阅读说明：本技术 海上中、高孔渗砂岩压裂效果预评估方法 (Method for pre-evaluating fracturing effect of offshore medium and high pore permeability sandstone ) 是由 张明 马英文 张璋 张启龙 李�东 张晓诚 祁晓 刘峰 韩耀图 余涵 杨喜 张 于 2021-08-18 设计创作，主要内容包括：一种海上中、高孔渗砂岩压裂效果预评估方法,包括如下步骤：一：采集目的区块内井压裂前、后测井资料；二：计算压裂前、后阵列声波地层纵、横波时差及走时；三：计算压裂前、后阵列声波径向速度剖面之差；四：计算压裂前储层物性及岩石力学参数曲线；五：将参数曲线与压裂前、后径向速度剖面之差进行对比分析与提取；六：将孔隙度、岩石脆性指数与体积模量拟合,得到与压裂前、后的径向速度剖面之差更为吻合的BPB曲线；七：计算单井压裂前的储层物性参数曲线、岩石力学参数曲线,并使用PBP曲线对本井的压裂效果进行预评估。本发明通过对目标区块的压裂井,利用径向速度剖面差异进行压裂效果评估；其不受储层物性差异影响,评价结果可靠。(A pre-evaluation method for fracturing effect of medium and high porosity sandstone on sea comprises the following steps: firstly, the method comprises the following steps: collecting well logging data before and after well fracturing in a target block; II, secondly: calculating longitudinal and transverse wave time differences and travel time of the acoustic stratum before and after fracturing; thirdly, the method comprises the following steps: calculating the difference between the radial velocity profiles of the acoustic waves of the front array and the rear array before fracturing; fourthly, the method comprises the following steps: calculating the physical property of a reservoir before fracturing and a rock mechanical parameter curve; fifthly: comparing, analyzing and extracting the difference between the parameter curve and the radial velocity profile before and after fracturing; sixthly, the method comprises the following steps: fitting the porosity, the rock brittleness index and the volume modulus to obtain a BPB curve which is more consistent with the difference between the radial velocity profiles before and after fracturing; seventhly, the method comprises the following steps: and calculating a physical property parameter curve of the reservoir and a rock mechanics parameter curve before fracturing of the single well, and pre-evaluating the fracturing effect of the single well by using the PBP curve. The fracturing effect evaluation is carried out on the fracturing wells of the target block by utilizing the radial velocity profile difference; the method is not influenced by the physical property difference of the reservoir, and the evaluation result is reliable.)

1. A pre-evaluation method for fracturing effects of medium and high porosity sandstone on sea is characterized by comprising the following steps:

the first step is as follows: collecting conventional well logging data before and after well fracturing in a target block and array acoustic well logging data;

the second step is that: calculating the stratum longitudinal and transverse wave time differences and travel time of the array sound waves before and after fracturing;

the third step: calculating the difference of the radial velocity profiles of the array sound waves before and after fracturing;

the fourth step: calculating a physical property parameter curve of a reservoir before fracturing and a rock mechanics parameter curve;

the fifth step: comparing and analyzing the physical property parameter curve and the rock mechanics parameter curve calculated in the fourth step with the difference between the radial velocity profile before and after fracturing, and extracting a porosity parameter, a rock brittleness index parameter and a volume modulus parameter curve which have better consistency with the difference between the radial velocity profile;

and a sixth step: fitting the porosity, the rock brittleness index and the volume modulus to obtain a BPB curve which is more consistent with the difference between the radial velocity profiles before and after fracturing;

the seventh step: and calculating a physical property parameter curve of a reservoir before single well fracturing and a rock mechanical parameter curve, and pre-evaluating the fracturing effect of the well.

2. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the concrete steps in the first step are as follows: and respectively carrying out conventional well logging and array acoustic well logging in the well before and after fracturing in a given depth interval to obtain conventional well logging data before and after fracturing, namely: naturally gamma, caliper, neutron, density and array acoustic full wave column data.

3. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the second step is implemented by: the STC method of formula (1) is adopted to respectively process array sound wave full wave column data before and after fracturing so as to obtain longitudinal wave time difference and transverse wave time difference of the stratum before and after fracturing; then, combining the structure of an acoustic logging instrument and the speed of borehole fluid, calculating the arrival time of longitudinal waves and transverse waves of the stratum before and after fracturing by adopting an integration method of a formula (2), and explaining the arrival time calculation principle by taking the calculation of the time difference of the transverse waves of the stratum as an example;

calculating a two-dimensional correlation function Corr (s, T) according to a formula (1) for a certain period of the whole waveform or the waveform and a given slowness interval, and solving the time difference of longitudinal waves and transverse waves of the stratum by the corresponding s value when the correlation function takes the maximum value;

TTS＝DTF×(CAL-TXDIA+CAL-RXDIA)/2+DTS×TRSP (2)。

4. the method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 3, wherein D is shown in the formula (1)_m: the representation is the waveform on the mth receiving transducer in the array waveform, d: representing the spacing, T, of the receiving transducers of the acoustic wave_w: represents the length of a time window representing the integral of the function, N: represents the total number of receivers, m: denotes the mth receiver, s: representing a slowness value;

in formula (2), DTF: representing the wellbore fluid velocity, typically: 189us/ft, CAL: denotes the hole diameter, TXDIA: representing transmitter probe diameter, RXDIA: denotes the receiver probe diameter, DTS: for stratum transverse wave time difference obtained by adopting an STC method, TRSP: representing the distance that the formation shear wave travels along the formation between the transmitter and receiver.

5. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the third step is implemented by:

firstly, respectively carrying out radial velocity profile inversion on array acoustic data before and after fracturing; to calculate the travel time of the sound wave propagating to the first receiver in the array sound wave, and define it as the reference travel time: TT_refThe formula is as follows:

comparing the reference travel time with the actual measurement travel time in the formula, and comparing the reference travel time with the actual measurement travel time to obtain the v_zThe reference travel time is consistent with the actual measurement travel time of the stratum without radial change; when the sound velocity increases along the radial direction, the actually measured travel time is the time of the ray entering the stratum from shallow to deep and then refracting back due to the v in the formula_zThe velocity of the maximum penetration depth, therefore, the reference travel time calculated by the above equation (3) is smaller than the measured travel time, i.e.: actually measuring the travel time lag to the reference travel time;

in order to more intuitively display the change of the longitudinal wave velocity of the near-borehole wall stratum, a velocity model needs to be established, the reference travel time is coincident with or close to the actual measurement travel time by continuously updating the velocity model, the velocity model at the moment is an absolute velocity profile required to be acquired, and meanwhile, a relative velocity profile can be acquired;

and subtracting the result of the radial velocity profile before fracturing from the result of the radial velocity profile after fracturing to obtain the difference between the radial velocity profiles before and after fracturing, and directly evaluating the fracturing effect according to the change of the difference between the radial velocity profiles.

6. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 5, wherein in the formula (3), v is_z: representing a stratum longitudinal wave sound velocity curve extracted by array sound wave processing, wherein the curve is the velocity of the maximum penetration depth; the upper and lower integral limits are respectively: the depth position of the sound source s and the first receiver R1; TT_f: representing the propagation time of the longitudinal wave in the well fluid.

7. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the fourth step comprises the following specific steps:

the method comprises the following steps of calculating to obtain a stratum porosity curve by adopting a neutron and density intersection graph method: POR, using the formula of Timur, calculating to obtain a formation permeability curve: PERM;

the shear modulus is calculated by utilizing the stratum density curve and the stratum shear wave time difference, and the formula is as follows:

in the formula, ρ: representing conventional log measured density values, V_S: representing the difference value of the horizontal waves;

thirdly, calculating the volume modulus by utilizing the shear modulus, the stratum longitudinal wave time difference and the stratum density, wherein the formula is as follows:

in the formula, V_P: representing the longitudinal wave time difference value;

fourthly, calculating the Young modulus by using the shear modulus and the volume modulus, wherein the formula is as follows:

fifthly, calculating the Poisson ratio by using the volume modulus and the Young modulus, wherein the formula is as follows:

sixthly, calculating a brittleness index by utilizing the Young modulus and the Poisson ratio, wherein the formula is as follows:

8. the method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the concrete steps in the fifth step are as follows: and calculating the physical property parameters, such as: porosity, permeability, rock mechanics parameters such as: shear modulus, bulk modulus, poisson's ratio, brittleness index, respectively, compared to the difference between the radial velocity profiles before and after fracturing.

