BHP Billiton managing director Andrew Mackenzie says the shale oil and gas revolution will not be as widespread as was thought when the company spent $US20 billion buying into the sector in the US, meaning investment opportunities the company had hoped to pursue have not appeared.While the company has not stepped back from its belief in the areas it bought into in 2011 under former chief Marius Kloppers, attractive investments elsewhere have been few and far between.“At the beginning of the shale revolution, we would have considered the attraction of shale meant it had the potential to compete against opportunities in conventional petroleum,” Mr Mackenzie told The Australian.“The thinking was that this was going to become a global phenomenon and offer a range of opportunities beyond our initial investment in the US.”But a review of opportunities has shown this is not the case.“Our current analysis of shale potential, beyond the areas we currently own, is less attractive for future investment than we thought in the early stages,” Mr Mackenzie said. The position is a big shift from the enthusiasm the company showed for shale after spending $US5bn to buy the Fayetteville gas assets of Chesapeake in Arkansas and $US15bn to take over Petrohawk to buy the rest of its portfolio, containing oil-rich assets in the EagleFord and Permian regions of Texas.In November 2011, after BHP had bedded down the Petrohawk takeover, then oil and gas chief Michael Yeager told investors BHP would be looking internationally for shale opportunities.“It’s irrefutable that the shale business is a game-changer for energy supply across the US for the next 50 years,” Mr Yeager said at the time. “We think its irresponsible for this corporation to not be a part of that game-changing aspect that’s going to be not only here in the US, but worldwide.”The new position on shale is also a poor reflection of the potential of Australia, where BHP had been investigating potential shale acquisitions and where larger international players such as Chevron and Hess have abandoned shale exploration ground.BHP’s changing attitude to shale was first publicly evident in February’s half-year profit briefings to analysts, when both Mr Mackenzie and his oil and gas chief, Tim Cutt, started referring to the shale oil boom as being “short-lived” and saying US production was close to a plateau and would start to fall within 10 years — mainly because of geology.Last September, when BHP gave its most recent oil and gas briefing, Mr Mackenzie said he would not be opposed to growing the company’s proportion of shale assets over conventional oil and gas if shale showed better returns. There is now little prospect of this.“Shale will be more constrained to the US,” Mr Mackenzie said. “To create opportunities for growth going forward, we have to increase our appetite for investment in our conventional business.”The potential investments include a $US10bn expansion of the Mad Dog field it holds in partnership with BP in the US Gulf of Mexico and acquisitions if something attractive were to appear amid current depressed prices.The comments come after BHP has slashed spending across its US shale business in the face of sliding oil prices and a company focus on productivity and conserving cash.From an original planned spend of $US6bn a year that was cut to $US4bn, BHP is now spending at a rate of $US2bn a year, focusing just on its prime Black Hawk oil ground in the EageFord shale.But BHP is not becoming less publicly enamoured with the assets it has bought in the US, maintaining it has a portfolio that includes some of the most attractive liquids acreage the Black Hawk and Permian and some of the best US gas assets that are just waiting for depressed US gas prices to come good.Still, BHP has pulled back hard in the Permian, limiting activities to retaining acreage and labelling it a medium-term play. And development of Fayetteville which BHP tried to sell last year and the Haynesville gas ground, in Louisiana, has been deferred.