RU2475640C2 - Method of hydrodynamic investigations of oil wells equipped with electric-centrifugal pumps with converter of current frequency - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to methods of hydrodynamic investigations of oil wells equipped with submersible electric-centrifugal pumps and control stations with frequency converters, and it may be used for choice of optimum operating mode of well. Method of hydrodynamic investigations of oil well involves connection of electric-centrifugal pump to production electric network through converter of frequency of current supplied to electric-centrifugal pump. Well flow rate is measured as per oil during operation in mode of rated power frequency. Depression is created by means of increase in electric-centrifugal pump efficiency due to increase in current frequency to the value providing steady mode of well operation under which well flow rate as per fluid is maximum. Well flow rate is measured as per fluid, also water content of its products is measured during operation in mode of rated frequency. When maximum value is reached current frequency is reduced to the value providing steady mode of well operation under which well flow rate as per fluid is minimum. Increase and reduction of current frequency is performed during continuous operation of electric-centrifugal pump with repeated measurement of pressure and temperature at pump suction, well flow rate and water content on wellhead. As per the measurements results curve is built for pressure recovery during transition of well operation mode at which well flow rate as per fluid is maximum to operation mode at which well flow rate as per fluid is minimum. Then hydro- and piezo-conductivity, permeability, supply contour radius, skin factor are determined. Also optimum frequency of current supplied to electric-centrifugal pump, under which reduction of water content and increase in flow rate as per oil relative to analogous values during well operation in mode of rated frequency is provided, is determined.

EFFECT: improving efficiency of determination of optimum mode of removals from formation under which product water content is reduced and flow rate as per oil relative to analogous values during well operation in mode of rated frequency increases.

3 cl, 9 dwg

Description

The invention relates to methods for hydrodynamic studies of oil wells equipped with submersible electric centrifugal pumps (ESP) and control stations with frequency converters, and can be used to select the optimal operating mode of the well.

A known method of exposure to the bottomhole zone of a well during its operation / SU 1262026, IPC ЕВВ 43/00, publ. 1986.10.07 /, which includes connecting a borehole electric centrifugal pump to an industrial power grid through a thyristor current frequency converter and creating depression by increasing the productivity of a borehole electric centrifugal pump by increasing the current frequency.

The disadvantage of this method of operating a well pump is that in the process of conducting research, the well stops, which leads to losses in oil production.

There is also known a method of hydrodynamic research in a well equipped with an electric centrifugal pump with a variable frequency drive, made on a mobile vehicle / RU 2370635, IPC ЕВВ 43/00, Е21В 47/00, publ. 2008.03.20 /, including hydrodynamic studies of wellhead parameters of a well and a fluid in a well by steady-state sampling, determination of a reservoir productivity coefficient at various bottomhole pressures, and ultimate fluid shear stress. For monitoring and automatic registration in digital form of wellhead parameters of the well, a hardware-software complex is used. The reservoir productivity coefficient and the ultimate shear stress are determined at least at any three frequencies of the supply voltage: 40 ± 2, 45 ± 2, 50 ± 2, 55 ± 2 and 60 ± 2 Hz and pressure and temperature are measured on the buffer and dynamic fluid level and pressure in the annulus of the well, as well as the density of wellhead fluid samples and flow rates. The ultimate fluid shear stress is determined by recalculating the measurement results to bottomhole pressures with the construction of a rectangular coordinate system on the plane where the bottomhole pressure values are plotted on the ordinate axis, and the flow rate, an indicator diagram of the flow rate versus bottomhole pressure, are extrapolated to the axis on the abscissa axis ordinate, the intersection point with which shows the value of the bottomhole pressure, above which the movement of formation fluid into the well does not occur.

The disadvantage of this method with respect to the claimed one is that the studies do not include measuring the parameters of the well at maximum and minimum fluid rates, i.e. the studies are not carried out in full, which does not allow to establish the optimal well operation mode, in which there is a decrease in water cut and an increase in oil production. The absence of a thermomanometric system at the pump intake does not allow obtaining reliable data on bottomhole pressures in the well at different modes. In addition, the ongoing studies do not allow to obtain the pressure recovery curve (HPC) due to the absence of a transition from the current frequency at which the flow of fluid from the formation is maximum to the frequency at which the flow of fluid from the formation is minimal.

