In this paper, resistance against flow of polyacrylamide solution through porous media is analyzed in comparison with viscosity measurements through capillary viscometer. Resistance against flow of polymer solution through porous media is not caused only by viscosity of polymer solution, but also affected by energy dissipation due to the rarefaction and compression of polymer solution while flowing alternately in the throat connecting pores and in the open pores. Shear-thinning viscometric behavior of polymer solution is also observed even in the flow through porous media within a critical limit of shear rate, beyond which viscous force is not so important any more as a resistance against flow in comparison with the energy dissipation by elastic oscillation of normal stress working on polymer solution. Quantitative analysis of normal stress effects specific to fluid flow with elasticity is made with such simple models of flow medium as a series of connecting capillary tubes of different sizes or capillary tubes packed by glass beads of different sizes.
When producing fluid from an unconsolidated sandstone reservoir or producing fluid with high viscosity such as an oil sand, sand production may cause well damage and reduce production rate. Therefore sand control is a very important factor for an efficient and economical fluid production in the above situation. This paper discussed experimental results on mechanical sand control methods with a screen (wire gauge) or gravel (glass beads) obtained through one dimensional flow model that visualized sand grain movement. Following conclusions were obtained. (1) Sand production could be controlled by a screen having a larger slot width than sand grain size. This was because the sand bridge was formed on screen slot surface. (2) The maximum screen slot width was four or five times larger than the 50 percentile sand grain size. (3) It was observed that there existed an optimum screen width which could control sand and keep minimum pressure loss in laminar or turbulent flow respectively. (4) It could be noted that screen (wire gauge) could control sand better than gravel (glass beads) from our experimental results.
The thick Cretaceous-Tertiary sediments which cover the Tenpoku and Haboro area, the northern part of Hokkaido, is believed to possess substantial hydrocarbon potential. More than seventy anticlinal structures have been recognized in this area, but to date only eight wells have penetrated the Paleogene section while four have drilled to Cretaceous sediments. Four types of anticlinal structures are recognized as interpreted from well data and seismic profiles. The Kitakawaguchi feature represents the first type of anticline. Two wells have been drilled on this structure and seismic profiles are available. A gentle antiform exists as the Paleogene section drapes across thrust-faulted Cretaceous sediments. A more pronounced Neogene anticline is superimposed upon the pre-existing structure. The later structure was formed by flowage of Miocene shales and associated thrust-faulting. The Miocene shales exhibit abnormally high pressure and steep dips. Small rim synclines commonly exist on the flanks of this type of structure. The Uttsu Anticline illustrates the second type of anticlinal feature. The MITI Enbetsu well was drilled to test this structure. The anticline was formed by deep-seated vertical thrust-faulting which affected Paleogene and Cretaceous strata. The formation of the anticline produced an important effect on Tertiary sedimentation. Similar features are thought to exist along the Horonobe and Magaribuchi-Toyotomi fault systems. The Rikibiru structure is an example of the third type of anticline and is located in the southern part of the study area. The MITI Rumoi was drilled on the western flank of the feature. Dipmeter logs indicate that this deep Cretaceous structure is quite huge and broad with gently dipping flanks. The thick sequences of coarse-grained Miocene sediments deposited in this area contrast with the predominantly shaly strata seen to the north. The formation of the Rikibiru Anticline is thought to have formed due to loading of the thick Miocene section. Shale flowage did not occur in this area due to the lack of thick shale sequences. The Maruyama Anticline illustrates the fourth type of anticlinal structure. No wells have been drilled to date on this type of feature. These anticlines are broad and gentle-dipping and are surrounded by rim synclines similar to those exhibited by the first anticline type. Growing mechanism, timing and distribution of each type of anticline are discussed with the view of petroleum geology.
A thick sedimentary sequence of Tertiary and Quaternary ages, which chiefly consists of turbidites, is developed in the Omaezaki district, Shizuoka Prefecture. Structural traps such as anticlinal, fault and combination traps are found in this area. Fine-grained sandstones in the Sagara and Kurami Groups of Miocene age are considered to be main reservoirs. The source rocks are argillaceous sediments in the lower Miocene as indicated by total organic carbon content, type of organic matter and its maturity. However, the potential for yeilding hydrocarbons is relatively low in comparison with the potential of source rocks in the Niigata district. Geochemical data of source rocks and of oil and gas in reservoirs suggest that the B Formation in the MITI Sagara well is the possible source rock for the oil and gas which are produced from the Sagara oil field and also from this well. In the offshore area, several structures remain undrilled, and there is a possibility that hydrocarbon pools (mainly gas) may be discovered.
An interpretation is presented for the Cenozoic geological evolution of the offshore San' in and Kita-Kyushu areas around the western part of Japan on the basis of seismic survey. Along with well data obtained from the study area, geophysical data describe the rifting of the Sea of Japan in the early Miocene which caused rapid subsidence and wrench deformation in the San' in and Kita-Kyushu areas, respectively. As for the San' in area, it seems that stress regime changed from E-W to N-S compression in the late Miocene. Based on a quantitative basin analysis model, immature potential source rocks in the San' in area can be attributed to the reduced heat flow through the late Miocene.
