Many rotary steerable systems are married to their measurement-while-drilling/logging-while-drilling (MWD/LWD) strings. A new system developed for one of the world's deepest wells is designed to work with anyone's LWD string.

The Well Director Rotary Steerable System (WD-RSS) developed by Noble Technology Services is designed as an alternative to commercially packaged systems. The WD-RSS can be run below any MWD/LWD system or can stand alone with its own internal MWD measurements and telemetry pulser. Using a design concept developed in Germany for the celebrated KTB well, Noble's system is unique in its approach. The WD-RSS uses push-the-bit technology to steer the well, but unlike other RSS systems it has four steering ribs mounted to a non-rotating sleeve instead of three rotating pads. The ribs are considerably larger in area than most RSS pads making the tool ideal for steering in unconsolidated sediments or in rugose holes. The larger, longer ribs spaced every 90? around the tool help support and guide the tool in long horizontal sections giving maximum side thrust capability.

Tool Systems

Presently three sizes exist, a 95/8-in. system capable of drilling up to 143/4-in. holes, and a 63/4-in. system that can drill up to 83/4-in. holes. A second-generation, 43/4-in. system called ExpressDrill, has been developed and three prototype tool systems are undergoing field trials. The 63/4-in. system's inclination sensors are only 3.6-ft (1.1-m) above the bit, with directional sensors at only 4.3 ft (1.3 m). For the 95/8-in. system, the spacings are 3.9-ft (1.2-m) and 1.4-m) respectively; both are solid state triaxial magnetometer/accelerometer designs. The tool accepts real-time downlink commands via mud-pulse telemetry during drilling so it can make instantaneous course corrections as required. In addition to directional MWD data, tool function data can be monitored in real-time. Data can be analyzed by Noble's DrillSmart, OptiDrill and DrillGraph, surface systems and software designed to help optimize both the drilling operation for maximum tool performance and rates of penetration, and the wellbore trajectory for quality and accuracy. Alternatively, the tool can be programmed to follow a predetermined trajectory on command from a closed loop system. Power to operate tool electronics is supplied by long-life batteries. However, a 200-W turbine generator unit is currently under development.

The tool's reliability comes mostly from its simplicity. Field proven hydro-mechanical technology and rugged solid state electronics modules combine with short length to enable high dogleg severity up to 9?/100 ft (30.5 m).

The new slim profile ExpressDrill system offers several improvements over its larger diameter brothers. The electronics package has been improved and both azimuth and inclination sensors are co-located 3.9 ft (1.2 m) above the bit. The steering unit size has been reduced and the four hydraulically-actuated steering pads are electrically-controlled. Answering operators' demands for higher temperature ratings, the directional instrumentation has been built to withstand temperatures to 350?F (175?C), the highest in the industry. Power is supplied by a turbine generator sub, and modular electronic components are designed to plug-and-play to facilitate rig up and maintenance. A self-retracting feature allows the tool to return to a slim profile in the event of power failure. Eight possible steering vectors are available for precision steering. The ExpressDrill system is expected to make its commercial debut later this year.

A niche market

Developers of the system envision serving a market where operators are focused on steering the well, with or without sophisticated LWD measurements. It is believed that this capability will open up a competitive market for independent directional drilling companies and national oil companies. Noble offers to train and support independent directional drillers who want to use the Well Director system, and believes that the added flexibility to interface with anyone's LWD system will be valued by the market.
Field test results

The Well Director has had a successful field test period with several wells in East and South Texas, Alberta, Wyoming and in the Gulf of Mexico. During the field test period, drilling runs averaged about 3,000 ft (915 m), and early results indicated significant time savings off the drilling curve. Excellent accuracy was maintained with actual wellbore trajectories planing designed trajectories. The tool system has demonstrated its ability to drill out of a casing shoe and kick-off from vertical; both qualities are in high demand. It can be used to drill very accurate vertical wellbores or complex directional wellpaths with or without additional MWD sensors.