Kang-Shi Wang

Evaluation of Effects of Selected Wax Inhibitors on Paraffin Deposition

Abstract Deposition from decane solutions of model paraffins such as n-C24H50 (C24), and n-C36H74 (C36), as well as a mixture of n-alkanes (C21 to C44) was examined with and without chemical wax deposition inhibitors. The device used to produce the deposits investigated was a “Cold Disk” Wax Deposition Apparatus (CoDWaD) capable of producing field like deposits with relatively small volumes of oil in minutes. It was found that most of commercial wax inhibitors tested could decrease the deposition of low molecular weight paraffins (C34 and below), while having little effect on the wax deposition for high molecular weight paraffins (C35–C44). In many cases, although the total amount of wax formed on the cold plate was reduced, the absolute amount of deposition for high molecular wax was actually increased. Therefore, the net effect of many commercial inhibitors is to make even harder wax under the tests conditions studied here. One intriguing result was that the addition of an oleic imidazoline c rrosion inhibitor improved the performance of two wax inhibitors tested. It was also observed that there are subtle differences in inhibitor performance depending on whether the test solutions are binary mixtures, synthetic wax mixtures, or crude oil.

Dissolution of the barite (001) surface by the chelating agent DTPA as studied with non-contact atomic force microscopy

Abstract DTPA (diethylenetriaminepentaacetic acid) is a chelating agent widely used for removal of barium sulfate (barite) scale in the petroleum industry. In this paper we report ex-situ investigations of barite dissolution in deionized water and in 0.18 M DTPA aqueous solutions. Non-contact atomic force microscopy (NC-AFM) was used to observe dissolution on the BaSO 4 (001) cleavage surface. Dissolution was carried out at room temperature in a 10 ml reactor. Each sample was first etched in solution and dried before examination by NC-AFM. Dissolution on the BaSO 4 (001) surface took place via development of etch pits. In deionized water, triangular etch pits were observed on the (001) terraces at room temperature. And, zigzag shaped etch pits were found at the edges of steps. In DTPA solutions, etch pits on the (001) terraces were observed and these became deeper and longer with increasing time. The geometry of these etch pits was trapezoidal, and/or trapezohedral. To explain this characteristic morphology caused by dissolution we suggest that the active sites of one DTPA molecule bind to two or three Ba 2+ cations exposed on the (001) surface.

Improved Processes to Remove Naphthenic Acids

In the second year of this project, we continued our effort to develop low temperature decarboxylation catalysts and investigate the behavior of these catalysts at different reaction conditions. We conducted a large number of dynamic measurements with crude oil and model compounds to obtain the information at different reaction stages, which was scheduled as the Task2 in our work plan. We developed a novel adsorption method to remove naphthenic acid from crude oil using naturally occurring materials such as clays. Our results show promise as an industrial application. The theoretical modeling proposed several possible reaction pathways and predicted the reactivity depending on the catalysts employed. From all of these studies, we obtained more comprehensive understanding about catalytic decarboxylation and oil upgrading based on the naphthenic acid removal concept.

Evaluation of Effects of Selected Wax Inhibitors on Wax Appearance and Disappearance Temperatures

Abstract In this investigation, a light transmittance method was used to evaluate the wax appearance temperatures (WAT) and wax disappearance temperatures (WDT) of model paraffin compounds (n-C24H50 (C24) and n-C36H74 (C36)) in n-decane (C10) solutions both with and without wax inhibitors. The change in WAT at different paraffin concentrations in the presence of an inhibitor behaves as though there is a constant amount of paraffin removed by the inhibitor. However, the amount of apparent paraffin reduction by an inhibitor (e.g. 160 g of C24 by one gram of an inhibitor) indicates that the inhibition mechanism cannot easily be explained by a simple “sequestering” effect. Wax inhibitors that decrease the WAT tend to also increase the WDT. Most of the wax inhibitors tested at a dosage of 100 ppm did suppress the WAT of lower molecular weight paraffin (C24) solutions, but had little or no effect for higher molecular weight paraffin (C36) solutions. Side-chain length of polymethacrylate wax inhibitors is an important performance parameter. Of the three polymethacrylate wax inhibitors tested, the one with the longest alkyl side-chain (C18) had the most effect on suppressing the WAT and increasing the WDT of the binary mixtures (n-C10–n-C24 solutions).

