The hardware used in casing while drilling operations over the past 5 years has proved to be robust and reliable. Several directional wells have been drilled successfully with casing using positive displacement motors (PDMs), but the drilling efficiency was significantly degraded in most of them. This paper documents the drilling of the first two wells to utilize a rotary steerable system (RSS) to improve drilling efficiency when drilling with casing. Combining an RSS with casing while drilling operations seemed to be a natural way to eliminate the major weaknesses in motor bottomhole assembly (BHA) designs. Rotary steerable systems had not previously been used with casing while drilling because both are new technologies focused on different environments. Casing while drilling developed on land operations while rotary steerables have been popular for offshore projects. ConocoPhillips has drilled more than 94 wells in the Lobo trend of South Texas since 2001 using the new technique. As part of a technology demonstration project to accelerate the technology to offshore applications, two wells were drilled with an RSS. The first was an operational test conducted by drilling vertically with the RSS. The second was a full directional test with a build to 29° and then a drop to vertical, including a 100° directional turn. Introduction ConocoPhillips embarked on an active field development program in 1997 aimed at drilling hundreds of wells over the next few years in the Lobo trend of South Texas. Since that time, over 900 wells have been drilled through the Wilcox (Lobo) section ranging in depth from 7,500 to 13,000 ft. However, in 2001, after drilling about 600 wells, the drilling efficiency had stagnated. A program was undertaken to find ways to reduce drilling costs sufficiently to extend the development potential for several years. In the previous years, great strides had been made in increasing rate of penetration (ROP), drilling each hole section with a single bit, and in improving general rig operation efficiency. Any major reduction in drilling time had to address the flat time more than the "making hole" times. The most significant flat times were associated with keeping and protecting the hole, trouble time which averaged about 1.5 days per well, and casing running operations. Stuck pipe and lost circulation were the most consistent contributors to the trouble events and accounted for about 75% of the trouble time in 2000 and 2001. A casing while drilling system was chosen for a five-well pilot project to evaluate the impact that this technology might have on the particular problems encountered at Lobo. Sufficient progress was made in drilling these first wells to justify moving to a second phase of drilling. The second phase proved that casing while drilling could eliminate the formation-related trouble time experienced with conventional drilling. A major finding was the confirmation that lost circulation was almost completely eliminated, allowing the drilling of additional wells formerly considered uneconomical. The wells were not drilled trouble-free, but the trouble was associated with the mechanical equipment limitations, which were overcome on the phase-two wells. Fontenot1,2 provides more information about the Lobo field and the performance on these early wells. Full-scale implementation of the Lobo casing while drilling program was initiated by bringing in three new rigs in late 2002 and early 2003. These 15,000-ft rigs,3 built specifically for ConocoPhillips, were introduced to optimize the drilling process. They provided an increased hookload rating; much better mobility for intrafield moves, a reduced footprint, and a semi automated casing handling system. The overall drilling program at Lobo has been scaled down, with one casing while drilling rig still operating. More than 94 wells have been drilled with casing in the area. The incidents of lost circulation have been almost totally eliminated in the casing drilled wells. The difficulty of balancing lost circulation at the intermediate casing shoe while controlling a reservoir pressure of up to 15 ppg during the trip out to run production casing has been eliminated. In some cases, casing drilled wells are completed with three strings of casing when four would be required if the wells were drilled conventionally.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses the design and testing of 10 ¾-in. and 7 5/8-in. casing directional drilling equipment and procedures that ConocoPhillips plans to use on a mature North Sea asset. ConocoPhillips has worked with Tesco Corp. and Schlumberger in assembling the tools necessary to complete this task. These include: downhole casing drilling tools, underreamers, positive displacement motors, MWD tools, rotary steerable systems (RSS), and high capacity winches for this work. Testing this equipment in commercial North Sea operations is prohibitively expensive. Therefore, tests were conducted at a drilling test facility near Cameron, Texas, where operations were conducted over a wide range of rotating speed, weight and flow conditions as well as inclinations from vertical to horizontal. High frequency surface and downhole drilling mechanics measurements assisted in diagnosing problems and improving the systems. The project serves as a blueprint for managing technical developments among multiple operators and service companies.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOver 300 commercial well intervals have been drilled with casing and retrievable BHA systems in the last five years. This activity has been focused mainly on drilling vertical wells with only about a dozen of these wells being directional. However, there is growing interest in applying the techniques to directional wells.Steerable positive displacement motors (PDM's) have been used for most directional wells drilled with casing. However, rotary steerable systems (RSS's) have recently been run while drilling with casing. This provides another avenue for improving directional casing while drilling (CwD) performance.The combination of rotary steerable systems and CwD is a natural solution to directional wellbore stability problems. It capitalizes on the pinpoint control of RSS's while rotating the casing to heal wellbore wall problems. This paper presents a comparison of casing directional drilling with steerable motors and rotary steerable systems and discusses the procedures that were developed to make casing directional drilling routine.

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