NEW YORK (AP) â¿¿ BHP Billiton expects to book charges of more than $3 billion to reflect declining values of its U.S. natural gas reserves and a nickel mine in Australia. CEO Marius Kloppers and the head of the company's petroleum division, Mike Yeager, said they would not accept a bonus this year. Global natural resource and mining companies are pulling back in many regions with so many signs pointed to a slow global recovery, particularly for China. "These are difficult times, particularly for those companies and their shareholders who are being affected by global uncertainty," BHP Chairman Jac Nasser said. "Notwithstanding the prevailing environment we are confident in the outlook for the United States natural gas market and the role our shale assets will play in BHP Billiton's portfolio." The Australian mining and energy company said that it will take a $2.84 billion impairment charge to reflect a decline in the value of its shale gas assets in the U.S. Values of U.S. gas assets have declined for the entire industry as a surge in domestic supplies and the sluggish economy 'pushed prices to the lowest level in a decade. BHP also will take a $450 million charge against the carrying value of its Nickel West assets in Australia. The company said it needed to book that charge to reflect a decline in profit margins. The company made the decision to book the charges as part of its annual asset review. The review will be completed on Aug. 22. Shares of BHP Billiton Ltd. rose by $1.22, or 1.9 percent, to $67.33 in premarket trading.