Directional Casing While Drilling : Challenges and Constraints in Drilling into Carbonate Reservoir through a Dual Splitter Wellhead System

Abstract

Casing while drilling is seen as a cutting edge technology which enables operators to save time and successfully deliver a well's objective. The reliability of the system often results in the technology to be deployed in challenging environments. In this campaign, operator encountered an unforeseen layer of carbonate (thief zone) during the first well of the campaign which resulted in a change of direction in the well planning and engineering of subsequent 2 wells which were drilled through a dual splitter wellhead system. This paper will discuss on the strategies, challenges and operational steps taken to successfully drill through and cased off the said carbonate formation, by using Directional Casing while Drilling (DCwD) in dual splitter wellhead system. Casing while drilling has shown high reliability in combating top hole section drilling with fluid losses and hole stability issues. However, there are only a handful of cases worldwide where DCwD has been deployed in managing severe losses conditions such as total loss. The presented case took place in a matured development field where severe losses occurred after unexpectedly penetrating a carbonate formation in top hole section which was not experienced in any of the nearby offset wells. To mitigate the wellbore issues, DCwD was utilized for the subsequent wells. Several different approaches were taken in completing both wells in a dual splitter wellhead system. The engineering design, drilling practices, cementing strategies and best practices which were refined over time based on lessons learnt during the campaign will be shared in this paper. This information is coupled with analysis and reasoning behind each procedure that were used to complete these wells. Both wells were successfully drilled and cased off, with less time spent to combat formation related challenges compared to conventional drilling. Intended top of cement in the annulus was achieved by improving the cementing strategy which minimizes time and cost to seal the thief zone. A few new challenges emerged during the execution and these challenges are discussed and addressed in this paper. Even though there are numerous challenges in completing both wells, it can be concluded that DCwD is a viable technology in helping to mitigate wellbore issues (total loss carbonate section). The change of strategies to deploy DCwD has proven to be viable with 2 wells successfully drilled and cased off under splitter wellhead system. The concept, challenges and best practices presented in this paper will help to provide valuable reference as well as a guideline for future similar operations.