A known method of dynamic well operation by an electric pump with a variable frequency drive / RU 2322611, IPC ЕВВ 43/00, Е21В 47/00, publ. 2008.04.20 /, based on periodic repetition of cycles, including starting the electric pump at an increasing frequency of the supply voltage, supplying liquid to the electric pump at a given speed, while pumping the liquid out with an electric pump with a valve electric motor, when the electric pump is in stationary mode at predetermined time intervals determined by the duration of transients in the system "reservoir-well", periodically increase the frequency of rotation of the valve motor by a predetermined value, about defined by the sensitivity threshold of the current of the valve motor until the current of the valve motor decreases below its threshold value at a given rotation speed corresponding to a disruption in the supply of the electric pump, by which it is judged that the critical dynamic level of fluid in the well is reached, and the threshold value of the current of the valve motor is determined by bench characteristics taking into account the density coefficient of the actually pumped liquid, after determining the supply failure, the electric pump is transferred to waiting for a reduced speed at which overheating of the valve motor is prevented, for a time sufficient to achieve a dynamic level at which the pump operates without interruption of supply, at the end of which the speed of the electric pump is again increased to a value less than at least a predetermined value than the rotation frequency at which the supply of the electric pump was interrupted, after which the electric pump is put into operation near the critical dynamic level of the fluid in the well, s maximum inflow.

The disadvantage of this method is that the studies are aimed at obtaining the maximum flow of fluid from the reservoir, which for highly watered wells does not always lead to an increase in oil flow, since in some cases an increase in oil flow and a decrease in water cut occurs when the current frequency decreases below the industrial frequency . The current studies do not allow to obtain HPC due to the lack of transition from the maximum current frequency to the minimum.

The closest in technical essence to the claimed invention is a method of influencing the bottomhole zone of a well during its operation / RU 2082879, IPC ЕВВ 43/25, publ. 1997.06.27 /, which includes connecting a borehole electric centrifugal pump to an industrial power grid through a thyristor current frequency converter and creating depression by increasing the productivity of a borehole electric centrifugal pump by increasing the current frequency, while increasing the current frequency to a value that ensures a stable maximum flow rate of the well in liquid, after which they hold a pause, and then reduce the frequency of the current supplying an electric centrifugal pump to an industrial value and switch an electric centrifugal pump powered by an industrial power supply network, while the duration of a depressive effect on a formation is limited by the moment of interruption of the electric centrifugal pump supply.

The disadvantage of this technical solution is that the reduction in the frequency of the supply current is carried out to a nominal value, which does not allow to fully investigate the ESP operating modes and select the optimal mode, since in some cases, with an increase in depression, there is no increase in oil flow from the formation to the well , and when the current frequency decreases below the nominal value, along with a decrease in liquid withdrawals, a decrease in water cut and an increase in oil production relative to similar indicators when operating gruzhnogo motor (SEM) in industrial frequency mode. The transfer of the well at the end of the research to the industrial frequency mode provides only a short-term effect. In addition, during the research process, the well stops, which leads to losses in oil production.

The objective of the invention is to provide a method for conducting hydrodynamic studies in oil wells equipped with an ESP with a frequency converter, which allows to determine the optimal production mode from the reservoir, in which there is a decrease in water cut and an increase in oil production relative to similar indicators when the well operates in nominal frequency mode.

The problem is solved due to the fact that in the method of hydrodynamic studies of an oil well equipped with an electric centrifugal pump with a frequency current converter, including connecting the electric centrifugal pump to an industrial power grid through a frequency converter supplying an electric centrifugal pump, measuring the oil flow rate when operating in nominal industrial frequency mode creating depression by increasing the performance of an electric centrifugal pump by increasing the frequency of the current to a value that ensures a stable mode of operation of the well, at which the maximum liquid flow rate of the well, according to the invention, measures the flow rate of the well in liquid and water cut of its production when operating in the nominal frequency mode, after reaching the maximum value, the current frequency is reduced to a value that ensures a stable mode of operation wells, in which the flow rate of the well is minimal, while increasing and decreasing the current frequency is carried out during continuous operation of the electric centrifugal pump with a constant by measuring pressure and temperature at the pump intake, well flow rate and water cut at the wellhead, a pressure recovery curve is constructed according to the measurement results when the well operating mode is switched, at which the well’s liquid flow rate is maximum, and the mode of operation, where the liquid’s flow rate is minimal, s the subsequent determination of hydro- and piezoconductivity, permeability, radius of the power circuit, skin factor, and also determine the optimal frequency of the current supplying the electric centrifugal pump, at which it is ensured lower s water content and increase oil production rate with respect to similar parameters during operation of the well in the nominal frequency mode.

