CN116136606A - Fracture logging identification method and system under oil-based mud conditions - Google Patents

Abstract

The invention provides a crack logging identification method and a crack logging identification system under an oil-based mud condition, which can improve the precision of crack logging identification under the oil-based mud condition, effectively evaluate the development degree of stratum cracks and judge the filling property of the cracks. S1, calculating a rock wave impedance value according to a density curve and a longitudinal wave acoustic wave time difference curve based on conventional logging data of a stratum to be analyzed; s2, correcting the calculated rock wave impedance value according to a clay content curve in conventional logging data, calculating according to a preset correction formula to obtain a corrected wave impedance value, and drawing a corrected wave impedance curve graph; and S3, judging whether the crack of the stratum to be analyzed is developed or not based on the calculated corrected wave impedance value, if the corrected wave impedance value is not greater than a preset wave impedance threshold value, indicating that the crack of the corresponding stratum is a developed crack, otherwise, indicating that the crack is an undeveloped crack.

Description

Fracture logging identification method and system under oil-based mud conditions

technical field

The invention relates to the technical field of tight sandstone fracture logging evaluation methods, in particular to a fracture logging identification method and system under oil-based mud conditions.

Background technique

At present, for tight oil and gas reservoirs, the development of fractures determines the enrichment and high production of tight oil and gas. However, due to the lack of coring and thin section data, it is particularly important to use logging data, especially imaging logging data, to realize logging discrimination of fractures.

However, under the condition of oil-based mud, micro-resistivity imaging logging is affected by oil-based drilling fluid and the electrical conductivity of the formation fails, so it is difficult to finely identify and evaluate fractures. Currently, the logging identification of fractures under oil-based mud conditions There are mainly the following problems:

1. Due to the limitation of accuracy, it is difficult to accurately identify fractures in micro-resistivity imaging logging under oil-based mud conditions. Compared with water-based mud conditions, it is more difficult to identify fracture traces;

2. Due to the influence of oil-based mud, it is difficult to identify the filling properties of fractures on micro-resistivity imaging logging.

Contents of the invention

In order to solve the problems existing in the prior art, the present invention provides a fracture logging identification method and system under oil-based mud conditions, which can improve the accuracy of fracture logging identification under oil-based mud conditions, and effectively monitor the development degree of formation fractures. Evaluation, and at the same time judge the filling performance of the fracture.

To achieve the above object, the present invention provides the following technical solutions:

A fracture logging identification method under oil-based mud conditions, comprising the following steps,

S1. Based on the conventional logging data of the formation to be analyzed, the rock wave impedance value is calculated according to the density curve and the compressional wave acoustic wave time difference curve;

S2. Correct the calculated rock wave impedance value according to the shale content curve in the conventional logging data, calculate and obtain the corrected wave impedance value according to the preset correction formula, and draw the corrected wave impedance curve;

S3. Based on the calculated corrected wave impedance value, it is judged whether the fractures in the formation to be analyzed are developed. If the corrected wave impedance value is not greater than the preset wave impedance threshold, it means that the fractures in the corresponding formation are developed fractures, otherwise they are not developed fractures.

Preferably, S1 also includes stripping the calculated abnormal rock wave impedance value;

Among them, the abnormal judgment standard is that the calculated rock wave impedance value deviates from the preset range of the rock wave impedance value corresponding to the normal rock physical properties.

Preferably, in S2, the correction includes,

Select multiple undeveloped fractures at different shale content positions in the core, and calculate the change value of rock wave impedance corresponding to the change of shale content;

Comparing the relationship between the change of shale content and the change of rock wave impedance value, the correction formula is obtained as,

When the buried depth is ≤5000m, the corrected wave impedance value Z’=Z+1.3VSH, where VSH is the mud content and Z is the rock wave impedance value;

When the buried depth is >5000m, the corrected wave impedance value Z'=Z-1.3VSH.

Preferably, based on multi-well data, the preset acoustic impedance threshold is set to 1300Kg/cm ³ ·s.

Preferably, it also includes qualitatively judging the fracture development degree of the well section to be analyzed according to the corrected wave impedance value;

According to the corrected wave impedance curve, the fracture-developed layers of the well section are divided;

The degree of fracture development is the ratio of the thickness of the fracture-developed interval to the depth of the entire well section. The larger the ratio, the higher the fracture development degree of the well section.

