In the past two decades, the point-the-bit rotary steerable system (RSS) has been widely used for high-profile directional drilling jobs in challenging environments, which require accurate directional control. A new inertial steering mode of the point-the-bit RSS was developed by using accelerometers and a rate gyroscope sensor to achieve toolface control in environments, where magnetometers cannot be used for steering. This inertial steering mode effectively expands the operational envelope of point-the-bit RSS by improving its steering ability when magnetic interference, such as drilling out of whipstock window and close to offset wells or ferrous formations, is present or within a Zone of Exclusion (ZOE). Furthermore, the new steering mode can be used as a redundancy scheme in circumstance during magnetometer failures. Through close collaboration between Research and Development (R&D) and field operation, the inertial steering mode of the point-the-bit RSS has been successfully applied in four wells in Middle East oilfield. In the first well, the new steering mode was used to kick off two 8 3/8" hole sections after setting whipstocks in near vertical wells and it completed the kick-offs in desired directions with accurate toolface control in a high magnetic noise environment. In the second well, the new steering mode was used to exit the casing and drill to TD by using a whipstock. In the third and fourth wells, 12 ¼" hole sections passing through the ZOE were successfully drilled according to the well plan. The application of the new steering mode in these wells saved extra BHA trips, which would have been required if without this new steering mode. The successful application of the new steering mode in the Middle East oilfield has proven its technical advantages and business benefits.
Khafji Joint Operations (KJO) is operating a key oil-producing field. This field has been developed extensively via horizontal drilling technologies for the past two decades. With excessive time and costs required for new offshore structure installation, the utilizing of the existing wells to drill re-entry horizontal wells became imperative and economical solution for further field developing, while minimizing the cost per foot required for well delivery. Horizontal Re-entry operation in KJO has always been deemed totally undoable due to the fact that the 7 inch production liner in most of the old wells was tied back and cemented to surface. Hence, re-entry sidetrack operation would not have enough conventional casing strings options to allow the drill ahead to reservoir while having enough mechanical barriers to isolate the unstable shale zones. Also, slimming down the well design could not be a favored option as it does not accommodate the geo-steering, formation evaluation and completion requirements; which are essential for placing and producing the re-entry wells within KJO reservoirs. To enable these re-entry wells, the Khafji drilling teams have performed a comprehensive study and risk assessment to re-define the strategy for drilling these horizontal re-entry wells. The new strategy divided the targeted re-entry wells into three main categories based on the challenges and complexity underlying each well. Each category was then assigned key enabling technologies in mud, drilling systems, optimum drilling practices, and completion techniques. These strategies along with enabling technologies were successfully implemented in a new horizontal re-entry campaign in KJO and have managed to deliver eight of these challenging wells during years 2013 and 2014.
The history of wellbore trajectory control can be traced back to the days of drilling with rotary assemblies. During that time, experienced directional drillers (DDs) used their knowledge about the response of bottomhole assemblies (BHA) in a specific area or field by means of drilling parameters and assembly configurations changes. This method required intensive field and human experience and still resulted in considerable deviations from the required trajectories. Technologies evolved with the introduction of motor and rotary steerable systems that have additional predicted directional responses, however, considerable human intervention was still required to control the trajectories. As the rotary steerable system (RSS) tools matured, entire sections of the well trajectories were automated with closed-loop trajectory control that required minimum human intervention. However, the curved sections continued to be drilled in manual modes with DDs interventions. A major operator focused on evaluating and validating a novel approach from its major directional drilling service provider using the auto-curve drilling mode to automatically drill the curved sections without human intervention and complete the missing puzzle of the autonomous well construction. The system is based on a minimum curvature method, which updates the target inclination and azimuth in a closed-loop system, similar to the one used in the hold inclination & azimuth method. Expected run rate of penetration (ROP) and planned dogleg severity (DLS) are needed while programming the tool for the RSS calculation update. Once the auto-curve mode is engaged in the RSS tool, updating the target inclination and azimuth will continue along the well to deliver the programmed DLS as per the ROP input. A detailed comparison of the measurements has been performed through three directional drilling curve sections in three wells. Combining the data of the three wells, 5,632-ft were drilled in different sections. The results were promising and showed an average of 70% reduction of human intervention. Furthermore, regarding the well positioning, the new auto-curve automation technology delivered the wells within the required profile target tolerances with minimum tortuosity. The novel autonomous curve drilling technology helped to minimize human error, enhance the accuracy of well positioning, and improve hole quality for drilling and workover operations. The system proved that this autonomous drilling technology is capable of improved well trajectory delivery with minimum intervention, faster well delivery, and reduction in operation costs.
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