Akita Oil Field Research Articles

Clay Minerals and Organic Matter in Neogene Carbonate Rocks of Akita Oil Fields of Japan

Clay Minerals and Organic Matter in Neogene Carbonate Rocks of Akita Oil Fields of Japan

Isolation and Characterization of Long-Chain-Alkane Degrading Bacillus thermoleovorans from Deep Subterranean Petroleum Reservoirs.

Two extremely thermophilic alkane-degrading bacterial strains, B23 and H41, were respectively isolated from deep subterranean petroleum reservoirs in the Minami-aga (Niigata) and Yabase (Akita) oil fields. Both strains were able to grow at temperatures ranging from 50 to 80 degrees C, with optimal growth at 70 degrees C for B23 and 65 degrees C for H41. From 16S rRNA gene sequence analysis and physiological characterization, both strains were identified as Bacillus thermoleovorans (identities of 99.5% and 99.6% to strain DSM 5366, and 98.3% and 98.7% to the type strain LEH-1(TS), respectively). Strains B23 and H41 effectively (60%) degraded n-alkanes longer than C12 and C15, respectively, at 70 degrees C, while strain LEH-1(TS) degraded undecane (C11) most effectively. When B23 and H41 were cultivated in the presence of heptadecane, heptadecanoate and pentadecanoate were specifically accumulated in the cells. These results strongly suggest that the two strains degraded n-alkanes by a terminal oxidation pathway, followed by a beta-oxidation pathway.

ABSTRACT: Deposition of source and reservoir rocks and formation of trap structures in response to basin inversion of rift basins in Niigata and Akita oil fields, Japan

ABSTRACT: Deposition of source and reservoir rocks and formation of trap structures in response to basin inversion of rift basins in Niigata and Akita oil fields, Japan

秋田，新潟地域における根源岩の有機地球化学的相違

The Neogenesedimentary basins in Akita and Niigata area are typical of marine oil producing sedimentary basins in Japan. Middle Miocene source rocks of the Onnagawa Formation in the Akita oil field are characterized by a high abundance of biogenic silica. Contemporary source rocks of the Lower Teradomari and Nanatani Formations in the Niigata oil field are argillaceous with significant clay-rich clastic rocks. In order to clarify organic geochemical differences between the source rocks from these two basins, source rocks and crude oils were analyzed for biomarkers, aromatic sulfur compounds (ASC), kerogen sulfur concentrations, and oil generation kinetic parameters.Regular sterane compositions of crude oils from both basins are similar, showing major contributions from zoo- and phytoplankton. However, Akita crudes are characterized by low pristane/phytane (Pr/Ph), low diasteranes/regular steranes (Dia/Reg), low oleanane/hopane (Ole/Hop), and high benzothiophenes/dibenzothiophenes (BTs/DBTs) compared to Niigata crudes. Although the potential source rocks showed a significant variation in their organic compositions, kerogen in the Akita basin tends to have the higher atomic S/C and O/C, and lower activation energy for oil generation. Some kerogens from the central part of the Akita basin are classified as Type II-S kerogen, which are generally rich in 24-norcholestane derived possibly from diatom. Kerogens from the southern part of the Niigata basin are characterized by the lowest sulfur concentrations and the highest generation activation energies. Notably, the Onnagawa source rocks have significantly lower Dia/Reg and higher BTs/DBTs than the Teradomari and Nanatani source rocks with the same maturity levels. These organic geochemical differences between Akita and Niigata basins can be interpreted in terms of differences in oxic-anoxic condition and primary productivity at the time of deposition, the consumption of H2S by terrigenous iron at the sediment/water interface, and the abundance of clay minerals which can act as catalysts for the isomerization of regular steranes to form diasteranes during diagenesis.

