Different methods of reverse circulation drilling technology have different process characteristics and uses. Pumping reverse circulation drilling is mainly used for drilling shallow water wells. Generally, it can drill about 100m, but it is easy to be restricted by faucet and drilling equipment sealing conditions. After that, it cannot be drilled normally. The gas lift reverse circulation drilling technology is mainly applied to the drilling of water wells, hydrogeological boreholes, and large-caliber engineering construction holes, which can solve the problem of sand carrying in well leaks and large bore wells. Double-wall drilling air reverse circulation drilling is mainly applied to the development of low-pressure, low-permeability and fractured oil and gas reservoirs, which can avoid the damage of drilling fluid, cuttings and pump pulses to the exposed reservoir. From the principle of reverse circulation, it is mainly divided into gas lift reverse circulation and air reverse circulation drilling, that is, a reverse circulation is established by pressure difference, and a reverse circulation is established by pressure.
1. Gas lift reverse circulation drilling technology
1) Process principle
Gas lift reverse circulation drilling is the injection of compressed air through the gas faucet and other gas injection joints, injected into the annular space of the inner and outer tubes of the double-drilling tool, the gas flows to the bottom of the double-drilled rod, and is injected into the inner tube through the mixer to form Numerous small bubbles, which rise rapidly along the inner tube and expand at the same time. As the compressed air continuously enters the drilling fluid, a low-density mixture is formed in the upper part of the mixer, and the drilling fluid outside the drill pipe has a high density, and the annular drilling fluid Enter the water eye in the drilling tool to form a reverse circulation flow, and carry out the bottom cuttings continuously out of the surface and discharge into the grit chamber. The sedimented mud is injected into the wellbore and enters the space of the circulating fluid in the drill pipe through the bottom of the well, so that it continuously circulates to form a continuous drilling process.
2) Advantages and uses
(1) Elimination of annular air pressure during reverse circulation, applied to low-pressure, low-permeability reservoirs, can create negative pressure at the bottom of the well, which is conducive to the discovery and protection of oil and gas reservoirs.
(2) When the gas lift reverse circulation drilling, the drilling fluid at the drill bit produces a twitching effect on the bottom of the well, and the cuttings are taken away in time without the pressure holding effect. When the drilling of the leakage layer, the cutting debris can be repeatedly broken. Can increase the rate of mechanical drilling and increase drilling efficiency.
(3) It can reduce or eliminate the leakage of drilling fluid and save a lot of drilling fluid material consumption. Can drill through the layer that cannot be crossed due to loss, and drill the target layer.
(4) When using gas lift reverse circulation drilling, the role of the drilling pump is to fill the drilling fluid into the annulus, the pump load is greatly reduced, and the service life of the pump is increased.
(5) Both positive and negative circulation can be used to kill the well, and the well control is flexible.
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