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Due to the declining reservoir pressures in some of its onshore gas carbonate fields, ADNOC decided upon an initial 3 well UBCTD, (Underbalanced Coil Tubing Drilling), campaign in its onshore Asab and Bab fields, with 2 wells to be drilled in Asab and 1 in Bab. Both target fields have high H2S concentrations up to 6% and ADNOC undertook the necessary candidate selection process, Basis of Design, and equipment selection to enable them to drill these wells using UBCTD techniques. Due to the high H2S content, it was required that a closed loop system design was implemented, which was the 1st successful one implemented in the Middle East. The project's given objectives were analyzed, and the planning was conducted considering the different aspects to achieve ADNOC's objectives and expectations. Several challenges were faced during the designing phase which had to be resolved prior the operations start-up. These challenges included extended drilling reach, closed loop returns handling system, handling high H2S levels at surface amongst others. One of the main design objectives, the drilling reach, was improved by optimizing the trajectories Dog Leg Severity, (DLS), and Bottom Hole Assembly, (BHA), configuration. Instead of a conventional mud motor, a turbine was used to give power to the bit and allowed having a lower Weight on Bit, (WOB), to drill the formation, thereby increasing the depth of the section. The trajectory was planned in a way to maximize the reservoir contact within the production layers and reduce footage in the non-productive zones between the producing formations, therefore maximizing the well productivity. Increasing the well production was key to the project economics and to prove the value brought by the UBCTD to ADNOC's hydrocarbons production. Several business disciplines collaborated closely under the IWC, (Integrated Well Construction), stewardship to provide practical solutions and design a system specifically tailored to achieve the objectives and overcome the various challenges associated with this project. The final solution was a closed loop system capable of:removing solids/drilled cuttings from the system.measuring flow rates of different fluid phases (gas, condensate & water).treating and removing H2S.exporting gas and condensate to ADNOC's production facility.whilst drilling the well in Underbalanced conditions. After the operations start-up on the 1st well, the returns handling system was modified to improve the efficiency and enhance the safety of the personnel and equipment. This paper will discuss the design and planning involved in the successful drilling of these three wells and the operational challenges and mitigations encountered while drilling.
Due to the declining reservoir pressures in some of its onshore gas carbonate fields, ADNOC decided upon an initial 3 well UBCTD, (Underbalanced Coil Tubing Drilling), campaign in its onshore Asab and Bab fields, with 2 wells to be drilled in Asab and 1 in Bab. Both target fields have high H2S concentrations up to 6% and ADNOC undertook the necessary candidate selection process, Basis of Design, and equipment selection to enable them to drill these wells using UBCTD techniques. Due to the high H2S content, it was required that a closed loop system design was implemented, which was the 1st successful one implemented in the Middle East. The project's given objectives were analyzed, and the planning was conducted considering the different aspects to achieve ADNOC's objectives and expectations. Several challenges were faced during the designing phase which had to be resolved prior the operations start-up. These challenges included extended drilling reach, closed loop returns handling system, handling high H2S levels at surface amongst others. One of the main design objectives, the drilling reach, was improved by optimizing the trajectories Dog Leg Severity, (DLS), and Bottom Hole Assembly, (BHA), configuration. Instead of a conventional mud motor, a turbine was used to give power to the bit and allowed having a lower Weight on Bit, (WOB), to drill the formation, thereby increasing the depth of the section. The trajectory was planned in a way to maximize the reservoir contact within the production layers and reduce footage in the non-productive zones between the producing formations, therefore maximizing the well productivity. Increasing the well production was key to the project economics and to prove the value brought by the UBCTD to ADNOC's hydrocarbons production. Several business disciplines collaborated closely under the IWC, (Integrated Well Construction), stewardship to provide practical solutions and design a system specifically tailored to achieve the objectives and overcome the various challenges associated with this project. The final solution was a closed loop system capable of:removing solids/drilled cuttings from the system.measuring flow rates of different fluid phases (gas, condensate & water).treating and removing H2S.exporting gas and condensate to ADNOC's production facility.whilst drilling the well in Underbalanced conditions. After the operations start-up on the 1st well, the returns handling system was modified to improve the efficiency and enhance the safety of the personnel and equipment. This paper will discuss the design and planning involved in the successful drilling of these three wells and the operational challenges and mitigations encountered while drilling.
ADNOC Onshore initiated a pilot implementation of Under Balanced Coiled Tubing Drilling technologies for Gas Reservoirs with this being the first time in the ADNOC Group of Companies. Detailed planning was carried out for this project implementation and the onward optimization for the 3rd well based on lessons learnt was carried out. This 3 well pilot Underbalanced Coiled Tubing Drilling, UBCTD, pilot campaign involves the sidetracking from a pre-drilled 6" hole and then drilling 3-¾" laterals with the laterals drilled in a carbonate gas reservoir utilizing UBCTD technology and methods with these being applied to eliminate formation damage, enhance production, and improve drilling performance.
With the depletion of reservoir pressure in low permeable formation, drilling (overbalance) always become challenging and thus the productivity due to high invasion. In order to opt the unconventional solution to maximize the recovery, it requires integrated approach such as underbalance coil tubing drilling with closed loop. The reason for opting the coiled tubing rather conventional underbalance drilling is due to high H2S in reservoir and closed loop system added to reduce emissions during projects. Since the world demands more energy with less emission, Under Balanced Drilling is one of the solutions to prevent formation damage while drilling alongside of production from well. The UBCTD (Underbalance Coil tubing Drilling) planning requires detailed feasibility study, well configuration design along with completion design. Extensive safety reviews of all the surface network and equipment was conducted to minimize the risk of operations. Live Real time data accusation, remote well control system, continuous Nitrogen purging for handling of highly volatile condensate & H2S & SO2 dispersion modeling were conducted and implemented for successful operation. ADNOC successfully conducted first trail of technology on one of the operating brown field. The well was freshly drilled, cased and cemented to the top of desired formation. The rig was released after running the completion and later coiled tubing brought to site to drill three lateral hole through specially designed BHAs (Bottom Hole Assembly) and maintaining continuous underbalance conditions. Selection of appropriate material from sub-surface to surface equipment's is the key consideration for success of project. The well was drilled under-balanced to allow wellbore cleaning and returns (drilling / formation fluids) were routed to closed loop separation system. The produced gas & condensate was routed towards plant via the production line through compression system. The drill cuttings dumped to the mud pits and the drilling fluid was re-circulated. Flaring of high H2S & CO2 gases impacting the environment were totally removed. Three laterals were drilled successfully with coil tubing underbalance drilling technology, the well was successfully tested with almost triple production from conventional lateral drilling. Further evaluation is in progress to develop the reservoir through technology. The trials proved a success in developing the depleted tight reservoirs with no Flaring thus saving environment and enhancing the productivity. This paper will elaborate the integrated approach for planning UBCTD (Underbalance Coil tubing Drilling) operation without flaring considering the operational, Safety and subsurface aspects. Furthermore, it will highlight, how the pilot technology can contribute towards ADNOC strategy towards net zero emission as one of the key pillars of sustainability.
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