Because of the high interfacial tension between water and oil, the injection pressure of water in water flooding is fairly high and the subsequent oil displacement efficiency is rather low. Then the improvement was aimed for the reduction of injection pressure and the efficient displacement by adding a small amount of surfactant into the injection water. Surfactants used were Polyoxyethylenenonylphenylether HLB=17.1 and 12.6 as nonionic, and SDBS as anionic. These were separately used as water solutions of 300ppm in concentration without any additives like alcohols as co-surfactants. Results are summarized as follows. (1) Adding a surfactant into the injection water can reduce the injection pressure surprisingly even if the concentration of the surfactant is as low as 300ppm, which is 1/50 to 1/100 of that in the low concentration surfactant flooding. Results were correlated with the capillary number as shown in Fig. 10. (2) 300ppm surfactant-water solution was able to increase the oil recovery. This may be caused by the snap-off mechanism proposed by ARRIOLA et al. (3) krw/kro decreases with decreasing the interfacial tension, that is to say, the oil gets to flow easily compared to the water as the interfacial tension decreases. This effect was related to the shift of residual oil saturation with the interfacial tension.
In this paper, the distribution of carbon dioxide in natural gases recovered from the Platong gas field and its origin are discussed on the basis of geological evidences. Carbon dioxide content in gases of this field is average 15% and partly more than 40%. Gas bearing Tertiary sediments are dominated by gas-prone woody-coaly organic matters. Main east-dipping faults in the western flank of this structure cut basement complex. Gas reservoirs containing rich carbon dioxide, more than 40%, are locally distributed in the northwestern part of this field. The spatial spread is clearly oblique to stratigraphic markers and is like “conical mass”. This mass is characterized by high density shale more than 2.70gm/cc and very low Cl- content in formation water. The above marked features suggest that carbon dioxide has been generated from woody-coaly kerogen in sediments during thermal diagenesis, and also has been supplied from “magmatic origin” through the faults, and/or formed by oxidation of hydrocarbons through contact with mineralized waters, which have ascended into Tertiary sediments along fractures and fault zones.
Chemical and isotopic analyses were applied to characterize genesis of natural gases commercially produced in north-east Japan, so called “Green Tuff” region. Concentrations of He and N2, isotopic ratios of 3He/4He and 4He/20Ne, δ13C values of CH4 showed positive correlations with stratigraphy of gas reservoirs. Especially isotopic values of He included in the deepest gases from volcaniclastic rocks in Nanatani and Nishikurosawa Formations were almost equivalent to those of volcanic fumaroles in the Japanese Islands, suggesting high contribution of mantle materials. On the other hand the genetic diagram of hydrocarbon compositions versus δ13C values of methane attributed hydrocarbon compounds exactly to pyrolysis products of organic matters in sedimentary rocks regardless of their reservoir rock types. No more than 1% of methane seems to be derived from upper mantle, whose contribution may be estimated by comparing CH4/3He values of Green Tuff gases with those of hydrothermal fluids according to studies of EPR.
The spatial distribution of transmissivity in the water-dissolved gas field (G6 formation) in the Nishikanbara district, Niigata prefecture, was estimated using time histories of the groundwater heads which were calculated from the production data such as flow rate, gas-water ratio and wellhead pressure etc. at a number of wells. A quasi-linear approach was used to estimate the transmissivity. The estimated values of transmissivity were in the region of 2.0×10-4-7.8×10-2m2/s, and in the same accuracy as the values of transmissivity which were estimated using time histries of the groundwater heads including the errors which were expressed by random numbers of normal distribution N (0, 4.92).