In addition, continuous measurement of pressure and temperature at the pump intake can be carried out using the on-line thermomanometric system, and continuous measurement of well flow rate and water cut using a mobile metering system.

In addition, based on the results of measurements of the flow rate of the well in terms of liquid and pressure at the pump intake, an indicator chart can be constructed with the subsequent determination of the productivity coefficient and reservoir pressure.

The urgency of the problem lies in the fact that in order to obtain data on the hydrodynamic parameters of the formation in the area of well drainage, such as reservoir pressure, productivity coefficient, hydraulic conductivity, permeability, etc., a long shutdown of the well is necessary to remove a full-scale reservoir pressure method by echometry, or according to indications Thermomanometric system systems, leading ultimately to losses in oil production. The proposed method for researching wells eliminates all of the above negative points. The results ultimately obtained can be used in constructing isobar maps, solving hydrodynamic modeling of reservoir development processes, selecting downhole pumping equipment, and evaluating the effectiveness of geological and technical measures (geological and technical measures).

Currently, many fields are at a late stage of development, which is characterized by high water cuts and low oil production rates. A change in the frequency of the alternating current leads to a change in bottomhole pressures, and consequently, depressions created on the matrix-fracture formation system in the area of well drainage, which, in turn, allows for additional oil production either by connecting productive layers, previously not completely involved in the operation process, either by forcing the withdrawals, or by reducing the percentage of produced water along with a decrease in withdrawals. The proposed method allows you to choose the optimal mode of operation of the well, in which the oil production rate is maximum, the water cut is minimal.

The implementation of the method of hydrodynamic research of wells is illustrated in the following figures: figure 1 presents a diagram of the operation of well "A" during the period of hydrodynamic research (GDI); figure 2 is a diagram of the operation of the well "A" during the period of well testing and in the period preceding it; figure 3 - KVD wells "A"; figure 4 is an indicator diagram of the well "A"; figure 5 is a diagram of the operation of the well "B" during the period of well testing; figure 6 is a graph of the distribution of the water cut of the production of the well when conducting well testing; Fig.7 is a graph of the well "B" in different modes; on Fig - KVD wells "B"; figure 9 is an indicator diagram of the well "B".

The method is as follows.

When conducting research using a control station with a frequency converter, the ESP works in the following order:

- "nominal" mode;

- step-by-step transition to the mode of maximum possible selection of formation fluid;

- mode of the smallest possible fluid withdrawal;

- the optimal mode in which there is a maximum selection of oil with minimal water cut.

ESPs are connected to the industrial power grid through the frequency converter of the supply ESP current, which is located in the ESP control station at the wellhead. When the ESP operates at the nominal current frequency, a meter is connected to the well, for example, a mobile meter (UZM.T) manufactured by Sibnefteavtomatika OJSC [1] and the production rate and water cut of the well are measured. A stepped increase in the current frequency of the ESP is transferred to the maximum possible selection (flow rate) mode. Upon reaching the established mode of operation of the well (the well’s liquid flow rate and pressure at the pump intake are stable), determined on the basis of the measurements of ultrasonic testing and thermomanometric system (TMS), for example, TMS SKAD developed by RUE Belorusneft Production Association [2 ], The ESP is transferred to the next mode of operation. An increase and decrease in the frequency of the current is carried out during continuous operation of the electric centrifugal pump with constant measurement of pressure and temperature at the pump intake using the TMS "SKAD", well flow rate and water cut at the wellhead using USM.T.

At the end of the research, the well is transferred to the optimal operating mode, established as a result of research using a frequency converter, in which there is a decrease in water cut and an increase in oil production.

