RU2517824C1 - Method for determination of productive formation status by pulsed neutron method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: logging device is moved along the borehole, a repetitively-pulsed fast neutron flux is generated in the well, a time analysis of the thermal neutrons flux rate is carried out for each quantum of the formation depth, values of baseline decrements are determined for the drop in the thermal neutrons flux rate. A chemical solution containing compounds with anomalously high macro cross-section of nonfission neutron absorption is pumped into the well under pressure, then values of baseline decrements are determined for the drop in the thermal neutrons flux rate repeatedly, ultrasonic radiation is generated in the well and the formation is impacted by this radiation, thereafter values of baseline decrements are determined for the drop in the thermal neutrons flux rate for satisfaction of the respective system of inequalities containing values of decrements obtained at all three stages of measurements. Against satisfaction of these inequalities a judgement is made about potential maintenance of the well flow rate at the operational level with periodical impact on the formation by a longitudinal acoustic pressure wave.

EFFECT: possible identification of productive formations where usage of acoustic impact on the formation to maintain the well flow rate gives positive result.

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Description

The invention relates to nuclear methods for monitoring the condition of wells during the development and operation of oil fields using neutron fields generated in small accelerator tubes.

Known are pulsed neutron methods for studying well sections, in which the differentiation of the elemental composition of the strata is carried out according to the measured values of the decrement of the density of thermal neutrons in the stratum determined by the macro section of radiation neutron capture [1-3].

Closest to the proposed technical solution is the pulsed neutron method described in [3], which can be taken as a prototype.

. Этот способ позволяет устанавливать местонахождение пласта, содержащего продуктивный углеводород.According to the prototype method, the logging tool is moved along the wellbore, a pulse-periodic flow of fast neutrons is generated in the well, a temporal analysis of the thermal neutron flux density in the formation is carried out, for each depth quantum with number n = (1 ÷ N), into which the formation is divided with power H, determine the decrement decrement values of the density of thermal neutrons-λ at points

. This method allows you to locate the reservoir containing the productive hydrocarbon.

During the operation of the existing well, its state changes in the direction of decreasing production rate, as a result of clogging of the productive fluid extraction zone with various contaminants. To restore the flow rate and maintain it at the operational level, it is possible to carry out an acoustic impact on the formation with a longitudinal ultrasonic pressure wave, thus cleaning the fluid extraction zone from the above impurities [4]. It should be noted that this method of recovery and maintaining the flow rate can not always lead to a positive result. There are oil reservoirs with such physicochemical properties and structure, in which the acoustic impact cannot have a significant effect on the permeability of the formation and the ability to clean the area adjacent to the well.

The disadvantage of the prototype method is the impossibility of isolating productive formations in which the application of the acoustic stimulation method to maintain the production rate of the well at an operational level gives a positive result. Thus, the impact on a significant number of objects is not effective. At the same time, the cost of preventive work on cleaning wells in this region is significantly increased.

The technical result of the proposed method is to reduce the cost of preventive work to increase the flow rate of wells.

пласта, согласно предлагаемому способу, закачивают в скважину под давлением раствор-реагент, содержащий соединения элементов с аномально высоким макросечением радиационного захвата нейтронов (Cl, В, Cd, Gd, Sm, Eu, Dy), вторично определяют значения декрементов спада плотности тепловых нейтронов - λ₁ в точках x_n, генерируют в скважине ультразвуковое излучение с частотой f=(10÷25) кГц, воздействуют этим излучением на пласт, после чего снова определяют значения декремента спада плотности тепловых нейтронов - λ₂ в точках х_n и по выполнению неравенствThis result is achieved by the fact that in the known method [3], including the generation of a pulse-periodic flow of fast neutrons in the well, a time analysis of the density of the thermal neutron flux in the formation at each depth quantum with the number n = (1 ÷ N) into which the formation is divided with power Н, determination of background decrement values - λ _f at points

the reservoir, according to the proposed method, a reagent solution is injected into the well under pressure, containing compounds of elements with an abnormally high macro-section of radiation capture of neutrons (Cl, B, Cd, Gd, Sm, Eu, Dy), the values of thermal neutron density decrease decrements are determined a second time - λ ₁ at points x _n , generate ultrasonic radiation in the well with a frequency f = (10 ÷ 25) kHz, act on the formation by this radiation, and then again determine the values of the decreasing coefficient of thermal neutron density - λ ₂ at points x _n and using the inequalities

,

,

Where

- statistical error in determining the decrement decreasing density of thermal neutrons on the nth quantum of depth in the reservoir,

Δλ _Ф (х _n ), Δλ ₁ (х _n ), Δλ ₂ (х _n ) - statistical errors in determining λ _Ф , λ ₁ and λ ₂ at each measurement stage, judge about the possibility of maintaining the well flow rate at the operational level with periodic exposure to formation of a longitudinal acoustic pressure wave.

The first inequality was established in the process of processing the data of an experiment on testing the proposed methodology at various active oil wells in Western Siberia, obtained by employees of the Institute of Geophysical and Radiation Technologies of the International Academy of Higher Education Sciences. Violation of inequality (1) means in the case of an oil reservoir that it has such physicochemical properties and structure in which the acoustic effect cannot have a significant effect on its permeability and cleaning ability. The share of such wells in Western Siberia according to the results of the research is approximately 30%.

