Method for active monitoring and optimization of hydraulic fracturing in real time

Abstract

FIELD: hydraulic fracturing.SUBSTANCE: invention relates to the field of hydraulic fracturing (HF), in particular to a method for HF correction in real time. The method for correcting hydraulic fracturing (HF) in real time is characterized by the fact that full-wave modelling is first performed based on a geological and geophysical model of the site with the calculation of reference difference wave fields for normal and undesirable scenarios of fracture development, while the modelling is performed using an elastic physical model, according to which the zone of increased stress is associated with the fracture and is commensurate with the length of the seismic wave, and the increase in stress corresponds to an increase in the propagation velocity of elastic waves. The field of reflected waves on the surface is linked to the borehole using vertical seismic profiling (VSP) data, and multi-level borehole seismic equipment is used to record the wave field at internal points of the environment, while on the surface, a profile of seismic receivers and a source of elastic vibrations are used, while the borehole and surface equipment are made with similar amplitude-frequency characteristics, and the recording work is carried out simultaneously. A background measurement of the wave field is carried out before the start of hydraulic fracturing, with registration by both borehole and surface receivers and with field referencing according to VSP data. During the hydraulic fracturing process, the current wave field of reflected waves is continuously recorded using the same observation system. The difference wave field between the current measurement and the background measurement is calculated in real time. A continuous comparison of the obtained difference field with the reference difference fields calculated at the full-wave modelling stage is carried out. The dynamics of changes in the stress state of the environment and record deviations from the given crack development scenario are evaluated. If deviations are detected, immediate correction of the hydraulic fracturing process is carried out by temporarily suspending the operation, introducing insulating material, or changing the process parameters.EFFECT: increasing the accuracy of monitoring the stress state of the environment, ensuring the possibility of early detection of deviations from the specified crack development scenario, increasing the efficiency and safety of hydraulic fracturing, ensuring reliable support of multi-stage hydraulic fracturing in horizontal wells with the possibility of adapting the monitoring system to each stage.6 cl, 1 dwg

Description

[0001] Technical field

[0002] The invention relates to the field of hydraulic fracturing (HF), in particular to a method for correcting hydraulic fracturing (HF) in real time.

[0003] Technology Level

[0004] Various methods for monitoring hydraulic fracturing (HF) are known, based on recording process parameters (pressure, flow rate, proppant concentration) and microseismic monitoring. In particular, a method for borehole seismic exploration for monitoring HF is known from the prior art, according to patent RU 2490669 C1 (published August 20, 2013). This method includes recording seismic vibrations before and after hydraulic fracturing at various azimuthal directions, and determining the fracture zone configuration based on azimuthal changes in kinematic and dynamic parameters.

[0005] The disadvantage of this method is the lack of the possibility of prompt intervention in the hydraulic fracturing process, since the analysis is carried out post factum.

[0006] Microseismic monitoring methods are known that make it possible to determine the location and orientation of cracks based on the recording of acoustic emissions that occur during the development of cracks.

[0007] However, these methods have limited accuracy in determining the stress state of the medium and do not allow for prompt correction of the process in real time based on comparison with model data obtained using the full-wave modeling method.

[0008] The closest analogue (prototype) is the method disclosed in patent application US 2014 / 0278488 A1, according to which the stress state of the environment is monitored using seismic signals.

[0009] However, the prototype does not provide:

[0010] - use of identical recording systems both downhole (to obtain data at internal points in the environment) and at the surface (to record the field of reflected waves). Moreover, work to link background measurements to the well is carried out during the preparatory stage before hydraulic fracturing;

[0011] - preliminary full-wave modeling for calculating reference difference wave fields taking into account the elastic model of fracturing, according to which the zone of increased stress is associated with the crack and is commensurate with the length of the seismic wave;

[0012] - shift of the observation system (source and receiver profile) when moving to the next stage of multi-stage hydraulic fracturing to ensure the passage of reflected waves through the zone of the current stage;

[0013] - continuous comparison of difference fields with model data and immediate process correction.

[0014] Disclosure of the essence of the invention

[0015] The objective of the proposed invention is to create an effective method for correcting hydraulic fracturing (HF) in real time, ensuring prompt prediction and prevention of undesirable crack development scenarios, including when carrying out multi-stage HF (MS HF) in horizontal wells.

[0016] The technical results of the invention are:

[0017] - increasing the accuracy of monitoring the stress state of the environment through the combined use of borehole and surface seismic measurements performed with the same type of equipment;

[0018] - ensuring the possibility of early detection of deviations from the specified fracture development scenario, including cases of drainage of the layers surrounding the target horizon;

[0019] - increasing the efficiency and safety of hydraulic fracturing due to immediate process correction based on continuous comparison with model difference fields;

[0020] - ensuring reliable monitoring of multi-stage hydraulic fracturing in horizontal wells with the ability to adapt the monitoring system to each stage.

