Express-diagnostics of rods’ parting-twist off at wells equipped with sucker rod pump

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The development of fields that are at a late or final stage of operation is carried out mainly with the use of downhole sucker rod pumps. The most characteristic failures for these installations are rods’ parting-twist off and malfunctions of pump valves. The methods of eliminating these accidents vary significantly – the parting or twist off of the rods involves lifting of the downhole equipment, and the "sticking" of the shut-off valve assembly of the pump is eliminated by "resuscitation" of the downhole equipment (flushing with water, hot oil or solvent). An error in fault identification leads to incorrect planning of work to restore the operability of the downhole equipment and, as a result, to economic losses.

The cause of malfunctions of the downhole equipment of downhole rod pumping units, as a rule, is determined by analyzing dynamograms. However, in many cases dynamograms do not allow to distinguish the lower twist off of the rods from the malfunction of the valves of the rod pump. In the presented work, a method for the operational determination of the parting or twist off of rods in the well is considered, which consists in creating an electrical circuit "rod string –tubing string" and monitoring its integrity. To determine the type of malfunction, the synchronization unit measures the resistance of the system on the dielectric insert via the electromagnetic channel. In case of parting or twist off of the rods, the electrical resistance of the "tubing-pump-rod string" circuit will be much higher (more than 2 ohms) than in the absence of this failure (0...2 ohms).

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Currently, a significant part of the oil-producing fund of wells is operated by the installations of rod borehole pumps (USSHN). Installations of this type can be conditionally divided into two parts: ground drive and downhole layout.
Monitoring of the technical condition of the ground part does not cause objective difficulties, at the same time, monitoring of the serviceability of equipment lowered into the well is usually carried out by indirect signs. The above situation is caused by the impossibility of visual control, the inaccessibility of downhole equipment and difficult working conditions, in particular, cyclic loading of the column of rods. At the same time, a significant proportion of emergency failures are caused by the breakage or lapel of the rods (OOSH) [1-5].


Monitoring of the technical condition of the downhole layout, as a rule, is carried out by analyzing dynamograms (DG).
Dynamometry allows you to determine most types of emergency failures, comparing the received dynamogram with the reference one, determine deviations in the operation of the USN.
But, despite the known advantages of this method, there are certain disadvantages, since the assessment of the technical condition is carried out by indirect parameters. One of the significant drawbacks is the practical difficulty of determining the lower OOSH, which graphically coincides with the malfunction of the SHGN valves.
An error in fault recognition leads to incorrect planning of work to restore the operability of downhole equipment. In this regard, there are unnecessary costs associated with the "resuscitation" of downhole equipment (flushing with water, hot oil, solvent).


To detect the lower OOSH, the following is proposed [6, 7] (Fig. 1): at the wellhead using a stabilized current source connected by one contact (clamp) to the ground part of the metal column of rods, and by the other contact (clamp) to the receiving electrode at the mouth, which is used as a column of pump-compressor pipes (tubing), a constant current, stabilized in magnitude, is fed into the well, which creates a potential difference at the ends of the ohmic resistance, separating the metal electrical circuit and having a finite known resistance :
, (1)

In this case, the voltage at the mouth (at the source of the stabilized current) is equal to:
where is the resistance of the column of rods, pump and tubing,
– resistance of the reservoir fluid column in the annular space between the tubing column and the rod column:

, (3)

where is the resistivity of the extracted fluid (oil + water), D inside. and dvneshn. – respectively, the diameters of the inner tubing and the outer column of rods, – the length of the column of rods from the mouth to the submersible pump.
Moreover, in the absence of a lower OOSH, the resistance of the entire circuit is equal to:

, (4)

since it is small: , since the tubing and rod columns are metal and have large cross sections (more than 150 mm sq.m.), and it is large: , since the resistivity of water-oil mixtures is close to the conductivity of oil and is greater than 10 to the degree of -10 (Ohm.m).

Fig. 1. The device for detecting the lower OOSH: 1 - a source of stabilized current, 2 - a contact to the ground part of the column, 3 - a column of metal rods, 4 - a receiving electrode, 5 - a tubing column, 6 - a voltage change registration unit, 7 - a separator of known electrical resistance, 8 - a depth pump, 9 - stuffing box made of dielectric material, 10 - a centralizer scraper made of dielectric; the dotted line shows the electrical circuit being created


The purpose of conducting tests to simulate the flow of current through the "TUBING - rod" channel was to substantiate the possibility of its use in wells equipped with rod deep pumping units.
The stand consists of 4 models of a coaxial conductor - an analogue of the communication channel "TUBING - column of rods", which are metal tubes of a certain diameter and length.
Inside each tube (model), there is a coaxially mounted metal (copper) wire of a certain diameter, centered with the help of dielectric insulating centralizer bushings (Fig.2). Each tube has a rubber plug with a hole through which the wire is passed and connected to a clamp for signaling.

