As multilateral applications evolve into the mature stage, this paper looks at the role and field performance of mechanical trip retrievable whipstock's (MTRW) in the Middle East. Although more sophisticated multilateral tieback systems are gaining acceptance, the MTRW is economically extending the life cycle of old wells and provides the lowest cost method to drill multilateral's through casing in new wells.
Whipstock's and multilateral's have been applied in the oil industry for well over a half century, yet it was not until the mid 1980s that their mutual features were brought together to provide benefits that operators enjoy today.
Since 1992, the use of these technologies in the Middle East has seen significant growth to the extent that the Middle East is one of the most active areas in the world for multilateral applications. In the U.A.E., Egypt, Oman, Pakistan, Yemen and Saudi Arabia, retrievable whipstock's are being applied in multilateral drilling and workover operations. (Fig. 1) Their use is integral to overall objectives that extend the life cycle of vertical wells, increase oil production, eliminate water coning or improve oil recovery.
Although the benefits of multilateral technology are well documented, a popular application is for new well situations where the lower lateral is drilled and completed with a combination slotted liner and production packer. The second lateral is drilled from the casing bore above the production packer in the same formation but different direction. Optionally, laterals 3&4 are drilled from the casing bore in different formations and directions as required. Multilateral completion's require retrieval of the MTRW while single laterals may or may not require retrieval. (Fig. 2)
Even though whipstocking procedures are fundamentally the same world-wide, each area has developed variations that realize differences in casing sizes and grades, formation hardness, depth, lost circulation, deviation, etc. Procedures in the Middle East have been 'fine tuned' over the past three years to the point that an average job takes 2.5 days to mill the window and 1 day to retrieve.
Well Preparation: To insure a trouble free run with the MTRW, it is important that the well bore is free of internal restrictions. A taper mill with an O.D. equivalent to the casing drift and a casing scraper is run before running the MTRW.
Casing couplings need to be located either by CCL or correlating D.P. to casing tally measurements so that milling through a coupling is prevented.
To prevent cuttings from fouling the setting mechanism, it is preferred to displace a 200 foot high-vis gel pill above the plug or packer that the MTRW will trip on.
BHA #1. Once the well bore is prepared, the whipstock and starting mill is made up as follows: MTRW, starting mill, bit sub, 1 jt. drill pipe (DP), orienting sub or MWD, drill collars (DC) or HWDP as applicable and DP to surface.
On surface, orient the MTRW to face "high side" of directional equipment and RIH at 1 hr/1000' to 20' above "bottom." At this point, orient the MTRW to its planned direction and continue lowering to within 5' of the plug. Re-check orientation and then set down 6000 - 8000 lbs to active the MTRW. The whipstock can be raised to the planned setting depth or left on top of plug.