Core samples were recovered from the 2, 900 meter B gas bearing bed of HigashiNiigata NS-13 well. Purpose of this paper is to verify the log analysis results derived from various porosity tools by some special core analysis data. Recently, much progress of porosity tools was achieved. Combination of any tools may be useful for evaluating the effective porosity and clay (shale) content of reservoir rock. In this study, core porosities were measured after the method proposed by Associate Prof. Hirakawa in 1, 959. Porosities under the reservoir conditions were properly obtained from this method. Then, the porosities of this reservoir rock range from 12 to 15 percents. On the other hand, cross-plot of Sonic-Formation Density shows the effective porosities of about 10 percents. Thus, it is shown that the correlation of data obtained from both log interpretation and special core analysis methods was established fair well. On the contrary, core porosities measured by the routine core analysis procedure were extremly high. Dehydration and drying of the core samples at considerable high temperatures should give a fracturing effect on the shale fraction contained in the reservoir rock. Insofar as the (very) shaly formations found in Japanese fields frequently, porosity values derived from the routine analysis procedure are not the representatives of porosity in situ. Clay and/or shale contents in the reservoir rock were analysed in the laboratory using the X-ray diffraction and dry sieve analysis methods. According to these methods, clay and/or shale contents are considered to be in the range from 10 to 20 percents. Cross-plots of Sonic-Density and DensityNeutron, however, show the abnormally high contents of shale fraction (p percents) ranging from 63 to 76 percents. Megascopically, core samples collected from 2, 900m B gas bearing bed seem relatively to be clean as the Japanese reservoirs. It appears that above mentioned shale contents obtained from cross-plots may be overestimated. Lack of compaction above the sediments and/or high content of residual gas in the reservoir around the bore hole would give an erroneous effects on the measured values by various logging tools. Studies on the relation between the lithologically measured shale fractions and p percents values derived from logs should be advanced drastically based on the laboratory experiments and field examples.
As a result of laboratory experiments and analyses of field data, four equations of bit performance were suggested as in the previous papers, i.e., euqations of performance line, penetration rate at the separation point, relative penetration rate and bit life. In this paper methods obtaining such factors as penetration rate, drilling time and length of a bit, and optimum combination of bit weight and rotary speed, are generally discussed by using of oremantioned equatious with the efiect of hydraulics included. An impact force developed at a bit nozzle is governed by quantity of drill collars to be used; penetration rate, rate of drilling operation, and drilling time and length of a bit may be affected by quantity of drill collars to be used. There is the optimum bit weight which gives the maximum penetration rate under a given rotary speed, and, in the most case, the rate of drilling operation also attains at the maximum value under the same conditions. As an example of application of it to actual driling practices, influences on the penetration rate of pump operations, i.e., single pump operation and parallel operation of two pumps, and also quantity of drill collars are examined on the basis of analyses of field date.
It is well known that a response of the Neutron log for hydrocarbon bearing formation is affected by mud filtrate invading into a formation. In this paper, the empirical relationships between the Neutron response and mud invasion are described, by giving examples of the Rantau oil field. It can be said empirically by the field studies that the degree of mud invasion into a formation is proportional to the square root of the time of exposure to the drilling mud. And there are mutual relationships between the time of exposure to the drilling mud (√T)and the Neutron responses. Thus from cross plots of √T vs. the Neutron response, the gas zones can be distinguiched from the oil reservoirs.