Abstract
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.
