Step Change in CTD Strategy of Multilateral Drilling Using Under-Balanced Coiled Tubing Drilling (UBCTD) Technique in an Onshore Sour Gas Field-UAE-Case Study
Authors: Osama Mohamed , Sumaida Ali Sulaiman Bin , El Shahat Ayman , Al Mutawa Ahmed , Almazrouei Saeed , Saleh Abdalla , Yousfi Fawad Zain , Ali Almteiri Nama , Baslaib Mohamed , Deshmukh Rohit V. , Solaiman Tarek , Abdulsallam Fouad , Mantilla Alfonso , Ladmia Abdelhak , Rangel Pedro , Rennox John , Cui Shuai , Jumagaliyev Yerlan , Basha Maged 
Published: March 2024

Abstract
The Oil and gas industry is facing increasing demands that require new business models to sustain and maximize our resources to serve and support humanity's needs across the globe. The United Arab Emirates is seeking to become self-sufficient in gas supply by 2030. This has led the country to initiate several exploratory and appraisal projects to achieve this goal. This study covers one such pilot project targeting production from tight gas reservoirs in three wells through a coiled tubing (CT) underbalanced drilling (UBD) project in an onshore field.
The technology directly serves the operator's visionary objective by sustaining production and meeting the energy mandates that would reduce the number of rig years.
The Under Balanced Coiled Tubing Drilling (UBCTD) technology has a globally proven record of enhancing the production rate compared with conventional overbalanced techniques.
The lateral length is limited due to buckling and lock-up of the coiled-tubing string, hence the multilateral drilling can overcome this limit and increase the well drainage compared to long horizontal sections. Implementing CTD with Multi-Lateral overcomes CTD limitation need for a single extended reach horizontal hole as conventional drilling, due CT lower Buckling limit, thus shorter lockup depth and reach in comparison with Conventional Horizontal Section.
Detailed planning was carried out for the technology implementation and there were many challenges in the operations, nevertheless, this is the first project of it is kind for the operator company The lessons gained from daily challenging operations are considered the stepping stones for the technology implementation in Abu Dhabi.
The technique for multilateral drilling is characterized according to definitions established in 1997 during the Technology Advancement of Multilaterals (TAML3) Forum held in Aberdeen. These standards classify junctions as TAML Level 1, 2, 3, 4, 5, or 6 based on mechanical complexity, connectivity, and hydraulic isolation. In UBCTD wells, the most common multilateral technology is with TAML level 1, which is done by open-hole sidetracks with barefoot completion.
Comprehensive planning and simulations were done to overcome the challenge of different reservoir pressures, wellbore instability, and the absence of side-track operations history with CTD.
Multilateral drilling with CTD proved to be successful, one UBCTD well completed, yielded gas production rates around two to three conventional wells.
The UBCTD pilot was extremely successful in all aspects compared to the pre-set success factors as directed by the feasibility study that defines the following success criteria:Adhere to Healthy Safety and Environmental Considerations.Drill 4000 ft using CTD.Drill the well laterals completely underbalanced.Achieve a 1.6-2 times production increase compare to Conventional Well.
This paper shall spotlight the project challenges and learnings gained from coiled tubing drilling (CTD) in all drilled wells and focus on a multi-lateral game plan to meet the project objectives.