秋田油田新第三系・第四系層序に関する最近の変革

Neogene stratigraphy of the Akita oil fields (s.l.) was first established by OHASHI (in TOYAMA, 1925) in the Oga Peninsula, and later by OMURA (1928, 1930) in and around Akita City, which is an important oil-producing area in the region. The oil-bearing marine strata in the Akita City area belong to the Onnagawa, Funakawa, Tentokuji and Sasaoka Formations, the type locality of the former two is in the Oga Peninsula. The Tentokuji and Sasaoka Formations were designated in the Akita City area and have been correlated with the Kitaura and Wakimoto Formations of the Oga Peninsula. The stratigraphic succession in the Akita City area has long been regarded as the standard succession not only for the Akita oil fields but also for the Neogene sequences along the Japan Sea coastal regions.Recent studies in magnetostratigraphy and in biostratigraphy based on diatoms, calcareous nannoplankton and planktonic foraminifera indicate that the correlation, so far established between the successions in the Oga Peninsula and Akita City area, is not valid. Based on these studies, the Onnagawa Formation of the Akita City area is correlated with the lower to middle part of the same formation of the Oga Peninsula, and the Funakawa Formation of the Akita City area is correlated with the upper part of the Onnagawa to the basal part of the Funakawa Formation of the Peninsula. The Tentokuji and Sasaoka Formations are correlated with most of the Funakawa Formation of the Peninsula, unlike the usual practice of correlating them with the Kitaura and Wakimoto Formations. It is after the deposition of the Sasaoka Formation that the Early Pleistocene Kitaura and Wakimoto Formations were deposited in a marine basin, which existed as a remnant of the earlier one, to the west of the present coast line of Akita-Noshiro.The Kitayuri thrust system along the present coast line seems responsible for the difference in the sedimentary environment of the two areas since the time of deposition of the upper part of the Onnagawa Formation in the Oga Peninsula.

日本海側における海成下部中新統の発見と東北日本の台島期‐西黒沢期における環境変動

We describe in detail the calcareous nannofossil biostratigraphy of the lower to middle Miocene formations distributed along the coast of the Japan Sea. The lowermost marine sediments overlying the “Green Tuff” volcanics in these areas are characterized by the occurrence of Helicosphaera ampliaperta, Discoaster deflundrei, Sphenolithus heteromorphus, and Cyclicargolithus floridanus. These assemblages indicate that the first marine environment invaded the coast of the Japan Sea side in NN 4 Zone of Martini's zonation (16.01Ma-18.74Ma) in Early Miocene.The lithofacies of these formations in NN 4 to NN 5 zones (13.17Ma-18.74Ma) are composed of fossiliferous sundstone and mudstone in the Dewa Mountains area and the Sekiryo area (Ou Backbone Range) respectively. In contrast to these areas, the Akita Oil Field, trending north to south along the coast of Japan Sea on the west of the Dewa Mountains area, is characterized by the tholeiite type basalt activity in this age. Simultaneously with the end of basaltic volcanic activity at NN 5/NN 6 boundary in the Akita Oil Field, the lithofacies of sediments have changed from fossiliferous sundstone to mudstone in the Dewa Mountains area, and from mudstone to fossil bearing sandy siltstone in the Sekiryo area.Based on these facts, we conclude that the lowermost marine sediments distributed in the Japan Sea side are correlated to Early Miocene NN 4 Zone. The Akita Oil Field on the west of the Dewa Mountains is characterized by the basaltic volcanic activity during NN 4 to NN 5 zones, and the end of its activity is related to the paleoenvironmental change from shallow to bathyal in the Dewa Mountains areas and bathyal to shallow in the Sekiryo area at the NN 5/NN 6 boundary in early Middle Miocene.

沖積地盤の傾動とその自由地下水の水位および水質の変化

The Alluvial ground undulates incessantly at Tegata in the Akita Oil field in the North Japan. The tiltings are composed of (1) annual cyclic variation, (2) progressive inclination to ENE, and (3) short period seesaw movements.The annual cyclic variation, to incline relatively to SE in winter and to reduce the angle in summer almost regularly, is related with the fluctuation of free groundwater table. The inclination increases in general as the water table gets higher. The two are especially intimate in winter. It may de due to both the reduction of permeability and the variations of permeability by temperature at the lower temperatures than probably 12° C.The progressive inclination to ENE is certainly related with the movements of the Miocene silty bed rocks.The short period undulation reflects surely the movements of the bed rocks, and related to the occurrences of earthquakes and the volcanic eruption of Mt. Koma in 1970.In the case, the inclination increases to some extent, the groundwater generally gets higher in resistivity and becomes lower in Redox potential. Resistivity, Redox potential and pH sometimes vary to large degree even without remarkable variation of inclination. Although the mutual relations of tilting, resistivity, Redox potential and pH are complicate, their variations suggest the squeezing-out of groundwater by the crustal lateral pressure, occasionally relating to the occurrences of earthquake.

