In last article 8 Points on How to Select Water Well Drilling Rig, the Drilling method are mentioned, here we will give some further introduction on reverse circulation drilling system.
Reverse Circulation(RC) Working Principle
- The drilling theory of air reverse circulation is similar with the theory of drawing water with air compressor.
- The air flows down the annulus between inner tube and outer tube and go inside single wall pipe right at air water mixer, where produces countless tiny bubbles. These bubbles going up along the pipe and expanding simultaneously. Due to the air continuing going inside the fluid, it formed lower density mixture of air and water upper the mixer. It leads the higher density fluid in the well go up with cuttings because of the pressure difference. In this way the cuttings are brought out of the well hole very fast.
Configuration of Reverse Circulation Drilling System
Here are the main advantages of RC(reverse circulation) drilling compared to DC(direct circulation) drilling:
1. High Drilling Efficiency
- The Velocity of cuttings flowing up is 10 – 50 times faster than direct circulation drilling
- According to the historical data, for clay layer the drilling speed achieves 12 m/h maximum
- For sand it is 20 m/h
- For gravel cobble it is 1 – 1.5 m/h.
- For f 4 – f 6 level rock condition it is 1 – 3 m/h.
- In general, drilling speed is 1.2 – 3 times faster than direct circulation drilling.
2. Giving sampling faster and more accurate
- The direction of flushing air flowing is same with core going inside tube, which cuttings are not contaminated by sloughing formation off the hole walls.
- It helps to get integrated core and giving an accurate formation log
3. High ratio of actual drilling time/ preparing time
- For rock condition, when drilling with tricone bit, the actual drilling time/whole rig working time is around 80 – 90%
4. High quality well achieved
- Less deviation on hole diameter from top to bottom,
- Clean on well bottom and less slope of well. All of these can lead to higher water yield.
- In average, it is 2 times less than direct circulation for time spent for washing well, meanwhile one third higher water yield compared to direct circulation
5. Lower drilling cost
- The reverse circulation drilling has higher drilling efficiency and can get better quality well, longer lift time for drill bit.
- The total cost is lower. Compared to direct circulation drilling, it is around $5 lower per meter.
6. Larger diameter hole can be drilled
- Drillers usually use it to drill large diameter hole due to it is easier and fast to clean the hole, especially for softer formation.
Above is all about the comparison or difference between Reverse circulation and Direct circulation, in next blog we will give introduction on how to select or design the high level reverse circulation drilling system.