There is always gas when oil is discovered (gas is embedded in the oil and releases as it rises up towards the surface due to decreasing pressure), but gas can be present without oil.
So, I would say if a flare stack is going up then that is a sign that testing will begin, either for oil/gas or gas. It's likely a requirement from Israel that gas is burned during testing and therefore installing a flare stack is simply in prep for testing.
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