9. The method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1, wherein the sixth step comprises the following specific steps:

fitting the three sensitive parameter curves with better consistency obtained in the fifth step with a difference curve between the radial velocity profiles before and after fracturing to obtain a reconstructed curve BPB, wherein the curve expression is as follows:

10. the method for pre-evaluating the fracturing effect of medium and high permeability sandstone in sea according to claim 1 or 8, wherein the concrete steps in the seventh step are as follows: and (3) calculating a BPB curve before fracturing of a single well by using a formula (9), further performing pre-evaluation on the fracturing effect of the well, and guiding the preferable design content of the well section of the fracturing scheme.

Technical Field

The invention belongs to the field of geophysical logging, and particularly relates to a method for pre-evaluating fracturing effects of marine medium and high pore permeability sandstone.

Background

Since the Bohai sea oil field enters exploration and development, the stratum of the third period is a main target layer system for increasing reserves and improving the yield, and along with continuous deepening of exploration and development, more and more blocks obtain good oil and gas display in the sandstone reservoir of the third period, so that the exploration potential is huge.

However, because the fracturing system has the characteristics of multiple objectives, multiple levels, dynamics, incomplete information and the like, the existing fracturing evaluation method mainly evaluates the post-fracturing effect by using a microseism monitoring technology, an acoustic logging technology and the like after fracturing measures are taken, but the evaluation effect has a very limited guiding significance on fracturing scheme design.

Currently, in fracture scenario design, the pre-evaluation methods used are mainly directed to: the compressibility of low-porosity permeable stratum such as dense gas, shale gas, coal bed gas and the like is calculated, and the evaluation contents mainly surround: rock mechanics parameters spread out (tensile strength, brittleness, modulus, etc.). However, in the third era of the Bohai sea oil field, particularly in the recent reservoir, sandstone with medium and high porosity and medium and high permeability is taken as the main reservoir, and the influence of physical properties on the fracturing effect is higher than the influence of mechanical properties of rocks, so that the conventional fracturing effect pre-evaluation method is not applicable.

Disclosure of Invention

The invention aims to provide a method for pre-evaluating the fracturing effect of medium and high pore permeability sandstone on the sea, which aims to solve the technical problems that a BPB parameter with better correspondence to the fracturing effect is reconstructed by using a bulk modulus parameter, a brittleness index parameter and a porosity parameter which have high sensitivity and good contrast on the fracturing effect, and the parameter is adopted to pre-evaluate the fracturing effect of the medium and high pore permeability sandstone reservoir.

In order to achieve the aim, the specific technical scheme of the method for pre-evaluating the fracturing effect of the medium and high pore permeability sandstone on the sea is as follows:

a pre-evaluation method for fracturing effect of medium and high porosity sandstone on sea comprises the following steps:

the first step is as follows: collecting conventional well logging data before and after well fracturing in a target block and array acoustic well logging data;

the second step is that: calculating the stratum longitudinal and transverse wave time differences and travel time of the array sound waves before and after fracturing;

the third step: calculating the difference of the radial velocity profiles of the array sound waves before and after fracturing;

the fourth step: calculating a physical property parameter curve of a reservoir before fracturing and a rock mechanics parameter curve;

the fifth step: comparing and analyzing the physical property parameter curve and the rock mechanics parameter curve calculated in the fourth step with the difference between the radial velocity profile before and after fracturing, and extracting a porosity parameter, a rock brittleness index parameter and a volume modulus parameter curve which have better consistency with the difference between the radial velocity profile;

and a sixth step: fitting the porosity, the rock brittleness index and the volume modulus to obtain a BPB curve which is more consistent with the difference between the radial velocity profiles before and after fracturing;

the seventh step: and calculating a physical property parameter curve of a reservoir before single well fracturing and a rock mechanical parameter curve, and pre-evaluating the fracturing effect of the well.