Fig. 2. Diagram of the test stand: 1 - contacts for connecting the signal generator, 2 - wire;
3 - pipe, 4 - medium filling the pipe, 5 - dielectric plug, 6 - power supply connection contacts

The pulses were recorded using a two-channel oscilloscope GW Instek gds-71042:
- channel A - control of the signal at the entrance to the tube,
- channel B - control of the signal at the outlet of the tube.
In order to evaluate the wave resistance of a coaxial "cable" filled with air, the first series of tests was carried out without filling the annular space with liquid. For the convenience of consideration, the pulse frequencies were combined into bands of 1...5 kHz and 6 ... 10 kHz.
The amplitude of the output signal, In
the number of the prototype 1 2 3 4
Pipe diameter, mm 6.2 10.3 14.2 16.6
With air filling
Band 1...5 kHz 8.8 8.8 8.8 8.8
Band 6...10 kHz 8.8 8.8 8.8 8.8
With distilated water filling
Band 1...5 kHz 6,8 6,2 6,4 6,4
Band 6...10 kHz 6.4 6.2 6.4 6.8
With fresh water filling
Band 1...5 kHz 2.4 1.2 1.0 0.8
Band 6...10 kHz 2.2 1.0 0.85 0.7

It is found that at these frequencies the wave resistance does not affect the signal passage, and the air is an ideal dielectric.
In the second part of the experiment, the pipes in the test stand were filled with distilled water.
It is found that the conductivity of the distillate is significantly higher; accordingly, the output signal is ~20% less, and regardless of the model number. In addition, signals of different frequencies undergo the same attenuation (within the measurement error, 5%).
In the third part of the experiment, the pipes in the test stand were filled with fresh water.
For fresh water, the complex resistance (ohmic + capacitive) turns out to be significant, and there is a significant attenuation of the signal (from 3.5 times for model No. 1 to 11 times for model No. 4), and regardless of the signal frequency. At the same time, it can be seen that the 6...10 kHz band is fading out more.
Experiments have shown the possibility of using the flow of current through the "TUBING - rod" channel to control the integrity of the electrical circuit and, accordingly, the column of rods.


When a lower OOSH occurs, the electrical resistance of the "TUBING-pump-separator-rod column" circuit will increase sharply, since at the same time:
, (5)

which will cause a synchronous increase in U to maintain the Istab., which means:
/ , (6)

The latter will serve as a criterion for detecting the lower OOSH.
Accidental closures of the column of rods during bends (in particular, when going down), and accordingly, the resistance drops to almost zero,

, (7)

they do not affect the reliability of determining the lower OOSH with this method, because the synchronization unit included in the wellhead unit is configured to register an increase in the resistance of the circuit much more.


Practical tests were carried out at 3 wells: 68A; 4051; 2823 of the Yelnikovsky oil fields with a preliminary cause of failure - breakage of rods.
Well 68A of the Yelnikovsky deposit. During the bypass, the operator found no supply through the well. After the production of GDI (according to the dynamogram, the loads were about 3 tons), it was decided to perform an unscheduled flushing with hot oil. After flushing the well, the supply to the mouth did not appear, non-working valves were also observed according to the DG (loads after flushing with hot oil were about 2.5 tons). A decision was promptly made to set up a TCRS brigade.






Fig. 3. Dynamogram of well 68A

Before lifting the pumping rods, the resistance of the chain column of rods-pump-tubing column was measured (Fig.4). To do this, one of the contacts was fixed on the column of pumping rods, the other contact was connected to the air defense. The insulation resistance was 3.79 Mohm, which tells us about a possible breakage of the rods.
When lifting the pump, a break was found between 95 and 96 of the pump rod on the coupling. The reason for the breakage was the high intensity of the set of curvature of the borehole in this area. After the lifting work of the GNO, a pump of the previous standard size (NN-57) was lowered, and pumping rods with centralizers were introduced into the interval of a high set of curvature. The economic costs associated with the hot treatment, as well as excessive downtime of the well, could be avoided in case of timely detection of the lower breakage of the rods, which cannot be determined by the DG.


Fig. 4. Measurement of the insulation of the TUBING circuit-pump-rod column at well 68A.
Well 4051 was stopped in February 2019 with a lack of supply. The dynamogram (Fig. 5) shows that both valves do not work at the well. The well after hydraulic fracturing in May 2018, the operating time was 212 days. After flushing the well, the pump performance was not observed, a decision was made to set up a TCRS team.






Fig.5. Dynamogram for borehole 4051

When measuring the insulation of the tubing-pump-column rod system, the insulation resistance was 0 ohms, which indicates that there is no breakage of the rods. The rise of the downhole layout confirmed the absence of a break.


About the authors

A. S. Galeev

Almetyevsk State Petroleum Institute

Author for correspondence.

доктор техн. наук, профессор

Russian Federation, Almetyevsk

S. L. Sabanov

Almetyevsk State Petroleum Institute


канд. техн. наук, доцент


Rais N. Suleymanov

Ufa State Petroleum Technical University

ORCID iD: 0000-0003-2510-3703
SPIN-code: 4245-2811
ResearcherId: ABB-3047-2021

канд. техн. наук, доцент

Russian Federation, Ufa

O. V. Filimonov

Ufa State Petroleum Technical University


канд. техн. наук, доцент

Russian Federation, Ufa

T. A. Utemisov

Ufa State Petroleum Technical University


канд. техн. наук, доцент

Russian Federation, Ufa

Zh. K. Zhanturin

NAO “Atyrau University of Oil and Gas named after S. Utebayev"


канд. техн. наук, доцент

Kazakhstan, Atyrau


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Copyright (c) 2022 Galeev A.S., Sabanov S.L., Suleymanov R.N., Filimonov O.V., Utemisov T.A., Zhanturin Z.K.

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