Effect of Flow Rate on Paraffin Accumulation in Plastic, Steel, and Coated Pipe

Abstract

Published in Petroleum Transactions, AIME, Volume 213, 1958, pages 80–84. Introduction The accumulation of paraffin deposits in tubular goods has been recognized as a major production problem since the inception of the petroleum industry. This problem is not limited to any particular geographical area nor is it limited to a specific type of crude oil. Generally speaking, "paraffin" deposition pertains to the deposition of any predominantly organic material in flow lines, and possibly even at the sand face, which would hamper the production of oil. In some fields, a continuous effort is required to remove deposits of paraffin and in order to accomplish this, many unique methods have been devised. The best solution to this problem, however, is to prevent the formation of such deposits. One method which has been tried in a number of fields is the use of plastic pipe. The purpose of this investigation is to compare the relative effectiveness of several plastic materials to aid in the reduction or prevention of paraffin accumulations in surface flow lines. Composition of Paraffin Deposits By definition, paraffin deposits are those materials which are insoluble in crude oil at the prevailing producing conditions of temperature and pressure. Such deposits usually consist of small particles of petroleum wax intermixed with resins, asphaltic material, and crude oil. They may also contain a variety of foreign materials such as sand, silt, water, various metal oxides, sulfates and carbonates of iron, barium, and calcium. The petroleum waxes deposited in flow strings usually consist of both a "hard" and a "soft" wax fraction. These waxes are largely aliphatic hydrocarbons with smaller amounts of aromatic and naphthenic compounds. Nathan has classified the hard and soft wax fractions. The aliphatic hydrocarbons present are those of high molecular weight with high melting points. Reistle pointed out that these high molecular weight compounds first separate from the oil due to a sharp decrease in solubility as the melting point increases. The identification of the resins and asphaltic materials rests, at present, on an arbitrary solubility procedure. Under certain conditions, materials which are insoluble in pentane (ASTM D–893) are defined as resins and asphalts. Subgrouping of these materials is made on decreasing solubility in benzene and carbon disulfide. Shock found some correlation between the solvent response and the pentane insoluble content of paraffins; higher pentane insoluble fractions are less soluble in any of the commonly used commercial solvents.

Multifunctional anti-wax coatings for paraffin control in oil pipelines

“…Therefore, in a large number of experiments, the inner walls of pipes were coated with low surface energy polymer composite coatings, and their properties to inhibit paraffin deposition were investigated by controlling the free energy of the substrate surface (Dotto and Camargo 2010). Jessen and Howell (1958) studied the paraffin deposition on the surface of different pipe materials (Jessen and Howell 1958). It was found that the paraffin deposition on the surface of smooth plastic was much smaller than that on a steel surface and maintained a low paraffin deposition for a long time.…”

Treating paraffin deposits in producing oil wells

“…Many of the authors listed in the bibliography have studied the deposition of paraffin; this section will summarize their observations. For more detailed information, the reader is referred t", : Agrawal et al (1989), Agrawal et al (1990), Brown (1940), Bucaram (1967), Burger et al (1981), Charles (1984), Cole and Jessen (1960), Gdanski (1984), Howell and Jessen (1956), Hunt (1962), Jessen and Howell (1958), Jorda (1966), Matloch and Newberry(1983), Mills (1932), , Newberry and Barker (1985), Patton (1970), Price (1971), Reistle (1928), Reistle and Blade (1932), Shock et al (1955), Sutton andRoberts (1974), Thomas (1988), Uren (1953), Weingarten and Euchner (1988), Won (1986), and Wright (1951 Other less widely used tests for the examination of wax are: (1) a visual study to determine the color and particulate adherence qualities;…”

“…Other things being equal, the rate of deposit was governed by surface roughness alone. Jessen (1958) carded out a series of deposition experiments, the conclusions of which were as follows: (1) the rate of deposition in a steel pipe varied with flow rate, reaching a maximum just prior to change from viscous to turbulent flow. (2) deposition of paraffin on various kinds of plastic pipe showed the same general dependence on flow rate as for steel pipe; however, the amount accumulaP._xiwas appreciably less on plastic than on steel pipe, 3when cooling of the oil from temperatures above the cloud point took place at the pipe wall, an increased deposit of paraffin resulted when compared with that obtained when the oil had been cooled below the cloud point prior to circulation through the pipe, (4) the rate of accum_alation of paraffin on plastic pipe seemed to increase with the degree of wettability by the crude oil, (5) plastic pipe did not entirely eliminate the problem, but the rate of deposition on plastic or plastic lined pipe was substantially lower than on steel or aluminum pipe and (6) predictions as to the severity of the paraffin problem must be based not only on cloud point but also on concentration of wax in _lution.…”

Effect of pour point on wax deposition under static cooling conditions

“…The influencing factors of wax deposition include crude oil composition, transportation temperature, temperature difference between oil and pipe wall, flow velocity, flow pattern, material of pipe, deposition time, and so on. Consequently, scholars have researched the problem of wax deposition for a long time; however, the mechanism of wax deposition is still not recognized thoroughly . The concept of ‘aging’ is a good supplement to the traditional wax deposition mechanism .…”