RU2109925C1 - Method for gassing off oil-gas well - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this prevents undesirable oil and gas appearance and improves quality of cementation of wells. According to method, plugging solution is injected into annular space of well. Subsequently, plugging solution is subjected to treatment by acoustic field with frequency characteristic which is close to frequency of natural oscillation of casing string. Aforesaid acoustic field is created by source which is movable in casing string. Source generates single pressure pulses for possible creation of decaying oscillations in solution at initial pressure amplitude of 0.8-2.0 MPa. Treatment of solution is started at lowering of source of oscillations from well head towards bottom hole. In this case, time of reaching bottom hole by oscillation source is taken as equal to time of reducing pressure of plugging solution column down to reservoir pressure. During moving of oscillation source from bottom hole upwards, treatment of plugging solution is effected in two stages. At first stage, source moving speed is such that time of treating solution is near or equal to optimal time of acoustic treatment. This is maintained up to mark above which plugging solution acquires strength of structure which reduces column pressure down to reservoir pressure. At second stage, source moving speed is increased to value within which treating effect leads to complete destruction of plugging solution structure. Interval of source movement at this stage is determined by mark above which reduction of pressure of plugging solution column down to reservoir pressure is sufficient for return of oscillation source at same speed to initial mark for performing first step of next stage. After that, stages are repeated subsequently up to complete treatment within plugging solution location interval beyond string. EFFECT: higher efficiency. 4 dwg

Description

 The invention relates to the mining industry, and, specifically, to oil and gas and is intended for fastening oil and gas wells.

 A known method of fixing oil and gas wells, including pumping cement slurry with additives in the annulus and subsequent processing of it with a thermoacoustic field in the frequency range 10 - 100 kHz with an intensity of (0.2-0.5) • 10 W / m (a.s. 574523 , CL E 21 B 33/14, 1974).

 The disadvantages of the method include the following: the elimination of the "freezing" of cement slurry is not ensured, which means that the pressure of the solution column is maintained at a level above the reservoir; it does not take into account the coordination of the amplitude-frequency characteristics of the acoustic impact signal with the natural frequency of oscillations of the cylindrical shell (casing), which significantly reduces the transmission coefficient of the acoustic signal from the source to the grout; local processing of grouting mortar allows to obtain high quality cementing only in a separate section of the well; the maximum processing time and the optimal time of application of the acoustic effect to the grouting mortar, which allow the most efficient use of the acoustic effect, are not taken into account; the use of an acoustic signal of a harmonic type as an effect, which, in terms of the effectiveness of eliminating the “freezing” of cement slurry during the waiting period for cement hardening (OZC), is inferior to the pulse action.

 The closest in technical essence to the proposed invention is a cementing method (US patent N 4658897, class E 21 B 33/14, 1987), which consists in pumping cement slurry into the annulus followed by its processing by an acoustic field, with a frequency response close to frequency natural vibrations of the casing, created by the source of action moving in the casing.

 However, the application of this method does not maintain the pressure of the column of cement slurry above the reservoir. As in the previous case, the method does not take into account the limiting processing time and the optimal time of application of acoustic impact, which has a harmonic waveform.

 The aim of the present invention is the elimination of oil and gas occurrences and improving the quality of cementing wells by maintaining the pressure of the column of cement slurry above the reservoir pressure and performing processing within close to the optimal time of application of the impact.

 This goal is achieved by a method including pumping cement slurry into the annulus of a well, followed by treatment with an acoustic field, with a frequency response close to the natural frequency of the casing string generated by the source of action moving in the casing string, in which, according to the invention, an acoustic field in the cement slurry is created by application single pressure pulses generated by the source with the possibility of creating damped oscillations in the solution with an initial pressure amplitude (0.8 - 2.0) MPa, and the treatment of the solution begins when the source of the impact is lowered from the wellhead to the bottom, while the time the source reaches the bottomhole is equal to the time to reduce the pressure of the column of cement slurry for the formation, then when the source moves from the bottom, the solution is processed stepwise in two stages. At the first stage, the speed of the source is set at which the time of application of the impact to the solution is close to or equal to the optimal time of acoustic treatment, and it is maintained up to the point above which the solution gains structure strength, reducing the pressure of the column to the formation pressure. At the second stage, the speed of the source is increased to a value within which the effect completely resolves the structure of the solution, while the interval of movement of the source at this stage is determined by a mark above which the decrease in the pressure of the column of the solution to the reservoir in time is sufficient to return to the original speed at the same speed marking and completing the first stage of the next step. After this stage, they are successively repeated until the processing interval for the solution location behind the column is completely processed. An electrohydropulse device is used as a source of acoustic exposure.

