Fun game but there are further shortcomings that deserve mentioning:
1.After playing about half of each area, all the juicy spots are gone and you have to slog through half-empty plots for the remainder. It kills any sense of progress having to spend hours drilling the tiniest patches and barely making a profit, right after having made 100k drilling in the land of plenty. Especially when you know the next five levels will be the same.
2. There is no reward for being quick (besides a very minor money-back mechanism) It is always trivial to mine all oil well within the time limit so the optimal play is to hold back on upgrading your pipes to save money. This also makes most speed upgrades (e.g. faster drilling) a complete waste of money. Why not have enough oil on each level that you cannot mine it all in time? Then there is an actual incentive to mine faster. Then diffentiate the different plots not by amount of oil but fx density and size of the oil and gas patches.
3. The AI for oil carts is terrible: expect carts to drive to unconnected rigs when your active ones are spilling, and to see a handful of almost empty carts leave your only rig so you have to manually buy new carts every few seconds until the initial group returns.
4. Small oil and gas patches often become unreachable because you have a pipe ending right next to them, blocking any other pipe in the area.
5. The gas mechanic is awkward at best. And half of the mechanic is useless since it speeds up your mining instead of increasing profits, which means it's like throwing away money.
6. The mini game for buying plots becomes inane: The best plot is often obvious and the gameplay amounts to clicking the same spot repeatedly until the AI buckles and picks another. Which on my old IPad 3 takes about a minute of laggy animations.
I see a lot of potential but there sure is room for improvement. Right now it feels a bit like a bunch of ideas thrown together and not really working as a whole. A Blizzardesque amount of play testing and fine tuning of mechanics would have done wonders.