Pakistan's First Alternate Energy Technology Company
Pakistan's First Alternate Energy Technology Company

Geothermal Plays – Assessment

Assessment of the Geothermal Energy resource in a Geothermal play would involve several steps as described below. 

The probability of success can be estimated by considering geological and related commercial factors.  Four components of site-specific data shown on the previous flyer are needed:  (1) Structure; (2) Trap Integrity; (3) Geothermal Reservoir; and (4) Heat Flow.  Data would need to have been gathered to investigate each component for the particular type of Geothermal play.  Assuming the data indicates potential, conceptual reservoir numerical simulation models would be prepared to be able to help determine predicted reservoir heat and flow transport outcomes for the initial and boundary conditions.  A range of stochastic outcomes would be used as inputs for the surface power generation equipment and economic evaluations.

The extraction of heat energy from the Geothermal reservoir would involve circulating fluids (either surface fluids for petrothermal reservoirs or existing subsurface fluids for hydrothermal reservoirs) to the surface where their heat could be used in Binary Organic Rankine Cycle (ORC) power generation equipment to generate electricity.  Once heat was extracted, the fluids would be reinjected back down into the reservoir.  The amount of electricity produced would be a function of the amount of enthalpy available and the effectiveness of the ORC system (including its working fluid cooling subsystem).  Economic evaluations would be able to consider stochastic ranges of electricity produced, life cycle costs and revenue.

As fluids are circulated through Geothermal systems, heat losses at the surface would mean that the reinjected fluids would be somewhat cooler.  Back in the Geothermal reservoir, these fluids would need to be reheated and/or recharged to recover this heat loss.  Over time in some reservoirs this is not fully effective, and there could be a decline in heat available to be extracted as the reservoir cools somewhat.  Any declines would need to be included in economic evaluations.  To mitigate such declines, there could be constraints on fluid circulation rates and well numbers and locations in a reservoir.

Another assessment step is estimating the amount of energy stored in the Geothermal reservoir.  For new developments, there are two approaches:  (1) static resource estimation based on the total volume method; and (2) dynamic resource estimation where fluid and heat recharges are also considered.  The static resource estimation would be a volumetric “heat in place calculation” that is typically a big value, but it is not necessarily useful since practical recovery factors would significantly reduce this value.  A dynamic resource estimation would consider potential changes in reservoir models and outcomes over time including heat and fluid recharges.  Stochastic variation of input data would help establish the potential outcome ranges (i.e., P90, P50, P10) for economic evaluations and decisions.

Finally, the United Nations Framework Classification for Energy and Mineral Reserves and Resources (UNFC-2009) scheme is a principles based system used to assess potential developments on three criteria (“E” – economic and social viability; “F” – field project status and feasibility; and “G” – geological knowledge) to establish commerciality.  Specifications for application of UNFC-2009  to Geothermal Energy were issued in 2016.