Recent trends in the Oil & Gas industry have been toward the utilization of new technologies in order to optimize production and improve recovery. The National Oil Corporation (NOC) of Libya is considering deploying Under-balanced Drilling (UBD) technology as one of the most effective methods when it is effectively applied in conjunction with horizontal and/or Multi-lateral well drilling and completion techniques

Under-Balanced Drilling Technology has enabled the commercial development of numerous oil and gas reservoirs around the world that would have otherwise not been exploited due to technical and/or economic limitations. Under-Balanced Drilling has only become possible as a result of the integration of many developing technologies that facilitate directional control of the well trajectory, control of the bottom hole circulating pressure and the safe handling of drilling fluids and drill cuttings on surface.

When drilling Under-balanced, the annular pressure profile is maintained below the expected reservoir pore pressure and is particularly beneficial in evaluating the productivity of prospective formations in their virgin state. This means that the formation can be evaluated without being subjected to damage during conventional drilling and the required clean-up operations.

As of today, a total of three wells have been drilled under-balanced by ZUEITINA Oil Company in Libya. Through three examples, the paper will demonstrate that the key to selecting appropriate Reservoir candidates for UBD is achieving a balance of Technical, Safety and Economic factors.

This paper describes the Front End Engineering Design, Project Management, Risk Mitigation, Operational Results and Lessons Learned for this project.


The Underbalanced Drilling (UBD) emerged as a distinct technique in the late 1980s in the USA and Canada. Since then, it has gained acceptance among the operators and many wells have been drilled around the world employing this technology.

The benefits of underbalanced drilling (UBD) are well recognized by the industry and there is increasing raise in interest in this technology. The benefits from UBD generally fall into two classes:

  • Drilling Performance: including mitigation of conventional drilling problems such as lost circulation and differential sticking reduction in stimulation and cleanup costs, etc.

  • Reservoir Benefits: including productivity improvement, increase in ultimate recovery, and real-time reservoir characterization while drilling.

As operators strive to increase production from existing reservoirs with depleted pressure, the use of underbalanced drilling combine with horizontal drilling is becoming more widely used in order to maximize oil recovery and reduce exploitation/drilling costs.

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