Preferably, it also includes acquiring the oil-based mud imaging logging image, and comparing it with the corrected wave impedance curve to establish a fracture identification plate;

Among them, for the fractures that can be directly identified on the oil-based mud imaging logging image, based on the comparison between the calculated corrected wave impedance value and the preset wave impedance threshold, it is judged whether the fractures in the formation to be analyzed are filled. If the corrected wave impedance value If it is greater than the wave impedance threshold, it means that the fractures in the corresponding formation are filled;

For the fractures that cannot be directly identified on the oil-based mud imaging logging image, proceed to step S3 to determine whether the fractures are developed.

Preferably, the calculation formula of the rock wave impedance value in S1 is,

Rock wave impedance value Z＝10 ⁵ ×DEN÷3.28DTC,

Among them, DEN is the density value, and DTC is the longitudinal wave sound wave time difference.

A fracture logging identification system under oil-based mud conditions, comprising:

The calculation module is used to calculate the rock wave impedance value based on the conventional logging data of the stratum to be analyzed according to the density curve and the compressional wave acoustic time difference curve;

The correction module is used to calculate and obtain the corrected wave impedance value according to the shale content curve in the conventional logging data and the preset correction formula, and draw the corrected wave impedance curve;

The comparison module is used to determine whether the fractures in the formation to be analyzed are developed based on the calculated corrected wave impedance value. If the corrected wave impedance value is less than the preset wave impedance threshold, it indicates that the fractures in the corresponding formation are developed fractures.

Preferably, an imaging module is also included, which is used to obtain the oil-based mud imaging logging image, and compare it with the corrected wave impedance curve to establish a fracture identification plate.

Compared with the prior art, the present invention has the following beneficial effects:

The invention provides a fracture logging identification method under the condition of oil-based mud, including calculating the rock wave impedance value based on the density curve and the longitudinal wave acoustic wave time difference curve in the conventional logging data; The shale content of the formation is used to correct the calculated wave impedance value, so that the influence of the sandstone lithology on the wave impedance value can be eliminated, and the fracture development status of the formation to be analyzed can be judged by comparing the corrected wave impedance value with the wave impedance threshold value. It can improve the accuracy of fracture logging identification under oil-based mud conditions, and can effectively evaluate the development degree of formation fractures in the absence of imaging data.

The invention can perform more accurate logging identification on fractures under the background of oil-based mud. One is that the present invention can realize high-precision fracture logging identification under the background of oil-based mud by combining acoustic and electric methods with imaging logging images and core data; the other is that the present invention can also be applied to fracture identification under water-based mud conditions , in the absence of imaging data, the development degree of formation fractures can be effectively evaluated; third, the present invention can identify the fracture filling property in the background of oil-based mud to a certain extent.

Description of drawings

Fig. 1 is the flow chart of identification method of the present invention;

Fig. 2 is a tight sandstone fracture core identification plate in the embodiment of the present invention;

Fig. 3 is a curve diagram of rock wave impedance value on a single well in an embodiment of the present invention;

Fig. 4 is a curve diagram of the corrected wave impedance value corresponding to formation fractures in the embodiment of the present invention;

Fig. 5 is a chart for identifying cracks under the background of oil-based mud in an embodiment of the present invention;

Fig. 6 is a diagram of crack traces identified on the imaging image in the embodiment of the present invention;

Fig. 7 is a diagram showing the results of oil-based mud single well fracture logging identification in the embodiment of the present invention.

In the figure, a, horizontal tensile fractures; b, low-angle fractures; c, high-angle fractures; d, multiple groups of high-angle fractures; e, network fractures; f, low-angle fractures filled with gypsum; g, high-angle fractures filled with calcite ; h, fracture dissolution; i, calcite filling and fracture dissolution.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

A fracture logging identification method under the oil-based mud condition of the present invention, as shown in Figure 1, comprises the following steps,

S1. Based on the conventional logging data of the formation to be analyzed, the rock wave impedance value is calculated according to the density curve and the compressional wave acoustic wave time difference curve;

S2. Correct the calculated rock wave impedance value according to the shale content curve in the conventional logging data, calculate and obtain the corrected wave impedance value according to the preset correction formula, and draw the corrected wave impedance curve;

S3. Based on the calculated corrected wave impedance value, it is judged whether the fractures in the formation to be analyzed are developed. If the corrected wave impedance value is less than the preset wave impedance threshold, it means that the fractures in the corresponding formation are developed fractures, otherwise they are not developed fractures.