Further, the specific implementation in the first step is as follows: and respectively carrying out conventional well logging and array acoustic well logging in the well before and after fracturing in a given depth interval to obtain conventional well logging data before and after fracturing, namely: naturally gamma, caliper, neutron, density and array acoustic full wave column data.

Further, the second step is specifically performed by: the STC method of formula (1) is adopted to respectively process array sound wave full wave column data before and after fracturing so as to obtain longitudinal wave time difference and transverse wave time difference of the stratum before and after fracturing; then, combining the structure of an acoustic logging instrument and the speed of borehole fluid, calculating the arrival time of longitudinal waves and transverse waves of the stratum before and after fracturing by adopting an integration method of a formula (2), and explaining the arrival time calculation principle by taking the calculation of the time difference of the transverse waves of the stratum as an example;

calculating a two-dimensional correlation function Corr (s, T) according to a formula (1) for a certain period of the whole waveform or the waveform and a given slowness interval, and solving the time difference of longitudinal waves and transverse waves of the stratum by the corresponding s value when the correlation function takes the maximum value;

TTS＝DTF×(CAL-TXDIA+CAL-RXDIA)/2+DTS×TRSP (2)。

further, in the formula (1), D_m: the representation is the waveform on the mth receiving transducer in the array waveform, d: representing the spacing, T, of the receiving transducers of the acoustic wave_w: represents the length of a time window representing the integral of the function, N: represents the total number of receivers, m: denotes the mth receiver, s: representing a slowness value;

in formula (2), DTF: representing the wellbore fluid velocity, typically: 189us/ft, CAL: denotes the hole diameter, TXDIA: representing transmitter probe diameter, RXDIA: denotes the receiver probe diameter, DTS: for stratum transverse wave time difference obtained by adopting an STC method, TRSP: representing the distance that the formation shear wave travels along the formation between the transmitter and receiver.

Further, the third step is specifically:

firstly, respectively carrying out radial velocity profile inversion on array acoustic data before and after fracturing; to calculate the travel time of the sound wave propagating to the first receiver in the array sound wave, and define it as the reference travel time: TT_refThe formula is as follows:

comparing the reference travel time with the actual measurement travel time in the formula, and comparing the reference travel time with the actual measurement travel time to obtain the v_zThe reference travel time is consistent with the actual measurement travel time of the stratum without radial change; when the sound velocity increases along the radial direction, the actually measured travel time is the time of the ray entering the stratum from shallow to deep and then refracting back due to the v in the formula_zThe velocity of the maximum penetration depth, therefore, the reference travel time calculated by the above equation (3) is smaller than the measured travel time, i.e.: measured travel time lags behind the referenceExamination and walking;

in order to more intuitively display the change of the longitudinal wave velocity of the near-borehole wall stratum, a velocity model needs to be established, the reference travel time is coincident with or close to the actual measurement travel time by continuously updating the velocity model, the velocity model at the moment is an absolute velocity profile required to be acquired, and meanwhile, a relative velocity profile can be acquired;

and subtracting the result of the radial velocity profile before fracturing from the result of the radial velocity profile after fracturing to obtain the difference between the radial velocity profiles before and after fracturing, and directly evaluating the fracturing effect according to the change of the difference between the radial velocity profiles.

Further, in the formula (3), v_z: representing a stratum longitudinal wave sound velocity curve extracted by array sound wave processing, wherein the curve is the velocity of the maximum penetration depth; the upper and lower integral limits are respectively: the depth position of the sound source s and the first receiver R1; TT_f: representing the propagation time of the longitudinal wave in the well fluid.

