RU2013533C1 - Method for detection of technogenic fluids accumulation in geological objects uncovered by wells - Google Patents

Abstract

FIELD: downhole logging. SUBSTANCE: in a shut-down well at least two thermograms are recorded, with simultaneous time registration. The temperature is measured both at locations of supposed leaks and in a reference layer with consists of dense impermeable rocks, with the first measurement made 15 hours after shutting the well off. Then at a reference layer level a curve of temperature recovering is determined for a time adequate for determination the hole temperature change velocity

. After Dt time interval determined from the formula

Description

 The invention relates to field-geophysical research of wells and can be used to monitor the ecological state of the subsoil of the sub-productive stratum of oil, gas, gas condensate fields and underground gas storages.

 A known method for determining annular circulation by pumping into the well of radioactive isotopes and recording its progress using radio logging.

 The disadvantage of this method is that the information obtained is not always unambiguous, since some of the radioactive isotopes remain in the wellbore. When implementing this method, contamination of the well and subsoil with radioactive isotopes occurs. In addition, the use of this technique is complicated by increased safety requirements.

 A known method for determining casing leakage and annular circulation by recording the temperature distribution in the interval of geothermal disturbance, subsequent change in the liquid column in the selected interval, re-registering the temperature distribution within 1-2 hours after changing the liquid column and comparing the obtained thermograms.

The disadvantages of the method are, firstly, the need for prolonged shutdown of production wells to restore the geotherm in it. The downtime of the well 3-4 times should be longer than the well;
secondly, re-registration of temperature after changing the fluid column is carried out after 1-2 hours. Therefore, the interpretation of the results is ambiguous, since it is impossible to take into account the influence of such factors on the temperature change in the well, such as the process of pressure restoration in the well bore, changes in the thermophysical elements of the well (design and the thermophysical properties of the fluid filling the wellbore) and the thermophysical parameters of the rocks surrounding the well.

. (1)
Недостатками способа являются то, что, во-первых, он не позволяет определять наличие утечек газа из ствола и латерального (горизонтального) движения его за колонной, если утекающий из ствола скважины газ внедряется непосредственно в коллектор и в нем накапливается, т. е. за колонной имеется только горизонтальное движение; во-вторых, использование данных термометрии, полученных в первые 3, 5 и 10 ч простоя скважины, приводит к неоднозначности результатов интерпретации, так как на поведение температуры в стволе скважины в это время действуют несколько факторов, вклад которых нельзя оценить: предыстория работы скважины (длительность периода закачки или отбора), процесс восстановления давления, влияние конструкции скважины и теплофизических параметров пород, окружающих скважину; в-третьих, снятие 5-6 термограмм в остановленной скважине приводит к увеличению материально-технических затрат как на проведение геофизических исследований, так и из-за большого времени простоя скважины.The prototype of the proposed method is a method for determining vertical annular gas flows, which consists in taking background thermograms (geotherms) in observation and long-standing idle wells, conducting thermal logging in production wells at the time of gas injection or sampling, and then taking 5-6 thermograms in a drilling well in 3 , 5 and 10 hours after stopping and, if necessary, 3, 5 and 10 days before the establishment of the stationary regime, the construction of these curves in the form of a temperature distribution with depth, comparison and x with the background and theoretical distribution, detecting temperature anomalies in the range of the assumed vertical flows and determining from these curves the normalized heat transfer coefficient B (m), which depends on the weight flow rate according to formula (1):
B =

. (1)
The disadvantages of the method are that, firstly, it does not allow to determine the presence of gas leaks from the wellbore and lateral (horizontal) movement of it behind the column, if the gas leaking from the wellbore is introduced directly into the reservoir and accumulates in it, i.e. the column has only horizontal movement; secondly, the use of thermometry data obtained during the first 3, 5, and 10 hours of well shutdown leads to ambiguous interpretation results, since several factors can affect the behavior of the temperature in the wellbore at this time, the contribution of which cannot be estimated: the history of the well’s operation ( the duration of the injection or selection period), the pressure recovery process, the effect of the well design and the thermophysical parameters of the rocks surrounding the well; thirdly, the removal of 5-6 thermograms in a stopped well leads to an increase in material and technical costs both for geophysical surveys and because of the long downtime of the well.

 The aim of the invention is the ability to determine leaks in the casing string, the intervals of lateral (horizontal) movement of fluids through the reservoirs and secondary accumulations in them, i.e., expanding the functionality of the method.

