Analysis of Causes of Hign-Rate Corrosion Occurring at Electric Motors of Submersible Pumps

Abstract

The problem of corrosion damages of submersible equipment installed in wells does exist in almost all the oil producing regions in spite of different production conditions, equipment operation and produce composition. The analysis of submersible pump operating conditions at RN-Purneftegas JSC has shown that cavitation-erosion effect exerted on the equipment under the conditions of extremely high fluid flow velocities in the electric motor-flow tubing annular space is one of the principal causes of rapid corrosion of submersible electric motors. The corrosion process under high watercut conditions (>80%) is encouraged should the formation water saturated with dissolved carbon dioxide contact the electric motor exterior surface. Resulting corrosion reduces the well overhaul period by a factor of ten. The annual loss amounts to 130 mln. roubles. To increase the mean-time-between-failures of electrical centrifugal pump (ECP) units the procedures have been worked out to improve the operational integrity of the submersible pumping equipment and methods of corrosion activity reduction by means on inhibiting the produce. Introduction In the last year's submersible equipment installed at RN-Purneftegas JSC producers has been failing due to corrosion more and more frequently. Corrosion of both inside tubing walls and exterior surfaces of submersible electric motors (SEM) is observed. SEM corrosion is the cause of approximately 70% of well failures due to corrosion. In all the number of submersible equipment failures due to corrosion have increased by a factor of 4 – 5 for the last two years. At present they account for 13 – 15% of the producing well stock. Overhaul period of wells exposed to corrosion varies from 27 to 300 days and makes up on the average 100 days. It should be noted that the mean total overhaul period is 300 days. Oil production losses due to well failures resulting from corrosion run into 2000 t/year.