Publications

Underbalanced drilling (UBD) and managed pressure drilling (MPD) are gaining in popularity as a drilling methodology due to their capability to control severe fluid losses and other problems that are inherent to conventional overbalanced drilling. As a result, considerable increase in their usage has been noted, however, with these increases, it has become apparent that there is a great deal of confusion concerning the basic concepts of each technique and when each should be used. Generally speaking, UBD can be described as a reservoir performance improvement and characterization tool that also solves drilling problems such as lost circulation and differential sticking. Another advantage is that UBD can offer a unique well testing environment in which the properties of reservoir layers can be determined while drilling. MPD, on the other hand, primarily addresses drilling-related problems including reduced potential for lost circulation and differential sticking and possibly minimizing wellbore breathing that result in nonproductive time (NPT) in drilling scenarios. Sometimes, however, there are well scenarios in which both techniques might be needed in the same well but in different sections of the wellbore. UBD cannot be applied where the open hole will be unstable, if there is the potential for very high H2S release rates near a population center or where regulations prohibit the production of hydrocarbons to the surface or flaring. MPD can be applied in these situations since it is similar to overbalanced drilling and only the margin of overbalance has been reduced. However if hole stability is not mitigated by a small degree of overbalance, and a high degree of overbalance is required then MPD is not applicable. For both conventional techniques considering both the drilling costs as well as any savings in terms of time addressing drilling problems, side tracking, mud losses, number of bits saved and also the revenue addition due to improved productivity. These values must be compared to offset wells drilled conventionally to see if there is an economic advantage.This paper focuses on where each concept should be used and what benefits can be expected from their application. Reservoir information gained during underbalanced drilling also can help reduce the time and cost associated with gathering and analyzing well-test data post-completion with conventional methods. Techniques have been developed to quantify reservoir properties and characteristics for homogenous and heterogeneous and/or fractured reservoir systems.Results from UBD and MPD case histories are used to quantify the results from these operations. Differences between the two techniques concerning equipment requirements and reservoir characterization potential are also analyzed.