マルチフィードに対応した坑井シミュレータMULFEWSの開発と八丁原フィールドデータ解析への適用
2005 年 27 巻 1 号 p. 11-26
詳細
2005 年 27 巻 1 号 p. 11-26
Geothermal production wells with multiple feed zones often show complicated performance over time in terms of deliverability, reflecting changes in surrounding reservoir conditions. For the purpose of clarifying the reservoir properties of each feed zone and their contributions to the productivity of a well with multiple feed zones, a multi-feed wellbore simulator named MULFEWS has been developed. The numerical model at the heart of MULFEWS describes a well surrounded by porous reservoirs and was designed so that it can be applied to calculate not only pressure, temperature and velocity distributions in a well, but also deliverability curves at wellhead, which represent relationship between wellhead pressures and steam, water and total mass flow rates. MULFEWS was applied to the analysis of field data from a production well H-27 at the Hatchobaru geothermal field in Japan, which has four main feed zones and has shown a tendency to increase its water flow rate over time. Consequently, a close matching of measured and calculated results was successfully obtained. The results of the analysis suggest that the reservoirs should be classified into two types, shallower and deeper reservoirs. The shallower reservoirs have changed from a steam and liquid two-phase system to a liquid single-phase system due to a decrease in reservoir temperature. On the other hand, the deeper reservoir has mostly remained liquid single-phase system. The liquid in deeper reservoir has flowed into the wellbore and then begun to flash near the bottom of the hole, although the liquid had initially begun to flash within the formation. Those changes are considered to occur due to the inflow of low temperature fluids from the surrounding formations. The migration of a flash point from the formation to the inside of the well has remarkably increased the water-flow rate. MULFEWS can be used for the interpretation of a well with multiple feed zones to quantitatively explain changes in the reservoir properties of each feed zone and their impact on deliverability.
