Removal of Organic and Inorganic Scale from Electric Submersible Pumps

Abstract

Abstract There are a number of fields that produce heavy crude. In some of these fields, the run life of electrical submersible pumps (ESP) is greatly reduced by organic and inorganic deposits. This results in lost production and in many cases, additional time and cost to pull and repair the ESPs. A study showed that the problem of organic-paraffin deposits is related to the crude oil cooling and the volatile/lighter fractions separating near to the pump intake, plugging the pump. In the case of wells with a high water cut, inorganic scaling occurs in the pump intake, mainly due to the pressure drop in the wellbore. It was also noted that paraffin did not precipitate in wells with a high water cut because there was less cooling of the fluid in the in the wellbore due to the higher thermal capacity of water. The organic deposits can be removed by displacing jet fuel through the pump, while the continuous injection of jet fuel or high concentrations of paraffin inhibitors is an effective solution to preventing paraffin deposits. However, attempts made to dissolve inorganic scale are usually unsuccessful due to heavy crude adhering to the surface of the scale, preventing solvents such as xylene to contact the scale, even with the addition of mutual solvents. More recent work with crude oil viscosity reducers has shown that both inorganic and organic scale deposits can be successfully removed by spotting/jetting with coiled tubing without the need of a workover (WO) rig. When a treating fluid containing the viscosity reducer is mixed with highly viscous crudes, it creates a water-external pseudo-emulsion, which decreases the apparent viscosity of the crude by several orders of magnitudes, removing over 60% of the heavy crude from the surface of the scale and accelerating the dissolution of organic deposits. This enables the chemical treatment to dissolve the inorganic deposits, allowing the pump to be restarted without the need to pull out the completion. The new fluid systems have made it possible to systematically remove organic and inorganic deposits from ESPs, extending the average run life from 40 to 140 days, and to eliminate the requirement for WO rigs, with an average rig cost saving of 6 days per well and an average saving of USD 1.5 million in deferred production.