The invention provides a fracture logging identification method under the condition of oil-based mud, which includes calculating the rock wave impedance value based on the density curve and the longitudinal wave acoustic wave time difference curve in the conventional logging data; according to the difference in the buried depth of the formation, a limit of 5000m is established Correct the calculated wave impedance value by using the formation shale content calculated by well logging, so as to eliminate the influence of sandstone and mudstone lithology on the wave impedance value, and compare the corrected wave impedance value with the wave impedance threshold value to be analyzed The development status of formation fractures can improve the accuracy of fracture logging identification under oil-based mud conditions, and can effectively evaluate the development degree of formation fractures in the absence of imaging data.

Further, S1 also includes stripping the calculated abnormal rock wave impedance value, and by stripping out the abnormal section of the logging value, the judgment result can be made more accurate and the error can be reduced;

Among them, the criterion for judging abnormality is that the calculated rock wave impedance value deviates from the preset range of rock wave impedance value corresponding to the normal rock physical properties, which is generally one or two orders of magnitude different from the normal range. In this embodiment, in S2, the correction includes,

Select multiple undeveloped fractures at different shale content positions in the core, and calculate the change value of rock wave impedance corresponding to the change of shale content;

Comparing the relationship between the change of shale content and the change of rock wave impedance value, the correction formula is obtained as,

When the buried depth is ≤5000m, the corrected wave impedance value Z’=Z+1.3VSH, where VSH is the mud content and Z is the rock wave impedance value;

When the buried depth is >5000m, the corrected wave impedance value Z'=Z-1.3VSH.

The invention obtains the corrected wave impedance value through the shale content, and eliminates the influence of sand and mudstone lithology on the wave impedance value.

In this embodiment, based on multi-well data, the preset acoustic impedance threshold is set to 1300Kg/cm ³ ·s.

Further, it also includes qualitatively judging the fracture development degree of the well section to be analyzed according to the corrected wave impedance value;

According to the corrected wave impedance curve, the fracture-developed layers of the well section are divided;

The degree of fracture development is the ratio of the thickness of the fracture-developed interval to the depth of the entire well section. The larger the ratio, the higher the fracture development degree of the well section.

Further, it also includes obtaining the oil-based mud imaging logging image, and comparing it with the corrected wave impedance curve to establish a fracture identification plate;

Among them, for the fractures that can be directly identified on the oil-based mud imaging logging image, based on the comparison between the calculated corrected wave impedance value and the preset wave impedance threshold, it is judged whether the fractures in the formation to be analyzed are filled. If the corrected wave impedance value If it is greater than the wave impedance threshold, it means that the fractures in the corresponding formation are filled;

For the fractures that cannot be directly identified on the oil-based mud imaging logging image, proceed to step S3 to determine whether the fractures are developed.

The present invention also provides a method for comprehensively utilizing the calculation of rock wave impedance and the comparison of oil-based mud imaging and logging images to establish a fracture identification plate under the background of oil-based mud, and the method of combining sound and electricity can more accurately identify cracks under the background of oil-based mud and other steps. Among them, the rock impedance value can be calculated based on the rock density value and P-wave acoustic time difference data obtained by conventional logging (rock wave impedance = rock density x P-wave velocity); since the wave impedance value will be affected by lithology, the tight sandstone In the formation, it is necessary to correct the influence of shale on wave impedance according to the shale content value, so as to obtain the corrected wave impedance value, and combine multi-well data with the corrected wave impedance curve to divide the fracture-developed zone; finally, through conventional logging Acoustic-electric combination—wave impedance method, imaging logging image and core comparison can realize high-precision fracture logging identification in the background of oil-based mud. Through the above steps, the present invention can perform more accurate logging identification on fractures in the background of oil-based mud. One is that the present invention can realize high-precision fracture logging identification under the background of oil-based mud by combining acoustic and electric methods with imaging logging images and core data; the other is that the present invention can also be applied to fracture identification under water-based mud conditions , in the absence of imaging data, the development degree of formation fractures can be effectively evaluated; third, the present invention can identify the fracture filling property in the background of oil-based mud to a certain extent.

In this embodiment, the calculation formula of the rock wave impedance value in S1 is:

Rock wave impedance value Z＝10 ⁵ ×DEN÷3.28DTC,

Among them, DEN is the density value, and DTC is the longitudinal wave sound wave time difference.

