Optimizing Powered Rotary Steering Through Better Understanding of the Downhole Environment
Authors: Al-Bani F. , Galindez N. , Carpen P. , Mounzer F. , Kent D. 
Published: October 2008

Abstract
This paper discusses drilling optimization in two major fields operated by Saudi Aramco. Both fields have layered limestone reservoirs consisting of tight zones alternating with porous zones and are drained using innovative MRC (Maximum Reservoir Contact) techniques along with real-time geosteering.
The well profiles produce difficult torque and drag environments. While drilling rigs employed have upgraded to top drive systems, traditional drilling practices still rely primarily upon surface measurements provided by the drilling contractor. Often these gauges are rudimentary and their measurements unrepresentative of downhole conditions, particularly when operating at a great depth in horizontal holes.
In the applications discussed in this paper, the situation was greatly improved by introducing a new downhole drilling sensor tool. Integrated into a high-speed rotary closed-loop drilling system, powered by an integral modular motor, a step change in drilling performance has been achieved.
In most applications, the new tool has been placed between the modular motor and the steering head to give the directional drilling crew a clear understanding of the true environment being encountered by the steering head and bit. Optimization of performance with such advances has resulted in a 100% increase in overall rate of penetration (ROP) in some applications.
Using real well examples, this paper discusses: measurements the tool records and transmits; dramatic differences between downhole measurements and surface indicators; how information is applied to optimize the real-time drilling process, and how this continuous application evolved from the original research initiative.

Introduction
In the last few years, rotary steerable drilling systems (RSS) have become the preferred tools for drilling complex or lengthy drain holes, primarily because the tools can negotiate the planned well path without stopping to "steer" as with conventional steerable (motor) systems. The advantages of these tools has been exhaustively described in numerous papers and articles, in trade journals and with the SPE since the introduction of these systems began in the early 90s. One hallmark of RSS has been the ability to average a significantly higher overall ROP over a given section of hole primarily for the same reasons as described above. A feature of these tools that most interests the reservoir department is the capability for geosteering to very precise tolerances. RSS tools can steer to a true vertical depth (TVD) target or, if preferred, hold an exact angle to intersect zones of interest.
Despite the large gains in applied technology in downhole drilling and measurement systems and widespread upgrade of rig-rotary drive systems in the last decade, drilling rig measurement gauges have seen comparatively little advancement. Used to monitor vital drilling information, many drilling rigs still rely upon deadline weight indicators, surface rotary torque gauges, and surface standpipe pressure gauges. These gauges are typically of robust construction to withstand the rough handling often encountered during drilling or while the rig is being moved (as in land rigs). Calibration is typically fairly rudimentary (as compared to scientific instruments), and sensitivity is poor.
In practical terms, for most operations the gauges and measurements are more or less fit for purpose.