Fracture attribute and topology characteristics of a geothermal reservoir: Southern Negros, Philippines

Abstract

The characterization of fracture networks using attribute and topological analyses has not been widely applied to the understanding and prediction of the secondary porosity, permeability and fluid flow characteristics of geothermal resources. We acquired fracture length, aperture, intensity and topological data from remotely sensed images and surface exposures of the Cuernos de Negros region and compared these data with well cores and thin sections from the underlying active geothermal reservoir: the Southern Negros Geothermal Field, west central Philippines. We show that the fracture attributes of the analogue and reservoir are best described by a power law distribution of fracture length and aperture intensity across six to eight orders of magnitude. This characterization of outcrop and borehole fractures validates the use of surface exposures as analogues for the Southern Negros Geothermal Field reservoir rocks at depth. An observed change in the scaling exponent in the 100–500 m length scale suggests that regional to sub-regional fracture systems scale differently from those at the meso- and macroscale, which may be a strata-bound effect or a sampling issue. Topological analyses show a dominance of Y-nodes and doubly connected branches, that indicates a high degree of fracture connectivity, which is important for effective fluid flow.Supplementary Material: Slopes, coefficient of determination and Aikake information criterion values of the cumulative frequency v. length and aperture plots of all fracture transects are available at https://doi.org/10.6084/m9.figshare.c.4960559Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

Multiscale Characterisation of Fracture Patterns of a Crystalline Reservoir Analogue

“…Cumulative length distributions of discontinuities were then analysed and fitted to a power law. On a local scale, log-normal and exponential fits may also be valid [60][61][62][63]. However, the multiscale character of the fracture network investigated here requires a power law.…”

Fracture attribute scaling and connectivity in the Devonian Orcadian Basin with implications for geologically equivalent sub-surface fractured reservoirs

“…ENE-WSW-trending faults dominate in this region (see SJ rose diagram in Fig. 5a) and show corridor arrangements in the sense of Questiaux et al (2010). The orientations of these faults are comparable to the two main fault sets seen onshore at locations such as St John's Point (Fig.…”

Structural Architecture and Permeability Patterns of Crystalline Reservoir Rocks in the Northern Upper Rhine Graben: Insights from Surface Analogues of the Odenwald

“…The rasters are then converted into hill shade layers, with N000 • E, N045 • E, N090 • E, and N135 • E orientation, to avoid misinterpretation of the lineament and fracture network, as explained in [12,13]. The following properties of the fracture network are extracted from GIS views (Table 3, Figures 4 and 5): length, orientation, linear density (P10), areal density (P20), areal intensity (P21), connectivity (C L ) [85], spacing (C V ) [86] and node topology [87,88]. The fracture clusters are extracted from the LiDAR and GIS analyses, with the input parameters for a stochastic distribution modelling, to be implemented in the DFN models (Tables 4 and 5).…”

“…Profile n length, orientation, linear density (P10), areal density (P20), areal intensity (P21), connectivity (CL) [85], spacing (CV) [86] and node topology [87,88]. The fracture clusters are extracted from the LiDAR and GIS analyses, with the input parameters for a stochastic distribution modelling, to be implemented in the DFN models (Tables 4 and 5).…”