CN106908837A - A kind of fracturing fracture form and fracture height determine method - Google Patents

Abstract

The invention discloses a method for determining the shape and height of a fracturing fracture, which is specifically as follows: using acoustic logging to obtain unipolar and dipole waveform data before and after fracturing in the depth interval and performing depth correction; then using the waveform coherent superposition method to calculate the depth The longitudinal wave velocity before and after fracturing and the shear wave velocity in different azimuths; according to the curve formed by the shear wave velocity in different azimuths before and after fracturing, calculate the orthogonal dipole anisotropy value before and after fracturing; Calculate the difference between the average elastic wave velocity after fracturing and before the shear wave velocity or the shear wave velocity in different azimuths, and calculate the difference between the orthogonal dipole anisotropy after fracturing and before the fracturing, and then according to the difference between the average elastic wave velocity and Orthogonal dipole anisotropy difference to determine the shape of the fracturing fracture, and at the same time determine the height of the fracturing fracture at the depth position according to the difference of the average elastic wave velocity, and then determine the height of the fracturing fracture in the depth range. It can quickly and effectively identify the shape and height of fractured fractures.

Description

A Method for Determining Fracture Shape and Fracture Height

technical field

The invention relates to the technical field of acoustic well logging, in particular to a method for determining the shape and height of a fracturing fracture.

Background technique

As global energy demand continues to rise, unconventional oil and gas resources are expected to become the driving force for future energy and economic development in the world. The main characteristics of the lithological formations where unconventional oil and gas resources are located are high density, heterogeneity and strong anisotropy. It is difficult to form industrial oil and gas if only relying on its own production capacity, so it is necessary to perform fracturing, acidizing, etc. Only by reforming and creating a fracture network system for oil and gas migration can economic exploitation be realized. Among them, hydraulic fracturing is the main production stimulation method for unconventional oil and gas production.

At present, the commonly used logging methods for evaluating the height of wellbore fractures in tight reservoirs mainly include well temperature logging, isotope logging, boron injection neutron logging, compensated neutron logging, and dipole acoustic logging. Among them, well temperature logging has low accuracy and is greatly influenced by human factors, so it is generally only used as an auxiliary means. The operating procedures and evaluation principles of isotope logging and boron injection neutron logging are basically the same, but both have certain radioactive pollution, and are rarely used at present. Non-radioactive tracer ceramsite can be used in compensated neutron logging, but due to the influence of fracturing technology such as screenout, the type and calibration of instruments before and after fracturing, the measurement results have certain uncertainties. Dipole acoustic logging mainly evaluates the fracture height by comparing the anisotropy difference around the wellbore before and after fracturing. It is currently the most commonly used logging method for evaluating fracture height. Moreover, the existing acoustic logging technology takes a long time to evaluate the fracture height, and cannot accurately evaluate the fracture shape.

Contents of the invention

In view of this, it is necessary to provide a method that can quickly and effectively identify the shape and height of fractured fractures.

A method for determining the shape and height of a fracturing fracture, comprising the following steps:

Step 1: Perform acoustic logging in the depth range to obtain unipolar and dipole waveform data before and after fracturing;

Step 2: performing depth correction on the obtained data in the depth interval;

Step 3: Obtain the data of a depth position in the depth interval;

Step 4: Using waveform coherent superposition method to analyze the data at one depth position, and calculate the longitudinal wave velocity before and after fracturing and the shear wave velocity in different azimuths;

Step 5: Calculate the orthogonal dipole anisotropy value before and after fracturing according to the curve formed by the shear wave velocity in different azimuths before and after fracturing at the one depth position;

Step 6: Calculate the average elastic wave velocity before and after fracturing according to the longitudinal wave velocity before and after fracturing in step 4 or the shear wave velocity in different azimuths, and calculate the difference between the average elastic wave velocity after fracturing and before fracturing; Orthogonal dipole anisotropy difference between before and after the fracture, according to the average elastic wave velocity difference and the orthogonal dipole anisotropy difference, determine the fracturing fracture shape at the depth position; when the average elastic wave velocity When the difference is greater than zero, the sampling interval of the acoustic logging instrument is recorded as the height of the fracturing fracture at the one depth position;

Step 7: Obtain the data of the next depth position in the depth interval, repeat steps 4 to 6; until all depth positions in the depth interval are traversed; enter step 8;

Step 8: Counting the number of depth positions where there are fracture heights, the fracture heights in the depth range can be obtained.

