Some of the factors that cause instability of the well include the well path, the direction and magnitude of the stresses, the geomechanical characteristics of the drilling layers and the pore pressure of the layers, which causes slitting and tensile fractures in the well wall.
Wellness instability is one of the main problems in oil well drilling, this problem can be reduced by determining the proper drilling mud.
The main purpose of drilling operations is to maintain the well wall during operation. It is clear that the problems of instability of wells are a set of events that are caused by interactions between rock and fluid, the conditions of tensions, abnormal behavior, and inappropriate drilling practice.
The above-mentioned cases make the drilling operation time-consuming and cost-intensive. Under balanced drilling operations have been optimized for drilling, which results in more recycling of the reservoir.
Due to the fact that most of the formations of Iran are of carbonate type and these fields have a long history, they are compressed over time and it seems that it is imperative that submersible Under balanced drilling replace over balanced drilling in these carbonate formations because Utilizing a Under balanced drilling technique in these fields improves the utilization index along with the reduction of drilling problems and increases the rate of drilling penetration, but widespread increases the risk of instability of the well wall.
In the under balanced drilling technique, the hydrostatic pressure of the mud column in the wells is less than the pore pressure of the fluid in the well. The lower the pressure of the mud causes the well to be unstable mechanically, and even the well wall may collapse and the well will be lost.
Mechanical factors Instability of a well wall is often a combination of factors that are uncontrollable (natural) or controllable. The most important chemical instability is due to water absorption in formations such as shale or due to the dissolution of salt formations in fluid water.
Water absorption in the Chilean Formation can lead to shale swelling and reduction of rock resistance, which may cause the well to grow larger and cause a hole, or if the rock stays healthy, it will reduce the diameter of the well. Salt salting may result in large holes around the well and strongly infect mud drilling mud. In this case, the drilling mud should be completely changed, which can be prevented by selecting the correct type of drilling mud.
Causes of oil wells instability:
1. Torque and high friction
2. Increase the diameter of the well
3. Suspension of drilling, septum, and brain tubes
4. Reduce the diameter of the well
5. Increase circulation of flowers
6. Increase drilling depths
7. Tube tightness
8. Increasing the volume of cavities
9. Fracture in the field of drilling
10. There is a cavity on the wall surface
11. Excellent drilling depth
12. Filling the well after each operation
13. Lift up the pipe
14. Well control deflection problems
15. The need for large volumes of cement
16. Failure to drive images
17. Weak image responses
18. Gas leaks from the analos due to poor cement performance
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