Reservoir gas-bearing evaluation method based on seismic wave elastic parameter difference ratio

Abstract

The invention belongs to the technical field of reservoir prediction, and particularly provides a reservoir gas-bearing evaluation method based on a seismic wave elastic parameter difference ratio, and the method comprises the steps: obtaining a seismic processing sub-offset superposition data volume of a target region; well seismic fine calibration and horizon tracking are carried out; performing pre-stack inversion to obtain a transverse wave impedance data body and a Poisson's ratio data body of the target area; calculating a transverse wave impedance difference and a Poisson's ratio difference between the target reservoir and the cover layer by using the transverse wave impedance data body and the Poisson's ratio data body based on horizon calibration; determining an effective closure threshold value of the cover layer; and according to the construction formula, calculating the sealing coefficient of the target reservoir and the cover layer, and according to the effective sealing threshold value of the cover layer and the sealing coefficient of the target reservoir and the cover layer, determining whether the sealing performance is effective or not, and determining the gas-bearing property of the target reservoir. The problem that the gas-bearing property of the unconventional natural gas reservoir cannot be effectively predicted in the prior art is solved, and the effectiveness of the gas-bearing property of the unconventional natural gas reservoir such as limestone and deep coal rock gas can be evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of reservoir prediction, and in particular relates to a reservoir gas-bearing property evaluation method based on a seismic wave elastic parameter difference ratio. Background Art

[0002] The Taiyuan Formation of the Permian System in the Paleozoic Era in the Ordos Basin has developed large-scale limestone, and even the entire North China Basin has developed it extensively. The thickness of the Taiyuan Formation limestone in the basin is 5 to 30 meters, between 5# and 8# coal. It has long been believed that the reservoir is dense, and exploration has not made a breakthrough. In 2021, the deployment and implementation of risk exploration well gas testing obtained a high-yield gas flow of 549,000 cubic meters per day, proving that the Taiyuan Formation limestone has good exploration and development potential and is the main successor area for future resources. However, due to the thin layer, it is impossible to form an independent seismic reflection, and the reflection information is submerged in the strong reflection of the coal seam, which brings great difficulties to the prediction of limestone gas reservoirs and makes seismic prediction difficult.

[0003] At present, there are relatively few researches on limestone seismic prediction technology, and most of them follow the idea of ​​sandstone reservoir seismic prediction. In terms of limestone reservoir identification, the commonly used prediction technologies are mainly seismic attribute analysis, deterministic inversion and random inversion, but seismic attribute analysis is a qualitative prediction with certain uncertainty; while deterministic inversion can realize quantitative reservoir identification compared with seismic attribute analysis, but due to the limitation of seismic frequency, it is generally difficult to identify reservoirs with a thickness of less than 10m; random inversion has higher vertical resolution than deterministic inversion, and can obtain multiple inversion results with equal probability, but it requires a large amount of well logging information, which is not applicable to new exploration areas. In addition, the current prediction methods mainly focus on limestone lithology identification, and there are few predictions for reservoir gas content. At present, the efficient development of unconventional source gas reservoirs such as limestone gas reservoirs in the Ordos Basin requires accurate gas content prediction.

[0004] A Chinese patent document with publication number CN112305617A discloses a method and device for geophysical identification of unconventional gas reservoirs in coal-bearing rock systems, which relates to the technical field of geophysical exploration of unconventional gas reservoirs, including: identifying the physical properties of the reservoir by a comprehensive reservoir physical property identification method to obtain target physical parameters of the reservoir; identifying the geological properties of the reservoir by a reservoir seismic geological identification method to obtain geological parameters of the reservoir; identifying the lithology of the reservoir by a reservoir lithology identification method to obtain lithology identification results of the reservoir; identifying the gas content of the reservoir by a reservoir gas content identification method to obtain gas content identification results of the reservoir; and determining the target physical parameters, geological parameters, lithology identification results and / or gas content identification results as geophysical identification results. The prediction method of this document includes the following methods for identifying the gas content of the reservoir: pre-stack AVO (Amplitude Versus Offset, amplitude varies with offset) inversion method and pre-stack simultaneous inversion method; the gas content of the reservoir is identified by the reservoir gas content identification method to obtain the gas content identification result of the reservoir. This method cannot effectively predict the gas content of unconventional natural gas reservoirs such as Taiyuan limestone and deep coal-rock gas. Summary of the invention