Two stratigraphic test wells, the MITI Takadaheiya and the MITI Kashiwazaki Oki, were drilled in the southwestern part of Niigata prefecture during the 6th term of MITI's Five-Year Plan. Geological studies were made in the Kubiki area using analytical data of above wells and the Kubiki Oil Field. It is known that thick alternations of sandstone and mudstone from the Nanatani stage to the Lower Teradomari stage, so-called the “Nambayama Facies”, are distributed in the Kubiki area, of which facies are confirmed of existence in the above two wells. However, in the MITI Naoetsuoki Kita, which was located in the offshore Naoetsu, the Nambayama Facies mentioned above are changed into mudstone facies at the Nanatani stage. The MITI Takadaheiya shows that the top of oil window is about 1, 800m in depth and the gradient of maturity is very large. The source rock of the Kubiki Oil Field has not specified in the section of Kubiki area yet: therefore, the oils are assumed to have come from the northern or eastern part of the areas where kerogens are expected to be matured. The MITI Kashiwazaki Oki indicates that the top of oil window is about 2, 200m in depth and the gradient of maturity is very gentle as compared with the MITI Takadaheiya. Mudstones in the Nanatani stage are correlated to oils obtained from the Shiiya formation by the biomarker and carbon isotope data. It is interpreted that the oils have moved from the Nanatani formation to the Shiiya formation through thrust faults formed in the middle of Nishiyama age.
Reservoir property of Green Tuff is controlled by the initial volcanic rock facies and alteration. Some hydrothemal alteration increases the secondary porosity and permeability. Altered basalt lava is the main reservoir in the Yurihara oil field. Four depth zones are defined by characteristic secondary minerals: 1) smectite, 2) thomsonite-corrensite, 3) laumontite-albite, 4) laumontite-prehnite-pumpellyite-chlorite. These alteration is estimated to have taken place at sub-seafloor right after the basaltic eruption by hydrothermal fluid originated from seawter. The main oil production zone is from the prehnite zone. High temperature (150-220°C) dehydration alteration have prevented porosity reduction caused by low temperature alteration. Green Tuff in the Katakai gas field is mainly composed of rhyolite. They are mostly recrystallized to form quartz, albite, sericite, calcite, dolomite, siderite, and chlorite. Rhyolite lava is rich in Na and albite, poor in K and sericite. In contrast, hyaloclastite (or pumice tuff) is rich in K and sericite, poor in Na and albite. The alteration in Green Tuff in the Katakai gas field is divided into dolomite-dominant type alteration, which is rich in Fe-Mg carbonate and poor in chlorite, and chlorite-dominant alteration. Dolomite type rhyolite lava is rich in intercystalline pore and dissolution pore, poor in pore plugging clay minerals, and serves as productive reservoir. Andesitic rocks in the MITI Sado-oki are suffered from diagenesis and hydrothermal alteration. The center of hydrothermal alteration zone is reached out by acidic fluid, and shows high permeability.
Thick basaltic piles of Nishikurosawa stage of early to middle Miocene age are widely distributed from Akita through Yamagata to Niigata oil fields along the Japan Sea side. Recently, MITI Nikaho Well and MITI Niigata-heiya Well were drilled at the foot of Mt. Chohkai in the southern part of Akita, and at the central part of the Niigata plain, respectively. Both wells encountered a thick basaltic layer ranging up to 1, 400 meters of the Nishikurosawa stage. We studied micropaleontological features and petrochemical characters about the basaltic layers from the wells and their surrounding areas. The basaltic piles, described collectively as the Nishikurosawa stage in Akita and Niigata areas, are divided into two groups erupted in substages of NN 4 Zone (eary Nishikurosawa age) and NN 5 Zone (middle Nishikurosawa age) of Martini's zonation. The basalt of the midde Nishikurosawa age consists of relatively undifferentiated type in FeO*/MgO ratio with less than 1.4% of TiO2 content. On the other side, the basalt in early Nishikurosawa age is slightly differentiated and rich in TiO2 content compared with the above. In the present paper, we discuss the volcanostratigraphy of the Nishikurosawa stage in Akita and Niigata oil fields.
Japan Sea Legs 127 and 128 of Ocean Drilling Program were conducted in the summer of 1989. The drilling results at 6 sites during the cruises gained our understanding on the history of the Japan Sea. Based on the new chrono-stratigraphic informations, opening of the Japan Sea started at least before 18 to 20Ma, which is much older than the age of 15Ma estimated from paleomagnetic evidence by OTOFUJI and MATSUDA (1983). Lithostratigraphy of the sediments above the acoustic basement was established, which was proved to be correlatable throughout the Japan Sea. The lithostratigraphy is also correlatable with that in oilfield areas in the Tohoku region. The change in lithology through time is probably influenced by global changes in sea level as well as climate. Seismic stratigraphy is correlated with lithostratigraphy at 3 sites drilled during Leg 127. The result suggests remarkable coincidence of opal-A/CT diagenetic boundary with the Bottom Simulating Reflector [BSR]. These results will have profound influences on stratigraphic studies in the Japan Sea and its environs.