A fracture logging identification system under oil-based mud conditions, comprising:

The calculation module is used to calculate the rock wave impedance value based on the conventional logging data of the stratum to be analyzed according to the density curve and the compressional wave acoustic time difference curve;

The correction module is used to calculate and obtain the corrected wave impedance value according to the shale content curve in the conventional logging data and the preset correction formula, and draw the corrected wave impedance curve;

The comparison module is used to determine whether the fractures in the formation to be analyzed are developed based on the calculated corrected wave impedance value. If the corrected wave impedance value is less than the preset wave impedance threshold, it indicates that the fractures in the corresponding formation are developed fractures.

Among them, an imaging module is also included, which is used to obtain the oil-based mud imaging logging image, and compare it with the corrected wave impedance curve to establish a fracture identification plate.

Further, the identification method provided by the present invention can be implemented in Techlog or Reform software platform, but not limited thereto.

Example

In this embodiment, by implementing in Reform, its specific implementation is as follows:

(1) Obtain the fracture development characteristics of tight sandstone through core observation, including fracture occurrence, fracture trace, fracture filling, etc.

① As shown in Fig. 2, fractures can be divided into high-angle fractures, oblique fractures, low-angle fractures and near-horizontal fractures in terms of occurrence;

②Because of being filled with different fillers, the fractures present different characteristics. According to the filling properties, fractures can be divided into unfilled fractures and filled fractures.

(2) Calculate the rock wave impedance value by using the density curve and P-wave acoustic time-difference curve in the conventional logging data, and the rock wave impedance Z=rock density×P-wave velocity.

Among them, the actual calculation formula using conventional logging data is Z=10 ⁵ ×DEN÷3.28DTC;

Z is the wave impedance, the unit is Kg/cm ³ ·s, DEN is the density value, the unit is g/cm ³ , DTC is the longitudinal sound wave time difference, the unit is μs/ft.

Among them, for the section with abnormal logging value, that is, the logging curve value deviates from the corresponding logging value of normal petrophysical properties, and usually differs from the normal range by one or two orders of magnitude, it should be stripped, as shown in Figure 3.

(3) Correct the calculated wave impedance based on the shale content curve VSH obtained from conventional logging data to obtain the corrected wave impedance value.

① Select the imaging logging and several places in the core without fractures and with different shale content to obtain the change value of wave impedance under the change of shale content.

②By comparing the relationship between shale content and wave impedance in unfractured formations in multiple wells, it is found that for every 1% increase in shale content, the change of wave impedance is about 1.3Kg/cm ³ ·s;

Affected by the burial depth, when the burial depth is <5000m, the wave impedance of sandstone > the wave impedance of mudstone, and the correction formula is: corrected wave impedance Z’=Z+1.3VSH;

When the buried depth is >5000m, sandstone wave impedance < mudstone wave impedance, the correction formula is: corrected wave impedance Z’=Z-1.3VSH.

③Combined with the multi-well data to calculate the wave impedance comparison, it is considered that when no fractures are developed, the formation wave impedance value is >1300Kg/cm ³ ·s, so it is set to 1300Kg/cm ³ ·s as the boundary, when the wave impedance value is <1300Kg/cm ³ · s, it is determined that fractures are developed in the formation, as shown in Fig. 4.

(4) Using the corrected wave impedance curve and the obtained oil-based mud imaging logging image and core comparison to establish a fracture identification chart under the oil-based mud background.

① Comparing the fracture-developed zone zone divided by the corrected wave impedance curve with the oil-based mud imaging logging image to establish a chart, as shown in Fig. 5;

②Obvious fracture traces are found on the oil-based mud imaging logging image, which can be picked up directly on the image, and judge whether the corrected wave impedance value of the fracture is greater than 1300Kg/cm ³ ·s. If it is greater, it indicates that it is a filled fracture. This can identify the fracture filling property to a certain extent, as shown in Fig. 6.

③The traces of fractures on the oil-based mud imaging logging image are blurred, and there may be a phenomenon of missing recognition, or for wells lacking imaging data, it is judged whether the fracture can be picked by comparing the corrected wave impedance curve, if the corrected wave impedance value If it is less than 1300Kg/cm ³ ·s, it indicates that it is developed fractures, and the fracture development degree of the well interval can be qualitatively judged by dividing the fracture development interval of the well interval through the corrected wave impedance curve. The larger the ratio, the more developed the cracks, as shown in Figure 7.

