Mapping Reservoir Permeability with Geoelectrical, FMS and Spinner Data, Kamojang Field, Indonesia

Abstract

More than 60 wells have been drilled at the Kamojang field, a vapor-dominated resource with 140 MWe installed capacity. The resource is hosted by Quaternary volcanics, and fracture permeability is provided by horst and graben structures that intersect with volcanic collapse features. Resistibility data suggest that the resource covers 21 km2. Production from wells in the northern and southern sectors of the field is reduced because of low permeability, although the wells encountered high temperatures.

The reservoir rocks are composed of the Rakutak basaltic andesite formation (~2 my) overlying the Gandapura andesite formation (~0.4 my). Petrographic studies of hydrothermal alteration in the reservoir rocks show that the Gandapura formation exhibits strong argillic alteration while the Rakutak formation exhibit low to moderate intensity propylitic alteration.

In order to map the permeability structure of the reservoir, geoelectrical data from CSAMT (Controlled Source Audio Magneto Tellurics) and MAM (Mise-A-la-Masse) have been analyzed together with bore hole data, including well production rates, permeability indication from lost circulation, and limited FMS (Formation Micro Scanner) and spinner data. The results are incorporated into a map of reservoir permeability. Good permeability extends to the NE and NW while moderate permeability extends to the south. A low permeability barrier is found inside the field. Spinner data indicate that higher productivity is associated with higher evaluation reservoir feed zones. These studies of reservoir permeability indicate that both fault planes and the contact zone between the Pakutak and Gandapura formations provide important controls on reservoir permeability.

The permeability structure map can be used for planning the drilling strategy at the Kamojang field. In particular, these results support exploration drilling in the northeastern and northwester sectors of the field.