RU2361079C1 - Method of detecting cross-flows in well - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil and gas industry and can be implemented at detecting cross-flows in well. The essence of the invention is as follows: according to the method pressure in the well is measured with a high sensitive pressure gauge capable to register change of pressure of 0.001 MPa during hydro-interception from surrounding disturbing pressure wells operating for separate reservoirs as communicating, as well as not communicating, or not intended to communicate with the well. Operation of disturbing wells is carried out at periods of disturbance of various durations. Presence or absence of periodical change of pressure in a surveyed well from operation of the disturbing well characterised with amplitude of the first harmonic of pressure change is chosen as criteria of detecting presence or absence of cross-flows in the well.

EFFECT: upgraded accuracy of detecting well communication with watered reservoir.

1 ex

Description

The invention relates to the oil and gas industry and may find application in determining the flow of fluid in a well.

A known method for determining leakage of a casing string of a well equipped with a tubing string, comprising registering a flow rate of a fluid injected into a well with a flow meter that is lowered below the funnel of the tubing string. The registration of the flow rate of the injected fluid is carried out simultaneously at the wellhead with a flowmeter of the same design as that launched into the well, on a pipe segment in the injection line located in the gap between the pump unit and the wellhead. By the mismatch of the injected water costs recorded by the flow meters, the leakage of the production string is judged. As flowmeters use flowmeters of electromagnetic action, and the diameter of the pipe segment is chosen equal to the diameter of the production casing of the well. In this case, electrically conductive fluid is selected as the injected fluid into the well (RF Patent No. 2211327, publ. 2003.08.27).

The method is based on the determination of flow. The method is complex, requires equipment with special devices, is not always accurate enough.

Closest to the invention in technical essence is a method for monitoring the tightness of an injection well, including measuring pressure at the mouth at the inlet to the tubing string and in the annulus. The registration of pressure changes is carried out by comparing the pressures before and after stopping the well by the rate of pressure drop at the wellhead and in the annulus after shutting down a working well and by comparing the pressures before and after starting the well for injection by the rate of pressure increase at the wellhead and in the annulus after starting the well for download. For the criterion for assessing the tightness of the annular space take the estimated value of the flow rate of fluid entering or leaving the annular space of the well (RF Patent No. 2246613, publ. 2005.02.20 - prototype).

The known method does not take into account possible violations of the tightness of the tubing string and their influence on the accuracy of pressure measurement. The method does not allow to determine the reservoir as a source of fluid flow into the well or as a zone of fluid absorption from the well.

The proposed invention solves the problem of increasing the accuracy of determining the communication of a well with a flooded formation.

The problem is solved in that in the method for determining inter-reservoir flows in a well, including measuring pressure in the well, according to the invention, pressure measurement in the well is carried out with a highly sensitive pressure gauge during hydro-listening from surrounding perturbing injection wells operating on separate layers, either communicating or non-communicating or not properly communicated with a well, the work of disturbing wells is carried out at disturbance periods of different durations, and for the criterion for assessing the presence or absence of fluid flows in the well, respectively, the presence or absence of a periodic change in pressure in the investigated well from the operation of the disturbing well, characterized by the amplitude, is selected.

The features of the invention are:

1) measurement of pressure in the well;

2) pressure measurement with a highly sensitive pressure gauge;

3) the same when hydro-listening from surrounding perturbing injection wells operating on separate layers, both communicating and non-communicating or not necessary to communicate with the well;

4) the work of disturbing wells at periods of disturbance of different durations;

5) the criterion for assessing the presence or absence of fluid flows in the well, respectively, the presence or absence of a periodic change in pressure in the investigated well from the operation of the disturbing well, characterized by amplitude.

Sign 1 is common with the prototype, signs 2-5 are the salient features of the invention.

SUMMARY OF THE INVENTION

A lot of work has been devoted to the definition of crossflows in a well, however, well-known technical solutions do not allow us to determine with sufficient reliability which reservoir, i.e. from what source does the fluid enter the well or into which layer does the fluid leave the well. Often, after the installation of a cement bridge, after elimination of annular crossflows in the well, a flow of fluid whose source is unknown is noted, and therefore, the way to eliminate such a violation is not defined. Often, due to the installation of a cement bridge or for some other reason, there is no sump in the well. The distance from the lower perforation holes to the cement bridge is so small that under the perforation interval it is not possible to place in-depth research instruments such as flowmeters, thermometers, pressure gauges, etc. In this case, using known methods for determining flows is impossible. For this case, the proposed method solves the problem of not only establishing the fact of the undesirable flow of fluid into the well, but also determining the source of its flow, i.e. improving the accuracy of determining the message of a well with a flooded reservoir. The problem is solved as follows.

To determine fluid flows, a pressure is measured in the well with a highly sensitive pressure gauge during hydro-listening from surrounding disturbing injection wells operating on separate layers, either communicating or non-communicating or not communicating with the well. In this case, the work of disturbing wells is carried out at periods of disturbance of different durations, and for the criterion for assessing the presence or absence of fluid flows in the well, the presence or absence of a periodic change in pressure in the studied well from the operation of the disturbing well, characterized by amplitude, is selected.

