System features dual downlinking, improved pad actuator with metal-to-metal sealing
By Jorge Luis Hernández Jurado, PDVSA, and Cesar Figueredo, Schlumberger
Directional drilling has revolutionized oil and gas production, enabling operators to venture into new frontiers and geologically challenging reservoirs that once were inaccessible. A technology that has expanded the operations envelope in the growing number of horizontal and deviated wells is rotary steerable systems (RSS), which can provide continuous rotation, constant steering and smoother boreholes.
As wells have become more complex, with high-angle deviations, hard and unstable formations and harsh environments, rotary steerable technology has continued to evolve to optimize drilling efficiency through improved rates of penetration (ROP) in longer laterals, reduced drag and stick-slip, and superior hole-cleaning.
Three types of RSS address specific drilling applications. Point-the-bit RSS tools use an internal bend to change the well trajectory while push-the-bit tools use pads to steer the tool. Hybrid systems are also available. The systems remove stationary components that cause friction and inefficiency and anchor the bottomhole assembly (BHA) in the hole. Flow of drilled cuttings past the BHA is improved because annular restrictions are not created in the wellbore.
Today, new features have been incorporated into rotary steerable technology to provide greater precision, durability, flexibility and reliability. Next-generation RSS also aim to reduce runs and trips in and out of the wellbore.
Venezuelan oil company Petróleos de Venezuela S.A. (PDVSA) decided to implement a new RSS technology to complement a new well design and deliver precise directional control in a geologically complex formation. In one problematic well section, the push-the-bit RSS allowed PDVSA to drill the high-angle, harsh-environment section in one run, significantly reducing time and cost.
Schlumberger’s PowerDrive Orbit was developed to improve the robustness of the PowerDrive RSS technologies, which included all three types of RSS and have been used to drill more than 130 million ft in the 16 years since their introduction.
One run from shoe to TD
The RSS provides greater steerability and durability in harsh and rugged environments, enabling operators to plan one run from shoe to TD, reducing the number of trips in and out of the hole. It also decreases the risk of differential or mechanical sticking and achieves optimum hole-cleaning and conditioning. The system also features a modular design that is compatible with a variety of BHA components.
In environments where two or three runs are typically required to drill one section, the new system has allowed operators to drill a section in one run. It also expands the RPM limit, tolerating up to 350 RPM while maintaining directional control.
With an improved pad force, push-the-bit system for drilling consistent dogleg severity (DLS) sections at higher RPM, the new technology also expands the capability of PowerDrive push-the-bit systems. Combined with the PowerDrive vorteX-powered RSS, for example, it offers a greater tolerance for higher RPM and more torque downhole. The tool also includes a high-resolution gamma ray sensor that serves as a well placement alternative for shale wells that lack sufficient conductivity contract for accurate well placements with logging-while-drilling (LWD) tools.
Another feature is a six-axis roll that provides stable, automatic hold inclination and azimuth (HIA) capability for better automatic trajectory control to drill more deviated wells, such as those with S, J or horizontal profiles. The multi-axial feature provides more precise kickoffs from the vertical section, a high level of total vertical depth definition and smoother boreholes.
In straight sections with a tangent, this feature has the capability of making an automatic adjustment in a closed-loop system with defined direction to keep a specific inclination and azimuth, resulting in a smoother tangent with less tortuosity. This saves time and results in better hole quality.
The system also includes a new pad actuator with metal-to-metal sealing instead of rubber, which enhances flexibility and reliability, and self-steering automation with dual-downlinking capability to provide better trajectory control. An optional, stronger pad design can be used when needed for achieving greater durability when drilling highly abrasive formations.
Complex, offshore application
The need for greater durability, flexibility and steering precision influenced PDVSA’s decision to deploy the RSS technology in the high-angle section of an offshore well in the Lagotreco oilfield. The operation was aimed at draining the oil reserves of the subunits of the prolific Misoa Formation, located northwest of Venezuela.
The reservoir, sandstone in nature, is characterized by cross-interbedded layers of hard and soft formations that had presented drilling challenges for PDVSA in its attempts to access the sweet spot. In previous sections, drilling the hard formations proved particularly difficult due to the shock and vibration, caused by the interbedded layers, in the BHA. This impacted the drilling components, resulting in failures and the need to frequently pull out of the hole.
Adding to the complexity of the field were temperatures ranging from 280-300°F. While such temperatures are not generally considered especially high, they added to the complexity of the operation when combined with severe stick-slip and the strong tendency of the formation to turn the system to the right.
Conventional RSS technology had not been able to address this tendency in previous well sections.
In addition, previous wells drilled in the same area but with different well configurations needed motors to be run, and the motors did not reach the desired inclination.
The selection of the PowerDrive Orbit RSS technology was based on several design features, including the system’s compatibility with the BHA design, its ability to steer in hard and soft formations and the capability of the new pad actuator to function in a wider pressure window, allowing for the pad opening to be expanded to improve the tool response. This provided greater consistency on the pad force to push the formation in an efficient manner at the given conditions.
The new design also increased the pad opening angle to facilitate a greater formation contact load.
Automatic trajectory control
The geosteering plan for the PDVSA operation required navigating through an 8 ½-in. section while building an angle from 41.5° to 45° in just 300 ft and keeping the azimuth at 230° in one run. This requirement made the operation ideal for the PowerDrive Orbit system in its ability to provide an accurate HIA algorithm for better automatic trajectory control.
The accuracy of the HIA algorithm also helped to reduce the number of downlinks required downhole for communication, resulting in time savings and less disturbance to the drilling operation. The dual-downlink feature gave drillers the option of activating downlinks by either the traditional flow change command or by changing the collar rotation rate.
With the flow variation option, the command is less affected by high stick and slip. With the collar RPM variation, the command is less affected by the slow reaction from the drilling fluid pumps when drilling with small mechanical rigs. This application means the RSS can be run on mechanical rigs without silicon-controlled rectifier (SCR) that cannot activate the flow change commands that require fast-reaction manipulation of surface pumps to different levels.
The improved pad-actuating force allowed for greater load of contact to provide the steering efficiency necessary to resist the natural turning tendency within the section. The pad-actuation feature also improved tool response in the harsh, high-temperature environment. The metal-to-metal sealing design, which tolerates more aggressive drilling fluids characterized by a high content of low-gravity solids, enabled the additional flexibility that was required for drilling through the interbedded layers of hard and soft formation.
The RSS service enabled PDVSA to efficiently drill the 8 ½-in. section in a single run, saving 8.8 days of expected operations. The service drilled an MD of 1,187 ft and achieved the desired inclination of 45° in 177 ft, reaching the goal 123 ft ahead of the plan, while holding both inclination and azimuth.
The section was drilled in approximately three days with no incidents, achieving an average ROP of 16 ft/hr that surpassed the estimated 8 ft/hr.
The RSS service, which can be continuously monitored with a dedicated template using the OmniView real-time drilling dashboard, has achieved successful runs in several regions, including the Middle East, US land, US Gulf of Mexico, Colombia, Mexico, China and the North Sea.
PowerDrive Orbit, PowerDrive, PowerDrive vorteX and OmniView are marks of Schlumberger.