Greendykes Bing: was the shale industry energy efficient?

The landscape of West Lothian is littered with these enormous spoil heaps. The y are a relic of the Victorian shale oil industry that meant that Scotland was exporting more oil than any other nation at the time. The spoil heaps are called bings. This one is estimated to contain 15 million tonnes of waste. Another statistic is that 7 tonnes of waste rock were produced for every 10 barrels of oil. I looked up the energy in a barrel of oil https://en.wikipedia.org/wiki/Barrel_of_oil_equivalent I'm using 6 x 10^9 Joules. So 10 barrels would produce 6 x 10^10 Joules. Energy would be needed to bring the 7 tonnes of rock to the surface. If mgh = 6 x 10^10, using mass = 7000kg you get a mine depth of nearly 1000 km. Even allowing for heat energy used in the extraction process, it seems as though the oil would be worth the energy expended collecting it. Here's a lovely film showing the bing in all its glory https://www.youtube.com/watch?v=v5wiv5zobAQ