Asphaltene deposition : an experimental study using Quartz Crystal Microbalance technology

Abstract

Asphaltene deposition is a significant flow assurance challenge in oil production. Any factor interrupting the thermodynamic equilibrium that keeps asphaltenes miscible with the liquid phase can result in precipitation, accumulation, and potential deposition. This may deposit in the formation, wellbore, or production lines, causing reduced flow or complete blockage. Chemical inhibitors are mainly used to mitigate asphaltene deposition risk in the field. The type of oil and the production conditions dictate the use of various chemistries, making laboratory-based test methods for asphaltene inhibitor screening crucial for recommending the best chemical solution. Recent interest in the industry has shifted towards the use of a real-time deposition-based sensor called Quartz Crystal Microbalance (QCM) for problematic crude oils, especially with low asphaltene content (< 1%). Testing such crude oils using more traditional techniques is often difficult because they produce a very small gravimetrically measurable deposit. Often, only a limited amount of crude oil is available for laboratory testing, exacerbating this challenge. This is where the nano-gram detection resolution of QCM can be beneficial. QCM testing is susceptible and very sensitive to the test conditions used, as the vibration frequency of the quartz crystal is impacted by a multitude of factors, including pressure and temperature, viscosity, localized gas bubble formation, and film buildup/adhesion of non-analyte materials onto the crystal surface. As future oil production moves to more problematic and challenging reservoir and production conditions, it is necessary to look beyond conventional methods for improved lab-to-field correlation. Therefore, this thesis aims to develop procedure of an experimental st-up that can measure all phase changes in live crude oils across a broad range of pressure and temperature in a single test. That helps evaluate/develop chemical inhibitors in more realistic conditions with optimum time. If you design the control system and test program appropriately, QCM testing can provide useful information. Results demonstrate the high pressure/high temperature (HPHT~) QCM to be a very promising tool for asphaltene inhibitor evaluation, with clear variations in anti-deposition performance seen for different chemicals. The HPHT QCM studies presented here can address the challenge of accurately measuring chemical effectiveness in problematic crude oils containing low asphaltene content. Accordingly, an interesting trend was noted in shifting frequency trend at asphaltene onset pressure (AOP) and relative asphaltene mass deposition on QCM with different chemical treatments under high pressure and temperature conditions relevant to field conditions. In addition to mass build-up, the shift in AOP can be another useful key performance indicator (KPI) for chemical effectiveness, which needs further understanding. In this work, evaluating the oil sample under various simulated realistic production scenario aids in comprehending the test's limitations and consolidating the optimal program design for HPHT QCM. Also, results from atmospheric pressure dead oil titration tests often match up well with results from re-liven HPHT tests. However, there are big differences for some inhibitors, which means that the results from atmospheric pressure dead oil titration tests may not always reflect real conditions. The chemical performance from re-livened HPHT tests were significantly influenced by diverse setting conditions, promoting the design of practical inhibitors tailored to address each proposed case. Overall, these observed differences may go some way to explain problematic discrepancies between traditional results using laboratory test methods results and real-field chemical treatment performance, i.e., where an inhibitor performs well in the laboratory, but not in the field.