Using multilateral technique to retain deep horizontal pilot wellbore in Xinggu7-H208

Usually horizontal pilot wellbore is abandoned by cementing and sidetrack drilling. But in some deep blocks as Xinggu7 block, the construction time of the horizontal pilot wellbore is long and the cost is high, and the pilot wellbore is useful. In response to these factors, by the application of casing program optimization, window cutting and well construction management in deep impure granite formation that is cased with thick wall casings of high grade, well path control measures of multilateral horizontal borehole and up-casing down–barehole inside–inserting cementing technique, multilateral technique is successfully used in Xinggu7-H208 well to retain pilot well, and the sidetrack point is within ?244.48 mm casing in the buried hill reservoir. In the process of field implementation it is proved that the existing window milling tools are not suited to the formation whose hardness class is 8 or above, and the milling operation is completed by the renewal of whipstock, more trips of milling tools and secondary rock milling by bit. The target vertical depth of Xinggu7-H208 is 4000 m, and the pilot section is 875 m long whose drilling period is 43 days. As Xinggu7-H208, in some deep horizontal well using multilateral technique to retain pilot wellbore can avoid much waste of drilling cost, which is of promotion of value.