Degree

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

Document Type

Dissertation

Abstract

The main objective of this work is toimprove the accuracy on calculations of design set pressure and performance curves (sizing equations) for Gas-Lift Valves (GLVs) at high pressure (real conditions). This improved calculation method is demonstrated to have an important effect on well unloading and production operations.

The analysis of the valve design set pressure includes an experimental evaluation of the effect of internal dome volume changes on the design set pressure due to the presence of silicone and thermal effects. The evaluationis carried out for different levels of GLV silicone fill, pressures and temperatures. Silicone fills covered 7.5, 10, 25, 50 and 75%. Initial pressure ranges are from 975 to 1,250 psig, andtemperature range is from 60 to 175 °F. These experimental conditions cover the conventional operating range in the industry.

The analysis for the GLV flow equations includes a numerical study of the effect of using fluid properties at real conditions on the accuracy of gas-lift performance curves. A software is used to estimate the real fluid properties at high injection pressure for natural gas. These properties are used as a modification on the current model to account for the fluid properties at real conditions. The velocity of sound concept is used as a proof to validate the suggested modifications on the current model.

The results provide an enhanced model for improving the GLV design set pressure especially for refurbished GLV with large silicone fills. It also provided a successful well unloading design under all the investigated conditions, while utilizing other models lead to multi-point of injection problem. The new model overpredicts the design pressure by an average of 1.45% for all experimental points. The VPC model overpredicts the design pressure by an average of 2.71%, and the current practice (N2) model underpredicts the pressure by -3.56%. Furthermore, the model suggested for the GLV sizing equation provided a better improvement on estimating the flow through GLV especially in the critical region. Under the investigated conditions, the new improvement enhanced the flow rate estimate by 19%. This improvement may affect unloading operation of wells.

Date

12-7-2018

Committee Chair

Waltrich, Paulo

Available for download on Monday, December 06, 2021

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