AMIGE have available own two special vessels, M/V BAVENIT and M/V KIMBERLIT, and a drilling pontoon (mini jack-up drill unit) designed for geotechnical drilling and soil sampling. By now more than 1300 geotechnical and CPT boreholes of total depth exceeding 42,000 m were drilled with these vessels on the Arctic shelf.
Geotechnical drilling procedures and equipment to be used depend on the target application: taking of undisturbed soil samples from the given drilling depth and definition of physical and mechanical soil properties in-situ.
Special machinery onboard M/V Bavenit allows performance of complex geotechnical operations both downhole and outboard as follows:
1. Drilling with coring (to take undisturbed soil samples) with “Wirth” VA-NA 108E drilling tool, and “Wipsampler Mk-2” (wireline push sampling equipment). Soil sampling is carried out with advance heading at 1m spacing.
2. Drilling with CPTU using drilling equipment VA-NA 108 “Wirth” and “WISON Mk III” or “Wison XP” Cone Penetration Test (CPT) System. CPT measurements are taken below the bottom-hole at intervals of 3 meters with probes provided with special cones to determine unit cone resistance (qc), side friction (fs), pore pressure (dU2), and temperature (T). When it is required additional measuring devices are used like seismic tools, vanes and etc.
3. Also, CPT is performed with an outboard “Fugro Wheeldrive” system down to 40 m depth below the seabed. The system operational parameters are the same as of the downhole system.
4. Soil samples are taken with outboard equipment “Fugro Stacorer” down to 40 m depth below the seabed.
5. The seabed surface soil samples are taken with a sampling device “Boxcorer”
Geotechnical drilling is performed with “URB 3A3” drilling unit or “URB 2M” (equipped with a swivel).
Undisturbed soil samples are taken with advance heading using downhole hydro corers PGS-132 at drilling intervals of 2 m. Penetration rate is ranging from 0.1 m to 3 m per minute. Rotary drilling with coring is performed with a core barrel of 127 mm, 108 mm and 89 mm in diameter. Drilling unit drive is equipped with an electric motor of 50 kW. Each of two drill pumps NB-32 is provided with a drive and an electric motor of 35 kW.
Cone Penetration Tests are performed using special equipment consisting of CPT thrust system ROSON 40 KN (A.P. van den berg, the Netherlands), a CPT string of 36 mm and a cone penetrometer provided with a memory module. The system allows penetration with CPT measurements down to 20 m below the seabed. Penetration rate is 1 m per minute.
- operation water depth range: up to 500 m,
- Pushing/pulling force — 40 kN,
- Driving/ pulling speed — 20 mm/s,
- Drive: electrically driven wheels,
- 10 cm² (36 mm OD) CPT string
- power consumption – 17 kW,
- weight in air – 4,044 kg.
To record measurements CPT probes provided with memory modules are used for determinations of unit cone resistance (qc), side friction (fs), and pore pressure (dU2).
Drilling pontoon with AQUALOCK system allows taking of undisturbed soil samples at the target depth without well casing at the sea depths ranging from 0.5 m to 7 m. Diameter of a core receiver is 70 mm; length is 2 m. A drill string penetration with 2 m runs is provided by drill unit “CompactVibroSonic” (180 Hz). Maximum borehole depth is 30 m. Rotary drilling with a core barrel is also possible to arrange.
- Required power: 55 kW
- Vibration capacity: 27 kW
- Rotation capacity: 27 kW
- Frequency: 200 Hz
- Vibration force: 10 t
- Rotating speed: 0 — 200 rpm
- Rotation torque: 4.0 kNm
- Maximum hydraulic flow: 210 Bar
When geotechnical drilling is required to perform onshore, AMIGE use a special drilling rig PBU-2 mountable on a heavy truck (KAMAZ). PBU-2 is a drilling rig with a swivel provided with a mechanical drive in combination with a hydraulic feeding device.
PBU-2 drilling rig mounted on KAMAZ heavy truck
PBU-2 operation parameters:
- Stroke: 1.8 m
- Forward force: 3,000 kgf.
- Spindle rotation speed: 28-430 rpm.
- Torque: 500 kgm
- Winch hoisting capacity: 2,600 kgf
Geotechnical boreholes are drilled in process of core drilling with runs of 0.3-0.5 m and air blasting provided with air compressor PK8. A core barrel tube is of 112/108 mm in diameter. Hard alloyed core bits SA6-93 are used as a rock cutting tool.
Geotechnical drilling is always accompanied by examination, description and testing of a core retrieved from a core receiver. Core spacing (interval) and type of tests to be performed are stipulated by reference documents and special Programs of Works.
Filed laboratory tests are performed both offshore and onshore. As a rule, they include determinations for natural water content, soil density, and express-tests for soil strength properties with a pocket penetrometer and a torvane, as well as undrained shear tests with a lab vane.