Which type of soil is generally the best for drilling?

Gravelly soil is generally considered the best for drilling due to its favorable characteristics. This type of soil typically has good drainage and allows for better stability during the drilling process. The larger particle size associated with gravel helps to minimize the potential for clogging and blockages in drilling equipment. Additionally, the void spaces in gravel allow for efficient circulation of drilling fluids, which aids in cooling the drill bit and removing cuttings from the borehole.

The other soil types present challenges that make them less ideal. Silty soil can retain water and may lead to instability, while clayey soil can expand when wet, causing difficulties in maintaining a borehole. Sandy soil, while better than silty or clayey, can still pose challenges in terms of fine particulates that lead to potential instability and loss of well integrity. Hence, gravelly soil is preferred in drilling applications for its structural integrity and effectiveness in mitigating drilling issues.