Paraffin Crystal and Deposition Control By Emulsification

Abstract

Abstract 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.1 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.2,3,4A 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.5,6