[0005] The invention provides a reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio, which aims to overcome the problem in the prior art that the gas content of unconventional natural gas reservoirs such as Taiyuan limestone and deep coal-rock gas cannot be effectively predicted.

[0006] To this end, the present invention provides a reservoir gas-bearing property evaluation method based on the seismic wave elastic parameter difference ratio, comprising the following steps:

[0007] S1. Obtain the target area seismic processing offset stacking data volume;

[0008] S2. Carry out fine calibration of well seismic data and stratum tracking in the target area;

[0009] S3, using the seismic processing of step S1 to perform pre-stack inversion on the offset stacking data volume, to obtain the shear wave impedance data volume and Poisson's ratio data volume of the target area;

[0010] S4, based on the horizon calibration of step S2, using the shear wave impedance data volume and Poisson's ratio data volume of step S3, calculating the shear wave impedance difference and Poisson's ratio difference between the target reservoir and the cap rock;

[0011] S5. determining a threshold value of effective sealing of the cap layer;

[0012] S6. According to the constructed formula, the sealing coefficient of the target reservoir and the cap layer is calculated. According to the effective sealing threshold value of the cap layer and the sealing coefficient of the target reservoir and the cap layer, it is determined whether the sealing is effective, and then the gas content of the target reservoir is determined.

[0013] Preferably, the offset stacking data volume in step S1 includes a near-offset processing stacking data volume, a mid-offset processing stacking data volume, and a far-offset processing stacking data volume.

[0014] Preferably, the step S2 performs fine well-seismic calibration and layer tracking on the target area, specifically: using the completed well information in the target area to calibrate the layer synthesis record, establish a communication bridge between seismic and geological, and then perform fine interpretation of multiple target layers on the seismic data body, and use this as a constraint to establish a low-frequency model.

[0015] Preferably, the prestack inversion in step S3 is prestack geostatistical inversion.

[0016] Preferably, the specific method for calculating the shear wave impedance difference between the target reservoir and the cap layer in step S4 is: based on the layer calibration, extracting the root mean square attribute of the shear wave impedance target layer in the target segment on the shear wave impedance data body, extracting the root mean square attribute of the shear wave impedance value of the upper cover layer of the target segment, and subtracting the former from the latter to obtain the shear wave impedance difference.

[0017] Preferably, the specific method for calculating the Poisson's ratio difference between the target reservoir and the cap rock in step S4 is: based on the horizon calibration, extracting the root mean square attribute of the Poisson's ratio in the target segment on the Poisson's ratio data volume, extracting the root mean square attribute of the Poisson's ratio of the upper cap rock in the target segment, and subtracting the former from the latter to obtain the Poisson's ratio difference.

[0018] Preferably, the step S5 of determining the effective sealing threshold value of the cap rock specifically comprises: based on the lithology combination and gas content interpreted by logging of completed drilling wells, the effective sealing threshold value of the cap rock is obtained by multi-well intersection.

[0019] Preferably, the construction formula of step S6 is: Where S is the shear wave impedance; Pr is the Poisson's ratio; C is the sealing coefficient between the target reservoir and the cap rock.

[0020] Preferably, in step S6, when the sealing coefficient between the target reservoir and the cap rock is greater than the cap rock sealing threshold value, the sealing is effective; when the sealing coefficient between the target reservoir and the cap rock is less than the cap rock sealing threshold value, the sealing is ineffective.