A method for determining the shape and height of a fracturing fracture according to the present invention determines the shape of the fracturing fracture according to the difference in average elastic wave velocity and the difference in orthogonal dipole anisotropy between the post-fracture and before fracturing at each depth position, At the same time, the height of the fracturing fracture at the depth position is determined according to the difference of the average elastic wave velocity, and then the height of the fracturing fracture at the depth interval is determined. The whole method is simple and can quickly and effectively identify the shape and height of the fracturing fracture.

Description of drawings

Fig. 1 is a flow chart of a method for determining the shape of a fracturing fracture and the height of a fracture in the present invention;

Figure 2 is a diagram of the experimental results.

detailed description

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the invention.

The flow chart of a method for determining the shape of a fracturing fracture and the height of a fracture provided by the present invention is shown in Figure 1, and the specific process is as follows:

Step 1: Perform acoustic logging in the depth interval to obtain unipolar and dipole waveform data before and after fracturing.

In the present invention, an array acoustic logging tool can be used for acoustic logging.

Step 2: Depth correction is performed on the obtained data in the depth interval.

Step 3: Obtain data of a depth position in the depth interval.

Step 4: Analyzing the data at the one depth position by using the waveform coherent superposition method, and calculating the compressional wave velocity before and after fracturing and the shear wave velocity in different azimuths.

Specifically, the waveform coherent superposition method is as follows:

Among them, Corr(v,T) represents a two-dimensional correlation function; X _m (t) is the mth receiving transducer in the receiving transducer array of N acoustic logging tools, and d is the receiving transducer of the acoustic logging tool T is the position of the time window T _w , and v is a certain speed value in the speed interval.

Using formula (1) to calculate the v value when Corr(v, T) takes the maximum value, the compressional wave velocity before and after fracturing and the shear wave velocity in one direction can be calculated. The shear wave velocity in different azimuths can be calculated by repeatedly using formula (1).

Step 5: Calculate the orthogonal dipole anisotropy value before and after fracturing according to the curve formed by the shear wave velocity in different azimuths before and after fracturing at the one depth position.

The specific process is as follows:

Step 5.1: Obtain the shear wave velocity curve V _Φ formed by the shear wave velocity at different azimuths Φ before and after fracturing;

Step 5.2: Obtain the fast shear wave velocity V _fast and the slow shear wave velocity V _slow according to the shear wave velocity curve V _Φ . Among them, V _fast is the maximum value of the set {V _Φ }, V _slow is the minimum value of the set {V _Φ }, Φ∈[0 2π];

Step 5.3: Calculate the orthogonal dipole anisotropy value δ before and after fracturing according to the fast shear wave velocity V _fast and the slow shear wave velocity V _slow . in,

Step 6: Calculate the average elastic wave velocity before and after fracturing according to the longitudinal wave velocity before and after fracturing in step 4 or the shear wave velocity in different azimuths, and calculate the difference between the average elastic wave velocity after fracturing and before fracturing; Orthogonal dipole anisotropy difference between before and after the fracture, according to the average elastic wave velocity difference and the orthogonal dipole anisotropy difference, determine the fracturing fracture shape at the depth position; when the average elastic wave velocity When the difference is greater than zero, the sampling interval of the acoustic logging tool is recorded as the fracture height at the one depth position.

