Colombia's oil reserves had risen 2.9 percent to 2.445 billion barrels by the end of 2013, up from 2.38 billion barrels a year earlier, taking reserves to their highest despite a missed exploration target, the energy ministry said on Monday. Foreign investment into the Andean nation's oil and gas sector has surged in recent years and the government is preparing to tap non-conventional or shale resources offering such blocks in its 2014 oil auction which concludes in July. Though security has improved massively in the last 10 years due to increased military pressure on the leftist FARC and ELN guerrilla groups, the rebels have intensified bomb attacks on oil pipelines, with 259 attacks in 2013 alone, the oil industry association said.