Strategies for Early Detection of Downhole Casing Failures Caused by Corrosive Formations

Abstract

The Middle Eastern formations E & K are aquifers which are commonly problematic due to their corrosive characteristics, have been known to directly cause downhole casing completion leaks, and hence require careful risk assessment. If severe corrosion is not detected early then related leaking completions can lead to water from these upper formations cross flowing down into producing reservoirs with results being economic loss due to reservoir damage and/or direct loss of production. Environmental impacts of hydrocarbons leaking into shallow aquifers are an obvious risk of a leaking casing. The worst-case scenario is when production fluids, particularly methane and H2S, enter these formations via near-surface casing leaks and migrate to the surface where the potential for catastrophe is highest. This investigation explores causes and effects of severe external well casings corrosion in an oil-producing brownfield in the Middle East. This research utilizes advanced corrosion monitoring technology, capable of measuring total wall thickness of concentric casings, which were logged in adjacent wells within a one-half mile radius. An important part of the well assessment strategy also includes examining historical drilling and cementing of several other completions in the same field to categorize the probability of integrity failure due to external corrosion. Observations include establishing correlations between these lost circulation formations and measured external casings corrosion wall loss. The corrosive characteristics and impact of these dynamic, near-surface aquifers is also discussed to establish the root cause of external casing leaks. The objective of this study is to share these lessons-learned and develop a strategy for recognizing, mitigating, and/or avoiding similar well integrity conditions. By instituting a well-to-well pattern recognition classification of known problematic wells, promoting an enhanced corrosion surveillance frequencies.