The number of rigs drilling for Bakken Shale oil in North Dakota has dropped sharply as a result of the decline in crude oil prices, a development that may affect the state’s budget, the head of the North Dakota Department of Natural Resources said Friday. North Dakota has been one of the biggest beneficiaries of a boom in North American crude oil output, becoming the country’s second-largest producer after Texas. But a slide in crude prices threatens to slow the pace of drilling in the Bakken, where production costs are higher than for many other oil plays. Crude oil output in the state hit a record 1.18 million barrels a day in September, the latest figure available, but the number of drilling rigs has dropped from 195 that month to 186 currently, according to state data. That was down from a high of 218 rigs in May 2012. “The number one reason for the rig count drop is the lower oil price,” said Lynn Helms, director of the North Dakota Department of Natural Resources, at a news conference.