Paraffin Crystal and Deposition Control By Emulsification

This laboratory investigation considers the effects of emulsions (via adding surfactants) and the formation and deposition of paraffin wax. This study relates the properties of added surfactant and emulsion characteristics with their wax deposition tendency. Parameters considered include the surfactant HLB (Hydrophilic Lipophilic Balance), molecular weight, and surfactant concentration. Two different series of commercial nonionic surfactants are included in this study; Triton-X (ethoxylated phenols) and Tween (sorbitan) products. The hydrocarbon phase is a model oil; a mixture of paraffin’s with carbon numbers from C21 to C48 dissolved in n-decane (C10). Emulsion characterization was done by IFT (interfacial tension), viscosity measurement, and optical microscopy. The wax deposition measurements were performed in a novel cell apparatus where stirring controls the hydrodynamics and mixing energy. The study results indicate adding surfactants to promote emulsification can reduce the tendency for wax deposition. Properties that induce tighter emulsions such as lower interfacial tension and greater shear rate lead to reduced paraffin deposition. Furthermore, the wax that does deposit from an emulsion is softer (lower average molecular weight) versus wax that deposits in the absence of any chemical. In contrast, the wax that deposits in the presence of some commercial polymer-based wax inhibitors can be even harder (higher average molecular weight) than the deposit formed in the absence of any chemical additive. Introduction Wax deposition in production tubing and in surface facilities and pipelines has been and continues to be a challenge to the successful production, transportation, and refining of crude oil. As oil development sites move to deeper and therefore colder water, the appearance of wax deposition on pipe walls becomes inevitable. Wax deposits can restrict the flow of oil and cause the plugging of pipelines. Maintenance operations can lead to frequent production interruptions. The cost of remediation increases with water depth. Finding economic and technical solutions for the prevention, management, and remediation of wax deposition problems in pipelines carrying produced fluids or dry oil has become a hurdle for producing new deep-water resources. Therefore, eliminating or avoiding deposited wax remains a key factor in flow assurance strategies for developing deep-water reservoirs. Petroleum waxes that is, saturated carbon numbers ranging from C18 to C90, are soluble in the crude oil, but will begin to precipitate as the oil cools to the wax appearance temperature (WAT), also termed the cloud point. The chemical composition of precipitated waxes is different from that of the crude oils, the deposit being enriched in the higher carbon number components. The deposition of these paraffin components occurs on the walls of pipes or vessels, which are cold surfaces relative to the warmer crude oil being transported through them. This phenomenon of wax deposition has been the subject of many studies, but largely confined to experimental investigations that evaluate the behavior only of the subject oil. 2,3,4 A test procedure that considers only the oil phase such as the measurement of the WAT or amount of material that deposits on a cold finger or in a flow loop is simpler to design and implement, but it neglects the presence and possible effect of an aqueous phase on the wax deposition process. This mixed water/oil phase case is a common and practical situation where raw produced fluids are transported through pipes in cold environments and have a risk of wax forming on the pipe walls. With the presence of water, paraffin-related issues involve not only the deposition of wax on the pipe walls, but also wax particles that may form but stay suspended in solution. Experience has shown that wax and other solids may stabilize produced oil/water mixtures, with the operational concern that this stabilized emulsion will impede the efficient separation of the produced fluids into a clean water and oil phases at the surface treatment facilities. The subject of this paper is a laboratory investigation of wax formation deposition in the presence of water, and in particular, the effect of surfactants included in the water/oil mixture designed to create emulsions. The literature reports field cases and laboratory studies that demonstrate the addition of a surfactant to a water/waxy oil mixture can reduce the wax deposition on a cold surface. The study reported here confirms this may be an option for wax control and considers the possible mechanisms for this effect. To perform this study we rely on a novel stirred cell device that can mimic the S. Ahn , K.S. Wang, and P.J. Shuler, SPE, California Inst. of Technology; J.L. Creek, SPE, ChevronTexaco Energy