Further, the specific implementation in the fourth step is as follows:

the method comprises the following steps of calculating to obtain a stratum porosity curve by adopting a neutron and density intersection graph method: POR, using the formula of Timur, calculating to obtain a formation permeability curve: PERM;

the shear modulus is calculated by utilizing the stratum density curve and the stratum shear wave time difference, and the formula is as follows:

in the formula, ρ: representing conventional log measured density values, V_S: representing the difference value of the horizontal waves;

thirdly, calculating the volume modulus by utilizing the shear modulus, the stratum longitudinal wave time difference and the stratum density, wherein the formula is as follows:

in the formula, V_P: representing the longitudinal wave time difference value;

fourthly, calculating the Young modulus by using the shear modulus and the volume modulus, wherein the formula is as follows:

fifthly, calculating the Poisson ratio by using the volume modulus and the Young modulus, wherein the formula is as follows:

sixthly, calculating a brittleness index by utilizing the Young modulus and the Poisson ratio, wherein the formula is as follows:

further, the concrete method in the fifth step is as follows: and calculating the physical property parameters, such as: porosity, permeability, rock mechanics parameters such as: shear modulus, bulk modulus, poisson's ratio, brittleness index, respectively, compared to the difference between the radial velocity profiles before and after fracturing.

Further, the specific implementation in the sixth step is as follows:

fitting the three sensitive parameter curves with better consistency obtained in the fifth step with a difference curve between the radial velocity profiles before and after fracturing to obtain a reconstructed curve BPB, wherein the curve expression is as follows:

further, the specific implementation in the seventh step is as follows: and (3) calculating a BPB curve before fracturing of a single well by using a formula (9), further performing pre-evaluation on the fracturing effect of the well, and guiding the preferable design content of the well section of the fracturing scheme.

The method for pre-evaluating the fracturing effect of the medium and high pore permeability sandstone on the sea has the following advantages:

1. the method comprises the steps of evaluating the fracturing effect by utilizing the difference of radial velocity profiles of fracturing wells of a target block;

2. on the basis of pre-evaluating the fracturing effect of a low-permeability reservoir by using rock mechanical parameters, introducing physical parameters for a medium-porosity reservoir and a high-porosity reservoir, and carrying out sensitivity analysis on the physical parameters of the reservoirs and the rock mechanical parameters;

3. according to the invention, the BPB parameter with better corresponding to the fracturing effect is reconstructed by utilizing the volume modulus parameter, the brittleness index parameter and the porosity parameter which have higher sensitivity and better contrast to the fracturing effect;

4. the parameters are adopted to pre-evaluate the fracturing effect of the medium and high porosity sandstone reservoir;

5. the method has the characteristics of good application effect, no influence of reservoir physical property difference, high applicability and reliable evaluation result.

Drawings

FIG. 1 is a schematic flow diagram of the present invention;

FIG. 2 is a schematic diagram showing the comparison between the mechanical parameters of rocks in a certain well and in a high pore-permeability section in the Bohai reclamation block and the radial velocity profile before and after fracturing (which is an actual graph on a screen);

FIG. 3 is a schematic diagram showing conventional well logging and comparison between reservoir physical property parameters and the difference between the pre-fracture radial velocity profile and the post-fracture radial velocity profile of a certain well and a high pore permeability section in a Bohai reclamation block according to the present invention (which is an actual graph on a screen);

fig. 4 is a schematic diagram showing comparison between the BPB parameter reconstructed in a middle and high pore shale section of the bohai reclamation block and the radial velocity profile before and after fracturing (which is an actual graph on a screen).

Detailed Description

In order to better understand the purpose, structure and function of the invention, the method for pre-evaluating the fracturing effect of medium and high permeability sandstone in the sea is described in further detail below with reference to the accompanying drawings.

