In recent years, exploration and development targets on offshore oil and gas fields have been smaller in size and deeper in water depth. Japan National Oil Corporation (JNOC) has been conducting Joint Industry Project (JIP) titled “Offshore Marginal Oil Field Development Technology” together with many Japanese private companies for the past ten years. There are 18 sub-themes in the JIP, 11 of which are related to software developments including several optimization programs for floating production systems and other 7 sub-themes are focused on new hardware developments of subsea production facilities, mooring and riser systems. In the first phase of the JIP (1985-1989), JNOC and 11 Japanese oil exploration and production companies developed the selection and evaluation program called “NEPTUNE” for offshore marginal oil field development systems up to 300m water depth. This program has 5 platform concepts (jacket, semi-submersible, jack-up, tanker and barge) and works on the IBM mainframe computer. In the second phase of the JIP (1990-1994), JNOC and 11 Japanese oil E & P companies have been jointly developing the new program called “NEW NEPTUNE.” This new program can handle oil and gas fields up to 500m water depth and as many as 9 platform concepts including tension-leg platform, compliant tower and concrete gravity platform. The new program is more user-friendly than the old one and can be operated on workstations.
The highest economic justification category for offshore production are the unmanned operations. Personnel located on offshore platforms require support facilities such as accommodation and catering facilities on the platform and helicopter and/or service boats support from onshore facilities. Even with unmanned or de-manned operations there exists a requirement to temporarily accommodate supporting facilities which would cover a minimum requirement and be designed to the ultimate safety standards. Innovative SCADA/DCS technological applications can have a direct influence on unmanned or de-manned offshore operations. In offshore applications, economic technical and safety considerations involve the cost benefits achieved by unmanned platform operations thereby providing substantial economic benefits in offshore operation. Some of the safety aspects arising from the Piper Alpha North Sea tragedy and the subsequent recommendations outlined in Lord Cullen's report are included in this study.
The paper describes a recent case of the abandonment and removal of an offshore platform in the Sea of Japan. The Agaoki-kita platform which is sustained with twelve piles where the water depth is 90 meters, consists of a steel jacket structure which weighs approximately 6, 070 tons and a topside load of 3, 520 tons weight. Firstly, the topside was cut and divided into seven pieces, and then they were transported by cargo barges to the shore for scrapping. Secondly, ten conductor pipes were cut by the explosives installed internally at 5 meters blow the seabed. All eight main piles and four skirt piles were also severed by explosives resulting in the jacket being toppled down on the seabed. Finally, four large buoyancy tanks were attached to refloat the jacket in a horizonal position, and then it was towed about 10 kilometers and sunk down to the seabed for use as an artificial reef.
Thick Miocene basaltic pile has been confirmed in the MITI “Kanazawa-Oki” well which was drilled in the Hokuriku Basin upon the eastern part of Southwest Japan backarc shelf. Utilizing refractive index of plagioclase and lithology, the upper part (500m thick) of the volcanics is correlated with the Kurokabe Pyroclastic Rocks near Kanazawa City. Seismic data estimates the volume of the Miocene basalts aroand the well to be ca. 100km3. Major constituent of the basaltic body is inferred to be porous hyaloclastite on the basis of two dimensional gravity modeling which shows a subtle positive Bouguer anomaly on the moand. Magneto- and biostratigraphy elucidates that the basalts rapidly erupted at aroand 16Ma, when Southwest Japan was rotating clockwise associated with formation of the Sea of Japan back-arc basin. The specific volcanism is attributed to tensional thinning of lithosphere considering paleoenvironment of the Hokuriku Province und geochemical data of volcanic rocks. Higher temperatures in the rift stage and subsequent gradual cooling is inferred from maturation level at the bottom of the well.
A three-dimensional basin simulator was developed to reproduce long-term processes of oil field formation. The simulator treats one-dimensional compaction of sediments, chemical kinetics of petroleum generation and maturation of organic matters, three-dimensional two-phase fluid flow, and three-dimensional conductive/convective heat flow. This paper describes details of numerical treatments of geological processes, physical properties of fluids, solids, and solid/fluid systems, and methods to solve coupled and highly nonlinear equations. Evolution of an imaginary sedimentary basin was simulated both by three-dimensional model and by two-dimensional cross-sectional one using the developed simulator for comparison. Calculated results of a two-dimensional model differed from those at equivalent cross-section of a three-dimensional one mainly because patterns of fluid flow were strongly governed by spatial distribution of lithologies. Thus, it is suggested that three-dimensional analyses are necessary in general for basin modelling.