High-Impact-Resistant Cement Allows Challenging Sidetrack in Abu Dhabi

Abstract

The process of sidetracking an existing borehole with a balance cement plug has historically been time consuming and problematic for the drilling industry. The formations in the Middle East are classified as some of the most competent formations in the industry. These formations present its own challenges when attempting to sidetrack because of changes in the drilling trajectory. Historically, the operator has faced problems sidetracking in the Shilaif formations, where longer drilling time and/or numerous cement plugs are required to achieve this objective. These requirements lead to an increased in drilling costs. Traditionally, a conventional cement system with a high compressive strength is used for sidetracking purposes. However, these cement systems have low resistance to impact and shock and hence will fail through rupture when placed across the competent formations. An optimized particle sized distribution cement system, combined with engineered metallic micro ribbon technology has allowed the sidetracking to be achieved efficiently. The technology improves the durability and the resistance of the cement to load bearing capacity and fracture propagation. Further laboratary testing comparisons have confirmed the enhanced mechanical properties of this cement system. As a rule of thumb, the industry relied on the rate of penetration (ROP) as an indicator of how good a cement plug is for sidetracking purposes. It is believed that the lower the ROP is, the easier the sidetrack can be achieved. As the technology is "tougher" than the formations, the drilling bottom hole assembly (BHA) can be deflected/ sidetracked efficiently and drilling operations resumed, in a shorter period of time compared to using conventional cement systems. Introduction Setting cement plugs is an operation commonly performed while drilling the well. The objectives of the cement plugs are generally eitherplugging back an existing open hole to ensure zonal isolation orsidetracking the wellbore to change the well trajectory The process of spotting a cement plug to facilitate a sidetrack can be challenging. Problems related to this operation have been well documented in the industry 1,2,8. Some of the problems frequently encountered are:Cement plug sinking or stringing out from the wellbore while pulling out the cement tubingSoft, unset cement due to fluids contaminationExcessive wait on cement (WOC) timeLow compressive strength cement systemCement plug rupture Today as the industry is drilling more challenging wells to reach complex reservoirs, it is also faced with increasing costs associated with the drilling operations. Therefore any failures of the sidetrack cement plugs will result in job repetition, which can lead to extra rig time and costs to the operator. Many studies and advancement have been successfully made to improve the success rate of placing a sidetrack cement plug 1–3. Despite improvements in the process and better selection of proper conventional cement system, problems are still encountered while sidetracking. This is especially true in certain formations that are harder and tougher than the cement system. Therefore, there is a need for a sidetrack cement plug that exhibits greater strength and resistance compared to the conventional cement system. This paper describes a new cement system that has superior properties compared to conventional cement slurry, further optimizing the mechnical durability of the set cement. Field case histories are presented illustrating the success of the new cement system in sidetracking wells for a major operator in Abu Dhabi.