What are the possible causes of wellbore collapse according to the analysis of geological drill pipes?
22 Jun,2020
Water-sensitive mudstone formations absorb water and swell, weakening the bonds between their layers and ultimately leading to collapse—examples include the Zhiluo Formation, Fuxian Formation, Liujia Gou Formation, Shiqianfeng Formation, and others.
(1) Reasons inherent in the geological strata
1. Water-sensitive mudstone formations absorb water and swell, weakening the bonds between their layers and ultimately leading to collapse—examples include the Zhiluo Formation, Fuxian Formation, Liujia Gou Formation, Shiqianfeng Formation, and others.
2. In formations with abnormally high pore pressure in mud shale, when Geological drill pipe When the hydrostatic pressure of the drilling fluid is lower than the formation pore pressure, and if the shale contains very small pores with extremely low permeability, even a slight overbalance can cause the shale to be instantly pushed into the wellbore—leading to a collapse and stuck pipe situation. This type of collapse-related stuck pipe often occurs unexpectedly when drilling into the Yanchang Formation.
3. If the lateral pressure from the formation exceeds the hydrostatic pressure of the drilling fluid column inside the well, the formation rocks will collapse inward into the wellbore.
4. The strata have a steep dip, poor stability, and are highly prone to collapse.
5. The fractured zone formed by the fault.
6. Unconsolidated or poorly cemented sandstones and conglomerates are highly prone to collapse after drilling through them.
7. Unconsolidated quicksand, silt, coal seams, and similar materials.
(II) Reasons related to the drilling fluid
1. Geological drill pipe The drilling fluid has a low density, so the resulting hydrostatic pressure fails to balance the formation pressure, leading to wellbore collapse.
2. The drilling fluid experiences high fluid loss and low mineralization, causing the mudstone to absorb water, swell, and lose structural integrity, ultimately leading to flaking.
3. The drilling fluid has a high flow rate and return velocity, flowing in a turbulent state, which severely erodes the wellbore walls and leads to wellbore losses.
4. Prolonged drilling pauses have led to continuous flaking and spalling in the water-sensitive shale layers, ultimately resulting in wellbore collapse.
5. Failure to circulate mud during tripping out, or insufficient mud circulation.
6. Well leakage causes the drilling fluid level to drop.
7. The blowout caused the well to collapse.
8. Prolonged well flushing in sections prone to collapse.
(III) Engineering-related reasons
1. The effects of wellbore deviation and azimuth—particularly determining the torque direction in easily collapsed well sections—are most likely to trigger wellbore instability and collapse.
2. The clearance between the drill string and the wellbore is too narrow, which can easily lead to pressure surges and compromise wellbore stability.
3. Geological drill pipe Overly rapid pump activation or excessively fast drill string descent can cause the instantaneous wellbore pressure to exceed the formation's fracture pressure, leading to formation fracturing.
4. Drilling out too quickly creates suction pressure, compromising wellbore stability.
5. Bending the drill pipe to bump against or tap the wellbore wall.
6. Use the rotary table to unscrew the drill bit in sections prone to collapse.
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