SU695296A1 - Probe device for x-ray radiometric logging of horizontal boreholes - Google Patents

Description

The source holder holds a pool 6 of tungsten pseudo-alloy, which provides directional irradiation of a samarne target with radiation of source 7 of americium-241 (lAm). Two holes 8 are provided in the pool through which the test medium is irradiated with direct radiation from the source. The source holder is threaded on a common holder of the probe device 9. The latter is connected to the housing of the downhole tool 10. Lead screen 11 provides directional detection of 12 gamma quanta from a specific area of the medium under investigation by the detector. The detector consists of a photomultiplier tube FEU-85 articulated with a thin crystal NaJ (Tl). A beryllium window 13 is provided in the probe device for the free passage of soft gamma quanta.

Under the force of gravity of the additional lead shield 3, the shield 1 with the samarium target 2, rotating on the ball bearings 4, constantly looks at the upper hemisphere of the well, regardless of the orientation of the casing of the borehole tool.

Thus, using the proposed probe device, the upper hemisphere of the well is investigated, which eliminates the influence of interfering factors spreading cassiterite in the wellbore during the washing process and cavities filled with water, and also reduces the effect of its slushiness on the RRB results.

In the proposed probe device of the downhole tool, the measurement geometry is realized, close to the backscatter geometry (scatter angle: 140 °).

The investigated upper hemisphere of the well is irradiated with two radiation streams with different photon energies. The flux of radiation with lower photon energy provides effective excitation of the characteristic radiation of tin, and the flux of photons with higher energy to create scattered radiation used as a standard - the background. The use of two primary radiation fluxes minimizes the effects of the absorption properties of the medium under study, and the measurement in the backscatter geometry provides a weak dependence of the measured spectral ratio on the gap between the probe and the upper hemisphere to 50-60 mm.

A source of

 Am whose radiation is used

at the same time to form a stream with

greater photon energy and for irradiation

targets whose radiation provides

effective fluorescence excitation

K-series tin.

The use of a probe device for RRB horizontal wells allows to significantly improve the quality and reliability of the results obtained; eliminate the effect of the consequences of flushing the squall (distribution of cassiterite through the wellbore) on the RRB results; to reduce unproductive time losses on the re-logging, aimed at finding out the results on slagging and watered areas of the well.

The invention can also be applied for well logging to other (especially heavy) elements.

Claims (2)

1. Artsybashev V. A. Nuclear geophysical prospecting. M., Atomizdat, 1972, with. 120-122. 2. Filippov E.M. Nuclear Geophysics, vol. 1, “Science, Novosibirsk, 1973, p. 318-319 (prototype).