Occurrence of High Pressure Zone in Akita Oil-Field

In diagenesis of mud deposits, abnormal high pressures are expected at certain depths and stages of sedimentation. The high pressures are considered to be due to excess free water released from rigid ice layers of clay and zeolitic minerals in alterative temperature and overburden pressures. In addition to the process which schemed by W. D. KELLER as montmorillonite plus potassium to illite and glauconite mica, the alteration of vitric tuff to clinoptilolite and clinoptilolite to analcime were very common in the Funakawa Formation of the Akita oil-field. High pressure mudstones were investigated by core analysis, well-log analysis, X-ray measurements and bottom-hole evidences. A reservoir is built up with fluid migrated into porous media along innumerable of fractures and pore spaces opened by excess high pressures and extensional stresses in the muddy rocks, of which pre- and post-alteration mudstone close and hold the containing pressure. Calculations for several models of high pressure domain show that reservoir maintenance was continued for a period of million years for an ordinary impermeable cap rock.

Zeolitic Alteration of Vitric Tuffs in the Akita Oil Field (Part 3) On the Noshiro sedimentary basin

Zeolitic alteration of vitric tuffs from the Neogene oil-bearing deposits of the Noshiro basin (Fig. 1) in the Akita oil field shows regular zonal arrangements, in descending order as (Fig. 2), fresh glass zone-clinoptilolite zone-analcime zone-authigenic albite zone. Each zeolite zone considerably varies with the localities (Figs. 3 and 4) in both stratigraphic horizons and thickness.The natural densities of the mudstone at the top of the clinoptilolite zone is measured to be 1.87± and that of the analcime zone 2.15± (Fig. 5). From the thickness of the strata (Fig. 6) above the mudstone, the initial thickness before burial is calculated to be 830m+ above the clinoptilolite zone and 1500m+ above the analcime zone.The zeolitic alterations of the vitritic tuffs in the Noshiro basin are interrelated to their overburden thickness (Figs. 7-11). Such differences of sedimentation are inferred to be due to the differential movements of the sedimentary basin caused by the Dewa Disturbance during the later Funakawan and the early Tentokujian stages.

Distribution and Origin of the Neogene Carbonate Rocks in the Akita Oil Fields, Japan

Since 1967, the writers have studied the stratigraphical and geographical distributions of carbonate rocks of the Funakawa, Onnagawa and Nishikurosawa formations of the Neogene in the Akita oil fields, Japan. They considered the origin of these carbonate rocks from the geological and mineralogical points of view. The results are summarized as follows:1. Stratigraphically, these carbonate rocks are generally distributed in the following formations;uppermost horizon of Nishikurosawa formationuppermost horizon of Ormagawa formationlower horizon of lower Funakawa formationuppermost horizon of upper Funakawa formationGeographically, the carbonate rocks are remarkably distributed in the Onnagawa and Nishikurosawa formations along the southern coast of Oga peninsula, in the Nishikurosawa formation of the eastern part of Kameda-machi and in the Onnagawa formation of the Southern part of Yajima-machi.2. The detrital substances derived from the inorganic and organic matters are the main source materials for these carbonate rocks, while the chemical deposits from the sea water occupy only a part of the carbonate rocks. Depositional environments of these rocks are ranged from the inner-neritic to bathyal conditions.The supply of both calcium and magnesium is necessary for the formation of carbonate rocks from the source materials because of the poorness of these elements in them. Concerning the carrier waters of calcium and magnesium and the geologic stages of supply of these elements, it is considered that the supply of calcium and magnesium from the salt water originated from the earlier lithification during the period of syn-diagenesis is more effective to the transformation of source materials than the supply of these elements from the water originated from the ana-diagenesis, epi-diagenesis and hydrothermal alteration. Also, the additional supply of these elements from the volcanic detritus in the sea may sometimes be very important.In the studied area, the formation of chemical deposits is very rare, and genetically, this formation is mainly controlled by the following two factors; one is the abnormal increase in magnesiun and calcium contents of the sea water caused by the supply of large amount of volcanic detritus in the sea, and the other is the temperature rise of the sea water caused by the same phenomenon.

Zeolitic Alteration of Vitric Tuffs in Akita Oil Field

The zeolitic alteration of vitric tuffs in the Neogene oil-bearing formations in Akita oil field was studied. Zeolitic zonation at Yuri hilly land is shown in Fig. 1, and Table 2. Zeolitic columnar sections of underground rocks at lowland are shown in Figures 2 and 3. Zeolitization of underground vitric tuffs at the lowland area more moved upwards in geologic horizen as compared with that of the hilly land. Two different types of alteration facies, the upheavaltype and the depression type, are distinguished among the underground tuffs, as showing in the following table:Marginal area of the Akita sedimentary basin, in which Yuri hilly land is situated, were widely and largely upheaved by the Dewa disturbance. After this disturbance, the physical conditions under which vitric tuffs had been altered into zeolite was diminished in these upheaved area. In the remainedbasin, where the depression was succeeded, the zeolitization upwardly somewhat increased. During the Tentokujian stage, the sedimentary basin was differentiated into raised belts and depressed zones. At the raised belt the favorable condition for zeolitization gradually decreased. While, in the depressed zone younger formations successively deposited and increased the zeolitic alteration of vitric tuffs until the end of the Sasaokan stage.In Akita oil field, pyroclastic rocks, of which acidic tuffs are most extensive, are commonly intercalated in oil-bearing formations, and they often formed oil and natural gas reservoirs.