, где Δτ - временной промежуток;
δ t - абсолютная погрешность измерения температуры;
t'_τ - скорость измерения температуры в стволе остановленной скважины, для чего после снятия первой термограммы в остановленной скважине на одном из срезов реперного слоя снимают кривую восстановления температуры в течение отрезка времени Δτ, об интервалах утечек, латерального движения их за колонной и образования вторичных скоплений судят по наличию интервалов с аномальной температурой на кривой температуры пород, окружающих скважину, рассчитываемую по данным термометрических исследований.The goal is achieved in that, in addition to recording the initial geothermal temperature distribution in observation and long-standing idle wells, taking thermograms in production wells (pumping or sampling fluid) in the operating mode and after they are stopped, at least two thermograms are taken in a stopped well with simultaneous recording of them in time, taking temperature measurements in the places of the alleged leaks and accumulations and in the reference layer, consisting of dense impermeable rocks, and the first thermogram is taken es 15 h after shut, and the second - after a time defined by the formula
Δτ ≥

where Δτ is the time period;
δ t is the absolute error of temperature measurement;
t ' _τ is the temperature measurement speed in the wellbore of a stopped well, for which, after taking the first thermogram in a stopped well, one of the sections of the reference layer takes a temperature recovery curve over a time interval Δτ, about leakage intervals, their lateral movement behind the column and the formation of secondary clusters judged by the presence of intervals with anomalous temperature on the temperature curve of the rocks surrounding the well, calculated according to thermometric studies.

 According to thermometric studies according to the well-known formula (2), the temperature of the rocks is determined and temperature anomalies are determined due to fluid leaks from the wellbore, their lateral movement through the reservoirs and the formation of secondary accumulations in them.

= 1-0.5A(τ_o+τ)·(ln 8aτ/γ $\genfrac{}{}{0ex}{}{\text{2}}{\text{с}}$ -1) (2) где t_o - температура в скважине в момент прекращения термического воздействия, т. е. перед остановкой скважины;
t_п - температура пород, существовавшая до начала эксплуатации скважины;
t - текущая температура в скважине в момент времени после остановки;
tau<N>_o - время термического возмущения (длительность закачки или отбора);
τ - текущее время с момента остановки;
а - коэффициент температуропроводности пород, окружающих скважину;
γ_c - радиус скважины.

= 1-0.5A (τ _o + τ) · (ln 8aτ / γ $\genfrac{}{}{0ex}{}{\text{2}}{\text{with}}$ -1) (2) where t _o is the temperature in the well at the time of termination of the thermal effect, that is, before shutting down the well;
t _p - rock temperature, which existed before the start of the operation of the well;
t is the current temperature in the well at a time after a stop;
tau <N> _o - time of thermal disturbance (duration of injection or selection);
τ is the current time since the stop;
a is the thermal diffusivity of the rocks surrounding the well;
γ _c is the radius of the well.

. (3) Формула (2) справедлива при условии (4)

=

>5. (4)
Существенные отличия способа следующие.A (τ _o + τ) =

. (3) Formula (2) is valid provided that (4)

=

> 5. (4)
The significant differences of the method are as follows.

, (5) где Δτ - временной промежуток;
t'_τ - скорость изменения температуры в стволе остановленной скважины;
δt - абсолютная погрешность измерения температуры.Removal of at least two thermograms in a stopped well within the interval of 15 - 100 hours after shutdown. The time intervals between the removal of thermograms are selected from the condition
Δτ ≥

, (5) where Δτ is the time interval;
t ' _τ is the rate of temperature change in the wellbore of a stopped well;
δt is the absolute error of temperature measurement.

 The boundaries of the time interval of 15 and 100 hours are determined by the need to exclude the effects of temperature recovery and the nonlinearity of the temperature recovery curve in semi-log coordinates for short and long times (Figs. 2 and 3).

≈

, (6) где Δt - разность значений температуры (Δt≥δt);
δτ - временной промежуток между измерениями температуры.Determination of t ' _τ values when taking all thermograms in a stopped well, except for the last one. The determination is made by twice measuring the temperature with a stationary device and numerical differentiation according to the formula
t

≈

, (6) where Δt is the temperature difference (Δt≥δt);
δτ is the time interval between temperature measurements.

 The use of a reference layer, consisting of dense impermeable rocks, in which there is no lateral (horizontal) movement of fluids and their secondary accumulations. This allows us to find the value of the duration of the thermal disturbance at a known equilibrium geothermal temperature distribution within the layer.

 The temperature in a stopped well is recorded as a function of depth and time.

