Rotary closed-loop steering systems are well known in the oil and gas industry and have become the accepted standard for drilling complex 3-D well paths and extended reach wells. These system's continuous drillstring rotation eliminates static friction between the string and the borehole permitting longer horizontal displacements in the reservoir and improving hole cleaning by stirring up the solids in the mud. While a 3-D rotary steering system could also be used to drill the hole's vertical top section, a closer examination reveals that efficiently drilling the top hole section requires a completely different approach. Static friction and solids settlement are not critical issues in vertical hole sections - permitting the design of a Vertical Drilling System engineered to run without string rotation in sliding mode. This approach protects the borehole walls from mechanical damage and leads to improved hole quality. To compensate for the lack of drill string rotation, the system design incorporates a latest generation power section which delivers almost double the torque of a conventional power section of the same length. Also, because a Vertical Drilling System's sensor package typically requires only inclination measurements and does not need azimuthal data, the system's electronic design is simplified. Although there are basic differences between 3-D rotary steering systems and Vertical Drilling Systems, there are also features which can be shared between both technologies - simplifying the service provider's engineering, maintenance, manufacturing and logistic efforts1. Examples of shared components include a steerable stabilizer to keep the BHA exactly on the desired (vertical) wellpath, the downhole power supply, the internal closed-loop information system and bi-directional data transmission. The Vertical Drilling System is designed to keep the top hole vertical without interaction from surface and without compromising critical drilling parameters (flow rate, WOB or bit speed) while maintaining high ROP along the entire section and avoiding time-consuming correction runs. The resulting improvement in hole quality and the precise wellpath allows the use of "lean casing profiles"2,3- reducing the amount of steel, cement, mud and cuttings. Vertical Drilling Systems are also beneficial in reducing the wellhead spacing at surface. All of these benefits result in significant cost savings to any operator. The paper describes the features of a Vertical Drilling System, presents case histories from 8–1/2" to 26" hole sections from various areas around the globe and gives an overview about the fast emerging market of this technology. Development of Rib Steering Systems for Vertical Holes While "rib steering systems" are receiving a great deal of attention in the drilling industry, the majority of the notice is focused on the impressive success rate of 3-D rotary steering systems. However, rib steering technology has also improved efficiency in both coiled tubing operations and vertical drilling applications. Typically, these systems all possess a steering head with three steering pads. It is often mistakenly assumed that there is no real difference between these systems with the exception of the tool size. However, the requirements and expectations for vertical drilling systems and directional drilling systems are as different as their applications - resulting in different designs. Advanced 3-D rotary steering systems are designed to drill complex well paths or long horizontal sections through the reservoir. Conventional motor assemblies are not always suitable for this purpose as directional corrections require stopping drillstring rotation. This lack of string rotation results in excessive static friction between the string and the borehole wall - making it difficult, or even impossible, to apply the necessary weight on the bit. Rotary steering systems overcome this problem by using pads to steer while rotating continuously. Eliminating static friction extends the hole's maximum horizontal displacement significantly. Similarly, string rotation is also very beneficial in removing cuttings from long, horizontal sections and cleaning the hole.

This papar was prepared for presentamn at the lS9d SPE European Petroleum Confefenca held m MlIan, Italy, 22-24 October 199STtus paper was selecled for pres6Waticmw an SPE Prqram Committee following review of information ccataimd in an abstract subm-,itbdby the author(s). Ccalen!s of the paper, as presented, have not ken rev!ewd by lhe Sc.oeiy CJPetroleum Engineers and we subjsct!0 correction~the author(s). The material, as presented, does not necessarily retlect any psition of the SocIely of Petroleum Engineers, its officers, or membels. Papers presemti al SPE mm3tlng8are subj8ct to publiMion revmw by Edtiorial Committees of tfm S&5efy of Petroleum En@wers, Permissionm copy Is reslncted to an abstracf d not more Ihan S00 wards, Illustrallons may not tm copied. The absfract should contain conspicuous acknowledgnmt of where and by tiom the pa$w was presented. Wriie Liixarian, SPE. PO. Box 8338S8, Rrhardscm, TX 75083-3s36, u.S A., fax Of -2 14-952-943&

This paper was prepared for presentation at the 1999 SPE Annual Technical Conference and Exhibition held in Houston, Texas, 3–6 October 1999.