Gulf Keystone has started drilling its Shaikan-2 appraisal well in Kurdistan as part of a programme to significantly increase reserves.So-called P90 volumes - a low-case resources estimate with a 90% probability of being realised - are currently at 1.9bn barrels of oil in place."In the upside case, we would, of course, also hope for a further upward movement of our P10 volume which is currently independently estimated at 7.4bn barrels of oil in place," chief operating officer John Gerstenlauer said Wednesday.Drilling and testing at Shaikan-2, the explorer's first deep appraisal well on the Shaikan structure, is expected to take six months.Gulf Keystone has an effective 75% working interest in the Block and is partnered with the MOL subsidiary, Kalegran, which has 20% and Texas Keystone International with the other 5%.