Geothermal energy is the renewable energy continuous generated from the earth, and stored in the earth either in forms of fluids or solids. Unlike solar energy, it is a stable resource and not dependent on the weather condition. Due to the advantages of non-polluting, environment friendly, low running costs and sustainable utilization, the geothermal energy utilization are receiving increasing attention. During the past few decades, a large number of technologies have been developed and utilized for geothermal energy exploitation. The produced geothermal energy have been widely utilized in thermal therapy, heating or cooling building and electrical power generation due to the attractive advantages of high efficiency and environmental friendliness. The geothermal resources vary from a few meters to several thousands of meters, and are typically based on the depth of exploitation divided into shallow (<400 m) and deep (> 400 m) systems. Thus, several technologies are developed and utilized for these two kinds of geothermal energy exploitation systems. Furthermore, there is also an increasing need to numerically model different geothermal scenarios. In this thesis, several typical mathematical methodologies which were implemented in numerical modelling and various types of software packages that applied for simulation of geothermal energy exploitation are introduced. The developments of mathematical methodology, that from the earliest Kelvin’s line source theory which has been developed for calculating of ground temperature surrounding the borehole, to the finite element method which can provide three-dimensional discretised models, were introduced in this thesis. According to the main features of software packages, three categories were divided and introduced in this thesis: the system simulation tools, the CFD software packages and the geological simulation packages. Some representative software packages of each category were introduced in detail. Geothermal has some major barriers to entry to the mainstream energy markets, the largest barriers include the high-initial capital costs related to drill and construct new geothermal wells, long payback periods, and the risk associated with unknown formation performance when drilling in a new area (Jamie Hutchins, 2011). According to the existing oilfield infrastructures, numerous abandoned oil/gas wells, mature production technologies and rich reservoir data and also rich geothermal resources occurring in oil and gas sedimentary basins, the petroleum industry provide a promising opportunity to develop and utilize geothermal resources. By considerations of large potential of geothermal exploitation in petroleum industry, in this thesis two software packages were selected for the studies of numerical modelling of geothermal exploitation systems by using deep wells: one is geothermal modelling of deep borehole heat exchanger exploitation system by using computer program ANSYS Fluent, and another is the modelling of hydrothermal doublet for exploitation deep hydrothermal resources by using computer program SHEMAT. The two numerical modelling were used to examine the capability of selected software packages for designing, analysing and performance prediction of the geothermal exploitation system.