By Ali Lyon Shell kicked off a $3.5bn share buyback programme today as it posted better-than-expected numbers for the second quarter despite a previously announced $2bn (£1.6bn) impairment and a slide in revenues. The London-listed oil major reported adjusted earnings of $6.3bn (£4.91bn) for the three months to June 30, beating analyst consensus of $5.9bn (£4.6bn). Revenue was down quarter-on-quarter, falling 19 per cent from $7.7bn in the first quarter, as lower liquified natural gas trading and refining margins, and a weaker oil price led weighed on the firms earnings. The dent to earnings a…