Underbalanced drilling has been proven to mitigate formation damage, increase rate of penetration (ROP), and reduce differential sticking of the drill string. This paper describes the benefits of using open hole multistage (OHMS) completion systems in unconventional wells that have been drilled underbalanced. While underbalanced drilling and completion is not the standard, it is being utilized significantly in the United States due to reservoir characteristics. This paper discusses four types of underbalanced wells where open hole multistage completion systems have been installed: air drilled and nitrogen fractured, low bottom hole pressures, lost circulation scenarios, and those drilled underbalanced for reservoir benefits. Each scenario offers its own unique advantages specific to the reservoir, but also distinct operational challenges. Detailed discussion of the formation characteristics, and drilling, and installation operations for each of the four case study scenarios of underbalanced wells coupled with OHMS completion systems is provided. Case studies covering examples in shale, sandstone and carbonate plays in the United States are presented. With over a thousand wells completed with OHMS systems in managed pressure situations, this paper will provide a detailed evolution of operational best practices for installation of OHMS systems in these wells. Therefore, the information presented will address operator concerns regarding the risk of completing underbalanced wells with multiple tools on a single casing string.
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