Title:

Pioneering Use of Natural Fracture Characterization for Well Placement at Darajat Field, Indonesia

Authors:

Rindu Grahabhakti INTANI, Fanji Junanda PUTRA, Meiyanto Joko PURNOMO, Gregg NORDQUIST, Glenn GOLLA, Richard GUNDERSON, Jean Pierre JOONNEKINDT, Francisco DIAZ, Russell DAVIES, Paul HULTZSCH, Sri MULYANI

Key Words:

natural fracture prediction, fracture drivers, Discrete Fracture Network, Probability of Permeability, Darajat

Conference:

Stanford Geothermal Workshop

Year:

2022

Session:

Modeling

Language:

English

Paper Number:

Intani

File Size:

1288 KB

View File:

Abstract:

A key consideration in the development of geothermal resources is the placement of each new well to maximize production. A small increase in production based on improved subsurface characterization and “sweet spot” maps can have a major impact on company revenue and profits. Sweet spots in these fields are defined by distributions of connected natural fractures conductive to fluids. In this paper, we describe novel methods to characterize fractures to generate sweet spot maps for drilling locations in the Darajat geothermal field in Indonesia, operated by Star Energy Geothermal. The subsurface geometry of the field was characterized initially from remote sensing methods, geophysical study (gravity, resistivity, MEQ), subsurface geology (core, cutting) and surface geology to locate the intrusions, faults and associated pyroclastics and overlying sediments. Despite the more than 50 wells drilled, relatively high uncertainty remains in locating future steam make-up well locations, as these wells will be in step-out locations. We are attempting to reduce the uncertainty in future well locations by modeling natural fractures, applying methods used successfully in oil and gas reservoirs, and creating permeability sweet spot maps. The modeling of natural fractures utilizes fracture drivers to generate and attempt to match fractures interpreted from image logs. Two of these drivers are fault-related; one being distance-to-fault (damage zone), and the other a geomechanical method to model fractures in the perturbed stress field around mapped faults. Additional drivers include the pressure stress effects of igneous intrusions and the thermal cooling effects of these same intrusions. These drivers have been applied in sequential steps, and fractures generated from the driver-specific constraints were used to define volumetric fracture intensities. The intensity and orientation of fractures generated by each driver are composited, and these composite parameters are used as input for creating a discrete fracture network (DFN) across the field. The DFN models were then used to calculate fracture permeabilities throughout the geothermal field, using measured productivity indices to help calibrate fracture apertures and length distributions. The completed models show a heterogeneous permeability distribution for future well planning placed into the context of a sweet spot map. This was the first geothermal application of the modeling techniques of natural fracture characterization developed for oil and gas projects. A second phase of the project has now been started to incorporate uncertainty modeling. We envisage that the tools and methods developed for the natural fracture characterization in this study will be applicable to other geothermal fields, but also to fields in oil and gas.


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