Gas Venting Stations: What's The Big Deal?
Gas venting stations sometimes release natural gas at extremely high pressures, so there is a risk of strong updrafts or turbulence. In any case if you fly directly over you may be going through a cloud of combustable gas which could possible ignite. It's a low risk, but given it's rarely a problem going around them it would be my advice to do so. 

I've flown over one without realizing and it put me in a 1200ft climb, I had to cut throttle in a hurry and dive to stay out of the London TMA. After that I paid attention to them.