A study of production/injection data from slim holes and large-diameter wells at the Takigami Geothermal Field, Kyushu, Japan

A Study of Production/Injection Data from Slim Holes and Large-Diameter Wells at the Okuaizu Geothermal Field, Tohoku, Japan

“…The single-phase (liquid) productivity and injectivity index data for Sumikawa, Takigami, and Kirishima boreholes do not display a systematic correlation with borehole diameter (Garg et al, 1998). However, the injectivity and productivity indices for Oguni boreholes display a strong dependence on borehole diameter.…”

“…The productivity index for OA-4 (Table 4.1) is smaller by a factor of five or more than the productivity indices for large-diameter production wells at Okuaizu. Garg, et al (1998) remarked that a productivity index of the order of 0.3 kg/s-bar is required to obtain economically significant discharge rates from large-diameter wells with two-phase feedzones. Since the productivity index for OA-4 is only 0.035 kg/s-bar, it is clear that OA-4 is located in an unproductive area and is not representative of boreholes drilled within the main production area at Okuaizu.…”

Slimhole Handbook: Procedures and Recommendations for Slimhole Drilling and Testing in Geothermal Exploration

“…Like the Oguni slim holes, most ofthe slim holes at Takigami were also drilled with a complete loss of circulation, but this apparently did not result in any impairment ofborehole injectivity/productivity. Unfortunately, the borehole data from the Kirishima Geothermal Field l9 , 23 were not well-suited for evaluating the effect of borehole diameter on the injectivity/productivity index. Most ofthe slim holes -drilled early in the exploration phase -are located in the less permeable parts of~he reservoir, whereas a large fraction ofthe large-diameter production/injection wells were drilled to intersect the extremely permeable Ginyu fault zone.…”

“…To illustrate the computational procedure, slim hole KEI-6 was examined19. 23 A characteristic discharge test was performed from July 4 to July 8,1983. The borehole discharged a mixture ofwater and steam with wellhead enthalpies ranging from 937 kJ/kg to 1009 kJ/kg.…”

“…Despite considerable experimentation 23 involving well geometry and other model parameters, it proved impossible to match the downhole pressure profile ofJuly 11, 1983 using the reported discharge rate (10.07 tonslhour = 2.80 kg/s). Simply stated, a discharge rate of2.80 kg/s is inconsistent with the measured pressure profile in the cased part ofthe borehole (i.e., above -1000 meters).…”