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Home / Issue Archive / 2006 / June #6 / Computer and Nanotechnologies in Oil Pump Engineering

№ 6 (June 2006)

Computer and Nanotechnologies in Oil Pump Engineering

There are at least two reasons to apply computer modeling methods in the design and upgrade of submersible electrical centrifugal pump units (ESPs.)

By A.V. Lukin, N.N. Smirnov, N.I. Smirnov

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First, it is necessary to get a better idea of the physical nature of failures and basic processes in the pump, which save on the cost of experience. Second, it is important that the engineering by modern. For years, oilmen have had the headache of a sudden breakup of basic parts of the pump, tubing, and fall of the unit to the bottomhole. Such problems were solved by separate technical solutions, often ineffective, without serious investigation of reasons for the failure.
We propose a systematic approach to improving the reliability of the ESP, which involves three major stages of investigation: formation of a physical failure model on the basis of statistical data on the equipment operation; mathematical modeling of failure conditions; identification of "weak" components and details; development and commercial application of so-called "long-life" technologies. A new mathematical model of the ESP unit dynamics taking into account friction pair wear was developed in the package MSC/NASTRAN, this model allows the calculation of the mode of deformation of components and details, investigation of wear changes in time, and the determination of dynamic characteristics.
The calculation of the ESP unit dynamic behavior is an intricate nonlinear problem, which has many parameters set with high uncertainty (contact stiffness, abrasive properties of mechanical impurities, etc.). In addition to other ways, calculation accuracy is ensured by performance of stand model tests. Tests of friction pairs of pump stages made of various materials and in different environments enabled determination of coefficients of damping, wearing capacity, friction, etc., which were later used in the calculations. Modeling area includes the whole pump unit and a section of tubing 17 m long, with the most detailed modeling of the pump sections.
Dynamic analysis of ESP unit shows that there are 10..11 natural vibration frequencies in the range 10..13 Hz. Motion of the shaft with blade wheels in this case is asynchronous precession, and shaft protection barrels and distributor are wearing uniformly along the circumference. In the frequency area close to 50 Hz, synchronous precession appears which is conditioned by the maximum effect of unbalances and low damping level, and shaft protection barrels are wearing non-uniformly.
Mathematical model enables the users to study effects of blade wheel unbalance distribution, conditions of ESP casing contact with the casing pipe, its curvature, formation fluid properties and other factors on the mode of deformation.
Investigation of the mode of deformation of ESP components makes it possible to predict the probability of failure by the strength condition ("fall"). It is proved that it is conditioned by unfavorable factor combination. Most significant factors include: distribution of blade wheel unbalances in the course of operation, wearing capacity of friction pairs, quality of assemblage (tightening force, etc.) and tripping operations (speed of running-in and pulling-out), borehole curvature, formation fluid corrosive characteristics. Calculated strains in the pump casing (Fig. 1) caused by external loads, and fatigue tests of fasteners and end pieces enabled us to assign appropriate lifetime requirements to fabrication of the latter and to propose a technique of incoming inspection, which is actually a standard for fabrication of ESP details determining its lifetime. Appropriate ("long-life") fasteners designed by IMAShresurs with utilization of the results of mathematical modeling made it possible to exclude destruction at flanged and bolted connections of ESP. 
Pump wear modeling makes it possible to determine kinetics of friction pair wear, Fig. 2, which affects the dynamics. Dynamic loads, in turn, can affect the intensity of wear, especially of fragile ceramic materials. Application of these results is important for determination of optimal location of intermediate bearings and analysis of different layouts of pump componentry. Designed by ALNAS test benches and techniques enable the users to determine frictional characteristics of bearings and pump stages under conditions similar to actual ones. They can be recommended as a base for certification tests for friction and wear. On the basis of the requirements to wearing capacity of friction pairs, ALNAS designed materials to replace cerium-boron iron and commercial Ni-resist cast iron. Wearing capacity of the modified Ni-resist cast iron, obtained in the result of tests in abrasive-containing media (Table 1) considerably exceeds values of the commercial materials.
Application of nanotechnologies is a promising way to improve wearing capacity of friction pairs of ESP units. Hard alloy VK8nano modified with nano-additives was designed, this alloy exceeding wear capacity of VK8 two-three times, Fig. 3. VK8nano has great potential as material for intermediate bearings and seals to be applied in wells with gas or proppant blows.
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