New Technique to Sidetrack Across Hard Formation in North Oman

Abstract

In a north Oman field, it is common practice to cement vertical pilot holes up to the kickoff point. A cement plug is then used to initiate the sidetrack through extremely hard formations. Previously, it has taken several attempts to sidetrack these holes and, in some cases, a mechanical whipstock had to be used.There are challenges when trying to initiate the sidetrack because the formation hardness far exceeds that of the kickoff cement plug. As a result, the sidetracking assembly is repeatedly directed back into the relatively softer cement plug (i.e., vertically). Gravity also plays a role to some extent in bringing the sidetracking assembly back into the vertical hole, increasing the challenge.This paper documents successful implementation of modifications to the slurry design and cementing procedure, as well as the successful use of a side-tracking method/technique in North Oman.The compressive strength of cement has been increased from 5,000 to around 9,000 psi for standard, 17-lbm/gal, Class G cement.The effect of oil-based mud (OBM) contamination has been examined and spacer designs have been improved to help ensure good mud displacement while performing cementing operations.The sidetracking method and tools have also been improved with impressive results. This includes proper selection of the kickoff point based on the drill-speed log of the vertical pilot hole, selecting the correct combination and configuration (e.g., outside diameters of components and angle setting) for the bottomhole assembly (BHA), and using the correct application parameters and techniques while initiating the sidetrack, which is also called "time-drilling." This paper investigates the new techniques applied in detail and clearly illustrates their development. Some case histories are also presented.