Abstract
Summary Core sampling is one of most important methods for gaining knowledge on formation properties below the seafloor or for extracting such potential new energy resources as methane hydrates. The riser-equipped deep-sea drilling vessel Chikyu carries out scientific expeditions for such underwater formation core drilling to analyze the origin of hydrate generation near the coast of Japan. Among the various systems available, continuous coring using wireline is the most promising for obtaining a steady supply of core samples. Although measuring-while-drilling/logging-while-drilling (MWD/ LWD) methods are deployed, an advanced directional control system specifically for deep-sea coring is currently under technical development. Core barrels consisting of the inner and outer barrels have been designed with an inner barrel that is retrievable and resettable. The new method combines an adjustable bent-housing sub that is located between the outer barrel and just above the inner core tube. Laboratory tests in which the inner barrel is passed through the bent housing section have been performed, with results showing bent housing angles of 0.25-2.0°. Land drilling tests with the bent housing were also performed in order to ensure drilling efficiency and core recovery. This paper presents the progress of our newly developed coring system with an integrated analysis of directional-drilling and coring capabilities.
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