The Fastest Way to the Bottom: Straighthole Drilling Device - Drilling Concept, Design Considerations, and Field Experience

Abstract

The Fastest Way to the Bottom: Straighthole Drilling Device - Drilling Concept, Design Considerations, and Field Experience A. Ligrone, SPE, AGIP S.p.A., J. Oppelt, SPE, Baker Hughes INTEQ, A. Calderoni, SPE, AGIP S.p.A., J. Treviranus, Baker Hughes INTEQ Abstract A straight top hole section in many cases is a strict requirement to be able to drill deeper sections with complex well geometries. Especially in an environment where the geological parameters tend to deviate the course, and if the hole stability is a risk, drilling of a straight surface portion of hole is a must. Conventionally, this will be achieved by applying steerable motors and changing between sliding mode for directional changes and rotary mode to drill straight ahead. The Straighthole Drilling Device, SDD, has been developed as a fully automated instrumented downhole motor with integral expandable ribs to steer a permanent vertical well path without any supervision required from the surface operator. This technology had first been verified through long-term continuous application in the KTB ultra deep scientific well bore in Germany, which was drilled solely for scientific purposes. Only through consequent application of the automated vertical steering could the very critical hard rock formation be drilled with minimum deviation and dog leg severity, thereby exceeding the 9,000 meter goal. Today, the basic technology has been converted into a highly durable drilling tool to be applied in commercial oil wells. The first part of this paper will be a description of technical concept, details and performance features of the Straighthole Drilling Device. The second half will emphasize drilling experiences. AGIP has identified some fields in the south of Italy as ideal candidates to prove both the technology and the economic benefits of SDD. The main idea is to drill quickly a straight and vertical top hole section without the need to ream the hole as is required with traditional methods. Field results from southern Italy are reported. Introduction Early need for an automated guiding device for straight vertical boreholes occurred in the mining industry during the late 70's. Up to then the state-of-the-art had been to operate passive devices to maintain the direction of a borehole, such as large-diameter, ultra-heavy drill collars. Such means utilize the earth gravity force and a tight annular gap to guide the direction of the borehole as close as possible to the anticipated course. Since, in many cases, the natural forces of the formation dip could not be overcome in this way, the concept of active steering devices was investigated with special focus on providing a vertical borehole course. Such development activities were all limited to shallow wells of a few hundred meters depth until the management of the "Continental Deep Drilling Program" (KTB) adopted the same concept for their ultra-deep scientific borehole in 1989. P. 115