3D MODELING OF HELLISHEIDI GEOTHERMAL FIELD USING LEAPFROGPresented at GEORG workshop, Reykjavik, 25th of November 2016

1. Goals of the project

3D modeling of Hellisheidi Geothermal field using LeapfrogCollaborative project between ISOR and Orkuveita Reykjavikur Leapfrog Geo is a modeling software developed by ARANZGEO

− Compile all relevant data on geothermal research and drilling in Hellisheiði.

− Build a first simple geological and structural model of Hellisheiði, − Establish an alteration mineralogy model,− Integrate the temperature and resistivity models from previous work,− Increase the understanding of the Hellisheidi geothermal field

2 Project frame

Generalities:− SW-Iceland, about 30 km east of

Reykjavik− Hengill volcanic system− Currently 210 MW

Study area− Based on well locations

and future drilling targets

− Oriented SW-NE − 7,80 km x 9,55 km − Approx. 74,55 km2− 56 deep production wells (HE)− 17 deep injector (HN)− 71 groundwater wells

3 Data compilation

Category Data integrated

Surface data

DEM gridAerial pictureWell locationGeological mapFaultsEruptive fissuresSurface manifestations

Well data

Directionnal surveysLithologyIntrusive formationsAlterationMineralogyOxydationFracture fillingAquifersDrilling parameters

Well logging data

Temperature logsGeophysical logs - Gamma - Neutron-Neutron - Resistivity 16/64 - CaliperTeleviewer data

Geophysics

AeromagneticsGravity mapMT (1D and 3D inversion)Seismicity recordsGPS surface displacement

Laboratory work / desktop studiesXRD analysisAquifer studies

Detailed structural analysis

4. Building the models

Five models were generated:- Lithological model- Structural model- Alteration model- Temperature model - Resistivity model

The lithological and structural models were combined to create the geological model.The temperature and resistivity models are based on work done previously and were integrated in Leapfrog Geo.

4. Building the models

Lithological model:

Surface geology shows: - Central Hyaloclastite ridge- Holocene lava flows- Eruptive fissures

Main obstacles:- Thickness, grain size and extend of lava flows varies greatly- Hyaloclastite formation includes glassy basalt, basaltic breccia and basaltic tuff which can

be very irregular- Rare intermediate and acidic intrusions, no correlation possible

- Group in three major lithologies: basaltic flows, basaltic intrusions and hyaloclastites. - Units less than 10 meters not considered

4. Building the models

Lithological model:Step 1: Simplify the lithological logs

4. Building the models

Lithological model:Step 2: Correlate and build the basaltic flows and basaltic intrusions

Basaltic flows:- grouped based on their elevation, thickness and location,- 13 major basaltic flows modeled,- The basement is constituted of basalt to – 3000 m bsl. (assumption),- Surface geologic boundaries digitized and integrated

Basaltic intrusions- grouped based on their vertical and horizontal alignment,- matched with surface faults associated to the rifting,- 15 intrusions were modeled- 2 of the intrusions related to the recent surface eruptive fissures,- Surface geologic boundaries digitized and integrated.

4. Building the models

Lithological model:Step 2: Correlate and build the basaltic flows and basaltic intrusions

4. Building the models

Lithological model:Step 3: Fill the empty volume

The volume left is filled with the hyaloclastite formations.Topography is used as the upper boundary

4. Building the models

Lithological model:

4. Building the models

Structural model:

Two major fault systems were integrated:- Faults associated to the rifting, generated using the surface fault mapping in

correlation with Basaltic intrusions and drilling parameters such as loss of Circulation, as well as geophysical logs (Gamma, NN, Resistivity)

- Faults associated to the Transform Seismic Zone related to the shift of the rit activity, using seismic events alignments (based on work from Árnason and Magnússon, 2001). Two main directions of faulting: N 80-85° and N 05°, presented as vertical structures.

4. Building the models

Structural model:

4. Building the modelsGeological model:Combination of the lithological and structural models

4. Building the modelsAlteration mineralogy model:Based on the results of X-Ray diffraction analyses on XX samples in XX wells, and on the apparition of Epidote in the cuttings

4. Building the modelsAlteration mineralogy model:A 3D model is generated from the well data and few manual input were necessary.

4. Building the modelsTemperature model: Based on formation temperature surveys, model generated by OR

4. Building the models

Resistivity model:

The model is based on the 3D inversion of the data generated during three research projects

- Total of 148 MT soundings, coupled with TEM soundings (15 soundings of poor quality removed)

Processing and interpretation during the Advanced 3D Project (Árnason et al., 2010, Rosenkjær et al., 2015; Gasperikova et al., 2015)

4. Building the modelsResistivity model:

− Leapfrog can combine several models (or elements of models) together and calculate their volumetric intersections

− 3 combined models were generated:− Low resistivity and alteration mineralogy model

− Temperature on Basaltic intrusions

− Alteration mineralogy at T ≥ 280°

5. Model combinations

5. Model combinationsAlteration mineralogy and low resistivity (≤ 10 ohm.m):

5. Model combinationsTemperature on basaltic intrusions:

5. Model combinationsAlteration mineralogy at T ≥ 280°

6. Well prognosis

- Well HE-59 was drilled in June 2016 for OR

- Directionally drilled toward the WSW

- Drilled down to 2381 m with full losses from 838 m and the last cuttings at 902 m

- Temperature log allowed to locate major aquifers

HE-59

6. Well prognosis

7. Conclusion

− A new methodology has been implemented to use well data to generate a geological model in Leapfrog and could be applied to other area with similar geological settings,

− The accuracy of the interpretation for lithology, structure or alteration minerals is related to the density of wells in a given area, the East / South East part of the model contains less data from wells,

− When new data are available (new well, geophysics...) or more detailed work is available, the model should be refined and improved,

− The high density of faults and limited structural analyses available make it complicated to generate a structural model and to take account of the offset of the faults