 Comparative analysis with the prototype shows that this method is characterized by the presence of new operations, their execution modes, the totality and sequence of operations.

 Thus, this method meets the criteria of novelty of the invention. Comparison of the proposed solution with other technical solutions shows that the operations described in the method are known.

 However, their use in the indicated combination, sequence and modes of their execution, allows the proposed method to increase the backpressure time on the developing formations and create the optimal treatment regime for grouting mortar, which eliminates oil and gas manifestations and improves the quality of well cementing. This allows us to conclude that the technical solution meets the criterion of significant differences.

 Acoustic treatment of cement slurry after it is pumped into the annulus allows direct and comprehensive influence on the factors determining the quality of cementing of wells. The acoustic effect eliminates the process of “hanging” of the cement slurry due to the destruction of its coagulation structure, while the strength of the mortar structure is reduced to a minimum and the pressure of the solution column is restored to a value close to the original. This allows you to maintain the pressure of the solution column at a certain level, which eliminates oil and gas manifestations and increases the strength of the contact zones of the cement stone, because the pressure in the contact zone positively affects these characteristics [1].

 When acoustic treatment of grouting mortar, the strength characteristics and tightness of groutstone and its contact zones increase, sedimentation stability increases and the setting time of grouting mortar is reduced, the negative effects of contracting phenomena are reduced, which ultimately leads to an increase in the quality of well cementing.

 The use of acoustic exposure for processing cement slurry in a well has features that hinder the implementation of this method in the practice of well construction. These include the following.

 This is the influence of a multilayer medium and, first of all, of a casing string on the passage of an acoustic signal from an impact source to a cement slurry. The results of our calculations are shown in the form of graphs in FIG. 1. In FIG. 1a shows the dependence of the oscillation amplitude (δ), and in FIG. 1b is the dependence of the amplitude of the acoustic pressure at the outer surface of the casing (P) on the angular frequency (w) of the disturbing signal. The maximum intensities created by the harmonic signal sources according to [2] are as follows: for piezoceramic emitters they reach 1.5 • 10 W / m, for magnetostrictive ones - 10 W / m, which corresponds to acoustic pressures in water or clay solution, which are used as squeezing fluids during well cementing, respectively, P = 0.22 MPa and P = 0.55. Graphs 1 in FIG. 1 correspond to the acoustic pressure of the disturbing signal P = 0.55 MPa, and the graphs 2-P = 0.2 MPa. From the graphs obtained, it can be seen that even at a frequency of the disturbing signal close to the frequency of the natural oscillations of the casing, i.e. in the resonant mode, the signal amplitude of the generated sources is reduced by 4 times. When the frequency deviates from the resonance by 2 times, the attenuation of the signal amplitude is already more than 20 times.

 Further, this is the limitedness of the acoustic energy generated by the sources and its intensity, due to their weight and size characteristics in relation to the diameter of the casing and the curvature of the wellbore, throughput of the energy transfer channel from the power source at the wellhead to the emitter, and the dependence of the efficiency of the impact source on the well conditions, for example , from the "inhibitory" action of hydrostatic pressure, etc.

 And finally, the limited processing time for grouting mortar, due to the cost of pumping the mortar into the annulus of the well, the need to process the entire interval of the location of the mortar behind the column to create a reliable and durable channel for supplying oil and gas from the reservoir to the wellhead. In this regard, it is necessary to know the maximum time of application of acoustic effects to the grouting mortar from the beginning of cementing.

 This is due to the fact that the application of acoustic influence to the solution gives a positive effect in the initial stages of the formation of the structure of grouting mortar (stone), while for others it has a negative effect. Thus, knowledge of the time limit for application of the action to the solution makes it possible to bring processing time as close to it as possible and thereby achieve the greatest acoustic energy generated by the source for well conditions, which positively affects the quality of the disconnected system. In addition, it is known that there is an optimal time for acoustic treatment of cement slurry, the effectiveness of which is several times higher with respect to processing immediately after mixing the mortar. This time was taken by us as the limiting time for processing the solution. For normal conditions, this time is known. We need to know this time for well conditions, where it depends mainly on temperature, which increases with depth, as well as on sedimentation processes, formation permeability, etc. Given that the proposed method is used in combination with the preparation of the wellbore by wave hydrodynamic mudding, we can only talk about temperature, as a factor determining the named time. We determined this time for well conditions and it is shown in FIG. 2 curve 2, which shows the operation of the electrohydropulse device.

