A Miocene carbonate platform, named Central Luconia carbonate platform, is widely extended in offshore. Sarawak, Malaysia. There are some 200 of Miocene-Pliocene carbonate build-ups are developed on the carbonate platform, and some 70 of them have been tested so far, of which around 40 have been proved to be gas-bearing and the rest were water-bearing.
Through the exploration activity over the Central Luconia area by Nippon Oil Exploration Co. Ltd. since 1987, it was found that five main geological factors, i.e. (a) Cycle I/II gas focal structure, (b) Upper Cycle V thief beds, (c) crest/flank faults, (d) the balance between seal collapsing critical pressure and build-up formation pressure, and (e) gas chimney, can be utilized for gas prospect screening and gas column height prediction.
Through the several carbonate studies, a probable theory of gas migration and accumulation system has been led; 1) gas migration and focusing in Cycle II focal structure, 2) gas leakage from the crest of the Cycle II focal structure due to pressure unbalance, 3) vertical migration through fractures in Cycle III shale sections, 4) gas accumulation in Cycle IV/V carbonate build-ups which are located just above the crest of the Cycle II focal structures, 5) gas leakage from the crest of Cycle IV/V carbonate build-ups due to pressure unbalance (gas chimney). Four mega-sized high structures were found in the study area as the location where such a series of gas migration and accumulation system is under performing.

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Enterobacter cloacae TU-7A strain is a CO₂ producing bacterium and is being used as one of the injecting bacteria in Jilin Oil Field, China. For monitoring the metabolic activity of TU-7 A, possibility of utilization of 2, 3-butanediol, which is one of the metabolites, is discussed. Results are summarized as follows.
1) TU-7A has two (main) metabolic pathways for producing CO₂, that is butanediol fermentation and enzymatical decomposition of formic acid which is one of the metabolites. The amount of CO₂ calculated on the base of these pathways agreed fairly well with that measured by gas analysis.
2) Influence of the concentration of molasses as substrate and the addition of phosphate into the medium on the production of CO₂ may be taken into account.
3) In the formation water of target block of the oil field and the molasses medium, there is no bacterium which produces 2, 3-butanediol.
4) Absorption test of 2, 3-butanediol on silica sand grains clarified no consumption, so that the quantity of butanediol may be measurable by analyzing the produced water.
5) All results may confirm the possibility of utilization of 2, 3-butanediol for monitoring the amount of CO₂ produced.

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For successful application of forward in-situ combustion to recover additional oil, oil must have the property to form sufficient amount of coke by thermal cracking. This was believed to lead the criterion that the oil must be heavy, to some extent.
However, our combustion tube experiments showed that Yabase crude oil were suitable to the in-situ combustion, due to the formation of w/o emulsion, with the consumption of only 5% of initial oil in place.
Also, experimental results on the behavior of in-situ combustion after recovering oil by air injection showed that the production began at three hours after the initiation of ignition with high production rates of oil lasted about eight hours, followed by the sudden decrease of production rates at the end of oil production in the oil bank.
Numerical calculations with our new 4 phase 8 component model which included the mechanism of emulsion formation and the flow characteristics of emulsion simulated well the experimental results described above.

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Radioactive ¹²⁹I method is very useful for petroleum exploration. ¹²⁹I is naturally produced by cosmic-ray-induced spallation of ¹²⁹Xe in the upper atmosphere, and by spontaneous fission of ²³⁸U in the Earth's crust.
¹²⁹I dating method gives an isolation age of interstitial water from the sea to the sedimentary system. A half-life of ¹²⁹I is 15.7m.y., so that its application age is restricted between 3 to 90Ma. This is the first and the only geochronologic method to determine the age of fluid in the Tertiary sedimentary basin, while conventional methods are available only for solid or younger fluid. An application to U.S. Gulf Coast basin (Moran et al., 1995) revealed vertical migration of brine from older, deeper sources to present young host formations.
Another application of fissiogenic ¹²⁹I as a tracer in Paleozoic Anadarko basin, Oklahoma (Moran, 1996), to determine the source rock was also presented.
¹²⁹I dating method will be expected to give geochemical evidences about fluid migration in the basin, and resolve the genetics of dissolved-in-water type iodine-natural gas deposits in Neogene to Quaternary sediments in Japan.

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Vitrinite reflectance is a very important thermal maturity indicator in petroleum exploration, but there are two major problems: one is the identification of vitrinite in dispersed organic matter and the other is the suppression or enhancement of vitrinite reflectance. It can be extremely difficult to correctly identify minute vitrinite grains in shapes using conventional microscopy. Even if the vitrinite identification is accurate, however, perhydrous compositions will lead to suppression of measured vitrinite reflectance and subhydrous compositions to enhancement. The fluorescence alteration of multiple macerals (FAMM) technique has been developed at CSIRO Petroleum in Australia to overcome these problems. The main advantages of the FAMM technique are 1) the occurrence and amount of suppression or enhancement of vitrinite reflectance are indicated, 2) identification of specific macerals is commonly not necessary for the analyses, 3) rocks containing very rare or no vitrinite can generally be measured, providing that a suite of other macerals are present and 4) problems of contamination and cavings can be resolved. Thermal maturity measurements with the FAMM technique have been done on more than 2, 500 samples comprising Paleozoic to Tertiary coals and petroleum source rocks from around the world. Application of the FAMM technique to Japanese source rocks can help develop petroleumexploration in Japan.

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This article reviews history and current status of Neogene radiolarian biostratigraphy in Japan, with an emphasis on its applicability for petroleum exploration.
A collective database of Neogene radiolarian biostratigraphic records from various localities through Japan is also presented.
In earlier days, radiolarian biostratigraphic subdivisions of the Neogene in Japanese oil-fields were due much to the work of Nakaseko and his co-workers. They recognized a lot of radiolarian assemblages which were then classified into several types of assemblages on the basis of dominant species. As a consequence, four assemblage zones were defined for the Neogene. By using these biostratigraphic criteria, subdivisions and correlation of the Neogene sequences were performed in most of the major sedimentary basins during the past thirty years from the mid-1950's to the mid-1980's.
The radiolarian zones in current use are essentially worked out in deep sea cores and are potentially useful for more refined correlation of the oil-bearing Neogene of Japan. Possible minor limitation of their use due to biogeographic provincialism and burial diagenetic alteration of siliceous tests is also discussed.

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K-Ar age of the Am-4 Tuff in the Miocene marine sequence of the Kanigawa section in the Boso Peninsula, central Japan, was determined. The obtained age is 11.73±0.24Ma (1σ error), which represents an age of the last occurrence (LO) horizon of Cyclicargolithus floridanus, because this biohorizon locates only two meters below the dated tuff (Mita and Takahashi, 1998). As the LO horizon of C. floridanus almost coincides with the first occurrence (FO) level of Discoaster kugleri, defining the CN5a/CN5b boundary of calcareous nannofossil zone of Okada and Bukry (1980), the age of the Am-4 can be regarded as an age of the CN5a/CN5b boundary. Precisely established age for the CN5a/CN5b boundary in central Japan is well concordant with previous estimation of Berggren et al. (1995).

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