[0021] Beneficial effects of the present invention:

[0022] The reservoir gas-bearing property evaluation method based on the seismic wave elastic parameter difference ratio provided by the present invention comprises the following steps: S1, obtaining a target area seismic processing offset stacking data body; S2, performing well seismic fine calibration and layer tracking on the target area; S3, performing prestack inversion using the seismic processing offset stacking data body of step S1 to obtain a shear wave impedance data body and a Poisson's ratio data body of the target area; S4, based on the layer calibration of step S2, using the shear wave impedance data body and the Poisson's ratio data body of step S3, calculating the shear wave impedance difference and the Poisson's ratio difference between the target reservoir and the cap layer; S5, determining the effective sealing threshold value of the cap layer;

[0023] S6. According to the constructed formula, the sealing coefficient of the target reservoir and the cap layer is calculated. According to the effective sealing threshold of the cap layer and the sealing coefficient of the target reservoir and the cap layer, it is determined whether the sealing is effective, and then the gas content of the target reservoir is determined; the gas content of the target reservoir (unconventional natural gas reservoirs such as Taiyuan Group limestone and deep coal-rock gas) can be evaluated under the reservoir-cap relationship model, and the combination relationship between the target section and the cap layer of its overlying lithology is analyzed through the difference ratio of seismic elastic wave parameters shear wave impedance and Poisson's ratio. The established formula can effectively evaluate the sealing of the cap layer, and then achieve the evaluation of the effectiveness of the target reservoir, and make technical reserves for the implementation and large-scale development of unconventional natural gas reservoir resources such as Taiyuan Group limestone and deep coal-rock gas in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Figure 1 It is the cross-plot of shear wave impedance and Poisson's ratio of limestone and caprock;

[0026] Figure 2 It is the cross plot of shear wave impedance and difference ratio of limestone caprock;

[0027] Figure 3 It is a plan view of the gas-bearing properties predicted by the sealing coefficient C of the limestone target reservoir and cap rock in the M75 three-dimensional area in the eastern part of the basin;

[0028] Figure 4 It is the cross-sectional diagram of the difference ratio between the shear wave impedance and Poisson's ratio of the inline421 survey line in the three-dimensional area;

[0029] Figure 5 It is a cross-sectional diagram of the difference ratio between the shear wave impedance and Poisson's ratio of the crossline174 survey line in the three-dimensional area. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0031] Embodiment 1:

[0032] A reservoir gas-bearing property evaluation method based on seismic wave elastic parameter difference ratio comprises the following steps:

[0033] S1. Obtain the target area seismic processing offset stacking data volume;

[0034] Furthermore, the offset stacking data volume includes a near-offset processing stacking data volume, a mid-offset processing stacking data volume, and a far-offset processing stacking data volume.

[0035] S2. Carry out fine calibration of well seismic data and stratum tracking in the target area;

[0036] Furthermore, the detailed well seismic calibration and layer tracking of the target area are as follows: the layer synthetic record calibration is performed using the completed well information in the target area to establish a communication bridge between seismic and geological data, and then a detailed interpretation of multiple target layers is performed on the seismic data body, and this is used as a constraint to establish a low-frequency model.

[0037] S3, using the seismic processing of step S1 to perform pre-stack inversion on the offset stacking data volume, to obtain the shear wave impedance data volume and Poisson's ratio data volume of the target area;

[0038] Furthermore, the prestack inversion is prestack geostatistical inversion.

[0039] S4, based on the horizon calibration of step S2, using the shear wave impedance data volume and Poisson's ratio data volume of step S3, calculating the shear wave impedance difference and Poisson's ratio difference between the target reservoir and the cap rock;

[0040] Furthermore, the specific method for calculating the shear wave impedance difference between the target reservoir and the cap rock is as follows: based on the layer calibration, the root mean square attribute of the shear wave impedance target layer in the target segment is extracted on the shear wave impedance data body, and the root mean square attribute of the shear wave impedance value of the upper cover layer of the target segment is extracted, and the shear wave impedance difference is obtained by subtracting the former from the latter.

