Permeability through porous media was evaluated theoretically by using a network model. In this model, a porous material is assumed to be a network which is composed of a large number of pore segments of a constant length. The pore diameter distribution is also assumed to be the normal, the RosinRammler or the logarithmic normal distribution. The flow rate through a network was calculated with the Kirchhoff' low under a certain pressure difference between the both sides of the network. Then the permeability was calculated from the rate. The following results were obtained. 1) Permeability varies with the broadness of the pore diameter distribution. 2) Permeability decreases with the number of pore segments increasing. 3) There is little difference among the results calculated from the network model in which the pore diameter distribution is assumed to be the normal, the Rosin-Rammler or the logarithmic normal distribution. 4) Purcell's factor can be evaluated from the network model. The factor varies with the broadness of the pore diameter distribution.
The solid material deposited in the Minamiaga crude oil, (so-called paraffin), has distinctive characteristics: i. e., it does not totally dissolve in any organic solvents, nor disperse into the crude oil if ordinary paraffin dispersant applied. So we designated it as "paraffin" in order to distinguish it from usual paraffin whose main component is aliphatic hydrocarbon or paraffinic wax. The composition of the "paraffin" and the mechanism of its deposition were studied in the laboratory by means of analytical techniques. At first, "paraffin" was divided into six components, i.e., oily hydrocarbon, paraffin, petrolene, asphaltene, carbene and carboid, by their selective solubility in organic solvents. Then the relative content of each component and the ratios of petrolene/carboid and carboid/paraffin were calculated for reference. Next, the same experiments were carried out with regard to several topped crude oils including Minamiaga crude oil. As a result, it was clarified that the main component of the Minamiaga "paraffin" is carboid which is insoluble in any organic solvents, and that the petrolene/carboid ratio of the Minamiaga crude oil is far smaller than those of the other oils where paraffin problems are less serious. Conclusively, the leading role of the "paraffin" trouble at the Minamiaga field is not paraffin but carboid, and relatively low content of petrolene in the Minamiaga crude oil seems to make the problem more difficult.
As discussed in the previous paper (Part 1), the Minamiaga "paraffin" is featured by a relatively large quantity of carboid and a small quantity of petrolene contents. Owing to the peculiarity of the "paraffin", special consideration should be given to prevent the "paraffin" trouble. Laboratory experiments for deposition and inhibition of the "paraffin" were carried out on Minamiaga crude oil with available chemicals having surface activity. To mitigate the trouble, an addition of chemicals like petrolene was expected to be effective because petrolene (which was extracted from other crude oil) added to Minamiaga oil had revealed the tendency to reduce the deposition of solid. Among the 11 materials tested, two chemicals were selected. One was pour point reducer, the main component of which was alkylnaphthalene, and the other was sludge disperser, and the mixture of the two (in the ratio of two to one) showed better effect than in the case of separate application. Following the laboratory tests, field test was run at the Minamiaga field. The well stream of Minamiaga-28W was divided into two equal flows at the well-head, then the mixture of the said two chemicals were added continuously at the rate of 300ppm to one of the streams. (There took place some intermittent interruptions due to mechanical reasons.) The none additive flow was for a blank test. The experiment lasted for 108 days in winter season. The result of the field test was favorable in spite of the interruptions of chemical addition into the crude oil. It would be reasonable to establish a hypothesis that some kinds of alkylnaphthalene act as an inhibitor for coagulation precipitation of solid by bridging carboid with liquid oil. Consequently, the Minamiaga "paraffin" trouble should be prevented by adding the inhibitor.