By generally accepted methods, the results are processed. The obtained pressure recovery curve during the transition of the well operation mode from “maximum” to “minimum” is processed using the appropriate methods to obtain data on hydro- and piezoconductivity, permeability, radius of the power circuit, and skin factor. Based on the recalculated bottomhole pressures and the flow rate of the well in liquid at different filtration modes, an indicator chart is built with the subsequent determination of the productivity coefficient and reservoir pressure. Taking into account the oil production rate and water cut, a well operation diagram is constructed in order to determine the optimal operating mode of the “formation-well” system in a pore-fractured reservoir.

All field studies are carried out with the meter connected to the well by a metering mobile stepwise switching the frequency of the supply voltage and removing information on electronic media. All studies are carried out without interruption of the operation of the electric centrifugal pump, which avoids losses in oil production.

Consider the implementation of the method on the example of hydrodynamic studies of wells "A" and "B".

Reduced water cut and increased oil production rate in well “A” were obtained by connecting interlayers that were not previously fully involved in the production process. Figure 1 presents a diagram of the operation of the well "A" during the period of the GDI.

An increase in the frequency of alternating current from nominal (50 Hz) to 53 Hz led to an increase in oil production by 155% and a decrease in water cut by 19.5% relative to similar indicators when operating in the nominal current frequency mode. The effect obtained was preserved with a subsequent decrease in the current frequency to 48 Hz. When working in this mode, the increase in oil production was 56%, the decrease in water cut was 10.6% relative to the nominal performance of the well.

Based on the analysis of the studies conducted on well “A”, the optimal operating mode was established - the selection mode at a frequency of 53 Hz, at which the water cut of the well’s production is minimal, and the oil production rate is maximum.

The decrease in water cut and the increase in oil production rate is associated with a change in the filtration flows and the inclusion of interlayers that were previously not fully involved in the operation process. As you know, in the vast majority of cases, a change in filtration flows and groundwater flow paths leads to a significant change in the density of associated waters. The latter may depend on the “flushing” of the new filtration channels, the number of secondary salt fillings located on the filtration paths of the injected water, and also on the amount of produced formation water. In any case, a change in the density of the associated water indicates a change in filtration flows and indicates a rather high quality of the work aimed at this. So, during the pilot field studies using a frequency converter on well "A", the average density of the associated water decreased from 1.146 to 1.139 g / cm ³ (Fig. 2).

The conducted studies allowed us to obtain the pressure recovery curve of well “A” during the transition from 53 to 48 Hz (the transition of the well operation mode from “maximum” to “minimum”). The well schedule during the transition from the maximum selection mode to the minimum selection mode is presented in Fig.3. As a result of the HPC processing, information was obtained on the permeability coefficient, hydraulic conductivity, piezoconductivity, power radius, and skin factor. Taking into account the obtained data on current reservoir pressures and productivity coefficients, the optimal size of the pump and the depth of its descent were calculated.

For this well, based on the recalculated bottomhole pressures and fluid flow rate in various selection modes, an indicator chart was constructed, shown in Fig. 4, and the formation pressure and productivity coefficient were determined from the results of processing it.

Reduced water cut and increased oil production rate for well B were obtained by reducing the volume of withdrawals when operating in a mode with a current frequency below the nominal. Figure 5 presents a diagram of the operation of the well "B" during the period of well testing.

An increase in the current frequency from the nominal to 55 Hz led to an increase in oil production by 71% and a decrease in water cut by 6.39% relative to similar indicators when operating the SEM at the nominal frequency. After 52.5 hours, the well was switched to a 60 Hz production mode. During the operation in this mode, the oil flow rate increased by 164.9%, the water cut decreased by 4.29% compared to the nominal indicators and amounted to 82.06%. Reducing the current frequency to 40 Hz led to an increase in oil production by 62.5% and a decrease in water cut by 14.32% relative to similar indicators when operating at the nominal frequency. After 43 hours, the water cut was 72.03%. As part of the experimental work, the well was switched to an operating mode of 45 Hz, which led to a decrease in oil production by 31% and an increase in water cut to 83.56%. Further, the well was re-switched to 60 Hz mode. According to UZM.T, the oil production rate was 42.6% relative to the nominal indicator, the water cut was 88.87%. When switching to this selection mode, the water cut values ranged from 57% to 100%. The distribution graph of the water cut of the production of the well during the well test is shown in Fig.6.

