Geothermal Energy Recovery from Hydrocarbon Settings: Potential and Challenges
Approach and Goals
Investigation to determine the economic feasibility of geopressured geothermal energy production generally centered either on reservoirs performance or financial viability of field development. This approach may be compromised because for the past two decades, no complete studies characterizing commerciality of geopressured reservoirs have been performed. This study combines reservoir performance, facility efficiency and financial constraints to determine a range of potential outcomes for sustainable commercial development of geopressured geothermal reservoirs.
The reservoir performance model utilizes a commercial reservoir simulation program (Computer Modeling Group Ltd, CMG) to predict the production rates from aquifers under constrained surface pressure. Sensitivities consider single- well developments. Reservoir model components are varied to determine a wide range of reservoir productivities. Characteristic parameters include bulk volume, depth, porosity/permeability, initial pressure and temperature gradient, salinity, formation compressibility, maximum allowable flow rate, wellbore radius, and initial gas saturation. The facility model uses reservoir temperature, wellhead pressure, and flow rate from the reservoir performance model to estimate the net electric output of the energy recovery system. The financial model computes the discounted cash flow of geopressured aquifer developments. Input parameters for the financial model are net electric output, electricity price, capital and operational costs, severance taxes and net revenue interest. By combining the results of the reservoir, facility, and financial models, a range of input parameters that yield a positive life-cycle cash flow are delineated. The ranges can be applied to evaluate geopressured-geothermal resources and identify areas where additional research is warranted.
Each of these components identify to evaluate the viability of geopressured utilization is defined by a different set of variables. Some of these variables are inter-related (e.g., flow rate affects reservoir performance, facility process design, and financial constraints). The following sections describe a methodology to determine potential commerciality of geopressured reservoirs. Variables expected to affect the commerciality of geopressured reservoirs are defined.
