Geomechanical Evaluation of the Fractures Productivity in Geothermal Resources

Abstract

Geothermal development has seen an increasing trend in the recent years in Indonesia to fulfill the increase in energy demand. Subsurface-related aspects in the development of geothermal resources is an integral part that requires a comprehensive analysis in order to expedite the geothermal development; one of which is their geomechanical aspect. This aspect is mainly associated with the in situ stress in the reservoir that plays an important role for a successful planning, drilling and production of the resources. Although the geomechanical aspect of geothermal may seem to be overlapped with petroleum, there are a subset of problems that is inherently unique to geothermal settings. For instance, the effect of the high temperature on the stability of the wellbore and the examination of the quality of the fractures affecting the productivity of the energy source. One needs to address these unique challenges to ensure the development of the geothermal resources can be optimised. In this paper, one of the cases that will be discussed is regarding the productivity assessment of fractures through geomechanical evaluation. The potential contribution of fractures to the production will be examined by assessing their tendency to open or close under shearing. The stress acting on each fracture will be first computed through which their slip tendency can be determined. Depending on the relative orientation between the fracture and the in situ stress, their slip tendency can be obtained. This integrated yet simple analysis is found to be meaningful in geothermal development. For a given fracture set, the relative magnitude of the in situ stress can potentially lead to a different conclusion if not accurately determined. To ascertain this, a profile showing the maximum shear stress acting for various fracture orientations is then overlapped with the fractures. It is confirmed that fractures will tend to open for the orientation associated with the high shear stress. Hence, detailed knowledge on the in situ stress magnitude and orientation is just as important as the knowledge on the distribution of the fractures.