- формула определения амплитуды первой гармоники разложения Фурье изменения давления в исследуемой скважине, где Δp₀ - амплитуда первой гармоники разложения Фурье изменения давления в исследуемой скважине, МПа; a_K, b_K - коэффициенты Фурье.If there is a hydrodynamic connection between the well and the formation in which the disturbance is caused, a response to this disturbance inevitably arises in the well. In the absence of hydrodynamic coupling, such a response does not occur in the well. The proposed method is built on this principle. First, an injection well is selected that obviously has a hydrodynamic connection through the reservoir to the reservoir with the studied well, and which does not have a hydrodynamic connection with other reservoirs opened by the studied well. In the selected injection well, a disturbing effect is carried out by stopping the injection of the working agent and restarting the injection. Periods of disturbance, i.e. the duration of the download stop, change. The most desirable periods are injection stops at 96, 48 and 24 hours. The well under investigation is stopped, a deep highly sensitive pressure gauge, for example, AMTB type, is placed in it, and the change in pressure is recorded. The sensitivity of the pressure gauge is 0.001 MPa. Then, another injection well is selected that does not have a hydrodynamic connection with the previous formation, but has a hydrodynamic connection with the formation, from which liquid can enter the well. In a new injection well, a disturbing effect is carried out and a disturbance response is recorded in the investigated well. If several strata have been uncovered by the well under investigation, then an injection well is discovered for each such stratum that has opened this stratum, a disturbance is made in it, and the response is recorded in the investigated well. It doesn’t matter if this layer communicates directly with the well under investigation or is it insulated, for example, by setting up a cement bridge, cut off by a packer, blocked by an overlap, plugged, etc. If there is a response on an insulated formation, an assumption is made that there is a flow into the well from this formation. The final answer about the presence of overflow is made according to the criterion for assessing the presence or absence of fluid overflows, according to which the amplitude of the recorded pressure signal in the studied well is determined using the Fourier analysis. If the amplitude of the first harmonic signal is lower than the resolution of the pressure gauge, i.e. less than 0.001 MPa, it is concluded that there is no overflow. Otherwise, a conclusion is drawn about the presence of overflows. When determining the use of the following ratio:

- the formula for determining the amplitude of the first harmonic of the Fourier decomposition of the pressure change in the studied well, where Δp ₀ is the amplitude of the first harmonic of the Fourier decomposition of the pressure change in the studied well, MPa; a _K , b _K are the Fourier coefficients.

A simpler way is the graphical method for determining the amplitude and phase shift of the registered signal.

Concrete example

The flow of liquids is determined in an oil well that has uncovered three layers at depths of 1598.7-1600.4, 1601.9-1603.4, 1604.7-1610.4 m. The upper layer is operated by a well with a flow rate of 5 m ³ / day. The two lower layers are worked out, watered and covered by a cement bridge. In the well, there is an increased water cut of the produced oil, which is not characteristic of the working formation. The composition of produced water in the middle and lower reservoir is the same. Due to the cement bridge, the well is deprived of a sump and the placement of deep measuring instruments below the working perforation interval is impossible. As a result, determine the source of fluid flows in the well by traditional methods of flowmetry, thermometry, etc. does not seem possible.

The well is stopped. In the well at a depth of 1598 m, a highly sensitive stand-alone pressure gauge-thermometer-moisture meter АМТВ is placed with the possibility of recording a pressure change of 0.001 MPa. Find 1 injection well at a distance of 400 m, which opened the upper layer and does not have hydrodynamic connection with two other layers. In the selected injection well, a disturbing effect is carried out by stopping the injection of the working agent and resuming the injection for periods of 96, 48 and 24 hours. In the test well, a change in pressure is recorded. Find 2 injection wells at a distance of 1000 m, which revealed the middle layer and does not have hydrodynamic connection with two other layers. In the selected injection well, a disturbing effect is carried out by stopping the injection of the working agent and resuming the injection for periods of 96, 48 and 24 hours. In the test well, a change in pressure is recorded. They find 3 injection wells at a distance of 800 m, which revealed the upper layer and does not have hydrodynamic connection with two other layers. In the selected injection well, a disturbing effect is carried out by stopping the injection of the working agent and resuming the injection for periods of 96, 48 and 24 hours. In the test well, a change in pressure is recorded. Thus, they perform hydro-listening from surrounding perturbing injection wells operating on separate layers, both communicating and non-communicating or not communicating with the well. The results of determining the change in pressure during hydro-listening are given below. For the criterion for assessing the presence or absence of fluid flows in the well, the presence or absence of a periodic change in pressure in the investigated well from the operation of the disturbing well, characterized by amplitude, is selected accordingly.

For the middle reservoir, the amplitude is

For the lower reservoir, the amplitude is

From the results of hydraulic tapping, it follows that the cement bridge in the interval of the middle layer is leaky. From the middle layer there is a flow of fluid into the well. The cement bridge is under repair.

Thus, the proposed method allows you to accurately determine the message of the well with a flooded reservoir.

Application of the proposed method will improve the accuracy of determining fluid flows in the well.

Claims (1)

A method for determining inter-reservoir flows in a well, including measuring pressure in the well, characterized in that the pressure in the well is measured by a highly sensitive pressure gauge with the possibility of recording pressure changes of 0.001 MPa during hydro-listening from surrounding disturbing injection wells operating on separate layers, both communicating and non-communicating or non-communicating with the well, the operation of the disturbing wells is carried out at periods of disturbance of different durations, and for the criterion for assessing the presence or the absence of fluid flows in the well, respectively, the presence or absence of a periodic change in pressure in the investigated well from the operation of the disturbing well is selected, characterized by the amplitude of the first harmonic of the pressure change.