Application of Geophysical and Remote Sensing Techniques in Mapping Faults in Olkaria Geothermal Field, Kenya

Abstract

The main structures controlling fluid movement within the Olkaria geothermal reservoir are the fault and the ring structures. The Olkaria West Field (OWF) and East fields are separated by a low-temperature zone; the wells also show different reservoir fluid characteristics. Gravity and magnetics exploration in the field has been done before but not analysed to demarcate structures separating these zones and the features therein. This research aimed to re-evaluate geophysical data from Olkaria central field to identify faults network replenishing the reservoir. Mapping of structural lineaments was done by integrating remote sensing, gravity and magnetics geophysical methods. Sentinel-1 data was obtained from European Space Agency (ESA) open source and the Sentinel Application Platform (SNAP) software was used. Gravity and magnetics data was collected by Kenya Electricity Generating Company (KenGen). Gravity data was corrected to give a Complete Bouguer Anomaly (CBA) and magnetics data was pole-reduced to improve geometric response. The First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) was used to enhance data for both gravity and magnetics data. Automatic lineament extraction from residual contour maps was done using the LINE module algorithm, it was fast compared to other methods of obtaining lineaments. From the lineament and lineaments density maps the area has many lithological boundaries. Orientation of lineaments matched those of previous studies. Correlation of high density lineaments was done through visual interpretation, which showed correlation in the three methods. Integration of three techniques brought out a better display of faulting and fracturing of the reservoir, where highly fractured zones were distributed rather than appearing in a north south orientation between the East and the West field. Line module algorithm is capable of extracting lineaments from mapped data and integrating various methods provide more reliable results and can be applied in other techniques of geophysical mapping.