Deepest Deviated HPHT Gas Well Drilling and Testing Challenges in an Offshore Island Case-study

Abstract

Deepest Deviated Appraisal well in Upper Khuff reservoir in a small artificial island, located about 100 KM away from Abu Dhabi shore was successfully drilled and tested. The well has been recognized as the deepest deviated well on offshore Island with highest bottom hole reservoir temperature in UAE about 375 deg F (190 degrees C) and exceeding 9000 psi reservoir pressure complemented with impurities of H2S ranging from 10-22% and CO2 between 9-20%. The challenges were immense, from designing to execution, including securing special materials for the unique well design to accommodate the sour environment of Khuff reservoir as exploring new reservoirs always counter many risks comparing to developed reservoirs. The execution was driven with the focus of maximizing the ultimate value and benefit for ADNOC, our respected partners, the community and the UAE. The field is located in the most sensitive and ecological important area and is under UNESCO Biosphere reserve. The appraisal well was successfully drilled to Khuff reservoir at a depth of 19000 ft. The well test using Drill stem test (DST string) was conducted. Multiple challenges ranging from HSE, material selection, drilling and logging tools availability, limitations and procuring them in time were overcome by utilizing the World First Integrated Zero Waste Discharge Solution in Restricted & Highly Environmentally Sensitive Areas. Another major challenge faced during the drilling deeper reservoir was mud rheology changes due to high temperatures. The logging program was tailored to overcome the challenges posed by the mud, high temperature, high pressure, sour condition and to gain maximum representative reservoir data in a reservoir where high-pressure steaks and geological unconformities were anticipated. The Drill stem test, (DST) string was successfully POOH after acquiring all the objectives from Khuff K-4 testing under above mentioned harsh environment. The zonal isolation was carried out with cement and rig was released. The drilling and testing operation was conducted with high level of cooperation and excellence accomplishing the well set objectives without (Lost Time Injury). Lessons learned are widely shared with all the teams across the region to expedite and improve on the technologies used for sour gas production. ADNOC Onshore demonstrated 100% HSE, full commitment, high collaboration and efficient outcome ensuring safety compliance for the successful delivery of this highly critical project. This paper presents the various challenges faced and overcome while carrying out the Drilling and testing of the HPHT Sour well offshore.