Among them, the specific way to calculate the difference Δs of the average elastic wave velocity after fracturing and before is:

Δs = P/V _{after fracturing} - P/V _{before fracturing} (3)

Among them, P is a constant, for example, the value is 10 ⁶ ; V _after fracturing is the average elastic wave velocity after fracturing, and V _{after fracturing} is the mean value of the longitudinal wave velocity after fracturing or the shear wave velocity in different azimuths; _Before fracturing is the average elastic wave velocity _{before fracturing, and Vbefore fracturing} is the mean value of the compressional wave velocity before fracturing or the shear wave velocity in different azimuths.

Among them, the formula for calculating the difference Δδ of orthogonal dipole anisotropy after fracturing and before is as follows:

Δδ = _after δ _{fracturing - δ before fracturing} (4)

Among them, after δ _fracturing is the value of orthogonal dipole anisotropy after fracturing, and _{before δ fracturing} is the value of orthogonal dipole anisotropy before fracturing.

Among them, the specific process of determining the fracturing fracture shape at a depth position is as follows:

When Δs=0, that is, when the average elastic wave velocity difference is equal to zero, the rock at the one depth position is not fractured.

When Δs>0 and Δδ>0, that is, when the average elastic wave velocity difference velocity difference is greater than zero and the orthogonal dipole anisotropy difference is greater than zero, it is determined that the fracturing fracture at the one depth position is a directional fracture .

When Δs>0 and Δδ≤0, that is, when the average elastic wave velocity difference velocity difference is greater than zero and the orthogonal dipole anisotropy difference is not greater than zero, it is determined that the fracturing fracture at the one depth position is network of cracks.

In addition, when Δs>0, the sampling interval of the acoustic logging tool is recorded as the fracture height h at the one depth position.

Step 7: Obtain the data of the next depth position in the depth interval, and repeat steps 4 to 6; until all depth positions in the depth interval are traversed; go to step 8.

Step 8: Counting the number of depth positions where there are fracture heights, the fracture heights in the depth range can be obtained.

If the counted number of depth positions with fracture heights is n, the height of fractures in the depth interval is n×h.

An experiment was carried out by using a method for determining the morphology and height of the fracturing fractures of the present invention, and the experimental results are shown in FIG. 2 . The first track in Fig. 2 is the well diameter and natural gamma ray curves, the second track is the shear wave slowness curve before and after fracturing, the third track is the depth interval and perforation interval, and the fourth track is the positive and negative curves before and after fracturing. Cross dipole anisotropy. It can be seen from the first track that X950m-X972m is a sandstone section, and the well diameter of this section has no abnormalities. From the second track, it can be seen that the shear wave slowness of the formation increases significantly after fracturing, which indicates that the rock shear wave velocity decreases, which indicates that cracks are generated when the rock around the wellbore breaks, forming rock expansion. Orthogonal dipole anisotropy can be judged that the height of the fracturing fracture is 20m, and the depth range of the fracturing fracture is X955m-X975m. According to the fracturing fracture judging condition of the present invention, it can be further judged that the form of the fracturing fracture of the reservoir is a directional fracture. In addition, the whole method is simple, so the method for determining the shape and height of a fracturing fracture of the present invention can quickly and effectively identify the shape and height of a fracturing fracture.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (5)

1. A method for determining fracture morphology and fracture height is characterized by comprising the following steps:

step 1: performing acoustic logging in a depth interval to obtain monopole and dipole waveform data before and after fracturing;

step 2: carrying out depth correction on the obtained data of the depth interval;

and step 3: acquiring data of a depth position of the depth interval;

and 4, step 4: analyzing the data of the depth position by adopting a waveform coherent superposition method, and calculating longitudinal wave speeds before and after fracturing and transverse wave speeds in different directions;

and 5: calculating the anisotropy values of the orthogonal dipoles before and after fracturing according to a curve formed by the transverse wave speeds of different directions before and after fracturing at the depth position;

