This paper describes steamflood experiments carried out using a visual reservoir model. The objective of this work was to examine the effect of gravity on the steamflood performance in an inclined reservoir. The model 45cm long by 15cm high by 1cm thick was a bakelite container having a transparent side and was filled with glass beads and saturated with the nondistillated oil. In this work, three different steamflood experiments of updip injection (dip angle=-45 degrees), downdip injection (dip angle=+45 degrees) and horizontal injection, were performed with saturated steam injection. The results were as follows: (1) The effects of gravity override and oil displacement efficiency by steam depend on inclination of the reservoir. This is reflected in oil recovery performance. (2) The experimental results describe the strong effect of condensed water on oil production performance. (3) In the case of updip injection, as augmentation of steam zone growth, the shape of steam zone estimated by the LOOKEREN's formula has been shown to be in good agreement with the observed shape.
There is a sedimentary basin filled with thick Tertiary sediments lying from the northern to southern end in Central Hokkaido. The southern part of the basin is covered by younger sediments except for the eastern marginal part. Therefore, the lower Neogene in this region has been remained unsolved in definite stratigraphic relationship. Fortunately, many wells for oil exploration have been recently drilled in this region and some of them penetrated the Neogene. These wells provided valuable informations on the subsurface distribution of the lower Neogene and the original feature of the sedimentary basin at that time. The Takinoue Formation, Early-Middle Miocene, encountered in the Nishiumaoi and Abira wells is more than 2000m in thickness and contains a warm pollen flora in the lower part, while in the eastern surface area it is usually 300-600m thick and the lower part containing the warm pollen flora is lacking or very thin. From these facts it is presumed that the formation accumulated with on-lap structure. The center of the basin has been presumed to be situated in the neighbour of the Nishiumaoi and Abira wells. However, it is clarified by the present pollen analytical study that the formation becomes thicker estwards from the wells and the thickest part is concealed under the block which was pushed up from the east by a great thrust (Fig. 8). This means that the basin was far wider than that estimated from the present distribution of the formation in the surface. Considering the distribution of the magnetic field together with gross structure of Hokkaido (Fig. 1), the author concludes the center of the sedimentary basin stretches northwards to the Uryu region, although concealed under the blocks which were pushed up by thrusts. Although many arguments have been done on the existence of the Lowest Miocene sediments in the central part of Hokkaido, it is most probable that only the Fukuroji Formation in the Uryu region falls to it (SATO, 1976). The formation is presumed from the investigation of foraminiferal fossils to have been accumulated in a bay. As the lowest Miocene is not found northwards in the Haboro and Tempoku regions the bay should have had a connection with the Pacific Ocean southwards through the Ishikari-Hidaka region; the sea connecting to the Pacific Ocean was just situated at the above-noted central part of the basin, which is now concealed deeply under the ground. Holes 438 and 439 of DSDP are situated at the southern marginal part of the sedimentary basin discussed here. Considering the result of the present study, that is, the lowest Miocene in this basin is expected to exist only in the central part of the basin, the lowest Miocene established in these Holes is presumed to be younger in geologic age.
A well control model for the numerical simulation is presented. The model bases on the Wait and Weight method, and simulates both of liquid and gas kicks. For a behavior of an influx in a well, it is assumed that the influx holds constant mass during a kill operation, and does not rise through the mud by the gravity effect. Other assumptions are as follows: 1) The bottom-hole pressure is maintained at a given value during the kill operation. 2) The influx stays at the bottom until resuming circulation. 3) The influx temperature does not change during the kill operation. Simulated behaviors of well pressures of gas kick are compared with those of liquid kick. On the occasion of the gas kick, the casing pressure rises rapidly when the gas approaches the wellhead, and falls steeply with the gas discharges. Changes of the gas discharge rate and the pit volume increment are also simulated. On the occasion of the liquid kick, the casing pressure decreases monotonously as the liquid ascends, and falls stepwise at the liquid discharge. The model is written in BASIC, and small units of programs are linked successively by “R” option to be adapted easily to a small memory capacity computer such as PC-8001.
At the Iwafune-oki oil field which is located offshore Niigata Prefecture, multiple layers of sandstone forming a thick wedge exist at the lowermost portion of the Nishiyama Formation and a stratigraphic and structural combination trap is formed on the southwest nose of the Iwafune-oki anticline. The sandstone is interpreted to have been deposited as turbidite under the upper to upper middle bathyal environment, from the results of the analyses of fossil foraminifera and lithofacies on the core samples. The examinations of the lithofacies based upon the classification proposed by MUTTI and RICCI LUCCHI (1972) indicate that the sandstone possess the characteristics of middle to outer fan. Taking the information on paleocurrent and paleobathymetry into consideration, the writers experimented with modelling of a small submarine fan on the sandstone isopach map derived from the seismic records, well logs and geological information of the wells and the conclusion was that the fan must have grown northward. It is inferred, based upon the examination of the lithology of the gravels contained in the sandstone, that the source material of the sandstone was supplied from the east or southeast mountainous area far from the offshore oil field. The same source may be said for the sandstone of the Shiiya and Nishiyama ages located around the Shintainai and Nakajo gas fields onshore, possibly through the same feeder channels.