RU2796265C1 - Method for determining zones of development of cracks in multi-stage hydraulic fracturing - Google Patents

Abstract

FIELD: hydraulic fracturing of reservoirs.

SUBSTANCE: invention can be used for determining parameters used in the process of calculating and analysing operations of stimulation of fluid inflow from the reservoir, in particular for determining the fracture closure pressure and fracture pressure during hydraulic fracturing (HF). The method for determining the zones of development of fractures in multi-stage hydraulic fracturing includes the following sequence of actions: installing a pressure sensor at the wellhead and turning on the device for collecting pressure data for recording, commencement of an HF stage with at least two injections. At the end of the injections, from the recorded pressure signal, areas of pressure oscillations that occur after the pumps are turned off are isolated. Next, the resulting signal is pre-processed with a band-pass filter in order to remove noise, after which the wave propagation time in the well from the reflection point to the wellhead pressure sensor is determined from the resulting signal. Next, the wave propagation velocity is determined taking into account the given well geometry, the parameters of the injected fluid (temperature, density, and the distance) between the reflection points of the pressure oscillation wave in the well and the pressure sensor at the wellhead. The required number of cycles is repeated at subsequent HF stages and, as they are performed, the distance of the depth of events between the reflection points of the pressure oscillation wave in the well and the wellhead pressure sensor, taking into account the results obtained at previous stages.

EFFECT: increased efficiency of hydraulic fracturing.

1 cl, 4 dwg

Description

The invention relates to the field of hydraulic fracturing of reservoirs and can be used in determining the parameters used in the process of calculating and analyzing operations in the stimulation of fluid inflow from the reservoir, in particular in determining the fracture closure pressure and fracture pressure during hydraulic fracturing (HF).

The control of well assembly serviceability during non-invasive hydraulic fracturing at the wellhead is relevant, since it allows almost real-time monitoring of the well integrity during operation without the use of technologically sophisticated equipment.

A known method for determining the parameters of hydraulic fracturing (see patent RU No. 2734202, IPC E21B 47/10, E21B 47/06, publ. 13.10.2020), including

- pumping hydraulic fracturing fluid into the reservoir to create a hydraulic fracture, recording pressure and supply;

- stopping the injection of fluid into the reservoir, recording the pressure drop;

- obtaining a data set of pressure changes in the well before, during and after stopping the injection of fluid;

- loading into the software and visualization of pressure change data in the format of graphs of pressure in the well versus time;

- determination of the approximate value of the instantaneous injection stop pressure ISIP;

- display of pressure change data and semi-logarithmic derivative of pressure on the diagnostic Log-Log graph;

- identification of the mode of linear flow of hydraulic fracturing fluid in the fracture and the presence or absence of the mode of secondary influence of the wellbore;

и значения ΔР в 2 раза численно превышают значения полулогарифмической производной;- correction of the diagnostic Log-Log graph by bringing it to a normalized form by finding such an ISIP value at which the ΔР curve and the semi-logarithmic derivative in the section of the linear fluid flow in the fracture are parallel to each other, the tangent of the slope of the tangent to both curves is

and the values of ΔР are 2 times numerically higher than the values of the semilogarithmic derivative;

- determination of the fracture closure time using a normalized Log-Log diagnostic plot, in this case, in the presence of an identified wellbore secondary influence mode, the initial divergence of the semi-logarithmic derivative with a straight line with a tangent of the angle of inclination to the OX axis equal to 1 is selected as the fracture closure time, and in the absence of an identified regime of the secondary influence of the wellbore, the initial divergence of the semi-logarithmic derivative with a straight line with the tangent of the angle of inclination to the OX axis equal to the Larger image (opens in a separate window) is selected as the fracture closure time;

- determination of the fracture closure pressure using the graphs of the hydraulic fracturing fluid leakage function at the fracture closure time obtained in the previous paragraph;

- determination of pressure in the fracture Pnet.

