Oil or gas production causes reservoir depletion. It occasionally induces reservoir compaction and subsidence and horizontal earth surface movement. Oil and Gas are found in 3D shape structures such as anticline, or inclined fault traps. In addition, the ground surface, where we observe the earth surface movements above such 3D reservoirs, may not be flat. The earth surface movements are affected by topography of ground surface above reservoirs and 3D reservoir shape. However, the 3D-analysis of subsidence problem has not been researched sufficiently for the complexity of 3D structural modeling. This paper analyzes 3D reservoir and earth surface geometry effect on subsidence and horizontal earth movement during reservoir compaction, using a 3D boundary element model(BEM). BEM is suitable for the 3D subsidence model, because the complex topography of ground surface and 3D reservoir meshes can be easily constructed. The conclusion shows that(1)if the reservoir depth is large, or small but reservoir shape isn't very complex, the results produced by conventional models(flat and horizontal reservoir with a flat ground surface)give similar results for subsidence and horizontal movement if some adjustment is made for reservoir area, depth, and thickness. Therefore, for the analysis of subsidence and horizontal movement, we can use the conventional models made for geological adjustments. However, for the inversion problem(ex. Inversion analysis of reservoir compaction using surface movements as input data), the 3D position of reservoir plane must be input from other information such as seismic analysis;(2)if the reservoir depth is small, the exact 3D reservoir shape and non-flat ground surface topography with mountains or valleys should be modeled to simulate the subsidence and horizontal movement during reservoir compaction, because the subsidence and horizontal movement are uniquely affected by each 3D reservoir shape and mountain or valley size and location.
The purpose of this study is to develop practical and versatile analytical solutions of well testing for the reservoir with radial property variation. Here, “practical” means that the calculation cost is not so expensive and “versatile” means that the algorisms are numerically stable”. Two analytical solutions for this problem are presented and improved. The first is the perturbative solution which was introduced by Oliver. Although this solution could treat the continuous function of permeability variation, the first order perturbation remains some errors when the center of the perturbation is set to constant. Thus, we develop a new function to estimate an adequate average permeability which should be applied in order to obtain the good approximation of pressure calculation. The result is excellent; however, this solution is a little tedious to apply for the porosity variation problems. In addition, it is difficult to expand this solution for the problem that the reservoir property changes with time. The second solution is multi-composite solution which is appeared in several papers. “Multi-composite model” treats of permeability and porosity variation as stair-step functions, however, the excellent approximation will be obtained on the condition that the “steps” are enough fine. The fine steps require high calculation cost. This paper presents several mathematical techniques in order to save this cost as well as to obtain numerical stability. Moreover, “Stepwise approach” enables us to treat the time dependent reservoir parameter, such as permeability change with time. Because “Stepwise approach” does not require any superposition of rate, calculation speed is very fast even in the case that production rate is frequently changed.
Almost all sedimentary basins of the world have already been explored and field data have been accumulated. However, available statistical methods for predicting future discoveries (e.g. creaming curve) are qualitative or semi-quantitative, and no real quantitative method has been established to date. In this study, assuming power-law (fractal) distribution for subsurface field size and treating exploration as a stochastic process consisting of random walks, a fully quantitative method is developed for predicting number, size and cumulative reserves of future discoveries. First, the concept of the method is explained using discrete binomial distribution for fluctuation, and then, an “exploration simulator” is introduced applying continuous normal distribution and Monte Carlo simulation. The application to a number of basins of the world has verified the validity of this method, which can provide useful guidance for the future exploration efforts and reliable supply-side information for the “peak oil” argument.
In recent years, high pressure air injection (HPAI) into a light oil reservoir has been proven as one of valuable EOR technologies. HPAI is applied for light oil reservoirs where reduction of viscosity by thermal effect is not so important, because the original viscosity of light oil is not as high as heavy oil. As one of the most important recovery mechanisms of HPAI is immiscible flue gas flooding, HPAI process has sometimes been comparable to flue gas or nitrogen injection in general. But this is true only when the oil saturation of the reservoir is high enough and if the reservoir is waterflooded, distillation process by its thermal effect at combustion front is a critical factor for improved oil recovery. This paper discusses the applicability of HPAI for highly water saturated light oil reservoirs, by combustion tube tests (CT tests) and numerical simulation studies. One CT test was conducted with waterflooded core. Additional oil recovery was confirmed in this test, which implies the successful oil recovery from highly water saturated light oil reservoirs. To investigate oil recovery mechanism, a series of simulation studies of CT test was conducted. Through these studies it was clarified that the important oil recovery mechanism for high water saturation reservoir is the distillation process. By this mechanism oil bank was created at the combustion front and significant oil production was observed after some amount of water production in both CT test and its simulation.
Thirty years passed since the Cretaceous Oceanic Anoxic Events were proposed by Schlanger and Jenkyns (1976). Three events, OAE1 to 3 were recognized at the beginning of the research. Nowadays, however, OAE1 is subdivided into four subevents, OAE1a, b, c, and d. The OAE1b subevent is further subdivided into three components, Jacob, Paquier, and Leenhardt. The existence of Mid-Cenomanian Event (MCE) between OAE1d and OAE2 is drawing attentions of world scientists. A concise review of the researches on these events and subevents is followed by more detailed descriptions of the synonymy (local names), geographic distribution, age, stable carbon isotope fluctuations, extinction and/or radiation of fossils, major synchronous events, characteristics including the duration and the types of kerogen, and their causal factors. It is recognized that all OAEs do not have the same causal factor. The western part of the Tethys and the narrower early Atlantic were rather closed basins, where anoxic to dysoxic conditions easily occurred through the stratification of water column by run off, like the Sapropel event 1 in the Holocene Mediterranean Sea. The Cretaceous global OAEs may have occurred either by the stagnation of the deep water associated with the global warming or by propagation of marine organisms. Due to a large amount of input of terrestrial siliciclasitics, the regional influence of OAEs in the Japanese Cretaceous strata may differ from that of the Tethyan/Atlantic region, even if the occurrence of OAEs is ocean wide or globally synchronous.