(Not a rocket scientist or mathematician, but I spent 100s of hours playing KSP RP-1)
Just doing some estimates using data from the wikipedia page:
The dV (delta-V) needed to get into low Earth orbit is around 9.4km/s.
The dV for K2-18b might be around 19km/s, more than double that of Earth's.
It's practically impossible I think, you would need such a massive launch vehicle. For double the dV, you would need exponentially more fuel assuming current rocketry tech (fuel+oxidizer tanks and engines). There wouldn't be any single-stage or two-stage rockets that could do this. With a 3 or 4 stage rocket maybe? But you would be sending nearly 100% fuel off the launchpad with virtually zero payload.
Check out the "tyranny of the rocket equation". The more propellant you need to lift heavier rockets, the more propellant you need to lift that extra propellant and so on and so on.
I tried to factor in:
spoiler
- Atmospheric drag - K2-18b's atmosphere is quite dense with a huge radius:
The density of K2-18b is about 2.67+0.52/−0.47 g/cm3—intermediate between that of Earth and Neptune—implying that the planet has a hydrogen-rich envelope. [...] Atmosphere makes up at most 6.2% of the planet's mass
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Since the atmosphere is so thick and takes up a lot of mass, I've picked 500km as the low orbit altitude (comparing to Earth's ~100km Karman line, it makes you appreciate how thin our atmosphere is ).
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Rotational assist - I'm assuming it's tidally locked since it orbits so closely to its star (33 day years), and so you wouldn't get the assist from rotation like you do on Earth:
The planet is most likely tidally locked to the star, although considering its orbital eccentricity, a spin-orbit resonance like Mercury is also possible.