In the last article, we talked about that water well drilling rigs can be categorized into percussion drilling rigs, rotary drilling rigs (rotary table drilling rigs and hydraulic top drive drilling rigs) and composite drilling rigs according to the drilling method.
Today, we will talk about the classification according to the circulation mode. According to the circulation method:
Core Equipment: Reciprocating Mud Pumps
Applicable depth：<1000m
Principle: Positive circulation is actually a hydrulic top drive drilling rig stacked with a mud pump, which is commonly known as the water drilling method. The mud pump sends mud through the inner cavity of the drill pipe to the bottom of the hole, the drilling slag floats up through the mud, thus playing the role of slag removal and well wall protection.
Application：clay layer, sand layer, bedrock.
Advantages: Mature technology, simple operation, low price of mud pump itself. And this method is applicable to a wide range of depths, from a few hundred meters to thousands of meters are not a problem; wall protection effect is good (positive circulation in the mud carrying drilling slag from the hole into the sedimentation tank, will be in the hole wall formed a thick layer of mud film).
Disadvantages: Lower efficiency compared with air type and reverse circulation type; low upward return flow rate of flushing liquid, large particles of drilling slag may not be discharged in time, which may aggravate the wear and tear of drilling tools and enhance the drilling cost, so the applicable hole diameter is limited (mostly used for holes within 800mm hole diameter)
Principle: The difference between positive circulation and reverse circulation is that the mud flows in different directions. Positive circulation mud from the drill pipe from the top down into the mud, and then the mud to the bottom of the hole with slag from the hole from the bottom up out of the hole, after precipitation of the mud and then into the next cycle.
The reverse circulation is opposite. The flushing fluid flows into the hole and carries the slag from the middle of the drill pipe from the bottom up to the sedimentation tank.
Application: sand layer, pebble gravel layer, soft and hard rock layer.
Advantages: Higher slag removal efficiency and consequently the hole formation efficiency, and smaller the wearness on the drilling tools.
Disadvantages: The well wall protection effect is worse than positive circulation.
In addition, the reverse circulation can be subdivided into three basic forms according to how the water rises in the drill pipe, which are pump suction reverse circulation, air lift reverse circulation and jet reverse circulation.
Core equipment: centrifugal pump
Applicable depth: <120m
The pump in pump suction reverse circulation drilling rig refers to gravel pump, which belongs to centrifugal pump in mud pump. And the mud pump we use in the positive circulation drilling method belongs to reciprocating pump. There is also a screw type mud pump.
Principle: Centrifugal pump with high efficiency and large pumping capacity, the mud with drilling slag inside the drill pipe rises by the its strong suction force formation. When it is running, there will be pressure difference between the pump suction port and the liquid level of the well, thus lifting and conveying the mud with drilling slag.
Application: wells in strata with high water table and small water leakage. The drilling efficiency is higher when the hole depth is less than 50 meters, but when the drilling depth is increased or the water leakage is larger, it is easy to produce insufficient water supply and make the dynamic water level in the well hole decrease, which exceeds the effective suction range of the gravel pump and the pump can’t work normally.
Core equipment: air compressor, gas-liquid mixer, special drilling rods
Also known as compressed air reverse circulation drilling rig. Like conventional air drilling rigs, we will provide the air compressor in the program for our customers, the difference is that the slag discharge system and the end drilling system.
Principle: The air compressor sends compressed air to the air-liquid mixer in the lower part of the drilling pipe through the air delivery pipeline, so that the compressed air mixes with the mud inside the conduit to form mud-air mixing slurry whose density is smaller than that of the mud outside the conduit. The mixed slurry rises along the inner lumen of the conduit under the action of the pressure difference between inside and outside the pipe, and is discharged to the sedimentation tank through the slag discharge pipe, so it does not need a gravel pump. After precipitation, the slurry flows back into the hole continuously, forming a reverse-circulation. As followed pic.
Compressed air reverse circulation drilling rig of the drill pipe and water pipeline internal diameter is generally larger, and there is no section shrinkage, chip discharge conditions are better. As the upward flow rate of water in the drill pipe is related to the specific gravity difference between the liquid column inside and outside the drill pipe, when the depth of the well increases, as long as the pressure and volume of air supply is increased accordingly, the drilling efficiency can still be maintained at a high level, and it can still work normally when the leakage from the hole wall increases and the water level in the hole drops more, so it can also drill in the leaky formation.
Advantages: high drilling efficiency, long bit life, good well quality
Disadvantages: The gas-liquid mixer has to been put a certain submergence depth, so the part within 9 meters from the surface needs to be drilled by auger bit or other method.
Different inner diameters of the drill rods are matched with different air volumes. For drill pipes with inner diameters of 120, 150, 200 and 300 mm, air volumes of 4.6, 6.6, 10 and 15-20 m³/min are generally used respectively. The effective suction pressure is generally 0.25 to 0.3 MPa. The drilling depths achievable with drill pipes of different internal diameters are: 400 m for 150 mm drill pipes, 500 m for 200 mm drill pipes and 750 m for 300 mm drill pipes.
Core equipment: Jet pump
Applicable depth: <50m, max depth=250m
Principle: The outlet pipe of the jet pump is connected to the bottom of the well, and the water is injected into the drill pipe from below through the nozzle, and the rising water carries the rock chips through the drill pipe and out of the well.
The pump pressure should be able to overcome the friction losses in the line and the weight of the water column at the corresponding height, generally 0.7 to 0.8 MPa. The flow rate of the water pump depends on the drilling diameter and the inner diameter of the drill pipe. When the diameter of the well is 0.5-1.5 meters and the inner diameter of the drill pipe is 89-114 mm, the flow rate of the water pump is 300 m³/hour; when the diameter of the well is 0.3-0.5 meters, the flow rate can be 120-150 m3/hour.
Advantages: It is easy to change the piping arrangement from reverse circulation to positive circulation, which is favorable for drill plugging and rapid replenishment of water to the well when the water level in the well suddenly drops. In addition, the working medium of the pump is clear water, and the wearness is small for the pump casing and vanes.
Disadvantages: the nozzle in the drill pipe to form a section of the contraction, reducing the free passage diameter of the circulation pipeline, affecting the discharge of large diameter pebbles. Greater than 50m efficiency, as the depth increases the efficiency decreases with it.
Core equipment: air compressor, impactor
Applicable depth: <500m
Principle: drilling rig is connected to the air compressor, the drill pipe is connected to the dth hammer and the drill bit. In addition to the torque provided by the drilling rig, the compressed air provided by the air compressor enters the dth hammer through the drill rod, and drives the dth hammer through a series of piston components to drive the drill bit to form a downward high-frequency reciprocating impact to break the rock. The excess compressed air will be discharged through the hole of the drill bit, and the compressed gas is continuously discharged to fill the hole, thus bringing the rock chips out of the hole.
Advantages: High drilling efficiency due to the addition of impact force; Low efficiency of slag discharge within a certain depth
Disadvantages: As the hole is drilled deeper, there is a serious loss of gas, whether it is to provide a power source for the dth hammer or to discharge rock chips, and the further down the hole you go, the more the effect will be reduced. The deeper the hole, the higher the cost of the compressor; at the same depth, the cost of the solution is higher than that of other types of drilling rigs.
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