Date of Award

August 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Kegang Ling

Abstract

Gas well deliquification is a crucial process in the oil and gas industry, focused on maintaining or restoring production rates by removing liquids that impede gas flow. This is a recurring challenge that is prominent in many gas wells across North Dakota. Surfactants play a vital role in this process by altering the interfacial tension between gas and liquid phases, alleviating liquid accumulation in these wells. However, due to their high production costs, non-biodegradability, and toxicity, the use of synthetic surfactants has raised environmental concerns. The pursuit of sustainable and environmentally friendly alternatives has led to the exploration of natural surfactants. In this context, there is a growing interest in understanding the properties and applications of soybean derived surfactants (SODS). This research focuses on its potential as eco-friendly substitutes for traditional surfactants, thereby addressing the pressing need for more environmentally suitable solutions in the petroleum industry.In this research, we synthesized an anionic surfactant in the laboratory utilizing soybean as a precursor. The surfactant was characterized through Fourier transform infrared spectroscopy (FT-IR), Thermal Gravimetric Analysis (TGA), Nuclear Magnetic Resonance spectroscopy (H1NMR), and critical micelle concentration (CMC) value. Subsequently, we conducted a series of experimental investigations to evaluate the performance of SODS in various gas well conditions. These experiments involved small-scale and large-scale setups simulating real-life gas well environments. In the small-scale facility, we examined the foaming properties and unloading potential of SODS under controlled conditions. Its foamability is tested and compared with other surfactants using a modified Bikerman setup, where foam is created by introducing nitrogen gas across the solution containing all the surfactants. We measured the weight of the foam over a period of time. The foam density is determined by considering both the weight and the velocity of the foam. We conducted an analysis on the impact of SODS concentration, gas and liquid flow rates, as well as environmental factors on foam generation and stability. Through thorough literature review, we identified dynamic surface tension (DST) and equilibrium surface tension (EST) as critical surfactant properties influencing foaming. Furthermore, my dissertation delves into how DST and EST affect the foaming capacity of SODS through specifically designed experiments. After confirming the foamability and stability of the biosurfactant, we investigated its suitability on liquid loading and the results are compared with Sodium Dodecyl Sulphate (SDS), a widely used commercial surfactant in a large-scale facility situated at the Hess Innovation Laboratory within UND's Department of Energy and Petroleum Engineering. This facility consists of a 10-ft vertical pipe with varying inner diameters of 2 inches and 3 inches. Hydrodynamic foam flow experiments were conducted using the UTP-flow loop setup, with air and water at atmospheric conditions, both with and without the two surfactants under study. Various foam flow characteristics, including gas and liquid flow rates, flow regimes, total pressure gradient and its components, pipe diameter, surfactant type, and surfactant concentration, are investigated to simulate real-world conditions. Qualitative visualization of the effects of the surfactants were observed through the high-speed camera. It was observed that the formulated SODS can delay the liquid loading as the equilibrium when the gravitational forces and the interfacial friction are altered, these enables annular flow at low gas velocities which reduces the liquid holdup in foam flow and film density. Also, due to a drop in film density and an increase in interfacial friction, foaming delays film reversal in the presence of SODS solution and improves flow consistency at low superficial gas velocities. The observed shift increases with higher biosurfactant concentration and is more noticeable in the 2-inch pipe compared to the 3-inch pipe. In other words, the advantages of biosurfactants are significantly more pronounced in the 2-inch pipe than in the 3-inch pipe, indicating the potential of SODS to mitigate liquid loading in gas wells. In addition, the investigations conducted on foam flow demonstrated that the inclusion of SODS reduces the pressure gradient (dP/dZ) for low-medium gas superficial velocities (V_sg). However, at higher V_sg, the presence of SODS may lead to an increase in dP/dZ this may be attributed to the preponderance of frictional forces. The results showed that an optimal concentration of 800 ppm for SODS, along with ideal superficial velocities of gas and water (V_sg and V_sl), led to the lowest possible pressure gradient profile. At this point increase in the concentration of SODS had had a minimal or no effect on reducing dP/dZ. I also considered the chemical composition of water simulating real-life operational condition of gas well conditions by examining the impact of NaCl and CaCl2 concentrations on the flow of dynamic foam in vertical pipes by conducting additional experiments. The results indicated that SODS was compatible with both salts. The presence of salts had a negligible effect on reducing the rate of change of pressure with respect to height (dP/dZ) the foam flow successfully in the experiments. This approach holds the potential for developing a comprehensive model that can quantitatively predict the effectiveness of the surfactant generated from soybean (SODS) in mitigating liquid loading in gas wells. While this research provided qualitative insights into the impact of SODS on gas-liquid flow and the deliquification of gas wells, a physically based model is necessary for quantitative analysis in large-scale gas wells. Such a model necessitates characterization of the foaming behavior of SODS-liquid mixtures using a small-scale setup. However, we discovered that the traditional hydrodynamics in small-scale sparging setups were inadequate for the hydrodynamics of annular and churn flow. Overall, this research contributes to the development of environmentally friendly and sustainable solutions for gas well deliquification, with the potential to enhance productivity and efficiency in the gas industry in North Dakota.

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