For the effective design of the disposal of the water-waste from oil and gas fields in the subsurface, the estimation of clay mineral content, its mineralogical studies, and the flood test, which is the continuous measurements of water-permeability of cores during the circulation of brine with varied salinity water, have been conducted in the pyroclastics of Takinoue Formation “T1 member”in Yufutsu Oil and Gas Field, Hokkaido, Japan. The mineralogical study showed that the clay mineral in T1 pyroclastic member can be identified with a smectite. The smectite expanded more after dropping brines with thinner salinity on the smectite. According to the chemical composition and concentration, the expandability of smectite, which can be detected in the measurements of space (d001) by X-ray diffractmeter, varied. More water-permeability of T1 cores decreased more with increasing smectite content, when the brine with relatively thinner salinity was injected through the core. These results suggest that smectite expanded and stuffed more pore space with decreasing salinity of brine, and then the permeability decreased. Meanwhile, the standard mineral of montmorillonite supplied by The Clay Science Society of Japan showed the same trend in the variation of d011 of the T1 smectite qualitatively, but differed from the T1 smectite quantitatively. It means that quantitative feature of the expandability of smectite should be required for the detail design for the water-waste. And these data could be also useful to evaluate the effects of the formation water on the permeability of the production zone.
The Tertiary Phitsanulok basin is well known for the Sirikit field which is the largest onshore oil field in Thailand. However, in the northern part of the basin, no oil field was discovered by previous operators who drilled some 12 vertical wildcats based on 2D seismic data in the 1980s. Geology of the basin is similar to that in the Gulf of Thailand. Its main reservoirs are lower Miocene fluvial sandstones which are thin bedded, poorly connected and compartmentalized by many faults. Moeco, who has produced oil and gas in the Gulf as a non-operator for 30 years, has applied the technologies used in the Gulf, and successfully discovered oil, and is currently conducting long term production testing in the onshore area. To increase the wildcat success ratio and to maximize the number of stacked pays discovered in fluvial sediments, crucial technologies employed include precise 3D seismic interpretation and drilling of deviated wells close to fault planes. Multiple stacked oil zones were discovered particularly in fault blocks sealed updip by normal faults that dip toward to the basin center. Moeco also has utilized technologies of slim well design, batch drilling and comingled oil production through 2-7/8” tubing to reduce drilling and operation cost and to make relatively small oil accumulations commercial.
This study aims at developing a new population-based global optimization algorithm, called iterative Latin hypercube samplings (ILHS), and applying the ILHS to a global optimization of well placement for geological storage of CO2. The ILHS utilizes a space-filling property specific to the Latin hypercube sampling (LHS) : each independent variable xj(j=1, …, d) is divided into n strata of equal marginal probability and sampled once from each stratum. In the ILHS, the LHS is generated iteratively while a cumulative distribution function for each variable at the current step is updated from the fitnesses evaluated at the previous step. This iterative process enables us to search a global optimum in a derivativefree way. Considering a global minimization of an objective function involving only continuous independent variables, the mathematical formulation of the basic algorithm is described first. In general, in order to carry out a numerical simulation of CO2 migration in the subsurface, the target domain is divided into multiple grids and the well placement is indicated by the grid index. Therefore, we need to consider a global optimization of an objective function involving discrete independent variables. Here, a brief handling method toward the application of the ILHS involving discrete independent variables is introduced and we attempt to find an optimal well placement using the ILHS so as to minimize the amount of mobile CO2. The results for example problems confirm that our proposed algorithm can search an optimal solution effectively within a practical number of simulation runs.
Isotopic studies for 20 gas samples and 17 water samples from three water-dissolved gas fields, the Nichinan, Miyazaki and Sadowara fields, in Miyazaki Prefecture, were carried out. Their results are summarized as follows. 1) Hydrocarbons are the major components in all gas samples. These hydrocarbons are chiefly composed of methane. The Kitago gas contains some carbon dioxide whoseδ13CCO2 value suggests a magmatic origin. 2) The δ13C values of hydrocarbons indicate that the origin of the gases in the Nichinan and Miyazaki fields is thermogenic. Because their maturity of the gases is estimated to be about 0.8% Ro equivalent based on the δ13C2-δ13C3 plot, they were probably generated in the Paleogene Nichinan Group. 3) Most of the hydrocarbon gases in the Sadowara field are microbial and mixed with a small amount of low maturity thermogenic gases which were supposed to be generated within the late Miocene to Pliocene Miyazaki Group. 4) Hydrocarbons in the Nichinan sample (Kitago) and one sample (Oyodo) of the Miyazaki field are biodegraded. 5) Formation waters in the Sadowara field are altered sea water trapped during deposition, whereas those in the Nichinan and Miyazaki fields are interpreted to be a mixture of meteoric water and fossil sea water. 6) Formation waters in the Sadowara field have relatively homogeneous 87Sr/86Sr ratios which are slightly lower than the ratio of sea water in the period of deposition.