[0041] Furthermore, the specific method for calculating the Poisson's ratio difference between the target reservoir and the cap rock is as follows: based on the stratigraphic calibration, the root mean square attribute of the Poisson's ratio in the target segment is extracted on the Poisson's ratio data volume, and the root mean square attribute of the Poisson's ratio in the upper cap rock in the target segment is extracted, and the Poisson's ratio difference is obtained by subtracting the former from the latter.

[0042] S5. determining a threshold value of effective sealing of the cap layer;

[0043] Furthermore, the determination of the effective sealing threshold value of the caprock is specifically as follows: based on the lithology combination and gas content interpreted by logging of completed drilling wells, the effective sealing threshold value of the caprock is obtained by multi-well intersection.

[0044] S6. According to the constructed formula, the sealing coefficient of the target reservoir and the cap layer is calculated. According to the effective sealing threshold value of the cap layer and the sealing coefficient of the target reservoir and the cap layer, it is determined whether the sealing is effective, and then the gas content of the target reservoir is determined.

[0045] Furthermore, the construction formula of step S6 is: Where S is the shear wave impedance; Pr is the Poisson's ratio; C is the sealing coefficient between the target reservoir and the cap rock.

[0046] Furthermore, in step S6, when the sealing coefficient between the target reservoir and the cap rock is greater than the cap rock sealing threshold value, the sealing is effective; when the sealing coefficient between the target reservoir and the cap rock is less than the cap rock sealing threshold value, the sealing is ineffective.

[0047] The present invention can evaluate the gas content of target reservoirs (unconventional natural gas reservoirs such as Taiyuan Group limestone and deep coal-rock gas) under the reservoir-cap relationship model, and analyze the combined relationship between the target section and its overlying lithological cap rock through the difference ratio of seismic elastic wave parameters shear wave impedance and Poisson's ratio. The established formula can effectively evaluate the sealing property of the cap rock, and then achieve the evaluation of the effectiveness of the target reservoir, making technical reserves for the implementation and large-scale development of unconventional natural gas reservoir resources such as Taiyuan Group limestone and deep coal-rock gas in the future.

[0048] Embodiment 2:

[0049] On the basis of Example 1, taking the M75 well area in the Ordos Basin as an example, the limestone distribution in the whole area is stable, but the gas-bearing sweet spot area is unclear. A reservoir gas-bearing property evaluation method based on the difference ratio of seismic wave elastic parameters is used to predict the gas-bearing property of limestone and the reservoir distribution, including the following steps:

[0050] S1. Obtain the offset stacking data volume of M75 seismic processing in the Ordos Basin;

[0051] The offset stacking data volume includes three offset stacking data volumes, namely, a near offset processing stacking data volume, a medium offset processing stacking data volume and a far offset processing stacking data volume.

[0052] S2, fine calibration of well seismic and stratum tracking for M75 in the Ordos Basin;

[0053] The information of completed wells in the target area is used to calibrate the synthetic records of the layers, and a bridge of communication between seismic and geological data is established. After that, multiple target layers are finely interpreted on the seismic data body, and a low-frequency model is established based on this as a constraint. The establishment of a low-frequency model is an existing technology, and it can be operated according to the actual situation to meet the needs.

[0054] S3, using seismic processing of three offset data volumes to perform prestack geostatistical inversion to obtain inversion results, the inversion results including shear wave impedance inversion results and Poisson's ratio inversion results, to obtain shear wave impedance data volume and Poisson's ratio data volume of the target area;

[0055] S4, based on the horizon calibration of step S2, using the shear wave impedance data volume and Poisson's ratio data volume of step S3, calculating the shear wave impedance difference and Poisson's ratio difference between the target reservoir and the cap rock;

[0056] Specifically, based on the stratum calibration of the completed wells, the root mean square attributes of the shear wave impedance target layer of the Taiyuan Formation limestone section are extracted on the shear wave impedance data body, and the root mean square attributes of the shear wave impedance value of the overlying strata of the Taiyuan Formation limestone are extracted. The shear wave impedance difference is obtained by subtracting the former from the latter.

