Abstract

Petroleum industry has been more and more concerned about the effects of produced water disposal in the environment, particularly in offshore fields. Increasing amounts of produced water have being processed by companies and the search to alternatives for the produced water destination has become a priority for the major operators.

As oilfields reach their maturity, the water cut increases, and Produced Water Re-Injection (PWRI) in the producing formation seems to be a convenient way for its destination. Disposal in adjacent, non-oil bearing formations is also an attractive option to be considered.

This paper presents an overview of the main PWRI projects in Petrobras. Petrobras has been re-injecting water in their mature onshore fields for many years, and it is starting re-injection projects in offshore Campos Basin.

Technical, economical and environmental aspects of PWRI are presented. Related topics, like injectivity loss due to PWRI, injection above the fracture propagation pressure, PWRI effects on oil recovery and reservoir souring potential are discussed.

Introduction

Produced water is a consequence of an oilfield explotationthat uses waterflood or steam injection or has an aquifer linked to the reservoir [1]. High volumes of produced water should be expected and the final disposal of this effluent projected.

Reinjection and discharge after treatment are the most usual disposal ways of produced water. To discharge the produced water, companies should meet some requirements imposed by enviromental regulations [2]. Those requirements are becoming more tighter, leading companies to invest in new technologies and processes. Costs and dimensions of these developments are still so high that their use seems to be adverse to the field's financial project.

PWRI becomes a better solution for produced water disposal because has lower environment impact and costs. In other hand, there are some doubts about PWRI and its influence on souring. scale and formation damage control. Benefits and disadvantages of PWRI should be weighed for an efficient evaluation. In this work, we enumerate the pros and cons of PWRI and discuss its effects in souring and formation damage.

PWRI performance
Injectivity decline

Water has been injected to enhance oil recovery for several decades. Theoretical models and experimental tests have been frequently published, all of them searching a model that, using injection water and rock characteristics, can predict the injectivity decline over next years. Some authors [3,4,6] got good results, most of them considering "traditional" injection waters, i.e., water with solid particles only.

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