[0021] The stated technical results are achieved by a method of correcting hydraulic fracturing (HF) in real time, characterized by the fact that:

[0022] - full-wave modeling is first performed based on a geological and geophysical model of the site with the calculation of reference difference wave fields for normal and undesirable crack development scenarios, while the modeling is performed using an elastic physical model, according to which the zone of increased stress is associated with the crack and is commensurate with the length of the seismic wave, and the increase in stress corresponds to an increase in the propagation velocity of elastic waves;

[0023] - the field of reflected waves on the surface is linked to the borehole using vertical seismic profiling (VSP) data, with multi-level borehole seismic equipment used to record the wave field at internal points of the environment, and a profile of seismic receivers and a source of elastic vibrations on the surface, with the borehole and surface equipment being made with similar amplitude-frequency characteristics, and the recording work being carried out simultaneously;

[0024] - perform background measurements of the wave field before the start of hydraulic fracturing with registration by both borehole and surface receivers and with field referencing according to VSP data;

[0025] - during the hydraulic fracturing process, the current wave field of reflected waves is continuously recorded using the same observation system;

[0026] - calculate in real time the difference wave field between the current measurement and the background measurement;

[0027] - perform a continuous comparison of the obtained difference field with the reference difference fields calculated at the full-wave modeling stage;

[0028] - assess the dynamics of changes in the stress state of the environment and record deviations from the specified crack development scenario;

[0029] - if deviations are detected, immediate correction of the hydraulic fracturing process is carried out by temporarily suspending the operation, introducing insulating material or changing the process parameters.

[0030] Brief description of drawings

[0031] Fig. 1 shows a block diagram illustrating the sequence of operations of the proposed method for correcting hydraulic fracturing (HF) in real time.

[0032] In Fig. 1 the following are indicated:

[0033] 101 Block "Background measurement (before GRP)"

[0034] 102 Block "Current measurement (during the GRP process)"

[0035] 103 Block "Calculation of the differential wave field"

[0036] 104 Block "Full-wave modeling (reference difference fields)"

[0037] 105 Block "Comparison of the difference field with the model fields"

[0038] 106 Block "Deviation detected?"

[0039] 107 Process Correction Block

[0040] 108 Temporary Suspension Block

[0041] 109 Block "Introduction of insulating material"

[0042] 110 Block "Changing process parameters"

[0043] 111 Block "Continuation of GRP".

[0044] Implementation of the invention

[0045] The method is implemented as follows.

[0046] Step 1. Preparation and full-wave modeling

[0047] Based on the geological and geophysical model of the site (including well logging data, velocity model, lithology, and anisotropy parameters), using the full-wave modeling method, reference difference wave fields are calculated for various scenarios of changes in the stress state:

[0048] - standard scenarios - crack development within the target interval;

[0049] - undesirable scenarios - penetration of a crack into an overlying or underlying horizon, formation of excessive fracturing, drainage of surrounding layers.

[0050] The modeling is carried out taking into account the elastic model of crack formation established as a result of pilot industrial work: the zone of increased stress is associated with the crack and is commensurate with the length of the seismic wave, the increase in stress corresponds to the increase in the velocity of elastic waves.

[0051] Step 2. Placement of the surveillance system

[0052] A multi-level borehole seismic instrument (e.g., VSP-Monitoring 50 or similar) is lowered into a well located near the fracture zone (this could be any well close to this zone) with 7 to 11 or more modules spaced evenly. The following are placed on the surface near the projection of the fracture zone:

[0053] • source of elastic vibrations (explosive, pneumatic or vibration, providing high signal repeatability);

[0054] • profile of surface seismic sensors of the same type as borehole ones (identical seismic receivers, same amplitude and frequency characteristics).

[0055] This technical solution ensures consistency of data obtained at internal points of the environment and on the surface, minimizes and even completely eliminates digital processing of seismic data, which is critical for fast and reliable comparison of the analysis of difference wave fields.

[0056] Step 3. Background metering

[0057] Before hydraulic fracturing, background wavefield recording is performed: signals from reflected waves passing through the suspected fracture zone are recorded. The obtained data is stored in the monitoring system database.

[0058] Stage 4. Carrying out hydraulic fracturing with continuous monitoring

[0059] While pumping the working fluid, the current wave field is continuously recorded using the same monitoring system. At each time interval (e.g., every 5-10 seconds), the difference wave field between the current measurement and the background measurement is calculated.

[0060] Step 5. Comparison with model data

[0061] The calculated difference wave field is compared with the library of reference difference wave fields obtained in step 1. The comparison is performed using correlation analysis methods, spectral matching, or machine learning algorithms.

[0062] Step 6. Identifying Deviations

[0063] If the differential field matches one of the standard scenarios, the hydraulic fracturing process continues unchanged. If the differential field matches an undesirable scenario, the system automatically generates a deviation detection signal.

