Well integrity has always been a major concern during the well design phase. But after some of the recent events in the oil industry, Macondo being the one still fresh in everyone's mind, it has turned into a critical concern. The need for monitoring well integrity, from the construction through its lifetime, became unavoidable.
In particular, for Petrobras Pre-Salt fields, these concerns are boosted by the uncertainties in the salt layer geomechanical properties and its interaction with the cement and casing. Wells in the Pre-salt are designed for a 30 year lifespan, with a minimum number of interventions during their lifespan. Indeed, the expected interval between interventions is not shorter than 10 years, even for recompletion, making traditional cement or casing logging tools less useful. Continuous monitoring may provide not only the current status of the casing or cementing but also the evolution of the parameters, allowing a condition based (predictive) intervention to be planned.
A research and development project is being conducted to investigate, design and evaluate continuous monitoring tools to verify and ensure the integrity of the cement sheath and of the casing.
The first and more obvious challenge is to install sensors in the casing annulus: there are severe restrictions in footprint of the components; there is also the problem of getting the data to the surface without compromising well safety barriers. The required metrology need to be investigated in order to determine the best sensing technology for each parameter, and even those must be determined to achieve the best correlation with well integrity status.
This paper discusses the current perspectives on the monitoring of well integrity. Parameters already identified and some alternatives to monitor them will also be presented.
Uncertainties in the salt layer geomechanical models as well as in the interactions between the salt formation, cementing, and casing impose great concern regarding structural integrity of Pre-Salt wells1–3. This is particularly true taking into account the extension of the Brazilian Pre-Salt and the existence of very few wells for correlation and validation of the models. Wells in these oilfields are being projected for a thirty year lifespan, with as little interventions as possible, even for completion. Hence, casing and cement logging runs will not be likely to occur during intervals between interventions.
An R&D project is being conducted aiming at the development of continuous monitoring tools for well structural integrity parameters to be used in complement to logging tools. Initially, the project will identify parameters that need to be monitored in order to ensure casing and cement sheath integrity. In a second phase, the project will develop sensor prototypes and their testing programs, which include laboratory validation and field tests.
This project focuses on the Brazilian Pre-Salt scenario and the monitoring of the production casing, specifically on the salt region and above, since some of the effects of integrity failure can be sensed above the cement sheath (e.g. gas migration). The reservoir is considered to be very stable and it is not expected damage to the casing or liner due to subsidence in this region.
