Investigation of Asphaltene Deposition at High Temperature and under Dynamic Conditions

Abstract

Asphaltene deposition is one of the major flow assurance problems that can potentially deteriorate due to the current tendencies to produce from the deep-water environment or as a result of enhanced oil recovery operations based on miscible gas injection. The deposited asphaltenes in the wellbores and on the surface of the oilfield pipelines can impede the productivity of the wells significantly. The comprehensive understanding of the mechanisms and the techniques to control asphaltene deposition at high temperature and under dynamic conditions can help resolve this critical issue. Thus, it is imperative to develop reliable, straightforward, and inexpensive tools to investigate the asphaltene deposition tendency and the performance of asphaltene inhibitors in the laboratory. In this work, a new stainless steel packed bed column deposition system that was inspired by the work of Vilas Bôas Fávero et al. was successfully developed. The packed bed design allows the feasibility of investigating a variety of factors affecting the deposition process under a wide range of temperature (20–300 °C) and gauge pressure (0–3000 psi). The impacts of operating temperature, type of precipitant, degree of asphaltene stability, and chemical additives on the deposition tendency of asphaltenes were investigated. It was found that the solubility of asphaltenes, the diffusion of precipitated asphaltenes, and the formation of aged asphaltene aggregates were competing factors controlling the deposition of asphaltenes under different operating temperatures. Additionally, asphaltenes precipitated by n-pentane induced more deposition than those destabilized by n-heptane. The liquid-like deposits collected from the experiment with n-butanol provided evidence that stronger ability to retain the softness reduced their tendency to build up aged asphaltene deposition on the metallic surface. Variation of the precipitant-to-oil ratio showed that the rate of asphaltene deposition increased linearly with the driving force toward asphaltene precipitation. Furthermore, a comparison between the capillary flow loop and the packed bed column on the assessment of asphaltene inhibitors was conducted. It was found that higher dosage of the asphaltene inhibitor seemed to delay the onset of deposition but did not further reduce the amount of deposition. With this packed bed column operating at high-pressure and high-temperature conditions, advanced simulation tools to predict asphaltene deposition under more realistic production conditions can be developed. Also, it can be used to assess asphaltene deposition inhibitors and solvents to prevent and remediate the asphaltene deposition problems.

Review of the Current Laboratory Methods To Select Asphaltene Inhibitors

“…An alternative approach was recommended by Gon et al 58 to cut the capillary into segments before solvent wash and quantification. This approach was also used in the study by Kuang et al 86 After the deposition experiment, the capillary tube was cut into 10 similarly sized (1 ft) segments, and the amount of asphaltene was quantified for each section. Figure 6 presents the asphaltene deposition profile along the capillary.…”

“…These end effects are an artifact caused by a change in the flow field at the fitting. 86 A similar experiment was performed with a crude oil sample treated by 28 ppm of an asphaltene inhibitor. As shown in Figure 7, the addition of inhibitor reduced the deposition in the last segment of the capillary.…”

“…Kuang et al 86 investigated the effect of a commercial asphaltene inhibitor on the deposition in the packed bed column. The deposition experiments were conducted with a dead oil sample at 80 °C and 50 psi backpressure.…”

“…(5) The effect of water, material composition, corrosion, and various surface properties on asphaltene deposition and the performance of inhibitors can also be studied. 18,52,86 The RealView deposition cell is one of the few deposition tests operated using live oil samples at HPHT and under either laminar or turbulent flow conditions. In these tests, the asphaltene precipitation is initiated by pressure depletion rather than the addition of a precipitant.…”

“…Results of Packed Bed Column DepositionExperiments with a Dead Oil Sample with and without an Asphaltene Inhibitor86 …”