Before any Produced Water Re-Injection (PWRI) project, specifications of water quality in terms of solid and oil contents must be determined to allow designing water treatment facilities. Also, specifications of injection pressure must be determined to allow designing injection pumps and network. An incorrect design may lead to significant injectivity declines, to injection volumes below target and therefore to loss of production. These specifications are usually provided by considering re-injection in fracturing flow regime because it is the only regime that can sustain the injectivity of wells on the long term. However, even if the matrix flow period which precedes the fracture initiation is also fundamental in determining these specifications, it currently remains considered in only very few commercial softwares.

It is fundamental to model the matrix flow period especially in terms of damage mechanisms. Indeed, this period can be of relatively long duration and can dominate the well behavior before the initiation of any fracturing. For example, this is the case of gas fields where only small volumes of water are produced during the first years of production. Taking into account this period can also help in optimizing water quality and pressure specifications by selecting the most appropriate completion for wells. In fact, the same water quality could lead to different damage potentials and thus to different fracturing pressures inititation that depend on the well completion scheme selected, whether open hole (OH) or cased and perforated (CP).

Even if a lot of models dealing with formation damage already exist for oil and gas producers, only very few models are available for CP water injectors. This paper presents a new model which allows simulating formation damage occurring while injecting in this type of wells. This model extends the standard CP calculations with the modeling approaches for external and internal damage which have already been available in Total's in-house simulator for OH completions. This paper also presents how water quality and injection pressure specifications are predicted for CP wells, the key parameters in perforation strategy to optimize them and why these specifications differ from one completion to the other. Finally, an example of field application of the model to design of PWRI project in a CP disposal well will be discussed.

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