Title:

Geothermal Modelling: Industry Standard Practices

Authors:

Rony P. NUGRAHA, John O’SULLIVAN, Michael J. O’SULLIVAN, Fathan H. ABDURACHMAN

Key Words:

reservoir, modelling, geothermal, conceptual model, numerical model, natural state, history matching, future scenario, boundary condition, AUTOUGH2, Leapfrog, Waiwera

Conference:

Stanford Geothermal Workshop

Year:

2022

Session:

Reservoir Engineering

Language:

English

Paper Number:

Nugraha

File Size:

2336 KB

View File:

Abstract:

Geothermal reservoir modelling is essential for the successful development of geothermal fields. It assists geothermal companies in decision making and planning for the development of a geothermal resource. However, the approach used for generating a geothermal reservoir model depends on the company, university, or consultant involved as there is no standardised approach. Each entity has a different approach in making geothermal models based on their chosen or given reservoir tools and work-flow. This variability in approach is further exacerbated by the limited functionality of some reservoir tools. Commonly, simplification to the boundary conditions in the model are made in the hopes of simplifying the model setup process. These simplifications include the use of a constant pressure and temperature water table at the top of the model, constant pressure and temperature at the bottom boundary, and the inclusion of only a small part of the reservoir within the area covered by the model grid. These simplifications may cause the model’s future scenario simulation results to be unreliable and not useful for decision making. Furthermore, the numerical model used for the reservoir simulation process often does not align with the conceptual model of the field. All this, in turn, will prevent the use of the simulation results from the numerical model in refining the conceptual model. This paper aims to help the geothermal community to develop guidelines for conducting geothermal reservoir modelling. The final output is expected to be a comprehensive Term of Reference (TOR) to ensure the final reservoir model is based on the accepted standard practices and provides value for the developer. Modern technologies in geothermal modelling will be presented in this paper. We will describe the numerical model development work-flow developed by the Geothermal Institute at the University of Auckland, and utilised by several developers worldwide. Moreover, we will elaborate on the key requirements that must be met at each stage of making a robust reservoir model. The aim is to eliminate unnecessary approximations and to ensure the model is based on correct reservoir physics. These stages include (1) making a 3D digital conceptual model which will be the basis of the numerical model, (2) selection of the grid for the model based on the advantages and disadvantages of each type of grid, (3) selecting appropriate data to be used for the natural state model calibration process and completing the calibration, (4) history matching with production data, and (5) setting up and running future scenarios.


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