Drag Reduction with a Polymeric Additive in Crude Oil Pipelines

Abstract

Abstract A polymeric drag reducer has been tested in an 8-in. diameter crude oil pipeline. The test segment was 28 miles long. At the normal flow velocity in the 8-in. line of about 6 ft/sec, drag reductions of 16, 21 and 25 percent were obtained at polymer concentrations of 300, 600 and 1,000 volume ppm. A series of tests was run to determine the effect of flow velocity on drag reduction. Drag reduction decreased as the flow velocity decreased. An additional test in a 12-in. pipeline, 32 miles long, supported the results obtained in the 8-in. pipeline. In none of the tests did the polymer appear to degrade or lose effectiveness because of turbulent shear in the lines. Tests were run for the polymer and various polyisobutylenes in a 1-in.-ID laboratory pipe polyisobutylenes in a 1-in.-ID laboratory pipe viscometer. These tests covered a range of concentrations and flow velocities. The results obtained in the 1-in. line showed the same general characteristics as those obtained in the large pipelines. An equation is presented that correlates pipelines. An equation is presented that correlates the 8-in. and 12-in data as a function of flow velocity and polymer concentration. Introduction Drag reduction, as defined by Savins, is the increase in pumpability of a fluid caused by the addition of small amounts of additive to the fluid. The mechanism of drag reduction is not well understood. An extensive discussion on the subject is presented by Patterson et al. Drag reduction occurs only in turbulent flow. Despite this limitation, drag reduction has a wide potential application within the oil industry. At present, however, the only extensive use of drag reducers has been in hydraulic fracturing operations. Water-soluble polymers have been effective in reducing horsepower requirements and/or increasing injection rates during treatments. The drag reduction phenomenon has not been used in the pipelining of large quantities of crude oil and of pipelining of large quantities of crude oil and of petroleum products. Little use has been made of petroleum products. Little use has been made of it in hydraulic fracturing with oil base fluids. One of the main reasons for this situation is that until recently very few materials were available to reduce drag in aliphatic hydrocarbons. Several polymers may be used as drag reducers in aromatic polymers may be used as drag reducers in aromatic or chlorinated solvents. However, drag reduction in aliphatic hydrocarbons has been limited to polyisobutylene and crepe rubber. Another reason polyisobutylene and crepe rubber. Another reason is that there have been discouraging predictions about the performance of drag reducers in large pipes. Ram et al. studied polyisobutylenes in pipes. Ram et al. studied polyisobutylenes in small brass tubes (3.15 to 13.7 mm) and concluded that the critical velocities for onset of drag reduction ranged from 8.5 to 14.2 ft/sec. These velocities were considered usually too high for actual pipeline applications. These researchers also concluded that degradation of long-flexible polymeric chains in turbulent flow was an extremely polymeric chains in turbulent flow was an extremely serious problem. Seyer and Metzner concluded that little or no drag reduction can be expected in large tubes using presently available polymer materials. In this paper we present data on a polymer that gives substantial drag reduction in crude and diesel oils in small and large pipes. Some comparative data obtained with high molecular weight polyisobutylenes are also presented.