Sanema - development of geophysical instruments and electronics for the needs of the oil industry.

Device for monitoring the technical condition of casing strings of oil and gas wells«MID-NM»

Example of calculation of thickness NKT and production string Fig.1 Thickness calculation example NKT and production string
At a depth 3770 m – shoe technical columns.
The total thickness of the pipes in the zone of “confidence” calculation of the thickness of the second column is 20 mm, above the shoe of the technical column is 32 mm
D60, D70 – дdifferential defectograms;
Тнкт мм – thickness NKT;
ТЭК мм – production string thickness;
Твнешн – fluid temperature;
Color scan – integral defectogram.

Tasks to be solved:

To solve these problems, the company Ltd "SANEMA" based on the method of magnetic pulse defectoscopy produces a series of flaw detectors MID-NM, the main technical characteristics of which are presented on the page production.All flaw detector modifications are delivered in a corrosion-resistant version for operation in an environment with a hydrogen sulfide content of up to 30%.

The method of magnetic pulse defectoscopy is based on the effect of induction of an induction current in the column by exposure to a pulsed magnetic field with subsequent registration by the receiving coil of the decay of electromotive force (EMF) induced in the pipes.

EMF attenuation depends on the design of the well (the number of studied columns), the total wall thickness of the columns, their diameter, electromagnetic properties of the metal used: conductivity and magnetic permeability.

The nature of this attenuation determines the thickness of the columns and assesses the presence and nature of the defects. The advantage of this method mainly lies in the possibility of conducting research in one-, two- and multi-column structures.

Carrying out magnetic pulse flaw detection does not require special preparatory measures for the well, flushing, killing the well or dismantling the tubing.

The flaw detector has 5 physical sensors in its composition:

Long probe designed to study the integral characteristics NKT and production casing, for the study of large diameter pipes, determining the location of the structural elements of wells and confirming the design of multi-column wells. On Fig.1 thickness calculation example is shown NKT and production casing with localization shoe technical columns.

Short probe designed for detailed studies (localization of defects, determination of perforation zones, calculation of thickness) in NKT or in the absence thereof, the column closest to the downhole tool with an inner diameter of up to 120 mm. On Fig.2 shows the location of the “crevice perforation” defect or filter with long and short probes on a 168 mm column. It is seen that the defectograms of the short Sxx probe localize this zone of violations in the column in more detail.
Thickness calculation example NKT and production casing Fig.2 Fig.2 An example of determining a slotted filter with long and short probes.
Lхх – EMF decay values recorded by a long probe;
Sхх – EMF decay values recorded by a short probe;
Color scan - integral defectogram;

The presence of highly sensitive temperature and pressure sensors in the equipment makes it possible to measure these parameters along the wellbore with high accuracy and obtain additional information about the technical condition of the well. The resolution of the pressure sensor allows you to calculate the fluid density and, if necessary, determine the location of the boundaries of the intervals of oil or gas inflow in the well (construction of the inflow profile).

A temperature thermometer with a time constant of 2 seconds is used to record temperature anomalies arising from leaks in sleeve joints and structural heterogeneities in wells, for example, the shoe zone of a technical column in Fig. 1, and to confirm the perforation zones of underground equipment.

When defining “column rupture” defects in flaw detectors of the MID-NM series, defectograms of early values of EMF decline are used. The presence of horizontal defects or ruptures of the columns leads to the appearance of additional magnetic gaps in the sensor - test medium system, which is recorded at the early times of the EMF decline (L8-L10 or 1-3 ms defectograms).

On Fig.3 localization shown horizontal column rupture on a model 73 mm pipe.


Localization of horizontal column rupture on a 73 mm model pipe Fig. 3 Fig.3 Recording on models. Localization of the transverse rupture
L8-L20 - defectograms of a long axial probe;
Т1 мм - integral column thickness;
Color scan - integral defectogram;

An example of successful work by the MID-NM flaw detector for monitoring the well’s technical condition NKT with corrosion wear presented on Fig.4.


Fig. 4. Example of corrosion wear NKT
Fig.4. Corrosion wear example NKT
L15-L18 – defectograms of a long axial probe;
Т1 мм – integral column thickness;
Thrm – fluid temperature;
Press – pressure;
Color scan - integral defectogram;

The detected defect is confirmed after dismantling the tubing by opening this interval Fig. 5..


