This paper describes application of openhole sidetrack (OHSDTR) technique to drill deep gas multilateral horizontal wells in Saudi Arabia. The drawbacks of earlier whipstock exits were studied and an alternate technique was proposed and implemented.
The typical approach to drilling Khuff dual laterals was to drill the lower lateral and then set whipstock, and cut a window in the base Khuff-B and drill the upper lateral. Various problems observed using this technique were:
Problem setting whipstock.
Premature setting while running in hole
Problem cutting the window. Mill twist offs leading to a long fishing operation; in some cases setting another whipstock and cutting another window.
Milling the top of the whipstock while cutting the window leading to a severe problem in retrieving the whipstock.
Whipstock from different companies were tried, however, we could not get rid of multiple failures while milling and retrieving the whipstock. Even with modifications, a new whipstock system was tried in which milling was done in two parts; a first run with the milling machine to mill only the casing, and a second run with different mills to cut the window through to formation, but problems continued. Saudi Aramco and Schlumberger D&M came up with the idea of drilling dual laterals using an OHSDTR technique to avoid complication due to whipstock failure. Well HRDH-XYZ was the first successful dual lateral horizontal Khuff-C gas producer drilled with the open hole sidetrack technique, in a record time of 98.8 days against the 165 days planned, the technique saved $975,000 and two weeks of rig time.
This was a step change in drilling practice, to drill dual laterals saving considerable rig days to Saudi Aramco, and removing the time consuming whipstock operation to the extent of losing the well, due to unsuccessful whipstock retrieval. This technique brought a transformation in the way dual lateral wells were drilled in deep gas drilling in Saudi Arabia, later on similar technique was applied in drilling dual laterals in Khuff-B reservoir as well. Since the introduction of this technique on well HRDH-XYZ, 50 wells have been drilled successfully saving (approximately) 735 days to Saudi Aramco. This paper further details challenges; lesson learnt and success story about introduction of Open Hole Sidetrack in deep Gas drilling.