Abstract
The nature of carbonate deposition as well as diagenetic processes can cause the development of unique geological features such as cavities, vugs and fractures. These are called karsts. Encountering karsts while drilling can lead to serious consequences such as severe mud losses, drops of bottom hole assembly and gas kicks. To improve drilling safety in intervals of karstification, it is important to detect karsts as early as possible, preferably in advance. In this paper, we review methods and technologies that can be used for the prediction and early detection of karsts. In particular, we consider acoustic, resistivity, seismic and drilling-data methods. In addition to the inventions and technologies developed and published over the past 40 years, this paper identifies the advantages, limitations and gaps of these existing technologies and discusses the most promising methods for karst detection and prediction.
Highlights
Drilling often follows complex well trajectories to reach a reservoir target or to geosteer away from geological objects that are dangerous for drilling [1]
We reviewed the methods and technologies that can be used for the prediction and early detection of karsts which are dangerous for drilling
The methods can be categorized into pre-drill and whiledrilling karst detection methods
Summary
Drilling often follows complex well trajectories to reach a reservoir target or to geosteer away from geological objects that are dangerous for drilling [1]. Examples of such dangerous objects, which often occur when drilling in carbonates, are caves or systems of cavities formed due to complex karstification processes. Encountering karsts while drilling can cause critical safety incidents. Depending on the size of the encountered karst, losses of drilling fluid can be uncontrollable, resulting in rapid gas migration to the surface and causing a loss of well control [3]. In the case of well-communicated fractures and caverns, which are common in some regions, losses can be treated without success for several weeks with the subsequent plugging and abandoning of the wells [4]
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