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Experimental study and CFD simulation of water coning phenomenon in perforated geometry
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The focus of this thesis is to further examine the water coning phenomenon in annular geometryin a horizontal well completion. This phenomenon is of particular interest to the oil & gasindustry, as it may restrict production rates, and lead to reduced production effectiveness dueto water carry-over. An overview of industry experience and a review of academic research conductedon the topic of water coning phenomenon is provided. The study has been carried outby conducting experiments of flow inside annular geometry of a horizontal well in a laboratorysetup and by utilizing CFD simulations. The experimental findings provided valuable inputsfor the CFD simulations, and the CFD simulations may in turn become a useful tool for testingICD designs. Furthermore, this study provides a detailed analysis and comparison of analyticalmethods that can be utilized to predict critical flow rates. The experiments were conducted using a simple, yet effective, setup with a symmetric inflow ofthe liquids. It was based on a 2D-principle giving good visualization of the experiments. Themain emphasis was placed on the single orifice geometry, but geometries with two orifices werealso used during the experiments. Two different oils were used: Nexbase 3080 due to its similarityto the North Sea oil regarding viscosity, andMarcol 52 to have an oil with a viscosity betweenthose of water and Nexbase. A total 766 experimental runs were conducted. From these experiments the effect of water coningwas studied in regard to the size of the annulus gap ±, the flow rate, the type of oil, differentplate geometries with one and two outlet orifices, and the distance between the water level andthe orifice. The results indicated that water coning features are highly dependent on and all of the parametersmentioned above. High flow rates and a short distance between the initial water level andthe orifice, both give a high tendency of water coning and large water cuts. However, large annulusgaps lower the tendency of water coning. Nexbase oil with its high viscosity demonstrateda larger tendency to induce water coning than the less viscous Marcol oil. Low flow rates, largeannulus gaps and large distances between the water level and the orificewillminimize the effect of water coning. A powerful and versatile CFD package that is well equipped to simulate coning phenomenon,ANSYS-CFX commercial code was utilized for running simulations. A total of 210 simulationswere set up and conducted, both in 2D and 3D. For this research study, it was important to conduct a large number of simulations in order tocorrectly observe trends when changing the input variables. The simulations were all plannedto ensure that an acceptable step size in variable changes was utilized. In this manner it waspossible to stay within a reasonable number of simulations while still being able to uncovertrends fromflow behaviour. The CFD-simulations conducted indicated that the two-dimensional modeling approach waseffective to study water coning phenomenon, in that the simulations displayed the same underlyingtrends observed in the experiments, and required a relatively short amount of computationaltime. The main focus of the analytical aspect of this study is directed towards a pressure balance analysis.However, dimensional analysis was utilized to forge a correlation for the critical flow rate.The comparisons of the different analyticalmethods indicate that the dimensional analysis approachmayprovide valuable insight to critical flow rates. Comparisons with experimental datasuggest that the analytical expression derived from pressure balances leads to a largely varyingmagnitude of discrepancy depending on the case in question.