POTENTIAL HEAT RECOVERABLE CAPACITY ESTIMATION BY NUMERICAL SIMULATION FOR GEOTHERMAL DIRECT USE APPLICATIONS IN OKLAHOMA

Abstract

Geothermal energy has gained significant attention as a renewable and sustainable energy source. Extracting geothermal energy from subsurface needs to drill a new well or repurposing abandon wells. Oklahoma has huge potential in exploring geothermal energy due to abundant inactive wells and subsurface resources. To access at least 1MWth geothermal recoverable capacity by cycling working fluid from the building to subsurface with different flow rates. A study of reservoir characterization is prerequisite. A viable and reliable reservoir characterization is crucial in simulation of recoverable capacity accurately. Comprehensive petrophysical properties from cores and well logs should be analyzed. Following that, a validated integrated reservoir model should be built and visualized.In order to achieve that, comprehensive petrophysical data were analyzed via core samples and well logs. Well logs, including gamma ray, resistivity, and porosity logs, are collected, and core samples are analyzed to obtain accurate rock and fluid properties. Core samples were collected from a satisfied well as a reference. Additionally, geological and petrophysical data from the region are integrated to construct a reservoir framework. Next, 3D petrophysical and facies distribution models would be developed based on the well logs and core data. A petrophysical calculation was performed using correlation functions. These functions used the acquired well log and core data to establish relationships between various petrophysical parameters, enabling the estimation of properties like permeability, porosity, and water saturation. The effectiveness of the integrated reservoir models is evaluated through a comprehensive analysis of the geothermal reservoir at Tuttle. Sensitivity analysis is conducted to identify the key parameters affecting geothermal energy production in the reservoir. In conclusion, under same reservoir conditions: 142 °F reservoir temperature, 8% - 17% of porosity, 4225 psi of fracture pressure, this research confidently concluded that the geothermal wells could produce 1 MWth at 3960 BPD within a range of 0.001-1000 mD permeability (upper case) in production zone and 3022 psi of bottom hole pressure which is less than the fracture pressure. In the lower case, due to the low permeability ranges, it requires high pressure to fracture the formation, making the fluid transport from injection well to the production well. Moreover, even though the injection rate reaches to 5000 bpd, the enthalpy changes does not achieve the 1MWth. Therefore, the lower case should be the worst scenario. In the base case, the enthalpy production rate was similar to the enthalpy changes in the upper case could be reached to at least 1MWth in 10-100 mD of the permeability in production zone. However, the simulated BHP was above the fracture pressure. Since the study contains uncertainties, a further test should be done to determine the accurate permeability. In addition, the temperature dropped 35.6 °F (2 °C) from the injection well and does not drop from production well in a year. It was observed that the distribution of cold water was based on permeability and lithology. For improving the enthalpy production, a sensitivity analysis should be completed. Permeability affected the enthalpy production rate in the most. The secondary factor is the thermal conductivity of rocks. Therefore, an accurate permeability value should be determined to make a more valid reservoir model and simulation than what this study did. To produce more enthalpy production rate, increasing permeability and thermal conductivity of rocks should be a good method.