Combustion tube experiments were carried out to investigate the basic behavior of fireflooding as an EOR method. And it was found that the vaporization-condensation mechanism was important to accumulate oil for making oill banks and oil banks formed moved toward the exit (production well).
As to the production, three stages would be seen. These are (1) the production of oil movable at a liquid state, (2) production of oil from the oil bank formed by means of fireflooding mechanism mentioned above, and (3) little production of oil after the production of oil bank. When the oil is at the residual oil saturation in the reservoir, no oil production at the first stage would be expected.
Adequacy of the simulator developed in the present study and described in the last paper was examined in detail by means of comparing results obtained both theoretically and experimentally. And it was shown that the simulator was preferable.

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This paper presents a method to estimate the volume of initial gas in place and apparent permeability by using surface measured flowing tubing pressure and gas flow rate. The method is essentially a material balance method, where static reservoir pressure is estimated This article describes the stepwise procedure of the method as well its theoretical background. The proposed method excludes any artist-like technique and provide only one set of answers from a set of surface flowing data. Four examples are presented to demonstrate the applicability of the method.

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The convective flow in a buried caldera was calculated by numerical simulation, and it was found that the upflowing hot water above the slope of the caldera basement could be generated as the convection mode of an isothermal basement model.
Temperature data from well loggings in the Hohi geothermal area indicate upflowing hot water above the slope of the basement.
The numerical simulation of the flow in Shishimuta caldera at the Hohi area reveals that the collision of downflowing cold water from the caldera rim and the upflowing hot water above the hot basement surface creates the upflow perpendicular to the basement surface.
The convective patterns for both an isothermal basement model and an uniform heat flow model were compared. The results are different. The calculated temperature of the uniform heat flow model shows some discrepancies with log data.
The effects of a local heat source on the basement and a horizontal impermeable layer in the upper part of the convection cell were examined, and they were found to influence the location and the shape of the upflow region. The effect of an impermeable layer is significant in case of the deeper heat source beneath the caldera.

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Geochemical studies were carried on formation fluids including gas, oil, condensate and formation water in reservoir rocks in the Green Tuff, especially in the Mitsuke oil field, and in the Shiunji, Yoshii-Higashi Kashiwazaki and Minami Nagaoka-Katakai gas fields.
Properties of oils and condensates seem to depend on temperatures of reservoir rocks, whereas those of gases reflect the conditions of their generation.
The origin of gases is considered to be thermogenic based on the data of δ¹³C₁ and C₁/∑C_n. Both data of δ¹³C₁ and i-C₄/n-C₄ indicate that the level of maturation of source rocks in the Minami Nagaoka-Katakai and Yoshii-Higashi Kashiwazaki gas fields is higher than that in the Mitsuke oil field and Shiunji gas field.
Chemical composition of formation waters is closely related to alteration of reservoir rocks. The Cl^- contents of formation waters in the Mitsuke oil field increase from SW to NE, which suggests that interstitial waters in the Teradomari formation flow from SW to NE.

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