 Due to the lack of sources of influence that could simultaneously create an acoustic field in the solution for some time, it is also necessary to know the timelines of the strength structure of the solution at each point of the solution location behind the column along the depth of the well, at which the column pressure decreases to the reservoir. We have determined such a graph and shown in FIG. 2 of curve 3. The time schedule for reducing the pressure of the solution column to the formation 3 qualitatively coincides with the schedule for the optimal time for acoustic treatment of solution 2, but in time it comes earlier. Both are characterized by an increase in time from the bottom to the wellhead. Graph 4 in FIG. 2 determines the time of reducing the pressure of the solution column to the reservoir after the source of exposure is lowered, graph 5 - after the complete treatment of the solution. The obtained graphs served as the basis for developing a working scheme of the source of exposure, which, taking into account the peculiarities of the process of processing the solution during the BPC period, allows optimal use of acoustic exposure. Graph 1 in FIG. 2 shows a flow chart of the source of action in a well during acoustic treatment of a cement slurry.

 From FIG. 2 it can be seen that the velocity of the source of action during descent, provided that it reaches the bottom by the time the pressure of the column of the solution drops to the reservoir, should be significant and it is about 0.8 m / s. At such a speed, the time of application of the action to the solution is limited, but at the same time, the destruction of the structure of the solution must be ensured in order to eliminate the "hang" of the cement slurry.

 In this regard, we conducted experimental studies to study the destruction of the cement slurry structure by acoustic exposure. In FIG. Figure 2 shows the dependence of the speed of sound (s) on the duration of application of the impact (t). The speed of sound here characterizes the strength of the structure of the solution. Its maximum value corresponds to the strength of the solution structure, at which the pressure of the solution column is 25% lower than its initial value and close to the reservoir. And the minimum value corresponds to the minimum strength of the solution structure, at which the pressure of the solution column is close to its initial value. Graph 1 characterizes the named dependence when a harmonic acoustic signal is applied to the casing with P = 0.22 MPa, and graph 2 - with P = 0.55 MPa. In FIG. Figure 4 shows the dependence of the amplitude of the initial pressure wave of damped oscillations in the solution (P), at which the maximum destruction of the solution structure occurs, on the time of application (t) of a single pulse creating these oscillations. The maximum time of application of the pulse action is equal to the time at which the initial column pressure decreases by 25% and is close to the reservoir. From FIG. 4 it follows that the maximum degree of destruction of the structure of the solution can be achieved instantly when exposed to the column with a single pulse, creating damped oscillations in the cement slurry with an initial pressure amplitude of 0.8 MPa. Moreover, the acoustic energy spent on destruction is 2.5 times less than when exposed to a harmonic acoustic signal. Thus, to eliminate the suspension of cement slurry for deep wells, where the exposure time and the energy value of the emitting device are limited, it is preferable to use pulsed sources. The results obtained confirm the literature on the destruction of various bodies under acoustic exposure. From the analysis of this literature it follows that the rate of increase of the created deformations can have a significant effect on the stresses arising in the bodies. So, at the slew rates, the created strains are significantly lower than the relaxation rates, the bodies have the properties of a liquid, and in the opposite situation, the same body has the properties of a solid (brittle fracture). This is explained by the varying degree of relaxation of elastic stresses at different slew rates of the created strains. In this regard, in order to increase the destruction efficiency, it is recommended to deform bodies with a speed of a greater rate of their relaxation. The strain rate depends on the duration of the pressure rise front and its amplitude. The duration of the pressure front determines the frequency of the impact signal, which should be close to the frequency of the natural oscillations of the casing string; it cannot be changed due to the frequency mismatch. The strain rate in this case can be increased by increasing the pressure amplitude. The pressure amplitude created by existing sources of harmonic-shaped acoustic signals suitable for operation in a well, as already mentioned, is limited to 0.55 MPa. A large pressure amplitude, while limiting the power consumed by the source of exposure, can be achieved in devices with the accumulation of energy in time and its subsequent radiation in a short period, i.e. the creation of powerful single pressure pulses. The upper limit of the initial pressure amplitude is limited to 2.0 MPa. At pressures above this value, the acoustic impact, according to [3], decolmates and destroys the near-stem part of the wellbore.

 The implementation of the method is shown on the example of a well with a depth of 3000 m by a besieged column with a diameter of 146 mm.

 The method is as follows.

 The estimated volume of the grouting solution is pumped into the annulus of the well. The column pressure of the cement slurry, including cement and gel cement, should be 25% higher than the reservoir. The reservoir pressure at a depth of 3000 m is 35.8 MPa. To ensure this condition, the location interval of cement mortar with a density of 1820 kg / m is 2500-30000 m (500 m) and gel cement with a density of 1.55 kg / m 0 - 2500 m (2500 m), and the column pressure at this ratio is 47 , 85 MPa. After receiving the “Stop” moment, the pressure at the wellhead is reduced to atmospheric pressure, the non-return valve is pressurized and, provided it is airtight, the cementing head is turned off. The operation time should not exceed 30 minutes.

