Main boring diameter for petroleum well is $20-30$ cms in diameter, while the depth of the oil well may be about $\_\_\_\_\_\_\_\_\_$ kms$.$

$0\mathrm{.}1$ to $0\mathrm{.}5$

$1\mathrm{.}5$ to $4\mathrm{.}5$

$7\mathrm{.}5$ to $12\mathrm{.}5$

$15-20$