Downhole tools and methods for detecting a downhole obstruction within a wellbore. The downhole tools include a positioning mechanism, which is configured to facilitate positioning of the downhole tool within a target region of a wellbore of a hydrocarbon well, an acoustic pulse generator, which is configured to generate an acoustic pulse within a wellbore liquid that extends within the wellbore and fluidly contacts the downhole tool, and a sensor assembly, which is configured to detect a reflected acoustic pulse within the wellbore liquid. The methods include positioning a downhole tool within a target region of a wellbore, generating an acoustic pulse, propagating the acoustic pulse within a wellbore liquid, and reflecting the acoustic pulse from a downhole obstruction. The methods also include propagating a reflected acoustic pulse within the wellbore liquid, receiving the reflected acoustic pulse, and characterizing the downhole obstruction based upon the reflected acoustic pulse.