Prerequisites
The prerequisites that lead to formation leakage are as follows:
First, there are pores, fractures or faults and caves in the strata, and they are interconnected, so that the mud has a flow channel.
Second, the mud column pressure is greater than the pressure of liquid and gas in the formation.
Third, the mud column pressure and its lateral pressure are greater than the formation rupture pressure, which will fracture the formation and produce well leakage.
Main factors
Improper operation, resulting in well leakage
The blockage of the wellbore and collapse will block the outer ring of the Water well DTH Drill Pipe, and the formation will be blocked when the pump is opened.
The water well is not clean, there are too many rock chips and pieces, the mud circulation is not smooth, and the pump pressure is too high, which causes leakage of the formation.
The slurry has a large specific gravity, high viscosity and high shear force. The mud pressure is greater than the formation pore pressure, resulting in well leakage.In this case, the mud specific gravity, viscosity and shear force will be reduced, and the well leakage will stop.
The DTH drill bit causes the pump pressure to rise and leak the formation.
When the mud is stationary in the well for more than 24 hours, a strong mesh structure strength is formed. When Water well DTH Drill Pipe drilling down, there is no segmented circulation, but it goes straight to the bottom of the well, resulting in high pump pressure when the pump is opened, and finally the formation is blocked.
The displacement of the mud pump is not enough, the amount of cuttings in the well is large, the pump pressure rises, and the formation is pressurized.
The water well DTH Drill Pipe was drilled too fast, resulting in too high agitation pressure and pressure leakage of the formation.
There was originally a well leak and blowout in the water well , but when the mud was increased, the mud was too heavy and a well leak occurred again.
Fracturing action
Fracturing increases the permeability of the formation by forcing natural fractures or forming new fractures in the formation with high pressure fluid.If the fracture extends to the natural fault or high permeability zone, it is easy to form leakage channel. The excessive expansion of the fracture or communication with adjacent high-permeability layers (such as karst caves and faults) leads to the direct leakage of drilling fluid into the deep formation.
Acidification transformation
Acid dissolves rock minerals (such as carbonate rocks and cement), expands pores or erodes natural micro-fractures, and forms a high-conductivity network. If the acidization intensity is too strong, it may damage the integrity of the formation and induce leakage.
In the acid soluble rock strata such as limestone and dolomite, the risk of leakage is significantly increased after the development of acid erosion holes.
Water injection cleaning
Continuous water injection is used to increase the formation pore pressure and reduce the effective pressure difference between the wellbore and the formation. When the water injection pressure is close to or exceeds the formation fracturing pressure, hydraulic splitting occurs in the rock mass around the well, which aggravates the leakage.
Others
Continuous pumping from wells around the drilling site has led to a significant drop in groundwater levels, causing a reduction in formation pore pressure and creating localized negative pressure zones. When the DTH bit penetrates these formations, the negative pressure difference between the drilling fluid pressure inside the hole and the formation pore pressure (drilling fluid pressure <formation pore pressure) causes the drilling fluid to rapidly leak into the formation through fractures or pore channels, resulting in severe fluid loss.
