Development of the Waste Mud Treatment System for Drilling Vessel "CHIKYU"

Abstract

The deep sea drilling vessel "CHIKYU" was completed in July 2005. The mission, which will be carried out with "CHIKYU ", is to gather geologic core samples under the seabed at the sea of deep water depth. The core samples and the drilled holes from which the core samples will be gathered will be used for the scientific studies to make clear the global environmental change, earthquake outbreak mechanism and biosphere under the sea-bed. The studies for these areas have been carried out under a scientific plan of Integrated Ocean Drilling Program (IODP). It is necessary to gather core samples from a deeper formation so that we can make these studies succeed Riser system and mud circulation system have been adopted to "CHIKYU " in order to gather core samples from a deep formation under the seabed. This is one of the drilling technologies used in the oil industry to enable drilling deeper. The mud circulation system is a system to circulate mud between drilling vessel and drilled hole. Risers are used as a return line of mud from the drilled hole. Mud is liquid of high specific gravity and high viscosity, and takes a lot of important roles, such as keeping the pressure balance between in and out of a hole, carrying the cuttings from a well out, protecting the wall of a hole, and so on. This means that mud circulation is be able to stabilize a well and as a result enables great depth drilling. On the other hand, mud circulation generates drilling waste such as waste mud and cuttings on board. In the oil industry, the drilling waste is usually abandoned into the sea. However, in late years the interest for an environmental problem has risen, and a standard of underwater abandonment of a drilling waste tends to become severe. In response to this situation, we decided to treat waste mud and cuttings adequately on "CHIKYU" as our policy from the viewpoint of environmentally friendship. "CHIKYU" is the first drilling vessel that has facilities to treat drilling waste called Waste Mud Treatment system. The drilling waste is classified to three kinds, waste mud, drill drain and cuttings. The mud used on "CHIKYU" is water base mud with a few exceptions. The principal ingredients are barite and bentnite basically. The drill drain is the thin muddy water that is occurred by washing of equipments for mud circulation. The cuttings is transferred to "CHIKYU" through the riser with mud, and they are separated from mud using shale shakers. The Waste Mud Treatment System consists of three sub-systems in correspondence with them. The waste mud is treated as follows. Firstly, solids in mud are cohered by chemicals. And the cohesion thing is squeezed by a screw press. The squeezed liquid from the cohesion thing is treated with drill drain together. The drill drain is thickened being heated, and thickened drill drain is treated with waste mud together. The solid squeezed from waste mud and the cuttings are stabilized with cement. In this way, the Waste Mud Treatment System has realized zero discharge of a drilling waste from "CHIKYU". This paper describes the summary of the Waste Mud Treatment System.