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3.3 Core drilling equipment3.3.1 The wireline-76 systemFor drilling the cored part of borehole KFM06C, a wireline-76 system, type Hagby Bruk Onram2000 CCD, was employed. The drilling process is operated by an electrically-driven hydraulicsystem supplied with a computer control. The drilling capacity for 76–77 mm holes is maximumc. 1,500 metres. The drill pipes and core barrel used belong to the Hagby WL76 triple-tubesystem. Technical specifications of the drilling machine with fittings are given in Table 3-1.3.3.2 Flushing/return water system – function and equipmentCore drilling involves pumping of flushing water down the drill string, through the drill bitand out into the borehole in order 1) to conduct frictional heat away from the drill bit, and2) to enhance the recovery of drill cuttings to the ground surface. The cuttings, suspended inthe flushing water (in general mixed with groundwater), are forced from the borehole bottomto the ground surface via the gap between the borehole wall and the drill pipes. However, ifthe borehole has penetrated water conductive rock fractures, part of, and sometimes all of thereturn water from the borehole, including drill cuttings, may be forced into these fractures. Thisrenders a correct characterization of the in situ hydraulic and hydrogeochemical conditions moredifficult, due to partial or complete clogging by drill cuttings and due to the contribution of‘foreign’ flushing water in the fracture system.In order to reduce these negative effects, SKB has developed a specially designed flushingwater and return water system. The equipment consists of the components shown in Figure 3-3.The system includes equipment for pumping, transport and storage of water. The flushingwater-/return water system may be divided into:• equipment for preparing the flushing water,• equipment for measuring flushing water parameters (flow rate, pressure, electricalconductivity and dissolved oxygen),• equipment for air-lift pumping while drilling,• equipment for storage and discharge of return water.Table 3‐1. Technical specifications of the Onram 2000 CCD-system from Hagby-Asahiwith appurtenances.Unit Manufacturer/Type Specifications RemarksOnram 2000 Hagby-Asahi Capacity for 76–77 mmholes maximum approx.1,500 mFlush water pump Bean Max flow rate: 170 L/minMax pressure: 103 barsSubmersible pump Grundfos SQ Max flow rate: 200 L/minMobile electricalplantP250HE with diesel enginePerkins GCD 325250 KVA, 200 kW, 360 A.Compressor Atlas Copco GA75P-13 Max pressure: 12 bars Electrically suppliedFlow: > 5 L/secCCD-system Dunfoss Standard system modified forcore drilling by the manufacturer15