Conclusion

The main research features and results arising from the research and the simulator performance are summarised as follows.

6.2.1

The analytical model

A numerical model has been developed for calculation of heat transmission at any single point along a well depth. The algorithm of calculation has been expressed in section 3.3.4, and the major findings can be summarised as follows:

• The application of basic heat transfer mechanisms along with energy, momentum and conservation of mass equation as well as thermodynamics principles produce an applicable analytical model. The analytical model is applied throughout this study to develop a tool for prediction of heat transmission at any single point of a wellbore.

• Thermal resistivity of each layer surrounding the wellbore controls the rate of heat transmission between the wellbore fluid and the earth. For example, the thermal resistivity of different layers around a wellbore such as annulus fluid, cement sheaths and earth affect the overall heat transfer coefficient and finally the rate of heat transmission between wellbore fluid and the earth. In this study a method for calculation of overall heat transfer coefficient based on the heat resistivity of different layers around a wellbore has been developed.

• The study investigates and reveals the significant effect of radiation heat transfer caused by the annulus. For a typical case study(detailed in chapter three) the temperature of the casing at the surface when considering radiation heat transfer mechanism is about 39% more than when radiation effects are ignored.

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• In the current study, it is investigated that ANSYS software may be a useful tool for evaluation of temperature loss at any single point in the wellbore. ANSYS may be useful to analyse the temperature effects in the localized area in the wellbore. However, it not convenient to generate the temperature along the long wellbore, which requires a very long computational time involving with very cumbersome modelling process.In this study, the ANSYS was used for the purpose of validating the results from the study of temperature loss (gain) at any single point in a wellbore to its surroundings.

6.2.2

Features of the WTP simulator

The WTP simulator can be used as a powerful tool to general flowing temperature profile theoretically; and applicable to analyse injection production scenarios to identify many issues, and/or well problems based on temperature anomalies. Followings are main features of this simulator. .

• This simulator can simulate a wide range of production and injection scenarios as well as covering different types of fluid flow along a wellbore such as gas, liquid and multiphase fluid.

• The simulator simply requires very basic information related to wellbore such as tubular sizes and its material properties (i.e. mechanical and heat transfer properties), well depth, size and geothermal properties of wellbore surroundings (e.g. rocks), injection/production related parameters such as production rate, pressure, geothermal temperature, and PVT properties of flowing fluids, to generate the temperature profile for a given condition. .

• The simulator has the capability of dealing with the any gas mixture regardless whether the composition of that gas mixture is known or unknown.

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• The simulator has the capacity to predict the flowing wellbore temperature profile for both injection and production case.

• The simulator works based on simplified numerical model which requires significantly low computation time and hence very appropriate for routine industry works.

6.2.3

Performance of the WTP Simulator

Eleven cases are simulated to justify the capability, applicability and accuracy of calculations and the performance of this WTP simulator. It is established from the case study that the WTP simulator is capable of dealing with various production/injection situations for single and multiphase for the prediction of wellbore temperature profile. This simulator also has the potentials to simulate CO2 injected well.

6.2.4

Research Outcomes and Findings

The main findings of this research have been summarized below:

• As a major outcome of this study, the Wellbore Temperature Profile (WTP) simulator has been developed, which can be successfully used to predict flowing temperature profile of injection/production well with reasonable accuracy and have wide capabilities to deal with single and multiphase fluid flow.

• For the case of gas production, a wide range of study has been done to investigate the Joule Thomson (JT) effect on the wellbore temperature profile as well as the surface flowing temperature. It is inferred that the Joule Thomson effect has significant impact on the flowing temperature, especially in the case of gas flow. The JT effect increases significantly specifically at

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the high gas production rate, which can cause a substantial drop in temperature especially at the entry point.

• In case of a well producing water and gas, as the amount of water increases with produced gas, the temperature drop at the entry point decreases due to Joule Thomson effects, whereas for the same production case, the surface temperature increases due to the presence of water.

• In case of gas well producing with impurities such as water, N2, CO2, H2S and so on can affect the JT effect. However, among these impurities, water production has more influence than the others on the JT effect.

• In case of a production well producing single oil and/or liquid (i.e. oil plus water), the behaviour flowing temperature profile along the wellbore and final surface temperature would vary depending on well completion profile and the rate of production. For instance, wells with the same well completion profile, the surface and wellbore temperatures are higher for higher oil production rate.

• Obviously the wellbore flowing temperature for production cases decreases with increase in the size of tubing diameter (i.e. internal diameter of tubing), as the larger tubing diameter facilitates larger surface area for transferring heat between wellbore fluid and its surroundings. However, the effect is opposite in case injection scenarios, where it may conversely cause temperature gain.

• The produced oil gravity (API number) plays a significant role on the behaviour of flowing temperature profile. For instance, higher the degrees of API gravity is lower the surface temperature.

• In case of liquid (e.g. liquefied N2) injection, increasing injection rate increases the temperature at the entry point to the reservoir due to the fact that the fluid with lower injection rate has more time to gain heat from surrounding while moving from surface to the reservoir.

• In case of multiphase flow, the phase contribution effects the temperature profiles substantially.

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