| Abstract |
Eight wells intersected the Gagak Fault in the Darajat Geothermal Field. Of these wells, seven are capable of producing 10-30 MWe per well. An extensive study using Formation Micro Scanner (FMS) was conducted to identify density and orientation of the open fractures associated with the Gagak Fault. At subsurface, the Gagak Fault Zone is characterized by the appearance of high-density minor fractures (open fractures with narrow width size) and less dense major fractures (open fractures with larger width size). These fracture zones are usually associated with lost circulation zones, drilling breaks and steam entries during drilling. The density of open fractures increases with greater depth and this may be related to the rock type encountered (more abundant brittle lava and microdiorite at greater depth). The orientation of open fractures (major and minor fractures) is predominantly north-northeast to south ñ southwest. Surface traces of the Gagak Fault also indicate a similar trend, which is northeast to southwest. The FMS data shows that most of the open fractures are high angle fractures in the range of 700-800, and dipping to the east or southeast. The distribution and orientation of deep Micro Earthquakes (MEQ) support this interpretation. Higher volume steam entries or feed-zones are principally associated with the main Gagak Fault Zone at an elevation of 500 ñ 800 meters above sea level. Outside of the main fault zone, the steam is produced from the high-density minor fractures at a lower elevation. Along the Gagak Fault Zone, healed fractures (fractures filled by mineralization) occur mainly above 1000 meters above sea level. Study of the density and orientation of open fractures along the Gagak Fault Zone will assist to define the most permeable parts of the zone. Similar fracture studies can be applied in other geologic structures to define the most permeable areas in the field. |