Abstract

The hydrocarbon basins in the Sultanate of Oman are in the desert where rig rates are low. This is not the typical environment for sophisticated drilling systems such as rotary steerables. However there are a number of niche applications where the use of this technology makes business sense. This paper will describe each application, explaining how a particular problem was solved with the use of rotary steering. Some of these applications are more unusual than others. For example one application is efficient directional drilling in hard abrasive layered formations of S-shape and J-shape profiles. Another is drilling buildups to precise horizontal landing depths, or drilling absolutely vertical holes in wells that have long heavy-wall liner sections that are run with inner strings and mechanical-set liner hanger packers. The consequence of a dog leg has been a liner that would not go down, but too heavy to retrieve. The rotary steerable applications also include assisting the acquisition of geological data. For example drilling extended reach smooth boreholes in fractured carbonate so they can be logged with imaging tools conveyed on drill pipe that cannot be rotated. The measure of success, and a large part of the remuneration, is based on the imaged meterage not drilled meterage. These wells were drilled with an inclination-hold feature that kept the trajectory as straight as possible. Another geological example is the use of rotary steerables to accompany an azimuthal deep reading measurement used to geosteer the well. The elimination of sliding removed the blind zones that are a consequence of azimuthal logs, and the near-bit inclination helped the directional driller avoid over steering when the geosteering team requested an inclination change.

Introduction

Drilling motors drill straight when rotating and have to be slid to drill a curve. Rotary steerable systems drill both straight and curved sections while rotating. Eliminating sliding solves many drilling problems such as maintaining the tool face orientation, slow sliding or inability to slide, poor hole cleaning when sliding, poor hole quality from rotating the motor bend and borehole tortuosity.

There are several rotary steerable systems. Both tools used in the examples in this paper use an internal geostationary reference with everything external rotating at the drillstring rpm. The directional force on the bit in one tool is applied with a hydraulically activated pad; in the other the bit itself is tilted. Both tools have near-bit inclinometers, of which one was used for closed loop steering to hold a constant inclination. This continuous inclination is available in real-time, although it is not necessary to have communication to surface for this automated directional control.

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