The well-known method described above was developed on the assumption that a downhole pressure sensor is used, which complicates the practical use of the technology.

A method for detecting objects reflecting a hydraulic signal in a well is known, adopted as the closest analogue (see patent RU No. 2709853, IPC G01V 1/44, G01V 1/46, E21B 43/26, E21B 49/00, publ. 23.12.2019 .), in which:

(a) provide a well filled with a fluid that provides the passage of a hydraulic signal;

(b) providing at least one hydraulic signal source in fluid communication with the well for generating a hydraulic signal;

(c) providing at least one pressure sensor for detecting a hydraulic signal and in fluid communication with the well and at least one source of the hydraulic signal;

(d) registering a hydraulic signal with at least one pressure sensor during downhole operations;

(e) forming a pressure cepstrogram and detecting an intense signal on the pressure cepstrogram;

(f) detecting in the well at least one object reflecting the hydraulic signal, based on the peaks of the detected intense signal on the pressure cepstrogram.

The well-known method described above uses a cepstrogram as a key element for analyzing the received signal (echo registration), all other elements, such as placing a pressure sensor in the well line, recording this pressure with some given frequency (for example, 1-200 reports per second, Hz) are generally accepted methods for monitoring well operations. The present invention uses echo extraction methods other than cepstral analysis, and also takes into account the influence of well design on the formation of the reflected signal, which allows you to separate the desired and spurious signal in the analysis of pressure data.

The task of the proposed technical solution and the expected technical result is to increase the efficiency of the hydraulic fracturing process due to the configuration of the fractures obtained in the process of hydraulic fracturing, as well as to expand the operational capabilities of the method in complicated geological and physical conditions.

The technical result is achieved by the fact that the method for determining the zones of development of fractures in hydraulic fracturing of a multi-stage hydraulic fracturing includes the following sequence of actions:

- installation of a pressure sensor at the wellhead and the inclusion of a device for collecting pressure data for recording;

- product of the hydraulic fracturing stage containing at least two injections;

- at the end of pumping, selection from the pressure signal of areas of pressure oscillations that occur after the pumps are turned off;

- carrying out pre-processing of the resulting signal with a band-pass filter in order to remove noise;

- determination from the resulting signal of the wave propagation time in the well from the reflection point to the wellhead pressure sensor;

- determination of the wave propagation velocity, taking into account the given well geometry, the parameters of the injected fluid (temperature, density);

- determination of the distance between the reflection points of the pressure oscillation wave in the well and the wellhead pressure sensor;

- repetition of the required number of cycles at subsequent stages of hydraulic fracturing and, as they are performed, determination of the distance (depth of events) between the reflection points of the pressure oscillation wave in the well and the wellhead pressure sensor, taking into account the results obtained at the previous stages.

The claimed technical solution is illustrated by drawings, where in Fig. 1 shows a schematic diagram of the measurement of reflected waves during hydraulic fracturing, Fig. 2 is a block diagram of signal processing, FIG. 3 - data of recording fluctuations at the wellhead after stopping the hydraulic fracturing pumps during testing (sampling frequency 3 kHz) and the corresponding wavelet transform spectrum, in fig. 4 - results of processing according to the corresponding algorithms.

The implementation of the proposed technical solution is carried out as follows.

A pressure sensor and data collection equipment are installed at the wellhead. At least two injections of the injection fluid are made, after which the hydraulic fracturing pumps are stopped. When the hydraulic fracturing pumps are stopped at the wellhead, the pressure sensor registers a rarefaction wave (water hammer), as well as a signal generated by the reflected waves. The received signals are processed using algorithms (Fig. 2), namely: windowed Fourier transform, Wavelet transform and Cepstral transform, after which the most optimal result in terms of calculated accuracy is taken as the basis from the results obtained, which allows positioning the injection fluid entry point.

