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In order to maximize the recovery from Low permeability tight reservoirs, several treatments are possible to remove post (overbalanced) drilling damage; however, the desired well performance has not been achieved. As an alternative Under Balanced Coiled Tubing Drilling implementation has been considered for ADNOC Onshore gas wells as pilot trial in attempt to counteract the invasion of drilling mud into the formation. The recovery of (low perm) tight reservoirs is always affected by overbalanced drilling. As an alternative solution to stimulation jobs to remove the damage (skin), which has been used widely but still not getting the desired results, Under Balanced Drilling is one of the solutions to not impair the formation while drilling thus providing clean flow area/ connection. However, considering H2S contents and limitation of Well Control Barriers for Gas wells, the conventional Under Balanced Drilling is not suitable. Considering the current challenge in sour gas environment, Coiled Tubing Underbalanced Drilling is considered for pilot implementation of 3 wells in ADNOC Onshore; in which drilling of reservoir section is carried out after running the completion and continuous underbalance conditions are maintained. This CT-UBD implementation planning included detailed planning /feasibility study and well design finalization including updating completion design. Accordingly, the well was tied-in to facilities before starting the implementation. This also included developing detailed engineering design and complete project planning including but not limited to HazID, HazOp, Engineering design, procedures finalization, contingency planning and detailed execution program. This paper will examine a detailed approach used for planning the CT-UBD job for the first time in ADNOC Group of companies covering subsurface, operational and HSE aspects that impacted positively on the project success. |