The identification method provided by the present invention, through the comparison of the wave impedance method with the imaging logging image, reflects its better identification effect, and it can also be seen that the wave impedance method has a good correction and discrimination for the missed fractures in the imaging logging image effect.

Claims (9)

1. A crack logging identification method under the condition of oil-based mud is characterized by comprising the following steps,

s1, calculating a rock wave impedance value according to a density curve and a longitudinal wave acoustic wave time difference curve based on conventional logging data of a stratum to be analyzed;

s2, correcting the calculated rock wave impedance value according to a clay content curve in conventional logging data, calculating according to a preset correction formula to obtain a corrected wave impedance value, and drawing a corrected wave impedance curve graph;

and S3, judging whether the crack of the stratum to be analyzed is developed or not based on the calculated corrected wave impedance value, if the corrected wave impedance value is not greater than a preset wave impedance threshold value, indicating that the crack of the corresponding stratum is a developed crack, otherwise, indicating that the crack is an undeveloped crack.

2. The method for identifying a fracture log under oil-based mud conditions according to claim 1, wherein in S1, the method further comprises stripping the calculated abnormal rock wave impedance value;

the abnormal judgment standard is that the calculated rock wave impedance value deviates from a preset range of the rock wave impedance value corresponding to the normal rock physical property.

3. A method of fracture log identification in oil based mud conditions as set forth in claim 1 wherein, in S2, said correcting comprises,

selecting a plurality of undeveloped cracks at different argillaceous content positions in the rock core, and calculating a change value of a rock wave impedance value corresponding to the change of the argillaceous content;

comparing the relation between the change of the clay content and the change of the rock wave impedance value to obtain a correction formula,

when the burial depth is less than or equal to 5000m, correcting the wave impedance value Z' =Z+1.3 VSH, wherein VSH is the clay content, and Z is the rock wave impedance value;

when the burial depth is >5000m, the corrected wave impedance value Z' =z-1.3 VSH.

4. The method for identifying a fracture log under oil-based mud conditions according to claim 1, wherein the preset wave impedance threshold is set to 1300Kg/cm based on multi-well data ³ ·s。

5. The method for identifying a fracture log under oil-based mud conditions according to claim 1, further comprising qualitatively determining a fracture development level of the well section to be analyzed based on the corrected wave impedance value;

dividing a crack development interval of the well section according to the correction wave impedance curve chart;

the crack development degree is the ratio of the thickness of the crack development interval to the depth of the whole well section, and the greater the ratio is, the higher the crack development degree of the well section is.

6. The method for identifying a fracture log under oil-based mud conditions of claim 1, further comprising acquiring an oil-based mud imaging log image and comparing with a corrected wave impedance profile to create a fracture identification template;

for the cracks which can be directly identified on the oil-based mud imaging logging image, judging whether the cracks of the stratum to be analyzed are filled or not based on the comparison between the calculated corrected wave impedance value and a preset wave impedance threshold value, and if the corrected wave impedance value is larger than the wave impedance threshold value, indicating that the cracks of the corresponding stratum are filled;

and (3) continuing to carry out the step (S3) to judge whether the crack is developed or not for the crack which cannot be directly identified on the oil-based mud imaging logging image.

7. The method for identifying a fracture log under oil-based mud conditions according to claim 1, wherein the calculation formula of the rock wave impedance value in S1 is,

rock wave impedance z=10 ⁵ ×DEN÷3.28DTC，

Wherein DEN is a density value, and DTC is a longitudinal wave acoustic wave time difference.

8. A fracture log identification system under oil-based mud conditions, characterized in that it comprises, based on the fracture log identification method of any one of claims 1-7,

the calculation module is used for calculating a rock wave impedance value according to a density curve and a longitudinal wave sound wave time difference curve based on conventional logging data of the stratum to be analyzed;

the correction module is used for calculating to obtain a correction wave impedance value according to a clay content curve in conventional logging data and a preset correction formula, and drawing a correction wave impedance curve graph;

and the comparison module is used for judging whether the crack of the stratum to be analyzed is developed or not based on the calculated corrected wave impedance value, and if the corrected wave impedance value is smaller than a preset wave impedance threshold value, the crack of the corresponding stratum is a development crack.

9. The system of claim 8, further comprising an imaging module for acquiring an oil-based mud imaging log image and comparing with the corrected wave impedance profile to create a fracture identification map.

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