Kakizaki Oki TSI-1, -2 and -3 wells were drilled during 1983 and 1984 on the Kakizaki Oki Structure, situated 10km offshore the town of Kakizaki between Kashiwazaki city and the Kubiki Oil/Gas Field. In the Kakizaki Oki TSI-2 well, cores totalling 50m were taken from the III bed group and the IVa bed, which are the upper most part of the lower Teradomari Formation.
This paper studies the sedimentary environment and the reservoir quality of cores, and lithofacies distribution of the III bed group and IVa bed. These beds are of middle bathyal and/or deeper paleo water-depth from paleontological data, and they correspond to mid fan deposits for a submarine fan model proposed by WALKER (1978). Sandstones in core samples, taken from IIIc+d/IIIf beds and IIIg/IVa beds in descending order, are situated at the site of smooth portion of suprafan lobes on mid fan and at the site of braided channels around upper fan to mid fan deposits respectively. Sandstone cores from the smooth portion of suprafan lobes show good reservoir quality in terms of porosity (φ
He), permeability (Kair) and pore geometry. On the other hand, ones at braided channels mainly show poor reservoir quality.
Intergranular pores, the major pore type, are observed largely in IIIc+d/IIIf beds and are less common in IIIg/IVa beds which were cemented and compacted.“Micro pores”, found as intra-kaolinite cement pores and intra-matrix pores, are markedly recognized in IIIg/IVa beds. In IIIg/IVa beds, primary features and diagenetic changes in textures cause low permeability and a difference in the distribution of pore types.
A cosiderable amount of oil was discovered in the III and IV beds, but only in the TSI-1 well. Although core samples from the TSI-2 well correlated to oil-bearing horizones in the TSI-1 well showed good reservoir quality, only small amount of oil and gas was recognized by the production tests. One factor for poor productivity is assumed to be the low relative oil permeability in a high water saturated state.
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