Natural gas dissolved in water and iodine brine are produced in south Kanto area, Japan. Nowadays, most waste brine is discharged to the ocean or rivers. However, in the future, most waste brine might be required to inject into producing layers to avoid environmental issues. In this situation, it is important to evaluate the influence of waste brine injected into producing layers. This paper presents a simulation model for water-dissolved natural gas field which can handle iodine ion component in brine. The model was constructed by applying a commercial compositional simulator especially developed to simulate carbon dioxide storage in aquifer. At first, the model was validated against gas water ratio, static bottom hole pressure of production and injection wells, and iodine ion concentration in produced brine measured at real gas wells in Minami (South) Kanto water-dissolved natural gas field. Then the model was utilized to evaluate the influence of waste brine injected into producing layers and followings were obtained: 1) Even at homogeneous reservoir, injected waste brine volume of shallower layers was larger than that of deeper layers. 2) Iodine concentration of shallower layers declined due to the injection of waste brine with low iodine ion concentration. 3) Estimation of breakthrough time by the variation of iodine or tracer ion concentration in produced brine might be appropriate compared with the estimation by that of gas water ratio. 4) Even after the breakthrough of injected waste brine, decrease of iodine ion concentration in produced brine was so gentle that iodine brine might be produced economically for a certain period of time. 5) Bottom hole pressure drop of a producing well was depressed to a certain level by injecting waste brine into producing layers. The model presented in this paper might be useful for making optimum development plan of water-dissolved natural gas field.
Thick and porous reservoirs induce significant compaction with production, resulting in screen and casing failures within the reservoir section and inducing casing tensile/shear failures within the cap rock section. Designing these wells based on the conventional API specification requires excessively heavy duty casings, resulting in low hydrocarbon productivity with a high cost. However, casing failure problems often have not been eliminated by using high duty casings. The problem is the higher grade casings show a tendency to be more brittle than lower grade casings. In actual fields, casings are often used beyond the yield point. Casings can be used as long as they don't excessively distort even if the stress exceeds the yield point to some extent. Therefore, this research focuses on the possibility of using casings under extreme conditions. This research provides a new design concept based on the ultimate tensile strength and the strain. These values are obtained from the tension tests conducted for casings ranging from high grades to low grades. Especially, this paper emphasizes the importance of the strain rather than stress for judging the ultimate casing failure.
Most of the conventional EOR processes have already been established, and the development of a new innovative EOR process is quite difficult. Therefore, the sweep efficiency improvement (SEI) is more important for an efficient EOR. Several SEI methods have been applied actually in many fields. However, the injected EOR fluid tends to flow selectively in the already swept high permeable zones, and the sweep efficiency is poor as the result. In this case, in-depth profile modification by blocking such the already swept high permeable zones with a polymer gel would be a more effective than already existing SEI methods. In this study, numerical simulations to confirm the effect of the in-depth profile modification on SEI has been conducted to thirty-two heterogeneous reservoir models under the several blocking conditions. The relation between the blocking effect on SEI and the heterogeneity indexes, which are Dykstra-Parsons coefficient for vertical heterogeneity and correlation length for horizontal heterogeneity, is also investigated. From this study, following results have been obtained. First, the blocking effect increases with the increase in the volume of injected polymer gel and the decrease in the volume of chase water. That is to say, the blocking effect increases when the blocking is done more perfectly. Second, the blocking effect increases with the increase in the vertical heterogeneity, and horizontal heterogeneity is less correlated to the blocking effect compared to the vertical heterogeneity.