Demystifying Well Drilling Technology: The Complete Process from Soil to Rock Formations

Demystifying Well Drilling Technology: The Complete Process from Soil to Rock Formations

Drilling a well is a complete process, starting from the surface and traversing different strata until a stable water source is found. Depending on the changes in underground soil and rock, drilling techniques need to be flexibly adjusted, mainly divided into two stages: dealing with soft soil layers and hard rock layers, forming a coherent technical chain.

Stage 1: Drilling through soft soil layers. The goal of this stage is to quickly penetrate loose surface soil, sand, and gravel layers while protecting the drilled borehole walls to prevent collapse. A common method is rotary drilling, using a large drill bit to rapidly rotate and cut the soil. Simultaneously, a special "mud" is pumped into the borehole. This mud not only cools the drill bit and carries the drilled mud and sand to the surface, but more importantly, it forms a thin, strong protective film on the borehole wall, firmly supporting it, like putting a "cement shirt" on the wellbore. In particularly loose or easily collapsible strata, steel protective casing is lowered into the borehole for direct support while drilling.

Phase Two: Conquering Hard Rock Formations. When the drill bit encounters hard bedrock, rotary cutting becomes too inefficient. At this point, a change in drill bit and drilling technique is necessary. Typically, impact crushing is used, employing heavy-duty drill bits to repeatedly hammer the rock, breaking it apart; or a roller cone bit with carbide teeth is used to roll and crush the rock under high pressure. If the rock formation is particularly hard and intact, a more efficient down-the-hole hammer drilling technique is employed, utilizing high-pressure air to drive high-frequency impacts within the drill bit, drilling as efficiently as a pneumatic drill. In this phase, the borehole wall is generally relatively stable, and the drilling mud primarily serves for cooling and cleaning.

Throughout the drilling process, it is necessary to accurately determine the current formation based on changes in the returned cuttings (rock cuttings) and adjust the drill bit, drilling pressure, rotation speed, and drilling mud properties accordingly. Once the designed depth is reached and a good aquifer is confirmed, the final well casing and filter pipe are lowered, and the drilling mud is completely replaced with clean water. Finally, the well is repeatedly flushed with water until the water is clear and the sand is removed, completing the well with a stable water supply.