Drilling of HP / HT well have been always challenging due to contrast in formation pressure. These challenges become more complex particularly when drilling a formation of high H2S content. Kuwait has a structure of very high H2S content (20%-35%), located in the North Field which are drilled and developed under extreme precautionary measures considering the highest potential risks on simultaneous operations and infrastructures in the area. Formations of this structure are deep (13000 – 17000 ft) and naturally fractured reservoir with very low porosity and permeability. Since the reservoir is rated as HPHT and sour, it was a highly challenging experience to manage drilling operations and preventing well control situation. Unfavorable conditions such as high pressure, high temperature and high H2S content require special attention on appropriate mud weight balancing formation pore pressure, mud loss scenario and availability of ready to use adequate quantity of LCM pill to prevent well control situation through integrity of surface equipment such as well head, kill line, choke manifold, high pressure cementing unit, BOP and H2S Management Plan. During drilling of the targeted formations at one of the wells, a severe mud loss situation was encountered followed by H2S alarm and subsequent Well Control Scenario, which brought forward weakness in confirming wellhead integrity due to lack of secured system for periodical BOP function test. The situation was brought under control through well-coordinated effort without causing any injury to the crew at site. The several simultaneous operations (SimOps) like drilling, well servicing, hydrocarbon processing, gas injections etc at nearby facilities such as wells, flowlines, pipelines, manifolds, ESP, rigs, processing facilities makes the matters further challenging, which needs to be cautiously managed without aggravating the situation. Aim of this paper is to describe the actual challenges encountered and lessons learned from HP / HT extremely sour well under well control scenario with complex SimOps environment. This paper also aim to present techniques and approach adopted to address the operational risk and HSE issues for BOP functional test, wellhead integrity, mud management priority supported with comprehensive H2S management program.


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