The importance of the carbonate rocks as reservoirs is underscored by the fact that they are host to about 46 percent of the oil in the “giant oil fields”. So, lately the studies have been published on the carbonate source rocks and organic geochemistry of the carbonate rocks. However, the objects of those studies were not limited on the source rocks of “reservoir oil”. Consequently, some of those studies conducted the incorrect conclusions. The object of this study is limited on the source rocks of “reservoir oil”. The lithology of the carbonate source rocks of “reservoir oil” is the impure and/or argillaceous carbonate rocks. These carbonate source rocks are deposited on the stable shelf, intershelf, platform or ramp with minor episodes of terrigenous influx. Water depth of the sedimentary environments are intertidal to subtidal or shallow to moderately deep marine. These environments are essentially anoxic or disaerobic. Total organic carbon contents of the carbonate source rocks are 0.5wt.% and over, and these values are equivalent to the contents of the shale source rocks. And EOM and HC contents are equivalent to EOM and HC contents of the shale source rocks too. The CPI values of extracted n-alkane are 1 or less than 1.
In this paper, as a series of studies concerning the carbonate source rocks, characteristics of Rock-Eval analysis and petroleum derived from carbonate source rocks are discussed. Many Tmax values of Rock Eval analyses of carbonate source rocks indicate early mature or immature stage, though those rocks generated reservoir petroleum. And a few Tmax values indicate over mature stage. The kerogen type is the oil prone I or II. The pristane/phytane ratio and the saturate/aromatic hydrocarbon ratio are increase with maturation. Oil gravity and sulfur content are controlled by maturation and the low matured oils are heavy and have high sulfur contents and the high matured oils are light and have low sulfur contents. As the oil generated from carbonate rocks may have a tendency of low maturation, consequently the tendencies that the oil generated from carbonate source rocks are heavy and have high sulfur contents may be recognized. The CPI values of n-alkane extracted from oil are 1 or less than 1.
The boundary element method (BEM), successfully used for the solution of fluid flow problems in porous media, has shown its flexibility and computational efficiency superior to domain methods, such as finite differences or finite elements. Especially in discretization-sensitive problems, since the BEM does not require any discretization in the flow domain, its superiority over others becomes much more attractive. Steady-state flow problem including sink-source can be described by Poisson's equation and boundary conditions. To this day, this problem has been investigated by using the BEM only with vertical wells as sinks and/or sources. These wells are represented as points in a two-dimensional (2D) domain. This paper presents an extension of the BEM applicability to horizontal or hydraulically fractured wells which can be represented as line-sources in a 2D domain, if we postulate 2D flow. Through mathematical manipulations starting from the second form of Green's theorem, the BEM treatment of line-sources yielded a line-integral of Green's function. With the developed BEM program, solved were streamline and displacing front tracking problems. For both point and line sources, the BEM was found to be an excellent means to the end of fluid flow computations.
The buoyed weight method, and the weight (in the air) and pressure method have been used to calculate the weight of a string in a well. These methods have also been used to determine an axial load at any point in a string. Though an axial load must be determined, for instance, to make a bi-axial correction of collapse resistance of a casing and to practice the tri-axial stress casing design method, conventional methods to know axial loads can not be applied to strings in directional wells. A theoretical investigation of loads in strings in directional wells was performed. Then a simple method to determine axial loads of strings in directional wells was developed. The key parameters of this method are vertical lengths of pipes, weight (in the air)/foot of pipes and hydrostatic pressures on pipes. The axial loads at the surface calculated with this new method almost coincide with actual field data. This paper presents the investigation of loads in strings in directional wells and describes the new method to determine axial loads of strings. This paper also describes an idea how to predict drags of strings in directional wells.
The conventional fluorescence reaction by UV light is a very popular and simple method for oil show detection of cuttings or core samples at oil field. This method is, however, unreliable because of detection with naked eye and it is impossible to distinguish between crude oil and mud materials, especially derived from petroleum products having strong fluorescence. In this report, a new synchronous spectrofluorimetric method for making a discrimination between crude oils and the mud materials is described. Although synchronous fluorescence spectra of the mud materials are similar to those of crude oils, it is possible to distinguish clearly between the mud materials and crude oils having density more than 0.8g/cm3 by comparing fluorescence strengths of monoaromatic (MA), diaromatic (DA) and triaromatic (TA) compounds in the spectra. The crude oils investigated have relatively high TA/DA and low MA/DA ratios, whereas the mud materials have high MA/DA and low TA/DA. When the data are plotted, with TA/DA as ordinate and MA/DA as abscissa, the location of the plot indicates whether the sample is crude oil or the mud materials. This method can be applied to oil show detection of core samples as the more reliable method than the fluorescence reaction method.
We describe in detail the calcareous nannofossil biostratigraphy of the lower to middle Miocene formations distributed along the coast of the Japan Sea. The lowermost marine sediments overlying the “Green Tuff” volcanics in these areas are characterized by the occurrence of Helicosphaera ampliaperta, Discoaster deflundrei, Sphenolithus heteromorphus, and Cyclicargolithus floridanus. These assemblages indicate that the first marine environment invaded the coast of the Japan Sea side in NN 4 Zone of Martini's zonation (16.01Ma-18.74Ma) in Early Miocene. The lithofacies of these formations in NN 4 to NN 5 zones (13.17Ma-18.74Ma) are composed of fossiliferous sundstone and mudstone in the Dewa Mountains area and the Sekiryo area (Ou Backbone Range) respectively. In contrast to these areas, the Akita Oil Field, trending north to south along the coast of Japan Sea on the west of the Dewa Mountains area, is characterized by the tholeiite type basalt activity in this age. Simultaneously with the end of basaltic volcanic activity at NN 5/NN 6 boundary in the Akita Oil Field, the lithofacies of sediments have changed from fossiliferous sundstone to mudstone in the Dewa Mountains area, and from mudstone to fossil bearing sandy siltstone in the Sekiryo area. Based on these facts, we conclude that the lowermost marine sediments distributed in the Japan Sea side are correlated to Early Miocene NN 4 Zone. The Akita Oil Field on the west of the Dewa Mountains is characterized by the basaltic volcanic activity during NN 4 to NN 5 zones, and the end of its activity is related to the paleoenvironmental change from shallow to bathyal in the Dewa Mountains areas and bathyal to shallow in the Sekiryo area at the NN 5/NN 6 boundary in early Middle Miocene.