What are the causes of borehole collapse under geological drill pipe analysis?

Classification:

Industry dynamics

Release time:

2020-06-22

【Summary Description】 The water-sensitive shale formations, such as Zhiluo Formation, Fuxian Formation, Liujiagou Formation, Shi Qianfeng Formation and so on, weaken their mutual connection force and eventually collapse.
(I) of the formation itself
1. The water-sensitive shale formations absorb water and swell, which weakens the connecting forces between them and eventually collapses, such as Zhiluo Formation, Fuxian Formation, Liujiagou Formation, Shiqianfeng Formation and so on.
2. High strata with abnormal pore pressure in shale, whengeological drill pipeThe pressure of drilling fluid column is less than the formation pore pressure. If the shale pore is very small and the permeability is very low, once the pressure difference exceeds the shale strength, the shale will be pushed into the well in an instant, resulting in collapse and sticking. When drilling to the extension group, collapse and sticking due to this reason will occur suddenly.
3. If the lateral pressure of the formation is greater than the pressure of the drilling fluid column in the well, the formation rock will collapse into the well.
4. The formation dip angle is large, the stability is poor, and collapse is easy to occur.
5. Fractional zones formed by faults.
6. Uncemented or poorly cemented sandstone and conglomerate are prone to collapse after drilling.
7. The flow sand, silt and coal layer without rock formation.
地质钻杆
Reasons for (II) of drilling fluid
1.geological drill pipeThe drilling fluid has a small specific gravity, and the resulting dip pressure cannot balance the formation pressure, resulting in bottom hole collapse.
2. The water loss of drilling fluid is large, the degree of mineralization is small, and the structural strength of shale is reduced and spalling occurs due to the water absorption and expansion of shale.
3. The drilling fluid has large displacement and high return speed, which is in turbulent flow state, seriously eroding the well wall and causing well leakage.
4. Long-time drilling stoppage leads to continuous spalling and falling of water-sensitive mud sheet layer, eventually causing well collapse.
5. No grouting or insufficient grouting during drilling.
6. Drilling fluid level drops due to lost circulation.
7. Well collapse caused by blowout.
8. The well is flushed in the section of easily collapsed well for a long time.
(III) engineering reasons
1. The influence of well deviation and orientation, especially in the direction of fixed torsion in the section prone to collapse, is most likely to cause well collapse.
2. The gap between the drilling tool and the borehole is too small, which is easy to produce pressure excitation and destroy the stability of the borehole wall.
3.geological drill pipeIf the pump is started too strongly or the drilling speed is too fast, the instantaneous well pressure is greater than the formation crushing pressure and the formation is fractured.
4. The tripping speed is too fast, resulting in suction pressure and damaging the stability of the borehole wall.
5. Bending or knocking of the bent drill pipe against the borehole wall.
6. The bit shall be unbuckled with the rotary table in the easy collapse section.

Key words:

weilida drill