed, a workflow for uncertainty management based on experimental design and Monte Carlo theories was implemented to combine the simultaneous effect of a relatively large number of uncertain parameters, each of them being characterized by its own probabilistic distribution. Two thousand simulations are systematically run and water quality as well as injection pressure specifications are supplied with a probabilistic value (P10, P50 and P90).

Application of this approach to real design examples are detailed and discussed in this paper.

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