New Applications for Underbalanced Drilling Equipment
Authors: Stone Charles R. Rick , Cress Larry A. 
Published: December 2007

Abstract
In 1987, horizontal operators in the fractured Austin Chalk of South Texas realized that conventional drilling techniques were not economical. The need for a nondamaging technique to drill and complete fractured carbonates spawned the creation of Flowdrilling (FD) and Underbalanced Drilling (UBD). The use of clear drilling fluids and the philosophy to address well control problems at the surface pushed the industry to develop new, specialized surface equipment for UBD drilling. By 1992, the surface Rotating Blowout Preventer (RBOP) had been developed and successfully field tested. As UBD became popular, and engineers began to understand the versatility of drilling underbalanced, new applications surfaced. Three different case studies in this paper demonstrate the success of horizontal UBD techniques and equipment to vertical wellbores.

Introduction
The hydraulically actuated Rotating Blowout Preventer has provided the missing link in surface equipment necessary to expand the flowdrilling techniques developed in Texas from 1987 to 1992. The natural progression for flow drilling was to expand to deeper and higher pressured reservoirs in other areas of the Austin Chalk formation. True underbalanced drilling techniques were developed in the Giddings. Texas area. In Giddings, the mudweights used while drilling were less than the reservoir pore pressure, hence the term underbalanced drilling. Underbalanced drilling resulted in higher surface pressures which had to be contained by additional blowout prevention equipment. With the expansion of the domestic market use of UBD, operators began considering this technology for other reservoirs throughout the world. UBD technology has recently included three different types of utilization in vertical well bores. The first case study was in South Louisiana on the re-entry of a well that was scheduled to drill through depleted sands at 16,300 feet. The operator made three attempts to re-enter and sidetrack around several fish that were left in the hole. Several different hole problems and well control problems existed that could be solved with UBD surface equipment and lower mudweights. The second case study was in East Texas. This application involved tight gas formations that would give false readings at the surface as to additional mudweight requirements. The third case study was in Mexico. This wellbore utilized UBD techniques to drill through a lost circulation zone that was on top of a higher pressured zone of interest. Previous attempts to set casing through the zone had failed or were not economical.

History
Flow drilling and underbalanced drilling were the final components that made horizontal technology flourish. A Rotating Blowout Preventer would allow the surface containment of fluids produced to be safely and effectively processed. Both gas and liquids must be contained under a variety of conditions. Effective processing of the gas and fluids at the surface ensures that the operation and flexibility of the equipment does not limit the ability to continue drilling. All pressure control equipment utilized must be easy to understand and operate by the drilling crew. The RBOP and its associated control equipment is user friendly and can be automated or manually controlled by the driller. See attached "RBOP Equipment" Drawing.
The RBOP uses an inner and outer packer element. A secondary expendable quick change packer (QCP) allows rotation of the drill string to occur while sealing around the kelly or drill pipe to prevent the escape of fluids to the surface. RBOP control panels are self-contained units. The typical installation time for the RBOP is four hours with one hour of training per crew. P. 909^