The stratigraphy of Late Cenozoic Niigata sedimentary basin has been examined since 1900's for exploring of oil and gas. The basic stratigraphical division was established by these works. Recent stratigraphical methods, biostratigraphies of planktonic foraminifers, diatoms and calcareous nannoplanktons, tephra-stratigraphy and paleomagneto-stratigraphy are very useful for detailed correlation and age determination. A combined method of several stratigraphies is effective for the purposes. In Niigata sedimentary basin the technique is adopted for stratigraphical studies. The history of the Sea of Japan has been discussed on the basis of field data taken from Niigata and Sado regions. The important events of geologic history are explained as following. 1) Early Miocene: the age of the eastern margin of continent, 2) Early/Middle Miocene: the age of great transgression, 3) early Middle Miocene: the age of deepening of a marginal sea I, 4) Middle and Late Miocene: the age of a deep sea, 5) Late Miocene/Early Pliocene: the age of uplifting and subsiding of a marginal sea, 6) Pliocene to Holocene: the age of climatic sea-level changes, subsiding of a sedimentary basin and uplifting of backbone ranges. The last age in Niigata region is divided into Pliocene marginal sea II, Early Pleistocene paleo-Uonuma plain, Middle-Late Pleistocene paleo-Echigo plain and Holocene Echigo plain.
During the Jomon period asphalt was used as a binder to fix a harpoon or a fishspear in its shaft, to tie a sring with a spoon-shaped lithic knife or a stone weight, and to mendbroken pottery (Figure 1). The use of asphalt began about 3, 300 B. C., saw its climax in the latter part of the Late Jomonand Final Jomon periods (about 1, 500-300 B. C.), and was suddenly abandoned in the Yayoi period.During the Jomon period, asphalt was collected only in the oil-fields along the Japan Sea side areasof the Tohoku district where it came out to the surface. Tukinoki and Komagata in Akitaprefecture and Yunodai in Yamagata prefecture are well-known locations of the surface asphalt. InNiigata prefecture oil-layers lie near the surface and, therefore, crude oil came out to accumulate inponds located on foothills and is found half-soild along the pond shore. During the Jomon period, the asphalt collected in the oil-producing areas was distributed in the whole Tohoku district alongseveral trading routes (Figure 2). Dr. Masa-aki Ogasawara from Hokkaido University started a chemical compositional analysisof asphalt. As the chemical analysis enables to source ancient asphalt, exchange networks of Jomonpeople and relationships between areas will be documented more clearly.
An ultimate goal of special core analysis (SCAL) is to provide correct petrophysical properties of a given rock sample such as relative permeability and capillary pressure. Introduction of X-ray CT scanner has revolutionized methodologies of SCAL. Namely, in-situ saturation monitoring during displacement experiments is now considered as a must so as to exclude from the measured data the influence of several experimental artifacts. For example, it was found from the CT derived saturation distribution data that waterflood performance would be very much distorted until and even after water breakthrough when the initial water saturation distribution was non-uniform. This can, consequently, lead to erroneous relative permeability curves. Another key factor that effects on the accuracy of relative permeability measurements in a laboratory is wettability. X-ray CT scanning also visualized that the waterflood performance of a Berea sandstone core plug under mixed-wet condition be totally different from that under water-wet. It provided clear 3-D images of the mixed-wet core that the water encroachment preferentially into the most porous laminae brought about the early water breakthrough, resulting in formation of no Buckley-Leverett type shock front. In such cases, application of the JBN method to obtain relative permeability, which has been most widely utilized in the oil industry, is a big question. This paper proposes core simulation technique so as to solve this problem and, hence, reach the true relative permeability.
A fully implicit compositional model is developed following the Coats approach. Although the fully implicit formulation guarantees a high degree of computational stability, it aggravates the computational efficiency due to the large number of independent variables. To relax this deficiency, a phase-stability analysis routine is included in the model. Adopting the Gibbs free energy as a stability criterion, we can estimate the number of phase present, prior to the flash calculation. If a single phase is detected, the subsequent flash computation routine can be detoured. The developed model is verified against an established model, an adaptive implicit compositional simulator, GEM. The computationa efficiencies with and without the stability analysis are evaluated to confirm the improvement in the iterative flash calculations. When there exists only one phase, the number of iterations is largely reduced by virtue of the stability analysis. In addition, even in two-phase situations. the flash computation is efficiently performed, because the stability analysis yields proper guesses. It is revealed that the stability analysis improves the computational efficiency regardless of the number of phases.