トレーサテストによる雄勝貯留層の特性評価

抄録

In order to characterize the Ogachi reservoir, four tracer tests have been carried out successfully, twice in 1994, one times in 1995 and 1997, respectively, at the CRIEPI's Ogachi HDR site in Akita prefecture, Japan. Since the response curve obtained from the tracer monitoring involves two curves due to the two reservoir, the upper and the lower, a numerical simulation of two flow path model was done to separate the response curve each other.
Using the response curves obtained by monitoring and calculation, the characteristics of the Ogachi reservoir was estimated. The results are as follows ;1) Considering the fitting of the synthesized and observed curves, the Ogachi reservoir is evaluated to have multiple paths.2) Modal volumes of the upper reservoir are estimated 9.5 m³ in 1994's 1st test, 12.5 m³ in 1994's 2nd test, 18.7 m³ in 1995, and those of the lower are estimated 298 m³, 249 m³, 106 m³, respectively. Through the circulation tests, the modal volume of the lower reservoir decreases gradually, and in 1995 test, the modal volume decreases remarkably, because of permeability improvement of the lower reservoir performed before the circulation.3) Values of width at 1/2 height which is assumed to represent dispersion of the reservoir decreases between 1994 and 1995, but the value increases in 1997. This increase is supposed to be based on the plugging to the fracture of the sand which is used before circulation, or the precipitation in the fracture because of the cooling down in the reservoir due to huge water injection to the reservoir before circulation.