Thus, a short-term (within the experiment) change in the frequency of the alternating current led to a change in flow rates and bottomhole pressures, and therefore, depressions created on the matrix-fracture formation system in the area of well drainage, which, in turn, allowed to reduce water cut and get additional oil production. When conducting field studies, an increase in withdrawals (60 Hz) led to an increase in the depression funnel and, as a result, pulling up of water pumped into a neighboring injection well. A 26% decrease in withdrawals (operating mode at 40 Hz) led to a decrease in the depression funnel and a decrease in water cut by 14.32% with an increase in oil production by 62.5%.

Based on the analysis of the studies conducted on well B, the optimal well operation mode was established - the selection mode at a frequency of 40 Hz, at which the maximum water cut was reduced (14.32%), the oil production rate increased by 62.5% (Fig. 7).

The studies conducted allowed us to obtain the pressure recovery curve of well “B” during the transition from 60 to 40 Hz (the transition of the well operation mode from “maximum” to “minimum”). The well schedule during the transition from the maximum selection mode to the minimum selection mode is shown in Fig. 8. As a result of the HPC processing, information was obtained on the permeability coefficient, hydraulic conductivity, piezoconductivity, power radius, and skin factor. Taking into account the obtained data on current reservoir pressures and productivity coefficients, the optimal size of the pump and the depth of its descent were calculated.

For this well, the interpretation of the obtained data was carried out according to generally accepted methods. Based on the recalculated bottomhole pressures and fluid flow rate in different selection modes, an indicator diagram was constructed, shown in Fig. 9, and the formation pressure and well productivity coefficient were determined from the processing results.

Thus, the use of the proposed method for conducting hydrodynamic studies of oil wells equipped with an ESP with a frequency converter, allows you to obtain a pressure recovery curve, as well as determine the optimal recovery mode from the reservoir, in which there is a decrease in water cut and an increase in oil production relative to similar indicators during well operation in nominal frequency mode.

Information sources

1. www.ingavtomatika.ru/upload/iblock/131/

2. www.irz.ru/files/9_3.pdf

Claims (3)

1. The method of hydrodynamic research of an oil well equipped with an electric centrifugal pump with a frequency current converter, including connecting the electric centrifugal pump to an industrial power supply via a frequency converter supplying an electric centrifugal pump, measuring the oil flow rate during operation in nominal industrial frequency mode, creating depression by increasing the efficiency of the electric centrifugal pump pump by increasing the frequency of the current to a value that provides a stable mode p bots of the well, in which the maximum flow rate of the well in liquid, characterized in that the flow rate of the well in liquid and water cut of its products is measured while operating in the nominal frequency mode, after reaching the maximum value, the current frequency is reduced to a value that ensures a stable mode of operation of the well, at which the flow rate fluid wells are minimal, while increasing and decreasing the current frequency is carried out during continuous operation of the electric centrifugal pump with constant measurement of pressure and temperature at the pump inlet, d well bit and water cut at the wellhead, according to the measurement results, a pressure recovery curve is built upon switching the well operating mode, at which the well’s liquid flow rate is maximum, to the operation mode, where the liquid’s flow rate is minimal, with subsequent determination of hydraulic and piezoconductivity, permeability , the radius of the power circuit, the skin factor, and also determine the optimal frequency of the current supplying the electric centrifugal pump, at which the reduction in water cut and the increase in oil production rate flax similar parameters during operation of the well in the nominal frequency mode. 2. The method according to claim 1, characterized in that the continuous measurement of pressure and temperature at the pump inlet is carried out using the on-line thermomanometric system, and the continuous measurement of well flow rate and water cut is performed using a mobile metering unit. 3. The method according to any one of claims 1 and 2, characterized in that according to the results of measurements of the flow rate of the well in terms of liquid and pressure at the pump intake, an indicator diagram is built with the subsequent determination of the productivity coefficient and reservoir pressure.

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