step 6: calculating average elastic wave speeds before and after fracturing according to the longitudinal wave speeds before and after fracturing or the transverse wave speeds in different directions in the step 4, and calculating the difference value of the average elastic wave speeds before and after fracturing; meanwhile, calculating the difference value of the anisotropy of the orthogonal dipoles after and before fracturing in the step 5, and determining the fracture form of the depth position according to the average elastic wave velocity difference value and the difference value of the anisotropy of the orthogonal dipoles; when the average elastic wave velocity difference is larger than zero, recording the sampling interval of the acoustic logging instrument as the height of the fracture at the depth position;

and 7: acquiring data of the next depth position of the depth interval, and repeating the steps 4 to 6; until all depth positions of the depth interval are traversed; entering a step 8;

and 8: and counting the number of the depth positions with the fracture heights to obtain the fracture heights of the depth intervals.

2. The method for determining the fracture morphology and the fracture height according to claim 1, wherein the specific process of the step 4 is as follows:

the waveform coherent addition method specifically comprises the following steps:

$Corr(v,T)=\frac{\underset{T}{\overset{T+T_W}{\∫}}|\underset{m=1}{\overset{N}{\Σ}}{X}_m\[t+(m-1)d/v\]{|}^{2}dt}{N\underset{T}{\overset{T+T_W}{\∫}}\underset{m=1}{\overset{N}{\Σ}}|X_m\[t+(m-1)d/v{|}^{2}dt}$

wherein, X_m(T) is the mth receiving transducer in the array of N sonic logging instrument receiving transducers, d is the spacing between sonic logging instrument receiving transducers, and T is the time window T_wV is a certain speed value in the speed interval; then, the v value when the two-dimensional correlation function Corr (v, T) takes the maximum value, that is, the v value is repeatedly calculatedLongitudinal wave velocities before and after fracturing and shear wave velocities at different orientations can be calculated.

3. A method for determining fracture morphology and fracture height according to claim 1, wherein the specific process of the step 5 is as follows:

step 5.1: obtaining a transverse wave velocity curve V formed by transverse wave velocities at different azimuths phi before and after fracturing_Φ；

Step 5.2: according to the transverse wave velocity curve V_ΦObtaining the velocity V of the fast transverse wave_fastAnd a slow transverse wave velocity V_slowWherein V is_fastIs a set { V_ΦMaximum of V_slowIs a set { V_ΦMinimum value of phi ∈ [02 pi ]]；

Step 5.3: according to the velocity V of the fast transverse wave_fastAnd a slow transverse wave velocity V_slowAnd calculating the values of the orthotropic dipole anisotropy before and after the fracturing, wherein,

4. a method for determining fracture morphology and fracture height according to claim 1, wherein the specific way of calculating the average elastic wave velocity difference Δ s between the post-fracture and the pre-fracture in step 6 is as follows:

Δs＝P/V_{after fracturing}-P/V_{Before fracturing}；

Wherein P is a constant; v_{After fracturing}Is the average elastic wave velocity after fracturing, and V_{After fracturing}The mean value of the longitudinal wave velocity after fracturing or the transverse wave velocities in different directions; v_{Before fracturing}Is the average elastic wave velocity before fracturing, and V_{Before fracturing}The velocity of the longitudinal wave before fracturing or the average value of the velocities of the transverse waves in different directions.

5. A fracture morphology and fracture height determination method according to claim 1, wherein in the step 6, the specific process of determining the fracture morphology at the one depth position according to the average elastic wave velocity difference and the orthogonal dipole anisotropy difference is as follows:

when the average elastic wave velocity difference is equal to zero, the rock at the one depth position is not fractured; when the average elastic wave velocity difference value is larger than zero and the orthogonal dipole anisotropy difference value is larger than zero, judging that the fracturing fracture at the depth position is a directional fracture; and when the average elastic wave velocity difference value is larger than zero and the orthogonal dipole anisotropy difference value is not larger than zero, judging that the fracturing fracture at the depth position is a net-shaped fracture.