The positive circulation speed is slow, the safety is high, the hole is not easy to collapse, and it is beneficial to hole formation. Reverse circulation works faster, which is more demanding, and is mainly used in good formations.
Advantages and disadvantages of positive circulation and reverse circulation of bored piles;
(1) positive circulation means injecting circulating mud from the drill pipe, and the cuttings float in the mud because of their lighter specific gravity, and rise to the top of the hole with the mud to be discharged. With the gradual increase of cuttings, the mud concentration is getting bigger and bigger, and the sediment of cuttings causes repeated grinding, which is inefficient. However, the thick mud is beneficial to drilling and wall protection, and it is not easy to collapse, so it is suitable for soil layers that are easy to collapse, such as quicksand.
(2) Reverse circulation means that the drill pipe sucks out the circulating mud while drilling, and replenishes mud at the top of the hole to keep the liquid level in the hole, thus ensuring the stability of the hole wall. Reverse circulation can greatly reduce the ineffective labor of repeatedly grinding drilling cuttings and greatly improve drilling efficiency. Suitable for rock stratum, gravel and dense soil layer.
Extended data:
Mud or water enters from the drill pipe and flows out from the wellhead. This is a positive circulation drilling rig. Mud or water is sucked out of the drill pipe and flows in from the wellhead. This is a reverse circulation drilling rig. Positive and negative circulation refers to the circulation mode of drilling fluid (mud or water) in the drilling rig. When drilling, the drill bit of the drilling rig will produce muck, slag stone and so on. Through positive and negative circulation, these dregs can be brought to the ground by mud, and then the mud returns to the borehole after settling in the sedimentation tank. This goes on and on, and finally becomes a hole. Reverse circulation can bring out slag with larger diameter.
The mud pump (drainage pump) of the existing reverse circulation drilling rig is set above the ground and needs to be drained before work. Mud pump can't work normally due to air leakage, and the operation procedure is complicated, which affects the working efficiency of drilling rig.
This patent completely solved these problems. Our reverse circulation drilling rig consists of hollow shaft (hollow drill pipe), mud pump (discharge pump), power head (reducer) and mud pump discharge pipe. The upper end of the hollow shaft is connected with the power head, the mud pump is arranged at the lower side in the hollow shaft, and the lower end of the discharge pipe of the mud pump is connected with the outlet of the mud pump.
This product is driven by the reducer to rotate the hollow shaft at low speed, and the mud pump works underwater (below the ground) in the rotating hollow shaft, which reduces the operating procedures, reduces the failure rate of the drilling rig, improves the working speed and increases the drilling depth of the drilling rig.
References:
Baidu encyclopedia-positive circulation drilling rig? Baidu encyclopedia-reverse circulation drilling rig