[0064] Step 7. Process Correction

[0065] Depending on the type of undesirable scenario identified, correction is carried out:

[0066] - at the initial signs of undesirable crack development - temporary suspension of pumping for 2-5 minutes to stabilize the stress state;

[0067] - when crack penetration into the adjacent horizon is detected - introduction of an insulating material (gel composition, cross-linked polymer system or filler particles);

[0068] - when excessive cracks are formed or crack parameters deviate from the specified ones - change the process parameters (reduce the injection rate, change the viscosity of the working fluid, adjust the proppant concentration).

[0069] Step 8. Resumption and Control

[0070] After correction and confirmation of the deviation's elimination (based on continuous comparison of difference fields), the hydraulic fracturing process is resumed in accordance with the specified scenario. Monitoring continues until the operation is completed.

[0071] Stage 9. Features of multi-stage hydraulic fracturing (MSHF)

[0072] When performing multistage hydraulic fracturing in a horizontal well, after each stage, the observation system is shifted: the seismic source and surface seismic receiver profile are positioned directly above the next hydraulic fracturing zone so that the reflected waves pass through the zone of the current stage. For each stage, steps 3-8 are repeated, with the measurement taken after the previous stage being used as a background measurement, allowing for the cumulative changes in the stress state of the medium to be taken into account.

[0073] The proposed method will allow for the highly accurate identification of undesirable crack development scenarios at the early stages of their formation and will ensure timely correction of the hydraulic fracturing process.

[0074] The prospects of using the claimed method have been proven during hydraulic fracturing in a number of wells of LUKOIL JSC (Western Siberia, Caspian Sea), where in a number of wells, zones of increasing longitudinal wave velocity in the directions of hydraulic fracturing crack development were identified based on the change in the differential hodograph.

[0075] Achievement of technical results is ensured by:

[0076] - the use of the same type of equipment for recording both at internal points of the environment (borehole probes) and on the surface, which ensures data consistency and increases the reliability of interpretation;

[0077] - application of full-wave modeling taking into account the established elastic model of crack formation, which allows for reliable prediction of changes in the wave field under various scenarios;

[0078] - displacement of the observation system over each zone of the MS GRP, which ensures the optimal trajectory of reflected waves through the area under study;

[0079] - continuous comparison of difference fields with model data in real time, which allows for early detection of deviations and prompt correction.

Claims

1. A method for correcting hydraulic fracturing (HF) in real time, characterized by the fact that: • full-wave modeling is first performed based on a geological and geophysical model of the site with the calculation of reference difference wave fields for normal and undesirable crack development scenarios, while the modeling is performed using an elastic physical model, according to which the zone of increased stress is associated with the crack and is commensurate with the length of the seismic wave, and the increase in stress corresponds to an increase in the propagation speed of elastic waves; • the field of reflected waves on the surface is linked to the well using vertical seismic profiling (VSP) data, and multi-level borehole seismic equipment is used to record the wave field at internal points of the environment, and on the surface - a profile of seismic receivers and a source of elastic vibrations, while the borehole and surface equipment are made with similar amplitude-frequency characteristics, and the recording work is carried out simultaneously; • perform background measurements of the wave field before the start of hydraulic fracturing with registration by both borehole and surface receivers and with field referencing according to VSP data; • during the hydraulic fracturing process, the current wave field of reflected waves is continuously recorded using the same observation system; • calculate in real time the difference wave field between the current measurement and the background measurement; • carry out a continuous comparison of the obtained difference field with the reference difference fields calculated at the stage of full-wave modeling; • assess the dynamics of changes in the stress state of the environment and record deviations from the given crack development scenario; • if deviations are detected, immediate correction of the hydraulic fracturing process is carried out by temporarily suspending the operation, introducing insulating material or changing the process parameters.

2. The method according to paragraph 1, characterized in that it is also used to accompany multi-stage sequential hydraulic fracturing (MS HF) in horizontal wells, wherein after the completion of each stage, the source of seismic waves and the profile of surface seismic receivers are shifted in such a way that the reflected waves during the next stage pass through the zone of the current stage, and the operations are repeated for each subsequent stage.

3. The method according to paragraph 1, characterized in that gel compositions, cross-linked polymer systems or filler particles are used as the insulating material.

4. The method according to paragraph 1, characterized in that the change in process parameters includes a decrease in the rate of injection of the working fluid, a change in the viscosity of the working fluid, or an adjustment in the concentration of proppant.

5. The method according to paragraph 1, characterized in that the comparison of the difference field with the reference fields is performed using correlation analysis, spectral comparison, or machine learning algorithms.

6. The method according to paragraph 2, characterized in that the background measurement for each subsequent stage of the MS GRP is performed after the completion of the previous stage, which makes it possible to take into account the accumulated changes in the stress state of the medium.

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