In FIG. 1 shows the results of mathematical modeling, reflecting the calculated temperature distribution, for a model with one absorbing layer with positive and negative thermal effects (the results of processing thermograms); in FIG. 2 - the results of mathematical modeling of the process of restoring dimensionless temperature in the wellbore after injecting warm gas for the reference layer composed of rock salt with a thermal diffusivity a = 0.2 ˙ 10 ^-5 m ² / s. A straight section is allocated from 2 to 150 hours, where A ≈ const, the temperature recovery depends only on the well history. Curve 3 - the results of calculations of temperature recovery by the formula (2), they completely coincide with the data of mathematical modeling and confirm the legitimacy of using this formula for these purposes; in FIG. 3 - similar to FIG. 2 data of mathematical modeling for terrigenous sediments with a = 0.2 ˙ 10 ^-6 m ² / s. In the range of 10 - 150 h, temperature recovery occurs at A ≈ const and depends only on the background; in FIG. 4 - temperature recovery curves experimentally measured in well N 124 of the State Farm underground gas storage for a reference layer composed of rock salt. A straight line is allocated to the section starting from 7 h, where A ≈ const, the restoration of temperature depends only on the history of the well. Compared to FIG. 2, it starts from 7 h instead of 2, which is due to the complex design of the underground equipment of the well in comparison with the model; in FIG. 5 - results of mathematical modeling of the temperature distribution in the wellbore after the cessation of injection for a 20 m thick layer, porosity of 10%, a permeability of 0.022 ² microns, absorbent warm gas having a temperature ^of 38.77 C, geothermal temperature before the start of injection, equal to 9.2 ^about C. The layer is distinguished by positive thermal anomaly; in FIG. 6 - the results of mathematical modeling of the temperature distribution in the wellbore after the termination of the warm gas injection (t = _about 30 ^{° C} when the geothermal _n t = 15 ° ^C) for a three-layer model, when the middle layer complex clastic deposition with a = 0,5 ˙ 10 ^{- 6} m ² / s, the upper and lower - rock salt with a = 0.2 ˙ 10 ^-5 m ² / s. FIG. 6 is similar to FIG. 5, therefore, when interpreting thermograms, it is necessary to take into account the influence of the thermophysical properties of the rocks surrounding the well; in FIG. 7 - results of thermal logging of production well N 124 of the State Farm Underground Gas Storage (SPHG), where t is the operating mode thermogram taken during gas injection; t ₀₁ , t ₀₂ , t ₀₃ - temperature curves taken in a stopped well after 15, 24, 33 hours of inactivity from the moment of shutdown; in FIG. 8 - the calculated temperature distribution of the rocks of the well N 124 SPGG (curve 2), restored according to the results of thermal logging according to the described methodology for processing the experimental results and the geothermal distribution (curve 1), taken in it before the start of operation. In the region of elevations of 68, 120, 164, 196, 314, 366 and 400 m, positive temperature anomalies are observed due to leakages of warm gas from the trunk, lateral movement of gas through the reservoirs and the formation of secondary gas accumulations in them; in FIG. 9 - the results of thermometric and acoustic studies of the control well N 2-K SPHG, drilled 50 m from the production well N 124 SPHG, with the aim of monitoring secondary accumulations of gas and its discharge. The thermogram was taken 06.89 g. At the mouth pressure of 0.2 MPa. The slots 57 - 72 and 80 - 105 are observed small positive temperature anomaly amplitude respectively 0.07 and 0.09 ^C. The hydrodynamic noise curve recorded during discharge hole into the atmosphere. Intervals of gas accumulations are distinguished in the noise figure by increased noise levels.

 The proposed method was tested on wells N 124, 120, 116 and 104 of the Sovkhoznaya SPGG. As an example in FIG. 7 - 9 show the results of studies of production well N 124 and a discharge well 2-K located 50 m from it.

The thermograms t, t ₀₁ , t _02, and t ₀₃ (Fig. 7) were recorded in the interval 0–600 m. The upper stratum of rocks from 0 to 365 m is represented by terrigenous deposits: interbedded clays, sand, sandstones with pebble beds. In this thickness, gas leaks from the wellbore, its lateral movement behind the column and the formation of secondary accumulations are possible. Below the section, rocks are composed mainly of rock salt with rare intercalation of anhydrites. As a reference layer, rock intervals composed of salt are used.

+

. (7) В координатах t_o - t, ln τ уравнение (7) является прямой линией
Δt= D+Blnτ. (8) Первое слагаемое - это свободный член, второе слагаемое - угловой коэффициент (см. фиг. 2 - 4).The methodology for processing the experimental results is as follows. Formula (2), taking into account (3), if in the latter we neglect (1) under the logarithm in the denominator (this is true even at 100 hours of well operation), we can rewrite it in the form:
t _about -t =

+

. (7) In the coordinates t _o - t, ln τ, equation (7) is a straight line
Δt = D + Blnτ. (8) The first term is a free term, the second term is an angular coefficient (see Figs. 2-4).

