Multidisciplinary Engineering Approach and Proper Planning Enables Successful Drilling of One of the Deepest Exploration HPHT Well in the Samgori-Patardzeuli Area, Georgia

Abstract

Exploration drilling in the Samgori-Patardzeuli area started in 1974 for the Lower Eocene – Paleocene formations, during the exploration campaign oil discoveries were made in Middle Eocene sediments. The Samgori-Patardzeuli Middle Eocene delivered the bulk of the production in Georgia and is now a depeleted reservoir. Although more than 200 well have been drilled up to date, only 13 wells from them were drilled to the Lower Eocene, therefore Lower Eocene have not been studied sufficiently and gas reserves have not been estimated. Despite this, 29.97 million m3 of gas has been prodused so far from the Lower Eocene sediments. This paper describes the successful experience of drilling one of the deepest exploration well PAT-E1 on the Patardzeuli field to evaluate Lower Eocene gas reservoirs. Exploration drilling for oil and gas involves numerous risks related with limited information about geological structure and drilling conditions. Successful drilling of planned deep exploration well requires good understanding of hole stability to find the optimal mud properties, proper casing seat selection and out-of-the-box engineering solutions to reach well objectives. Multidisciplinary team, including drilling engineers, reservoir engineer, geologist, geomechanicist, petrophysicist, drilling engineer, mud engineer worked in collaboration to design and drill one of the deepest exploration well in the area. Interval from surface till Upper Eocene was characterized by offset wells, but most of decisions were made based on trial and error. Main problems in the upper sections were related with extreme borehole breakouts and severe losses, while the lower sections was known for losses and gas kick. The PAT-E1 well was successfully drilled to the main target in the Lower Eocene and penetrated down to the top of Upper Cretaceous formation with well TD at 5020 m. Elimination one of intermediate sections allows to decrease well construction time and costs with controlled risks of borehole breakouts and losses. Geological support allowed to place casing shoes in a very narrow safe interval to separate the interval of high breakout risk and total loss interval of fractured reservoir with abnormally low pore pressure. Real time pore pressure and fracture pressure prediction service in the lower sections allowed to monitor hole condition in real time and provided timely recommendations for well control. The PAT-E1 well is first deep exploration well that was sucsesfully drilled Upper Cretaceous formation on Patardzeuli field which allow to complete advanced formation evaluation and testing. Best practices developed while drilling this well will be applied for future safe drilling in the region.

Petroleum Systems in the Rioni and Kura Basins of Georgia

“…Pyrograms suggest that HI values exceeding 220 mg HC/g TOC may have been caused by contamination in boreholes drilled with oil-based mud. A geochemical log of the upper part of borehole PAT-E1 drilled in the Patardzeuli area (Korelskiy et al, 2019;Fig. 17) supports the poor (to fair) petroleum potential of the Maikop Group (Figs 16a, b).…”