Paraffin Inhibition And Flow Improvement In Crude Oil Systems

Abstract

Abstract This paper discusses the apparatus used and the methods employed to study the flow characteristics of various crude oils below the cloud point, examines the effect of various additives on these flow characteristics and correlates any change with depositional tendency. THE ACCUMULATION of paraffin wax in petroleum reservoirs and production equipment remains a continuous problem and expense in the production of oil. To ease the problem, use of chemical additives as paraffin deposition inhibitors is becoming more prevalent. As no one additive has proved universally effective, the selection of an efficient additive and a better understanding of the mechanism of inhibition is necessary. Patton(1) and Chichakli(2) showed that high-molecular- weight fractions from crude oil significantly affect paraffin cryrstal growth and retard or prevent paraffin deposition. Hanke(3) and Birdwell(4) also found that these fractions were adsorbed preferentially to a metal surface. Other investigators attributed decreased deposition to modifying the paraffin wax crystals(5,6,7,8,9) or changing the wetting characteristics of the pipe surface(10,11,12,13). The purpose of this work was to develop a technique for studying the flow characteristics of crude oil at temperatures below the cloud point, examine the effect of various additives on these flow characteristics and correlate any change in the flow characteristics with depositional tendency. Hanke(a) discussed thoroughly the ideas presented by several investigators(14,15,16,17,18,19) concerning accumulation of paraffin waxes. Tronov(20) used a micro moving picture camera to record paraffin deposition in a flowing well. Hunt(17) and Jorda(21) consider surface roughness, the only factor controlling the amount and characteristics of paraffin deposits. Greenlee(22) concluded that an insufficient concentration of resins and aromatics in crude oil prevented effective suspension of collodial asphaltenes which helped cause deposits. The work of Howell(16) and of Gavlin, Swire and Jones(23) pertains to materials found to be effective in depressing pour point. Lorensen(18) concluded that alkylated aromatictype dispersants and methacrylates acted as crystal modifiers. Knox, Waters and Arnold(24) found that polycyclic aromatics were good paraffin inhibitors when added in the presence of asphalt. Briant and Mieulet and Peinado(25) believed that the inhibiting mechanism of polyethylene was the formation of a network to which paraffin microcrystals become attached Bucaram(26), on the other hand, felt that inhibition with polyethylene depended on similarity of structure of paraffin and polymer molecules which allowed the polyethylene molecule to incorporate into the growing wax molecule and prevented additional growth by virtue of the branched structure of the polymer. Crystal modifiers are also reported by Bilderback and McDougall(27) as proving very Effective in several areas in minimizing deposition. Hasiba(28) and Hanke(a) found preadsorbed films of heavy crude oil fractions on a metal surface would prevent strong bonding by the wax crystals. Cold Flow Appamt, is and Refrigeration System The cold flow cell, designed by Enjay Chemical Company and obtained from the Ethyl Corporation, is shown in Figure 1. The test cell consisted of a cylin4er divided into two sections with a capillary stainless steel tube opening connecting each section.