Based on the type of thermograms t ₀₁ , t ₀₂ , t ₀₃ (Fig. 7), the salt layer located at a depth of 500 m was selected as the reference layer. The logging results for this depth slice were constructed in the indicated coordinates, the values of the angular coefficient B = 1.21 and the free term D = 2.88. Their ratio allows you to determine a / γ _c ² = 0,031. Assuming that the geothermal temperature value is known for the reference layer (it can be determined from thermometric studies of closely spaced observation and long-idle wells or in some other way), it is possible to determine τ _o from the value of B. In this well, the geotherm was measured before the start of operation (curve 1, Fig. 8), using its value at a depth of 500 m, equal to 14, 46 ^о С, we obtain τ _o = 706 h.

The found value of τ _{o is} used to determine t _n in the upper and lower deposits.

For all other sections, the a / γ _c ² value is determined in the same way and, using the found τ _o and B, t _{n is} determined. Values B and D are determined graphically or by the least squares method according to the results of thermal logging at each section, for this it is necessary to take at least two thermograms after the well is stopped.

For example, for a cut of 120 m, B = 1.99, D = 426, and / γ _c ² = 8 x 10 ^-4 .

Following deposition of the depth of 500 m from the calculated curve unperturbed geotherms not exceed 1 ^{° C} and lies within the error of the method. In the overlying deposits, the deviations are much more significant and cannot be explained only by the error. Thus, calculations show that in the region of elevations of 68, 120, 164, 196, 314, 366 and 400 m, there are positive temperature anomalies that are caused by gas leaks from the trunk, its lateral movement behind the column and the formation of secondary clusters.

 The existence of secondary accumulations in the indicated intervals is confirmed by the results of logging of a 2-K discharge well drilled at a distance of 50 m from well 124. The logging results are shown in FIG. 9. The intervals of positive thermal anomalies due to secondary accumulations of gas practically coincide in both wells. A secondary deposit is unloaded through well 2-K, which recorded noise logging (Fig. 9).

, где Δτ - временной промежуток между снятиями термограмм;
δ t - погрешность измерения температуры;
t'_τ - скорость изменения температуры на данном срезе. В случае скважины N 124 были выбраны промежутки времени длительностью 9 ч. Соответствующие данные и условия выглядят следующим образом:
δ t = 0,05^оС; t₁' = 1,8 x 10^-5оС/с; t₂' = 1,6 x x 10^-5оC/с; Δτ₁≥ 7,7 ч; Δτ₂≥ 8,8 ч.When choosing time points for taking thermograms in a stopped well, they are guided by the inequality
^{Δτ ≥}

where Δτ is the time interval between taking thermograms;
δ t - temperature measurement error;
t ' _τ is the rate of temperature change at a given section. In the case of well N 124, time intervals of 9 hours were selected. The relevant data and conditions are as follows:
δ t = 0,05 ^{° C;} t ₁ '= 1.8 x 10 ^{-5 °} C / s; t ₂ '= 1.6 xx 10 ^{-5 °} C / s; Δτ ₁ ≥ 7.7 h; Δτ ₂ ≥ 8.8 hours

 The given example shows the feasibility of the proposed technical solution and the positive effect when using it.

Claims (1)

METHOD FOR DETECTING TECHNOGENIC FLUID CONSUMPTIONS IN GEOLOGICAL OBJECTS OPENED BY WELLS by recording the initial geothermal temperature distribution in observation and long-idle wells, taking thermograms in production wells at the operating mode (pumping or selection of the distribution of the fluid, after the formation of the temperature) with depth according to thermometric studies and the identification of temperature anomalies in the range of estimated vertical flows, differing the fact that, in order to expand the functionality, at least two thermograms are taken in a stopped well with simultaneous recording in time, while the temperature is measured in the places of the alleged leaks and accumulations and in the reference layer, consisting of dense impermeable rocks, and the first thermogram is taken through 15 hours after stopping the well, then in a stopped well at one of the slices of the reference layer, the temperature recovery curve is taken over the length of time necessary to determine the rate of change temperature in the borehole of a stopped well, t

and after a time Δ τ, determined by the formula
Δτ ≥

,
where δt is the absolute error of temperature measurement,
a second thermogram is taken, a temperature curve of the rocks surrounding the well is constructed, intervals with an abnormal temperature are identified on it, and leak rates, their lateral movement behind the column and the formation of secondary clusters are judged by their presence.

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