Study on Gravitational Compaction of Muddy Sediments in Akita Oil Field

Study on Gravitational Compaction of Muddy Sediments in Akita Oil Field

On the Nize Tuff in Akita Oil Field

Abstract: In 1936, the igneous rocks which are developed at Nize pass and the upper course of Babanome river, east of Gojome in Akita prefecture, are called "Nize Tuff" by Omura and he considered that these rocks consist mainely of basaltic and intrusive rocks of the pre-Onnagawa stage.According to the recent studies of the writers, the Nize tuff is not so simple as Omura considered, it is pyroclastic compound of Sunakobuchi formation, Onnagawa formation, dolerites, basaltic andesite and Manaitayama volcanic rocks. Excepting the Sunakobuchi formation, others are developed at the Nize pass, the type locality of the Nize tuff. They are effusive and intrusive products of the Onnagawa or the post-Onnagawa stage, and are clearly younger than the Nize tuff which Omura defined. The Sunakobuchi formation, which consists mainly of spilitic basalt and is older than the Onnagawa formation, does not expose at environs of the Nize pass, though it is widely distributed at eastern border of Akita oil field.The name of Nize tuff must be abolished or redefined, though it has been used by many oil geologist for long time.

Radioactivity Well Logging in Japan

The radioactivity well logging was applied to the Oil Mining Industry in Japan. This imported instrument was tested in Akita oil field. Reliable records were obtaind by four well loggings. Then, this method can be employed to obtain an information in secondary recovery operations.

Recent Development of Akita Oil Fields

Recent Development of Akita Oil Fields

Fluid-Level Measurement by the Echometer at the Akita Oil Field

Fluid-Level Measurement by the Echometer at the Akita Oil Field

Stratigraphy and Structure of Tertiary Deposits in Oga Peninsula Akita Prefeture

Tertiary deposits of the Oga peninsula in Akita prefecture affords an almost complete record of successive sediments The Tertiary stratigraphy of the peninsula has been studied by many geologists since 1892 and considered by them as a type locality of the Akita oilfields The writer who worked the geology of the peninsula during last six years wishes to propose the following revision of stratigraphic sequence of the Tertiary system in the peninsula in view of the cycle of sedimentation in descending orderbShibikawa beds(unconformity)Wakimoto ormationupper Kitaura formationHunakawa group middle Hunakawa formationLower Minamihirasawa formationOnnagawa formationDaijima group Nishikurosawa formationDaijima formation(unconformity)Sugoroku complexIn reference to the petroleum geology the Hunakawa group is most important the Kitaura and the Minamihirasawa formations being the oil-bearing depositsThe Oga peninsula is divisible into three different blocks on the basis of geologic structures. The west block is composed of marginal deposits and is faintly folded The middle which is seperated distinctly by the Minamihirasawa fault from the west and by the Hamamaguchi Wakimoto line from the east is monoclinally structured taking NW-SE strike and NS dip In the east the heavy Hunakawa group is normarly foldedAs a result of both stratigraphical and structural considerations of Tertiary deposits in the peninsula, a hopeful oil-productive fileldprobadlly develops east of the Hamamaguchi-wakimoto line In other words the productive oil-field of Akita may extend from Yabase to the Mt Kampu district crossing the Lake Hachiro.

A Consideration on tuff (-breccia) Beds in Oil-Fields of Japan

The writer descrives a tuff (-breccia) bed, named the Kamisannai Tuff (-breccia), which outcrops in the Iwami-sannai district to the east area of the Yabase oil-field, Akita Pref., showing interesting modes of occurrence, and he also mentions that it may be a deposition of detritus of submarin eruption, and that it is one of the characteristic modes of occurrence of tuff or tuff-breccia in the Akita oil-fields.

The Two Types of Deformation developed in the Akita Oil-Field (3)

The Two Types of Deformation developed in the Akita Oil-Field (3)

Geological Structure of the Akita Oil Field

Geological Structure of the Akita Oil Field