Royal Dutch Shell's earnings for the second quarter declined, mainly due to impairments.The oil's giant's earnings, on a current cost of supplies (CCS) basis, dropped to $2.4bn from $6.0bn for the same quarter a year earlier.The company blamed higher costs, exploration charges, adverse currency exchange rate effects and challenges in Nigeria."These results were undermined by a number of factors - but they were clearly disappointing for Shell," said Chief Executive Peter Voser. Oil theft and disruptions to gas supplies in Nigeria have been causing widespread environmental damage, and could cost the country's government $12bn in lost revenues per year.Voser said the group will play its part to help the government but "these are problems Shell can't solve alone".Cash flow from operating activities for the second quarter came to $12.4bn, compared with $13.3bn last year.The cash flow helped pay for Shell's dividends and investment in new projects, Voser added.Capital investment was $11.3bn for the quarter, while total dividends distributed were $2.8bn.Shell is paying a dividend for the second quarter of $0.45 per ordinary share and $0.90 per American Depositary Share, a 5.0% jump on the prior year. RD