Lost circulation in fractured carbonate formations: Mechanisms, treatment strategies and field evidence from Kurdistan Region of Iraq

Abstract
Lost circulation is a recurring and costly challenge in drilling operations, causing severe wellbore instability, non-productive time (NPT), and increased drilling costs. It remains one of the primary causes of drilling inefficiencies and well abandonment globally, and it is particularly critical in the fractured, cavernous, and unconsolidated formations encountered in the Kurdistan oilfields. This review provides a comprehensive assessment of lost circulation-related issues in the Kurdistan Region of Iraq. It aims to understand the causes, effects, and mitigation strategies of lost circulation by analysing field data from various well types, including injection, production, and workover wells. The objective is to compile, analyze, and synthesize knowledge from field experience and existing literature to support future applications and research. A broad range of lost circulation materials (LCMs) is examined, including conventional options such as calcium carbonate, natural fibres, granular and flaky materials, as well as emerging technologies such as nanomaterials, crosslinked gels, swellable polymers, and smart materials. The review also discusses detection mechanisms, classifications of lost circulation types, and treatment workflows, including the application of cement plugs and wellbore strengthening methods. Findings from Kurdistan case studies show that LCM pills were effective in managing partial losses in injection wells. However, severe or total losses in production and workover wells required cement plugging after LCM treatments were unsuccessful. The effectiveness of any treatment approach is strongly influenced by the formation type, severity of the losses, and the correct implementation of techniques. In conclusion, although conventional LCMs continue to play a significant role in lost circulation management, nanomaterials and smart LCMs present promising opportunities for improving loss control in fractured and highly permeable zones. Further research and field testing are essential to optimize their performance, lower treatment costs, and facilitate broader application within Kurdistan’s complex geological settings. Overall, this review combines global literature with field-based evidence from Kurdistan oilfields to provide both theoretical and practical insights into lost circulation management.