Analysis of Pressure Transient Data from ' Lte Sumika

The permeability structure of the Sumikawa geothermal field in northern Japan has been the subject of an extensive pressure-transient testing investigation since 1986. In this paper, various pertinent data sets are presented and analyzed, including results showing reservoir heterogeneity (i.e. boundary) effects and apparent double porosity behavior. Interference tests between wells SB-3 and SD-2 (both of which have feedpoints in dacitic layers in the "marine-volcanic complex" formation) were carried out during 1990. The results have been interpreted to indicate the presence of a moderately high permeability (4 darcy-meters) layer with two impermeable boundaries intersecting at a right angle. The 1988 pressure buildup data for well SN-7D are also explained by assuming two impermeable boundaries in a high transmissivity reservoir within the deep "granodiorite" formation. Interference tests between wells S-4 and KY-1 have suggested that a very permeable north-south channel is present in the "altered andesite" layer. Although the response was successfully interpreted using an "anisotropic line-source model" by Garg et a1.(1991), a "double porosity channel model" seems to be particularly applicable for explaining both the short-term and long-term behavior observed in this series of tests.