 Using a logging hoist, lower the source of impact into the casing. An electrohydropulse device described, for example, in [4] is used as a source of exposure. A feature of such devices over others is the receipt of powerful short-term pressure pulses with a small average power consumption due to the accumulation of energy in the device. Device characteristics: charging voltage 30 kV; energy storage capacity 1.6 μF; discharge circuit inductance 4.5 μH. A device with the specified characteristics ensures complete destruction of the structure of the solution behind the column with a diameter of 146 mm at a speed of 0.8 m / s or less.

 The operation scheme of the source of exposure is shown in FIG. 2 and is presented in graph 1. Processing of the cement slurry begins when the source of the impact is lowered from the wellhead to the bottom. The speed of movement is set equal to 0.8 m / s and it should provide the time for the source to reach the bottom by the time the pressure of the solution column drops to the reservoir (in Fig. 2, graph 3). The characteristics of the source of exposure should at a specified speed ensure complete destruction of the structure of the solution. The time curve for decreasing the solution column after the device is lowered is shifted, and in FIG. 2 is indicated by the number 4 and in the lower part of the well approaches curve 2 of the optimal solution treatment time. When the source moves from the bottom, the solution is processed in steps, in two stages. At the first stage, the minimum movement speed is set, which ensures the exposure time close to the optimal exposure time and is 0.25 m / s. This speed is maintained up to a mark of 2400 m, above which the solution gains structural strength at which the pressure of the solution column becomes close to the reservoir. From this point, the second stage is performed: the speed of the source is increased to a value of 0.8 m / s, which is the limit value at which the complete destruction of the structure of the solution occurs, while the interval at this speed is determined by the mark of 1200 m, above which the decrease in the pressure of the solution column enough time for the reservoir to return the source at the same speed to the initial mark of 2400 m and complete the first stage of the next stage. The first stage of the second step is performed at a speed of 0.3 m / s to a mark of 1200 m, the second stage of this step at a speed of 0.8 m / s to a mark of 50 m to the mouth and back. And finally, the first stage of the last step from the level of 1200 m to the level of 50 m to the wellhead at a speed of 0.2 m / s. 50 m before the wellhead, the source of exposure turns off, rises at the wellhead and prepares for the transport position.

 The acoustic field in the cement slurry is created by a pulsed action, which reduces the cost of acoustic energy and time to eliminate the process of "hanging" of the cement slurry. In this case, the maximum degree of destruction of the solution structure is achieved by pulsed action on the column creating damped oscillations in the solution with an initial pressure amplitude of 0.8 MPa or more, up to 2 MPa.

 As the diameter increases, the natural frequency of the casing string decreases and the amplitude of the pulse applied to the string. To bring the frequency response and pressure pulse amplitude into line with the diameter of the casing string, the energy stored in the source is increased by increasing the storage capacity of the drive, which is made in a modular design.

 Thus, the proposed method allows to increase the time of pre-pressure on the developing strata and to create the optimal mode of processing cement slurry in the well, which leads to the exclusion of oil and gas manifestations and to improve the quality of cementing of wells. Due to this, the loss of hydrocarbon raw materials is reduced, the cost of repair and restoration work is reduced, the service life of the wells is extended.

Claims (2)

 1. A method of attaching an oil and gas well, including pumping cement slurry into the annulus of a well and then treating it with an acoustic field with a frequency response close to the natural frequency of the casing produced by the source of action moving in the casing, characterized in that the acoustic field in the casing the solution is created by applying single pressure pulses generated by the source, with the possibility of creating damped oscillations in the solution with the initial with a pressure amplitude of 0.8 - 2.0 MPa, and the treatment of the solution begins when the source of the impact is lowered from the wellhead to the bottom, while the time the source reaches the bottom is equal to the time to reduce the pressure of the column of grout to the formation, then when the source moves from the bottom, the treatment is carried out stepwise, in two stages, while the first stage sets the speed of the source, at which the exposure time to the solution is close to or equal to the optimal time of acoustic processing and it is maintained up to the mark , above which the solution gains structural strength, which reduces the pressure of the column to the reservoir pressure, and in the second stage, the speed of the source is increased to a value within which the impact completely destroys the structure of the solution, while the interval of movement of the source at this stage is determined by the mark above which the pressure drop a column of solution to the reservoir in time is enough to return the source at the same speed to the initial mark and perform the first stage of the next stage, after this stage after thoroughly repeated until the complete processing of the interval the location of the solution behind the column.  2. The method according to claim 1, characterized in that an electrohydropulse device is used as a source of acoustic exposure.

Images