As a first step of our study, enrichment culture was carried out to cultivate microorganisms for microbial enhanced oil recovery. 49 samples were collected from places, like agricultural fields, small rivers running through cities and oil fields, where organic matters and/or hydrocarbons were thought to be present. As a result, 41 and 3 out of 49 samples cultivated enrichment cultures with the use of kerosene as substrates at 30 and 50°C respectively. The growth rate, and the pH and the interfacial tension as representatives of the function of bacteria were used for selection, and 9 enrichment cultures were selected: Two for large increase of cell number, three for decrease of pH, two for low IFT and two for thermostable metabolism at 50°C. As the influence of salinity, no growth was found at 5% salinity, though 8 out of 9 cultures grew at 2% salinity.
Enrichment culture has been carried out to develop microorganisms for microbial enhanced oil recovery. In the previous paper, it was reported that 49 samples were collected from places, like agricultural fields, small rivers running through cities and oil fields, where organic matters and/or hydrocarbons were thought to be present. As a result, 41 out of 49 samples developed cultures with the use of kerosene as substrates at 30°C. It was also reported that the growth rate, pH and interfacial tension as well as salt tolerance were used as representatives of the function of bacteria for selection, and 8 cultures were finally selected. In the present study, 4 cultures out of 8 mentioned above were chosen for isolation and 4 isolated bacteria were used for investigating the influence of concentration of metal ions of Fe2+, Mg2+, Ca2+ and Al3+ in the liquid medium. Results are summerized as follows. 1. Fe2+ increased the growth rate more or less for all four cultures tested. 2. Al3+ decreased the gorwth rate of all cultures. 3. In relation to the growth rate, there are two types of the pH-time dependency: One is the type of sharp decrease of pH after the exponential phase. Another is the type of decreasing pH on the half way of the exponential phase and keeping pH constant at the stationary phase. The metal ion seems to give the influence on the type of pH-time dependency. 4. The interfacial tension did not vary widely with the presence of metal ion except 3-H which was obtained from the drain of heavy oil tank in the oil refinary.
In the present paper, application and limitation of integral method of seismic data for recovery of acoustic impedance is described. After an approximate integral formula for acoustic impedance is derived, the limitations of its formula on the following items are investigated. 1. Effect of additive noise in seismograms. 2. Increase in error with time caused by noise in the estimated acoustic impedance. 3. Problem on recovery of acoustic impedance from band-limited seismic data. 4. Broadening of frequency contents of seismic data by wavelet processing. 5. Requirement for addition of low-frequency contents to acoustic impedance. As a result, the following conclusions are obtained. 1. When the reflection coefficients are known and noise free, the natural logarithm of the acoustic impedance of each layer is approximated by addition of the twice of integral of the reflection coefficients to the logarithm of the acoustic impedance of the first layer. 2. The approximate integral method of amplitude in seismograms is sensitive to noise. The accuracy of recovery of acoustic impedance decreases against arrival time because the noise is accumulated. 3. When the reflection coefficients are band-limited, the acoustic impedance is not accurately reconstructed by the integral method. Especially, a lack of low-frequency contents affects seriously the accuracy of recovery of acoustic impedance. 4. The seismograms after wavelet processing contain few low-frequency contents. Consequently, the acoustic impedance is not accurately reconstructed by the integral method. 5. The accuracy of acoustic impedance log is improved by addition of low-frequency contents of acoustic impedance log obtained from velocity analysis to high-frequency contents from seismograms after wavelet processing.
The reservoir of the Mobara gas field is restricted to the Kazusa group which is a sedimentary basin made up of sandstones and silty mudstones alternately. It was understood that the Mobara gas reservoir is a dual porosity type. We developped a mathematical model that is useful in simulating the Mobara type performance. Most of the gas generated in the mudstones is dissolved in the brine reserved in the both rocks. A little of the gas is distributed as discontinuous globules due to pore throats in the silty mudstones. The bubbles begin to move toward the sandstones when the formation pressure has been reduced. In this mechanism the rock properties are important, especially relative permeability and capillary pressure. Because the mobility of gas phase becomes better by far as compared with that of water phase, the gas water ratio increases continually.
In petroleum exploration, source-rock evaluation has become universally popular on the basis of the properties of kerogen. Here, a novel approach for potential oil source-rock evaluation that also takes expulsion into account was attempted using the one-dimensional maturity model MATOIL. Apparent oil saturations were calculated from the MATOIL output using some assumptions. Through comparison of the calculated saturations with an assumed critical oil saturation for oil expulsion, the sensitivity of the position of the top of the oil expulsion window to the type of kerogen, the concentration of kerogen, and the basement heat flow was examined. Oil-prone (Type I or II) kerogens generate more oil and yield higher apparent oil saturations than gas-prone ones (Type III). The apparent oil saturation increases with the concentration of kerogen. Even though a source rock contains Type III kerogen, it can get the oil saturation high enough to expel the generated oil, if the kerogen concentration is fairly high. Increasing heat flow makes the top of the oil expulsion window shallower and lowers the maximum oil saturation. In a given geological setting, the initial concentration of kerogen necessary for oil expulsion can be predicted for a given type of kerogen. Because expulsion may control the type of accumulation (oil or gas), source-rock evaluation should take the concept of the expulsion into account.