TX 75083-3836, U.S.A., fax 01-972-952-9435.
AbstractAt the present time, Rosneft Oil Company is applying various technologies to minimize scaling problem. One of these techniques is, for example, a continuous injection of inhibitors using surface dosing systems to protect downhole equipment from damage caused by scale deposits (more than 1200 wells are equipped with dosimeters). It has been discovered that this method has some disadvantages, in particular an abnormal high rate of downhole equipment corrosion. As a result, wells are destroyed within less than a year. Our estimation shows that for some cases the corrosion rate is higher than 20 mm/year. Corrosion types and mechanisms have been determined. Corrosivity testing of the production from the above wells has been performed using coupons made of the least corrosion resistant material in the injection system, and an industrial adaptation of the material followed the examination. The corrosivity has been studied in a wide temperature and partial pressure CO 2 range. Testing and selection of chemicals for corrosion prevention technologies have been carried out.
TX 75083-3836, U.S.A., fax 01-972-952-9435.
AbstractAt the present time, Rosneft Oil Company is applying various technologies to minimize scaling problem. One of these techniques is, for example, a continuous injection of inhibitors using surface dosing systems to protect downhole equipment from damage caused by scale deposits (more than 1200 wells are equipped with dosimeters). It has been discovered that this method has some disadvantages, in particular an abnormal high rate of downhole equipment corrosion. As a result, wells are destroyed within less than a year. Our estimation shows that for some cases the corrosion rate is higher than 20 mm/year. Corrosion types and mechanisms have been determined. Corrosivity testing of the production from the above wells has been performed using coupons made of the least corrosion resistant material in the injection system, and an industrial adaptation of the material followed the examination. The corrosivity has been studied in a wide temperature and partial pressure CO 2 range. Testing and selection of chemicals for corrosion prevention technologies have been carried out.
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.
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