[0057] Specifically, based on the stratum calibration of the completed wells, the root mean square attribute of the Poisson's ratio of the Taiyuan Formation limestone section is extracted on the Poisson's ratio data volume, and the root mean square attribute of the Poisson's ratio of the overlying strata of the Taiyuan Formation limestone is extracted. The Poisson's ratio difference is obtained by subtracting the former from the latter.

[0058] Table 1 shows the analysis of sensitive elastic parameters of 20 selected exploration wells, of which 8 wells have mudstone as caprock and 12 wells have sandstone as caprock.

[0059] Table 1 Statistical analysis of geophysical parameters of caprock

[0060]

[0061]

[0062] The relationship between the effective reservoir of Taiyuan Formation limestone and its thickness is not obvious. It is not the case that the gas content is good in thick limestone or poor in thin limestone. The effectiveness of the caprock is closely related to the gas content of the limestone. When the caprock is mudstone, the pores of the mudstone are not well developed and the sealing property is good, the gas content of the limestone reservoir is relatively good. When the caprock is sandstone, the porosity is relatively large. The natural gas in the limestone migrates to the sandstone under the action of capillary force, so dry layers are mostly developed in the limestone.

[0063] from Figure 1 The cross analysis of Poisson's ratio and shear wave impedance shows that there are clear boundaries between limestone, sandstone and mudstone, while there are overlapping areas between sandstone and mudstone as caprocks.

[0064] S5. determining a threshold value of effective sealing of the cap layer;

[0065] Specifically, based on the lithology combination and gas content interpreted by logging of completed drilling wells, a threshold value for caprock plugging is obtained through multi-well intersection.

[0066] from Figure 2The difference ratio between medium shear wave impedance and Poisson's ratio can clearly distinguish mudstone and sandstone caprock, and the threshold value is 8000.

[0067] Attached Figure 4 This is a profile of the difference ratio between shear wave impedance and Poisson's ratio of the Mi46-31 well measurement line in the three-dimensional area. The actual drilling results show that the Taiyuan Formation encountered a 5.5m gas-bearing layer, which is consistent with the predicted results.

[0068] Attached Figure 5 This is a profile of the difference ratio between shear wave impedance and Poisson's ratio in the three-dimensional area through the Y52 well survey line. The actual drilling results show that there is no gas-bearing limestone in Taiyuan, which is consistent with the prediction results.

[0069] S6. According to the constructed formula, the sealing coefficient of the target reservoir and the cap layer is calculated. According to the effective sealing threshold value of the cap layer and the sealing coefficient of the target reservoir and the cap layer, it is determined whether the sealing is effective, and then the gas content of the target reservoir is determined.

[0070] Specifically, the construction formula is:

[0071] Where S is the shear wave impedance; Pr is the Poisson's ratio; C is the sealing coefficient between the target reservoir and the cap rock.

[0072] Furthermore, in step S6, when the sealing coefficient between the target reservoir and the cap rock is greater than the cap rock sealing threshold value, the sealing is effective; when the sealing coefficient between the target reservoir and the cap rock is less than the cap rock sealing threshold value, the sealing is ineffective.

[0073] Figure 3 The gas-bearing plane results are predicted by using the sealing coefficient C of the limestone target reservoir and cap rock in the three-dimensional area. There are large areas of gas-bearing limestone distributed in the east and southeast of the three-dimensional area. The results of 33 completed wells are verified, and the actual drilling results of 29 wells are consistent with the predicted results, with a prediction compliance rate of 91%.

[0074] Figure 4 This is the profile of the difference ratio between shear wave impedance and Poisson's ratio of the M46-31 well line in the three-dimensional area. The actual drilling results show that the Taiyuan Formation encountered a 5.5m gas-bearing layer, which is consistent with the predicted results.

