Drilling Optimization for Ultra-long Slim Hole Horizontal Wells in Duvernay Shale project, Canada
Authors: Kong Lulin , Wang Haige , Cui Longlian , Zhao Xiangguo , Rao LiangYu , Zhang Shupin 
Published: November 2024

Objective/Scope(30-75): Drilling contractors have always strived to pursue higher single well production and lower well-construction cost in order to achieve higher return on investment. Efforts have been made in recent years to break technological barriers to create ultra-long(>3500m) slim hole horizontal wells in Duvernay shale project. However, there were many challenges while extending the 6.75-in. slim hole laterals, such as 1) difficulty in weight transfer regarding motor slide drilling, 2) high down-hole friction torque and high ECD, 3) short servicing life and low efficiency of MWD, 4) inability to tracking thin substrata with limited logging tool, 5) production casing deployment challenges including stuck pipe risk and long running time. To overcome these obstacles, systematic solutions were proposed for unconventional ultra-long horizontal wells. Methods, Steps, and Process(75-100) : This paper proposes an integral drilling program to enhance overall drilling performance of ultra-long horizontal wells. First, Slim hole design to reduce well-construction cost through a reduction in steel, cement and fluid costs. Second, the upper drilling string upgraded from 4-in. drill pipes to 4.5-in. drill pipe with an advanced reduced OD premium connections, while Bottom Hole Assembly (BHA) employed even-wall stator PDM and Motorized RSS to improve drilling efficiency; Third, the OBM system is optimized for strong stability, lower friction, and clay-free invert emulsion to ensure safety drilling of longer laterals. Additionally, the MPD is equipped to maintain a lower ECD with minimal downhole losses; Then, a near-bit vibration sensor integrated into the RSS was deployed to provide real-time assessment of the severity of downhole shock and vibration. Reasonable drilling parameters were adjusted to reduce or eliminate downhole vibration and mitigate motor and MWD failure. Next, Azimuthal Gammy Ray was adopted and incorporated with dynamic drilling parameters data in real-time to optimize wellbore placement. More than 25 downhole drilling parameters were transmitted through high speed dual-telemetry MWD(xBolt) tool, boosting data transmission speeds and accuracy of wellbore placement in such a narrow stratigraphic window. Finally, a well-proven, external-grip mechanical casing running tool (CRT) was implemented specifically for smaller diameter 5.5-in. casing and a robust two-step wedge thread casing connection was designed to provide premium over torque capacity to manage longer lateral. Results, Understanding and Conclusions (100-200): Through continuous optimization and improvement, several major milestones and records were achieved such as longest 6.75-in. slim hole section (4875m) with one bit run and Bottom Hole Assembly, longest single run 5.5-in. & 4.5-in. hybrid casing in Duvernay at 8157m utilizing CRT tool at the time, a recorded 19.2 days drilling performance from spud to TD was achieved without any accidents or incidents. More than 6 horizontal wells lateral length exceeds 4,000m, with an average horizontal ROP above 50m/h. Single well EUR increasing from 131,000 tons to 190,000 tons, much of this improvement was due to the use of longer Hz laterals drilling technologies. Innovation points, technological contributions, and Significance (30-75): The drilling technologies developed in Duvernay have significantly reduced costs per meter and improved efficiency, setting a new lateral record in the Western Canadian Sedimentary Basin. These advancements offer practical and effective references for horizontal wells in other regions, especially for unconventional gas/oil reservoir.