Case Study: Well Th-G15, Theistareykir Geothermal Field, Northeastern Iceland

The sensitivity of measurement in combination with 100% circumferential coverage makes acoustic borehole images useful for detecting drilling-induced fractures and breakouts, improving fracture analysis, and determining borehole stability. The accuracy of the borehole images paired with skilled image interpretation helps to understand if fractures are open or healed, which leads to optimized fracture characterization for enhanced well testing and production.

Production well ThG-15 was logged by Iceland GeoSurvey (Íslenskar Orkurannsóknir (ÍSOR)) on behalf of Landsvirkjun using an ABI-43 tool. The well is located in Theistareykir geothermal field, Thingeyjarsveit, northeastern Iceland.

The main objective of this study was to provide detailed fracture and fault analysis, including fracture and fault classification, and determination of the orientation and density of fractures and faults.

Fractures are well developed over almost the entire interval and are almost exclusively open; only 6 closed fractures were recognized. Discontinuous open fractures are the predominant fracture type: 2,065 were identified. 20 open faults were identified and demonstrate a high degree of scatter in strike direction and azimuth, and their dip magnitudes are also highly variable. 24 drilling-induced fractures were identified, with a dominant strike of NE-SW. 8 borehole breakouts were identified, with a dominant strike of NW-SE. There is significant variation in these orientations, with secondary NNE-SSW and ENE-WSW drilling-induced fracture strikes, and secondary NNW-SSE striking borehole breakouts.

Six fracture zones were determined, based mainly on fracture strike orientation and dip magnitude. Fracture zone 6 (2,223-1,761 m MD) had the highest rates of lost circulation. This fracture zone shows a high degree of scatter in strike and azimuth. Dip magnitudes of open fractures in this zone are also highly variable. These conditions may create a better fracture network. Zones of lost circulation and feed zones are mainly associated with large continuous and discontinuous open fractures, and possible open faults.

Download the full technical paper to learn more.