Analysis of well test data from Indonesia and Iceland

Abstract

Analysis were carried out for injection tests of four high-temperature wells; namely wells KMJ-42, 43 and 45 in Kamojang, Indonesia and well KJ-13 in Krafla, Iceland. Several analysing methods were applied in order to determine transmissivity and storativity values for the reservoirs and the skin value of the reservoir/well systems. All the methods are based on a simplified reservoir model. The reservoir is assumed to be horizontal of uniform thickness and of infinite areal extent. It is also assumed homogeneous, isothermal and isotropic. Reservoir fluid is single-phase and obeys the Darcy law. The well test data is of variable quality, and especially the data from well KMJ-43 was difficult to interpret due to short duration of injection steps. Estimated transmissivity values are similar for all the wells, or of the order of 10-8 m3/Pa/s, which is typical for geothermal wells. Estimated storativity values are relatively high, especially for the wells in Kamojang. An explanation of the high storativity is that Kamojang is a vapor dominated system, but it should also be remembered that injection tests are not ideal for storativity determinations compared with interference tests. Both the Kamojang and the Krafla reservoirs are fractured reservoirs. It is therefore not surprising that the well test analysis yield negative skin values for the wells.