| Title | Effective Tools for Exploring the Tectonic Evolution and Sub-surface Permeability of the Southern Negros Geothermal Field |
|---|---|
| Authors | Loraine PASTORIZA-PRIMALEON, Robert E. HOLDSWORTH, Kenneth J.W. MCCAFFREY, Edward DEMPSEY |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Southern Negros, tectonic evolution, palaeostress analysis, fracture attribute analysis, topology |
| Abstract | A fieldwork-based approach has been used to evaluate the potential fracture permeability characteristics of a typical high-temperature geothermal reservoir in the Southern Negros Geothermal Field, Philippines. Based on fault rock characteristics, alteration type, relative age of deformation, and associated thermal manifestation, two fracture groups have been identified with the youngest fractures mainly related to the development of the current geothermal system. Fault kinematics, cross-cutting relationships, and palaeostress analyses suggest at least two distinct deformation events under changing stress fields since probably the Pliocene, herein proposed to be influenced by the development of the Cuernos de Negros Volcano and the northward propagation of a major neotectonic structure located to the northwest, the Yupisan Fault. A combined slip and dilation tendency analysis of the mapped faults indicates that NW-SE structures should be particularly promising drilling targets under the inferred current stress regime. Frequency versus length and aperture plots of fractures across six to eight orders of magnitude can be described by a power law distribution, with a change in scaling exponent in the 100 to 500 m length-scale range. An evaluation of the topology of the fracture branches shows a dominance of Y-nodes that are mostly doubly connected suggesting good connectivity and permeability within the fracture networks. The self-similarity of the fracture size distribution of the outcrop and borehole datasets suggests that the fracture network mapped in the surface are good analogues for the fracture system at reservoir depths. This work illustrates how a range of table-based tools can effectively be applied to improve understanding of a geothermal system and reduce uncertainties during the exploration and development phases of a field. |