The HDT, in comparison with the three arm type CDM, has many advantages. However, due to its record being taken on magnetic tapes and fed into a computer, it requires some time until results can be obtained.
The writer has actually used the HDT recently and experienced the absolute need of hand comptuation from analog record. Therefore, the writer wishes to introduce the principle and methed of hand computation and the outline of machine computation, in order tc make a presentation of the difference between the two methods, and also to assist in the work of those persons engaged in well logging analysis who, the writer believes, will be having greater opportunities to come in contact with the HDT in the future.

View full abstract

Amakusa Well, a kind of exploratory drilling by the governmental base was drilled to depth of 2, 807m in the Upper Amakusa Island in 1972, from which the authors were given 8 kinds of core samples. In addition, 7 more kinds were collected from the surface localities in the Upper and the lower Amakusa lslands. These dry samples consisting of 10 sandstones and 5 shales ranging Eocene and Cretaceous in age were tested under high confining pressure up to 1, 500 bars. The experimental results are shown in Figs 2-10. Most sandstones are very hard, compact, medium alkose ones. Their porosity ranges between 0.4 and 3.6%. Under high pressure, they exhibit brittle behavior. The shales have also small value of porosity, from 1.4 to 2.5%, and they are brittle up to 1, 500 bars confining pressure.
Then, strength coefficient b, an indicator of physical potentiality determined by the following formula (Hoshino and Inami, 1974) was analysed.
n=A_0e^-bσ_s
where, n, σ_s, and A₀ are porosity, strength and a constant respectively. The strength coefficient for Amakusa was studied in comparision with that for northwestern Kyushu and Shikoku. It is indicated that the b value in both Amakusa (later Cretaceous) and northwestern Kyushu (OligoMiocene) are nearly normal, while in Shiratake Sandstone (Eocene) it is higher than normal. The meaning of the strength coefficient was further discussed in relation of geological setting of each sedimentary basin.

View full abstract