BUZZ-Oil stocks: Brent falls to $56
** Oil and gas producers' shares down as Brent falls 3 pct to $56.15, its weakest since May 2009
** Brent heading for its biggest annual decline since 2008
** U.S. crude down $1.19 at $52.93
** Oil under further pressure from a survey showing China's factory sector shrank for first time in seven months in December
** Pengrowth Energy Corp falls 3.5 pct to $3.01, EP Energy Corp 3 pct to $9.8, Sandridge Energy Inc 7.3 pct to $1.76, Key Energy Services Inc 9.1 pct to $1.69
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