This paper presents some of the most important aspects of water management in Petrobras offshore fields, as well as its challenges and perspectives.
Several studies related to water management have been conducted in order to understand and quantify the main uncertainties of waterflooding projects, such as the injectivity decline, the dynamics of fracture propagation in injection wells, the scale formation tendency, the reservoir souring potential, the environmental constraints and the development of new technologies.
The conclusions point out that all aspects related to the water management must be investigated and quantified since the very beginning of a waterflooding project.
Waterflooding is still the most common method used worldwide for improving oil recovery, either after production by primary mechanisms or even at the early stages of the field lifetime. For offshore fields, operators have been manipulating, in the recent few years, huge amounts of water from both the injection and production streams.
Figure 1 shows the water management cycle with all the concerns and main factors that affect waterflooding projects. The left side presents the technologies related to water injection, that is, with flow rate maintenance, which includes injectivity decline, water quality specification, fracture propagation, raw-water injection and dump flooding. The right side shows the subjects related to water production, such as water shut-off, scaling, souring, downhole oil-water separation and subsea oil-water separation. Other issues to be considered are environmental constraints, corrosion, and water content in oil transferred to onshore terminals, which can not be disposed close to shoreline.
In Brazil, Petrobras deals with over 3 million barrels of water per day, including injection, production and Re-Injection. In offshore fields (1, 2), the volumes of sea-water injected exceed 1,500,000 bbl/day and the water production reaches values over 600,000 bbl/day. Predictions are that, by the end of 2006, 3,200,000 bbl/day of water will be injected. Injection water flow rate maintenance and produced water management are the main challenges for the next years.
Due to the importance of water injection for the economics of Petrobras oilfields, water management has become one of the company main priorities. Several studies have been performed related to the water management cycle in order to understand and quantify the main uncertainties of a waterflooding project. These include modeling and monitoring of injectivity decline, produced water re-injection, injection with fracture propagation pressure, scale formation tendency, reservoir souring potential, environmental restrictions and subsea technologies.
It must be emphasized that problems which are usually simple when faced in onshore fields, such as stimulation of injection wells that have lost injectivity, are much more difficult to be solved in an offshore environment, especially where many wells are located in deepwater areas and completed as satellite wells. Consequently, any workover operation is extremely expensive, since it demands the presence of a floating rig. For such situations, bullheading operations should be considered as an alternative.
The next sections present some the most important aspects of the recent developments in water management for Petrobras offshore fields, as well as the current challenges and future perspectives.