The geothermal utilization of shut-in or abandoned hydrocarbon wells

Abstract

This research is intended to create an insight into the heat exchange occurring in a well and to find ideal well conditions in which the performance of the heat exchange is maximised. For demonstrating and studying these aspects the well of Grouw-01 is analysed. The well of Grouw-01 is a depleted gas well attained from Vermilion Energy and is in shut-in state. Re-using these shut-in or abandoned wells can provide fossil fuel-free energy for the local community. Such wells have the potential to be used for geothermal energy generation, either by using them to directly access warm water from a reservoir or as borehole heat exchanger, without direct connection to a potential reservoir. In this study there is no contact with the reservoir. As there is no contact, a method is created in which the injected fluid can reach the surface within the same well. This is done by creating a circulating system of a working fluid in the well in which the heat is extracted from the subsurface and carried to the surface by the working fluid. For the fluid to be able to circulate, a tubing is installed inside the well which is an inner-tubing. Such a well with circulating fluid systems is designed like a Deep Coaxial Borehole Heat Exchanger (DCBHE). The software COMSOL Multiphysics 5.4 is used for the reconstruction of the well design in 3-D. The model is based on the former gas production well Grouw-01, which has been in the shut-in phase for over 5 years. For such systems, the design conditions need to be optimized as these conditions can help increase the heat extraction. The different properties that can influence this are the type of working fluid, the material and thickness (insulation material) of an inner-tubing for fluid circulation, flowrates, outer-well size and injection temperatures. Finding an ideal design condition is the main goal. The software allowed an intense sensitivity analysis on the properties which can influence the heat extraction. The outcomes of the different sensitivity analyses show that
-The heat capacity of the working fluid is critical for the amount of power that the fluid delivers. Working fluids with high heat capacity deliver a higher power output compared to the working fluids with low heat capacity. However, a working fluid with low heat capacity normally delivers a higher production temperature. -The flowrate in which the fluid circulates, has an optimum limit in which fluid cooling is minimum during upward flow and heat extraction during downward flow maximum. -Insulation material of VIT (Vacuum Insulated Tubing) is crucial for the system to function, the properties of the VIT play a prominent role in this. A material with similar thermal properties can function as a replacement for the VIT. -Increasing the thickness of the inner-tubing (VIT) delivers a higher power output. This power increase is small compared to the increase of inner-tubing thickness. -The outer-tubing has similar effects on the power output. If the size of the outer-tubing is doubled there is a small increase in power generation. -The simulated different well depths show a linear relation of the temperature, power output and depth of a well. -Injection temperature of the working fluid should remain low for higher efficiency. -Simulating a reversed working fluid cycle, in which the fluid is injected through the inner-well and produced through the outer-well can cool down the working fluid if the flowrate is low. Based on the amount of energy that the Grouw-01 well can provide to the energy requirements of households, a system of heat supply and demand is created for an economic analysis. In the economic analysis the value of the different materials, project costs and revenues from this geothermal project are analysed in three different cases. The costs involved are divided in capital costs, operational costs and a government take in the form of taxes. The results of the economic analysis showed that the project is financially viable, unless there is an increase in the OPEX or if the project load hours are drastically reduced. In this thesis, based on sensitivity studies and the literature review, an efficient DCBHE is introduced. In addition, the economics will give an insight into the financial viability of this efficient system. This thesis provides information for geothermal engineers, well engineers, researchers and whoever are interested in alternative energy methods.