Simulation of fluid flow and heat transfer to study hot water production potential from naturally-fractured geothermal reservoirs

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Copyright: Shaik, Abdul Ravoof
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Abstract
Typically naturally fractured geothermal reservoirs has low matrix permeability, and fluid flow is primarily controlled by complicated fracture patterns. The major hurdles for estimating recoverable energy in such reservoirs are generation of a discrete fracture map and handling the vast amount of data on fracture geometry (aperture, length, and orientation) for simulation of fluid flow and heat transfer. To add complexity to the matter, dynamic heat transfer between fractured rock and circulating fluid must be investigated for better prediction of total heat recovered from naturally fractured geothermal reservoirs. To overcome some of these difficulties, a number of methods were proposed according to the representation of fractured medium, the type of fracture network, and the size of domain of interest. Most of the previous works in this area assumed either fractured geothermal system as cubic blocks separated by fractures or/and an instantaneous local thermal equilibrium while simulating heat extraction from the fractured geothermal systems. In the present work a 3D numerical model is developed to evaluate potential for heat recovery from naturally fractured geothermal reservoirs. For this purpose a numerical procedure is developed to address three major issues: characterization of naturally fractured reservoirs, simulation of fluid flow through interconnected fracture system, and heat transfer between matrix and circulating fluid. Field data is statistically analyzed (stochastic analysis) to develop discrete fracture network. A finite element based fluid flow model, vii which includes a permeability tensor model, is developed to simulate fluid flow through interconnected fracture system. Heat transfer model is based on rock fluid temperature approach to study thermal drawdown of a geothermal reservoir during its productive life. The proposed methodology has been validated against previously published results. Several numerical experiments are carried out to illustrate how the methodology could be used to evaluate geothermal potential of a reservoir and how different reservoir and operating conditions affect reservoir performance including fracture connectivity, production rate etc. From the results of this study it can be seen that characteristic properties of fractures, such as fracture interconnectivity, contact area between fluid and matrix and fracture density as well as flow rates affect heat recovery from naturally fractured geothermal reservoirs.
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Author(s)
Shaik, Abdul Ravoof
Supervisor(s)
Rahman, Sheik
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Publication Year
2012
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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