As shown in fig. 1, the present invention comprises the steps of:

the first step is as follows: collecting conventional well logging data before and after well fracturing in a target block and array acoustic well logging data;

the specific method comprises the following steps: and respectively carrying out conventional well logging and array acoustic well logging in the well before and after fracturing in a given depth interval to obtain conventional well logging data before and after fracturing, namely: natural gamma, caliper, neutrons, density and array acoustic full wave column data.

The second step is that: calculating the stratum longitudinal and transverse wave time differences and travel time of the array sound waves before and after fracturing;

namely: respectively processing array sound wave full-wave column data before and after fracturing by adopting an STC method (shown as a formula (1)) to obtain longitudinal wave time difference and transverse wave time difference of the stratum before and after fracturing; then, combining the structure of the acoustic logging instrument and the borehole fluid speed, calculating the arrival time of longitudinal waves and transverse waves of the stratum before and after fracturing by adopting an integration method, taking the calculation of the time difference of the transverse waves of the stratum as an example, explaining the arrival time calculation principle (as shown in formula (2))

In the formula, D_m: the representation is the waveform on the mth receiving transducer in the array waveform, d: representing the spacing, T, of the receiving transducers of the acoustic wave_W: represents the length of a time window representing the integral of the function, N: represents the total number of receivers, m: representing the mth receiver and s the slowness value.

And (3) calculating a two-dimensional correlation function Corr (s, T) according to a formula (1) for the whole waveform or a certain period in the waveform and a given slowness interval, and solving the time difference of longitudinal waves and transverse waves of the stratum by the corresponding s value when the correlation function takes the maximum value.

TTS＝DTF×(CAL-TXDIA+CAL-RXDIA)/2+DTS×TRSP (2)

Wherein, DTF: is the wellbore fluid velocity, typically 189us/ft, CAL: denotes the hole diameter, TXDIA: representing transmitter probe diameter, RXDIA: denotes the receiver probe diameter, DTS: for stratum transverse wave time difference obtained by adopting an STC method, TRSP: representing the distance that the formation shear wave travels along the formation between the transmitter and receiver.

The third step: calculating the difference of the radial velocity profiles of the array sound waves before and after fracturing;

firstly, respectively carrying out radial velocity profile inversion on array acoustic data before and after fracturing; to calculate the travel time of the sound wave propagating to the first receiver in the array sound wave, and define it as the reference travel time: TT_refThe formula is as follows:

in the formula, v_zA stratum longitudinal wave sound velocity curve extracted for array sound wave processing is the velocity of the maximum penetration depth; the upper and lower limits of the integral are the depth positions of the sound source s and the first receiver R1, respectively; TT_fIs the propagation time of the longitudinal wave in the well fluid.

Comparing the reference travel time with the actual measurement travel time in the formula, and comparing the reference travel time with the actual measurement travel time to obtain the v_zThe reference travel time is consistent with the actual measurement travel time of the stratum without radial change; when the sound velocity increases along the radial direction, the actually measured travel time is the time of the ray entering the stratum from shallow to deep and then refracting back due to the v in the formula_zThe velocity of the maximum penetration depth, therefore, the reference travel time calculated by the above equation (3) is smaller than the measured travel time, i.e.: the measured travel time lags the reference travel time.

In order to more intuitively display the change of the longitudinal wave velocity of the near-borehole wall stratum, a velocity model needs to be established, the reference travel time is coincident with or close to the actual measurement travel time by continuously updating the velocity model, the velocity model at the moment is an absolute velocity profile required to be acquired, and meanwhile, a relative velocity profile can be acquired.

And subtracting the result of the radial velocity profile before fracturing from the result of the radial velocity profile after fracturing to obtain the difference between the radial velocity profiles before and after fracturing, and directly evaluating the fracturing effect according to the change of the difference between the radial velocity profiles.

The fourth step: calculating a physical property parameter curve of a reservoir before fracturing and a rock mechanics parameter curve;

the method comprises the following steps of calculating to obtain a stratum porosity curve by adopting a neutron and density intersection graph method: POR, using the formula of Timur, calculating to obtain a formation permeability curve: PERM;

the shear modulus is calculated by utilizing the stratum density curve and the stratum shear wave time difference, and the formula is as follows:

where ρ is the conventional log density value, V_SIs the transverse wave time difference.

