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In 2023, our company executed a 118mm slimhole sidetrack directional well for an operator in the Liaobe Oilfield. The original casing string had an outside diameter (OD) of 139.7mm set at 2146.46 m. The sidetrack kickoff point (KOP) was at 1710 m depth. The sidetrack hole section was drilled to 118mm diameter and reached a total depth (TD) of 2530.53 m.
Well Schematic
1.Data Acquisition & Review：
Coordinated with the operator to collect and archive original data records from all relevant sources. Examples included: offset well completion reports, wireline logging data, upper hole section data, original wellhead coordinates, target coordinates, and engineering & geological design documents.
2.Execution Plan
(1)Well Path Design
The existing wellbore trajectory was utilized for the section above the sidetrack kickoff point (KOP).
Description | Measured Depth (m) | Inclination (deg) | Grid Azimuth (deg) | True Vertical Depth (m) | North Coordinate (m) | East Coordinate (m) | Vertical Section (m) | Dogleg Severity (deg/30m) | Closure Distance (m) | Closure Azimuth (deg) |
Kickoff Point (KOP) | 1710.00 | 16.87 | 354.89 | 1683.81 | 184.51 | -55.16 | 191.91 | 0.30 | 192.58 | 343.36 |
1768.40 | 16.74 | 327.73 | 1739.80 | 200.08 | -60.41 | 208.33 | 4.00 | 209.01 | 343.20 | |
2015.30 | 16.74 | 327.73 | 1976.24 | 260.21 | -98.38 | 278.17 | 0.00 | 278.19 | 339.29 | |
Target 1 | 2140.84 | 0.00 | 0.00 | 2100.00 | 275.61 | -108.10 | 296.05 | 4.00 | 296.05 | 338.58 |
Target 2 | 2500.84 | 0.00 | 0.00 | 2460.00 | 275.61 | -108.10 | 296.05 | 0.00 | 296.05 | 338.58 |
Total Depth | 2530.53 | 0.00 | 0.00 | 2490.00 | 275.61 | -108.10 | 296.05 | 0.00 | 296.05 | 338.58 |
(2)Tool Selection
Component | Size（mm） | Quantity | Remarks |
Orientation Sub | 105 | 2 | Connection211*211 |
Positive Displacement Motor | 90mm（Stabilizer114mm） | 2 | 1.25°Single Bend |
MWD | 48 | 2 |
(3)Bottom Hole Assembly
φ118mmPDC+φ90mm*1.25°PDM+Float Valve+Orientation Sub+105mm Non-Magnetic Drill Pipe+73mm Heavy Weight Drill Pipe*16+73mm Drill Pipe
(4)Drilling Procedures
-1710m-1768m (Window & Turn Section): Planned dogleg severity (DLS) was 4°/30m. Drag was anticipated in this section while using the PDC bit. Prior to sliding, the drill string was worked extensively to release torque. Directional drilling commenced only after the tool face stabilized. Build rate was carefully controlled, and allowance was built into the plan based on actual formation tendency to ensure successful tangent section drilling later.
-1768m-2015.30m (Tangent Section): Should inclination or azimuth deviate, drilling parameters were adjusted promptly and directional control was applied to maintain the planned tangent trajectory.
-2015.30m-2140.84m (Drop Section): Planned DLS was 4°/30m. Severe drag during sliding was anticipated in this section. Close coordination with the drilling crew and mud company ensured timely addition of lubricant. Tool face stability was maintained and reactive torque was continuously monitored and adjusted to ensure each stand achieved the desired directional outcome. Allowance in inclination and azimuth was built in advance based on rotary drilling performance to prevent increased difficulty in the subsequent tangent section.
-2140.84m-2500.84m (Tangent Section): Drilling parameters and directional control were adjusted as needed to maintain the planned tangent trajectory. Based on experience from offset wells, severe drag during sliding was expected in this section. Consistent communication with the drilling crew and mud company facilitated the timely addition of lubricant.
-To ensure wellbore quality, trajectory monitoring was intensified. Surveys were conducted every 10m in directional sections and every 20m in tangent sections.
-Anti-collision scanning was performed against trajectories of offset wells and the original wellbore.
3.Operations Execution
(1)Due to the small BHA size, tool face instability was encountered, with reactive torque exceeding 720°. Before sliding, the drill string was worked extensively (more than 3 times) until tool face stability was achieved. Directional drilling commenced with gradual weight application. The azimuth turn was executed effectively; sliding 1-1.5 m per stand achieved the required build rate. During rotary drilling, inclination and azimuth remained relatively stable (inclination held steady, azimuth exhibited a slight increase of approximately 1°). In the initial part of the drop section, to prevent DLS violations, sliding 2.5 m per stand achieved a drop rate of approximately 1.4° per stand.
(2)Severe drag was encountered in the drop section. Timely addition of liquid lubricant, facilitated through coordination, significantly mitigated the drag issue.
4.Operations Summary
Total drilled footage: 829 m,Total tool operating time: 300 hours,Total slide drilling footage: 78.83 m,Total rotary drilling footage: 750.17 m,Overall slide-rotate ratio: 9.51%,Target 1 center distance: 2.85 m,Target 2 center distance: 7.16 m,The entire well trajectory was successfully drilled with no dogleg severity (DLS) violations.