Wavelet transforms were used in the course of testing to determine the reflection time (Fig. 3). The first three signals correspond to injections in the first interval of the well (depths 3600 - 3425 m), the remaining three signals in the second interval (depths 3425 - 3325 m). Each three signals correspond to the following hydraulic fracturing operations: fluid replacement, mini-fracturing, main fracturing operation. As a result of processing, fluid entry points into the formation were obtained (Fig. 4), which, with a given uncertainty, fall within the given intervals for creating a hydraulic fracture. In cases of stimulation of another interval, leaks in another interval, packer failure, etc. these events will vary in time and identified and localized by the claimed method.

The basic algorithm for calculating the reflection depth of the events under study consists of the following steps:

(1) The recorded pressure signal up to 3000 reports per second (hertz) is filtered to remove noise from the useful signal. The filter is selected from the conditions of minimal distortion of the useful signal shape along the time axis.

(2) The entire received signal is analyzed for the presence of reflections from events known by the depth position and reflections from the events under investigation.

(3) Sections with reflections are processed using algorithms, namely: windowed Fourier transform, Wavelet transform and Cepstral transform, after which the most optimal result in terms of calculated accuracy is taken as the basis from the results obtained, which allows positioning the injection fluid entry point. At this stage, the times and their uncertainties of the reflection passage from the event to the pressure sensor are calculated.

(4) The results obtained in the previous paragraph (times of passage of the signal reflection) are used to calculate the depth of the event, together with the velocity of propagation (CP) of the reflection wave. SR can be determined in several ways: by reflections from objects of a known depth (for example, transition from a pipe of one diameter to another); according to known statistical data from adjacent wells of the same type, taking into account the temperature regime and the pressures used in the liquid; using the initial physical approximations of the speed; using optimization, statistical and probabilistic algorithms; using direct physical and mathematical modeling of reflection wave propagation. All methods for determining SR in this paragraph can be used simultaneously for graphical and algorithmic comparison of the found solutions with known reference points on the well (for example, the position of packers, the transition of pipe diameters, the position of ports, the depth of perforation and other elements of the well design) and then to determine the most probable depths of reflection of the events under study.

Using the claimed method, it is possible to determine:

- zones of hydraulic fracture development,

- leakage of the shut-off plug and production string,

- the presence of cross-flows through casing packers,

- confirmation of the opening of the hydraulic fracturing port in a given zone,

- determination of the presence of fluid injectivity below the hydraulic fracturing port (“ball through”, destruction of the hydraulic fracturing sleeve),

- confirmation of the injection of hydraulic fracturing in a given interval (assemblies with closed ports) during repeated multi-stage hydraulic fracturing,

- determination of the work of the diverter during repeated hydraulic fracturing on non-closable ports/perforation zones.

The claimed invention also allows monitoring perforation shots (the presence of a shot and its comparative amplitude) by recording pressure data.

In addition, the invention can use a second pressure sensor located on the surface, at a known distance from the main sensor (located at the wellhead) and used to calibrate the acoustic wave propagation velocity in the well as an additional source of information.

Claims (9)

A method for determining the zones of development of cracks in a multi-stage hydraulic fracturing (HF), including the following sequence of actions: - installation of a pressure sensor at the wellhead and the inclusion of a device for collecting pressure data for recording; - product of the hydraulic fracturing stage containing at least two injections; - at the end of pumping, selection from the recorded pressure signal of areas of pressure oscillations that occur after the pumps are turned off; - carrying out pre-processing of the resulting signal with a band-pass filter in order to remove noise; - determination from the resulting signal of the wave propagation time in the well from the reflection point to the wellhead pressure sensor; - determination of the wave propagation velocity, taking into account the given well geometry, the parameters of the injected fluid: temperature, density; - determination of the distance between the reflection points of the pressure oscillation wave in the well and the wellhead pressure sensor; - repetition of the required number of cycles at subsequent stages of hydraulic fracturing and, as they are performed, determining the distance - the depth of events between the reflection points of the pressure oscillation wave in the well and the wellhead pressure sensor, taking into account the results obtained at previous stages.

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