The development of underbalanced drilling (UBD) for production enhancement has advanced significantly since the advent of this technology in the early 1990s. The basis for the initial judgment as to the success of a UBD campaign was usually limited by the information that was available at the time of project completion: project execution success and initial production rates. However, the full scope of the effect of UBD on the overall economic success of a project remains unknown for many cases. While several underbalanced field developments have sufficient production history, drilling records, and cost data available for analysis, to date the body of published literature lacks thorough, long-term case histories.

This paper addresses this scarcity by analyzing several UBD projects in the Western Canadian Sedimentary Basin. The discussion includes a comparison of UBD and completed wells with the offsetting conventional producers in the same reservoir. Comparative analysis using industry-standard decline analysis and economic techniques yield technical and economic insight. To provide a balanced picture of the economic benefits that UBD can bring, both successful and unsuccessful projects are examined. The unsuccessful cases are analyzed to determine the reasons for underperformance, whether they fall into the categories of poor candidate selection or sub-optimal execution.

Understanding the magnitude and the driving factors behind the success and failure of UBD projects is critical to the growth and acceptance of the technology. This paper attempts to assist in that understanding and provide a benchmark for thorough comparisons of UBD case histories for the future.

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