Abstract

Exploration has evolved in Western Siberian Fields in recent years, due to demands to maintain production capacity driven in part by increasing energy consumption. The frontiers have therefore extended into the Arctic regions and to the deeper unconventional formations. To ensure a high degree of reliability, safety and efficiency, a more integrated and high-tech approach has been demonstrated to be essential when planning and executing the drilling and testing phases for such complex environments. At the exploration stage the quality of the acquired data must be high to achieve maximium value.

Previous exploration work on the Bolshekhetskaya Depression in Yamalo-Nenets Automonomous Area confirmed the geological complexity of the Jurassic and Achimov formations. The deep bedding, low formation permeabilities, abnormally high formation pressures, and complex geomechanics have made the previous well tests with conventional methods unachievable.

The 2011P exploration well of the Pyakyakhinskoye field was drilled at 4800 m and featured initial reservoir pressures up to 980 bara with the average permeability of the Jurassic formations less than 0.1 md. Such a combination makes the well unique. As a result of this complexity, an integrated well testing approach was chosen, which included a cased-hole completion with packer and a high-pressure Drill Stem Test (DST) string.

This paper presents the 2011P well test planning and execution for the Jurassic and the Achimov Formations of the Pyakyakhinskoye Field, in which four zones were sucessfully tested. The subsurface and surface equipment, well test data quality control (QA/QC), and the pressure-transient analysis are discussed herein. The geological data set included verified initial reservoir pressures and temperatures, horizontal permeability, and downhole fluid sample data. This enabled commercial reserve values to be fully obtained for the first time in the Jurassic and Achimov Formations of the Bolshekhetskaya Depression. The obtained results demonstrate the chosen equipment layout is fully applicable, this selection of equipment and lessons learned will allow execution of more efficient well testing jobs in the future.

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