[0075] Figure 5 This is the ratio profile of the difference between shear wave impedance and Poisson's ratio of the Y52 well survey line in the three-dimensional area. The actual drilling results show that there is no gas-bearing limestone in Taiyuan, which is consistent with the prediction results.

[0076] The present invention is aimed at predicting unconventional reservoirs that are thin, have no independent seismic reflection characteristics, and are associated with geological bodies such as coal seams with strong reflection interfaces. The present invention has made breakthrough progress in the prediction of unconventional reservoirs through innovations in interpretation ideas and seismic prediction, and has solved the problem of predicting reservoir-caprock combinations in unconventional reservoirs, which is quite different from the current conventional single prediction reservoir or single prediction caprock technology.

[0077] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A reservoir gas content evaluation method based on the difference ratio of seismic wave elastic parameters, characterized by: The steps include: S1. Obtain the target area seismic processing offset stacking data volume; S2. Carry out fine calibration of well seismic data and stratum tracking in the target area; S3, using the seismic processing of step S1 to perform pre-stack inversion on the offset stacking data volume, to obtain the shear wave impedance data volume and Poisson's ratio data volume of the target area; S4, based on the horizon calibration of step S2, using the shear wave impedance data volume and Poisson's ratio data volume of step S3, calculating the shear wave impedance difference and Poisson's ratio difference between the target reservoir and the cap rock; S5. determining a threshold value of effective sealing of the cap layer; S6. According to the constructed formula, the sealing coefficient of the target reservoir and the cap layer is calculated. According to the effective sealing threshold value of the cap layer and the sealing coefficient of the target reservoir and the cap layer, it is determined whether the sealing is effective, and then the gas content of the target reservoir is determined.

2. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The offset stacking data volume in step S1 includes a near-offset processing stacking data volume, a medium-offset processing stacking data volume, and a far-offset processing stacking data volume.

3. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The step S2 is to perform fine well-seismic calibration and layer tracking on the target area, specifically: use the completed well information in the target area to calibrate the layer synthesis record, establish a communication bridge between seismic and geological, and then perform fine interpretation of multiple target layers on the seismic data body, and use this as a constraint to establish a low-frequency model.

4. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The prestack inversion in step S3 is prestack geostatistical inversion.

5. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The specific method for calculating the shear wave impedance difference between the target reservoir and the cap layer in step S4 is: based on the layer calibration, extracting the root mean square attribute of the shear wave impedance target layer in the target segment on the shear wave impedance data body, extracting the root mean square attribute of the shear wave impedance value of the upper cover layer of the target segment, and subtracting the former from the latter to obtain the shear wave impedance difference.

6. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The specific method for calculating the Poisson's ratio difference between the target reservoir and the cap layer in step S4 is: based on the horizon calibration, extracting the root mean square attribute of the Poisson's ratio in the target segment on the Poisson's ratio data volume, extracting the root mean square attribute of the Poisson's ratio of the upper cap layer in the target segment, and subtracting the former from the latter to obtain the Poisson's ratio difference.

7. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 1, characterized in that: The step S5 of determining the effective sealing threshold value of the caprock is specifically as follows: based on the lithology combination and gas content interpreted by logging of completed drilling wells, the effective sealing threshold value of the caprock is obtained by multi-well intersection.

8. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 7, characterized in that: The construction formula of step S6 is: Where S is the shear wave impedance; Pr is the Poisson's ratio; C is the sealing coefficient between the target reservoir and the cap rock.

9. The reservoir gas content evaluation method based on the seismic wave elastic parameter difference ratio according to claim 8, characterized in that: In step S6, when the sealing coefficient between the target reservoir and the cap rock is greater than the cap rock sealing threshold value, the sealing is effective; when the sealing coefficient between the target reservoir and the cap rock is less than the cap rock sealing threshold value, the sealing is ineffective.

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