The values of decrements and errors Δλ _Ф (х _n ), Δλ ₁ (х _n ), Δλ ₂ (х _n ) should be determined during processing of pulsed neutron logging signals using a special computer program with a minimum confidence probability of 0.95 [5].

Consider an example of the method when analyzing the state of one of the layers of an existing oil well at the Talinsky field (Western Siberia).

In the experiment, we used the standard hardware and methodological complex of pulsed neutron logging based on a serial accelerator tube that generates a fast neutron flux as a result of the nuclear reaction T (d, n) ⁴ He [6] and a downhole ultrasonic emitter with an oscillation frequency of 20 kHz. We considered a section of a section of a well with a power of N = 3 m, containing N = 10 depth quanta. In the process, pulsed neutron logging was carried out before and after injection of the reagent solution, and as a result of computer processing of the results, the values of λ _Ф (х _n ), λ ₁ (х _n ) were determined for each quantum of depth. Then the ultrasonic emitter was launched. In this case, an acoustic field with an intensity of up to 10 kW / m ^{2 was} excited in the well. The intensity of the ultrasonic wave in the formation corresponds to this value, at a distance of 1 m from the borehole wall to 0.2 kW / m ² . After the emitter stopped working, pulsed neutron logging was carried out again and λ ₂ (x _n ) values were determined. Further, inequalities (1) were checked and a conclusion was drawn about the possibility of maintaining the well flow rate at the operational level with periodic exposure to a formation by a longitudinal acoustic pressure wave. The figure shows the dependences λ _Ф (х) - the lower graph, λ ₁ (x) - the upper graph and λ ₂ (x) - the average graph constructed by spline interpolation of the values λ _Ф (х _n ), λ ₁ (х _n ), λ ₂ (x _n ). The abscissa axis was the distance along the wellbore in m. The coordinate x = 0, which corresponded to the beginning of the investigated area. The ordinates were the values of decrements in relative units. The statistical error in determining the decrement of thermal neutron density decay on the nth depth quantum in the formation was determined by formula (2) using the program [5].

This example illustrates the situation where inequalities (1) are satisfied and the acoustic impact method can be effectively used to maintain the well flow rate.

Thus, the proposed method allows you to exclude from consideration oil wells for which the acoustic impact method cannot give a positive result, and thereby reduce the unproductive costs of maintaining the flow rate of wells.

Information sources

1. Physical fundamentals of pulsed neutron methods for researching wells / Shimelevich Yu.S., Kantor S.A., Shkolnikov A.S. et al. // M., Nedra, 1976, 161 pp.

2. Pulse neutron logging / Basin, Ya.N., Martyanov IA, Tseytlin V.G. et al. // M., VNIIAGG, 1984, 65 pp.

3. Remote radiation control with linear accelerators. T.2. Complexes of radiation monitoring / Bogdanovich B.Yu., Nesterovich A.V., Shikanov A.E. et al. // M., Mechanical Engineering, 2012, 284 p.

4. Environmental safety and acoustic impact / Atamanov VV, Zhuykov Yu.F., Zilonov M.O., Popova A.V. // Materials of the International scientific-practical conference “Problems of ecology and life safety” edited by prof. V.N. Pryakhina, c. 3, M., 2002, p. 218-222.

5. The INC data processing program based on a two-component signal model / Martyanov IA, Startsev AA, Fedyna EA and others // Scientific and Technical Bulletin "Logger", No. 52, Tver, 1998, p. 68-72.

6. Pulse neutron-neutron logging equipment for use in modern well research technologies / Amursky AG, Kurdyumov IG, Titov IA et al. // Sat. materials of the International scientific and technical conference "Portable neutron generators and technologies based on them", Moscow, VNIIA im. N.L. Dukhov, 2005, p. 253-255.

Claims (1)

A method for determining the state of a reservoir by a pulsed neutron method, in which a logging tool is moved along a wellbore, a pulse-periodic flow of fast neutrons in a well is generated, a temporal analysis of the thermal neutron flux density is performed on each depth quantum with number n = (1 ÷ N), which breaks up the reservoir with a power of H, determine the values of the background decrements of the decline in the density of thermal neutrons - λ _Ф at points

formation, characterized in that a reagent solution containing compounds of elements with an anomalously high macro-section of radiation capture of neutrons is pumped into the well under pressure, the values of thermal neutron density decrease decrement λ ₁ at points x _{n are} determined a second time, and ultrasonic radiation with a frequency of in the range f = (10 ÷ 25) kHz, they are affected by this radiation on the formation, after which they again determine the decrement values of the thermal neutron density decay - λ ₂ at the points x _n and the inequalities

,

,
Where

is the statistical error in determining the decrement of the decrease in the density of thermal neutrons on the nth depth quantum in the formation, Δλ _Ф (х _n ), Δλ ₁ (х _n ), Δλ ₂ (х _n ) is the statistical error in determining λ _Ф , λ ₁ and λ ₂ at each stage of the measurements, they judge the possibility of maintaining the production rate of the well at the operational level with periodic exposure to the formation of a longitudinal acoustic pressure wave.

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