The thick marine strata of the Cenozoic Erathem are developed extensively in the Boso and the Miura peninsulas, South Kanto Region, Japan. These strata have long been studied by various authors from several points of view. In the present paper, a tentative correlation of these strata is proposed by the writer from the viewpoint of the characteristic features of the molluscan fossil-coenoses, and the geological range of the important species of molluscan fossils found in the Cenozoic strata in the two peninsulas is tabulated according to the writer's opinion. (1) The Cenozoic strata excluding the nonmarine Pleistocene and the whole Holocene strata in the two peninsulas are divided lithologically into five groups in descending order as follows. 5. The Narita group 4. The Sagami group 3. The Kazusa group (=the "Kurotaki unconformity") 2. The Miura group 1. The Pre-Miura group (including the Mineoka and the Hota groups in the Boso peninsula and the Hayama group in the Miura peninsula) (2) Based on the marine molluscan and foraminiferal fossils as well as the land mammalian fossils, different opinions have hitherto been expressed by many Japanese geologists and paleontologists concerning the geological age and the correlation of the Cenozoic strata in the two peninsulas. However, the biochronologic method as was universally used in the past by many authors is not helpful in the marine Pliocene and Pleistocene strata because no remarkable biochronologic change in the contents of various kinds of fossils is recognized throughout the whole strata. Especially, so far as the marine Pleistocene strata are concerned such a method is not applicable in almost all cases, and it is possible to establish the accurate correlation on the basis of the changes both in sea-level and in thermal condition of sea-water. Here, it is necessary to discriminate the strata deposited in the colder water and lower sea-level stages from those in the warmer water and higher sea-level stages by the employment of the HDM (=Horizontal Distribution Means) and the VDM (=Vertical Distribution Means) characteristic curves. (3) According to the writer's recent studies, the correlation and the geological age of the Cenozoic strata excluding the nonmarine Pleistocene and the whole Holocene strata in the two peninsulas may be considered potentially as shown in Table 1. (4) Abundant molluscan fossils are yielded from the Cenozoic strata in the two peninsulas. Based on the writer's studies, however, the contents of the molluscan fossils change very gradually from the older up to the younger strata. Especially, no remarkable change of the contents of the molluscan fossils is seen throughout the Pliocene and the Pleistocene strata. Differences in the contents of the molluscan fossils found in the respective formations under consideration may be due merely to those in ecological and sedimentological conditions and not to biochronological factors. The geological range of the important species of molluscan fossils found in the Cenozoic strata in the two peninsulas is tabulated as shown in Table 5 on the basis of the present state of the writer's knowledge.
In this paper, the authors expained log interpretation of Induction-Sonic-Microlatero logging system for shaly sand deposited at the depth of shallower than 3, 000 meters in Niigata prefecture, Japan. The sands which were dealt with, were considered to be medium degree of hardness and from medium to slight degree of shaliness. The results of log interpretation from such sands were concluded as follows; 1) With gas reservoir, sonic transit time ΔT of sand appreciably increased due to gas effect and, also, it was of interest that ΔT of water formation which had residual gas saturation had a similar effect as gas reservoir. As regarding the data dealt here, it was necessary to use some correcting factor for gas effect, in the case of calculating porosities. 2) The relation between porosity and formation resistivity factor for the sand followed the wellknown Humble's formula. 3) As for the method of ploting Sonic transit time vs. depth for evaluating formation pressure, it was very useful, but, on the standpoint of field application, the authors thought that there existed in some cases the plot of ΔT sh vs. depth was more preferable than that of log (ΔTsh) vs. depth.
Abstract The Shaly formation can be evaluated with the value of porosity and water saturation which are derived from Well logging, whether it will produce hydrocarbon or not. Recently, values of water saturation of shaly farmation are mostly derived from Induction-Sonic Combiration. Porosity of shaly formation could be derived from Formation Density-Sonic Combination more reliably. The writer tried to predict the formation evaluation by well logging of the Minemiaga Oil field and the Matsuzaki gas field, taking the above mentioned method.
Since the introduction of Schlumberger Wineline Formation Tester (FT) in Japan (1955), about 240 tests were run. Statistics show that one third of these tests recovered considerable amount of reservoir fluids and formation evaluation could be made by means of FT. However the next one third showed dry and the remaining one third of the tests failed mechanically. For the successful test, it is important to properly select the formation to be tested. As the formation becomes thicker, the success ratio of FT becomes higher. Volcanic reservoirs are favorable but very shaly sands and tuffaceous sands are not suitable for the FT. Provided the results of FT do not show the promises, the well should not be abandoned immediately, because about ten percent of such tests shows productivity of the well after the completion tests.
The gamma ray-neutron Log interpretation methods applicable in Rantau Oil Field are described here with informations and several examples. A linear relationship is verified between the gamma ray values and SP values at the water bearing formations in this field, and the writer Concludes that gamm ray log is available to determine the shale percentage in this field. The porosity of the shaly formation can be derived successfully by using the combination of gamma ray and neutron values. The detection of gas bearing formation is possible by the cross plot of the porosities derived from the neutron log vs. the porosities derived from the Micro log, the open hole neutron vs. the cased hole neutron, and the dual spacing neutron.
Porosity values derived from various porosity tools are compared statistically with porosity values measured on core samples from Ratawi Limestone Reservoir of Khafji Oil Field, Kuwait-Saudi Arabia Neutral Zone. The dual spacing formation density log seems to have more advantagous to measure porosity than other tools such as Neutron log and Sonic log, when applied in the limestone reservoir.