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During the rainy season, large amounts of rainwater intrude into the mountainous areas, often resulting in rock instability and landslides or mudslides that cause heavy losses to people's lives and property. This phenomenon is similar to the mechanism of shaft collapse. During the drilling process, mud intrudes into the rock of the wellbore formation, destabilizing the wellbore wall and causing collapse of the well wall. It is the worst type of stuck pipe drilling accident, because the process of handling such accidents is the most complex, the most time-consuming, the most risky and the well is likely to be scrapped if not properly handled. Therefore, during drilling Try to avoid this kind of accident.

There are many reasons for the collapse of the shaft wall, including geological reasons, physical and chemical reasons, and drilling process. For some areas or a well, may be one of the main reasons, but for most wells, mostly due to a combination of reasons. Geological reasons are: the formation of the rupture caused by the original stress, stratum instability caused by the formation dip, the rock itself due to sedimentary environment, mineral composition, burial time, cementing compaction degree and other causes of instability, etc. . Physico-chemical reasons are as follows: Most of oil and gas drilling are stratigraphic sediments, while more than 70% of sedimentary rocks are hydrophilic shale. Among them, shale with high content of smectite is easily water-swelling and chlorite content High mud shale is susceptible to water splitting and peeling, which is the main reason for the collapse of the borehole wall during drilling. The main reasons for the process are: the pressure of the liquid column in the wellbore is lower than the pressure of collapse of the formation, the performance of the drilling fluid is not compatible with the lithology of the formation, and the stratum is unstable due to the drop of the drilling fluid level or pressure.

In order to prevent the borehole wall from collapsing during the drilling process, it is generally necessary to select the drilling fluid that matches the lithology of the formation, and it is better to use the drilling fluid with anti-collapse performance; to design the well structure scientifically and rationally; to adjust the performance of the drilling fluid Indicators; to maintain the pressure of slurry column slightly higher than the formation pore pressure; Drill down drilling speed should not be too fast, to avoid excessive pressure caused by excitement; for some reason to stop drilling construction, be sure to keep the mud inside the wellbore The liquid level, do not descend the wellbore surface due to seepage from the formation, and do not allow the drilling fluid to stand still longer in the well.

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