Fig. 5. Section NKT with corrosive wear
Fig. 5. Corrosion Wear Section NKT

The material presented is quite obvious and easy to interpret, since wear occurred in the pipe body and was most likely a consequence of the high flow rates of highly mineralized and flooded well products.

In the study of the technical condition, the wear of the pipes is detected by comparing the suspicious sections of the defectogram with the defectogram of the unworn intervals of the column, or by comparing the defectograms with previous studies. That is, for the correct assessment of the wear of structural elements of wells, it is necessary to collect statistics. Such statistics can be obtained by conducting background measurements immediately after the descent NKT   and periodic studies during the operation of the well.

Technical condition assessment example NKT based on two studies with a periodicity of 10 months presented at on Fig.6.

Analysis of the technical condition NKT was carried out by comparing the initial record of 2009 with the record of 2010, as well as comparing the calculated thicknesses. In the upper part of the column, up to approximately 2400 m, absolute identity was observed, both of the primary data and the calculated thicknesses. ON Fig.6. the absolute identity of the curves is visible. The presented results were the basis for the postponement of the well repair time.

In the lower part of the well, changes associated with increasing deflection of the tubes are visible NKT   and more pronounced eccentricity of the columns and the slight corrosion that appeared. On Fig.6. a fragment of a well with the alleged development of local corrosion at a depth of x090.5 m and developing corrosion at a depth of x095.5 m is presented. Fig. 6. Comparison of research results of technical condition NKT
Fig. 6. Comparison of research results of technical condition NKT.

To assess the sensitivity of the flaw detector to a change in thickness NKT or the development of corrosion, laboratory tests have been performed. On the outer wall NKT we modeled a non-penetrating defect measuring 55x20x1.5 mm (fig. 7) mm, measured with a MID-NM flaw detector. Then the “defect” was increased to 100x20x1.5 mm (fig. 8) and re-measured. Fig. 7. Modeling of an external defect 55x20x1.5 mm in 73 mm NKT with a wall thickness of 5.25 mm
Fig.7.Modeling an external defect 55x20x1.5 mm to 73 mm NKT with a wall thickness of 5.25 mm

Fig. 8. Modeling of an external defect 100x20x1.5 mm in 73 mm NKT with a wall thickness of 5.25 mm
Fig.8. Modeling of an external defect 100x20x1.5 mm to 73 mm NKT with a wall thickness of 5.25 mm

Direct processing of the results of the study does not give an answer about the presence of any violations of the NKT, the presence of a defect can be said only by the defectogram L16. When interpreting measurements in a real well, a defect of this kind is most likely not to be detected.

ПWhen comparing defectograms of defects 550x20x1.5 mm and 100x20x1.5 mm in the full time interval, the development of external “corrosion” is manifested more clearly(fig.9). From this experiment, one can also judge the sensitivity of the MID-NM flaw detector to the integral change in the wall thickness of a single column, which in this case is about 0.01 mm. Fig. 9. External defect 100x20x1.5 mm to 73 mm NKT localized after joint processing of two consecutive measurements.
Fig.9.An external defect of 100x20x1.5 mm in 73 mm NKT is localized after the joint processing of two consecutive measurements.

Thus, the equipment MID-NM it is an effective tool for organizing continuous monitoring of wells during their construction and operation with the aim of predicting the development of defects and determining the optimal time for repairing wells.

Flaw detector in modification MID-NMA designed to work offline on wire. To work with it, you need a mobile computer, to coordinate with the depth, you additionally need the Depth control module.

Flaw detector in modification MID-NMK Designed to work on a geophysical cable with a logging station equipped with a logging recorder such as Vulcan, Karsar, Kedr


On Fig.10 and Fig. 11 records are presented reflecting the operation of the MID-NM flaw detector in determining the design of the production casing and its defects through NKT


Fig. 10. Changing the design of the production (T2) casing; during the construction of the production casing, pipes with different wall thicknesses were used.
Fig.10. Changing the design of the production (T2) casing; during the construction of the production casing, pipes with different wall thicknesses were used.


Fig. 11. Detection of perforation of production casing through NKT.
Fig.11. Detection of perforation of production casing through NKT.
T1 – thickness chart NKT;
Т2 – production string thickness chart.
L28-L41 – defectograms.
Interval2743,3 - 2744,7 m – production casing pipe.
Intervals 2725 - 2730 m; 2732,7 - 2733,5 m – production string perforation.