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.


Horizontal wells can be a very effective field development technique for several reasons. Horizontal techniques excel in reservoirs that are naturally fractured or highly heterogeneous or that exhibit gas or water coning problems. Horizontal wells can also benefit low-permeability reservoirs by draining a larger area per well and thus reducing the number of wells needed to drain the reservoir.1

Formation damage in highly damageable reservoirs presents the main obstacles to achieving the benefits of horizontal wells. Delivering effective stimulation treatments in horizontal wells can be expensive and difficult, so formation damage can seriously limit the effectiveness of these treatments. UBD developed as a technique for minimizing invasive, drilling-induced formation damage to allow the drilling of effective horizontal wells in damageable reservoirs.

The development of horizontal UBD, in its current form, began in the early 1990s. Significant development has taken place in the areas of equipment design, operational techniques, and the understanding of what occurs in the reservoir during underbalanced operations. One considerable shortcoming, however, is the distinct lack of published literature that clearly demonstrates that horizontal UBD is an economically effective field development method compared to conventional drilling, completion, and stimulation techniques.

The majority of industry knowledge on horizontal UBD is based on anecdotal evidence, in-house analyses not available to the public, and case histories focused on operational aspects or very early time production results.2–8 Published literature that examines the long-term performance of previous UBD programs is virtually non-existent. This paper represents a first attempt at addressing this issue.

A number of underbalanced campaigns in the Western Canadian Sedimentary Basin have several years of production data. The following analysis of these case studies demonstrates that horizontal UBD is a viable field development technique and quantifies the significant economic benefit that can be achieved. The analysis also includes programs in which UBD was not successful and investigates the reasons for failure.

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