Pressure management marks a step change for drilling.

Can we imagine life without cordless power tools and appliances? They are a spin-off from technology developed for the Apollo space program. Computer-aided tomography scanners and magnetic resonance imaging technology also came from technology developed for the Apollo program to computer-enhance pictures of the moon.

The petroleum industry is no different. Many of the biggest discoveries have been made accidentally while searching for something else. While not as exciting as drilling into a "gusher," advances in well control have been made through the pursuit of solutions for other challenges.

The major thrust of the initial development of underbalanced drilling (UBD) was to enhance drilling performance. It was called "air-drilling." There was never any intention of drilling into productive reservoirs (particulary oil reservoirs) with this technique, but rather to encourage dramatic increases in penetration rate by reducing the overburden applied to the rock by drilling fluid hydrostatic pressure.

This technology spawned the earliest rotating diverters, a device that uses a rotating seal to enhance the lifespan of the rubber-sealing element against the drillstring. It is only through progress in this type of technology that the industry considered applying the concept of UBD to drilling reservoirs. This was initially done to overcome drilling challenges such as loss of circulation and differential sticking. However, in doing this, the industry learned that higher productivity could be achieved by drilling underbalanced and minimizing the degree of formation damage normally done by conventional drilling methods. This has now led UBD to be widely referred to as a "reservoir exploitation" tool instead of simply a method to overcome drilling challenges.

Technology advancements in UBD are now finding their way back into more conventional drilling as a means of overcoming more traditional drilling challenges associated with well control. Terms such as controlled-pressure drilling (CPD) and managed-pressure drilling (MPD) were coined to acknowledge the ability to "manipulate" the annular wellbore pressure profile to different degrees of underbalance or overbalance to suit a need.

One of the first major service providers of UBD technology recognized that being underbalanced wasn't always the desired objective, and therefore copyrighted the acronym CPD in an effort to solidify a technology-leading position. However, our innovative industry quickly found another "PD" derivative - hence, the birth of MPD.

The International Association of Drilling Contractors (IADC) convened a joint-industry committee in the mid-1990s for underbalanced operations (UBO) to establish industry standards and nomenclature and training recommendations and to provide input to certification bodies such as the American Petroleum Institute (API).

Recently, a new subcommittee of UBO was established to address the need for coming to terms with the growing demand for MPD. That subcommittee has developed this current working definition:
MPD is an adaptive drilling process used to precisely control the annular pressure profile throughout the well bore. The objectives are to ascertain the downhole pressure environment limits and to "manage" the annular hydraulic pressure profile.

The definition was carefully crafted to pacify two camps - those keen to differentiate MPD as a distinct drilling technology that is not UBD, and those keen to maintain focus on the significant efforts to bring UBD technology into the mainstream. Hence, a compromise was achieved recognizing that MPD may or may not involve underbalanced operations.

Most CPD, MPD or UBD operations involve the use of additional and specialized equipment to enhance the ability to control annular pressure profile. What uniquely distinguishes UBD technology is the addition of reservoir influx to the circulation stream.

So, is UBD merely a subset of MPD? What do we call it when we're simply trying to control the annular pressure profile to mitigate drilling problems? Shouldn't MPD then be a simpler subset of UBD technology? Remember air drilling? The original UBD technology had similar objectives to the new breed of MPD. Confusion reigns.

The only certainty is that there is a step-change occurring in our approach to drilling. Whether it is reservoir exploitation, enhanced well control or drilling optimization, the most significant paradigm shift has been acceptance of using mechanical equipment as the primary means of well control.

It may not be a giant leap for mankind like walking on the moon, but whether the acronym is CPD, MPD or UBD, the technology has the potential to be a significant step (change) for the drilling industry.

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