To study how the viscoelastic flow behavior of polymer solution described in Part. 1 (ref. 1) had an effect on oil-recovery performance, 1 D flood experiments were carried out with glass-bead packed cores. Two white mineral oils of viscosity about 25mPa•s and 50mPa•s were used as displaced fluids. In each experiment, water and polymer floods were done with the same core at a relatively-high flooding velocity above 16μm/s. In polymer floods, polymer concentration of effluents was measured by the spectrophotometric method of M.W. SCOGGINS and J.W. MILLER. In polymer floods, oil was recovered faster as flooding velocity became faster. In high flooding velocity, interstitial velocity of polymer solution in the core becomes high and shear rate for flow becomes larger, too. The viscoelastic flow behavior of polymer solution that increased its viscosity with increasing shear rate was thought to improve mobility ratio and make oil recovery faster. By analysis of polymer-concentration histories of effluents, water bank was observed to be produced from the core before breakthrough of injected polymer solution. This water bank was thought to originate from mobile water which was initially present in the core before the flood. The histories of pressure of oil and water phase at the center of cores during flood experiments were measured separately with semi-permeable filters made of teflon and ceramics. Oil pressure could be measured well, but the method to measure water pressure was remained to be a problem. These data obtained in this study will be compared with calculated results by the simulater in the next paper.
Concerning the origin and structural developments of sedimentary basins, detailed case studies were made in the eastern part of the Sea of Japan and the Beibu Gulf of China where enough well data and seismic data were accumulated. Through these studies, a quantitative analysis for the subsidence of sedimentary basin was investigated. Three patterns were recognized for the subsidence of these basins such as 1) the isostatic initial subsidence, 2) the thermal subsidence, and 3) the flexure. Each of them is deeply associated with the evolution of sedimentary basins. This analysis seems to be an effective approach for the comprehensive evaluation of the sedimentary basins, therefore a detailed procedure for the analysis will be introduced. From this study, the developments of the basins in the Sea of Japan and the Beibu Gulf were summarized as follows: 1. Phase of the isostatic initial subsidence. a. The eastern part of the Sea of Japan subsided with rates of 16 times larger in comparison with that of the Beibu Gulf. In the eastern part of the Sea of Japan, subsidence with such a large scale in short time could be resulted from prominent volcanic activities of the final stage of the Green Tuff movement. b. The both basins subsided to about 3, 000m in depth. Main structural elements such as grabens were formed in this phase. It is believed that the important source rocks deposited in the end of this phase. c. Some important reservoirs are developed in the Green-tuff Formation in Japan. In the Beibu Gulf, similar reservoirs are not developed because of weak volcanic activities there, and sandstones are important reservoirs of this phase. 2. Phase of the thermal subsidence. a. Crustal thinning (24-32km) caused the conversion of relatively thickened asthenosphere to slightly more dense mantle lid and the basins subsided slowly in accordance with the movement. b. The ultimate amount of thermal subsidence (Do) of the eastern part of the Sea of Japan is larger than that of the Beibu Gulf. Thus the sediments in the Sea of Japan are greater than the Beibu Gulf. c. Remarkable structural movements in large scale during this phase did not take place in both areas. Therefore, only stratigraphic traps and anticlines which resulted from differential compaction are expected in this phase. 3. Phase of the flexure. a. Subsidence in this phase was more vigorous because of plate deflections accelerated by thick sedimentary load in comparison with that of the preceding phase. b. Flexural rigidity in the eastern part of the Sea of Japan is smaller than that of the Beibu Gulf, therefore, deflections of the crust of the Sea of Japan are larger. c. Tilting of the basin led to reactivation of faults, decollement movements and gravity gliding, and structural traps were formed in this phase.
Geochemical framework coupled with fluid flow model makes up an integrated computer system for basin evaluation in actual petroleum exploration. The model in high dimensions are believed to be more sophisticated and to result in better solutions, however, a functionally-restricted one-dimensional model is also useful for evaluations of exploration potentials in frontier basins, where only sparse geologic data are obtainable. Two- or three-dimensional model needs more precise geologic data for its appropriate results, therefore, it might not work properly with such sparse data. One-dimensional model, which simulates petroleum generation and expulsion process under an independent cell condition, is successfully applied for this type of exploration setting. Using newly-developed version of maturity model, the method of determining paleo-heat flow is also discussed. In the applications, the procedure sequence for one-dimensional basin analysis is introduced using the data from only one well in the Abu Dhabi area. Multi-well analysis is also demonstrated for areal evaluation of source rock potential in the Northwest Jawa area.
Construction of a realistic and efficient basin analysis model is one of the primary objectives of Japan National Oil Corporation's research project “Correlation Technology of Crude Oil and Source Rocks.” It started in 1988 and is planned to be completed in 1992; the completed model will be equipped with an I/O system that will utilize digitizers and engineering workstations to facilitate its use. As the phenomena of oil generation and migration, particularly that of the primary migration, are not well known today, the aforementioned JNOC research project includes the relevant laboratory experiments. To quickly respond to and cope with the knowledge resulting from these experiments, it was decided to develop a generation-migration model of relatively small size separately from a sedimentation model. Therefore, the aim of this compact model was to seek, without spending excessive computer time, the mathematical description which satisfactorily reproduce laboratory observations, and at the same time to find the most suitable numerical technique to approximate the mathematical problem. After two years of research and programming, the first version model was completed and tested. This report briefly describes this oil generation-migration model and then shows the calculation results of a few example runs that simulate some features of laboratory experiments.
Petroleum explorations become more difficult recently, because its target is deeper and the trap types are more, complicated. This paper presents discussion about timing between formation of deep-seated fracture reservoir and trapping hydrocarbon (generation, migration and accumulation) in an area of the Hokkaido region. Tectonic stress is thought to be a main driving force of fracturing. In this tectonic simulation, formation and development of fracture in every sedimentation step is reproduced by using Virtual Basement Displacement Method (KODAMA et al., 1985). The plastic strain that formed fractured reservoir tends to concentrate in the surrounding area of Well A during all the geologic time except a period of depositing e formation. On the other hand, there are not so significant concentration around Wells B and C through the time. It can be thought that Well A and its surrounding area seem to be favorable for forming fractured reservoir. For the hydrocarbon generation, migration and accumulation simulation, large permeability value is input to a position of large plasitic strain observed by the tectonic simulation in order to investigate effect of tectonic fracturing. It is an evidence from the experiments by the model that fluid pressure around Well D should increase without tectonic fracturing whereas no excess pressure would be observed in the case that tectonic fracturing has occurred. This result is supported by the fact that density logging from Well D shows that all the data are plotted on the normal trend and there are no indication for abnormal pressure while drilling. Gas saturation around Well A is also higher as a result of effective flow into the reservoirs by the tectonic fracturing. The peak of generation rate of oil and gas exist during the period of depositing d formation and e formation. As a conclusion of the study of these simulations, the area has enough hydroacarbon generation potential. However, focusing on formation of the trap (fractured reservoir), Well A and its surrounding area has a possibility of forming fractured oil and gas field.