The drilling of thousands of unconventional horizontal wells in North America highlighted the impact of the landing zone on production, underscoring the importance of geosteering with the intention of staying in the most fracable rock. Unfortunately, the use of fast drilling motors combined with delayed logging tools, and insufficient data to quantify mechanical properties while drilling created multiple geosteering challenges. This paper describes a new technology that uses surface drilling data to estimate, in real time, the geomechanical properties needed to guide the steering of horizontal wells into the most fracable rock. The Mechanical Specific Energy (MSE) computed from commonly available drilling data such as torque, rate of penetration and weight on bit has been widely used to improve drilling efficiency. However, the more recent use of MSE for completion optimization has yielded conflicting results. This paper introduces the use of Corrected Mechanical Specific Energy (CMSE) where the friction losses along the drill string and wellbore are computed and accounted for in real time. CMSE is used to estimate, in real time, geomechanical logs and build a live geomechanical model that is used for steering into the most fracable rock. Once the drilling is completed, the frac stage spacing and cluster density is adjusted according to CMSE outputs which include pore pressure, stresses, and natural fracture index. The new approach was used on multiple shale wells where the geomechanical logs predicted from CMSE and subsequently estimated fracture index were validated with multiple data including image logs, microseismic, and elastic properties derived from seismic pre-stack elastic inversion. This technology represents a major step in completion optimization since it tackles the problem and provides the solution during the drilling phase. A major advantage of the new technology is its ability to be deployed on any rig without the use of additional surface gauges, sensors or downhole measurement tools, avoiding additional costs and risks of potential wellbore problems. Additional benefits of the technology include: no on-site personnel or permits, the use of existing real time drilling data streaming services to quickly steer in the fracable rock, and having completion design immediately following the completion of drilling. This contrasts dramatically with alternative completion optimization methods for which data delivery, analysis, planning and design can take many weeks.

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Technology Update Globally, increasing amounts of hydrocarbon resources are being found in fields that have very high thermal gradients. (It gets hot very quickly as you move downward.) On the drilling side, challenging, high-pressure/high-temperature (HP/HT) wells customarily have been drilled with the simplest of tools, such as turbines and mud motors, which have minimal electronics and make no measurements. Logging-while-drilling tools, which do contain electronics and require electrical power to operate, have not been used thus far in these wells. Most formation-evaluation tools have lots of electronic components, and so initially couldn’t be used in HP/HT wells. However, these wells are often located offshore, where high rig rates force operators to look for all possible means to increase drilling efficiency and optimize wellbore placement for maximum production. Meeting HT Challenges The main challenges in these environments are preventing the electronics from becoming damaged, maintaining measurement accuracy and precision, and generating or supplying the regulated power to the electronics reliably over the duration of the drilling effort. Several parallel technologies have been developed over the past 5 to 6 years that can be used on their own or in combination to address these issues. The technology developments have concentrated on three main themes: HT electronics and the operating environment, new sensor technologies and measurement methodologies to improve accuracy and precision, and active cooling. In this connection, a 2-year project to develop measurement-while-drilling tools that can record and transmit data at temperatures of 230°C—running for 14 days continuously—has been initiated by Halliburton. The purpose of this project was to finalize some of the ongoing developments in high-temperature electronics and sensor technologies and package them into a tool capable of performing in this environment.    In considering the operating life of electronics, one of the main issues in HT environments is the increased rate of chemical reactions that cause the electronics to fail. In 1889, Svante Arrhenius documented the fact that chemical reactions require activation energy to proceed. The Arrhenius equation provides the quantitative relationship between temperature and the rate at which a chemical reaction occurs. This relationship is important for our industry because it governs many of the failure mechanisms for downhole electronics.  The rate of chemical reactions is defined by the equation K=Ae–Ea/RT, which documents the exponential relationship between rate (K) and temperature (T). Ea is the activation energy for a particular process, and this value can be changed (by adding catalyst or inhibitor). Ae (pre-exponential factor) and R (gas constant) are empirically derived constants. Many reactions double their rate every 10°C.

Conventional positive displacement motors (PDM's) are widely used in most directional drilling jobs. Polycrystalline diamond compact (PDC) bits are often used with the PDM's because of their longer life and increased rate of penetration (ROP). But PDM's used with conventional PDC bits often create hole problems and high vibrations that result in stuck pipe, casing running problems, downhole equipment failure, and lost drilling time. A new steerable assembly has been designed with an extended gauge bit and matched motor. The main objectives are to improve hole quality, reduce vibrations, and increase ROP. This paper will describe the working principles of the new system and how it has performed for Sarawak Shell Berhad and Sabah Shell Petroleum Company (SSB/SSPC) wells in offshore Malaysia. Introduction Sarawak Shell Berhad and Sabah Shell Petroleum Company (SSB/SSPC) have been drilling in D-35 and Kinabalu in offshore East Malaysia since 1997. See Fig. 1 for the site map. The formations are predominantly reactive claystone and shale. The common problems while drilling with conventional drilling systems have been stuck pipe, tight hole, and hole packing off. The cause of stuck pipe is believed to be due to sticky shale formations coupled with poor hole cleaning. There were also problems in high erratic torque, stick-slip vibrations, and casing and liner hanging up above the planned setting depth. In addition, downhole tools and MWD equipment were often damaged during serious backreaming to remove the tight spots. These problems have been suspected to be caused by poor hole quality due to hole spiraling. Hole spiraling is often associated with the short gauge bits used by the conventional drilling systems. To reduce the hole spiraling and improve the drilling efficiency, SSB/SSPC has tried Halliburton's new steerable system, SlickBore®1,2,3,4 which has been successfully run in other regions of the world such as the North Sea, North America, Asia-Pacific, and Australia, etc. Advanced Steerable Motor System The SlickBore drilling system contains a specially designed mud motor from Sperry-Sun and an extended gauge bit designed by Security DBS. In addition, proprietary drilling methods are used with the SlickBore system to ensure the maximum performance. The SlickBore drilling system is differentiated from conventional steerable systems by three key principles:The extended gauge bit drills a smooth and straighter wellbore. In addition, extended gauge bits are far more stable than the conventional short gauge bits. Thus extended gauge bits better in resist bit whirl, that, in turn, results in lower vibration and better MWD and tool reliability.The mud-motor is designed with a "special connection" coupled with a short bit-to-bend distance as a primary objective. This design results in a lower BHA bending moment arm, allowing lower mud motor bend angle settings.Lower mud motor bend angle settings prevent the bent housing from contacting the wellbore. This feature results in less drag while oriented drilling and less vibration while rotary drilling. Fig. 2 shows the differences between the SlickBore drilling system and the conventional steerable motor system (PDM's).

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