Thirdly, calculating the volume modulus by utilizing the shear modulus, the stratum longitudinal wave time difference and the stratum density, wherein the formula is as follows:

in the formula, V_PIs the longitudinal wave time difference value.

Fourthly, calculating the Young modulus by using the shear modulus and the volume modulus, wherein the formula is as follows:

fifthly, calculating the Poisson ratio by using the volume modulus and the Young modulus, wherein the formula is as follows:

sixthly, calculating a brittleness index by utilizing the Young modulus and the Poisson ratio, wherein the formula is as follows:

the fifth step: comparing and analyzing the physical property parameter curve and the rock mechanics parameter curve calculated in the fourth step with the difference between the radial velocity profile before and after fracturing, and extracting a porosity parameter, a rock brittleness index parameter and a volume modulus parameter curve which have better consistency with the difference between the radial velocity profile; finding that the porosity, rock brittleness index and volume modulus have good correspondence with the difference between the radial velocity profiles before and after fracturing;

and calculating the physical property parameters, such as: porosity, permeability, etc., rock mechanics parameters such as: shear modulus, bulk modulus, poisson's ratio, brittleness index, etc., compared to the difference between the radial velocity profiles before and after fracturing, respectively. Through comparative analysis, the porosity, the rock brittleness index and the difference between the bulk modulus and the radial velocity profile have better correspondence.

And a sixth step: fitting the porosity, the rock brittleness index and the volume modulus to obtain a BPB curve which is more consistent with the difference between the radial velocity profiles before and after fracturing;

fitting the three sensitive parameter curves with better consistency obtained in the fifth step with a difference curve between the radial velocity profiles before and after fracturing to obtain a reconstructed curve BPB, wherein the curve expression is as follows:

the seventh step: calculating a reservoir physical property parameter curve before single well fracturing and a BPB curve of rock mechanical parameters, and pre-evaluating the fracturing effect of the well;

and (3) calculating a BPB curve before single well fracturing by using a formula (9), further performing pre-evaluation on the fracturing effect of the well, and guiding the design contents such as well section optimization of the fracturing scheme.

The method for pre-evaluating the fracturing effect of the offshore medium and high permeability sandstone is further explained by practical examples.

As shown in fig. 2, fig. 2 is a graph showing the effect of comparing the mechanical parameters of rocks at a sand shale section of a certain well in the reclamation block of the bohai sea oil field with the difference between the radial velocity profiles before and after fracturing.

The main lithology of the graph is sand-shale, the maximum porosity is about 30%, and the perforation intervals are 3352.0-3358.0 m; according to the difference result of the radial velocity profiles before and after fracturing, the zones with obvious changes of the reservoir are mainly concentrated in 3349.0-3361.0m and 3366.0-3374.0m, when the physical property of the reservoir is good, the influence of the physical property on the fracturing effect is higher than the influence of the mechanical property of the rock, so that the corresponding performance of the mechanical parameter response and the fracturing effect of the rock commonly used for fracturing evaluation of the low-pore-depth reservoir is poor, wherein only two parameters of the rock brittleness index BRIT and the bulk modulus BMOD have good corresponding relationship with the fracturing effect.

As shown in fig. 3, fig. 3 is a graph showing the effect of comparing the difference between the physical property parameter and the radial velocity profile of the conventional logging curve of the same interval in the same well; the results show that in the medium and high porosity section, there is a good correspondence between the porosity curve and the radial velocity profile.

As shown in fig. 4, fig. 4 is a graph of the effect of the difference between the reconstructed fracture effect pre-evaluation curve BPB and the radial velocity profile; the result shows that the BPB curve has better correspondence than rock mechanics, conventional logging curves and differences between physical property parameters of the reservoir and a radial velocity profile, and can more accurately pre-evaluate the fracturing effect of the reservoir.

The above-mentioned unexplained technologies are prior art and will not be described in detail.

It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.